Sensory evaluation, chemical structures, and threshold concentrations of bitter-tasting compounds in common foodstuffs derived from plants and maillard reaction: A review

Investigation of non-volatile metabolite variations during round green tea processing and effect of pan-frying degree using untargeted metabolomics and objective quantification

Round green tea (RGT) presents unique properties and is widely distributed in China, and during processing, it undergoes dynamic changes in non-volatile metabolites (NVMs), which are poorly understood. Utilizing UHPLC-Q-Exactive/MS analysis, this study comprehensively characterized 216 NVMs during RGT processing and identified fixation and pan-frying as key processes influencing NVMs. Additionally, 23 key differential NVMs were screened, with amino acid and flavonoid metabolism highlighted as key metabolic pathways for RGT taste and color quality. The impact of pan-frying degree on shape, color, and taste was also explored. Moderate pan-frying led to optimal results, including a tight and round shape, green and bright color, mellow and umami taste, and reduced astringent and bitter taste NVMs, including epigallocatechin gallate, procyanidin B2, myricetin 3-O-galactoside, quinic acid, strictinin, phenylalanine, and theobromine. This study addresses the NVM research gap in RGT processing, thus providing a technical foundation for the precision-oriented processing of high-quality tea.

Enhancement of rosehip bioactive compounds by cold plasma pretreatment and application of its extract as a functional ingredient in ketchup

The effect of cold plasma (CP) was investigated on rosehip characterization for 1,2.5, and 5 min. All of the samples that were treated with CP had higher amounts of total phenolic content (TPC), antioxidant activity, vitamin C, and lycopene compared to the control (P < 0.05). The extract obtained by rosehip pretreated for 1 min had the highest antioxidant activity as well as bioactive compounds (except anthocyanin) and was selected for application in ketchup. Utilizing the CP-treated rosehip extract (RE) in ketchup successfully enhanced TPC (by 1.44 times), flavonoids (by 1.31 times), antioxidant activity (by 1.21 times), carotenoids (by 1.74 times), lycopene (by 1.11 times), vitamin C (by 1.6 times), and anthocyanins (by 2.46 times) compared to the control (P < 0.05). Moreover, the phenolic profile demonstrated that the highest increase belonged to catechin. Therefore, the RE pretreated by CP has the potential to develop a functional ketchup with high bioactive substances.

Spatiotemporal analysis of microstructure, sensory attributes, and full-spectrum metabolomes reveals the relationship between bitterness and nootkatone in Alpinia oxyphylla miquel fruit peel and seeds

The Alpinia oxyphylla fruit (AOF) is a popular condiment and traditional Chinese medicine in Asia, known for its neuroprotective compound nootkatone. However, there has not been a comprehensive study of its flavor or the relationship between sensory and bioactive compounds. To address this issue, we examined AOF's microstructure, flavor, and metabolomic profiles during fruit maturation. The key markers used to distinguish samples included fruit expansion, testa pigmentation, aril liquefaction, oil cell expansion, peel spiciness, aril sweetness, and seed bitterness. A full-spectrum metabolomic analysis, combining a nontargeted metabolomics approach for volatile compounds and a widely targeted metabolomics approach for nonvolatile compounds, identified 1,448 metabolites, including 1,410 differentially accumulated metabolites (DAMs). Notably, 31 DAMs, including nootkatone, were associated with spicy peel, sweet aril, and bitter seeds. Correlational analysis indicated that bitterness intensity is an easy-to-use biomarker for nootkatone content in seeds. KEGG enrichment analysis linked peel spiciness to phenylpropanoid and capsaicin biosynthesis, seed bitterness to terpenoid (especially nootkatone) biosynthesis, and aril sweetness to starch and sucrose metabolism. This investigation advances the understanding of AOF's complex flavor chemistry and underlying bioactive principle, encapsulating the essence of the adage: "no bitterness, no intelligence" within the realm of phytochemistry.

