Development of Fermented Milk for Ambient Temperature Storage

• Main Authors: Waraporn Panpetch, 潘佩琪
• Other Authors: Pao-Chaun Hsieh
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/89731982901445524331

碩士 === 國立屏東科技大學 === 熱帶農業暨國際合作研究所 === 92 === In this study, lactic acid bacteria 365 isolates were obtained from various commercial fermented milk products. Two strains of lactic acid bacteria, which were rods- and coccal-shaped, were selected from the screening media. The coccal-shaped isolate was identified as Streptococcus salivarius ssp. thermophilus D1, while the rods-shaped isolate was belonged to Lactobacillus casei V5. These two strains were Gram-positive and catalase negative bacteria, not produce gas from glucose. S. thermophilus D1 being the only one capable of producing diacetyl, while the L. casei V5 showed a greater ability growth at low pH and high concentration of NaCl. The optimal growth temperature and pH of these 2 lactic acid bacteria were 37 oC and pH 6.5, respectively. Among the carbon sources tested, glucose and trehalose were the best supplements for L. casei V5 growth, while lactose and glucose provided the best result for S. thermophilus D1. The effect of nitrogen sources on LAB was investigated. Results demonstrated that yeast extract was the best supplement for both lactic acid bacteria. The growth of L. casei V5 and S. thermophilus D1 in mixed cultures presented in associative growth with the excess of acidity and cell viable count. Among the various carbon supplementations, glucose was selected to supplement L. casei V5 during growth in skim milk due to its providing in higher acidity and cell numbers. The optimal concentration of glucose supplementation was 1.2% (w/v) which was completely utilized by L. casei V5 after cultured for 48 hours. Protein content of yogurt was modified by addition of 12.5% (w/v) skim milk solids and 2.5% (w/v) whey protein to elevate the final protein content in yogurt higher than 1%, which was required by China National Standard (CNS). Various food additives were added to prolong cell viability in yogurt products during storage. However, fortification of yogurt with calcium lactate was more effective, which provide a significantly higher viability of lactic acid bacteria than 1´106 CFU ml-1 during storage at 50oC and 37oC approximately 6 days and 6 weeks, respectively (P<0.05).