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摘要
Plant-based diets (PBDs) are associated with environmental benefits, human health promotion and animal welfare. There is a worldwide shift towards PBDs, evident from the increased global demand for fresh plant-based products (PBPs). Such shifts in dietary preferences accompanied by evolving food palates, create opportunities to leverage technological advancements and strict quality controls in developing PBPs that can drive consumer acceptance. Flavor, color and texture are important sensory attributes of a food product and, have the largest influence on consumer appeal and acceptance. Among these, flavor is considered the most dominating quality attribute that significantly affects overall eating experience. Current state-of-art technologies rely on physicochemical estimations and sensory-based tests to assess flavor-related attributes in fresh PBPs. However, these methodologies often do not provide any indication about the metabolic features associated with unique flavor profiles and, consequently, can be used in a limited way to define the quality attributes of PBPs. To this end, a systematic understanding of metabolites that contribute to the flavor profiles of PBPs is warranted to complement the existing methodologies. This review will discuss the use of metabolomics for evaluating flavor-associated metabolites in fresh PBPs at post-harvest stage, alongside its applications for quality assessment and grading. We will summarize the current research in this area, discuss technical challenges and considerations pertaining to sampling and analytical techniques, as well as s provide future perspectives and directions for government organizations, industries and other stakeholders associated with the quality assessment of fresh PBPs.
植物性飲食(PBDs)與環(huán)境效益、促進人類健康和動物福利有關(guān)。從全球?qū)π迈r植物性產(chǎn)品(PBPs)需求的增加可以看出，全球正在向PBDs轉(zhuǎn)變。這種飲食偏好的轉(zhuǎn)變伴隨著不斷變化的食物口味，為利用技術(shù)進步和嚴格的質(zhì)量控制來開發(fā)能夠推動消費者接受的pbp創(chuàng)造了機會。風味、顏色和質(zhì)地是食品重要的感官屬性，對消費者的吸引力和接受程度影響最大。其中，風味被認為是影響整體飲食體驗的最主要品質(zhì)屬性。目前最先進的技術(shù)依賴于物理化學估計和基于感官的測試來評估新鮮PBPs中的風味相關(guān)屬性。然而，這些方法通常不能提供與獨特風味特征相關(guān)的代謝特征的任何指示，因此，只能以有限的方式用于定義PBPs的質(zhì)量屬性。為此，有必要對影響PBPs風味特征的代謝物進行系統(tǒng)的了解，以補充現(xiàn)有的方法。這篇綜述將討論在收獲后階段，利用代謝組學評估新鮮PBPs中與風味相關(guān)的代謝物的方法，以及該方法在質(zhì)量評估和分級中的應用。我們將總結(jié)這一領(lǐng)域的當前研究，討論與采樣和分析技術(shù)相關(guān)的技術(shù)挑戰(zhàn)和注意事項，并為與政府組織、工業(yè)界以及其他與新鮮PBPs質(zhì)量評估相關(guān)的利益相關(guān)者提供未來展望和發(fā)展方向。
Keywords:?關(guān)鍵詞：
plant-based diets;?plant-based products;?metabolomics;?sensory attributes;?flavor
植物性飲食；植物性產(chǎn)品；代謝組學；感官屬性；風味
1.1. 全球食品口味：邁向可持續(xù)的未來食品
Increasing urbanization, rising per capita incomes and affordability are shaping the way our food is produced and consumed globally. The associated changes in lifestyle are influencing the composition of food baskets, food consumption patterns and behaviors [1,2,3,4]. With the advent of digitalization and increased access to information, consumers are becoming more cognizant about food and its sources [5]. There is increasing focus on well-being and shifts in consumer preferences toward foods that are grown sustainably. Consequently, plant-based diets (PBDs) are gaining popularity owing to their numerous environmental and human health benefits [6].
日益加劇的城市化、人均收入的增加以及消費能力的提升正在全球范圍內(nèi)重塑食品的生產(chǎn)和消費方式。伴隨而來的生活方式變化正影響著食品籃子的構(gòu)成、食品消費模式和行為習慣[1,2,3,4]。隨著數(shù)字化時代的到來和信息獲取的便捷性提高，消費者對食品及其來源的認知度也在不斷增強[5]。人們越來越關(guān)注健康福祉，消費偏好也逐漸轉(zhuǎn)向可持續(xù)種植的食品。因此，植物性飲食（PBDs）因其眾多的環(huán)境和人類健康益處而日益受到歡迎[6]。
1.2. 植物性飲食：我們了解什么？
Diet refers to a lifestyle adopted by an individual, and largely relates to an eating plan and regimen for habitual nourishment. With PBD, an individual relies on plant-based products (PBPs) for his/her daily nutritional needs. Typical PBDs maximize the consumption of nutrient-rich plant foods while minimizing processed foods, oils, and animal foods (including dairy products and eggs) [7]. It is pertinent to note that at present, there are varying opinions in the scientific community about idealistic PBDs. However, there is a general cognizance that PBDs are associated with a multitude of human and environmental health benefits. Some epidemiological and interventional human studies have suggested that PBDs exert beneficial health effects against obesity-related metabolic dysfunction, type 2 diabetes mellitus and chronic low-grade inflammation [8,9,10]. Furthermore, the production of PBDs tend to be less resource-intensive and more environmentally friendly for various reasons, including lowered levels of greenhouse gas emissions (GHGEs), in comparison to raising animals for human consumption [11].
飲食是指個人所采取的生活方式，主要與日常飲食計劃和習慣營養(yǎng)有關(guān)。在植物性飲食（PBD）中，個體依賴植物性產(chǎn)品（PBPs）來滿足其日常營養(yǎng)需求。典型的植物性飲食會最大化營養(yǎng)豐富的植物性食物的攝入量，同時盡量減少加工食品、油脂和動物性食物（包括乳制品和雞蛋）的攝入量[7]。值得注意的是，目前科學界對于理想化的植物性飲食存在不同意見。然而，普遍認識到的是，植物性飲食與人類和環(huán)境的健康益處息息相關(guān)。一些流行病學和干預性人體研究表明，植物性飲食對與肥胖相關(guān)的代謝功能障礙、2型糖尿病和慢性低度炎癥具有有益的健康影響[8,9,10]。此外，與飼養(yǎng)動物供人類食用相比，植物性飲食的生產(chǎn)往往資源消耗較少且更加環(huán)保，包括溫室氣體排放量較低[11]。
As most PBDs rely heavily on plant-based products (PBPs), there will be an increased global demand for PBPs to meet the changing consumer preferences. For the purpose of this review, the scope will be limited to fresh PBPs at the post-harvest stage, where the produce makes its first entry for quality assessments.
由于大多數(shù)植物性飲食嚴重依賴植物性產(chǎn)品（PBPs），因此為了滿足不斷變化的消費者偏好，全球?qū)BPs的需求將會增加。為了本綜述的目的，其范圍將僅限于收獲后階段的新鮮PBPs，即這些產(chǎn)品在首次進行質(zhì)量評估時所處的階段。
1.3. 植物性產(chǎn)品：營養(yǎng)和感官特性
PBPs comprise of vegetables, fruits, lentils, grains, legumes, nuts and seeds. They offer a myriad of nutritional and functional benefits for human health promotion. Apart from macronutrients and micronutrients, many of these PBPs provide a range of bioactive compounds to combat inflammation, strengthen antioxidant defenses, and general immune system [12,13,14].
植物性產(chǎn)品（PBPs）包括蔬菜、水果、扁豆、谷物、豆類、堅果和種子。它們?yōu)槿祟惤】荡龠M提供了眾多的營養(yǎng)和功能益處。除了宏量營養(yǎng)素和微量營養(yǎng)素外，許多PBPs還提供了一系列生物活性化合物，以對抗炎癥、增強抗氧化防御和整體免疫系統(tǒng)[12,13,14]。
A considerable fraction of bioactive compounds/metabolites in PBPs, such as pigments, phytochemicals and other secondary metabolites, contribute to the sensory properties of fresh PBPs. Flavor, color and texture together contribute to the overall eating experience associated with PBPs, and are often a deterministic factor in influencing consumer acceptance. Among these three sensory properties, flavor often has the highest influence on consumer acceptance and behavior. Apart from being a critical quality attribute, flavor also provides valuable information about the nutritional quality of the food [15]. While consumers generally recognize flavor as the most dominant quality attribute for certain PBPs such as fruits and vegetables, it is the interaction of flavor and texture that has a significant effect on consumer acceptance of PBPs [16]. However, for the purpose of this review, we will focus on flavor-related attributes of fresh PBPs.?
在植物性產(chǎn)品（PBPs）中，相當大一部分的生物活性化合物/代謝物，如色素、植物化學物質(zhì)和其他次級代謝物，對新鮮PBPs的感官特性有所貢獻。風味、顏色和質(zhì)地共同構(gòu)成了與PBPs相關(guān)的整體食用體驗，并且通常是影響消費者接受度的決定性因素。在這三種感官特性中，風味往往對消費者的接受度和行為有最大的影響。除了是關(guān)鍵的質(zhì)量屬性外，風味還提供了關(guān)于食物營養(yǎng)質(zhì)量的有價值信息[15]。雖然消費者通常認為風味是某些PBPs（如水果和蔬菜）最顯著的質(zhì)量屬性，但風味和質(zhì)地的相互作用對消費者接受PBPs有顯著影響[16]。然而，為了本綜述的目的，我們將重點關(guān)注新鮮PBPs與風味相關(guān)的屬性。
Flavor is perceived primarily by the sense of taste and olfaction (aromatics/aroma) [17]. Aroma and taste receptors, located in the nose and mouth, respectively, are responsible for distinct flavor recognition. It is generally accepted that olfactory stimuli (aroma metabolites) contribute significantly to the flavor experience of most food products. The unique taste sensations and aroma associated with PBPs come from a complex mixture of compounds that belong to different chemical classes. They originate from the primary and secondary metabolism in PBPs and are generally bioactive, with aroma metabolites being volatile in nature while, the taste metabolites often being non-volatile. Both the volatile and non-volatile bioactive fraction in PBPs, such as phenols, flavonoids, isoflavones, terpenes, and glucosinolates, contribute to bitter, acidic, or astringent flavor profiles [18,19]. The presence of these bioactive compounds is an intrinsic property of PBPs, and their synthesis is often influenced by multiple genetic and environmental factors [20,21,22]. Considering the diverse nature of these bioactive compounds and their contribution to the flavor of fresh PBPs, an inclusive approach for their quality assessment at the post-harvest stage is valuable for entire supply chain management. The significance of including a detailed characterization of bioactive compounds for quality assessment has received considerable attention for certain processed food products [23,24,25]. However, quality assessment for fresh PBPs at the post-harvest stage mainly relies on conventional techniques, as discussed in the next section.
