Abstract:To screen a strain of GABA-producing lactic acid bacteria suitable for Aronia melanocarpa juice fermentation and optimize the fermentation process, this study employed response surface methodology (RSM) coupled with an artificial neural network-genetic algorithm (ANN-GA) model and evaluated the effect of fermentation on flavor. Six GABA-producing strains were initially screened using thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). The optimal strain for Aronia melanocarpa juice fermentation was determined through re-screening in the juice matrix combined with physiological characterization. Subsequently, the coupled RSM-ANN-GA model was used to optimize the fermentation process for GABA enrichment, and the impact of fermentation on flavor was assessed using sensory evaluation and electronic tongue analysis. Results showed that Levilactobacillus brevis Lj16 was identified as the most suitable strain, achieving a GABA yield of 2.07 mg/mL in Aronia melanocarpa juice, significantly higher than other strains (P< 0.05). Physiological characterization revealed that Lj16 exhibited a survival rate of 65.79% after 4 h of exposure to pH 2.5, a high glutamate decarboxylase (GAD) activity of 2.02±0.01 U/mL, and mild acid production (final pH 5.0), which favors sustained GAD activity. Using this strain, the optimal fermentation conditions determined by the coupled RSM-ANN-GA model were: L-monosodium glutamate 2.30%, yeast extract 2.40%, fermentation temperature 36.5 °C, and fermentation time 120 h. Under these conditions, the GABA yield reached 8.77±0.16 mg/mL. Sensory evaluation and electronic tongue analysis demonstrated that the fermented juice exhibited significantly reduced astringency and sourness, along with markedly improved flavor harmony. This study successfully screened a lactic acid bacterium suitable for GABA enrichment in Aronia melanocarpa juice fermentation. The coupled RSM-ANN-GA model effectively optimized the fermentation process, enhancing GABA accumulation while improving product flavor, providing both a valuable microbial resource and a process foundation for developing high-GABA functional fermented beverages.

Abstract:The decline in estrogen levels resulting from ovarian functional deterioration during perimenopause represents a critical contributing factor to osteoporosis, underscoring the significance of exploring safe dietary intervention strategies. To investigate the effects and mechanisms of concentrated sour cherry juice on bone metabolism during this transitional period, a naturally aging perimenopausal mouse model was employed. Mice were randomly allocated into four groups: control group, sour cherry juice group, positive drug control group, and phytoestrogen positive control group. Following 28 days of continuous intragastric administration, serum levels of estradiol, luteinizing hormone, follicle-stimulating hormone, and bone turnover markers were measured. Microstructural parameters of the distal femur were analyzed by micro-computed tomography, and the mRNA expression of estrogen receptors and key enzymes in the estrogen synthesis pathway in ovarian and uterine tissues was detected by real-time quantitative PCR. The results demonstrated that, compared with the control group, the sour cherry juice group exhibited elevated serum estradiol levels, decreased luteinizing hormone and follicle-stimulating hormone levels, upregulated bone formation markers including osteocalcin, and downregulated bone resorption markers such as tartrate-resistant acid phosphatase 5b. Micro-CT analysis revealed significant improvements in bone mineral density, bone volume fraction, trabecular number, and trabecular thickness, indicating ameliorated bone microarchitecture. Mechanistic studies further revealed that tart cherry juice upregulated the mRNA expression of estrogen receptor α, estrogen receptor β, and key synthetic enzymes 3β-hydroxysteroid dehydrogenase and 17β-hydroxysteroid dehydrogenase in the ovary, while enhancing estrogen receptor α expression in the uterus.Finally, by testing the contents of isoflavones, organic acids, sugars, mineral elements, and free amino acids in concentrated sour cherry juice, a preliminary mechanism was speculated. These findings indicate that tart cherry juice alleviates perimenopausal estrogen deficiency by enhancing local estrogen synthetic capacity in the ovary, thereby bidirectionally regulating bone metabolic balance, attenuating bone loss, and restoring bone microarchitecture, suggesting its potential for development as a functional food for skeletal health management during perimenopause.

Abstract:Histamine is a class of potentially harmful biogenic amines produced during the storage and processing of meat products. Its content is a key indicator for evaluating food freshness and safety. In order to meet the needs of rapid and sensitive detection of histamine in meat products, an electrochemical biosensor based on diamine oxidase (DAO) and graphite carbon nitride / titanium dioxide (g-C3N4/TiO2) heterojunction was constructed. The g-C3N4/TiO2 heterojunction material was prepared by one-step calcination method, and the structure was characterized by scanning electron microscopy, transmission electron microscopy and Fourier transform infrared spectroscopy. It was confirmed that TiO2 nanoparticles were uniformly loaded on the surface of g-C3N4 nanosheets, and a stable heterojunction interface was formed between them. Density functional theory calculations further confirmed that the heterojunction interface can effectively enhance histamine adsorption and promote interfacial charge transfer. Based on the theoretical calculation, the analysis of the heterojunction enhanced histamine absorption mechanism shows that the sensor enhances the enzyme immobilization efficiency and constructs an efficient electron transport channel, thereby realizing the effective conversion and amplification of the biological recognition signal to the electrochemical signal.The results showed that the sensor had a good linear relationship in the range of 0.05-9.00 mmol/L, the detection limit was 0.226 μmol/L(S/N=3), and the response interference deviation was less than 8% in the anti-interference experiment. In the actual meat sample detection, the relative standard deviation was less than 5%, showing good accuracy and reproducibility. The DAO/g-C3N4/TiO2 biosensor constructed in this study can be used for rapid screening and quantitative detection of histamine in meat products, aiming to provide a stable and reliable technical means for the accurate detection of histamine in food.

