The Research On The Fermentation Of Candida Utilis And Functional Properties

Though the YPD medium, the growth curves of Candida utilis were measured, drawn 12 hours was the optimal time for the growth of this yeast. Then on the production of Candida Yeast conditions of single-factor screening, including culture temperature, shaker speed, carbon-nitrogen ratio, there were the highest cell density in the temperature 30 Degrees Celsius, speed 180r/min, and carbon and nitrogen ratio (glucose and peptone mass ratio) for 3:1. Adopting L9(34) orthogonal experimental design, the various factors on yeast growth were determined. There were the highest cell density in optimum conditions for incubation time 13h, temperature 30 Degrees Celsius, speed 160r/min, carbon and nitrogen ratio of 3:1. All factors on yeast growth were no statistically significant effect (P> 0.05).By Candida utilis ultraviolet mutagenesis, the high-yield protein content of strains was screened out. The protein content of the mutagenic strains was 31.4% in the 15W UV (30cm), the irradiation 120S, mortality rate was 89%, compared with 22.9% of pre-mutation increased 37.12%. The property of this strain was stable (passed 10 times and made the protein measurement). The fermentation condition was optimized after mutation, including carbon and nitrogen sources, incubation temperature and dissolved oxygen. There were a higher level in protein content and bacterial biomass and protein content of 37% in the glucose as carbon source, a mixture of ammonium sulfate and yeast extract as nitrogen source , culture temperature was 32 Degrees Celsius, and speed of 160r/min. Than before to 31.4% increased 17.8%. With mutation and optimization of fermentation , the protein content increased 61.6% than the original strain of 22.9%.Comparing the functional between the Candida utilis powder (yeast protein powder) and the soy protein powder, there was showed that the Candida utilis powder as a single-cell protein additives was feasibility, of which a variety of protein-specific functionality. Through the experiments, the properties of Candida utilis powder in protein were more obvious, especially in the emulsion was superior in terms of soy protein. The foaming rate of yeast protein powder at a low level to the protein powder concentration was proportional to the slow upward trend. Yeast protein powder foam stability and soybean protein powder foam stability was essential in a level. Protein powder concentration of 5% of foam stability was best. NaCl concentration on the yeast protein and soy protein foaming rate trend was similar. In the NaCl concentration of 0.25mol / L, the bubble rate to a higher value. There was a higher value when yeast protein emulsion stability in the NaCl concentration of 0.2mol / L, but in NaCl concentration of 0.2mol / L below showed no regularity. As the NaCl concentration increased, yeast protein emulsion stability gradually increased. Overall, the yeast protein emulsion stability was higher than soy protein emulsion stability.By 0.2%, 0.4%, 0.6%, 0.8%, 1.0% Candida utilis powder added to the emulsion-type sausages, the feasibility of the powder was studied as a protein additive. To determining the sausage texture and sensory evaluation, it was found that adding the yeast protein in emulsion-type sausages overall sensory score was slightly lower than without yeast protein emulsified sausages, but was acceptable. Determination of texture properties showed that various properties of sausage did not have a huge impact to the addition of yeast proteins. Under addition of different yeast proteins, there were the hardness and cohesiveness of small changes in the texture properties of emulsion-type sausages, indicating a small amount of yeast protein had little effect on these two properties. And plastic viscosity, adhesion, at first the trend of high to low, for flexibility, variation was not obvious; adhesion showed an increasing tendency. During storage emulsion-type sausage texture index had changed significantly. 0.6% of the added volume in terms of texture properties and sensory than the other added content.