風味主要通過味覺和嗅覺（即香氣）來感知[17]。分別位于鼻子和口中的香氣和味覺受體負責不同的風味識別。通常認為，嗅覺刺激（香氣代謝產(chǎn)物）對大多數(shù)食品的風味體驗有著顯著的貢獻。與PBPs相關(guān)的獨特味覺感受和香氣來自于屬于不同化學類別的復雜化合物混合物。這些化合物來源于PBPs的初級和次級代謝，并且通常具有生物活性，其中香氣代謝產(chǎn)物具有揮發(fā)性，而味覺代謝產(chǎn)物則通常不具有揮發(fā)性。PBPs中的揮發(fā)性和非揮發(fā)性生物活性成分，如酚類、黃酮類、異黃酮類、萜烯類和硫代葡萄糖苷等，都會給風味帶來苦、酸或澀的特征[18,19]。這些生物活性化合物的存在是PBPs的內(nèi)在特性，并且它們的合成往往受到多種遺傳和環(huán)境因素的影響[20,21,22]?？紤]到這些生物活性化合物的多樣性和它們對新鮮PBPs風味的貢獻，在收獲后對它們進行質(zhì)量評估的全面方法對于整個供應鏈的管理具有重要意義。對于某些加工食品產(chǎn)品，在質(zhì)量評估中包括生物活性化合物的詳細表征已受到相當大的關(guān)注[23,24,25]。然而，對于新鮮PBPs在收獲后的質(zhì)量評估，主要還是依賴于傳統(tǒng)技術(shù)，這將在接下來的部分中討論。
PBPs的質(zhì)量評估
2.1. 收獲后處理：與風味相關(guān)屬性的當前先進技術(shù)
At present, the post-harvest quality assessment of fresh PBPs is effectively regulated for attributes related to food safety/human health risk (heavy metals, chemical contamination, microbiological), but loosely regulated for attributes associated with consumer acceptance and eating experience. These regulations are imposed both at international and national levels, as well as within the individual supply chains [26]. Current quality assessment parameters do not effectively inform on the kind of metabolites or chemical compounds that are responsible for the unique flavor profiles of fresh PBPs. However, this could be particularly important for formulating new products in this domain, keeping in mind the changing consumption trends and evolving flavor preferences.
目前，新鮮PBPs的收獲后質(zhì)量評估在食品安全/人類健康風險（重金屬、化學污染、微生物）相關(guān)的屬性上得到了有效的監(jiān)管，但在與消費者接受度和食用體驗相關(guān)的屬性上監(jiān)管較為寬松。這些監(jiān)管措施在國際、國家層面以及各個供應鏈內(nèi)部都得到了實施[26]。然而，當前的質(zhì)量評估參數(shù)并未有效地提供關(guān)于哪種代謝物或化學化合物負責新鮮PBPs獨特風味特征的信息。但是，這對于該領(lǐng)域新產(chǎn)品的配方制定可能尤為重要，特別是考慮到不斷變化的消費趨勢和不斷演變的風味偏好。
For any PBP, the relative importance of a quality attribute depends on the commodity and its end-use [27]. In general, the post-harvest handling steps for PBPs include identification of the key quality attributes from food safety/human health-related risks (minimum statutory requirements), followed by establishing quality control/quality assurance (QA/QC) procedures to (i) maintain acceptable quality level for the consumer; and (ii) ensure that minimum quality standards are met.
對于任何PBP，一個質(zhì)量屬性的相對重要性取決于該商品及其最終用途[27]。一般來說，PBPs的收獲后處理步驟包括首先識別與食品安全/人類健康風險相關(guān)的關(guān)鍵質(zhì)量屬性（法定最低要求），然后建立質(zhì)量控制/質(zhì)量保證（QA/QC）程序，以（i）保持消費者可接受的質(zhì)量水平；（ii）確保達到最低質(zhì)量標準。
The quality assessment of fresh PBPs routinely involves sensory and instrumental methods. In general, sensory methods are used for developing new products and determining product standards, while instrumental methods fare better in assessing the quality of the fresh PBPs on a routine basis [28]. Sensory evaluation is usually performed by a trained sensory panel, and it has two components: the analytical component, which is used to detect differences in products, and affective measurements, which determine preference. Instrumental measurements, on the other hand, focus on the chemical and physical characteristics of PBPs, and encompass a wide range of techniques to determine flavor attributes. For example, a hydrometer that can detect total soluble solids is often used to determine sugar levels while, pH meter is used to measure the level of sourness in food products [28].
新鮮PBPs（植物性產(chǎn)品）的質(zhì)量評估通常涉及感官方法和儀器方法。一般來說，感官方法用于開發(fā)新產(chǎn)品和確定產(chǎn)品標準，而儀器方法在日常評估新鮮PBPs的質(zhì)量方面表現(xiàn)更佳[28]。感官評價通常由經(jīng)過培訓的感官評估小組進行，包括兩個組成部分：分析性成分，用于檢測產(chǎn)品之間的差異；以及情感測量，用于確定偏好。另一方面，儀器測量則側(cè)重于PBPs的化學和物理特性，并采用多種技術(shù)來確定風味屬性。例如，檢測總可溶性固體的比重計常用于確定糖分水平，而pH計則用于測量食品產(chǎn)品的酸度水平[28]。
2.2. Gaps in Current Technologies and Need for Complementary Approaches
2.2 當前技術(shù)的不足與互補方法的需求
Instrumental techniques aimed at evaluating the physical and chemical characteristics of PBPs are advantageous as they: (i) provide high accuracy and great precision; (ii) are often more sensitive to small differences between samples, which assist in determining quality trends; and (iii) they are high-throughput and are often available in semi-automated and automated formats [29]. However, the physicochemical characteristics of PBPs have little relevance to consumer acceptability and thus, the results can be used in a limited way to define the quality attributes of PBPs [30]. For this purpose, sensory evaluation is often recommended to accurately assess the quality attributes of fresh PBPs. Sensory evaluation also has certain disadvantages as it requires a trained sensory panel and it is often time consuming, laborious and challenging.
旨在評估PBPs物理和化學特性的儀器技術(shù)具有優(yōu)勢，因為它們：（i）提供高精度和高準確性；（ii）通常對樣品之間的小差異更敏感，有助于確定質(zhì)量趨勢；（iii）具有高通量，并且通常以半自動和自動格式提供[29]。然而，PBPs的物理化學特性與消費者接受度之間的相關(guān)性很小，因此這些結(jié)果只能以有限的方式用于定義PBPs的質(zhì)量屬性[30]。為此，通常建議采用感官評價來準確評估新鮮PBPs的質(zhì)量屬性。然而，感官評價也存在一些缺點，如需要訓練有素的感官評估小組，且往往耗時、費力且具有挑戰(zhàn)性。
To complement and extend the repertoire of the existing methodologies, detailed and quantitative analyses to measure flavor-associated metabolites are warranted. Integrating such technologies in current quality assessment of fresh PBPs will (i) ensure product uniformity; (ii) strengthen consumer acceptability for PBDs and PBPs in general; (iii) complement current assessment platforms for quality and food safety of fresh PBPs; and (iv) aid in determining maturity and degree of ripening of PBPs at the post-harvest stage.
為了補充和擴展現(xiàn)有方法體系，對與風味相關(guān)的代謝產(chǎn)物進行詳細和定量的分析是必要的。將此類技術(shù)整合到新鮮PBPs（植物性產(chǎn)品）的當前質(zhì)量評估中，將（i）確保產(chǎn)品的一致性；（ii）增強消費者對PBDs（可能是指植物基產(chǎn)品或其他相關(guān)術(shù)語，但在此上下文中可能指的是廣義上的植物性產(chǎn)品）和PBPs的總體接受度；（iii）補充當前對新鮮PBPs質(zhì)量和食品安全的評估平臺；（iv）有助于確定收獲后PBPs的成熟度和成熟程度。
3. Metabolite Fingerprinting for Quality Assessment of PBPs
3. PBPs質(zhì)量評估的代謝物指紋圖譜
3.1 農(nóng)食領(lǐng)域的代謝組學：當前實踐
Metabolomics allows for studying multiple small molecules or metabolites in a cell, tissue or organism. It is defined as the comprehensive characterization of small molecules present in a biological sample [31,32,33]. Metabolomics routinely utilizes sophisticated and high-throughput analytical platforms such as gas chromatography and liquid chromatography–mass spectrometry (GC–MS and LC–MS) and nuclear magnetic resonance (NMR) spectroscopy [34]. With the advent of chemometrics and advanced analytical platforms, metabolomics has greatly facilitated our understanding of the global metabolome and pathway networks [35]. Metabolomics approaches involve untargeted or targeted analyses, and the selection of the approach is largely dependent on the experimental question and expected outcomes [36]. Untargeted analyses utilize an unbiased profiling or metabolic fingerprinting approach focused on uncovering the global metabolome to evaluate diverse chemical classes of metabolites associated with different pathways. On the other hand, targeted analyses rely on a priori knowledge of the class of metabolites or pathways that are of interest [37]. However, the combination of these analyses is often required to obtain complete information of interest.
代謝組學允許研究細胞、組織或生物體中的多種小分子或代謝產(chǎn)物。它被定義為對生物樣品中存在的小分子進行全面表征[31,32,33]。代謝組學通常使用復雜且高通量的分析平臺，如氣相色譜和液相色譜-質(zhì)譜聯(lián)用（GC-MS和LC-MS）以及核磁共振（NMR）光譜[34]。隨著化學計量學和先進分析平臺的出現(xiàn)，代謝組學極大地促進了我們對全局代謝組和代謝途徑網(wǎng)絡的理解[35]。代謝組學方法包括非靶向或靶向分析，方法的選擇很大程度上取決于實驗問題和預期結(jié)果[36]。非靶向分析采用無偏見的輪廓分析或代謝指紋圖譜方法，專注于揭示全局代謝組，以評估與不同途徑相關(guān)的多種化學類別的代謝產(chǎn)物。另一方面，靶向分析依賴于對感興趣的代謝產(chǎn)物類別或途徑的先驗知識[37]。然而，為了獲得完整的感興趣信息，通常需要將這兩種分析方法結(jié)合起來。
Over the past few decades, metabolomics has been extensively applied to various fields of science owing to new developments in analytical instrumentation and data-analytics platforms [38,39,40,41]. Although still in their infancy, metabolomics-based approaches have gained significant interest in the agri-food sector for a diversity of applications including food processing, quality control, plant breeding for improved crop varieties and product development [42,43]. However, at present, metabolomics-based approaches have not been adopted by the regulatory agencies for food quality assessment, although in some cases they have been found to be efficient, with clear benefits over conventional methods. For instance, metabolomics-based approaches have proved valuable to the food industry for the aroma analysis of fresh and processed PBPs [44,45,46,47]. It is pertinent to note that most of the current research in food metabolomics is focused on evaluating various quality attributes of processed/semi-processed food products. Efforts in the area of fresh produce are mostly restricted to economically important PBPs or PBPs grown for specific end-use [45].
