The effect of bacteriocins produced by Lactococcus lactis subsp. Lactis ATCC 11454 (T1); Lactobacillus acidophilus JCM 1229 (T2); Lactococcus lactis subsp. lactis ATCC 11454 & Lactobacillus acidophilus JCM 1229 (T3) and bacteriocin extracts from Lactococcus lactis subsp. lactis isolate (T4); Lactobacillus acidophilus isolate (T5); Lactococcus lactis subsp. lactis & Lactobacillus acidophilus isolates (T6) as a natural preservative in yoghurt compared with control yoghurt (C1) and yoghurt with nisin (C2) were evaluated. Use of nisin and bacteriocins produced or extracted with a level of ~100 AU/ml. Yoghurt samples were assessed for coagulation time, chemical analysis, rheological properties, microbiological quality, bacteriocin activity, sensory evaluation and shelf-life during storage for up to 28 days at ~ 5°C. Yoghurt treated with nisin or bacteriocins produced or extracted by some LAB increased coagulation time compared with control yoghurt. Existence of bacteriocins retarded growth of lactic acid bacteria, thereby delaying acid production. Progressive increases in acid production during storage were observed in control yoghurt compared with bacteriocins-treated yoghurt. The rheological properties, sensory evaluation and shelf-life of yoghurt were improved, when nisin and bacteriocins were used. The quality and shelf-life of yoghurt containing extracted bacteriocins or nisin were still acceptable after 28 days of storage (T4, C2, T6 and T5 respectively) followed, after 21 days with yoghurt containing bacteriocin producing bacteria (T1, T3 and T2 consequently) compared to 14 days for control yoghurt. It was concluded that the addition of bacteriocins extracted or nisin (~100 AU/ml) to milk could be produce yoghurt with good organoleptic properties and prolonged the shelf-life. |
