A study revealing the key aroma compounds of steamed bread made by Chinese traditional sourdough

Yeast diversity in pit mud and related volatile compounds in fermented grains of chinese strong-flavour liquor

Chinese strong-flavour liquor is produced via a traditional solid-state fermentation strategy facilitated by live microorganisms in pit mud-based cellars. For the present analysis, pit mud samples from different spatial locations within fermentation cellars were collected, and the yeast communities therein were assessed via culture-based and denaturing gradient gel electrophoresis (DGGE) approaches. These analyses revealed significant differences in the composition of yeast communities present in different layers of pit mud. In total, 29 different yeast species were detected, and principal component analyses revealed clear differences in microbial diversity in pit mud samples taken from different cellar locations. Culture-dependent strategies similarly detected 20 different yeast species in these samples. However, while Geotrichum silvicola, Torulaspora delbrueckii, Hanseniaspora uvarum, Saturnispora silvae, Issatchenkia orientalis, Candida mucifera, Kazachstania barnettii, Cyberlindnera jadinii, Hanseniaspora spp., Alternaria tenuissima, Cryptococcus laurentii, Metschnikowia spp., and Rhodotorula dairenensis were detected via a PCR-DGGE approach, they were not detectable in culture-dependent analyses. In contrast, culture-based approaches led to the identification of Schizosaccharomyces pombe and Debaryomyces hansenii in these pit mud samples, whereas they were not detected using DGGE fingerprints profiles. An additional HS-SPME-GC-MS-based analysis of the volatile compounds present in fermented grains samples led to the identification of 66 such compounds, with the highest levels of volatile acids, esters, and alcohols being detected in fermented grains from lower layer samples. A canonical correspondence analysis (CCA) suggested they were significant correlations between pit mud yeast communities and associated volatile compounds in fermented grains.

Metabolic Profile of Einkorn, Spelt, Emmer Ancient Wheat Species Sourdough Fermented with Strain of Lactiplantibacillus plantarum ATCC 8014

The continuous development of bakery products as well as the increased demands from consumers transform ancient grains into alternatives with high nutritional potential for modern wheat species. The present study, therefore, follows the changes that occur in the sourdough obtained from these vegetable matrices fermented by Lactiplantibacillus plantarum ATCC 8014 during a 24 h. period. The samples were analyzed in terms of cell growth dynamics, carbohydrate content, crude cellulose, minerals, organic acids, volatile compounds, and rheological properties. The results revealed significant microbial growth in all samples, with an average value of 9 log cfu/g but also a high accumulation of organic acids with the increase in the fermentation period. Lactic acid content ranged from 2.89 to 6.65 mg/g, while acetic acid recorded values between 0.51 and 1.1 mg/g. Regarding the content of simple sugars, maltose was converted into glucose, and fructose was used as an electron acceptor or carbon source. Cellulose content decreased as a result of the solubilization of soluble fibers into insoluble fibers under enzymatic action, with percentages of 3.8 to 9.5%. All sourdough samples had a high content of minerals; the highest of which-Ca (246 mg/kg), Zn (36 mg/kg), Mn (46 mg/kg), and Fe (19 mg/kg)-were recorded in the einkorn sourdough.

Evolution of volatiles and quality of Chinese steamed bread during storage at different temperatures

The aim of this work is to investigate the evolution of volatiles and quality of CSB during 4 d of storage at 4 °C and 25 °C, respectively. Rapidly increasing hardness and decreasing resilience were observed in CSB after 1 d of storage at 4 °C. However, relative soft CSB was found after 1 d of storage at 25 °C as a result of the lower rate of retrogradation. Volatiles were monitored by gas chromatography-mass spectrometer. Significant (P < 0.05) decrease of 4 esters and 2-pentylfuran were observed with prolonged storage time for CSB stored at both 4 °C and 25 °C. PCA analysis indicated that the storage temperature of 4 °C was beneficial to remain CSB volatiles during long storage time (2-4 d). These findings might be beneficial to retain more volatiles and quality and finally extend shelf-life of CSB.

