Co-culture fermentation by Saccharomycopsis fibuligera and lactic acid bacteria improves bioactivity and aroma profile of wheat bran and the bran-containing Chinese steamed bread.

Co-culture fermentation with yeast and lactic acid bacteria (LAB) exhibits advantages in improving the bioactivity and flavor of wheat bran compared to single-culture fermentation, showing application potentials in bran-containing Chinese steamed bread (CSB). To explore the effects of combination of yeast and different LAB on the bioactivity and flavor of fermented wheat bran, this study analyzed the physicochemical properties, phytate degradation capacity, antioxidant activities, and aroma profile of wheat bran treated with co-culture fermentation by Saccharomycopsis fibuligera and eight different species of LAB. Further, the phenolic acid composition, antioxidant activities, texture properties, aroma profile, and sensory quality of CSB containing fermented wheat bran were evaluated. The results revealed that co-culture fermentation brought about three types of volatile characteristics for wheat bran, including ester-feature, alcohol and acid-feature, and phenol-feature, and the representative strain combinations for these characteristics were S. fibuligera with Limosilactobacillus fermentum, Pediococcus pentosaceus, and Latilactobacillus curvatus, respectively. Co-culture fermentation by S. fibuligera and L. fermentum for 36 h promoted acidification with a phytate degradation rate reaching 51.70 %, and improved the production of volatile ethyl esters with a relative content of 58.47 % in wheat bran. Wheat bran treated with co-culture fermentation by S. fibuligera and L. curvatus for 36 h had high relative content of 4-ethylguaiacol at 52.81 %, and exhibited strong antioxidant activities, with ABTS•+ and DPPH• scavenging rates at 65.87 % and 69.41 %, respectively, and ferric reducing antioxidant power (FRAP) at 37.91 µmol/g. In addition, CSB containing wheat bran treated with co-culture fermentation by S. fibuligera and L. fermentum showed a large specific volume, soft texture, and pleasant aroma, and received high sensory scores. CSB containing wheat bran treated with co-culture fermentation by S. fibuligera and L. curvatus, with high contents of 4-ethylguaiacol, 4-vinylguaiacol, ferulic acid, vanillin, syringaldehyde, and protocatechualdehyde, demonstrated strong antioxidant activities. This study is beneficial to the comprehensive utilization of wheat bran resources and provides novel insights into the enhancement of functions and quality for CSB.

Mechanism underlying the weakening effect of ß-glucan on the gluten system.

The high ß-glucan content in barley disrupts the gluten network in dough. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FTIR), and solid-state nuclear magnetic resonance (NMR) techniques were used to clarify how ß-glucan affected the quality of the gluten network structure with ß-glucan contents of 0-2%. The results suggest that the physical hindrance of the ß-glucan gel destroyed the formation of the gluten network structure. When 1.0-2.0% ß-glucan was added, the percentage of α-helical structures increased significantly. When the added amount of ß-glucan reached 2.0%, the sulfhydryl group (SH) content increased from 8.06 to 10.27 µmol/g, and the disulfide bond (SS) content decreased from 240.09 to 217.38 µmol/g. The interaction between ß-glucan and gluten mainly resulted from the interaction of electron-withdrawing groups, such as carbonyl groups (CO) and double bond carbons (CC), and carbon atoms on the side chains of ß-glucan, which play an important role in the central structure of glutenin.

Effect of γ-polyglutamic acid on the physicochemical properties of soybean protein isolate-stabilized O/W emulsion.

An increased interest has been observed in the application of soybean protein isolate (SPI) into O/W emulsion because of the amphipathic characteristics of SPI. However, at pH around 4.5, SPI was almost lost its hydrophilic characteristic, thus greatly limiting its application in emulsion under an acidic environment. Therefore, this drawback of SPI needs to be urgently solved. This study aims to investigate the effect of γ-polyglutamic acid (γ-PGA) on physicochemical properties of SPI-stabilized O/W emulsion. The results suggested that the interaction between γ-PGA and SPI improved the SPI solubility in solution, and increased emulsifying properties of SPI in the pH range of 4.0-5.0 via electrostatic interaction. Meanwhile, the charge neutralisation between SPI emulsions with γ-PGA was confirmed via ζ-potentiometry. With the presence of γ-PGA in emulsion at pH 4.0 and 5.0, the electrostatic complexation between SPI and anionic γ-PGA exhibited decreased the viscosity of SPI emulsion, which might be related to the phenomenon as indicated by the confocal laser scanning microscope measurements. Therefore, the electrostatic complexation between SPI and γ-PGA suggested that the promising potential of γ-PGA to be used in SPI-stabilized O/W emulsion under an acidic environment.