Odor and taste characteristics, transduction mechanism, and perceptual interaction in fermented foods: a review

Fermentation is a critical technological process for flavor development in fermented foods. The combination of odor and taste, known as flavor, is crucial in enhancing people's perception and psychology toward fermented foods, thereby increasing their acceptance among consumers. This review summarized the determination and key flavor compound screening methods in fermented foods and analyzed the flavor perception, perceptual interactions, and evaluation methods. The flavor compounds in fermented foods could be separated, purified, and identified by instrument techniques, and a molecular sensory science approach could identify the key flavor compounds. How flavor compounds bind to their respective receptors determines flavor perception, which is influenced by their perceptual interactions, including odor-odor, taste-taste, and odor-taste. Evaluation methods of flavor perception mainly include human sensory evaluation, electronic sensors and biosensors, and neuroimaging techniques. Among them, the biosensor-based evaluation methods could facilitate the investigation of the flavor transduction mechanism and the neuroimaging technique could explain the brain's signals that relate to the perception of flavor and how they compare to signals from other senses. This review aims to elucidate the flavor profile of fermented foods and highlight the significance of comprehending the interactions between various flavor compounds, thus improving the healthiness and sensory attributes.

Bitter flavors and bitter compounds in foods: identification, perception, and reduction techniques

Bitterness is one of the five basic tastes generally considered undesirable. The widespread presence of bitter compounds can negatively affect the palatability of foods. The classification and sensory evaluation of bitter compounds have been the focus in recent research. However, the rigorous identification of bitter tastes and further studies to effectively mask or remove them have not been thoroughly evaluated. The present paper focuses on identification of bitter compounds in foods, structural-based activation of bitter receptors, and strategies to reduce bitter compounds in foods. It also discusses the roles of metabolomics and virtual screening analysis in bitter taste. The identification of bitter compounds has seen greater success through metabolomics with multivariate statistical analysis compared to conventional chromatography, HPLC, LC-MS, and NMR techniques. However, to avoid false positives, sensory recognition should be combined. Bitter perception involves the structural activation of bitter taste receptors (TAS2Rs). Only 25 human TAS2Rs have been identified as responsible for recognizing numerous bitter compounds, showcasing their high structural diversity to bitter agonists. Thus, reducing bitterness can be achieved through several methods. Traditionally, the removal or degradation of bitter substances has been used for debittering, while the masking of bitterness presents a new effective approach to improving food flavor. Future research in food bitterness should focus on identifying unknown bitter compounds in food, elucidating the mechanisms of activation of different receptors, and developing debittering techniques based on the entire food matrix.

Combined volatile compounds and non-targeted metabolomics analysis reveals variation in flavour characteristics, metabolic profiles and bioactivity of mulberry leaves after Monascus purpureus fermentation

BACKGROUND

Mulberry leaves (MLs) are widely used in food because of their nutritional and functional characteristics. However, plant cell walls and natural bitterness influence nutrient release and the flavor properties of MLs. Liquid-state fermentation using Monascus purpureus (LFMP) is a common processing method used to improve food properties. The present study used headspace solid-phase micro extraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) and non-targeted metabolomics to examine changes in volatile and non-volatile metabolites in MLs. The transformation mechanism of LFMP was investigated by microscopic observation and dynamic analysis of enzyme activity, and changes in the biological activity of MLs were analyzed.

RESULTS

LFMP significantly increased total phenolics, total flavonoids, free amino acids and soluble sugars in MLs, at the same time as decreasing phytic acid levels. In total, 92 volatile organic compounds (VOCs) were identified and quantified. VOCs such as (2R,3R)-(-)-2,3-butanediol, terpineol and eugenol showed some improvement in the flavour characteristics of MLs. By using non-targeted metabolomics, 124 unique metabolites in total were examined. LFMP altered the metabolic profile of MLs, mainly in plant secondary metabolism, lipid metabolism and amino acid metabolism. Microscopic observation and dynamic analysis of enzyme activity indicated that LFMP promoted cell wall degradation and biotransformation of MLs. In addition, LFMP significantly increased the angiotensin I-converting enzyme and α-glucosidase inhibitory activity of MLs.

