Dynamic characteristics of dough during the fermentation process of Chinese steamed bread

Evaluation of flavor characteristics in Chinese wheat flour paste using electronic-nose, electronic-tongue, and headspace-gas chromatography-ion mobility spectrometry at different fermentation stages

BACKGROUND

Wheat flour paste is a typical Chinese fermented food, valued for its distinct flavors and health benefits. However, evidence regarding volatile organic compounds (VOCs) in Chinese wheat flour paste is limited. This study aims to examine the effect of fermentation on the VOCs and their physicochemical properties. Chinese wheat flour paste fermented at different stages was characterized using headspace gas chromatography ion-mobility spectrometry (HS-GC-IMS) with an electronic nose (E-nose) and an electronic tongue (E-tongue).

RESULTS

The results revealed that around 76 VOCs were found in Chinese wheat flour paste from all stages of fermentation. These included esters, alcohols, aldehydes, ketones, acids, furans, and pyrazines. The E-tongue and E-nose analyses also showed high responses for saltiness, umami, WIW, and W5S. The fermentation process changed the color of the wheat flour paste, and the taste, and smell parameters. Principal component analysis (PCA) showed that taste parameters were positively associated with the volatile flavor profile detected in wheat flour paste. Partial least squares discriminant analysis also identified 28 VOCs as distinct flavor metabolites across fermentation stages.

CONCLUSION

At the 'after ripening' (AR) and 'sterilization' (S) stages of wheat flour paste fermentation there were strong umami and salty flavors, with minimal sour and sweet notes in comparison with the other stages. These stages were characterized by elevated terpene concentrations, inorganic sulfides, and key flavor enhancers such as 2-hexanol and propyl sulfide. Headspace gas chromatography ion-mobility spectrometry and E-nose technologies are recommended for a more precise assessment of volatile changes during fermentation. The findings indicate that the 'sterilization' stage of wheat flour paste fermentation is optimal for achieving the required flavor profile. © 2024 Society of Chemical Industry.

Improved properties of dough fermented with rice wine prepared by mixed Saccharomycopsis fibuligera SF7 and Saccharomyces cerevisiae SC1

In view of the special aptitudes of the yeast population in both rice wine production and dough fermentation, in this study, the characteristics of dough fermented with rice wine prepared from mixed Saccharomycopsis fibuligera SF7 and Saccharomyces cerevisiae SC1 (JFC) were evaluated and compared with those of dough fermented directly with the two yeast co-cultures (FC). Dough inoculated with JFC showed higher acidity, reducing sugar content and leavening activity than dough fermented with FC. The water distribution pattern and pasting properties of the JFC-fermented dough changed dramatically after fermentation, and the dough microstructure and extensibility were improved. The steamed bread made with JFC-fermented dough had improved specific volume and showed similar volatile compound profiles to that made with commercial Jiuqu. These results indicated that mixed S. fibuligera SF7 and S. cerevisiae SC1 could be used as defined starter cultures in rice wine preparation for steamed bread production.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-024-01598-w.

Response of the distribution and molecular transition of gluten proteins and quality of Chinese steamed bread to different hydration levels

This study systematically explored how different hydration levels (45 %, 50 %, and 55 % water addition) affect the evolution of gluten network morphology, distribution, conformational and molecular transition, and moisture migration during the processing of Chinse steamed bread (CSB), and their impact on quality formation. Higher hydration levels resulted in a more uniform distribution and fibrous structure of the gluten network during mixing. However, excessive hydration (55 %) caused gluten fibers to rupture during fermentation. This increased the specific volume but decreased the chewiness and stickiness of CSB. MRI results highlighted that differences in moisture migration and internal structure among samples with different hydration levels were enlarged after steaming. AFM images revealed the increase in both protein molecular chain height and width with increasing hydration level, particularly after steaming. Moreover, high hydration levels promoted the depolymerization of glutenin macropolymers during mixing, fermentation, as well as repolymerization during cooking. These results indicated that both macroscopic qualities and molecular structure of gluten protein became more sensitive to the physical and biochemical processes during CSB processing. These dynamic transitions play a crucial role in determining dough rheological properties and CSB's overall quality. This research offers theoretical insights for precise dough product regulation and understanding underlying mechanisms.