Effect of Alkali on the Microbial Community and Aroma Profile of Chinese Steamed Bread Prepared with Chinese Traditional Starter.

Alkali is an indispensable additive in Chinese steamed bread (CSB) production. This work aimed to evaluate the key roles of alkali in the microbial community of dough fermented using Chinese traditional starter (CTS) and the aroma profiles of CSB. The dominant fungi in CTS and fermented dough were members of the phylum Ascomycota and the genus Saccharomyces. Pediococcus, Companilactobacillus, and Weissella were the dominant bacterial genera in CTS and fermented dough. Adding alkali could retain the types of dominant yeasts and LAB derived from CTS, decrease the relative abundance of Companilactobacillus crustorum and Weissella cibaria, and increase that of Pediococcus pentosaceus, in fermented dough. Principal component analysis (PCA) indicated that adding alkali decreased the content of sourness-related volatiles in CSB fermented by CTS. Correlation analysis showed that Pediococcus and Weissella in fermented dough were positively correlated with the lipid oxidation flavor-related compounds in CSB, and Lactobacillus was positively correlated with sourness-related aroma compounds. Synthetic microbial community experiments indicated that CSB fermented by the starter containing P. pentosaceus possessed a strong aroma, and adding alkali weakened the flavor intensity. Alkali addition could promote the formation of ethyl acetate and methyl acetate with a pleasant fruity aroma in W. cibaria-associated CSB.

Comparative Transcriptomic Analysis of Staphylococcus aureus Reveals the Genes Involved in Survival at Low Temperature.

In food processing, the temperature is usually reduced to limit bacterial reproduction and maintain food safety. However, Staphylococcus aureus can adapt to low temperatures by controlling gene expression and protein activity, although its survival strategies normally vary between different strains. The present study investigated the molecular mechanisms of S. aureus with different survival strategies in response to low temperatures (4 °C). The survival curve showed that strain BA-26 was inactivated by 6.0 logCFU/mL after 4 weeks of low-temperature treatment, while strain BB-11 only decreased by 1.8 logCFU/mL. Intracellular nucleic acid leakage, transmission electron microscopy, and confocal laser scanning microscopy analyses revealed better cell membrane integrity of strain BB-11 than that of strain BA-26 after low-temperature treatment. Regarding oxidative stress, the superoxide dismutase activity and the reduced glutathione content in BB-11 were higher than those in BA-26; thus, BB-11 contained less malondialdehyde than BA-26. RNA-seq showed a significantly upregulated expression of the fatty acid biosynthesis in membrane gene (fabG) in BB-11 compared with BA-26 because of the damaged cell membrane. Then, catalase (katA), reduced glutathione (grxC), and peroxidase (ahpC) were found to be significantly upregulated in BB-11, leading to an increase in the oxidative stress response, but BA-26-related genes were downregulated. NADH dehydrogenase (nadE) and α-glucosidase (malA) were upregulated in the cold-tolerant strain BB-11 but were downregulated in the cold-sensitive strain BA-26, suggesting that energy metabolism might play a role in S. aureus under low-temperature stress. Furthermore, defense mechanisms, such as those involving asp23, greA, and yafY, played a pivotal role in the response of BB-11 to stress. The study provided a new perspective for understanding the survival mechanism of S. aureus at low temperatures.

On the Prediction of Biogas Production from Vegetables, Fruits, and Food Wastes by ANFIS- and LSSVM-Based Models.

This study is aimed at modeling biodigestion systems as a function of the most influencing parameters to generate two robust algorithms on the basis of the machine learning algorithms, including adaptive network-based fuzzy inference system (ANFIS) and least square support vector machine (LSSVM). The models are assessed utilizing multiple statistical analyses for the actual values and model outcomes. Results from the suggested models indicate their great capability of predicting biogas production from vegetable food, fruits, and wastes for a variety of ranges of input parameters. The values that are calculated for the mean relative error (MRE %) and mean squared error (MSE) were 29.318 and 0.0039 for ANFIS, and 2.951 and 0.0001 for LSSVM which shows that the latter model has a better ability to predict the target data. Finally, in order to have additional certainty, two analyses of outlier identification and sensitivity were performed on the input parameter data that proved the proposed model in this paper has higher reliability in assessing output values compared with the previous model.