Sourdough improves the quality of whole-wheat flour products: Mechanisms and challenges-A review

Increasing the intake of whole-wheat flour (WWF) products is one of the methods to promote health. Sourdough fermentation is increasingly being used in improving the quality of WWF products. This review aims to analyze the effect of sourdough fermentation on WWF products. The effects of sourdough on bran particles, starch, and gluten, as well as the rheology, antinutritional factors, and flavor components in WWF dough/products are comprehensively reviewed. Meanwhile, sourdough fermentation technology has a promising future in reducing anti-nutritional factors and toxic and harmful substances in WFF products. Finally, researchers are encouraged to focus on the efficient strain screening and metabolic pathway control of sourdough for WWF products, as well as the use of bran pre-fermentation and integrated biotechnology to improve the quality of whole-wheat products. This review provides a comprehensive understanding of the effect of sourdough fermentation technology on wholemeal products to promote WWF production.

Effect of Na2CO3 on quality and volatile compounds of steamed bread fermented with yeast or sourdough

The effects of Na₂CO₃ on the quality, change of protein subunits and volatile compounds of sourdough leavened Chinese steamed bread (sourdough-CSB) and yeast leavened CSB (yeast-CSB) were investigated. Results suggested that, low Na₂CO₃ level endowed both CSB with softer crumb and little change of surface color. Besides, Na₂CO₃ addition improved the overall aroma profile by inhibiting the production of aroma-negative compounds (butanoic acid, 1-octen-3-ol, hexanal and heptanal). Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis showed an obvious increase in intensity of protein bands with low molecular weight, consistent with the result of size-exclusion high-performance liquid chromatography analysis and free sulfhydryl group (SH) content, indicating the hydrolysis of glutenin macropolymer (GMP) under alkaline condition in yeast-CSB. While in sourdough-CSB, GMP and SH content firstly decreased at low Na₂CO₃ level (0-0.2%) and then increased at high Na₂CO₃ level (0.3%-0.5%).

Diversity of bacterial communities in traditional sourdough derived from three terrain conditions (mountain, plain and basin) in Henan Province, China

To elucidate the bacterial community composition of sourdoughs from different terrain conditions, thirty-two Chinese traditional sourdough samples were collected from three terrain conditions (mountain, plain and basin) in Henan Province. High-throughput sequencing and culture-dependent approaches were employed to identify the bacterial diversity of the sourdough samples. A total of two hundred and six isolates were characterized via 16S rRNA gene sequencing. Pediococcus pentosaceus was isolated from every sample and was the predominant species in the sourdough samples, accounting for 58% of the relative abundance. High-throughput sequencing revealed that the predominant genera (mainly Pediococcus) in the basin group were significantly different from those in the mountain and plain groups. The genus Lactobacillus was predominant in the plain and mountain sourdough samples. Pediococcus pentosaceus was the absolute dominant strain in the basin sourdough samples. Acetobacter, which was widely distributed only in mountain samples, was recognized as the representative genus of the mountain samples. Moreover, we first reported Gluconobacter oxydans in sourdough. This study provided insight into the bacterial diversity of sourdough from three terrain conditions (mountain, plain and basin) in Henan Province and could serve as a reference for the isolation of desired bacterial strains.

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

The fermentation process is crucial to the production of Chinese steamed bread (CSB). In order to select suitable indicators as the basis for further research of establishing intelligent monitoring method for dough fermentation state, this study investigated the dynamic characteristics of dough during fermentation. Indicators included water mobility and distribution, starch-pasting properties, content of free amino acid (FAA), volatile organic compounds (VOCs) and electronic nose (E-nose) response value. Starch-pasting properties of dough and relaxation time (T₂₁, T₂₂) did not change significantly during the fermentation process (p < 0.05). The VOCs and FAAs of the dough had significant differences (p < 0.05) in different fermentation times, but no rule was established. The E-nose response value to headspace was most suitable to monitor the fermentation of dough. Principal component analysis (PCA) was performed on E-nose data from 75 samples and the results indicated that samples of different fermentation states were accurately classified.

Identification of volatile compounds and odour activity values in quinoa porridge by gas chromatography-mass spectrometry

BACKGROUND

Quinoa porridge is becoming popular among Asian for its nutritional values; hence, it is important to understand its aroma characteristics.

