Effects of Different Lactic Acid Bacteria on Fermentation Characteristics and Texture of Set-style Yogurt Fortified with Lychee Juice
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Abstract:
Pure milk and lychee juice were used as the main raw materials, with Lactobacillus casei, Lactobacillus bulgaricus and Streptococcus thermophilus as fermentation strains. The effects of different combinations of three lactic acid bacteria on the fermentation characteristics and texture of set-style yogurt fortified with lychee juice were investigated. The results showed that L. casei showed relatively high ability to produce exopolysaccharide, with the exopolysaccharide content reaching 22.50 g/L when used alone (compared to 5.73 g/L and 0.29 g/L for the fermentation using S. thermophilus or L. bulgaricus alone). After fermentation with different combinations of the three bacteria, the apparent viscosity and water-holding capacity of the yoghurts were positively correlated (R2 = 0.98) with exopolysaccharide content. The L. casei showed a weak acid-producing ability, and the pH after fermentation with the strain alone was higher causing lower hardness, compared with those for the fermentation with its combinations of S. thermophilus or L. bulgaricus. However, the hardness and number of viable lactic acid bacteria were significantly (p < 0.05) higher for the yoghurt fermented by L. casei combined with S. thermophilus or L. bulgaricus, compared with those fermented with Lactobacillus casei alone. Therefore, when the fermentation is performed using the combination of L. casei with S. thermophilus and L. bulgaricus, the advantages of the three strains can be fully utilized, and the total number of colonies, exopolysaccharide content and texture can reach a higher quality level.
