Solid-state Fermentation Process Research Articles

Dynamic analysis Caffeic acid production driven by the key physicochemical factor and microbial community succession in Baijiu Daqu: A multi-microorganism fermentation of solid-state fermentation system

Daqu is a saccharifying fermenting agent in the solid-state fermentation process of Strong aromatic Baijiu, providing important raw materials, microorganisms and enzymes for the fermentation of Baijiu, however, a little information about organic acids production in Daqu until now. This work analyzed the correlation among microbial community succession, physicochemical factors and caffeic acid-producing metabolic pathways in key fermentation time-point of strong aromatic Baijiu Daqu, and the results showed that the main functional communities of caffeic acid metabolism were Staphylococcus, Klebsiella, Lactobacillus and Pichia, respectively. The correlation results showed that in the fermentation stage of the Daqu, caffeic acid was mainly influenced by miosture and reducing sugar. Co-occurrence network analysis showed that microbial interactions were stronger in days 0–8 than in days 10–27. The PICRUSt2 marker gene sequence was used to predict information on the function and abundance of enzymes related to different fermentation stages of Daqu, and combined with the related enzymes involve in caffeic acid metabolism, the results indicated that the microbial community in the pre-fermentation 0–8 days had the potential to produce caffeic acid. The results provide a theoretical basis for the analysis of the formation mechanism of phenolic acids in the multi-bacterial co-fermentation system of Daqu fermentation.

Optimization of tannase production by Aspergillus glaucus in solid-state fermentation of black tea waste

Tannases are valuable industrial enzymes used in food, pharmaceutical, cosmetic, leather manufacture and in environmental biotechnology. In this study, 15 fungal isolates were obtained from Egyptian cultivated soil and marine samples. The isolated fungi were qualitatively and quantitatively screened for their abilities to produce tannase. The selected fungal isolate NRC8 giving highest tannase activity was identified by molecular technique (18S rRNA) as Aspergillus glaucus. Among different tannin-containing wastes tested, the black tea waste was the best substrate for tannase production by Aspergillus glaucus in solid-state fermentation (SSF). Optimization of the different process parameters required for maximum enzyme production was carried out to design a suitable SSF process. Maximal tannase production was achieved with moisture content of 75%, an inoculums size of 6 × 108 spore/ml and sodium nitrate 0.2% (pH of 5.0) at 30 °C after 5 days of incubation. Box–Behnken experiment was designed to get a quadratic model for further optimization studies. Four-factor response-surface method with 27 runs was prepared using independent parameters including (moisture content %, initial pH, substrate concentration (g) and sodium nitrate concentration (g) for tannase model. The F- and P-values of the model were 4.30 and 0.002, respectively, which implied that the model is significant. In addition, the lack-of-fit was 1040.37 which indicates the same significance relative to the pure error. A. glaucus tannase was evaluated by the efficiency of conversion of tannic acid to gallic acid. Moreover, production of gallic acid from SSF process of A. glaucus using black tea waste was found to be 38.27 mg/ml. The best bioconversion efficiency was achieved at 40 °C with tannic acid concentration up to 200 g/L.Graphical

Design Optimization of a Tray Bioreactor for Solid-State Fermentation: Study of Process Parameters through Protein Modification of By-Products

This study investigated the design of a tray bioreactor for solid-state fermentation, applying Rhizopus oryzae to oilseed meals as the substrate. Two process variables were continuously monitored in the bioreactor to ensure precise control of the environmental conditions: temperature and relative humidity (RH). The comprehensive analysis covered the effects of different fermentation conditions on the protein content, technological properties, and molecular distribution of the samples. The study revealed that the configuration factors suffered a stratification within the three trays of the bioreactor. Notably, the upper tray registered the largest dispersion, with a range of 1.5 °C. When analyzing the differences between sensors within each tray, the largest difference was found in the lower tray (10.9%). Furthermore, higher EAI (Emulsifying Activity Index) values were observed in the upper tray (T3) for rapeseed. As for ESI (Emulsion Stability Index) values, no differences were observed between the trays or fermentation periods. Using the changes induced by Rhizopus oryzae fungal enzymes, the study quantitatively examined the changes in the by-product valorization. While the bioreactor factors did not affect the protein quantity itself, they had significant impacts on specific changes within the molecular weight protein fraction. The findings of this study offer significant insights into the complex dynamics of solid-state fermentation processes. The outcomes of this study not only advance understanding of solid-state fermentation but also offer practical guidance for the design and operation of fermenters in industrial applications.