Effects of pigment and citrinin biosynthesis on the metabolism and morphology of Monascus purpureus in submerged fermentation.

The effects of the secondary metabolite biosynthesis on the metabolism and morphology of the Monascus purpureus were investigated in this study. Hypha and septum length became longer after deletion of genes pigR and pksCT in M. purpureus LQ-6 by Agrobacterium tumefaciens-mediated transformation technology, highly branched hyphae, much smaller and freely dispersed mycelial pellets were observed in M. purpureus. Compared with that in the wild-type, the level of intracellular NADH and NADPH was almost constant in M. purpureus ΔpigR at 4 days, but the NADH and NADPH levels decreased by 1.58-fold and 3.71-fold in M. purpureus ΔpksCT. The present study can not only provide a kind of strategy to improve the Monascus pigments production, but also provide theoretical support for the further study of relationship between the secondary metabolites, metabolism and morphological change.

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.

Effects of freezing treatments on the quality of frozen cooked noodles.

Freezing process is one of the key steps in making frozen cooked noodles. Ice crystal formed in freezing process affects the quality of frozen cooked noodles. In this paper, we studied the effect of freezing treatment on frozen cooked noodles. Frozen cooked noodles were evaluated for microstructure and texture properties explored with a scanning electron microscope and texture analyzer at - 20 °C, - 30 °C and - 40 °C respectively. The results indicated that the microstructure and texture properties of frozen cooked noodles were significantly (P < 0.05) improved by a lower freezing temperature than a higher temperature. This present study also showed that the freezing rate is not the only parameter responsible for microstructure and texture properties that occur during freezing; the difference of flours also can be a factor. These findings, if generally applicable to frozen cooked noodle products, could have important economic implications for the convenience of the food industry.

Effect of potassium alum addition on the quality of potato starch noodles.

The objective of this study was to investigate the effects and mechanism of potassium alum (PA) on potato starch noodles to provide a theoretical basis for future searches for new alternatives for PA that are not harmful to the body. The amount of amylose leakage significantly decreased with the PA addition. SEM showed that the honeycomb structure of potato starch noodles with 0.1% PA was diminished. The number of internal pores and average area decreased from 92 and 580.09 units to 72 and 652.58 units, respectively. NMR indicated that the water holding capacity of potato starch noodles containing PA was greater than that of the control. XRD showed that the crystal structure of potato starch noodles was destroyed and that the crystallinity of potato starch noodles with PA increased from 16.65 to 19.64%. G' and G'' increased, but tanδ decreased. FT-IR showed that PA caused the O-H stretching vibration in the absorption peak to move in the high-field direction and that the ionic bond was dominant in the PA-potato starch interaction system.

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.

Comparative Proteomic and Morphological Change Analyses of Staphylococcus aureus During Resuscitation From Prolonged Freezing.

When frozen, Staphylococcus aureus survives in a sublethally injured state. However, S. aureus can recover at a suitable temperature, which poses a threat to food safety. To elucidate the resuscitation mechanism of freezing survived S. aureus, we used cells stored at -18°C for 90 days as controls. After resuscitating the survived cells at 37°C, the viable cell numbers were determined on tryptic soy agar with 0.6% yeast extract (TSAYE), and the non-injured-cell numbers were determined on TSAYE supplemented with 10% NaCl. The results showed that the total viable cell number did not increase within the first 3 h of resuscitation, but the osmotic regulation ability of freezing survived cells gradually recovered to the level of healthy cells, which was evidenced by the lack of difference between the two samples seen by differential cell enumeration. Scanning electron microscopy (SEM) showed that, compared to late exponential stage cells, some frozen survived cells underwent splitting and cell lysis due to deep distortion and membrane rupture. Transmission electron microscopy (TEM) showed that, in most of the frozen survived cells, the nucleoids (low electronic density area) were loose, and the cytoplasmic matrices (high electronic density area) were sparse. Additionally, a gap was seen to form between the cytoplasmic membranes and the cell walls in the frozen survived cells. The morphological changes were restored when the survived cells were resuscitated at 37°C. We also analyzed the differential proteome after resuscitation using non-labeled high-performance liquid chromatography-mass spectrometry (HPLC-MS). The results showed that, compared with freezing survived S. aureus cells, the cells resuscitated for 1 h had 45 upregulated and 73 downregulated proteins. The differentially expressed proteins were functionally categorized by gene ontology enrichment, KEGG pathway, and STRING analyses. Cell membrane synthesis-related proteins, oxidative stress resistance-related proteins, metabolism-related proteins, and virulence factors exhibited distinct expression patterns during resuscitation. These findings have implications in the understanding of the resuscitation mechanism of freezing survived S. aureus, which may facilitate the development of novel technologies for improved detection and control of foodborne pathogens in frozen food.

