To enhance the value-added utilization of chitin derived from crustacean waste, this study collected samples from the bottom of a shrimp farm in Guangxi. High-yield chitinase-producing strains were isolated through preliminary and secondary screening, followed by taxonomic identification. The optimal fermentation conditions were determined using single-factor experiments combined with orthogonal designs. Subsequently, the enzymatic properties and hydrolysis products of the chitinase produced by the selected strain were characterized. Results showed that initial screening on chitin-containing agar plates yielded nine strains capable of forming clear zones, among which strain GXUN-J3 exhibited the highest chitinase activity (297.24±10.77 U/L) and was identified as belonging to the genus Streptomyces sp. Under optimized fermentation conditions—6% (w/v) chitin, 0.25% (w/v) bean powder, an initial pH of 7.0, a fermentation temperature of 25 ℃, a liquid volume of 40 mL per 150 mL flask, and an inoculum size of 5% (v/v)—the chitinase activity reached 1026.72±18.69 U/L, representing a remarkable increase of 3.51-fold compared to the original process. Enzyme characterization revealed optimal activity at 50 ℃ and pH5.0. Among the metal ions tested, Mg²⁺ and Fe³⁺ significantly enhanced enzyme activity, whereas Fe²⁺, Mn²⁺, and Cu²⁺ exhibited significant inhibitory effects (P<0.05). Additionally, the chemical agents of EDTA, SDS, and methanol markedly suppressed enzymatic activity (P<0.05). Thin-layer chromatography (TLC) analysis demonstrated that the hydrolysis products primarily consisted of chitin dimer and N-acetyl-D-glucosamine, suggesting that this enzyme functions as an exo-chitinase. This study successfully established a process for producing chitinase and preparing chitin oligosaccharide using Streptomyces strain GXUN-J3, offering a promising approach for high-value utilization of crustacean waste.

The purpose of this study was to investigate the growth kinetics of Bacillus cereus in different milk products and its impact on milk quality. Fifty dairy products (including 25 raw milk from factory pre-treatment tanks and 25 commercial milk packaged in boxes) were collected, and suspected strains were isolated using Mannitol-Egg-Yolk-Polymyxin Agar (MYP). Morphological observation, protein toxin crystallization experiment, Vitek-2 biochemical identification, and 16S rRNA sequencing were used to isolate and identify B. cereus. Further, one strain with the fastest growth rate was selected as the experimental object, and the strain was inoculated into three different milk products (pure milk, lactose-decomposed milk, and grain milk) at initial concentrations of 10¹, 10², and 10³ CFU/mL. The growth kinetics of B. cereus in three different products were studied at two temperatures (25 ℃ and 35 ℃), and a Logistic equation was used to fit the growth model. The pH and sensory changes of the three milk products were simultaneously monitored. The results showed that the three strains (B1, B2, and B3) of B. cereus originated from raw milk were isolated and identified and they were not detected in commercial milk products. By measuring the growth curve, B1 strain with a faster growth rate was selected as the experimental object to study its effects on three different milk products. The results showed that temperature and initial inoculation concentration had a more significant impact on the growth of B. cereus. At 35 ℃ and high initial inoculation concentration, B. cereus in dairy products entered the logarithmic and stable phases earlier than at 25 ℃, with a shorter lag period. Among the three types of products, lactose-decomposed milk was more conducive to the growth of B. cereus. The fitting degree of the Logistic model was R²>0.9857. It was found that the pH of milk changed significantly as the bacterial concentration increased. Different dairy products had their own characteristics in terms of sensory degradation. Among them, the odor deterioration of lactose-decomposed milk was the most significant. This study provides a scientific basis for the early warning and safety control of B. cereus contamination in dairy products.

In this study, a novel fructosyltransferase (StFFase) was screened from Streptococcus troglodytae through gene mining. The enzyme was then engineered via computer-aided rational design to improve both its catalytic efficiency and thermostability. Based on EVCoupling predictions and experimental validation, three mutants (D104E, I232S, and S684P) with significantly enhanced enzymatic activity were selected from potential candidates. Their enzymatic activities were 2.20, 2.65, and 1.53 times that of the wild-type, respectively. Notably, the I232S mutant maintained high relative enzyme activity over a temperature range of 40~70 ℃, and its half-life at 50 ℃ was extended to 6.60 h, demonstrating superior thermostability. Kinetic analysis revealed that the I232S mutant exhibited improved affinity for the substrate sucrose, with the K_m value decreasing to 171 mmol/L, and a significantly enhanced catalytic efficiency. Furthermore, a conversion rate of 42.17% for 1-kestose was achieved using this mutant under conditions of 50% sucrose concentration (w/w) and an enzyme dosage of 15 U/g sucrose. Structural simulations revealed that the mutations improved catalytic performance and thermostability by eliminating electrostatic repulsion (D104E), forming new hydrogen bonds (I232S), and stabilizing β-turn conformations (S684P). This study provides a new strategy for the rational design of fructosyltransferases and highlights the potential of the engineered enzyme for industrial fructooligosaccharide production.