Agroindustrial and food processing residues valorization for solid-state fermentation processes: A case for optimizing the co-production of hydrolytic enzymes

In the pursuit of sustainability, managing agro-industrial and food processing residues (AFR) efficiently is crucial. This study proposes a systematic approach to convert AFR into valuable products via solid-state fermentation (SSF). Using fungal enzyme production as a case study, this adaptable methodology suits any SSF bioprocess. Initially, AFR's physicochemical properties were evaluated to assess their feasible use as carbon sources and solid matrices for SSF. Then, five strains were screened for their capability to produce enzymes (Xylanase, X; pectinase, P; cellulase, C). Apple pomace (AP) and brewery spent grain (BSG) with Aspergillus sp. (strain G5) were selected. Subsequent steps involved a two-phase statistical approach, identifying critical factors and optimizing them. Process conditions were screened using a Plackett-Burman design, narrowing critical variables to three (BSG/AP, pH, humidity). Response Surface Methodology (Central Composite Design) further optimized these factors for co-synthesis of X, P, and C. The humidity had the most significant effect on the three responses. The optimum conditions depended on each enzyme and were further validated to maximize either X, P or C. The obtained extracts were used for pectin extraction from orange peels. The extract containing primarily xylanase (X = 582.39, P = 22.86, C = 26.10 U mL−1) showed major pectin yield recovery (12.33 ± 0.53%) and it was obtained using the optimal settings of BSG/AP (81/19), humidity (50.40%), and pH (4.58). The findings will enable adjusting process conditions to obtain enzymatic cocktails with a tailored composition for specific applications.

A 3D printed plastic frame deeply impacts yeast cell growth.

Solid State Fermentation (SSF) processes have been explored for yeast growth and protein and metabolites production. However, most of these processes lack standardization. In this work, we present a polylactic acid (PLA) 3D printed matrix that dramatically enhances yeast growth when embedded in liquid media compared to equivalent static cultures, and changes yeast expression patterns at the proteome level (data are available via ProteomeXchange with identifier PXD043759). Moreover, differences in sugar assimilation and ethanol production, as the main product of alcoholic fermentation, are observed. Our results suggest that these matrixes may be useful for a vast range of biotechnological applications based on yeast fermentation.

Solid-state fermentation with Zygomycetes fungi as a tool for biofortification of apple pomace with γ-linolenic acid, carotenoid pigments and phenolic antioxidants

In the last few years, there has been a growing interest in the more efficient utilization of agricultural and food by-products. Apples are among the most processed fruits in the world that generate huge quantities of processing waste biomasses. Therefore, the objective of this study was to improve the nutritional value of apple pomaces with γ-linolenic acid (GLA) and carotenoid pigments by solid-state fermentation (SSF) using two Zygomycetes fungi (Actinomucor elegans and Umbelopsis isabellina). The impact of fermentation periods on the polyphenol content and antioxidant capacity of the bioprocessed apple pomace was also investigated. The accumulated lipids were composed primarily of neutral fractions (mostly triacylglycerols). SSF with U. isabellina yielded a 12.72% higher GLA content than with A. elegans (3.85 g GLA/kg DW of pomace). Contrary to the lipogenic capacity, A. elegans showed higher carotenoids and phenolic antioxidants productivity than U. isabellina. The maximum concentrations for β-carotene (433.11 μg/g DW of pomace-SSF with A. elegans and 237.68 μg/g DW of pomace-SSF with U. isabellina), lutein (374.48 μg/g DW- A. elegans and 179.04 μg/g DW- U. isabellina) and zeaxanthin (247.35 μg/g DW- A. elegans and 120.41 μg/g DW- U. isabellina) were registered on the 12th day of SSFs. In the case of SSF with A. elegans, the amount of total phenolics increased significantly (27%) by day 4 from the initial value (2670.38 μg of gallic acid equivalents/g DW) before slowly decreasing for the remaining period of the fungal growth. The experimental findings showed that a prolonged fermentation (between 8 and 12 days) should be applied to obtain value-added apple pomaces (rich in GLA and carotenoids) with potential pharmaceutical and functional food applications. Moreover, the SSF processes of simultaneous bioaccumulation of valuable fatty acids, carotenoids and phenolic antioxidants proposed in the present study may open up new challenges for biotechnological production of industrially important biomolecules using abundant and unexploited apple pomaces.

