摘要 : Yoghurt is increasingly being used as a carrier of probiotic bacteria for their potential health benefits. To meet with a recommended level of >=10⁶ viable cells/g of a product, assessment of viability of probiotic bact... 展开 Yoghurt is increasingly being used as a carrier of probiotic bacteria for their potential health benefits. To meet with a recommended level of >=10⁶ viable cells/g of a product, assessment of viability of probiotic bacteria in market preparations is crucial. This requires a working method for selective enumeration of these probiotic bacteria and lactic acid bacteria in yoghurt such as <i>Streptococcus thermophilus</i>, <i>Lactobacillus delbrueckii</i> subsp. <i>bulgaricus</i>, <i>Lb. acidophilus</i>, <i>Lb. casei</i> and <i>Bifidobacterium</i>. This chapter presents an overview of media that could be used for differential and selective enumerations of yoghurt bacteria. De Man Rogosa Sharpe agar containing fructose (MRSF), MRS agar pH 5.2 (MRS 5.2), reinforced clostridial prussian blue agar at pH 5.0 (RCPB 5.0) or reinforced clostridial agar at pH 5.3 (RCA 5.3) are suitable for enumeration of<i> Lb. delbrueckii</i> subsp. <i>bulgaricus</i> when the incubation is carried out at 45 degrees C for 72 h. <i>S. thermophilus</i> (ST) agar and M17 are recommended for selective enumeration of <i>S</i>. <i>thermophilus</i>. Selective enumeration of <i>Lb. acidophilus</i> in mixed culture could be made in Rogosa agar added with 5-bromo-4-chloro-3-indolyl- beta-d-glucopyranoside (X-Glu) or MRS containing maltose (MRSM) and incubation in a 20% CO₂ atmosphere. <i>Lb. casei</i> could be selectively enumerated on specially formulated <i>Lb. casei</i> (LC) agar from products containing yoghurt starter bacteria (<i>S. thermophilus</i> and<i> Lb. delbrueckii</i> subsp. <i>bulgaricus</i>), <i>Lb</i>. <i>acidophilus</i>, <i>Bifidobacterium</i> spp. and <i>Lb. casei</i>. <i>Bifidobacterium</i> could be enumerated on MRS agar supplemented with nalidixic acid, paromomycin, neomycin sulphate and lithium chloride (MRS-NPNL) under anaerobic incubation at 37 degrees C for 72 h. All rights reserved, Elsevier. 收起