To investigate the patterns and origins of ethylene release in Penicillium digitatum-citrus interaction, ethylene biosynthesis was analyzed both during the infection process and across distinct infection zones (green sporulation zone, white mycelial zone, macerated zone, and healthy zone) by gas chromatography. Additionally, the content of 1-aminocyclopropane-1-carboxylic acid (ACC) and the expression levels of ACC oxidase genes (ACO1 and ACO2) were measured in different infection zones. Citrus were treated with the plant ethylene biosynthesis inhibitor α-aminooxyacetic acid (AOA), as well as the fungal ethylene precursors α-ketoglutaric acid (α-KG) and 2-keto-4-methylthiobutyric acid (KMBA), to determine the ethylene level. The results showed that ethylene production significantly increased during P. digitatum-citrus interaction, characterized by an initial increase followed by a sharp decline. All infected zones accumulated significantly higher ethylene levels compared to the healthy zone, with the most pronounced accumulation in the green sporulation zone. Following the pharmacological inhibition of ethylene biosynthesis in citrus by AOA, ethylene production was partially suppressed. The highest ACC accumulation was observed in the green sporulation zone, while the expressions of ACO1 and ACO2 were nearly completely inhibited. Application of KMBA or α-KG resulted in markedly enhanced ethylene emission and accelerated disease development. In conclusion, ethylene production is significantly enhanced during the P. digitatum-citrus interaction, with varying contributions from different infection zones. Ethylene produced during infection originates from both the host fruit and the pathogen, with the fungal-derived ethylene functioning as a virulence factor. These findings provide new insights to understand the possible pathogenic mechanisms of P. digitatum.

To explore the potential of Artemia to be developed as a food resource, promote the diversified development of the Artemia industry, and expand the biscuit food market. Biscuits containing Artemia flavor were developed. Single-factor experiments were performed to evaluate the effects of the Artemia addition, quinoa flour supplementation, and baking time and temperature on the sensory scores of the biscuits. Subsequently, the optimal processing parameters were determined using both response surface methodology (RSM) and artificial neural network (ANN) modeling. Furthermore, the nutritional and flavor profiles of the Artemia biscuits were characterized by means of nutritional composition and electronic tongue analyses as well as headspace solid-phase microextraction-coupled gas chromatography-mass spectrometry (SPME-GC-MS). Compared with the RSM model, the ANN model exhibited superior predictive and optimization capabilities, as demonstrated by its lower root mean square error (RMSE) of 1.8614, higher correlation coefficient (r) of 0.9602, and smaller errors between the measured and predicted values. The ANN-optimized biscuit formulation was as follows: Artemia (13.56 g), quinoa flour (47.26 g), low-gluten wheat flour (100 g), milk (40 g), corn oil (30 g), butter (60 g), salt (2 g), and xylitol (25 g), baked at 150 °C for 20.70 min. This optimized process yielded the highest sensory score (73.00). Additionally, the biscuits contained 6.46 g/100 g protein and 30.30 g/100 g fat. Electronic tongue analysis indicated that the taste profile was dominated by umami and saltiness. Moreover, GC-MS identified 48 volatile compounds, primarily aldehydes, acids, esters, furans, and pyrazines, with (E,E)-2,4-decadienal exhibiting the highest content (103.7 µg/kg) and odor activity value (3840.74). The development of Artemia biscuits enriches the variety of products in the biscuit market and offers a novel approach and theoretical foundation for utilizing Artemia resources in the snack-food industry.