CONCLUSION

LFMP altered the flavour characteristics, metabolite profile and biological activity of MLs. These findings will provide ideas for the processing of MLs into functional foods. In addition, they also provide useful information for biochemical studies of fermented MLs. © 2023 Society of Chemical Industry.

Dual functional roles of nutritional additives in nutritional fortification and safety of thermally processed food: Potential, limitations, and perspectives

The Maillard reaction (MR) has been established to be a paramount contributor to the characteristic sensory property of thermally processed food products. Meanwhile, MR also gives rise to myriads of harmful byproducts (HMPs) (e.g., advanced glycation end products (AGEs) and acrylamide). Nutritional additives have attracted increasing attention in recent years owing to their potential to simultaneously improve nutritional quality and attenuate HMP formation. In this manuscript, a brief overview of various nutritional additives (vitamins, minerals, fatty acids, amino acids, dietary fibers, and miscellaneous micronutrients) in heat-processed food is provided, followed by a summary of the formation mechanisms of AGEs and acrylamide highlighting the potential crosstalk between them. The main body of the manuscript is on the capability of nutritional additives to modulate AGE and acrylamide formation besides their traditional roles as nutritional enhancers. Finally, limitations/concerns associated with their use to attenuate dietary exposure to HMPs and future perspectives are discussed. Literature data support that through careful control of the addition levels, certain nutritional additives possess promising potential for simultaneous improvement of nutritional value and reduction of AGE and acrylamide content via multiple action mechanisms. Nonetheless, there are some major concerns that may limit their wide applications for achieving such dual functions, including influence on sensory properties of food products, potential overestimation of nutrition enhancement, and introduction of hazardous alternative reaction products or derivatives. These could be overcome through comprehensive assay of dose-response relationships and systematic evaluation of the diverse combinations from the same and/or different categories of nutritional additives to establish synergistic mixtures.

Functional Properties and Acceptability of Potentially Medicinal Tea Infusions Based on Equisetum arvense, Desmodium molliculum, and Mentha piperita

Natural herbal teas are one of the three most consumed beverages in the world, and despite their frequent use in the cosmetic, food, and pharmaceutical industries, there is still much to about them. This study aimed to determine the functional properties of tea infusions made from dried Equisetum arvense (EA), Desmodium molliculum (DM), and Mentha piperita (M) grown in the Peruvian Andes. Next, using a simplex design with unrestricted centroid amplified centroid, 12 combinations were obtained for the combination of dried leaves with EA: 0∼100%, DM: 0∼100%, and M: 0∼100% optimal combination of EA: 6.59%, DM: 84.62%, and M: 8.79% maximizes functional components for total polyphenols (2,831.18 mg EAG/100 g), flavonoids (37.73 mg CAT/g), and antioxidant capacity (145.99 μmol Trolox/g). It can be confirmed that dried mixtures of these plants made into tea are a significant source of bioactive molecules, have a tolerable flavor, and can be used for therapeutic purposes when consumed.

Physical and Oxidative Stability of Emulsions Stabilized with Fractionated Potato Protein Hydrolysates Obtained from Starch Production Side Stream

