Investigation of the Interaction Between Lactones and Ketones in a Cheddar Cheese Matrix Using Feller's Additive Model, σ-τ Plots, U-Models, and Aroma Addition Experiments.

The objective of this study was to examine the sensory interactions between lactones and ketones in a cheddar simulation matrix through perceptual interaction analysis. The olfactory thresholds of 6 key lactones had values ranging from 8.32 to 58.88 µg/kg, whereas those of the 4 key ketones ranged from 6.61 to 660.69 µg/kg. Both Feller's additive model and σ-τ plots demonstrated complex interactions in 24 binary mixtures composed of the 6 lactones and 4 ketones, including synergy, addition, and masking effects. Specifically, we found that 6 binary mixtures exhibited aroma synergistic effects using both methods. Moreover, the σ-τ plot showed a synergistic effect of aroma in 3 ternary mixtures. The U-model further confirmed the synergistic effects of the 6 groups of binary systems and 3 groups of ternary systems on aroma at actual cheese concentrations. In an aroma addition experiment, the combination of δ-octalactone and diacetyl in binary mixtures had the most pronounced impact on enhancing milk flavor. In ternary mixtures, 2 combinations, namely δ-octalactone/δ-dodecalactone/diacetyl and γ-dodecalactone/δ-dodecalactone/acetoin, significantly enhanced the milky and sweet aroma properties of cheese, while also enhancing the overall acceptability of the cheese aroma.

Aroma Sensory Properties of Gouda Cheeses Based on Young Chinese Consumers' Preference.

The objective of this study was to examine the aroma profiles of 12 Gouda cheeses sold in China and determine which aromas were preferred by young Chinese consumers (n = 110). The consumers selected 11 descriptors of the aromas of the Gouda cheeses in a Check-All-That-Apply (CATA) questionnaire. These 11 descriptors were used by a panel of experts for sensory analysis to perform a Quantitative Descriptive Analysis (QDA) of the cheeses. A principal component analysis of the data from the QDA revealed that the characteristic aromas of the young Gouda cheeses, medium-aged Gouda cheeses and aged Gouda cheeses were "milky" and "whey"; "creamy"; and "sour," "rancid," "nutty," etc., respectively. The results of a penalty analysis combined with the CATA results and the preference scores showed that the 3 groups of young Chinese consumers (those who often ate cheese, occasionally ate cheese, and never ate cheese) preferred the Gouda cheeses with "milky" or "creamy" aromas and did not like those with "sour" or "rancid" aromas. Occasional cheese eaters comprised the majority of the young Chinese consumers, and they were more tolerant of the Gouda cheeses with "whey" and "sulfury" aromas than those who often ate cheese and those who never ate cheese. In addition, there was a positive correlation between the consumers' preferences for the aromas of the Gouda cheeses and their willingness to pay for the cheeses. Overall, the results of this study should help promote the development of Gouda cheeses and associated products that meet the preferences of young Chinese consumers.

Regulation of the pleiotropic transcriptional regulator CodY on the conversion of branched-chain amino acids into branched-chain aldehydes in Lactococcus lactis.

IMPORTANCE: Branched-chain aldehydes are the primary compounds that contribute to the nutty flavor in cheddar cheese. Lactococcus lactis, which is often applied as primary starter culture, is a significant contributor to the nutty flavor of cheddar cheese due to its ability of conversion of BCAAs into branched-chain aldehydes. In the present study, we found that the regulatory role of CodY is crucial for the conversion. CodY acts as a pleiotropic transcriptional regulator via binding to various regulatory regions of key genes. The results presented valuable knowledge into the role of CodY on the regulation and biosynthetic pathway of branched-chain amino acids and the related aldehydes. Furthermore, it provided new insight for increasing the nutty flavor produced during the manufacture and ripening of cheese.

Dynamics of microbial communities associated with flavor formation during sour juice fermentation and the milk fan drying process.