Effects of ZnO nanoparticle-coated packaging film on pork meat quality during cold storage.

BACKGROUND: There has been limited research on the use of ZnO nanoparticle-coated film for the quality preservation of pork meat under low temperature. In the present study, ZnO nanoparticles were mixed with sodium carboxymethyl cellulose (CMC-Na) to form a nanocomposite film, to investigate the effect of ZnO nanoparticle-coated film on pork meat quality and the growth of bacteria during storage under low temperature. RESULTS: When ZnO nanoparticle-coated film was used as the packaging material for pork meat for 14 days of cold storage at 4 °C, the results demonstrated a significant effect on restricting the increases in total volatile basic nitrogen and pH levels, limiting the decreases of lightness (increased L* value) and redness (increased a* value), and maintaining the water-holding capacity compared to the control pork samples (P < 0.05). The present study also discovered that the ZnO nanoparticle-coated film restrained the increase in total plate count (TPC). When Staphylococcus aureus was used as the representative strain, scanning electron microscopy revealed that ZnO nanoparticles increased the occurrence of cell membrane rupture under cold conditions. CONCLUSION: ZnO nanoparticle-coated film helps retain the quality of pork meat during cold storage by increasing the occurrence of microorganism injury. © 2016 Society of Chemical Industry.

Effect of hydrocolloids on the energy consumption and quality of frozen noodles.

Effects of hydrocolloids such as Sodium polyacrylate, xanthan gum and sodium alginate on the energy consumption and quality of frozen cooked noodles were investigated. Results showed that gelatinization temperature (GT) shortened significantly and texture properties (hardness, firmness, break strength) of frozen cooked noodle were significantly improved by adding different hydrocolloid additives (P < 0.05). Nevertheless, there were no significant differences of glass-transition temperature between hydrocolloid fortified and non fortified frozen cooked noodles. Moreover, the hydrocolloids improved quality of cooked noodle and increased energy consumption, however, xanthan gum showed the best results. The optimized constituents were: sodium polyacrylate 0.13 %, xanthan gum 0.86 %, sodium alginate 0.18 % with predicted sensory scores of 90.30. The study showed that hydrocolloids could be used as modifying agents in frozen cooked noodle process.

The Fluorescence Enhancement of Mercury Detected in Food Based on Rhodamine Derivatives.

Recently, the problem of food security is more and more serious, and people pay attention to mercury because of the toxic of it. A new approach for the determination of mercury content in foodstuff is devised. In this paper, first, we design and synthesis a new kind of fluorescent probe whose matrix based on rhodamine B, hydrazine hydrate and hydroxy benzaldehyde. Through the analysis of H-NMR spectra of the synthesized product L1, we confirm that the synthetic substance is the adjacent carboxyl benzaldehyde hydrazone structure generation of rhodamine B. Then, we measure the fluorescence signal intensity of the probe with different concentrations of mercury ions fully upon complexation by fluorescence spectrometer and we can study the relationship between the mercury ion concentration and the fluorescence intensity and draw the standard working curve. Following, It's time to discuss the microwave digestion processing of tea, after digestion we use the synthetic probe Li for determination of mercury content in tea. The experimental results show that the maximum excitation wavelength of the probe and coordination compound are 568. 05 and 560. 00 nm, the maximum emission wavelength are 587. 94 and 580. 00 nm. Then we can find the best testing conditions to improve the degree of accuracy, that is: room temperature, 50% the methanol solution, 3. 0 mL pH 4. 0 buffer solution, in the extent of 30 min. The experimental results show that Na+, K+, Ca2+, Cu2+, Zn2+, Al3+ have little impact on the fluorescence intensity of the:probe. Fe3+, Mg2+, Ba2+ has a weak enhancement to the fluorescence intensity of the probe. While a low concentrations of Hg2+ have an obviously enhanced effect on the fluorescence intensity of the probe. In contrast to other metal ions, the probe for Hg2+ has a good selectivity. Linear relationship between the magnitude of increase in fluorescence intensity and concentration of mercury ion was in the range of 5~20 ng . L-1 with detection limit (3S/N) of 1. 9 ng . L-1. The proposed method was applied to determination of mercury ion in samples of tea and sausage and the obtained result and sample recovery were all satisfactory. The methods of analysis instrument has the advantages of simple structure, sensitivity, high accuracy, good selectivity and less volume of simple, without the need for enrichment, being very practical.