Effects of Wickerhamomyces anomalus Co-Fermented with Saccharomyces cerevisiae on Volatile Flavor Profiles during Steamed Bread Making Using Electronic Nose and HS-SPME-GC-MS

Steamed bread is a traditional staple food in China, and it has gradually become loved by people all over the world because of its healthy production methods. With the improvement in people's living standards, the light flavor of steamed bread fermented by single yeast cannot meet people's needs. Multi-strain co-fermentation is a feasible way to improve the flavor of steamed bread. Here, the dynamic change profiles of volatile substances in steamed bread co-fermented by Saccharomyces cerevisiae SQJ20 and Wickerhamomyces anomalus GZJ2 were analyzed using the electronic nose (E-nose) and headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS). The five detectors of the E-nose rapidly detected the changes in volatile substances in different dough or steamed bread with the highest response value in co-fermented dough. A total of 236 volatile substances were detected in all the samples using HS-SPME-GC-MS, and alcohols were the most variable component, especially Phenylethyl alcohol. Significantly, more alcohols and esters were upregulated in co-fermented dough, and the addition of W. anomalus GZJ2 improved the key volatile aroma compounds of steamed bread using the relative odor activity value method (ROAV), especially the aldehydes and alcohols. Moreover, these key volatile aroma compounds can be quickly distinguished using the W2S detector of the E-nose, which can be used for the rapid detection of aroma components in steamed bread.

Technological and Nutritional Aspects of Bread Production: An Overview of Current Status and Future Challenges

Bakery products, especially bread, exist in many homes worldwide. One of the main reasons for its high consumption is that the main raw material is wheat, a cereal that can adapt to a wide variety of soils and climates. However, the nutritional quality of this raw material decreases during its industrial processing, decreasing the value of fibers, proteins, and minerals. Therefore, bread has become a product of high interest to increase its nutritional value. Due to the high consumption of bread, this paper provides a general description of the physicochemical and rheological changes of the dough, as well as the sensory properties of bread by incorporating alternative flours such as beans, lentils, and soy (among others). The reviewed data show that alternative flours can improve fiber, macro, and micronutrient content. The high fiber content reduces the quality of the texture of the products. However, new processing steps or cooking protocols, namely flour proportions, temperature, cooking, and fermentation time, can allow adjusting production variables and optimization to potentially overcome the decrease in sensory quality and preserve consumer acceptance.

Integration of non-targeted/targeted metabolomics and electronic sensor technology reveals the chemical and sensor variation in 12 representative yellow teas

Yellow tea is a lightly fermented tea with unique sensory qualities and health benefits. However, chemical composition and sensory quality of yellow tea products have rarely been studied. 12 representative yellow teas, which were basically covered the main products of yellow tea, were chosen in this study. Combined analysis of non-targeted/targeted metabolomics and electronic sensor technologies (E-eye, E-nose, E-tongue) revealed the chemical and sensor variation. The results showed that yellow big tea differed greatly from yellow bud teas and yellow little teas, but yellow bud teas could not be effectively distinguished from yellow little teas based on chemical constituents and electronic sensory characteristics. Sensor variation of yellow teas might be attributed to some compounds related to bitterness and aftertaste-bitterness (4'-dehydroxylated gallocatechin-3-O-gallate, dehydrotheasinensin C, myricitin 3-O-galactoside, phloroglucinol), aftertaste-astringency (methyl gallate, 1,5-digalloylglucose, 2,6-digalloylglucose), and sweetness (maltotriose). This study provided a comprehensive understanding of yellow tea on chemical composition and sensory quality.

Study on the Effect of Microwaved Brewer's Spent Grains on the Quality and Flavor Characteristics of Bread

To enable a wider utilization of co-products from beer processing and minimize the negative effect of added grain on bread quality, flavor, and other attributes, brewer's spent grains (BSG) are processed through microwave pretreatment, and then the microwave-treated BSG (MW-BSG) is added to bread. So far, there has been no investigation on the effect of microwave-pretreated BSG on bread quality and flavor. In this study, we examined the effects of diverse microwave treatment variables on the physicochemical structure of BSG and explored the consequences of MW-BSG on the quality and flavor of bread. The results showed that soluble dietary fiber and water-soluble protein levels in MW-BSG increased significantly (144.88% and 23.35%) at a 540 W microwave power, 3 min processing time, and 1:5 material-liquid ratio of BSG to water. The proper addition of MW-BSG positively affected the bread texture properties and color, but excessive amounts led to an irregular size and distribution of the bread crumbs. The result of electronic nose and HS-SPME-GC-MS analyses showed that the addition of MW-BSG modified the odor profile of the bread. A sensory evaluation showed mean scores ranging from 6.81 to 4.41 for bread containing 0-10% MW-BSG. Consumers found a maximum level of 6% MW-BSG acceptable. This study endeavors to decrease environmental contamination caused by brewing waste by broadening the methods by which beer co-products can be utilized through an innovative approach.