Milk fan is an acid-curd cheese with strong national characteristics (a traditional dairy product of the Bai nationality with a shape like a piece of paper) and a long history in Yunnan province, China. In our previous study, we characterized the microbial community diversity of milk fan, but the succession of microorganisms associated with flavor formation in milk fan is still unknown. Therefore, we examined the predominant microorganisms and their correlations with the formation of flavor in the fermentation of sour juice and drying of milk fan by gas chromatography mass spectrometry, high-throughput 16S rDNA sequencing, intergenic spacer sequencing and metatranscriptome analysis. We found that the relative abundances of Lactobacillus and Issatchenkia initially decreased and then increased with time during the fermentation of sour juice. However, the relative abundances of Acetobacter, Leuconostoc, Lactococcus, Geotrichum, and Dipodascus initially increased and then decreased. During the drying step, the relative abundances of Lactobacillus and Issatchenkia continuously increased and became the dominant microorganisms in the milk fan. The metatranscriptomes generated from the milk fan showed that "carbohydrate metabolism," "translation," and "signal transduction" were the main metabolic functions of the microbial communities. Rhodotorula and Yarrowia contained more differentially expressed genes than other genera, which indicated they may be associated with the production of the characteristic flavor. Furthermore, a Pearson correlation analysis showed that Lactococcus, Rhodotorula, Candida, Cutaneotrichosporon, and Yarrowia were significantly positively correlated with more aroma-active compounds, mainly ethyl acetate, 2-heptanone, isovaleraldehyde, butyric acid, nonanal, and hexanal. In conclusion, these findings contribute to a better understanding of the flavor production mechanism during the production of milk fan.

Unraveling the difference in flavor characteristics of Huangjiu fermented with different rice varieties using dynamic sensory evaluation and comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry.

To investigate the specific differences in flavor characteristics of Huangjiu fermented with different rice varieties, dynamic sensory evaluation, comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry (GC × GC-qMS) and multivariate statistical analysis were employed. Dynamic sensory evaluation methods including temporal dominance of sensations (TDS) and temporal check all that apply (TCATA) were applied to explore the differences and variations in sensory attributes. The sensory results showed that the intensity of astringency and post-bitterness in the Huangjiu fermented with glutinous rice was weaker while ester and alcoholic aroma were more prominent than the one fermented with japonica rice. The results of free amino acids and aroma compounds analysis indicated that the amino acids were mainly sweet and bitter amino acids, and some key aroma compounds were predominant in the Huangjiu fermented with glutinous rice, such as ethyl butyrate (OAV: 38-59), 3-methylthiopropionaldehyde (OAV: 47-96), ethyl caprylate (OAV: 30-38), while nonanal, phenyl acetaldehyde and vanillin contributed significantly to the Huangjiu fermented with japonica rice. The multivariate statistical analysis further confirmed that 17 compounds (VIP > 1 and p < 0.05) could be supposed to be the key compouns that cause significant flavor differences in Huangjiu samples fermented with different brewing rice. Moreover, partial least-squares analysis revealed that most compounds (ethyl butyrate, 3-penten-2-one, isoamyl acetate, and so on) correlated with ester and alcoholic aroma. The results could provide basic data and theoretical basis for the selection of raw materials in Huangjiu.

Rapid identification of adulteration in raw bovine milk with soymilk by electronic nose and headspace-gas chromatography ion-mobility spectrometry.

The adulteration of soymilk (SM) into raw bovine milk (RM) to gain profit without declaration could cause a health risk. In this study, electronic nose (E-nose) and headspace-gas chromatography ion-mobility spectrometry (HS-GC-IMS) were applied to establish a rapid and effective method to identify adulteration in RM with SM. The obtained data from HS-GC-IMS and E-nose can distinguish the adulterated samples with SM by principal component analysis. Furthermore, a quantitative model of partial least squares was established. The detection limits of E-nose and HS-GC-IMS quantitative models were 1.53% and 1.43%, the root mean square errors of prediction were 0.7390 and 0.5621, the determination coefficients of prediction were 0.9940 and 0.9958, and the relative percentage difference were 10.02 and 13.27, respectively, indicating quantitative regression and good prediction performances of SM adulteration levels in RM were achieved. This research can provide scientific information on the rapid, non-destructive and effective adulteration detection for RM.

Characterisation of the Aroma Profile and Dynamic Changes in the Flavour of Stinky Tofu during Storage.

