Comparative Study on Volatile Flavor of Chinese Acid-curd Cheese Using Sensory Evaluation, Gas Chromatography-Ion Mobility Spectrometry and Gas Chromatography-Mass Spectrometry

The difference in the volatile flavors of five different Chinese acid-curd cheeses including milk fan, milk cake, Qula (yak milk cheese), Hurood cheese and milk knot was analyzed by sensory evaluation, gas chromatography-ion mobility spectrometry (GC-IMS) and gas chromatography-mass spectrometry (GC-MS). The results of sensory evaluation showed that the five cheeses had a significant difference in flavor. Among them, dairy fan, with strong milky, fruity and bread-like aromas, had the best overall aroma performance and the highest preference score. The combination of GC-IMS and GC-MS expanded the detection range of volatile flavor compounds, and could more comprehensively reflect the volatile compounds in different Chinese acid-curd cheeses. The sensory evaluation results were verified by GC-IMS analysis. All five samples had their own characteristic peak areas, and the characteristic peak areas of dairy fan and Qula were significantly larger than those of the other samples. GC-MS analysis showed that the proportion of acids in dairy fan, Hurood cheese and Qula was the highest, the proportion of esters in milk cake was the highest, and the proportion of alcohols in milk knot was the highest. The calculation of odor activity value (OAV) combined with the results of principal component analysis (PCA) showed that ethanol, ethyl butyrate, ethyl caproate, 2-heptanone and δ-caprylactone were the major contributors to the flavor of dairy fan. Phenethyl formate, phenethyl acetate, caprylic acid, lauric acid and n-decanoic acid were the major contributors to the flavor of Qula. Dodecyl aldehyde was identified as the characteristic flavor compound of dairy cake. Partial least squares analysis (PLSA) revealed the correlation between aroma properties and volatile flavor compounds. Dairy fan has the potential to be developed and promoted in China because of its excellent flavor and consumer preference

Recent Advances in the Application of Molecular Simulation in Research on Cyclodextrin Inclusion

Cyclodextrin (CD) can form inclusion complexes with the guest molecule through supramolecular interaction, preserving or even enhancing the properties of the guest molecule. Molecular simulation is an important research tool to explore the interaction of CD with the guest molecule, which has been widely used in research on cyclodextrin inclusion reaction. In this paper, a brief overview of molecular simulations including quantum mechanics, molecular docking and molecular dynamics simulation was given, and the basic principles of and mainstream software and commonly used force fields for molecular docking and molecular dynamic simulation were summarized. Moreover, recent progresses on their application in cyclodextrin inclusion research were reviewed from four aspects: characterization of molecular structure changes, characterization of intermolecular interaction, solvent effects and synergistic stabilization. Research results show that the size of the hydrophobic cavity and the initial orientation of the guest within the cavity have very important effects on the structure of guest/cyclodextrin inclusion complexes; van der Waals interactions are the major driving force for the cyclodextrin inclusion reaction, and the formation of intermolecular hydrogen bonds is an important factor for the stability of the inclusion complex. The explicit solvent model is a powerful tool to study the solvent effect of the cyclodextrin inclusion reaction. Finally, the authors believe that molecular simulation will be useful for further investigations of the cyclodextrin inclusion process from the perspectives of multi-scale phenomena and machine learning

Aroma features of honey measured by sensory evaluation, gas chromatography-mass spectrometry, and electronic nose

To study the aroma features of different varieties of honey, five honey samples from different botanical origins were characterized by sensory evaluation, gas chromatography-mass spectrometry and electronic nose analysis. The sensory evaluation results gave a good reflection of the honey’s different aroma characteristics. A total of 55 volatile compounds were identified by headspace solid-phase micro-extraction followed by gas chromatography-mass spectrometry, and among these compounds, 13 were found in all of the honey samples. A number of differences were observed in the composition of volatile components from the five types of honey. Twenty-two compounds were selected as typical odor-active compounds which co-varied well with the five sensory attributes by partial least squares regression. The correlation results between the sensory profiles and electronic nose data showed that the electronic nose could give comparable results in predicting the sensory attributes of honey. In conclusion, the combination of sensory evaluation, gas chromatography-mass spectrometry analysis of volatile compounds, and electronic nose data with partial least squares regression analysis could be applicable for the overall analysis of aroma features for honey