To comprehensively utilize stalk residue of Pleurotus ostreatus, improve its added value, and develop a production base material for edible fungus condiments, this study carried out the following work: Using the concentrated enzyme-hydrolyzed solution of stalk residue of Pleurotus ostreatus as raw material, glucose was added, and the Maillard reaction was applied to prepare the flavor base material. Single-factor experiments and orthogonal experiments were used to optimize Maillard reaction conditions, with sensory score, system pH and browning degree as evaluation indicators. Free amino acid content was determined in the concentrated solution and the Maillard reaction products (MRPs) prepared under the optimal reaction conditions, and the contribution of amino acids to taste was also analyzed. The characteristic flavor of MRPs was analyzed using a gas chromatography-mass spectrometry (GC-MS) instrument, and the antioxidant capacities of the concentrated enzyme-hydrolyzed solution and MRPs were compared. The results showed that the order of influence of the four single factors on the Maillard reaction was: initial pH>glucose addition amount>reaction temperature>reaction time. The optimal conditions for the Maillard reaction were: 7.0% glucose addition, initial pH7.0, and reaction at 100 ℃ for 80 minutes. The prepared product was reddish-brown, with obvious umami taste and slight sweetness, and had a typical Pleurotus ostreatus aroma mixed with a roasted hazelnut scent. Seventeen free amino acids were detected in both the concentrated solution and MRPs, among which glutamic acid, serine, alanine, and tyrosine had relatively high contents. After the Maillard reaction, the content of bitter amino acids decreased; the content of umami amino acids (aspartic acid and glutamic acid) was 2.733 mg/g, accounting for 33.4% of the total free amino acid content. The taste activity values (TAV) of glutamic acid and alanine—both contributing significantly to taste—were 8.097 and 1.240, respectively, and the taste-active amino acid composition of MRPs was improved compared with that of the concentrated solution. A total of 42 volatile substances were detected and identified in MRPs, including 17 aldehydes, 10 ketones, 6 hydrocarbons, 5 alcohols, 3 heterocyclic compounds and 1 acid. The compounds with relatively high relative contents were heterocyclic compounds (44.93%) and aldehydes (33.07%). Relative odor activity value (ROAV) results show that 2,4-decadienal (ROAV=100), 2-pentylfuran (ROAV=50.29) and C₆~C₁₀ aliphatic aldehydes are the main aroma contributors of MRPs. Results of antioxidant experiments indicated that both the reducing power and DPPH free radical scavenging capacity (IC₅₀=0.86 mg/mL) of MRPs were significantly improved. This study established an effective method for the resource utilization of stalk residue of Pleurotus ostreatus, provided a new approach for condiment production, and had good market application prospects.

To improve the extraction efficiency of Tremella fuciformis polysaccharides (TP) and to investigate their structural characteristics and anti-inflammatory activity, dynamic high-pressure microfluidization (DHPM) was employed as an auxiliary extraction technique, and the extraction parameters were optimized using single-factor experiments and Box-Behnken response surface methodology. TP was structurally characterized by high-performance gel permeation chromatography (HPGPC), ion chromatography (IC), and Fourier transform infrared spectroscopy (FT-IR), and its anti-inflammatory activity was evaluated in a lipopolysaccharide (LPS)-induced RAW264.7 macrophage inflammation model. Results showed that a regression model with microfluidization pressure, solid-liquid ratio, and extraction time as independent variables exhibited good fitness. The optimal extraction conditions were determined to be a microfluidization pressure of 140 MPa, a solid-liquid ratio of 1:40 (g/mL), and an extraction time of 90 min, under which the TP yield reached 36.01%. Chemical composition analysis revealed that TP contained 86.12% total sugars and 33.11% uronic acids, with no detectable free proteins or monosaccharides, indicating that TP was a highly purified acidic polysaccharide. Structural analyses further showed that TP had an average molecular weight of 568385 Da and was composed of xylose, fucose, mannose, glucuronic acid, galactose, and glucose, in which the relatively high proportion of glucuronic acid confirmed its acidic characteristics. FT-IR spectra demonstrated that TP was mainly composed of β-pyranose-linked polysaccharide chains. In vitro experiments indicated that TP exhibited no cytotoxicity within the concentration range of 100~200 μg/mL and significantly reduced the LPS-induced secretion of NO, TNF-α, and IL-1β, while increasing the production of the anti-inflammatory cytokine IL-10 (P<0.05), demonstrating its notable anti-inflammatory potential. In conclusion, TP prepared by DHPM exhibits clear structural features, high purity, and remarkable anti-inflammatory activity, highlighting its potential as a natural functional ingredient for inflammation-related applications.

In order to fully utilize adlay bran resources and reduce the waste of protein resources, we prepared adlay bran peptides through alkaline protease hydrolysis of adlay bran protein, which was extracted from adlay bran. The preparation of adlay bran peptides-iron chelate (ABP-Fe) was optimized based on univariate analysis and orthogonal tests. The ABP-Fe was characterized using UV spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Also, its stability was explored and its Fe²⁺ release characteristics were investigated through in vitro gastrointestinal digestion simulations. The results showed that the optimized conditions for the preparation of ABP-Fe were pH5.0, peptide-to-iron mass ratio 3:1, reaction temperature 40 ℃ and reaction time 20 min. Under the optimized conditions, the chelation rate of Fe²⁺ in the ABP-Fe reached 76.33%. Characterization using UV and FTIR spectroscopy indicated that Fe²⁺ chelated with the carboxyl oxygen and amino nitrogen on the ABP peptide chains to form a new substance. Characterization using SEM and AFM revealed that the adlay bran peptides transform from smooth fragments into rough particles after chelation with Fe²⁺, with significant morphological differences. Additionally, the ABP-Fe exhibited good stability under varying pH and temperatures, and its Fe²⁺ release rate was higher than that of ferrous sulfate in the in vitro gastrointestinal digestion simulations. The as-prepared adlay bran peptide-derived iron supplement exhibited excellent chelation capability, good stability, and high release rate. This study provides insights for efficient utilization of adlay processing by-products and development of novel dietary iron supplements.