Stinky tofu is a traditional Chinese food with wide consumption in China. Nevertheless, the dynamic changes in the flavour of stinky tofu during storage have yet to be investigated. In this study, the flavour changes of stinky tofu over six different storage periods were comprehensively analysed through sensory, electronic nose and gas chromatography-mass spectrometry (GC-MS) analyses. The results of the sensory and electronic nose analyses confirmed the changes in the flavour of stinky tofu across different storage periods. In the GC-MS analysis, 60 volatile compounds were detected during storage, and the odour activity values indicated that 29 of these 60 compounds significantly contributed to the aroma profile. During storage, the alcohol concentration of the stinky tofu gradually decreased while the acid and ester concentrations increased. According to a partial least squares analysis, 2-phenylethyl acetate, 2-phenylethyl propanoate, p-cresol, and phenylethyl alcohol, which were detected after 10 days of storage, promoting the release of an overripe apple-like odour from the stinky tofu. Findings regarding the flavour changes and characteristics of stinky tofu during different storage periods can provide a potential reference for recognising the quality of these products.

Dynamic analysis of volatile metabolites and microbial community and their correlations during the fermentation process of traditional Huangjiu (Chinese rice wine) produced around Winter Solstice.

Traditional Huangjiu produced around Winter Solstice has higher quality and a more harmonious aroma. To investigate the variations of volatile metabolites and microbial communities during fermentation, gas chromatography-ion migration chromatography (GC-IMS), gas chromatography-mass spectroscopy (GC-MS) and high-throughput sequencing were employed. Aroma compounds results showed that alcohols and phenols increased before 45 days of fermentation and then decreased after 45 days, while esters gradually increased. Fungal genera Saccharomyces, Aspergillu, and Rhizomucor were dominant, whereas Staphylococcus, Pediococcus and Weissella were the dominant bacterial genera in the late stage. In addition, 11 genera such as Lactobacillus, Saccharopolyspora and Aspergillus (|r| > 0.6, p < 0.05) may contributed to traditional Huangjiu ecosystem stability. Moreover, correlation analysis indicated the dominant microorganisms (Saccharopolyspora, Staphylococcus, Lactobacillus, Saccharomyces and Aspergillus) were positively correlated with key compounds. These results provided theoretical guidance for further study on the flavor regulation of traditional Huangjiu via microbial community level and microbial augmentation.

Characterize the physicochemical properties and microstructure of pectin from high-pressure and thermal processed cloudy hawthorn (Crataegus pinnatifida) juice based on acid heating extraction.

Physicochemical properties and morphological features of pectin in high-pressure-processing (JHPP) and thermal-processing (JTP) treated cloudy hawthorn juice were investigated based on acid heating extraction. Pectin from hawthorn juice was identified as low methoxy pectin (41.77%), which was significantly reduced to 34.56%-39.51% from JHPP, while pectin esterification degree (DE) from JTP increased to 45.58%, which can also be confirmed by Fourier transform infrared spectroscopy. In comparison to control, pectin linearity of JHPP and JTP significantly decreased with more highly branched-chains. However, no significate difference was observed in thermostability, crystallinity and main functional groups. Interestingly, a large number of aggregations was observed in JHPP pectin, and the intermodular distance of JTP pectin was enhanced, which was consistent with the results of viscosity, molecular weight and DE. These findings provided insights into utilization of hawthorn pectin and application of high-pressure processing (HPP) for improving quality property of fruit products by pectin modification.

Antibacterial Activity and Mechanism of Oxidized Bacterial Nanocellulose with Different Carboxyl Content.

