In this study, a rapid and quantitative method for the detection of viable bacterial counts of Streptococcus thermophilus and Lactobacillus bulgaricus in fermented milk was established using propidium monoazide (PMA) combined with quantitative loop-mediated isothermal amplification (PMA-qLAMP). The PMA treatment conditions for S. thermophilus and L. bulgaricus were optimized. A linear relationship was fitted between the logarithm of bacterial concentration and cycle threshold (Ct) value. The limit of quantification for S. thermophilus and L. bulgaricus was 7.2 × 103 and 5.6 × 104 CFU/g, respectively. The PMA-qLAMP method was applied to measure viable bacterial counts in commercial fermented milk, demonstrating good sensitivity and practicality.

In order to prepare lyophilized cells of Bifidobacterium bifidum TMC3115 with high viability, the impact of the initial pH of the medium, different carbon and nitrogen sources, and inoculum quantity on the viable cell count was studied by the one-factor-at-a-time method. Subsequently, an orthogonal array design was applied to optimize combinations of carbon and nitrogen sources based on the pH of the medium at 16 h of culture, cell density (expressed as optical density) and viable cell count. The efficacy of 18 cryoprotectants on the probiotic strain was investigated, and the optimization of cryoprotectant blends was carried out using an orthogonal array design. The results showed that when the initial medium pH was 7.2 and the inoculum amount was 4%, the viable cell count reached the highest. The optimized medium was composed of glucose 25 g/L, tryptone 20 g/L, yeast peptone 10 g/L, yeast extract FM902 15 g/L, diammonium citrate 2 g/L, anhydrous sodium acetate 5 g/L, dipotassium phosphate 2 g/L, Tween-80 1 g/L, magnesium sulfate 0.58 g/L, manganese sulfate 0.25 g/L, and L-cysteine hydrochloride 0.5 g/L. The optimal cryoprotectant was composed of skim milk 12%, trehalose 12%, glycerol 1.2%, sodium glutamate 0.6%, and L-cysteine hydrochloride 0.15%. The viable cell count of the freeze-dried culture produced under the optimized conditions reached 4.26 × 1011 CFU/g.

Fermented milks were prepared using raw milk with different fat contents, and their flavor was evaluated. The pH trend during fermentation indicated that the change in milk fat content had no effect on the acid production of lactic acid bacteria. Rheological and texture measurements showed that with the increase in milk fat content, the elastic modulus and the viscous modulus decreased, hardness and cohesiveness did not obviously change, but gumminess significantly increased (P < 0.05). By gas chromatography-mass spectrometry (GC-MS), a total of 34 flavor substances were detected from 5 groups of fermented milk samples, including 7 hydrophilic ones and 27 lipophilic ones. Change in milk fat content greatly affected the content of flavor substanc es. Principal component analysis and correlation analysis showed that change in milk fat content caused significant differences in flavor between fermented milk samples, and the trend of flavor contents was related to their hydrophobicity. With the increase in milk fat content, the content of milk fat degradation products such as 2-nonanone and hexanal but not γ-butyrolactone increased first and then decreased. Among other substances, the content of hydrophilic flavor compounds increased first and then decreased, and the content of lipophilic compounds decreased continuously.

A probiotic lactic acid bacterium, named LC577, was isolated from Tibetan kefir. This bacterial strain was identified as Lactococcuslactis casei based on its morphologic properties, 16S rRNA sequence analysis and physiological and biochemical characteristics. The strain had a strong ability to produce acid, and produced a cheese-like aroma after fermentation in skim milk. In addition, it showed tolerance to acid and bile. After 4 h culture in a simulated gastric fluid, the viable count increased slightly, but decreased to 6.15 × 105 CFU/mL after exposed to 3 g/L oxgall for 4 h.

Beta-lactoglobulin (β-LG) is one of the most important allergens in whey protein. How to reduce the antigenicity of β-LG is a problem that needs to be solved. In this paper, alkaline proteinase, trypsin or their combination was used to hydrolyze whey protein, and samples were taken at different hydrolysis times. The degree of hydrolysis and molecular mass distribution of the hydrolysate with the lowest antigenicity of β-LG were analyzed, and its bitter taste was compared with that of two commercial hydrolyzed whey protein products. Overall, hydrolysis of bovine whey protein with a mixture of alkaline protease and trypsin (1:1, m/m) produced products with low bitterness and antigenicity (0.798 μg/mL). The process parameters were as follows: substrate concentration 15 g/100 mL, enzyme to substrate ratio 5 000 U/g (50% alkaline protease plus 50% trypsin), initial pH 8.0, and hydrolysis for 2.5 h at 48 ℃.

The purpose of this investigation was to study the influence of adjuvant starter cultures on the quality of fermented milk. Seven strains of common lactic acid bacteria, including Lactococcus lactis subsp. cremoris (Lcr), Lactococcus lactis subsp. lactis (Ll), Lactobacillus casei (Lca), Lactobacillus fermentum (Lf), Lactobacillus rhamnosus (Lr), and two Lactobacillus plantarum strains (Lp1 and Lp2), were used separately as adjuvants to a commercial starter culture for fermented milk. The results showed that addition of adjuvant starter cultures could shorten the fermentation time and affect the pH value of fermented milk during storage. Moreover, Lcr and Ll could cause significant changes in the oxidationreduction potential during fermentation. Rheological measurements indicated that these strains could increase the viscosity, and reduce the elasticity and fluidity of fermented milk. The texture analysis showed that all the strains could increase the water-holding capacity, and Lr, Lf and Lp1 could enhance the cohesiveness and adhesiveness of fermented milk. Gas chromatography-mass spectrometry (GC-MS) analysis and principal component analysis showed that Lr, Lp1, Lp2 had little effect on the flavor of fermented milk, while Lca could promote the formation of heptanol, benzaldehyde and 2-tridecanone, and Lf, Ll and Lcr could increase the content of flavor substances such as short-chain and medium-chain fatty acids in fermented milk.

Driven by the development of modern statistics, physiology and human bionics, sensory evaluation of dairy products nowadays has been increasingly mature and considered highly significant. This article reviews the definition and procedure for sensory evaluation of dairy products as well as the application of sensory evaluation for dairy products. Moreover, further prospects are discussed. The aim of this review is to provide a theoretical basis for sensory evaluation of dairy products.

Because of its gelling, thickening and stabilizing properties, marine polysaccharide can be used as stabilizer for stirred yogurt. In this study, the effects of carrageenan, sodium alginate, instant and ordinary agar on properties of stirred yoghurt were studied. The indexes observed were viscosity, acidity, fermentation state and flavor. In comparison, instant agar could improve the viscosity of yogurt, increase shear resistance, improve mouthfeel and enhance flavor, and decrease whey syneresis. The product with instant agar demonstrated smooth mouthfeel, a suitable viscosity, and extended shelf life. The stirred yogurt had the best taste when instant agar was added at 0.15%.

In order to obtain quality preference of caramel flavour, fruity, fermentation flavor, sweetness, acidity, astriction, combination weighting approach was employed by fuzzy mathematics comprehensive sensory evaluation expermienting 5 popular sterilization lactic acid fungus drink in market. Fuzzy relation curve was obtained finnally. Results showed that the overall sensory quality of 5 sterilization lactic acid fungus drink order was sample 5 > sample 2 > sample 4 = sample 1 > sample 3, which was slightly different from the results of simple ranking method: sample 2 > sample 4 = sample 1 > sample 5 > sample 3. The experiment results indicated that the fuzzy mathematics comprehensive sensory evaluation method was more scientific, reasonable and objective than simple ranking method.