RESULTS

Volatile compounds in porridge of 30 quinoa varieties were determined by gas chromatography-mass spectrometry combined with headspace-solid phase micro-extraction. In total, 53 volatile compounds were detected and grouped into 14 alkanals, four alcohols, seven ketones, 10 alkanes, 10 acids and esters, and eight heterocycles. The relative content of alkanes (22.97%), acids and esters (44.33%) was comparatively high, although alkanals (11.75%) may dominate the aroma. Most of the compounds were similar with respect to types and numbers, although they varied in amount, whereas 11 compounds varied significantly among different varieties. The 30 varieties could be divided into eight groups based on the concentrations of volatile compounds, although the same varieties would be divided into four groups if based on the relative odour activity values of twelve variable aroma compounds.

CONCLUSION

Nine compounds were identified as the main contributors to the quinoa porridge aroma, including hexanal, 1-octen-3-ol, 2-pentylfuran, nonanal, (E,E)-2,4-decadienal and 6,10-dimethyl-5,9-undecadien-2-one. Heptanal, benzeneacetaldehyde and decanal may play roles in harmonizing the overall aroma. It is also interesting to note that 6,10,14-trimethyl-2-pentadecanone, with a slightly fatty aroma, showed a high content in all varieties. © 2019 Society of Chemical Industry.

Application of Lactobacillus as Adjunct Cultures in Wheat Dough Fermentation

The purpose of this study was to evaluate the potential use of Lactobacillus from traditional Chinese sourdoughs of different regions as original adjunct cultures in the steamed bread making process. The effects of Lactobacillus on dough and steamed bread were evaluated. Some differences were obtained in the parameters of fermented dough (organic acid content, rheofermentative parameters, pH, and total titratable acidity [TTA]) and steamed bread (hardness, specific volume, organic acid content, shape, color, pH, TTA and sensory score) made with five different Lactobacillus strains (Pediococcus pentosaceus, Lactobacillus fermentum, Weissella confusa, Lactobacillus crustorum, and Pediococcus acidilactici). Steamed bread made with P. pentosaceus showed a significant increase in specific volume (from 2.19 to 2.41) and a decrease in hardness (from 3,158 g to 2,301 g). Dough leavened by L. fermentum showed significantly higher amounts of lactic acid and acetic acid than dough inoculated with W. confusa, which had values similar to those of the control. The dough fermented by P. pentosaceus exhibited the most gas production (1,811 mL), which is an important index of streamed bread quality. Our research provides a reference for making steamed bread with Lactobacillus. PRACTICAL APPLICATION: Probiotic Lactobacillus is widely used to produce fermenting foods and has been used in bread processing to improve the quality and characteristics of bread. Steamed bread is one of the most popular fermented foods in northern China. However, there is little information about the application of Lactobacillus in Chinese steamed bread. This study explored the potential use of Lactobacillus to improve the characteristics and quality of steamed bread.

Identification of Key Aroma Compounds in Type I Sourdough-Based Chinese Steamed Bread: Application of Untargeted Metabolomics Analysisp

Untargeted metabolomics is a valuable tool to analyze metabolite profiles or aroma fingerprints of different food products. However, less attention has been paid to determining the aroma characteristics of Chinese steamed breads (CSBs) by using this approach. The aim of this work was to evaluate the key aroma compounds and their potential generation pathway in Chinese steamed bread produced with type I sourdough by a metabolomics approach. Based on the aroma characteristics analysis, CSBs produced with type I sourdough and baker’s yeast were clearly distinguishable by principal component analysis (PCA) scores plot. A total of 13 compounds in sourdough-based steamed breads were given the status of discriminant markers through the untargeted metabolomics analysis. According to the odor activity values (OAVs) of discriminant aroma markers, ethyl acetate (fruity), ethyl lactate (caramel-like), hexyl acetate (fruity), (E)-2-nonenal (fatty) and 2-pentylfuran (fruity) were validated as the key volatile compounds in the breads produced with type I sourdough as compared to the baker’s yeast leavened steamed bread. The metabolite analysis in proofed dough indicated that esters are mainly generated by the reaction between acid and alcohol during steaming, and aldehydes are derived from the oxidation of palmitoleic acid and linoleic acid during proofing and steaming.