Regulation of baking quality and starch digestibility in whole wheat bread based on β-glucans and protein addition strategy: Significance of protein-starch-water interaction in dough

Whole wheat bread has high nutritional value but is characterized by inferior quality and a high glycemic index. Studies have shown that adding β-glucans and protein can improve bread quality. This study investigated the effects of added oat β-glucan, barley β-glucan, or yeast β-glucan on protein synergy and whole wheat dough and bread quality. The mixing properties, rheological properties, and scanning electron microscopy observations showed that the addition of β-glucan promoted the formation of gluten networks, while the synergy between the wheat proteins and β-glucan resulted in a more robust and stable gluten network and a stronger physical starch envelope. Rapid visco-analysis and thermal property evaluations showed that β-glucan addition inhibited the thermal degradation, gelatinization, and retrogradation of starch. Based on the bread quality results, it was found the β-glucan could cause some damage to the bread baking quality. For example, the hardness of samples with oats, barley, and yeast increased to 881.69 g, 952.97 g, and 631.75 g, respectively, compared to samples without β-glucan (317.49 g), whereas the inclusion of yeast β-glucan proved to be less detrimental. Protein and β-glucan both reduced starch digestion to some degree, and showed better synergistic effects, with the lowest estimated glycemic index of 70.08 observed in bread containing added yeast β-glucan and protein. Therefore, yeast β-glucan and protein mixtures could be selected as viable formulations for enhancing the quality of whole wheat bread.

Effect of fermentation methods on properties of dough and whole wheat bread

BACKGROUND

Whole wheat bread is high in nutritional value but poor in technological quality; therefore, research on how to improve its technological quality has attracted extensive attention. The effects of fermentation methods, including straight dough(STD), sourdough (SOD), sponge dough (SPD), and refrigerated SPD (RSD) methods, on the dough and bread quality of whole wheat bread were investigated, focusing on pasting properties, rheological properties, thermal properties, microstructure, basic quality, and starch digestibility.

RESULTS

The rapid viscosity analysis and rheological results demonstrated that SOD had the highest pasting temperature and the lowest viscosity, indicating an inhibition of starch pasting and partial protein hydrolysis, whereas the opposite trend presented by SPD and RSD indicated a greater starch hydration and a stronger gluten network. Thermal gravimetric analysis and differential scanning calorimetry results indicated reduced starch thermal degradation and increased starch pasting enthalpy in SOD and RSD. Scanning electron microscopy images revealed that the starch granules of SOD and RSD were tightly wrapped by a gluten network. SOD and RSD breads had the largest specific volume, the softest texture, and the lowest glycemic index.

CONCLUSION

The effects of different fermentation methods on dough and bread structure can provide instructive information for future studies on their applications in whole wheat bread production. © 2023 Society of Chemical Industry.

Enhancing the quality of steamed oat cake by partially gelatinized starch in oat flour and its molecular mechanism

The aim of this study was to investigate the effect and mechanism of partially gelatinized starch in oat flour on the rheological characteristics of the oat batter and the quality of steamed oat cakes. The results showed that an increase in the gelatinization degree of oat flour destroyed the starch granular structure and the long-range molecular order of starch, accompanied by a decrease of crystallinity from 22.28 % to 8.72 % and the formation of a starch-lipid complex. The increased gelatinization degree of oat flour destroyed the protein network and promoted the formation of the starch gel network in oat batter. Meanwhile, the addition of gelatinized oat flour enhanced the elastic behavior of the oat batter and the gas retention ability of the fermented oat batter, while decreased the total gas volume from 1075.5 mL to 827.0 mL. The steamed oat cake containing 50 % gelatinization degree of oat flour (G50) showed moderate hardness, springiness and chewiness, as well as the largest cell area fraction (37.35 %), due to the formation of a dense starch gel-protein double network and the enhancement of long/short-range molecular order of starch. Thus, this study provided the feasibility of improving the quality of oat-based fermented products by changing the gelatinization degree of oat starch.

