| The development of sucrose-free,herbal-flavoured fermented milk is of great significance to enrich and develop new fermented dairy products to meet the national aspiration for a better life.In this study,16 strains of lactic acid bacteria with high degradation rate of guanosine were selected,and one strain of Lactiplantibacillus plantarum grx03 with good fermentation characteristics was selected by comparing their characteristics of fermenting cow’s milk and fermenting soybean milk.Finally,the effects of three oligosaccharides and four herbal extracts on the fermentation performance,sensory characteristics and physicochemical properties of the fermented milk during storage were compared to prepare sucrose-free,herbal flavoured fermented milk.The main findings were as follows:(1)The curdling time of 16 strains of lactic acid bacteria fermented cow’s milk and fermented soy milk were compared,and the nine strains with shorter curdling time were selected for subsequent determination of acid production capacity,tolerance to artificial gastrointestinal fluid,and comparison of their water-holding capacity and viable count in fermented cow’s milk and fermented soy milk.The titratable acidity of the best acidproducing strain,Lactobacillus plantarum grx03,was 67°T,pH 4.54.The water-holding capacity of grx03 in fermented cow’s milk and soybean milk was 74.55%and 64.65%,and the viable counts in fermented cow’s milk and fermented soybean milk were 7.28 log CFU/mL and 6.48 log CFU/mL,and the survival rate of artificial gastrointestinal fluid tolerance was 31.93%.31.93%,and Lactiplantibacillus plantarum grx03 was identified as the optimal strain for single-strain fermentation using TOPSIS method.(2)Comparison of the effects of the addition of Streptococcus thermophilus on the characteristics of grx03 fermented buttermilk and fermented soymilk.The acidity of fermented buttermilk was 70°T and 76°T,hardness was 0.51 N and 0.62 N,and adhesion was 2.24 N/mm and 2.63 N/mm after the addition of Streptococcus thermophilus grx02 and Streptococcus thermophilus 937,respectively,indicating that the viscosity characteristics of fermented buttermilk with Streptococcus thermophilus 937 and Lactiplantibacillus plantarum grx03 mixed bacteria were better.The addition of Streptococcus thermophilus grx02 and Streptococcus thermophilus 937 resulted in acidity of 67°T and 71°T,hardness of 0.33 N and 0.35,and adhesion of 1.66 N/mm and 1.90 N/mm,respectively,indicating that Streptococcus thermophilus 937 and grx03 mixed bacteria fermented soymilk had better acid production characteristics.(3)To compare the effects of different ratios of cow’s milk and soybean milk on the texture,apparent viscosity and sensory characteristics of two-protein fermented milk.Comparing the three groups of 7:3,1:1 and 3:7 two-protein fermented milks,when the ratio of cow’s milk to soy milk was 7:3,the fermented milk had 81%water holding capacity,0.38 N hardness and 3.48 N/mm adhesion,and the fermented milk had better texture and sensory quality.(4)Preparation of herbal flavored double protein fermented milk.Firstly,suitable oligosaccharides were selected to be added to grx03 and 937 double-protein fermented milk.The acidity of the double-protein fermented milk was 78°T and 76°T after the addition of oligofructose and inulin,respectively;the apparent viscosity was 168.4 Pa/s and 495.8 Pa/s,respectively;the adhesion was 1.72 N/mm and 2.48 N/mm,respectively;the elasticity was 28.34 mm and 39.39 mm,respectively;although the texture and rheological characteristics of the double-protein fermented milk with the addition of inulin were better than those with the addition of oligofructose,the bean odor was heavier.Although the texture and rheological characteristics of the double-protein fermented milk with inulin were better than those with oligofructose,the bean smell was heavier.The fermented milk with the addition of oligofructose showed suitable sweetness and acidity,and had better flavor compared with oligomers and inulin.After adding herbs 1%chicory,1%kudzu,1%fu ling and 1%gardenia extract to grx03 and 937 double-protein fermented milk,the fermented milk showed bright yellow color with licorice flavor,water-holding capacity of 88.6%and viscosity of 2763 mpa/s.The changes of pH,live bacteria and water-holding capacity of grx03 and 937 double-protein fermented milk after 14 days of storage were measured as follows The physical and chemical properties and sensory changes were as follows:acidity from 85°T to 105°T,viable bacterial count from 8.85 log CFU/mL to 7.83 log CFU/mL,water holding capacity from 88.6%to 77.7%,and sensory score of 81.44 on day 14,which remained relatively stable during 14 days.Therefore,the fermented milk had good sensory flavor during the 14-day storage period. |
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