This work studies the emulsifying and antioxidant properties of potato protein hydrolysates (PPHs) fractions obtained through enzymatic hydrolysis of potato protein using trypsin followed by ultrafiltration. Unfractionated (PPH1) and fractionated (PPH2 as >10 kDa, PPH3 as 10-5 kDa, PPH4 as 5-0.8 kDa, and PPH5 as <0.8 kDa) protein hydrolysates were evaluated. Pendant drop tensiometry and dilatational rheology were applied for determining the ability of PPHs to reduce interfacial tension and affect the viscoelasticity of the interfacial films at the oil-water interface. Peptides >10 kDa showed the highest ability to decrease oil-water interfacial tension. All PPH fractions predominantly provided elastic, weak, and easily stretchable interfaces. PPH2 provided a more rigid interfacial layer than the other hydrolysates. Radical scavenging and metal chelating activities of PPHs were also tested and the highest activities were provided by the unfractionated hydrolysate and the fractions with peptides >5 kDa. Furthermore, the ability of PPHs to form physically and oxidatively stable 5% fish oil-in-water emulsions (pH 7) was investigated during 8-day storage at 20 °C. Our results generally show that the fractions with peptides >5 kDa provided the highest physicochemical stability, followed by the fraction with peptides between 5 and 0.8 kDa. Lastly, promising sensory results with mostly mild attributes were obtained even at protein concentration levels that are higher than needed to obtain functional properties. The more prominent attributes (e.g., bitterness and astringency) were within an acceptable range for PPH3 and PPH4.

Sequential culture with aroma-producing yeast strains to improve the quality of Kyoho wine

Despite many non-Saccharomyces yeasts being considered spoilage microorganisms, they can increase aroma and flavor diversity in alcoholic beverages. The purpose of this study was to investigate nontraditional inoculation strategies using aroma-producing yeast strains for Kyoho wine fermentation, followed by an instrumental analysis and sensory evaluation. The winemaking process was carried out using Saccharomyces cerevisiae Gr112, Hanseniaspora uvarum Pi235, and Pichia kluyveri Pe114. Multiple inoculation strategies were explored. In instrumental analysis results, mixed culture could promote the formation of esters (5.9-folds) and glycerol (1.3-folds) and reduce the content of ethanol (-0.5% [v/v]) in wine. The sensory analysis results suggested that the three yeast strains sequential inoculation treatment was associated with the aroma attributes "floral," "red fruity," and "tropical fruity." Co-cultivation contributed to an increase in complexity and aromatic intensity, with the three-strain inoculation treatment presenting a more distinctive appearance. PRACTICAL APPLICATION: The inoculation of S. cerevisiae improved the accumulation of volatile acids and esters by inhibiting the growth of non-Saccharomyces yeast strains. Inoculation of H. uvarum and P. kluyveri would effectively solve the defect of excessive content of higher alcohols in wines produced by S. cerevisiae. The suitable inoculation strategy between non-Saccharomyces yeasts could improve the overall quality of Kyoho wine whose starter might be widely used in fermentation industry.

Effects of moisture content on the enolization products formation in glucose-proline Maillard reaction models

BACKGROUND

2,3-Dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one (DDMP) and 5-hydroxymethylfurfural (HMF) are two main enolization products in the Maillard reaction and found in some foodstuffs. For many years, whether they are functional or noxious to human health has been a matter of debate. Thus, insight into their formation pathways is important to manage Maillard reaction products. In this study, DDMP and HMF were quantified and compared with regard to their formation and degradation in the d-glucose and l-proline Maillard reaction models using different moisture contents (0, 0.1, 0.5, 1.0, and 4.0 mL) at 150 °C for various heating times.

RESULTS

DDMP was predominantly generated in dry or low water-content heating models along with n increased 1-deoxyglucosone (1-DG) generation via 2,3-enolization. However, increasing moisture content resulted in a decay of reaction intensity, 1-DG, and DDMP due to a change in the reaction mechanism from 2,3-enolization to 1,2-enolization, which facilitated 3-deoxyglucosone (3-DG) and HMF formation.

CONCLUSION

Increased moisture content in glucose-proline models reduced reaction intensity and also inhibited DDMP and facilitated HMF formation by promoting the pathway change from 2,3-enolization to 1,2-enolization to generate more 3-DG. A water content of 1.0 mL was identified as a critical value, from which the 1,2-enolization became a primary pathway occurring in the Maillard reaction. © 2022 Society of Chemical Industry.