Effect of konjac glucomannan on aggregation patterns and structure of wheat gluten with different strengths

Konjac glucomannan (KGM) can act as a food additive to improve the quality of dough. The effects of KGM on the aggregation patterns and structural properties of weak, middle, and strong gluten were studied. We found that with a higher proportion of KGM substitution (10%), the aggregation energy of middle and strong gluten became lower than the control samples, while exceeding the control for weak gluten. With 10% KGM, aggregation of glutenin macropolymer (GMP) was enhanced for weak gluten, but suppressed for middle and strong gluten. The α-helix transferred to β-sheet in weak, but caused more random-coil structures for middle and strong gluten induced by 10% KGM. With 10% KGM, the network for weak gluten became more continuous, but severely disrupted for middle and strong gluten. Thus, KGM has distinct effects on weak, middle, and strong gluten, which related to the alteration of gluten secondary structures and GMP aggregation pattern.

The Effect of Co-Fermentation with Lactobacillus plantarum HLJ29L2 and Yeast on Wheat Protein Characteristics in Sourdough and Crackers

Sourdough fermentation has been widely used in food products. However, there has been limited study of the effect of co-fermentation with lactic acid bacteria and yeast on the dough and cracker products. In this study, the influence of co-fermentation with Lactobacillus plantarum HLJ29L2 (LP HLJ29L2) and yeast on wheat protein digestibility of cracker was studied, and the mechanism of the protein changes in sourdough during fermentation was further explored. Co-fermentation with LP HLJ29L2 and yeast (DN-1) strongly improved the protein digestibility of cracker. At the same time, the content of free amino acids in DN-1 crackers increased by 20%. Co-fermentation also had significant effect on the sourdough during fermentation. The SDS-soluble protein content in sourdough was increased, and large molecule proteins were significantly reduced in the DN-1 sourdough. This was due to the fact, that LP HLJ29L2 grew rapidly during co-fermentation and produced more organic acids, which led to an increase in protease activity in sourdough and promoted the degradation of protein by proteases. The results of this study provide an important theoretical basis for the application of lactic acid bacteria and yeast co-fermentation in crackers.

Study of ultrasonic treatment on the structural characteristics of gluten protein and the quality of steamed bread with potato pulp

Physicochemical properties and microstructure of gluten protein, and the structural characteristics of steamed bread with 30 % potato pulp (SBPP) were investigated by ultrasonic treatments. Results showed that 400 W ultrasonic treatment significantly (P < 0.05) increased the combination of water and substrate in the dough with 30 % potato pulp (DPP). The contents of wet gluten, free sulfhydryl (SH), and disulfide bond (SS) were influenced by ultrasonic treatment. Moreover, UV-visible and fluorescence spectroscopy demonstrated that the conformation of gluten protein was changed by ultrasonic treatment (400 W). Fourier transform infrared (FT-IR) illustrated that the β-sheet content was significantly (P < 0.05) increased (42 %) after 400 W ultrasonic treatment, and the surface hydrophobicity of gluten protein in SBPP increased from 1225.37 (0 W ultrasonic treatment) to 4588.74 (400 W ultrasonic treatment). Ultrasonic treatment facilitated the generation of a continuous gluten network and stabilized crumb structure, further increased the specific volume and springiness of SBPP to 18.9 % and 6.9 %, respectively. Those findings suggested that ultrasonic treatment would be an efficient method to modify gluten protein and improve the quality of SBPP.

Main factors affecting the starch digestibility in Chinese steamed bread

Chinese steamed bread (CSB) is one of the staple foods in China, although it has a high glycemic index (GI) value. Development of CSB with a slower starch digestibility is thus of great importance for the improvement of human health. Many factors are related to the starch digestibility in CSB. Most currently available strategies are focusing on the incorporation of other whole flours with high dietary fiber or polyphenols to reduce the starch digestibility. Although successful in reducing starch digestibility, the incorporation of these flours also deteriorated textural attributes and sensory characteristics of CSB. Much more strategies have been applied for the reduction of starch digestibility in breads, which should be further explored to confirm if they are applicable for CSB. This review contains important information, that could potentially turn CSB into a much healthier food product with slower starch digestibility.