Development of a novel pilot-scale tray bioreactor for solid-state fermentation aiming at process intensification

Solid-State Fermentation (SSF) processes have high contamination and low productivity rates, since it involves batch processes with multiple manual stages. In order to reduce handling in SSF processes, this research developed a pilot-scale tray bioreactor that enables process intensification by combining upstream operations and fermentation in a single equipment. Thus, a novel tray bioreactor was developed with an atomization system of spore suspension, nutrient solution, and cooling water above the fermentative medium. It also incorporates a sterilization system using steam. In order to validate the bioreactor, two case studies were conducted. In the first case study, the fungus Metarhizium anisopliae was cultivated on three types of agro-industrial residues. The conidia/mL obtained using the mixture of wheat bran and broken rice was (16.7±0.46)×108, which is statistically higher (α=0.05) than the fungus production of (8.59±1.60)×108 cultivated on the control (Type I Rice). In the second case study, lipases from M. anisopliae were produced on agro-industrial residues. The enzymatic activity average was 5.64±0.45U/mL based on 36 fermentations. The results have shown that the new tray bioreactor can produce the fungus and lipases in greater quantities than other systems reported in literature, while reducing handling, energy, costs, and process time.

Establishing Experimental Conditions to Produce Lignin-Degrading Enzymes on Wheat Bran by Trametes versicolor CM13 Using Solid State Fermentation

Valorisation of wheat bran can be achieved by solid state fermentation (SSF), through application of this material as a growth substrate for a natural white rot fungal isolate, Trametes versicolor CM13, to produce lignin-degrading enzymes. One of the main challenges in optimising and upscaling (SSF) processes is the accurate adjustment and maintenance of moisture conditions. This factor was assessed in the scale up of microcosms and was evaluated over 28 days, under two slightly different moisture contents, reflecting minor differences in experimental conditions during set up and operation of the SSF process. In addition, the microcosms were processed differently from the initial trial using homogenisation of whole microcosms to create a homogeneous mixture prior to sampling. This appeared to result in less variation among the collected samples from the microcosms. Variation of measured parameters as a percentage of actual values measured ranged from 1.33% to 144% in the unmixed microcosms and from 0.77% to 36.0% in the pre-mixed microcosms. Decomposition in the more saturated microcosms progressed more quickly as hemicellulose content decreased and reached a steady state after 14 days, whereas hemicellulose content continued to decrease until 21 days in the less saturated microcosms. Lignin-degrading enzyme activities were not significantly different between either sets of experiments except for laccase on day 7. Laccase and manganese peroxidase activities were highest on day 21 and were similar in both sets of experiments. Enzyme activities on day 21 in the microcosms at moisture content of 42.9% and at 54.6% for laccase activities were 750 ± 30.5 and 820 ± 30.8 units, and for manganese peroxidase, activities were 23.3 ± 6.45 and 21.4 ± 21.4 units, respectively. These results revealed different decomposition rates during the early stage of solid-state fermentation as a function of the initial moisture content, whereas final enzyme activities and fibre content during the later stage were similar in microcosms having different moisture contents at the start.

Application of solid-state fermentation using mushrooms for the production of animal feed.

The increasing growth of agroindustrial activity resulting in excessive amounts of agriwaste has led to the accumulation of a large quantity of lignocellulosic residues all over the world, in particular in deforestation initiatives for the removal of invasive trees in South Africa. These lignocellulosic residues are rich in energy resources and consist of a mixture of natural polymers based on lignin, cellulose, and hemicellulose. The use of lignolytic fungi such as mushrooms in solid-state fermentation could sufficiently degrade the indigestible lignocellulosic components and add medicinal and nutritional value to otherwise unusable, high-energy waste material, which in turn could yield a new method of producing energy-rich fodder for ruminant animals. The digestive type of animal for which the potential feed is developed must be identified and considered before deciding on the bioconversion method and process, as the outcomes for obtaining potentially high-quality feeds for nonruminant and ruminant animals are different. The current study presents data on the bioconversion of lignocellulosic substrate using solid-state fermentation with edible and medicinal mushrooms, Ganoderma lucidumand Pleurotus ostreatus, and a possible new species, to increase digestibility and nutritional value to be applied as ruminant animal feed. The solid-state fermentation process was optimized and the resulting product was analyzed for the degradation of the lignocellulosic components. Results indicated that the solid-state fermentation duration and mushroom species were key components in achieving significant degradation. Data obtained after 18 weeks of degradation indicated a significant (p < 0.05) reduction in the acid detergent fiber, acid detergent lignin, and neutral detergent fiber fractions of the biomass, with up to a 20% reduction in indigestible components. This increase in digestibility could contribute to increased energy availability for ruminant animals.