在過去的幾十年里，由于分析儀器和數(shù)據(jù)分析平臺的新發(fā)展，代謝組學已被廣泛應用于科學的各個領(lǐng)域[38,39,40,41]。盡管仍處于起步階段，但基于代謝組學的方法在農(nóng)食行業(yè)已經(jīng)引起了廣泛關(guān)注，并應用于多種領(lǐng)域，包括食品加工、質(zhì)量控制、作物品種改良和產(chǎn)品開發(fā)[42,43]。然而，目前監(jiān)管機構(gòu)尚未將基于代謝組學的方法用于食品質(zhì)量評估，盡管在某些情況下，這些方法已被證明是有效的，并且相對于傳統(tǒng)方法具有明顯優(yōu)勢。例如，基于代謝組學的方法在新鮮和加工PBPs的香氣分析方面對食品工業(yè)具有重要價值[44,45,46,47]。值得注意的是，目前食品代謝組學的大部分研究都集中在評估加工/半加工食品產(chǎn)品的各種質(zhì)量屬性上。而在新鮮農(nóng)產(chǎn)品領(lǐng)域的研究大多局限于經(jīng)濟上重要的PBPs或特定最終用途的PBPs[45]。
3.2 基于代謝組學評估新鮮PBPs中的風味相關(guān)代謝產(chǎn)物
Within the agri-food sector, several diverse areas utilize metabolomics approaches for a variety of applications, as discussed in the previous?Section 3.1. One such application involves evaluating the flavor-associated metabolites in fresh PBPs, which are determined by their biochemical composition. As stated in earlier?Section 3.1, flavor has the largest influence on consumer behavior and consumption pattern [15], and consequently, most of the research efforts in this domain are catered towards determining the flavor-related metabolites in PBPs. Perception of flavor involves both volatile aroma metabolites as well as non-volatile taste metabolites which belong to different classes.
在農(nóng)食行業(yè)中，如第3.1節(jié)所述，代謝組學方法被用于多種應用。其中一項應用就是評估新鮮PBPs中的風味相關(guān)代謝產(chǎn)物，這些代謝產(chǎn)物由其生化成分決定。正如第3.1節(jié)所述，風味對消費者行為和消費模式有最大影響[15]，因此該領(lǐng)域的大部分研究都致力于確定PBPs中的風味相關(guān)代謝產(chǎn)物。風味的感知既涉及揮發(fā)性香氣代謝產(chǎn)物，也涉及屬于不同類別的非揮發(fā)性味覺代謝產(chǎn)物。
3.2.1 香氣相關(guān)代謝產(chǎn)物
In fresh PBPs, a diverse set of volatile chemical compounds contribute to their natural aroma, increasing the complexity of these aroma-associated metabolites. This complexity is further compounded as the volatile compounds interact with each other to create a unique aroma profile for PBPs, which is not merely a sum of the volatile compounds present in them. To date, more than 7000 volatile compounds have been identified in foods, however, a relatively small number (300–400), in specific abundance and ratio, determine the characteristic aroma of the product [48,49].
在新鮮植物性產(chǎn)品（PBPs）中，一系列復雜的揮發(fā)性化合物共同構(gòu)成了其自然香氣，這使得香氣相關(guān)代謝產(chǎn)物的分析變得尤為復雜。這種復雜性還體現(xiàn)在揮發(fā)性化合物之間的相互作用上，它們共同創(chuàng)造出PBPs獨特的香氣特征，這種特征并非僅僅是這些揮發(fā)性化合物簡單加和的結(jié)果。迄今為止，食品中已鑒定出超過7000種揮發(fā)性化合物，但其中只有相對較少的一部分（300-400種），在特定的豐度和比例下，決定了產(chǎn)品的特征香氣[48,49]。
There are several known classes of volatile aroma metabolites that contribute to the unique flavor of fresh PBPs, such as esters, alcohols, aldehydes, ketones, lactones, terpenoids and apocarotenoids. However, derivatives of amino acids, lipids, phenolic acids and sesquiterpenes are known to be the most important aroma-associated metabolites in PBPs [50]. In certain PBPs, especially fruits and vegetables, sulphurous compounds and derivatives also contribute to their distinct aroma profiles [50].?
已知有多種揮發(fā)性香氣代謝產(chǎn)物對新鮮PBPs的獨特風味有貢獻，如酯類、醇類、醛類、酮類、內(nèi)酯類、萜類和脫輔基類胡蘿卜素等。然而，在PBPs中，氨基酸、脂質(zhì)、酚酸和倍半萜烯的衍生物被認為是最重要的香氣相關(guān)代謝產(chǎn)物[50]。在某些PBPs中，特別是水果和蔬菜，含硫化合物及其衍生物也對其獨特的香氣特征有重要貢獻[50]。
Volatile aroma metabolites associated with fresh PBPs are generally derived from phytonutrients belonging to fatty acids, amino acids, carotenoids and terpenoid classes [15,51] through a limited number of major biochemical pathways [52]. These pathways are mainly involved in the synthesis of the backbone, while the diversity of these volatiles is achieved via additional chain modification steps and further transformations. Fatty-acid derived volatiles such as alcohols, esters, ketones, acids and lactones form important character-impact aroma compounds that are responsible for flavors of fresh fruits mainly synthesized through?α-oxidation,?β-oxidation and the lipoxygenase pathway [53].
與新鮮PBPs相關(guān)的揮發(fā)性香氣代謝產(chǎn)物通常來源于脂肪酸、氨基酸、類胡蘿卜素和萜類化合物等植物營養(yǎng)素[15,51]，這些代謝產(chǎn)物通過有限的幾個主要生化途徑產(chǎn)生[52]。這些途徑主要涉及香氣化合物骨架的合成，而揮發(fā)性化合物的多樣性則通過額外的鏈修飾步驟和進一步的轉(zhuǎn)化來實現(xiàn)。脂肪酸衍生的揮發(fā)性物質(zhì)，如醇類、酯類、酮類、酸類和內(nèi)酯類，是構(gòu)成新鮮水果風味的重要特征香氣化合物，它們主要通過α-氧化、β-氧化和脂氧合酶途徑合成[53]。
Similarly, amino acid-derived volatile compounds are produced either through amino-acid precursors (direct) or through acyl-coAs (indirect) and they mainly belong to alcohols, esters, and vegetables. Amino acid-derived volatiles represent dominant classes in PBPs, specifically fruits, vegetables, and grains [15,19,54,55]. For instance, the amino acid proline is the nitrogen precursor for 2-acetyl-1-pyrroline, a volatile compound that is associated with the aroma of certain rice varieties. Similarly, methionine and tryptophan are involved in side-chain modifications of sulphur containing glucosinolates, which result in volatile degradation products, namely isothiocyanates, that contribute to the characteristic aroma associated with?Brassica?genus [56]. Terpenoids make up the largest class of plant secondary metabolites, many of them being volatile in nature, that contribute to the aroma of fresh PBPs. Hemiterpenes (C5), monoterpenes (C10), sesquiterpenes (C15), homoterpenes (C11 and C16), and some diterpenes (C20) have higher vapor pressure, allowing their release into the surrounding atmosphere and volatilize. All the terpenoids are derived from the universal C5 precursor isopentenyl diphosphate (IPP) and its allylic isomer dimethylallyl diphosphate (DMAPP) [57]. Many terpene volatiles are direct products of terpene biosynthesis enzymes, while some are derived through modifications and additional transformations of primary terpene skeletons, mainly via hydroxylation, dehydrogenation, acylation. For instance, hydroxylation of limonene results in the formation of?trans-isopiperitenol and?trans-carveol through different catalyzing enzymes and these hydroxylated terpenes are associated with characteristic flavor of certain PBPs [58,59]. Similarly, acetylation of certain terpenes like geraniol results in the formation of geranyl acetate, which has a pleasant fruity aroma and is found in many PBPs. Apart from fatty acid, amino acid and terpenoid pathways, carotenoid pathways represent another major class of volatiles in PBPs. Carotenoid derivatives mainly derived via the oxidation cleavage of carotenoids result in the formation of volatile apocarotenoid derivatives [60]. These volatiles contribute to the aroma of several vegetables and fruits [61].
萜類化合物是植物次生代謝產(chǎn)物中最大的一類，其中許多具有揮發(fā)性，對新鮮植物源性副產(chǎn)物的香氣有重要貢獻。半萜類（C5）、單萜類（C10）、倍半萜類（C15）、同萜類（C11和C16）以及某些二萜類（C20）具有較高的蒸氣壓，能夠釋放到周圍大氣中并揮發(fā)。所有萜類化合物都來源于通用的C5前體異戊烯基焦磷酸（Isopentenyl Diphosphate, IPP）及其烯丙基異構(gòu)體二甲基烯丙基焦磷酸（Dimethylallyl Diphosphate, DMAPP）[57]。許多萜類揮發(fā)性物質(zhì)是萜類生物合成酶的直接產(chǎn)物，而另一些則是通過初級萜類骨架的修飾和額外轉(zhuǎn)化產(chǎn)生的，主要通過羥基化、脫氫、酰化等方式。例如，檸檬烯的羥基化通過不同的催化酶作用產(chǎn)生反式異胡椒醇和反式香芹醇，這些羥基化的萜類與某些植物源性副產(chǎn)物的特征風味有關(guān)[58,59]。同樣地，某些萜類化合物如香葉醇的乙?；瘯纬上闳~基乙酸酯，它具有令人愉悅的果香，并存在于許多植物源性副產(chǎn)物（PBPs）中。除了脂肪酸、氨基酸和萜類途徑外，類胡蘿卜素途徑也是PBPs中揮發(fā)性化合物的主要類別之一。類胡蘿卜素衍生物主要通過類胡蘿卜素的氧化裂解形成，進而產(chǎn)生揮發(fā)性的脫輔基類胡蘿卜素衍生物[60]。這些揮發(fā)性化合物對多種蔬菜和水果的香氣有重要貢獻[61]。
In the past few years, several research studies have exploited metabolomics approaches to evaluate these diverse classes of aroma metabolites in a variety of fresh PBPs. We provide a representative summary for some of these aroma metabolites in selected fresh PBPs (Table 1). Studies have utilized different kinds of analytical platforms and extraction approaches to analyze chemical classes that contribute to the unique aroma and flavor of fresh PBPs, as summarized in?Table 1.
