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Walnut kernels, selected as the raw material, underwent hydrolysis with protein-glutaminase (PG) following pulping. This process laid the foundation for producing set-type walnut yogurt, involving steps such as blending, homogenization, sterilization, and fermentation. The study investigated the impact of protein-glutaminase and five distinct starter cultures labeled I~V on the quality of walnut yogurt. This was evaluated by examining the yogurt's fermentation characteristics, physicochemical indicators, and microstructure. Furthermore, walnut yogurt developed under these optimal conditions was compared to traditional milk yogurt to assess its quality and characteristics. The findings revealed a significant improvement in the fermentation characteristics and textural parameters of yogurt fermented by walnut milk following enzymatic hydrolysis compared to non-enzymatic walnut milk. The optimal conditions were identified as 0.2% enzyme concentration and a 40-minute reaction time, with the pH, acidity, hardness, and consistency of walnut yogurt being 4.3, 55°T, 85.30 g, and 583.96 g·s, respectively. Walnut yogurt developed using starter culture I exhibited the highest acidity level, maintaining minimal fluctuation over a 21-day storage period. In contrast, yogurts prepared with alternative starter cultures demonstrated varying degrees of stratification and sedimentation. The yogurt fermented with culture I showed superior viscoelastic properties, presenting a denser gel network. Conversely, yogurts fermented with cultures IV and V displayed reduced apparent viscosity, lower values of G' (storage modulus), and G'' (loss modulus), along with a looser gel structure. Additionally, walnut yogurt produced with starter culture I maintained bacterial counts exceeding 106 CFU/mL throughout the storage duration. Despite walnut yogurt requiring further refinement in aspects such as consistency, water-holding capacity, and whey release rate compared to milk yogurt, the overall impact of PG was positive, enhancing the gelation quality of walnut yogurt. The yogurt prepared with starter culture I (Lactobacillus bulgaricus and Streptococcus thermophilus) was notably improved, receiving favorable overall assessments.

In order to obtain candidate strains with strong colonization ability and excellent fermentation performance of goji berry juice, 3 strains of lactic acid bacteria were isolated and screened from human intestinal tract. They were identified by morphological, physiological and biochemical, 16S rDNA sequence analysis and phylogenetic tree construction, and their acid resistance, bile salt resistance, artificial gastric fluid, intestinal fluid resistance and fermentation performance were studied. The results showed that all three strains were identified as Pediococcus lactis, numbered NXU_220218, NXU_220219 and NXU_220220, respectively. The growth rate from 2 to 8 h, the ability of NXU 220218 to produce acid was stronger, and the tolerance to acid, bile salt and artificial gastric juice was better than NXU 220219 and NXU 220220. The survival rate of NXU_220218 was 67% at pH2, 65% in bovine bile salt at 0.3% concentration, 72% tolerance to artificial gastric juice, and 95% tolerance to artificial intestinal juice. Finally, the NXU_220218 strain was inoculated and used in the preparation of fermented goji berry juice. It was found that the reducing sugar content and the free radical scavenging rate in the fermented goji berry juice were significantly reduced and increased, respectively, compared with the unfermented goji berry juice, indicating that the NXU_220218 strain had good fermentation performance for goji berry juice and could be used as a candidate strain of lactic acid bacteria for the fermentation of goji berry juice.

In order to promote fungal polysaccharides development and utilization, ten kinds of fungal polysaccharides, including Flammulina velutipes polysaccharide, Pleurotus eryngii polysaccharide, Tremella fuciformis Berk polysaccharide, Auricularia auricularia polysaccharide, Flammulina velutipes polysaccharide, Porcini porcini polysaccharide, Coriolus versciclor polysaccharide, Ganoderma lucidum polysaccharide, Cordyceps polysaccharide and Volvaria volvacea polysaccharide were selected to explore the effects of fungal polysaccharides on the fermentation characteristics of yogurt starter in this study. The results showed as follows: Flammulina velutipes polysaccharide, Pleurotus eryngii polysaccharide, Tremella fuciformis Berk polysaccharide, Auricularia auricularia polysaccharide, Coriolus versciclor polysaccharide, Ganoderma lucidum polysaccharide, Cordyceps polysaccharide had a significant promotion effect on the fermentation characteristics of the starter (P