Comparative Analysis of Volatile Flavor Compounds in Strongly Flavored Baijiu under Two Different Pit Cap Sealing Processes.

The solid-state fermentation process of strongly flavored Baijiu is complicated by the co-fermentation of many different microorganisms in the fermentation pools. The traditional fermentation pools of strong flavor Baijiu are sealed with mud, and this sealed-pit mud is not easy to maintain; therefore, the pit cap is prone to cracks and to caving in. The destruction of the sealed-pit mud may lead to instability in the composition and an abundance of microorganisms in the fermentation process that results in fluctuations of product quality. Thus, the production method of replacing the mud cap with a new steel cap is gradually attracting the attention of scientific and technical workers in the industry. However, so far, there have been relatively few reports on the use of steel lids for sealing pits for fermentation and brewing. In this study, the volatile flavor components of 270 Baijiu samples from mud-sealing and steel-sealing pits of a Chinese Baijiu distillery were studied qualitatively and quantitatively using Gas Chromatography-Mass Spectrometry (Abbreviated as GC-MS). Our statistical methods included Hierarchical Cluster Analysis (Abbreviated as HCA), Principal Component Analysis (Abbreviated as PCA), and Discriminant Analysis (Abbreviated as DA). A statistical analysis was carried out on the yield of strongly flavored Baijiu, and we made a comprehensive evaluation of the Baijiu produced under the two pit-sealing modes with regard to flavor and economic efficiency. The yield of strong flavored Baijiu was 6.7% higher with steel-sealing pits compared with mud-sealing pits. Cluster analysis categorized the strongly flavored Baijiu samples into two categories initially: (1) samples produced using mud-sealing pits and (2) samples using steel-sealing pits. Our analysis also indicated that the 28 compounds used for quantification were selected correctly. Surprising to the experimental staff, the overall score for the steel-sealing pits was greater than that of the mud-sealing pits based on PCA. Using DA, the prediction results were 100% accurate. In summary, through a comparative analysis of the flavor and yield, which are the two main factors that affect the quality of Baijiu in a distillery, and systematic combination at both experimental and theoretical levels, the differences between the Baijiu production by steel-sealing and the traditional mud-sealing were clear. Regardless of the impact of age, the detectable flavor components of Baijiu from the mud-steeling pits were very consistent with those of the steel-sealing pits in terms of richness or concentration. However, steel-sealing pits were significantly superior to mud-sealing pits with respect to output, consistency in quality, and cost (human and economic) savings.

Pullulanase: unleashing the power of enzyme with a promising future in the food industry.

Pullulanases are the most important industrial group of enzymes in family 13 glycosyl hydrolases. They hydrolyze either α-1,6 and α-1,4 or both glycosidic bonds in pullulan as well as other carbohydrates to produce glucose, maltose, and maltotriose syrups, which have important uses in food and other related sectors. However, very less reports are available on pullulanase production from native strains because of low yield issues. In line with the increasing demands for pullulanase, it has become important to search for novel pullulanase-producing microorganisms with high yields. Moreover, high production costs and low yield are major limitations in the industrial production of pullulanase enzymes. The production cost of pullulanase by using the solid-state fermentation (SSF) process can be minimized by selecting agro-industrial waste. This review summarizes the types, sources, production strategies, and potential applications of pullulanase in different food and other related industries. Researchers should focus on fungal strains producing pullulanase for better yield and low production costs by using agro-waste. It will prove a better enzyme in different food processing industries and will surely reduce the cost of products.