Characterization of japonica rice aroma profiles during in vitro mastication by gas chromatography-ion mobility spectrometry (GC-IMS) and electronic nose technology

By simulating the aroma changes during in vitro mastication, we can better understand the aroma changes during rice eating, which is helpful in studying people’s sensory preferences. To investigate the rice aroma released during the in vitro mastication, the present study analyzed rice bolus’s odor fingerprints in vitro mastication using electronic nose and gas chromatography-ion mobility spectrometry (GC-IMS). The electronic nose analysis results showed significant differences in the flavor of japonica rice in vitro mastication. In addition, GC-IMS determined 30 volatile organic compounds (VOCs) during rice in vitro mastication. Among these compounds, the most important content was aldehydes, followed by ketones and alcohols. Although the concentration of various chemicals was relatively high in cooked rice, most compounds decreased after mastication. The concentration of propan-2-ol, ethanol, and methanol increased after mastication. Multivariate data analysis showed that isoamyl sovalerate, pentanal, hexanal, acetone, hexanal, and limonene were the main VOCs of japonica rice during in vitro mastication. GC-IMS and e-nose analyses are complementary and recommended for using the two techniques to achieve the VOCs’ rapid and comprehensive detection during in vitro mastication. Results from this study allowed us to understand rice flavor during oral processing.

Application progress of intelligent flavor sensing system in the production process of fermented foods based on the flavor properties

Fermented foods are sensitive to the production conditions because of microbial and enzymatic activities, which requires intelligent flavor sensing system (IFSS) to monitor and optimize the production process based on the flavor properties. As the simulation system of human olfaction and gustation, IFSS has been widely used in the field of food with the characteristics of nondestructive, pollution-free, and real-time detection. This paper reviews the application of IFSS in the control of fermentation, ripening, and shelf life, and the potential in the identification of quality differences and flavor-producing microbes in fermented foods. The survey found that electronic nose (tongue) is suitable to monitor fermentation process and identify food authenticity in real time based on the changes of flavor profile. Gas chromatography-ion mobility spectrometry and nuclear magnetic resonance technology can be used to analyze the flavor metabolism of fermented foods at various production stages and explore the correlation between flavor substances and microorganisms.

Characterization of selected Chinese soybean paste based on flavor profiles using HS-SPME-GC/MS, E-nose and E-tongue combined with chemometrics

Headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC/MS) with electronic nose (E-nose) and electronic tongue (E-tongue) was applied for flavor characterization of traditional Chinese fermented soybean paste. Considering geographical distribution and market representation, twelve kinds of samples were selected to investigate the feasibility. A total of 57 volatile organic compounds (VOCs) were identified, of which 8 volatiles were found in all samples. Linear discrimination analysis (LDA) of fusion data exhibited a high discriminant accuracy of 97.22%. Compared with partial least squares regression (PLSR), support vector machine regression (SVR) analysis exhibited a more satisfying performance on predicting the content of esters, total acids, reducing sugar, salinity and amino acid nitrogen, of which correlation coefficients for prediction (Rp) were about 0.803, 0.949, 0.960, 0.896, 0.923 respectively. This study suggests that intelligent sensing technologies combined with chemometrics can be a promising tool for flavor characterization of fermented soybean paste or other food matrixes.

Effect of Highland Barley on Rheological Properties, Textural Properties and Starch Digestibility of Chinese Steamed Bread

Highland barley has a different composition and structure to other crops. It has higher contents of total polyphenol (TPC), total flavonoid (TFC) and β-glucan, which can be supplemented to improve the nutrition of wheat-flour-based food. In this study, the flours of three different grain-colored highland barley varieties Beiqing 6 (BQ), Dulihuang (DLH), and Heilaoya (HLY), were added to Jimai60 (JM, a wheat variety with medium gluten) wheat flour at different substitution levels to investigate their effects on the unextractable polymeric protein (UPP) content, micro-structure, rheological properties and mixing properties of dough, and the color, texture, flavor, and in vitro digestion of Chinese steam bread (CSB). The results showed that the moderate substitution of highland barley (20%) increased the UPP%, optimized the micro-structure of gluten, and improved its rheological properties by increasing dough viscoelasticity. The CSBs made from the composite flours exhibited a similar specific volume, cohesiveness, springiness and resilience to wheat CSB, while the firmness of composite CSBs (particularly JM-HLY-20) was delayed during storage. Importantly, the addition of highland barley increased the contents of TPC, TFC and β-glucan, but decreased the in vitro starch digestibility of CSBs. A sensory evaluation showed that JM-HLY CSB was the most preferable. Taken together, highland barley can be used as a fine supplement to food products, with health-promoting properties.