Table 1.?Aroma-related metabolites determined using different analytical platforms in fresh plant-based products (PBPs). A representative summary of recent research studies in this area.
| S.no | Metabolites Classes | PBP Type | Analytical Platform | References |
|---|---|---|---|---|
| 1 | Esters, alcohols, aldehydes, ketones, lactones, terpenoids, sulphur compounds | Melons (Cucumis melo?L.) | GC-MS GC-O | [62] |
| 2 | Alcohols, acids, and carbonyl compounds, terpenoids and norisoprenoids, furan, phenols and phenylpropanoids, benzonoids, furans | Kiwifruit (Actinidia deliciosa) | GC-O | [52] |
| 3 | Monoterpene hydrocarbons and oxides, sesquiterpenes, aldehydes, alcohols, esters | Japanese citrus fruit (Citrus nagato-yuzukichi Tanaka) | GC-MS | [63] |
| 4 | Esters, alcohol, fatty acid esters, carboxylic acid esters | Pear fruit (Pyrus communis) | HRGC-C/P-IRMS | [64] |
| 5 | Esters, aldehydes, alcohol, benzenic derivatives, ethers | Ambul Banana (Musa acuminata, AAB) | GC-MS | [65] |
| 6 | Aldehydes and alcohols | Potato (Solanum tuberosum) | GC-FID | [66] |
| 7 | Aliphatic acids, aldehydes, alcohols, Oxygenated and nonoxygenated monoterpenes, phenolic derivatives, nor-isoprenes | Tomato (Solanum lycopersicum) | GC | [67] |
| 8 | C8-C9 unsaturated aldehydes and ketones | Oat (Avena sativa) | GC-MS, GC-O | [68] |
| 9 | Ketones, alcohols, esters, and heterocycle compounds | Intermediate wheatgrass (Thinopyrum intermedium) | GC-MS-O | [69] |
| 10 | Unsaturated hydrocarbons, carboxylic acid esters, phenol ethers | Rice (Oryza sativa) | GCGC-TOFMS | [70] |
| 11 | Alcohols, aldehydes, ketones, nitrogen-compounds, Straight- and branched-chain hydrocarbons | Jasmine brown rice (Oryza sativa) | GC-MS | [71] |
| 12 | Ketones, aldehydes, pyrazines, alcohols, aromatic hydrocarbons, furans, pyrroles, terpenes, and acids | Turkish Tombul Hazelnut (Corylus avellana?L.) | GC-MS | [72] |
| 13 | Alcohols, aldehydes, esters, benzene derivates, linear hydrocarbons, ketones furans | Dark Black Walnut (Juglans nigra) | GCMS | [73] |
| 14 | Monoterpenes | Pistachio nuts (Pistacia vera?L.) | GC-MS | [74] |
| 15 | Pyrazines, aldehydes, alcohols, ketones, esters, carbonic acids, furan derivatives, pyrroles, pyridines, pyran derivatives, hydrocarbons, phenols, sulphur compounds, lactones | Wheat flour bread (Triticum aestivum) | GC-MS | [75] |
| 16 | Aliphatic hydrocarbons, monoterpenes and such | Walnuts (Juglans regia?L.) | GC–MS | [76] |
| S.no | 代謝物類別 | PBP類型 | 分析平臺 | 參考文獻 |
|---|---|---|---|---|
| 1 | 酯類、醇類、醛類、酮類、內(nèi)酯類、萜類、含硫化合物 | 甜瓜（Cucumis melo L.） | GC-MS, GC-O | [62] |
| 2 | 醇類、酸類、羰基化合物、萜類和降異戊二烯類、呋喃類、酚類和苯丙素類、苯并類、呋喃類 | 獼猴桃（Actinidia deliciosa） | GC-O | [52] |
| 3 | 單萜烴和氧化物、倍半萜類、醛類、醇類、酯類 | 日本柑橘（Citrus nagato-yuzukichi Tanaka） | GC-MS | [63] |
| 4 | 酯類、醇類、脂肪酸酯類、羧酸酯類 | 梨果（Pyrus communis） | HRGC-C/P-IRMS | [64] |
| 5 | 酯類、醛類、醇類、苯衍生物、醚類 | 大蕉（Musa acuminata, AAB） | GC-MS | [65] |
| 6 | 醛類和醇類 | 馬鈴薯（Solanum tuberosum） | GC-FID | [66] |
| 7 | 脂肪酸、醛類、醇類、含氧和不含氧的單萜類、酚類衍生物、降異戊二烯類 | 番茄（Solanum lycopersicum） | GC | [67] |
| 8 | C8-C9不飽和醛類和酮類 | 燕麥（Avena sativa） | GC-MS, GC-O | [68] |
| 9 | 酮類、醇類、酯類和雜環(huán)化合物 | 中間型小麥草（Thinopyrum intermedium） | GC-MS-O | [69] |
| 10 | 不飽和烴類、羧酸酯類、酚醚類 | 水稻（Oryza sativa） | GCGC-TOFMS | [70] |
| 11 | 醇類、醛類、酮類、含氮化合物、直鏈和支鏈烴類 | 茉莉香米（Oryza sativa） | GC-MS | [71] |
| 12 | 酮類、醛類、吡嗪類、醇類、芳香烴類、呋喃類、吡咯類、萜類、酸類 | 土耳其Tombul榛子（Corylus avellana L.） | GC-MS | [72] |
| 13 | 醇類、醛類、酯類、苯衍生物、線性烴類、酮類、呋喃類 | 黑核桃（Juglans nigra） | GCMS | [73] |
| 14 | 單萜類 | 開心果（Pistacia vera L.） | GC-MS | [74] |
| 15 | 吡嗪類、醛類、醇類、酮類、酯類、碳酸類、呋喃衍生物、吡咯類、吡啶類、吡喃衍生物、烴類、酚類、含硫化合物、內(nèi)酯類 | 小麥面粉面包（Triticum aestivum） | GC-MS | [75] |
| 16 | 脂肪烴類、單萜類 | 核桃Walnuts (Juglans regia?L.) | GC-MS | [76] |
3.2.2. 味覺相關(guān)代謝物
Taste metabolites are quite closely linked with aroma metabolites. These metabolites are generally non-volatile in nature, and they contribute to the flavor profiles by enhancing the gustatory experience via accentuation of the volatile aroma metabolites. There are five kinds of taste perceptions, namely, sweet, salty, bitter, sour and umami. Different chemical classes of metabolites contribute to the taste sensation in PBPs. Sweetness generally comes from sugars, including sucrose, glucose, and fructose. The levels of these sugars are often influenced by genetic and environmental factors and are highly associated with the degree of ripening. A wide variety of PBPs, including fruits and vegetables, have varying levels of these sugars and their biosynthesis is genetically controlled and regulated. Sourness is derived from acids such as malic, citric, and oxalic acid. Bitterness is often associated with presence of polyphenols, alkaloids, tannins, certain glycosides, or peptides. For example, tannins provide the bitter notes and complements the flavor of several PBPs including tea and immature berries [77,78]. Among polyphenols, the taste of bitterness and tactile sensation are often associated with flavonoid phenols, including flavanols and flavonols. Some of the metabolites from these families such as proanthocyanidins or condensed tannins are abundant in wine and tea [79]. Salty and umami tastes are not common in PBPs. Among the taste sensations in PBPs, bitterness is the most complex, as structurally diverse chemical compounds/metabolites can elicit a single bitter taste, which suggests that multiple mechanisms are responsible for the perception and transduction of bitterness. It is also pertinent to note that small changes in chemical structure can transform bitter compounds to sweet or vice versa. Scientific evidence also suggests that bitter and sweet tastes, when present together, can enhance, or suppress each other [80]. In recent years, research initiatives have been directed towards evaluating metabolites that contribute to different taste sensations in a variety of fresh PBPs including fruits and vegetables. Among the taste-associated metabolites, polyphenols are studied extensively among a wide range of PBPs. Polyphenols are a ubiquitous class of non-volatile plant secondary metabolites and apart their sensory attributes, they are also known for their anti-inflammatory and other metabolic effects [81,82,83,84]. Polyphenols are biosynthesized by plants for chemical defense against predators and among them, class of flavonoids are associated with taste sensations in PBPs. Most of them contribute to a bitter taste in PBPs [77,78], but owing to their health benefits, several efforts are directed towards debittering the food products to increase its consumer acceptance [81]. This interest could also be partly responsible in the research impetus on understanding composition of polyphenols and their sensory attributes in PBPs. Representative research studies reporting diverse classes of polyphenols in various PBPs using various analytical platforms are summarized in?Table 2.
味覺代謝物與香氣代謝物聯(lián)系十分密切。這些代謝物在本質(zhì)上通常是不揮發(fā)的，它們通過增強揮發(fā)性香氣代謝物來增強味覺體驗，從而貢獻風味譜。有五種味覺，即甜、咸、苦、酸和鮮味。不同化學類型的代謝物有助于PBPs的味覺。甜味通常來自糖，包括蔗糖、葡萄糖和果糖。這些糖的水平往往受到遺傳和環(huán)境因素的影響，并與成熟程度高度相關(guān)。包括水果和蔬菜在內(nèi)的多種PBPs含有不同水平的這些糖，其生物合成受遺傳控制和調(diào)節(jié)。酸是由蘋果酸、檸檬酸和草酸等酸產(chǎn)生的。苦味通常與多酚、生物堿、單寧、某些糖苷或肽有關(guān)。例如，單寧提供了苦味，并補充了包括茶和未成熟漿果在內(nèi)的幾種PBPs的風味[77,78]。在多酚中，苦味和觸覺的味道往往與黃酮酚有關(guān)，包括黃烷醇和黃酮醇。這些家族的一些代謝物如原花青素或濃縮單寧在葡萄酒和茶中含量豐富[79]。咸味和鮮味在PBPs中并不常見。在PBPs的味覺感受中，苦味是最復雜的，因為不同結(jié)構(gòu)的化合物/代謝物可以引起單一的苦味，這表明苦味的感知和轉(zhuǎn)導有多種機制。同樣值得注意的是，化學結(jié)構(gòu)的微小變化可以將苦的化合物轉(zhuǎn)變?yōu)樘鸬幕衔?，反之亦然?？茖W證據(jù)還表明，苦和甜的味道如果同時存在，會相互增強或抑制[80]。近年來，研究的主要方向是評估在包括水果和蔬菜在內(nèi)的各種新鮮PBPs中有助于不同味覺感覺的代謝物。在與味覺相關(guān)的代謝物中，多酚在廣泛的PBPs中被廣泛研究。多酚是一種普遍存在的非揮發(fā)性植物次生代謝物，除了其感官特性外，它們還具有抗炎和其他代謝作用[81,82,83,84]。多酚是由植物生物合成的，用于抵御捕食者的化學防御，其中類黃酮與PBPs的味覺有關(guān)。它們中的大多數(shù)導致PBPs中有苦味[77,78]，但由于它們對健康有益，因此有幾項努力旨在通過扣除食品來提高消費者的接受度[81]。這種興趣也在一定程度上推動了對PBPs中多酚的組成及其感官特性的研究。表2總結(jié)了使用不同分析平臺的不同PBPs中不同類別的多酚的代表性研究。
Table 2.?Taste-related metabolites determined using different analytical platforms in fresh PBPs. A representative summary of recent research studies in this area.
