| In this thesis,the lactic acid bacteria isolated from Hurood was used as the research object.Firstly,the lactic acid bacteria with strong acid-producing ability,good flavor and short fermentation time were screened out.The fermentation acidity,end-point time and texture characteristics of the strains were determined to determine the ratio and combination of strains used in the Hurood auxiliary starter.Then,the optimal production process of Hurood was determined by single factor and orthogonal test of the amount of auxiliary starter strain,fermentation temperature and whey discharge temperature.In addition,the physical and chemical indicators,amino acid,fatty acid content and sensory characteristics of the finished product were detected and analyzed,and the effect of auxiliary starter on the quality of Hurood was discussed.Finally,the quality characteristics of the commercially available Hurood and the product produced in this experiment were compared and analyzed,and the influence of storage time on the quality of Hurood was analyzed.The results show:(1)Perform primary screening and re-screening on 9 strains of lactic acid bacteria isolated from Hurood,and obtain 4 strains of lactic acid bacteria with strong acid-producing ability,good flavor and short fermentation time.It is determined that the 4strains of lactic acid bacteria are suitable for production of Hurood.The 16 S rDNA sequence analysis identified the strains D655,686,NDF9-3 and MN1-7 as Lactococcus kimchii,Lactobacillus plantarum,Pediococcus acidilactici and Enterococcus faecium.(2)The results of 4 strains growth characteristics test showed that the optimal culture time of MN1-7 and NDF9-3 was 14 h,and the cultivation time of D655 and 686 was 16 h.The 4 strains have the strongest activity in the temperature range of 20-30℃,and they all have certain characteristics of acid resistance and bile salt resistance.(3)When 4 strains of lactic acid bacteria were mixed and fermented at 1:1 to produce Hurood,the results of acidity,fermentation end time and texture determination showed that the two combinations of D655:686 and D655: NDF9-3 performed the best.The two optimal combinations of 3 strains were compounded and fermented,and the best combination of test results was D655:686: NDF9-3=5:2:3.The combination was used as an auxiliary starter,and the process was optimized with the product elasticity,acidity and sensory score as indicators.The test results showed that the optimal auxiliary starter dosage was 3%,the fermentation temperature was 25℃,and the whey discharge temperature was 65℃,the elasticity of the Hurood is 0.92±0.05(g),the acidity is 70±1.2(°T),the sensory score is 83±0.2(points),the overall quality is the best.(4)The test results of Hurood quality characteristics showed that the moisture content of the experimental group were lower than the control group.There was no significant difference in ash content.The total amount of free amino acids in the Hurood of the test group was 27.854 mg/100 g,which was 0.4 mg/100 g higher than the control group.The experimental group has a better flavor,with a strong milk flavor and the characteristics of traditional dairy products.(5)During the storage period of Hurood at 4℃,the moisture content of Hurood was significantly reduced,the ash content was significantly increased,and there was no significant change in fat and protein.The color of the product deteriorated significantly,and a small amount of miscellaneous bacteria appeared after storage for 21 days. |
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