Evaluation of the effect of Saccharomyces cerevisiae on fermentation characteristics and volatile compounds of sourdough

The objective of this study was to unveil insights into the effects of Saccharomyces cerevisiae on the development of volatile compounds and metabolites during the dough fermentation in making Chinese steamed bread. Changes in gluten structure under the influence of baker's yeast were studied using scanning electron micrographs (SEM). A unique aroma profile was found comprising some previously reported aromatic compounds and some unreported aromatic aldehydes ((E)-2-Decenal and 2-Undecenal) and ketones (2-Heptanone and 2-Nonanone) in the baker's yeast fermentation. Among metabolites, the most preferred sugar for this yeast (glucose) showed a significant decrease in contents during the initial few hours of the fermentation and at last an increase was observed. However, most of the amino acids increased either slightly or decreased by the fermentation time. SEM of fermented dough showed that the yeast had a very little effect on starch stability. This study provided some fermentation features of the bakers' yeast which could be used for the tailored production of steamed bread.

Predominant yeasts in Chinese traditional sourdough and their influence on aroma formation in Chinese steamed bread

A total of 105 yeast isolates was obtained from 15 sourdough samples collected from different regions in China and subjected to random amplified polymorphic DNA (RAPD) analysis. Six species were identified including Pichia membranifaciens, which has not previously been reported in Chinese sourdoughs. Different species of yeast were used in single-culture fermentation to make Chinese steamed bread (CSB). The volatiles of the CSB were captured by solid-phase microextraction method, separated and identified by gas chromatography-mass spectrometry. In total, 41 volatile compounds were found in all the steamed breads. All CSBs showed a similar volatile profile; however, significant differences in the quantity of some volatile compounds were seen among the CSB fermented by different yeast species. A partial least squares discriminant analysis showed that the CSBs could be separated by their characteristic volatile profiles. The study suggested that the aromatic properties of CSB are determined by the yeast used.

Insights into the microbial diversity and community dynamics of Chinese traditional fermented foods from using high-throughput sequencing approaches

Chinese traditional fermented foods have a very long history dating back thousands of years and have become an indispensable part of Chinese dietary culture. A plethora of research has been conducted to unravel the composition and dynamics of microbial consortia associated with Chinese traditional fermented foods using culture-dependent as well as culture-independent methods, like different high-throughput sequencing (HTS) techniques. These HTS techniques enable us to understand the relationship between a food product and its microbes to a greater extent than ever before. Considering the importance of Chinese traditional fermented products, the objective of this paper is to review the diversity and dynamics of microbiota in Chinese traditional fermented foods revealed by HTS approaches.

Comparative Agreement Analysis of Differences in 1,5-Anhydroglucitol, Glycated Albumin, and Glycated Hemoglobin A1c Levels between Fasting and Postprandial States in Steamed Bread Meal Test

BACKGROUND

Our previous study indicated that serum 1,5-anhydroglucitol (1,5-AG) levels slightly increased after a glucose load; therefore, this study was conducted to explore short-term changes in 1,5-AG levels after a steamed bread meal test (SBMT) and compare the agreement of 1,5-AG, glycated albumin (GA), and glycated hemoglobin A1c (HbA1c) levels between fasting and postprandial states after an SBMT.

METHODS

104 participants were recruited and underwent a 100 g SBMT. Fasting, 30 min, and 120 min of 1,5-AG, GA, and HbA1c were measured.

RESULTS

Levels of 1,5-AG slightly increased from 30 to 120 min after an SBMT (P < 0.01), and HbA1c and GA levels showed stability at 30 and 120 min. The Passing-Bablok regression linear equation showed that postprandial 1,5-AG, GA, and HbA1c levels were well fitted (all P > 0.05), and Bland-Altman difference plot showed that 100% of data points for HbA1c₃₀ and HbA1c₁₂₀ fell within the limits of agreement; 94.2%, 96.2%, 95.2%, and 95.2% of data points for 1,5-AG₃₀, 1,5-AG₁₂₀, GA₃₀, and GA₁₂₀ fell within the limits of agreement, respectively.

CONCLUSION

Agreement analyses indicated good stability of 1,5-AG, GA, and HbA1c levels after the SBMT. HbA1c had an optimal stability, which was superior to that of GA or 1,5-AG.