表2。使用不同的分析平臺測定新鮮PBPs中的味道相關(guān)代謝物。該領(lǐng)域的代表性研究綜述。
| S.no | Metabolites Classes | PBP Type | Analytical Platform | References |
|---|---|---|---|---|
| 1 | Hydroxycinnamic acid glycosides, quercetin glycoside derivatives | Mountain papaya (Vas concellea pubescens) | LC-DAD-MS | [82] |
| 2 | Phenolics, myricetin hexoside, myricetin deoxyhexoside derivatives, quercetin hexoside, quercetin deoxyhexoside derivatives | Bayberries (Myrica rubra Sieb. et Zucc) | HPLC-DAD-ESI-MS | [83] |
| 3 | Simple phenolic and hydroxycinnamoylquinic acids and flavons, flavonols, flavanone and dihydrochalcone derivatives | Tomato (Solanum lycopersicum) | HPLC–ESI-QTOF | [84] |
| 4 | Anthocyanidins, aliphatic or aromatic acylated groups, sugar moieties | Eggplant (Solanum melongena); red leaf lettuce (Lactuca sativa); Pistachio (Pistacia vera) and others | HPLC-DAD-ESI-MS-MS | [85] |
| 5 | Proanthocyanidins, phenolic acids | Barley (Hordeum vulgare) | HPLC-DAD-MS | [86] |
| S.no | 代謝產(chǎn)物類別 | 植物基產(chǎn)品(PBP)類型 | 分析平臺 | 參考文獻 |
|---|---|---|---|---|
| 1 | 羥基肉桂酸糖苷、槲皮素糖苷衍生物 | 山木瓜（Vasconcellea pubescens） | 液相色譜-二極管陣列檢測-質(zhì)譜（LC-DAD-MS） | [82] |
| 2 | 酚類、楊梅素己糖苷、楊梅素脫氧己糖苷衍生物、槲皮素己糖苷、槲皮素脫氧己糖苷衍生物 | 楊梅（Myrica rubra Sieb. et Zucc） | 高效液相色譜-二極管陣列檢測-電噴霧電離質(zhì)譜（HPLC-DAD-ESI-MS） | [83] |
| 3 | 簡單酚類、羥基肉桂酰奎尼酸及黃酮類、黃酮醇類、黃烷酮類和二氫查爾酮類衍生物 | 番茄（Solanum lycopersicum） | 高效液相色譜-電噴霧電離四極桿飛行時間質(zhì)譜（HPLC–ESI-QTOF） | [84] |
| 4 | 花青素、脂族或芳香族?；鶊F、糖基 | 茄子（Solanum melongena）、紅葉萵苣（Lactuca sativa）、開心果（Pistacia vera）等 | 高效液相色譜-二極管陣列檢測-電噴霧電離串聯(lián)質(zhì)譜（HPLC-DAD-ESI-MS-MS） | [85] |
| 5 | 原花青素、酚酸 | 大麥（Hordeum vulgare） | 高效液相色譜-二極管陣列檢測-質(zhì)譜（HPLC-DAD-MS） | [86] |
Currently, for flavor-associated metabolite profiling, several extraction techniques and analytical platforms are employed to capture the analytes of interest, which are discussed in the next section. The number of studies reported in this area are progressively increasing with the advent of rapidly evolving analytical platforms, curated databases, automated sample, and liquid handling systems. There is a scientific cognizance about the potential of metabolomics for this growing field, although it has not been widely adopted for routine quality assessment due to a variety of factors including sampling considerations and technical challenges.
目前，在風味相關(guān)代謝物分析方面，采用了多種提取技術(shù)和分析平臺來捕獲感興趣的分析物，這將在下一節(jié)中詳細討論。隨著快速發(fā)展的分析平臺、經(jīng)過整理的數(shù)據(jù)庫、自動化樣品處理和液體處理系統(tǒng)的出現(xiàn)，該領(lǐng)域的研究報告數(shù)量正在逐漸增加。盡管科學界認識到代謝組學在這一新興領(lǐng)域的潛力，但由于采樣考慮和技術(shù)挑戰(zhàn)等多種因素，它尚未被農(nóng)業(yè)食品部門和監(jiān)管機構(gòu)廣泛采用于常規(guī)質(zhì)量評估。
3.3 代謝組學的采樣和其他考慮因素
As detailed in the earlier?Section 3.2, the use of metabolomics in evaluating flavor attributes of fresh PBPs is gaining considerable interest in the scientific community. However, its widespread adoption by agri-food related sectors and regulatory agencies would require streamlining (i) sampling protocols; (ii) pre-concentration and extraction procedures; and (iii) analytical platforms and approaches. We describe below these three important points for consideration in order to successfully employ metabolomics for evaluating flavor-associated metabolites in fresh PBPs.
如之前第3.2節(jié)所述，代謝組學在評估新鮮植物基產(chǎn)品（PBPs）的風味特性方面正受到科學界的廣泛關(guān)注。然而，要使其在農(nóng)業(yè)食品部門和監(jiān)管機構(gòu)中得到廣泛應用，需要優(yōu)化以下三個方面：（i）采樣協(xié)議；（ii）預濃縮和提取程序；（iii）分析平臺與方法。在成功應用代謝組學來評估新鮮植物基產(chǎn)品（PBPs）中的風味相關(guān)代謝物時，分析平臺與方法是另一個至關(guān)重要的考慮因素。
(i)Sampling protocols: As the biosynthesis of flavor-associated metabolites in fresh PBPs is often influenced by several genetic and environmental factors [87], sampling protocols are a critical step in determining true readouts. Environmental factors including farm/management practices, degree of maturity and post-harvest handling will affect the abundance of these bioactive metabolites in the fresh PBPs [88]. Apart from the environmental factors, the nature of these metabolites and their chemistries will also influence the sampling protocols and operational procedures as some metabolites are found in bound form, while others are released only upon tissue disruption.?
(i) 采樣協(xié)議：由于新鮮植物基產(chǎn)品（PBPs）中風味相關(guān)代謝物的生物合成往往受到多種遺傳和環(huán)境因素的影響[87]，因此采樣協(xié)議是確定真實結(jié)果的關(guān)鍵步驟。環(huán)境因素，包括農(nóng)場/管理實踐、成熟度和采后處理，都會影響這些生物活性代謝物在新鮮PBPs中的含量[88]。除了環(huán)境因素外，這些代謝物的性質(zhì)和化學結(jié)構(gòu)也會影響采樣協(xié)議和操作程序，因為一些代謝物以結(jié)合形式存在，而其他代謝物則僅在組織破壞時釋放。
For instance, certain aroma metabolites are only released upon cell disruption when enzymes and their corresponding substrates interact [89]. However, some aroma compounds are bound to sugars as glycosides or glucosinolates [90] and odorous aglycones could be released from the sugar moiety during post-harvest stages. Hence, it is pertinent to adopt sampling protocols that can capture the metabolites of interest in a PBP.?
例如，某些香氣代謝物僅在細胞破壞時酶與其相應底物相互作用時釋放[89]。然而，一些香氣化合物以糖苷或硫代葡萄糖苷的形式與糖結(jié)合[90]，在采后階段糖基部分可能釋放出有氣味的配基。因此，采用能夠捕獲PBP中感興趣代謝物的采樣協(xié)議至關(guān)重要。
To simplify, protocols can be standardized for certain families of PBPs, which are known to have similar metabolite classes. For instance, members of?Brassica?genus (such as broccoli, cabbage, kale) are known to contain glucosinolates (GSLs, sulphur rich secondary metabolites) contributing to their bitter taste and unique aroma [91], and sampling protocols can be standardized across members of this genus for efficient capture of GSLs. Alternatively, protocols can be standardized across different PBPs for the same families of metabolites, such as benzenoids, alcohols and esters.
為了簡化操作，可以對具有相似代謝物類別的某些PBP家族制定標準化的采樣協(xié)議。例如，十字花科屬（如西蘭花、卷心菜、羽衣甘藍）的植物以含有硫代葡萄糖苷（GSLs，富含硫的次級代謝物）而聞名，這些物質(zhì)為其提供了苦味和獨特香氣[91]，因此可以對該屬內(nèi)的成員制定標準化的采樣協(xié)議，以有效捕獲GSLs。另外，也可以針對不同PBPs中相同類別的代謝物（如苯環(huán)化合物、醇類和酯類）制定標準化的采樣協(xié)議。
Sampling time-points are equally important, as it is known that PBPs have varying levels and kinds of metabolites at different growth and maturity stages. For instance, it is known that the growth stage has an influence on specific GSLs composition and content among members from?Brassica?genus [92]. Similarly, anthocyanins are also regulated differently at different developmental and ripening stages [93].
采樣時間點同樣重要，因為已知PBPs在不同生長和成熟階段具有不同水平和種類的代謝物。例如，已知生長階段會影響十字花科屬成員中特定GSLs的組成和含量[92]。因此，在選擇采樣時間點時，應充分考慮PBPs的生長和成熟周期，以確保捕獲到最具代表性的風味相關(guān)代謝物。同樣地，花青素（Anthocyanins）在不同發(fā)育和成熟階段也受到不同的調(diào)控[93]。
(ii)Pre-processing and extraction procedures: Apart from sampling protocols, the choice and selection of pre-processing and extraction procedures are equally important due to the thermolabile nature and trace concentrations of these metabolites in fresh PBPs. Extraction procedures largely depend on (i) the nature and chemistry of metabolites (polar/non-polar; volatile/non-volatile); (ii) the thermal stability and sensitivity; and (iii) their occurrence and subsequent release. A variety of methods are prescribed for the extraction and characterization of metabolites linked to the flavor properties of fresh PBPs.?
