The effect of fermentation with Lactobacillus rhamnosus GG on the product quality of goat milk yogurt using traditional yogurt starter was studied through single-factor experiments and orthogonal experiments. The optimum fermentation condition was evaluated by the titratable acidity of goat milk yogurt, water-retaining capability, sensory score, and texture properties; the fatty acids of the fermented goat milk were determined by a gas chromatograph. Results indicate that high product quality of goat milk yogurt can be obtained and the content of short-chain and medium-chain fatty acids can be decreased significantly when amount of sugar added was 7%, inoculation amount was 3%, the ratio of 3 lactic acid bacteria--Lactobacillus delbrueckii ssp. bulgaricus, Streptococcus thermophilus, and L. rhamnosus GG--was 1:1:3, and fermentation temperature was 42°C.
The changes in packaged fresh-cut grape quality and microbial growth as affected by mild heat treatments and the retention of grape cap stems during 5 degrees C storage were evaluated. Each individual grape was either manually pulled off (stemless) from the stems, or cut (cut stem) to allow for a 1- to 2-mm cap stem remaining on the berry. The samples were sanitized in 100 mg/L chlorine solution for 1 min, followed by a mild heat treatment in a water bath (45 degrees C, 8 min) or an oven (55 degrees C, 5 min). After cooling, the berries were packaged in rigid trays sealed with a gas permeable film and stored at 5 degrees C. Product quality and decay rate were evaluated periodically during storage. The results indicate that in the package headspace for hot water treatment of stemless grapes, partial pressures of O(2) declined significantly (P < 0.05) less and C(2)H(4) increased significantly (P < 0.001) less than for the control and hot air treatment. Stem removal and heat treatment had significant (P < 0.05) effects on the decay rate of grapes during storage. Hot water treatment maintained a significantly lower decay rate than the control and hot air treatment throughout the entire storage. Color and texture were not significantly (P > 0.05) affected by either heat treatment or stem removal. Grapes that retained the cap stems and received hot water treatment had the lowest decay rate and lowest microbial growth with the absence of any negative impact on grape color, texture, and flavor.
An electronic nose based on metal oxide sensors was used to measure goaty flavor in goat milk samples. To study the relationships between electronic nose data, sensory data, and levels of free fatty acids (FFA), multivariate partial least square regression (PLS) was carried out. The electronic nose system evaluation correlated well with sensory evaluation. The coefficients of determination (R(2)) of the PLS models reached 90.0%. The electronic nose, combined with principal component analysis and linear discriminant analysis, can discern among goat milk samples with different goaty flavor intensities. In addition, Fisher discriminant analysis and back-propagation neural network were carried out to evaluate goaty flavor intensity, and the prediction accuracies were 98.2 and 100.0%, respectively. The electronic nose is a potentially useful tool to evaluate goaty flavor intensity in goat milk samples.
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