Oxidized bacterial nanocellulose (OBC) is reported to prevent microbial growth, but its antibacterial characteristics and mechanism are still unclear. Here, the antibacterial mechanism of OBC is explored by detecting and assessing the interaction of OBC with different carboxyl content on Staphylococcus aureus and Escherichia coli. The results show that OBC has strong antibacterial activity and antibiofilm activity against S. aureus and E. coli, which is positively correlated with the carboxyl content of OBC. After OBC treatment, the bacteria adhesion is inhibited and the cell membrane is destroyed leading to increased permeability. Further investigation reveals that the concentration of cyclic diguanosine monophosphate (c-di-GMP) that induced biofilm formation is significantly decreased to 1.81 pmol mg-1 after OBC treatment. In addition, OBC inactivates mature biofilms, with inactivation rates up to 79.3%. This study suggests that OBC has excellent antibacterial and antiadhesion properties, which can increase the cell membrane permeability and inhibit c-di-GMP formation. In addition, OBC also has a strong inactivation effect on mature biofilm, which can be used as an effective antibiofilm agent.

Aroma classification and characterization of Lactobacillus delbrueckii subsp. bulgaricus fermented milk.

The aroma of the fermented milk produced by twenty-eight Lactobacillus delbrueckii subsp. bulgaricus strains was evaluated via quantitative descriptive analysis. According to the sensory analysis results, the fermented milks were grouped into milky-type, cheesy-type, fermented-type and miscellaneous-type. The representative samples of cheese-type and fermented-type were analyzed by headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) and flavoromics. A total of 95 volatile compounds were identified and particularly, 12 aroma-active compounds were detected by using gas chromatography-olfactometry-mass spectrometry (GC-O-MS). Among the different aroma types, 2,3-butanedione, δ-decalactone, acetaldehyde, butanoic acid, acetic acid and hexanoic acid were finally screened out as the key aroma-active compounds by quantitative and odor activity value (OAV) analysis combined with aroma recombination, omission and addition experiments. These findings were valuable in developing specific fermented milk products with different aroma profiles.

Characterisation of the key volatile compounds of commercial Gouda cheeses and their contribution to aromas according to Chinese consumers' preferences.

A systematic flavoromics-based analysis of samples of 12 commercially available Gouda cheeses was performed to determine their key volatile components, the contribution of these components to the aromas of the cheeses, and which aromas were preferred by a panel of Chinese consumers. The sensory analysis results show that the Chinese consumers preferred young and medium cheeses, and that sensory attributes such as 'milk' and 'cream' were the most popular. Seventy-seven aroma compounds were identified by gas chromatography-mass spectrometry, and 28 of these were determined to be aroma-active compounds by gas chromatography-olfactometry analysis and calculation of their odour activity values. Partial least-squares analysis revealed that compounds such as diacetyl and acetoin correlated with aromas preferred by the Chinese consumers, while isobutyric acid, hexanoic acid and valeric acid correlated with aromas disliked by the Chinese consumers. Finally, the flavour contribution of each aroma-active compound was validated through aroma reorganisation and omission experiments.

Characterization of Bitter Compounds in Shaoxing Huangjiu by Quantitative Measurements, Taste Recombination, and Omission Experiments.

Excessive and uncoordinated bitterness of Shaoxing Huangjiu, a traditional Chinese rice wine, reduces its acceptance by consumers. To determine the compounds responsible for this bitterness, gas chromatography-mass spectrometry and high-performance liquid chromatography were performed on four types of Shaoxing Huangjiu (Yuanhong, Huadiao, Shanniang, and Xiangxue wine) for targeted quantitation of candidate compounds known to contribute to bitterness. Calculations of dose-over-threshold factors revealed that isoamyl alcohol, 1-hexanol, phenylethanol, ethyl butyrate, ethyl lactate, furfural, histidine, and arginine were important bitter compounds. Taste recombination experiments demonstrated that a recombination model constructed using the screened known bitter compounds showed good similarity with the original sample in bitter taste. Furthermore, omission experiments revealed that isobutanol, isoamyl alcohol, 1-hexanol, phenylethanol, ethyl acetate, ethyl butyrate, ethyl lactate, furfural, arginine, and valine were the compounds affecting the bitter taste perception. This study provides a certain guiding effect on the bitterness control and taste improvement of Shaoxing Huangjiu.

Simultaneous detection for adulterations of maltodextrin, sodium carbonate, and whey in raw milk using Raman spectroscopy and chemometrics.