Effects of different gelatinization degrees of starch in potato flour on the quality of steamed bread

The effect of four kinds of potato flour with different gelatinization degrees on the quality of steam bread was investigated in the present study. Results showed that medium-well flour (MWF) and potato flakes (PF) steamed bread, particularly MWF steamed bread, possessed the desired product properties liked by consumers. The MWF steamed bread had the highest appearance score (42.78) and total sensory evaluation score (81.60), and the PF steamed bread exhibited the highest specific volume (1.84 mL/g) and taste score (43.05). An increase in the degree of potato flour gelatinization led to an increase in dough gas retention coefficient from 80.20 mL/100 mL to 85.17 mL/100 mL and a more uniform and dense dough microstructure. During dough preparation, the increased gelatinization degree of potato flours enhanced the hydroscopicity competition between potato starch and gluten, resulting in a flocculent gluten network and increased potato starch volume during steaming. During steaming, steamed bread with higher gelatinization degree of potato flour formed a homogenous and dense starch gel-gluten double network, making them softer with more uniform gas cells and larger specific volume. Thus, this study provides a perspective of the effect of starch gelatinization on steamed bread quality.

Variation of Volatile Compounds and Corresponding Aroma Profiles in Chinese Steamed Bread by Various Yeast Species Fermented at Different Times

To control the fermentation process of yeast-Chinese steamed bread (CSB), the volatile compounds and odor profiles of yeast-CSBs during fermentation were comprehensively investigated by sensory evaluation, gas chromatography-mass spectrometry, gas chromatography-olfactometry (GC-O), and odor activity value (OAV). Eight sensory attributes were established, and quantitative descriptive analysis results showed that CF1303-CSB had intense sweet and sweet aftertaste attributes, CF1318-CSB was characterized by milky, wheaty, and yeasty attributes, while CL10138-CSB presented distinct sour, winy, and floury attributes. A total of 41 key aroma-active compounds were detected, and phenylethyl alcohol was the most potent aroma compound with a flavor dilution (FD) of 1024. CF1303-CSB, CF1318-CSB, and CL10138-CSB contained 24, 22, and 21 key aroma compounds, respectively, based on the OAV. These key aroma compounds can be used as the potential markers to monitor the yeast-CSBs during the fermentation process. Five compounds, including β-myrcene, 2-phenoxyethanol, methyl cinnamate, guaiacol, and o-cresol, were first identified in CSB. These results provide theoretical basis for processing and quality control of yeast-CSBs.

Detection of Salmonella Typhimurium contamination levels in fresh pork samples using electronic nose smellprints in tandem with support vector machine regression and metaheuristic optimization algorithms

Rapid detection and quantification of bacterial foodborne pathogens are crucial in reducing the incidence of diseases associated with meat products contaminated with pathogens. For the identification, discrimination and quantification of Salmonella Typhimurium contamination in pork samples, a commercial electronic nose with ten (10) metal oxide semiconductor sensor array is applied. Principal component analysis was successfully applied for discrimination of inoculated samples and inoculated samples at different contaminant levels. Support vector machine regression (SVMR) together with a metaheuristic framework using genetic algorithm (GA), particle swarm optimization (PSO), and grid searching (GS) optimization algorithms were applied for S. Typhimurium quantification. Although SVMR results were satisfactory, SVMR hyperparameter tuning (c and g) by PSO, GA and GS showed superior performance of the models. The order of the prediction accuracy based on the prediction set was GA-SVMR (R P 2 = 0.989; RMSEP = 0.137; RPD = 14.93) > PSO-SVMR (R P 2 = 0.986; RMSEP = 0.145; RPD = 14.11) > GS-SVMR (R P 2 = 0.966; RMSEP = 0.148; RPD = 13.82) > SVMR (R P 2 = 0.949; RMSEP = 0.162; RPD = 12.63). GA-SVMR's proposed approach was fairly more effective and retained an excellent prediction accuracy. A clear relationship was identified between odor analysis results, and reference traditional microbial test, indicating that the electronic nose is useful for accurate microbial volatile organic compound evaluation in the quantification of S. Typhimurium in a food matrix.