(ii) 預處理和提取程序：除了采樣協(xié)議外，選擇和確定預處理和提取程序?qū)τ谛迈rPBPs中這些代謝物的分析同樣至關(guān)重要，因為這些代謝物在新鮮PBPs中具有熱不穩(wěn)定性和痕量濃度的特點。提取程序主要依賴于（i）代謝物的性質(zhì)和化學結(jié)構(gòu)（極性/非極性；揮發(fā)性/非揮發(fā)性）；（ii）熱穩(wěn)定性和敏感性；以及（iii）它們的存在和隨后的釋放。針對與新鮮PBPs風味特性相關(guān)的代謝物的提取和表征，已經(jīng)規(guī)定了多種方法。
Due to the volatile nature of a variety of aroma-metabolites, headspace analyses involving the gas phase in equilibrium with PBPs are commonly utilized for flavor analyses. The headspace-solid phase microextraction (HS-SPME) is notable for being sensitive, solvent-free and has been successfully employed for flavor extraction of fresh PBPs [94,95]. SPME fiber coatings with different polarities are often required for effective capture of aroma-metabolites with varying chemistries and affinities [96]. However, the limitations of SPME have been pointed out for the quantitation of certain volatile classes of aroma-metabolites [97].?
由于多種香氣代謝物具有揮發(fā)性，因此常與PBPs處于平衡狀態(tài)的氣相進行頂空分析，以進行風味分析。頂空固相微萃?。℉S-SPME）因其靈敏度高、無需溶劑的特點而被廣泛應用于新鮮PBPs的風味提取[94,95]。為了有效捕獲具有不同化學性質(zhì)和親和力的香氣代謝物，通常需要具有不同極性的SPME纖維涂層[96]。然而，SPME在定量某些揮發(fā)性香氣代謝物方面存在局限性[97]。
Other techniques used for capturing volatile and semi-volatile metabolites from PBPs are solvent-less enrichment techniques, such as stir bar sorptive extraction (SBSE) [98] and headspace sorptive extraction, (HSSE) wherein stir bar (covered in polysiloxane) is exposed to the sample (either in gaseous or liquid sample media). After extraction, compounds are thermally desorbed before analyses. Extraction techniques assisted by solvents and thermal distillation have been utilized for certain classes of organosulphur metabolites. Steam distillation (SD), simultaneous distillation and solvent extraction (SDE), and solid-phase trapping solvent extraction (SPTE) are used to characterize sulphur-rich aroma-metabolites in certain fresh PBPs such as garlic and onion [98]. Similarly, liquid–liquid extraction (LLE) and solvent-assisted flavor evaporation (SAFE) are used as preferred extraction techniques for furan derivatives that contribute to flavor profiles of certain PBPs [99]. It is pertinent to note here that several extraction techniques have been evaluated based on trapping, capture and dissolution of metabolites to enhance metabolite coverage from plant matrices.
除了溶劑提取方法外，從植物源揮發(fā)性和半揮發(fā)性代謝物（PBPs）中捕獲這些物質(zhì)還采用了無溶劑富集技術(shù)，如攪拌棒吸附萃取（Stir Bar Sorptive Extraction, SBSE）[98]和頂空吸附萃?。℉eadspace Sorptive Extraction, HSSE）。在SBSE中，覆蓋有聚硅氧烷的攪拌棒被暴露于樣品中（樣品可以是氣態(tài)或液態(tài)介質(zhì)）。提取后，化合物在進行分析前會經(jīng)過熱解析。對于某些類別的有機硫代謝物，則采用了溶劑輔助和熱蒸餾的提取技術(shù)。蒸汽蒸餾（Steam Distillation, SD）、同時蒸餾萃取（Simultaneous Distillation and Solvent Extraction, SDE）和固相捕集溶劑萃?。⊿olid-Phase Trapping Solvent Extraction, SPTE）等技術(shù)被用于表征大蒜、洋蔥等某些新鮮PBPs中富含硫的芳香代謝物[98]。類似地，液液萃?。↙iquid-Liquid Extraction, LLE）和溶劑輔助風味蒸發(fā)（Solvent-Assisted Flavor Evaporation, SAFE）被用作提取某些PBPs中貢獻風味輪廓的呋喃衍生物的首選技術(shù)[99]。這里需要特別指出的是，已經(jīng)根據(jù)代謝物的捕獲、收集和溶解來評估了幾種提取技術(shù)，以從植物基質(zhì)中增強代謝物的覆蓋范圍。
(iii)Analytical platforms and approaches: As seen in the previous section, analytical approaches and platforms are also dependent on the metabolites of interest. GC-O or GC-MS (gas-chromatography-olfactory/gas-chromatography mass-spectrometry) are routinely employed for the detection of aroma- and odor-producing metabolites [63,65,69]. In olfactometric techniques, the nose is used as a GC detector. The GC system can be set up with the column split, and a portion of the effluent goes to the sniffing port and the remainder is fed to the GC detector (FID or an MS detector). GC-O produces an aromagram, which lists the odor character of each peak in a GC run. This method is dependent on the analyst and his sensory perception and, hence, this is a powerful technique which can bridge the conventional sensory evaluation and panel tests with more quantitative information. GC-O can be employed to distinguish between characteristic and off-odors in fresh PBPs, which will assist in quality assessment in terms of food safety and consumer acceptability. While GC-O is more to detect odor and aroma-metabolites, when it is paired with MS detector, it can be used as an identification tool to characterize and quantitate certain metabolites of interest [100]. Other instrumental methods used include NMR and LC-MS. LC-MS platforms are mainly restricted for non-volatile classes of metabolites [82,83,84] such as organic acids, sugars and certain polyphenols which contribute to characteristic taste notes in fresh PBPs.
（iii）分析平臺和方法：正如前一節(jié)所看到的，分析方法和平臺也取決于感興趣的代謝物。氣相色譜-嗅覺分析（GC-O）或氣相色譜-質(zhì)譜聯(lián)用（GC-MS）常用于檢測產(chǎn)生香氣和異味的代謝物[63,65,69]。在嗅覺測定技術(shù)中，鼻子被用作氣相色譜的檢測器。氣相色譜系統(tǒng)可以設置成分流柱，一部分流出物進入嗅探口，其余部分送入氣相色譜檢測器（FID或MS檢測器）。GC-O會產(chǎn)生一個氣味圖，列出氣相色譜運行中每個峰的氣味特征。這種方法依賴于分析人員及其感官感知，因此，這是一種強大的技術(shù)，可以將傳統(tǒng)的感官評估和小組測試與更多定量信息相結(jié)合。GC-O可用于區(qū)分新鮮PBPs中的特征氣味和異味，這將有助于食品安全和消費者接受度方面的質(zhì)量評估。雖然GC-O主要用于檢測氣味和香氣代謝物，但當它與MS檢測器結(jié)合時，可用作表征和定量某些感興趣代謝物的鑒定工具[100]。其他使用的儀器方法包括核磁共振（NMR）和液相色譜-質(zhì)譜聯(lián)用（LC-MS）。LC-MS平臺主要局限于非揮發(fā)性代謝物類別[82,83,84]，如有機酸、糖類和某些多酚，這些物質(zhì)對新鮮PBPs的特征風味有貢獻。
Lately, biosensors (such as electronic noses and electronic tongues) based on pattern recognition of flavor and aroma metabolites have been developed that can crudely mimic the human taste and olfactory receptors and their communication with the human brain [101,102]. These electronic noses (e-noses) and electronic tongues (e-tongues) do not generate information on sample composition but provide a digital fingerprint through pattern recognition. These devices are capable of mimicking human smell and taste sensors based on previous exposure leading to pattern recognition through neural networks. This is useful for routine post-harvest quality assessment of fresh PBPs to evaluate produce for optimum flavor attributes. For instance, it can be used to evaluate effects on storage conditions on quality of fresh PBPs [103]. Recently, e-noses have been utilized for diverse PBPs (especially fruits and vegetables) to evaluate volatile metabolites that are associated with flavor and/or post-harvest quality of PBPs [104,105,106]. Most often, these sensors have been used in combination with GC-O/ GC-MS techniques with or without sensory analyses, as summarized in?Table 3.
近年來，基于風味和香氣代謝物模式識別的生物傳感器（如電子鼻和電子舌）得到了發(fā)展，這些傳感器能夠粗略地模擬人類味覺和嗅覺受體及其與大腦的通訊[101,102]。這些電子鼻（e-noses）和電子舌（e-tongues）不產(chǎn)生關(guān)于樣品組成的信息，但通過模式識別提供數(shù)字指紋。這些設備能夠基于先前的暴露來模擬人類的嗅覺和味覺傳感器，并通過神經(jīng)網(wǎng)絡進行模式識別。這對于新鮮PBPs的日常收獲后質(zhì)量評估非常有用，可以評估產(chǎn)品的最佳風味特性。例如，它可以用于評估儲存條件對新鮮PBPs質(zhì)量的影響[103]。最近，電子鼻已被用于各種PBPs（尤其是水果和蔬菜）中，以評估與風味和/或收獲后質(zhì)量相關(guān)的揮發(fā)性代謝物[104,105,106]。這些傳感器通常與GC-O/GC-MS技術(shù)結(jié)合使用，無論是否進行感官分析，如表3所示。
Table 3.?Representative summary of recent studies reporting application of e-nose with or without other analytical platforms to evaluate flavor-associated metabolites in fresh PBPs.
表3. 近期研究報告中將電子鼻與其他分析平臺結(jié)合使用或單獨使用以評估新鮮PBPs中風味相關(guān)代謝物的代表性總結(jié)。
| Metabolites Class | PBP Used | Analytical Platform | Reference |
|---|---|---|---|
| Aldehydes, Alcohols and ketones | Apricots (Prunus armeniaca) | GC; e-nose; sensory analysis | [104] |
| Alcohols, terpene, aromatic hydrocarbons, aliphatic hydrocarbons | Mango (Mangifera indica) | GC; e-nose | [105] |
| Aromatic and aliphatic hydrocarbons | Blueberry (Vaccinium corymbosum) | e-nose | [106] |
| Alcohol, ester, aldehyde, terpenes | Grapes (Vitis vinifera) | GC; e-nose | [107] |
| Aldehydes, Alcohol, ketones | Tomato (Lycopersicon esculentum) | e-nose | [108] |
| Aldehydes, ketones, sulphur compounds, alkanes, terpenes, alcohols | Pineapple (Ananus Comosus) | e-nose | [109] |
| Acids, esters, Aldehydes, ketones, aliphatic and aromatic hydrocarbons | Citrus | GC-MS; e-nose | [110] |
| Ester, carboxylic acids, alcohols, Aldehydes, monterpenes | White and red fleshed peach (Prunus persica) | GC-MS; e-nose | [111] |
| Carboxylic acid, ester, alcohol, | Snake fruit (Salacca zalacca) | GC-MS; e-nose | [112] |
| Pyruvic acid | Onion (Allium cepa) | HPLC; e-nose | [113] |
| 物性生物產(chǎn)品（PBP） | 分析平臺 | 參考文獻 | |
|---|---|---|---|
| 醛類、醇類和酮類 | 杏（Prunus armeniaca） | 氣相色譜（GC）；電子鼻（e-nose）；感官分析 | [104] |
| 醇類、萜烯、芳香烴、脂肪烴 | 芒果（Mangifera indica） | 氣相色譜（GC）；電子鼻（e-nose） | [105] |
| 芳香烴和脂肪烴 | 藍莓（Vaccinium corymbosum） | 電子鼻（e-nose） | [106] |
| 醇類、酯類、醛類、萜烯 | 葡萄（Vitis vinifera） | 氣相色譜（GC）；電子鼻（e-nose） | [107] |
| 醛類、醇類、酮類 | 番茄（Lycopersicon esculentum） | 電子鼻（e-nose） | [108] |
| 醛類、酮類、硫化物、烷烴、萜烯、醇類 | 菠蘿（Ananas comosus） | 電子鼻（e-nose） | [109] |
| 酸類、酯類、醛類、酮類、脂肪烴和芳香烴 | 柑橘類 | 氣相色譜-質(zhì)譜聯(lián)用（GC-MS）；電子鼻（e-nose） | [110] |
| 酯類、羧酸類、醇類、醛類、單萜烯 | 白肉和紅肉桃（Prunus persica） | 氣相色譜-質(zhì)譜聯(lián)用（GC-MS）；電子鼻（e-nose） | [111] |
| 羧酸類、酯類、醇類 | 蛇皮果（Salacca zalacca） | 氣相色譜-質(zhì)譜聯(lián)用（GC-MS）；電子鼻（e-nose） | [112] |
| 丙酮酸 | 洋蔥（Allium cepa） | 高效液相色譜（HPLC）；電子鼻（e-nose） | [113] |
To summarize, reliable and credible estimations of metabolites corresponding to flavor-related sensory attributes in PBPs require careful sampling strategies, thorough pre-processing and extraction procedures followed by robust analytical platforms.