Response surface optimisation of technological parameters for producing Ganoderma lucidum by solid-state fermentation from Panax notoginseng residues and kinetics

The present work aimed to investigate the optimal control strategy for Ganoderma lucidum (Chuanzhi No. 6) fermentation from Panax notoginseng residue. Optimisation of the solid-state fermentation (SSF) technical parameters, including inoculum dosage, fermentation temperature, and fermentation time was carried out using the single-factor and Box-Behnken design methods. Results showed that the optimal technical parameters were inoculum dosage of 15.28%, fermentation temperature of 28.42°C, and fermentation time of 14 d. The predicted maximum biomass of G. lucidum was 0.4327 g, which was also verified by validation experiments. The biomass of G. lucidum increased significantly with optimised technological parameters. The logistic equation, the Boltzmann function, and the four-parameter logistic equation were respectively suitable for modelling G. lucidum growth kinetics (R2 = 0.9754), Ganoderma triterpene production kinetics (R2 = 0.9897), and the matrix consumption kinetics (R2 = 0.9826). These models can be used to predict the SSF process of G. lucidum, thus providing a theoretical basis for the development of new G. lucidum drugs, while at the same time recycle Panax notoginseng residue.

Microbial communities and their correlation with flavor compound formation during the mechanized production of light-flavor Baijiu

Light-flavor Baijiu fermentation is a typical spontaneous solid-state fermentation process fueled by a variety of microorganisms. Mechanized processes have been increasingly employed in Baijiu production to replace traditional manual operation processes, however, the microbiological and physicochemical dynamics in mechanized processes remain largely unknown. Here, we investigated the microbial community succession and flavor compound formation during a whole mechanized fermentation process of light-flavor Baijiu using the conventional dilution plating method, PacBio single-molecule real-time (SMRT) sequencing and headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry. The results showed that largely different fungal and bacterial communities were involved in the soaking and fermentation processes. A clear succession from Pantoea agglomerans to Bacillus (B.) smithii and B. coagulans in dominant bacterial species and from Cladosporium exasperatum to Saccharomyces cerevisiae and Lichtheimia ramosa in dominant fungal species occurred in the soaking processes. In the fermentation process, the most dominant bacterial species was shifted from Pantoea agglomerans to Lactobacillus (La.) acetotolerans and the most dominant fungal species were shifted from Lichtheimia ramose and Rhizopus arrhizus to Saccharomyces cerevisiae. The bacterial and fungal species positively associated with acidity and the formation of ethanol and different flavor compounds were specified. The microbial species exhibited strong co-occurrence or co-exclusion relationships were also identified. The results are helpful for the improvement of mechanized fermentation process of light-flavor Baijiu production.

Exploring the Effects of Solid-State Fermentation on Polyphenols in Acanthopanax senticosus Based on Response Surface Methodology and Nontargeted Metabolomics Techniques

In order to optimize the process of solid-state fermentation and understand the changes of active ingredients during fermentation of A.senticosus, we used response surface methodology to optimize the solid-state fermentation process of A.senticosus and analyzed the effect of fermentation on the active components of A.senticosus by nontargeted metabolomics techniques. The effects of fermentation conditions on polyphenol content were studied in terms of fermentation time, fermentation temperature, water content, and the inoculum level through Plackett–Burman design and response surface experiments. The optimized fermentation conditions were a fermentation time of 60 h, a fermentation temperature of 37°C, a water content of 55%, and an inoculum level of 12.5%, and the polyphenol content reached 10.25 ± 0.05 mg·g−1, which was 40% higher than that before fermentation. Furthermore, the metabolites and metabolic pathways of A. senticosus were analyzed before and after fermentation using nontargeted metabolomics techniques, and differences in metabolites were investigated based on the analysis of the principal components. The results showed that A.senticosus contained 57 phenolics, and a total of 12 polyphenolic metabolites were significantly different before and after fermentation (including phenols and isoflavonoids), among which the content of caffeic acid and its derivatives with antioxidant capacity was significantly increased, which may improve the antioxidant capacity of fermented A.senticosus. Therefore, solid-state fermentation opens new avenues for the clinical development and application of A. senticosus.