Abstract:To elucidate the microbial community structure of Ningxia traditional sourdough and develop a composite starter culture for dough fermentation, 12 traditionally fermented sourdough samples were collected from north to south across Ningxia. Metagenomic sequencing was performed on six of these samples to analyze their microbial communities. Subsequently, dominant strains were isolated and purified from all 12 samples, preliminarily identified, and then subjected to molecular identification. Their fermentation properties, including acid production rate, acid tolerance, ethanol production capacity, and dough leavening ability, were evaluated. Finally, selected dominant strains were combined in different formulations, and the dough leavening ability as well as the free amino acid composition of the fermented dough were determined.Results showed that the microbial communities in the six sourdough samples were dominated by lactic acid bacteria (LAB) and yeasts as core microbiota. Bacterial communities exhibited significant compositional differences, with dominant bacteria including Fructilactobacillus sanfranciscensis (24.54%), Pediococcus acidilactici (15.99%), Pediococcus pentosaceus (8.20%), and Leuconostoc mesenteroides (7.69%). Fungal communities were relatively uniform, largely dominated by Saccharomyces cerevisiae (90.99%), except for one sample where Candida zeylanoides (73.73%) prevailed. Through isolation and culture, a total of 26 LAB and 18 yeast strains were obtained from the 12 sourdough samples. Preliminary screening based on acid production capacity identified 10 LAB strains with acid production ≥15 g/L, indicating high acid-producing potential. Screening based on gas production capacity identified 11 yeast strains that filled more than three quarters of a Durham tube within 12 h, demonstrating rapid and efficient gas production. PCR amplification and sequencing of the 21 preliminarily screened strains (11 yeasts, 10 LAB) revealed that the 11 yeast strains belonged to three genera: seven were Saccharomyces cerevisiae, one was Pichia kudriavzevii, one was Clavispora lusitaniae, and two were Saccharomyces boulardii.Among the 10 LAB strains, eight were Pediococcus acidilactici and two were Lactiplantibacillus plantarum. Evaluation of acid production rates led to the selection of two LAB strains for co fermentation experiments. Evaluation of acid tolerance, ethanol production capacity, and dough leavening ability led to the selection of three yeast strains. The selected strains – two LAB (Lactiplantibacillus plantarum M6 1, Pediococcus acidilactici M10 1) and three yeasts (Pichia kudriavzevii Y1 1, Saccharomyces cerevisiae Y6 2, and Saccharomyces boulardii Y10 2) – were used to construct 25 different consortia. Results of the co fermentation experiments showed that the four strain combination (M6 1, M10 1, Y6 2, Y10 2) exhibited the best dough leavening performance and also yielded the highest total free amino acid content in the fermented dough, reaching 1253.24 mg/kg. This consortium demonstrates good application potential in fermented flour based product manufacturing and confirms the synergistic effect of LAB and yeasts as the core functional microbiota in sourdough. This study provides valuable strain resources and a theoretical basis for the development of composite starter cultures for traditional flour based products.

Abstract:Lycopene is a natural carotenoid with strong antioxidant properties, widely used in fields such as food, health products, and medicine. In recent years, the production of lycopene through microbial fermentation based on the isopentenol utilization (IU) pathway has shown great potential. To address the toxicity of IU pathway substrates isoprenol and prenol to the host, the molecular chaperone protein SecB was overexpressed in Escherichia coli (E. coli) BL21 (DE3). A series of E. coli cell factories for lycopene production were constructed through modular engineering strategies, and the fermentation conditions were optimized by single factor experiments. The results showed that overexpression of SecB helped maintain cellular structural integrity, significantly reduced cell specific surface area (area/volume), and significantly enhanced cell membrane integrity and maintained membrane potential, thereby effectively alleviating the inhibition of substrate toxicity on cell growth and metabolism. Among all the constructed cell factories, the recombinant strain LYC3 containing IU pathway module, lycopene synthesis module, and SecB expression module had the highest lycopene yield of 8.99 mg/L, indicating that overexpression of SecB could enhance the synthesis of lycopene by E. coli. The optimized condition for the shake flask fermentation of recombinant strain LYC3 were as follows: LYC medium, 40 mmol/L substrate, simultaneous addition of substrate and inducer, and fermentation for 72 h. Under this optimized condition, the lycopene yield was further increased to 51.90 mg/L. This study laid a theoretical and technical foundation for the efficient synthesis of lycopene based on the IU pathway, and provided a reference for improving the efficiency of biomanufacturing through substrate tolerance engineering.