總結(jié)來說，為了對植物性生物產(chǎn)品（PBPs）中與風味相關(guān)的感官屬性進行可靠且可信的代謝物估算，需要精心的采樣策略、徹底的預處理和提取程序，以及強大的分析平臺。
3.4 植物性生物產(chǎn)品的代謝組學與質(zhì)量評估
The quality of the fresh PBPs in terms of their nutritive value and flavor profiles is essentially driven by their biochemical composition. Biochemical composition is also a key factor in determining other important properties of fresh PBPs such as shelf life, nutritional stability, and economic value. New tools are required to define “quality” to include more quantitative information about the biochemical composition of food, as consumers’ expectations continue to grow with respect to food quality and safety [114]. Meanwhile, current quality assessment relies heavily on classical methodologies which can largely inform general consumer acceptability, but they lack the ability to provide detailed information on biochemical composition or metabolites that correspond to unique flavors of fresh PBPs.?
新鮮PBPs的營養(yǎng)價值和風味特征主要由其生化組成決定。生化組成也是決定新鮮PBPs其他重要屬性（如保質(zhì)期、營養(yǎng)穩(wěn)定性和經(jīng)濟價值）的關(guān)鍵因素。隨著消費者對食品質(zhì)量和安全性的期望不斷提高，需要新的工具來定義“質(zhì)量”，以包含更多關(guān)于食品生化組成的定量信息[114]。然而，目前的質(zhì)量評估主要依賴于傳統(tǒng)方法，這些方法雖然能在很大程度上反映一般消費者的接受度，但缺乏提供關(guān)于新鮮PBPs獨特風味對應生化組成或代謝物的詳細信息的能力。
To this end, metabolomics can pave the way for decoding the composition and nature of flavor-associated metabolites in fresh PBPs, which can open avenues for further improvements of PBPs [115,116]. As such, the scope of metabolomics in this domain extends beyond just quality assessment for flavor-associated metabolites; it can be further utilized for (i) biomarker-detection related to food safety; (ii) development of new crops with better genetic traits; (iii) determination of food contaminants/adulterants; and (iv) new investigations on food bioactivities [117,118,119].
為此，代謝組學可以為解碼新鮮PBPs中風味相關(guān)代謝物的組成和性質(zhì)鋪平道路，從而為PBPs的進一步改進開辟途徑[115,116]。因此，代謝組學在這一領(lǐng)域的范圍不僅限于風味相關(guān)代謝物的質(zhì)量評估；它還可以進一步用于（i）食品安全相關(guān)的生物標志物檢測；（ii）開發(fā)具有更好遺傳性狀的新作物；（iii）確定食品污染物/摻假物；以及（iv）對食品生物活性的新研究[117,118,119]。這些應用展示了代謝組學在提升PBPs質(zhì)量、安全性和市場價值方面的巨大潛力。
Although a distinct research area on food metabolomics has been established in the scientific community in relation to the application of metabolomics in food system processes [119,120] from farm to consumers, its widespread adoption comes with certain unparalleled challenges (as discussed in?Section 3.3). These challenges are often compounded by the nature of the food metabolome, which is complex and variable in nature as thousands of metabolites are present in fresh PBPs with varying polarities and chemistries [121]. Measuring and quantifying the metabolome that best represents the flavor profiles of fresh PBPs can pose analytical challenges as it may not be possible to detect all of them in a single analysis. To this end, utilizing multiple analytical techniques and approaches is often recommended in food metabolomics which can complement each other and provide a wider coverage [122,123].
盡管在科學界中已經(jīng)建立了與食品系統(tǒng)中從農(nóng)場到消費者過程中代謝組學應用相關(guān)的食品代謝組學這一獨特研究領(lǐng)域[119,120]，但其廣泛應用仍面臨一些無與倫比的挑戰(zhàn)（如第3.3節(jié)所述）。這些挑戰(zhàn)往往因食品代謝組的復雜性和可變性而加劇，因為新鮮PBPs中存在數(shù)以千計的代謝產(chǎn)物，它們具有不同的極性和化學性質(zhì)[121]。測量和量化最能代表新鮮PBPs風味特征的代謝組可能會帶來分析挑戰(zhàn)，因為可能無法在一次分析中檢測到所有代謝物。為此，在食品代謝組學中通常推薦使用多種分析技術(shù)和方法，它們可以相互補充，提供更廣泛的覆蓋范圍[122,123]。
In addition to this, the food matrix of PBPs will also affect the detection and quantification of compounds that are present at very low concentrations in fresh PBPs or are present in bound forms and unstable forms (as discussed in?Section 3.3). Apart from these analytical and sampling-related hurdles, there are certain challenges at downstream data processing and integration with current quality assessment methodologies, and these will be discussed in the next section.
除了這一點外，PBPs的食品基質(zhì)也會影響在新鮮PBPs中以極低濃度存在或以結(jié)合形式和不穩(wěn)定形式存在的化合物的檢測和量化（如第3.3節(jié)所述）。除了這些分析和采樣相關(guān)的障礙外，在下游數(shù)據(jù)處理和與當前質(zhì)量評估方法的集成方面也存在某些挑戰(zhàn)，這些將在下一節(jié)中討論。
4. 新鮮PBPs的風味評估：未來方向
As discussed in?Section 3.3?and?Section 3.4, there is an immediate need to extend and complement the current repertoire of sensory-based and coarse instrumental estimations to evaluate the flavor- associated metabolites in fresh PBPs. This need is fueled by several socio-economic and psychological factors that have been discussed in the earlier section (Section 1.1?and?Section 1.2). Against this background, the current quality assessment methodologies for fresh PBPs will need to be more inclusive of systematic metabolic estimations for flavor attributes in fresh PBPs. Metabolomics can prove to be a valuable tool in this regard, however, utilizing this technique with other routine quality assessment methodologies will require careful considerations at multiple levels. Additionally, it is pertinent to note here that although metabolomics can provide useful biochemical insights about flavor-associated metabolites in PBPs, it cannot provide any information on the human perception of food flavors, which is often influenced by physiological, psychological, genetics and other associated socio-cultural factors [124,125,126]. These factors contribute to the inter-individual variation and cause stark differences in perception of these metabolites by various population groups. To account for these differences, sensory-based tests will remain critical to obtain holistic understanding on consumer acceptance and behavior.
正如第3.3節(jié)和第3.4節(jié)所討論的，目前迫切需要擴展和補充基于感官和粗略儀器評估的現(xiàn)有方法，以評估新鮮PBPs中與風味相關(guān)的代謝物。這一需求受到前幾節(jié)（第1.1節(jié)和第1.2節(jié)）中討論的多個社會經(jīng)濟和心理因素的推動。在此背景下，當前對新鮮PBPs的質(zhì)量評估方法需要更加全面地納入對風味特性的系統(tǒng)性代謝評估。代謝組學在這方面可以證明是一個有價值的工具，然而，將這一技術(shù)與其他常規(guī)質(zhì)量評估方法結(jié)合使用時，需要在多個層面上進行仔細考慮。此外，值得注意的是，盡管代謝組學可以提供關(guān)于PBPs中與風味相關(guān)的代謝物的有用生化見解，但它無法提供關(guān)于人類對食物風味感知的任何信息，這種感知往往受到生理、心理、遺傳和其他相關(guān)社會文化因素的影響[124,125,126]。這些因素導致了個體差異，并導致不同人群對這些代謝物的感知存在顯著差異。為了解釋這些差異，基于感官的測試對于全面了解消費者的接受度和行為仍然至關(guān)重要。
To harness the potential of metabolomics for evaluating flavor-associated metabolites in PBPs, it is important to keep in mind that both pre and post-harvest procedures including the extraction and analysis of metabolites will have great bearing on the observed results (Figure 1). In order to complement the existing sensory-based and instrumental measurements, a clear interface and seamless integration has to be established between the pre and post-harvest procedure in order to s to ensure aa smooth workflow for rapid quality assessment of fresh PBPs (Figure 2).
為了利用代謝組學評估PBPs中與風味相關(guān)的代謝物的潛力，重要的是要記住，包括代謝物提取和分析在內(nèi)的采收前和采收后程序都將對觀察到的結(jié)果產(chǎn)生重大影響（見圖1）。為了補充現(xiàn)有的基于感官和儀器的測量方法，必須在采收前和采收后程序之間建立一個清晰的界面和無縫集成，以確保為新鮮PBPs的快速質(zhì)量評估提供順暢的工作流程（見圖2）。
Figure 1.?Considerations for utilizing metabolomics for evaluating flavor-associated metabolites in fresh PBPs. Here, we describe the various factors that will have an effect on metabolite estimations in fresh PBPs.
圖1. 利用代謝組學評估新鮮PBPs中與風味相關(guān)的代謝物的考慮因素。?在此，我們描述了各種將影響新鮮PBPs中代謝物估計的因素。
Figure 2.?Framework for integrating metabolomics with current state-of-the-art technologies for the organoleptic evaluation of fresh PBPs. While physicochemical measurements are coarse-scale estimations, metabolomics and sensory-based tests serve as fine-scale estimations to achieve a holistic flavor profiling of fresh PBPs. Data integration platforms would play a crucial role to achieve seamless data stitching for meaningful insights.