Improvement of the Nutritional Quality of Rapeseed Meal through Solid-State Fermentation with B. subtilis, S. cerevisiae, and B. amyloliquefaciens

In this study, the effect of solid-state fermentation with Bacillus subtilis GYB6, Saccharomyces cerevisiae NJ1, and Bacillus amyloliquefaciens Y8 on the anti-nutritional factors, nutritional components, bioactive compounds, antioxidant activity, functional properties, and structure of rapeseed meal (RSM) were investigated. Results showed that the action of three strains in the fermentation of RSM caused a significant decline in glucosinolates, phytic acid, crude fiber, and tannins by 99.18%, 42.41%, 27.21%, and 34.17%, respectively. The amount of crude protein, amino acids, and peptides of RSM increased significantly after fermentation. The SDS-PAGE results showed that 12S globulin and 2S albumin protein were almost entirely degraded. Fermentation considerably increased the concentration of total phenolics and flavonoids, and activated antioxidant activity and functional properties. Furthermore, the structural variation was observed by scanning electron microscopy and FTIR spectroscopy. Thus, these results indicated that the solid-state fermentation process in this study was a promising approach to enhance both the nutritional value and bioactivity of RSM, which could be used as value-added functional animal food ingredients.

Solid-state Fermentation of Cottonseed Meal with Saccharomyces cerevisiae for Gossypol Reduction and Nutrient Enrichment

Background: An experiment was conducted to study the effect of solid-state fermentation (SSF) of cottonseed meal (CSM) with Saccharomyces cerevisiae on anti-nutritional factors and amino acid profile. Methods: A finely ground CSM was fermented with baker’s yeast for 48 h at room temperature with periodic observations of pH, temperature and moisture. The fermented substrate was partially sun-dried and nutritional values were observed. Result: After the SSF process on dry basses, the protein content of CSM increased from 8.74% to 12.67%. Besides increasing the nutritional value, the SSF showed a clear significant effect in reducing the anti-nutritional factors content of raw CSM like total gossypol from 0.28% to 0.21%, phytic acid from 3.3% to 0.3% and total tannin from 1.42% to 0.68%. CSM fermented with S. cerevisiae improved concertations of essential amino acids viz., histidine, isoleucine, valine, methionine and phenylalanine. The protein quality evaluation showed a significant increase in its nutritional value. Based on the present result, it can be concluded that the fermentation of CSM with S. cerevisiae decreases the anti-nutritional factors and improves essential nutrients.

Modeling the microbial pretreatment of camelina straw and switchgrass by Trametes versicolor and Phanerochaete chrysosporium via solid-state fermentation process: A growth kinetic sub-model in the context of biomass-based biorefineries.

Advancing microbial pretreatment of lignocellulose has the potential not only to reduce the carbon footprint and environmental impacts of the pretreatment processes from cradle-to-grave, but also increase biomass valorization, support agricultural growers, and boost the bioeconomy. Mathematical modeling of microbial pretreatment of lignocellulose provides insights into the metabolic activities of the microorganisms as responses to substrate and environment and provides baseline targets for the design, development, and optimization of solid-state-fermentation (SSF) bioreactors, including substrate concentrations, heat and mass transfer. In this study, the growth of Trametes versicolor 52J (TV52J), Trametes versicolor m4D (TVm4D), and Phanerochaete chrysosporium (PC) on camelina straw (CS) and switchgrass (SG) during an SSF process was examined. While TV52J illustrated the highest specific growth rate and maximum cell concentration, a mutant strain deficient in cellulose catabolism, TVm4D, performed best in terms of holocellulose preservation and delignification. The hybrid logistic-Monod equation along with holocellulose consumption and delignification models described well the growth kinetics. The oxygen uptake rate and carbon dioxide production rate were directly correlated to the fungal biomass concentration; however, a more sophisticated non-linear relationship might explain those correlations better than a linear model. This study provides an informative baseline for developing SSF systems to integrate fungal pretreatment into a large-scale, on-farm, wet-storage process for the utilization of agricultural residues as feedstocks for biofuel production.

