Optimization of fermentation process of high-yield sterol Candida tropicalis and preparation of sterol-rich modified milk
In this study,using defatted milk powder and walnut oil as main raw materials,the freeze-dried sterol powder was prepared with high-yield sterol Candida tropicalis 1253,Lactobacillus bulgaricus and Streptococcus thermophilus as fermentation strains.On this basis,the sterol-rich modified milk was prepared.Using sterol yield as evaluation index,the fermentation process of strain 1253 was optimized by single factor tests and response surface tests.The quality and nutrition of sterol-rich modified milk was evaluated comprehensively,and the key differential metabolites and metabolic pathways were analyzed.The results showed that the optimum fermentation technology was culture time 97 h,temperature 30 ℃,inoculum 9.5%,walnut oil addition 4%.Under the optimized conditions,the sterol yield was 0.90 mg/g.The sensory score of sterol-enriched modified milk was(86.44±2.06)and the sterol content was(22.7±0.6)mg/g.Key differential metabolites such as pyridoxal,cholesterol,gamma-aminobutyric acid(GABA),acteoside and citric acid formed the characteristic flavors through enrichment of vitamin B6 metabolism,pentose phosphate pathway,ethoxylate and dicarboxy-late metabolism,fructose and mannose metabolism,and citric acid cycle.