To achieve rapid on-site identification of raw milk adulteration and simultaneously quantify the levels of various adulterants, we combined Raman spectroscopy with chemometrics to detect 3 of the most common adulterants. Raw milk was artificially adulterated with maltodextrin (0.5-15.0%; wt/wt), sodium carbonate (10-100 mg/kg), or whey (1.0-20.0%; wt/wt). Partial least square discriminant analysis (PLS-DA) classification and a partial least square (PLS) regression model were established using Raman spectra of 144 samples, among which 108 samples were used for training and 36 were used for validation. A model with excellent performance was obtained by spectral preprocessing with first derivative, and variable selection optimization with variable importance in the projection. The classification accuracy of the PLS-DA model was 95.83% for maltodextrin, 100% for sodium carbonate, 95.84% for whey, and 92.25% for pure raw milk. The PLS model had a detection limit of 1.46% for maltodextrin, 4.38 mg/kg for sodium carbonate, and 2.64% for whey. These results suggested that Raman spectroscopy combined with PLS-DA and PLS model can rapidly and efficiently detect adulterants of maltodextrin, sodium carbonate, and whey in raw milk.

Isolation and identification of bitter-tasting peptides in Shaoxing rice wine using ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry combined with taste orientation strategy.

The content of peptides in Shaoxing rice wine is high; however, their potential taste properties have not yet been studied. To isolate and identify bitter-tasting peptides in a popular Chinese rice wine, Shaoxing rice wine, a series of purification steps including ultrafiltration and gel filtration chromatography (GFC), combined with a taste orientation strategy, were used. According to the evaluation results of taste dilution analysis, a bitter peptide with the highest taste efficacy was isolated, and its purity was verified by high-performance liquid chromatography (HPLC). The amino acid sequence of peptide components was analyzed by ultra-performance liquid chromatography quadrupole time of flight mass spectrometry (UPLC-Q-TOF-MS). The bitter peptide Leu-Pro-Thr-Leu (LPTL) was successfully identified from Shaoxing rice wine. Then, taste addition experiments highlighted the bitter impacts of LPTL on sensory descriptors in Shaoxing rice wine. The LPTL peptide can contribute to bitterness in Shaoxing rice wine.

Rapid detection of neutralising acid adulterants in raw milk using a milk component analyser and chemometrics.

This study focused on the development of a method for the rapid detection of acid-neutralising adulterants in raw milk using a milk composition analyser. Qualitative analysis for the discrimination of different acid-neutralising acid adulterants in raw milk and quantification of NaSCN in adulterated raw milk were conducted, combined with chemometrics. The results showed that the milk component analyser combined with principal component analysis (PCA) could judge whether raw milk samples were adulterated but cannot identify the types of adulterated substances. Although partial least squares discrimination analysis (PLS-DA) can distinguish some adulterated raw milk samples, the accuracy rate was only 56.3%; the random forest (RF) model could recognise most adulterated raw milk samples with an accuracy rate of 97.5% and the F1-score was 0.9638. In the prediction model of NaSCN adulteration concentration in raw milk constructed by RF, the coefficient of determination (R2) was 0.9889, and the root means square error (RMSE) was 3.28 × 10-4, suggesting a high prediction performance of the model. The effectiveness of the method for the detection of real samples in practical production was also proved. Based on the above results, it could conclude that the milk component analyser, combined with chemometrics, effectively distinguished acid-neutralising adulterants in raw milk. These findings provide a reference for the rapid detection of adulterants and the quality control of raw milk.

Isolation, identification and sensory evaluation of kokumi peptides from by-products of enzyme-modified butter.

BACKGROUND: Enzyme-modified butter is used as a common raw material to obtain a natural milk flavor. Butter protein is a by-product in butter processing that can be used as substrate to produce taste-active peptides, which can create additional value and new application opportunities, making the method more environmentally friendly. RESULTS: Putative kokumi peptides from hydrolysates of protein by-products were isolated by gel filtration chromatography and reversed-phase high-performance liquid chromatography. The isolated peptide fraction with the most pronounced kokumi taste was screened by sensory evaluation and electronic tongue analysis. Eleven peptides were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Six peptides were synthesized to verify their taste characteristics. Five synthetic peptides (FTKK, CKEVVRNANE, EELNVPG, VPNSAEER and YPVEPFTER) showed different intensity levels of kokumi taste. Of these peptides, the decapeptide CKEVVRNANE had the highest kokumi intensity. CONCLUSION: The newly identified kokumi peptides increased the kokumi taste intensity and showed some synergistic effect with umami taste. Both termini of the peptides seem to play an important role in taste characteristic. Glu residue at both termini can increase the kokumi taste intensity. This work indicated that it was feasible to produce kokumi peptides by enzymatic hydrolysis of the protein by-products of butter. © 2022 Society of Chemical Industry.