Saponins from Pea Ingredients to Innovative Sponge Cakes and Their Association with Perceived Bitterness

Pea-based ingredients are increasingly being used in foods because of their nutritional, functional and environmental benefits. However, their bitter taste is not appreciated by consumers. Saponins have been reported to be bitter in whole pea flour (PF) but not in the purified ingredients obtained from it, such as pea protein isolate (PPI) and pea starch (PS). In addition, the evolution of saponins in cooked foods made from these ingredients and their relationship to bitter flavor has not been investigated. This study, therefore, explored the presence of two bitter saponins, βg and Bb, in whole pea flour (PF) and a composite flour reconstructed from the two main fractions (PS + PPI). In addition, it investigated the impact of baking on the chemical state of these compounds in a sponge cake. Finally, the sensory impact of the baking process on the perceived bitterness of cakes made with these two pea flours was also evaluated. High-Performance Liquid Chromatography–High-Resolution Mass Spectrometry (HPLC-HRMS) was used to identify and quantify pea saponins in the flours and cakes, and a descriptive sensory analysis was obtained by a trained panel to assess sensory differences in bitterness. Our results showed marked differences in saponin concentration and composition among the pea ingredients studied. Concentrations were highest in PPI (1.497 mg·g⁻¹ dry matter), with 98% of saponin Bb. PS had the lowest saponin concentration (0.039 mg·g⁻¹ dry matter, with 83% Bb), while 0.988 mg·g⁻¹ dry matter was quantified in PF, with only 20% Bb and 80% βg. This research also highlighted the thermal degradation of saponin βg to Bb in sponge cakes during baking at 170 °C. However, at a sensory level, these chemical changes were insufficient for the impact on bitterness to be perceived in cakes made with pea flour. Moreover, baking time significantly reduced the bitter flavor in cakes made with the composite flour (PS + PPI).

Genetic determinants of liking and intake of coffee and other bitter foods and beverages

Coffee is a widely consumed beverage that is naturally bitter and contains caffeine. Genome-wide association studies (GWAS) of coffee drinking have identified genetic variants involved in caffeine-related pathways but not in taste perception. The taste of coffee can be altered by addition of milk/sweetener, which has not been accounted for in GWAS. Using UK and US cohorts, we test the hypotheses that genetic variants related to taste are more strongly associated with consumption of black coffee than with consumption of coffee with milk or sweetener and that genetic variants related to caffeine pathways are not differentially associated with the type of coffee consumed independent of caffeine content. Contrary to our hypotheses, genetically inferred caffeine sensitivity was more strongly associated with coffee taste preferences than with genetically inferred bitter taste perception. These findings extended to tea and dark chocolate. Taste preferences and physiological caffeine effects intertwine in a way that is difficult to distinguish for individuals which may represent conditioned taste preferences.

The Effect of Prickly Ash (Zanthoxylum bungeanum Maxim) on the Taste Perception of Stewed Sheep Tail Fat by LC-QTOF-MS/MS and a Chemometrics Analysis

This work aims to explore the contribution of prickly ash (Zanthoxylum bungeanum Maxim) on the taste perception of stewed sheep tail fat. Liquid chromatography-tandem quadrupole time of flight mass spectrometry (LC-QTOF-MS) was applied to analyze the taste-related compounds. A total of 99 compounds in different sheep tail fat samples were identified. The semi-quantitative results showed that there were differences between the samples. The partial least squares discriminant analysis (PLS-DA) model without overfitting was used to investigate the effect of prickly ash. Eleven marker compounds were predicted with a variable importance for projection > 1, fold change > 2 and p < 0.05. An additional experiment showed that guanosine 5'-monophosphate, malic acid, inosine and adenosine 5'-monophosphate could improve the umami and saltiness taste of stewed sheep tail fat.