[Repair mechanism of frozen sublethally damaged Staphylococcus aureus].

OBJECTIVE: To study the repair mechanisms of frozen sublethally damaged Staphylococcus aurous cells. METHODS: We resuscitated frozen sublethally damaged S. aureus at 37 degrees C for different time within 3 h. Meanwhile, we compared the morphological changes of the frozen sublethally damaged cells after 1 h of resuscitation using transmission electron microscopy assay (TEM). The expressions of the transcriptional attenuator MsrR (msrR), iron (Fe3+) ABC transporter ATP-binding protein (fhuC), and cytochrome b (cytB) genes were quantitatively analyzed by real-time fluorescence quantitative PCR (Real-time PCR) method. The content of cells outside leakage, active oxygen (ROS), and superoxide dismutase (SOD) activity were also determined by ultraviolet spectrophotometry. RESULTS: More than 99% of the frozen sublethally damaged S. aureus repaired after 3 h. The resuscitated cells expressed an equal resistance to high concentration of NaCl. Real-time PCR results showed that the msrR and fhuC genes expressions were down-regulated, whereas the cytB gene expression was up-regulated significantly. The frozen sublethally damaged S. aureus cellar surface ultrastructure significant changed during resuscitation. The cell surface became compact and sturdy from smooth and transparent. The cell leakage rate of ultraviolet absorption material gradually decreased. Meanwhile, the intracellular ROS level declined along with the decrease of SOD activity. CONCLUSION: Frozen sublethally damaged cells may regain the capability of resistance to high salt stress by repairing cell membrane integrity, reducing the content of ROS through gene regulation, inhibiting the toxicity of active oxygen to the cells. Meanwhile, the regulation of metabolism related genes (cytB) provides the energy for the requirement of cells, therefore, the frozen sublethally damaged cells were repaired finally.

Inactivation and sublethal injury kinetics of Staphylococcus aureus in broth at low temperature storage.

Low temperatures are widely used to ensure food quality and safety. However, sublethally injured Staphylococcus aureus is an important microbiological safety concern in low temperature food. The objective of this study was to develop predictive inactivation kinetic models for the inactivation and sublethal injury of S. aureus in broth at different temperatures (4 to -18°C) and time points. S. aureus was diluted in tryptic soy broth plus 0.6% (wt/vol) yeast extract (TSBYE) to obtain approximately 10(8) CFU/ml and was stored separately at 4, -3, -11, and -18°C. After specific time points within 96 days, survival of S. aureus was determined on TSBYE and TSBYE agar plus 10% NaCl for enumeration of the total viable and noninjured cell numbers, respectively. Linear, Weibull, and modified Gompertz models were applied to determine survival curve regression. The combination of low temperature and time resulted in S. aureus inactivation, although the cells were able to survive in this sublethal state. Storage temperature was the critical parameter in survival of S. aureus. The modified Weibull model successfully described a second model of noninjured S. aureus cell survival at different low temperatures, whereas only the linear model was able to fit the total viable cells. The predictive model may be used to estimate the level of S. aureus contamination in food at low storage temperatures and times, and it provides new insight into the sublethally injured survival state of S. aureus in low temperature food.

Light exposure during storage preserving soluble sugar and l-ascorbic acid content of minimally processed romaine lettuce (Lactuca sativa L.var. longifolia).

Minimally processed romaine lettuce (MPRL) leaves were stored in light condition (2500lux) or darkness at 4°C for 7d. Light exposure significantly delayed the degradation of chlorophyll and decrease of glucose, reducing sugar, and sucrose content, and thus preserved more total soluble solid (TSS) content at the end of storage in comparison with darkness. While, it did not influenced starch content that progressively decreased over time. The l-ascorbic acid (AA) accumulated in light-stored leaves, but deteriorated in dark-stored leaves during storage. The dehydroascorbic acid (DHA) increased in all leaves stored in both light and dark condition, of which light condition resulted in less DHA than darkness. In addition, the fresh weight loss and dry matter significantly increased and these increases were accelerated by light exposure. Conclusively, light exposure in applied intensity effectively alleviated MPRL quality deterioration by delaying the decreases of pigments, soluble sugar, TSS content and accumulating AA.