Comprehensive two-dimensional gas chromatography mass spectrometry-based untargeted metabolomics to clarify the dynamic variations in the volatile composition of Huangjiu of different ages.

Aging plays an important role in the formation of aroma characteristics of Huangjiu, a traditional Chinese alcoholic beverage. Comprehensive two-dimensional gas chromatography mass spectrometry (GC×GC-qMS)-based untargeted metabolomics combined with a multivariate analysis was used to investigate the dynamic variations in the aroma profile of Huangjiu during aging process and to establish the relationship between the changing volatile metabolite profiles and the age-dependent sensory attributes. A total of 144 volatile metabolites were identified by GC×GC-qMS and 63 were selected as critical metabolites based on variable importance in projection values and p-values. Based on the results of principal component analysis, orthogonal partial least-squares discriminant analysis, and hierarchical clustering analysis, the samples of six different ages were divided into three groups: 1Y and 3Y samples, 5Y and 8Y samples, and 10Y and 15Y samples. The partial least-squares analysis results further revealed the relationship between the aromas attributes and variations of these volatile compounds. The high esters, aldehydes, and lactones contents contributed to the high intensities of the sweet and ester aroma attributes of the aged Huangjiu, while the high alcohols and ethyl esters contents contributed to the alcoholic and fruity aroma attributes of the newly brewed Huangjiu. These results improve our understanding of the chemical nature of the aroma characteristics of aged Huangjiu. PRACTICAL APPLICATION: Huangjiu is often labeled with its age as a measure of quality, which influences consumers' choice. Dynamic variations in volatile compounds of Huangjiu during aging and its contribution to the aroma characteristics of Huangjiu were figured out, which will assist the industry to produce better quality aged Huangjiu for consumers.

Effect of alsD deletion and overexpression of nox and alsS on diacetyl and acetoin production by Lacticaseibacillus casei during milk fermentation.

Diacetyl and acetoin are key aroma components of fermented milk but are produced in low concentrations by starter cultures. In this study, we expressed NADH oxidase, acetolactate synthase, and inactivated acetolactate decarboxylase in Lacticaseibacillus casei TCS to generate recombinant L. casei strains, and investigated the effects of the genes encoding these enzymes on diacetyl and acetoin production during milk fermentation. In the single-gene recombinant strains tested, diacetyl concentrations were highest in milk fermented by L. casei TCSI-nox (nox gene overexpressed, 3.68 mg/kg), whereas acetoin concentrations were highest in milk fermented by L. casei TCS-ΔalsD (alsD gene deleted, 32.94 mg/kg). Moreover, diacetyl and acetoin concentrations were higher in the inducible strains than in the corresponding constitutive strains (e.g., TCSI-nox vs. TCSC-nox, and TCSI-ΔalsD-nox vs. TCSC-ΔalsD-nox). This phenomenon was also reflected in the protein expression levels and enzyme activities. In the double-gene recombinant strains tested, the highest concentrations of diacetyl and acetoin were produced by L. casei TCSI-ΔalsD-nox (nox overexpressed and alsD deleted, 4.66 mg/kg, 69.62 mg/kg, respectively). The triple-gene recombinant L. casei TCS-ΔalsD-nox-alsS produced the highest concentrations of diacetyl and acetoin, which were 2.38 and 11.19 times, respectively, the concentrations produced by the original strain. These results show that the nox, alsS, and alsD genes make key contributions to the biosynthesis of diacetyl and acetoin by L. casei. The modification of multiple genes had a synergistic effect, leading to greatly increased synthesis of diacetyl and acetoin by L. casei during its fermentation of milk.