A study on the manufacture of goat milk yogurt using single and mixed strains of lactic acid starters

• Main Authors: Ju-Yin Shiao, 蕭如吟
• Other Authors: Li-Pyng Yan
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/67831075726769648269

碩士 === 東海大學 === 食品科學系 === 90 === The purpose of this research is to study the manufacture of goat milk yogurt by using single or mixed strains of Lactobacillus bulgaricus(CCRC 14009), Streptococcus thermophilus (CCRC 12257), Lactobacillus acidophilus (CCRC 10695), Lactobacillus casei (CCRC 10697), Bifidobacterium bifidum (CCRC 11844) and Bifidobacterium longum (CCRC 11847) as the starter organisms. The objective of the first part of this research - Experiment 1, was to compare the effect of using single-strain starters and mixed- strain starters on the viable count and characteristics（pH, titratable acidity and viscosity）of the goat milk yogurt during fermentation. The objective of the second part of this research - Experiment 2, was to compare the effect of using single-strain starters and mixed-strain starters on the nutrient contents（lactose, galactose, organic acid, L(+) lactate and folic acid）of the goat milk yogurt before and after fermentation . The objective of the third part of this research - Experiment 3, was to select the proper mixed-strain starters based on changes of viable count, titratable acidity, viscosity and syneresis during refrigerated storage of the yogurt. In Experiment 1, the yogurt inoculated with mixed-strain starters showed higher average viable count (＞1.0×109 CFU/ml or 9.0 Log CFU/ml) than that (＞1.0×108 CFU/ml or 8.0 Log CFU/ml) of the yogurt inoculated with single-strain starters. L. bulgaricus and S. thermophilus+ L. bulgaricus showed highest acid-producing ability, shortest fermentation time (pH=4.5) and highest viscosity among the single-strain starters and mixed-strain starters, respectively. Most mixed-strain starters had higher acid-producing ability and viscosity than single-strain starters. In Experiment 2, the residual lactose content was significantly least in yogurts inoculated with L. bulgaricus, B. longum and S. thermophilus+ L. bulgaricus, which expressed highest increase in galactose content consequently. Mixed-strain starters showed better lactose-hydrolyzing ability than single-strain starters. L. bulgaricus and S. thermophilus+ L. bulgaricus showed highest content of lactate and L(+) lactate among the single-strain starters and mixed-strain starters, respectively. Most mixed-strain starters had higher lactate and L(+) lactate-producing ability than single-strain starters. The acetate content, which may cause off-flavor in yogurt, was effectively reduced when using mixed-strain starters instead of single-strain starters of B. bifidum or B. longum. Folic acid content increased in yogurt inoculated with either single or mixed-strain starters. Among the single-strain starters, B. bifidum caused the highest increase of folic acid. In Experiment 3, viable counts of all yogurt samples inoculated with mixed-strain starters maintained above 5.0×108 CFU/ml (8.7 Log CFU/ml) at the end of 28-day storage. Titratable acidity and syneresis of yogurt increased with increased storage time. Viscosity of yogurt decreased with increased storage time. Among the 7 mixed-strain starters, B. longum+S. thermophilus+ L. acidophilus and B. bifidum+ S. thermophilus+ L. bulgaricus met the viable count and titratable acidity standards of CNS 3085 at the end of 28-day storage. The above-mentioned two mixed-strain starters also showed better ability in lactose hydrolysis, higher production of L(+) lactate, lower production of acetate and a significant increase of folic acid content after fermentation. Concluding from the above results, mixed-strain starters of B. longum +S. thermophilus+ L. acidophilus and B. bifidum+ S. thermophilus+ L. bulgaricus could be selected as the better starters to manufacture more nutritive products.