Preparation of soybean meal peptide for chelation with copper/zinc using Aspergillus oryzae in solid-state fermentation

This study investigated the optimal process of solid-state fermentation (SSF) using soybean meal (SBM) as substrate by Aspergillus oryzae and proteolysis of SBM to prepare SBM-derived peptide (SBMP) for chelating with Cu(Ⅱ)/Zn(Ⅱ). During the SSF of SBM, the alkaline protease activity of A. oryzae was higher than that of two other fungi, reaching maximum activity (574 U/g) at the fermentation time of 86 h, 43% inoculation ratio, and liquid–substrate (I/S) ratio of 0.8. The SBMP yield reached a maximum value at 55 °C for 6 h hydrolysis according to the analysis of the degree of hydrolysis (DH) and total Kjeldahl nitrogen (TKN) content in hydrolysates. After ultrafiltration, the SBMP of 1–5 kDa had the best ability to chelate with Cu(Ⅱ) and Zn(Ⅱ). Moreover, the SBMP displayed a higher capacity to chelate with Zn(Ⅱ) (222.7 mg/g) than Cu(Ⅱ) (68.3 mg/g) under optimal conditions. Aspartic acid, glutamic acid, lysine, arginine and histidine in SBMP played a critical role at the chelating Cu(Ⅱ)/Zn(Ⅱ). UV and FTIR spectrum analysis revealed that the –COOH and –NH2 in SBMP were the main bioactive groups for chelating with Cu(Ⅱ)/Zn(Ⅱ). SEM showed that the surface of SBMP–Cu(Ⅱ)/Zn(Ⅱ) chelate was rough and formed spherical aggregates. These results indicated that combining SSF and proteolysis exhibited great potential for preparing SBMP–metal chelates for developing organometallic supplements.

Solid-State Fermentation of Soybean Meal with Edible Mushroom Mycelium to Improve Its Nutritional, Antioxidant Capacities and Physicochemical Properties

Soybean meal is a class of by-products obtained from the processing of soybean products. Despite its high nutritional value, the presence of glycoside isoflavones limits human use of soybean meal. This study evaluated the effect of solid-state fermentation (SSF) with different edible mushroom mycelia (Pleurotus ostreatus, Hericium erinaceus, and Flammulina velutipes) on the proximate composition, antioxidant properties, and physicochemical properties of fermented soybean meal powder (SP). The results revealed that fermented SP had a higher nutritional value when compared to SP. P. ostreatus was the most pronounced among the three species. Crude protein content was found to have increased by 9.49%, while the concentration of glutamate and aspartic acid increased by 23.39% and 23.16%, respectively. SSF process significantly increased the total polyphenol content (TPC) and aglycone isoflavone content by 235.9% and 324.12%, respectively, resulting in increased antioxidant activity (evaluated by the DPPH, •OH, ABTS+ assays). Microstructural changes in fermented SP and nutrient degradation and utilization were observed. Thus, fermented SP can be used as a raw material with enhanced nutritional properties to develop new functional foods, such as plant-based foods represented by plant meat. It provides a promising approach for increasing the added value of soybean meal.

Uncovering acid resistance genes in lactic acid bacteria and impact of non-viable bacteria on bacterial community during Chinese strong-flavor baijiu fermentation

Chinese strong-flavor baijiu (CSFB) brewing is a spontaneously solid-state fermentation process for approximately 60 days. Numerous microorganisms grow, die, and spark a series of metabolic reactions during fermentation. In this study, the microbial community and structure between total and viable bacteria in zaopei from the 5- and 20-year pits of CSFB are revealed by amplicon sequencing. Metagenome sequencing was applied to investigate acid resistance genes in Lactobacillus and predict carbohydrate active enzyme in zaopei. Besides, SourceTracker was conducted to expose bacterial sources. Results revealed that there was no significant difference in the bacterial community and structure between the total and viable bacteria; Lactobacillus was the most dominant bacterium in zaopei of two types of pits. Meanwhile, acid resistance genes argR, aspA, ilvE, gshA, DnaK, and cfa were genes that sustained Lactobacillus survival in the late stages of fermentation with high contents of acid and ethanol, and glycosyltransferases were identified as the predominated enzymes during the CSFB fermentation which catalyzed the process of lactic acid generation via Embden-Meyerhof-Parnas pathway and Hexose Monophosphate Pathway. Moreover, the environment contributed most bacteria to zaopei of the 5- and 20-year pits. These findings will provide a deeper understanding of the microbial community structure of viable and total bacteria and the reason for the dominance of Lactobacillus in the later stages of CSFB fermentation.