Using dandelion roots as a raw material, dandelion root polysaccharides (DRP) were extracted using a complex enzymatic hydrolysis method, and the extraction process was optimized. The four polysaccharide components, denoted DRP-a, DRP-b, DRP-c, and DRP-d were separated using diethylaminoethyl column chromatography, and the structural characteristics and in vitro antioxidant activities of these five polysaccharides were investigated. In vitro digestion experiments were conducted on the components having the best antioxidant activity after separation to explore the variation patterns of total carbohydrates and reducing sugars during in vitro digestion. The results showed that using an enzymatic hydrolysis time of 1.6 h, enzyme addition ratio of 5:2, enzyme dosage of 3.5%, and pH of 4.30 was optimal, yielding 23.78% polysaccharides. All five compounds produced the typical absorption peaks of polysaccharides and were mainly composed of seven monosaccharides: rhamnose, glucuronic acid, galacturonic acid, glucose, mannose, arabinose, and galactose. The molecular weight of DRP-a was 8763 Da, those of DRP-b and DRP-c were 6396~51090 Da and 8067~52713 Da respectively, and that of DRP-d was 12389~229349 Da. Among the five polysaccharides, only DRP had a triple-helical structure, as well as an irregular fragmented surface morphology. DRP-a had a spherical packing structure, whereas DRP-b, DRP-c, and DRP-d had smooth and irregular fragmented structures. In vitro antioxidant experiments demonstrated that all five polysaccharides had good antioxidant capacities. The total sugar and reducing sugar contents of DRP-d after in vitro oral, stomach, and small intestine simulated digestion did not change significantly, indicating that DRP-d was stable during digestion, and, thus, reached the intestinal tract to exert its effects. Overall, the findings clarify the digestive characteristics of dandelion polysaccharides. Further, the results indicate that dandelion polysaccharides could be developed and utilized as prebiotics.

To realize the high-value utilization of sesame meal, this experiment employed sesame meal as the raw material to investigate the optimal fermentation process for preparing sesame rough peptide (SRP) via liquid-state mixed fermentation with Bacillus subtilis and Bacillus velezensis (1:1), as well as evaluate its in vitro antioxidant activity. Meanwhile, the amino acid composition and relative molecular weight of sesame meal before and after fermentation were analyzed. Ultrafiltration technology was adopted to fractionate SRP, and the in vitro antioxidant activity of different fractions was determined; the fraction with the optimal activity was selected for subsequent liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. After predicting potential active peptide sequences through virtual screening, molecular docking technology was applied to perform simulation analysis on the screened peptides, thereby identifying potential antioxidant peptides, whose in vitro activity was further verified using artificially synthesized peptides. The results demonstrated that the optimal process parameters for SRP preparation were as follows: inoculum size of 9%, fermentation temperature of 41 °C, and fermentation duration of 35 h. Under these conditions, the actual yield of SRP reached 24.98%, with a DPPH radical scavenging rate of 79.1%. In terms of amino acid composition of post-fermentation SRP, the content of hydrophobic amino acids increased significantly from 71.295 mg/g to 156.117 mg/g. Moreover, most of the post-fermentation products were small-molecule oligopeptides composed of 4~6 amino acid residues. Ultrafiltration results indicated that the fraction with molecular weight (MW)<3 kDa exhibited the superior in vitro antioxidant activity. At a concentration of 5 mg/mL, its antioxidant activity was characterized by a DPPH radical scavenging rate of 90.63%, an ABTS⁺ radical scavenging rate of 73.17%, a total reducing capacity of 0.806, and a Fe²⁺ chelation rate of 77.83%. Four antioxidant peptide sequences (FRAFDAEL, FDGF, DLFR, and FLVR) were obtained via virtual screening. These peptides could exert antioxidant effects through binding via hydrogen bonds and hydrophobic interactions. The determination of in vitro antioxidant activity of artificially synthesized peptides confirmed that all of them possessed high antioxidant activity. This study provides a theoretical basis for the development and application of SRP-based antioxidant peptide products.