Comparison of the effects of acetic acid bacteria and lactic acid bacteria on the microbial diversity of and the functional pathways in dough as revealed by high-throughput metagenomics sequencing

Knowledge of the effects of various strains of acetic acid bacteria (AAB) on sourdough remains limited. In this study, the diversity of microbial taxa in sourdoughs fermented by different starters was assessed and their functional capacity was evaluated via high-throughput metagenomics sequencing. Results showed that Erwinia (29.43%), Pantoea (45.89%), and Enterobacter (9.16%) were predominant in the blank CK treatment. Lactobacillus (91.40%), Saccharomyces (6.13%), as well as the AAB genus Acetobacter (0.61%) were the dominant microbial genera in the sourdoughs started by yeast and a strain of lactic acid bacteria (YL treatment). By contrast, the dominant genera in the sourdoughs started by yeasts and various LAB and AAB strains (YLA treatment) were Komagataeibacter (0.39%) except for the inoculated Lactobacillus (68.37%), Acetobacter (20.17%), and Saccharomyces (8.31%) species. Functional prediction of these changes in microbial community and diversity revealed that various metabolism-related pathways, including alanine, aspartate, and glutamate metabolism (21.95%), as well as amino acid biosynthesis (19.14%), were predominant in the sourdoughs started by yeast and an AAB strain (YA treatment). Moreover, arginine biosynthesis (11.65%) were the dominant pathways in the YL treatment. The fermented dough added with sourdoughs started with yeast + AAB and yeast + AAB + LAB strains had substantially higher contents (more than 48.58% in total) of essential amino acids than the dough added with sourdoughs started with yeast + LAB strain. These results demonstrated that amino acid biosynthesis has a beneficial effect on sourdoughs inoculated with an AAB strain.

Role of drying techniques on physical, rehydration, flavor, bioactive compounds and antioxidant characteristics of garlic

Various drying techniques play an important role in foodstuff preservation. However, the role of different drying techniques on garlic quality is limited. The purpose of this study was to investigate the effect of vacuum freeze-drying (VFD), hot air drying (HAD), infrared hot air drying (IRHAD), relative humidity drying (RHD) and pulsed vacuum drying (PVD) on the physical, rehydration, flavor, bioactive compounds and antioxidant characteristics of garlic slices. Results showed that garlic slices treated with VFD had an attractive color, low shrinkage, low hardness, and the lowest rehydration capacity. The volume shrinkage ratio, thermal stability and storage stability of garlic slices after HAD were the highest. Different dried garlic samples had different specific flavor fingerprints. IRHAD and RHD dried samples showed the highest rehydration capacity, content of bioactive compounds and antioxidant activity. The findings could provide a scientific basis to help in future large-scale production of good quality dried garlic products.

Application of terahertz spectrum and interval partial least squares method in the identification of genetically modified soybeans

Genetically modified soybeans are the world's most important genetically modified agricultural product. At present, the traditional methods for identifying genetically modified and non-transgenic soybeans are time-consuming, costly, and complicated to operate, which cannot meet the needs of practical applications. Therefore, it is necessary to discover a fast and accurate method for identifying transgenic soybeans. Terahertz (THz) time domain spectra were collected in sequence from 225 transgenic and non-transgenic soybean samples. Fourier transform was used to convert the terahertz time domain spectrum into a THz frequency domain spectrum with a frequency range of 0.1-2.5 THz. Firstly, the interval partial least squares (iPLS) method was used to remove interference spectral bands and select appropriate spectral intervals. Secondly, 168 samples were selected as the calibration set. Discriminant partial least squares (DPLS), Grid Search support vector machine (Grid Search-SVM) and principal component analysis back propagation neural network (PCA-BPNN) were used to establish a qualitative identification model. Afterwards, 57 test set samples were predicted. By comparing the experimental results, it was found that iPLS could effectively screen and remove the interference THz band, which was more helpful to improve the efficiency and accuracy of the identification model. After the iPLS and mean center pre-treatment technology, the Grid Search-SVM identification model had the best identification effect, with a total accuracy rate of 98.25% (transgenic identification rate was 96.15%, non-transgenic identification rate was 100%). This study shows that after selecting spectra from iPLS, THz spectroscopy combined with chemometrics can more accurately, quickly, and efficiently identify transgenic and non-transgenic soybeans.