CcpA-Dependent Carbon Catabolite Repression Regulates Fructooligosaccharides Metabolism in Lactobacillus plantarum

Fructooligosaccharides (FOSs) metabolism in Lactobacillus plantarum is controlled by two gene clusters, and the global regulator catabolite control protein A (CcpA) may be involved in the regulation. To understand the mechanism, this study focused on the regulation relationships of CcpA toward target genes and the binding effects on the catabolite responsive element (cre). First, reverse transcription-PCR analysis of the transcriptional organization of the FOS-related gene clusters showed that they were organized in three independent polycistronic units. Diauxic growth, hierarchical utilization of carbohydrates and repression of FOS-related genes were observed in cultures containing FOS and glucose, suggesting carbon catabolite repression (CCR) control in FOS utilization. Knockout of ccpA gene eliminated these phenomena, indicating the principal role of this gene in CCR of FOS metabolism. Furthermore, six potential cre sites for CcpA binding were predicted in the regions of putative promoters of the two clusters. Direct binding was confirmed by electrophoretic mobility shift assays in vitro and chromatin immunoprecipitation in vivo. The results of the above studies suggest that CcpA is a vital regulator of FOS metabolism in L. plantarum and that CcpA-dependent CCR regulates FOS metabolism through the direct binding of CcpA toward the cre sites in the promoter regions of FOS-related clusters

Aroma-sensory properties of Gouda cheeses based on young Chinese consumers' preferences

ABSTRACT: The objective of this study was to examine the aroma profiles of 12 Gouda cheeses sold in China and to 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 questionnaire. These 11 descriptors were used by a panel of experts for sensory analysis to perform a quantitative descriptive analysis of the cheeses. A principal component analysis of the data from the quantitative descriptive analysis revealed that the characteristic aromas of young Gouda cheeses, medium-aged Gouda cheeses, and aged Gouda cheeses were “milky” and “whey”; “creamy” and “sour”; and “rancid” and “nutty,” respectively. The results of a penalty analysis combined with the check-all-that-apply 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 enjoy 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 or never ate cheese. In addition, we identified a positive correlation between the consumers' preferences for the aromas of the Gouda cheeses and their willingness to pay for them. 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

Functional analysis of the role of CcpA in Lactobacillus plantarum grown on fructooligosaccharides or glucose: a transcriptomic perspective

Abstract Background The catabolite control protein A (CcpA) is a master regulator of many important cellular processes in Gram-positive bacteria. In Lactobacillus plantarum, CcpA directly or indirectly controls the transcription of a large number of genes that are involved in carbohydrate metabolism, aerobic and anaerobic growth, stress response and metabolite production, but its role in response to different carbon sources remains unclear. Results Here a combined transcriptomic and physiological approach was used to survey the global alterations that occurred during the logarithmic growth phase of wild-type and ccpA mutant strains of L. plantarum ST-III using fructooligosaccharides (FOS) or glucose as the sole carbon source. The inactivation of ccpA significantly affected the growth and production of metabolites under both carbon sources. About 15% of the total genes were significantly altered between wild-type and ccpA strains grown on glucose and the value is deceased to 12% when these two strains were compared on FOS, while only 7% were obviously changed due to the loss of CcpA when comparing strains grown on glucose and FOS. Although most of the differentially expressed genes mediated by CcpA are glucose dependent, FOS can also induce carbon catabolite repression (CCR) through the CcpA pathway. Moreover, the inactivation of ccpA led to a transformation from homolactic fermentation to mixed fermentation under aerobic conditions. CcpA can control genes directly by binding in the regulatory region of the target genes (mixed fermentation), indirectly through local regulators (fatty acid biosynthesis), or have a double effect via direct and indirect regulation (FOS metabolism). Conclusion Overall, our results show that CcpA plays a central role in response to carbon source and availability of L. plantarum and provide new insights into the complex and extended regulatory network of lactic acid bacteria

Legislative Documents

Also, variously referred to as: House bills; House documents; House legislative documents; legislative documents; General Court documents

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