圖2。將代謝組學與當前最先進的技術(shù)相結(jié)合的框架，用于新鮮PBPs的感官評估。雖然物理化學測量是粗略的估計，但代謝組學和基于感官的測試可以作為精細的估計，以實現(xiàn)新鮮PBPs的整體風味分析。數(shù)據(jù)集成平臺將在實現(xiàn)無縫數(shù)據(jù)拼接以獲得有意義的見解方面發(fā)揮關(guān)鍵作用。
Integrating metabolomics with the current state-of-the-art technologies for quality assessment will require synchronized efforts at several points—all the way from data collection to data analyses. To maximize the potential of metabolomics approaches, data collation from various platforms along with careful data interpretation will undoubtedly play a key role. This can lead to several other technical challenges, depending upon the category of PBPs in question, and the nature of information required. Some of the technical challenges could be related to the availability of (i) the right instrumental platform or extraction protocols for metabolites of interest; (ii) reference databases and spectral libraries for matching interesting metabolic features in PBPs; and (iii) the complete metabolome or databank for the plant source in question.
將代謝組學與當前最先進的質(zhì)量評估技術(shù)相結(jié)合，需要在從數(shù)據(jù)收集到數(shù)據(jù)分析的各個方面同步努力。為了最大限度地發(fā)揮代謝組學方法的潛力，來自各個平臺的數(shù)據(jù)整理以及仔細的數(shù)據(jù)解釋無疑將發(fā)揮關(guān)鍵作用。這可能會導致其他一些技術(shù)挑戰(zhàn)，這取決于所討論的pbp的類別和所需信息的性質(zhì)。一些技術(shù)挑戰(zhàn)可能與(i)合適的儀器平臺或感興趣的代謝物提取方案的可用性有關(guān);(ii)參考數(shù)據(jù)庫和譜庫，用于匹配PBPs中有趣的代謝特征;(iii)有關(guān)植物來源的完整代謝組或數(shù)據(jù)庫。
Owing to the rapid developments in extraction and analytical methodologies, several options are available to analyze metabolites with varying chemistries, thereby increasing the global metabolite coverage. With these developments, the first technical hurdle can be conquered with few rounds of trials and optimization. However, the second and third technical challenges pose the greatest difficulty, not just for the agri-food domain, but also for other scientific domains, as a lack of reference databases and metabolome information makes it difficult to interpret the data and obtain meaningful insights. Lately, several curated databases have been made available in the plant domain specifically for diverse phytochemicals and bioactive metabolites to help the research community [127,128]. As the plant metabolome is highly diverse, with thousands of metabolites, it presents a laborious and technically challenging task to annotate every single metabolite. To overcome this challenge, efforts can be strategized towards the identification of candidate/marker metabolic members from different classes that can best represent the specific PBPs. This would eliminate the need to identify each metabolite and, at the same time, will serve as reference for rapid screening of PBPs based on presence of certain key metabolite classes. The choice and selection of such metabolite classes would depend upon the type of PBPs and their ultimate end-use. Monitoring glucosinolates (sulphur containing metabolites) in members from?Brassica?genus can be a classical example for this, as these metabolites are (i) unique to?Brassica?family members; (ii) associated with the flavor attributes of these plant types; and (iii) known for their human health benefits. Similarly, eucalyptols (cyclic ether, monoterpenoids) are unique to members of the?Myrtaceae?family and they are known for imparting a mint-like aroma and spicy taste notes. Other examples include PBPs from?Amaryllidaceae?that contain S-alk(en)yl-l-cysteine sulfoxides. Another way to approach this challenge will be to generate reference metabolic fingerprints of PBPs and utilize machine learning-based algorithms for pattern recognitions and high-throughput screening. This approach relies on the premise that if sampling, extraction and analytical conditions are kept the same, metabolic fingerprint from two PBPs samples of same type would be identical or similar to a large extent. However, this approach should be utilized as a fast screen and for more quantitative information, in-depth analyses are recommended. Apart from these technical challenges, a systematic method to integrate and collate the data from various platforms is warranted to maximize the potential of multi-platforms in the sensory evaluation of fresh PBPs.
由于提取和分析方法的迅速發(fā)展，有幾種選擇可用于分析具有不同化學性質(zhì)的代謝物，從而增加了全球代謝物的覆蓋率。有了這些發(fā)展，第一個技術(shù)障礙可以通過幾輪試驗和優(yōu)化來克服。然而，第二和第三個技術(shù)挑戰(zhàn)帶來了最大的困難，不僅對農(nóng)業(yè)食品領(lǐng)域，而且對其他科學領(lǐng)域也是如此，因為缺乏參考數(shù)據(jù)庫和代謝組信息使得難以解釋數(shù)據(jù)并獲得有意義的見解。最近，在植物領(lǐng)域?qū)ｉT為各種植物化學物質(zhì)和生物活性代謝物建立了幾個數(shù)據(jù)庫，以幫助研究界[127,128]。由于植物代謝組具有高度多樣性，有數(shù)千種代謝物，因此對每一種代謝物進行注釋是一項艱苦且具有技術(shù)挑戰(zhàn)性的任務。為了克服這一挑戰(zhàn)，可以從不同的類別中確定最能代表特定PBPs的候選/標記代謝成員。這將消除識別每種代謝物的需要，同時，將作為基于某些關(guān)鍵代謝物類別的PBPs快速篩選的參考。這些代謝物類別的選擇將取決于PBPs的類型及其最終用途。監(jiān)測來自蕓苔屬成員的硫代葡萄糖苷(含硫代謝物)可能是一個典型的例子，因為這些代謝物是(i)蕓苔屬成員所特有的;(ii)與這些植物類型的風味屬性有關(guān);(三)以對人體健康有益而聞名。類似地，桉樹精油(環(huán)醚，單萜類)是桃金娘科成員所特有的，它們以賦予薄荷般的香氣和辛辣的味道而聞名。其他的例子包括來自Amaryllidaceae的PBPs，它含有S-alk(en)yl-l-半胱氨酸亞砜。解決這一挑戰(zhàn)的另一種方法是生成PBPs的參考代謝指紋，并利用基于機器學習的算法進行模式識別和高通量篩選。該方法的前提是，在取樣、提取和分析條件相同的情況下，同一類型的兩個PBPs樣品的代謝指紋在很大程度上是相同或相似的。但是，這種方法應該用作快速篩選，并建議進行深入分析以獲得更多定量信息。除了這些技術(shù)挑戰(zhàn)之外，需要一種系統(tǒng)的方法來整合和整理來自不同平臺的數(shù)據(jù)，以最大限度地發(fā)揮多平臺在新鮮PBPs感官評估中的潛力。
A significant improvement has been achieved in recent years in data integration and chemometrics pipelines, making it easier to obtain integrated biological outputs from different platforms. In recent years, numerous tools have been developed, written in most used programming languages such as Python, R, and Matlab??to aid in metabolomics data curation and management [127]. Additionally, several platforms are being made available for sharing scripts and workflows through open-access repositories (Github, StackOverflow). Interactive and intuitive data integration workflows are being developed that have adopted artificial intelligence (AI) and machine learning (ML) approaches [129,130]. Data integration platforms that combine e-noses and e-tongues with high resolution MS and analytical instrumentation could be a way to logically bridge current gaps between human-based sensory tests and metabolic estimations. Although these artificial sensory techniques cannot integrate taste and smell as can be done by the human sensory system, they can generate reliably consistent data in a high-throughput format. With the availability of the requisite computational power, it is possible to integrate such modular information from these artificial sensors to obtain meaningful insights [131,132].
近年來，在數(shù)據(jù)集成和化學計量學管道方面取得了重大進展，使得從不同平臺獲得綜合生物輸出變得更加容易。近年來，已經(jīng)開發(fā)了許多工具，用最常用的編程語言(如Python、R和Matlab?)編寫，以幫助代謝組學數(shù)據(jù)的管理和管理[127]。此外，有幾個平臺可以通過開放訪問存儲庫(Github, StackOverflow)共享腳本和工作流。采用人工智能(AI)和機器學習(ML)方法的交互式和直觀的數(shù)據(jù)集成工作流程正在開發(fā)[129,130]。將電子鼻和電子舌與高分辨率質(zhì)譜和分析儀器相結(jié)合的數(shù)據(jù)集成平臺可能是一種從邏輯上彌合目前基于人類的感官測試和代謝估計之間差距的方法。雖然這些人工感官技術(shù)不能像人類感官系統(tǒng)那樣整合味覺和嗅覺，但它們可以以高通量格式生成可靠一致的數(shù)據(jù)。有了必要的計算能力，就有可能整合這些人工傳感器的模塊化信息，以獲得有意義的見解[131,132]。
This will be particularly resourceful for innovations and new product developments in this domain as we continue to witness intense reformation and diversification of food palates globally. In addition, integrating these platforms with trained artificial intelligence can further uplift them to smart sensing platforms that can, to an extent, also predict emerging food safety threats in terms of adulterants and/or pathogens. To make this a real scenario, coordinated efforts and synchronized response will be required from several stakeholders working in this evolving domain.
隨著我們繼續(xù)見證全球食品口味的激烈改革和多樣化，這將為該領(lǐng)域的創(chuàng)新和新產(chǎn)品開發(fā)提供特別豐富的資源。此外，將這些平臺與訓練有素的人工智能相結(jié)合，可以進一步將其提升為智能傳感平臺，在某種程度上，還可以預測摻假和/或病原體方面出現(xiàn)的食品安全威脅。為了使這成為一個真實的場景，將需要在這個不斷發(fā)展的領(lǐng)域中工作的幾個利益相關(guān)者協(xié)調(diào)努力和同步響應。
5. 結(jié)論
To conclude, utilizing metabolomics for evaluating flavor-associated metabolites in PBPs would likely become a necessity in coming years and it will see multiple applications from product authenticity, quality assessment, new product development and enhanced food safety.
利用代謝組學來評估植物基產(chǎn)品（PBPs）中與風味相關(guān)的代謝物，在未來幾年內(nèi)很可能會成為一種必然需求，并且將在產(chǎn)品真實性驗證、質(zhì)量評估、新產(chǎn)品開發(fā)和增強的食品安全等多個方面展現(xiàn)出廣泛的應用。
原文鏈接：
Pavagadhi S, Swarup S. Metabolomics for Evaluating Flavor-Associated Metabolites in Plant-Based Products.?Metabolites. 2020; 10(5):197. https://doi.org/10.3390/metabo10050197
