Production of Sour-milk Using Mono- and Multi-cultures of Lactic Acid Bacteria Isolated from Nunu

Abstract

Production of nunu, a nutritious sour cow milk that serve as refreshing drink to many Nigerians, involve spontaneous fermentation by a diverse group of microbial contaminants resulting in products of varying flavor quality. This study investigated the effect of mono and multi-culture of lactic acid bacteria (LAB) as starter in sour-milk production. Organisms were isolated from nunu samples, characterized and identified using molecular techniques. The organisms were used to ferment fresh cow milk individually, and in various combinations. The sensory properties, pH and proximate composition of the products were compared. Among the three LAB
isolates, Lactobacillus helveticus NBRC15019 had the highest rate of acidification of about 30% pH reduction in 16 hours as against 20% and 15% for L. fermentum CIP102980, and L. helveticus DSM20075 respectively. There was exponential increase in the microbial load (from a minimum of 4.0 x 103 to 6.6 x 1013) within the 24 hours period of fermentation. Consumer ratings favored L. fermentum CIP102980 over the others. Fermentation generally improved the protein content from 3.07% in the raw milk sample up to 3.47% in the sample fermented with a combination of the three LAB and compared favorably with that of the commercially sourced nunu
sample while the sugar content was reduced from 5.63% to as low as 4.1%. Lactobacillus helveticus NBRC15019 has been proved as the most efficient organism in milk acidification. However, combination with the other two LAB strains may help to improve the sensory and nutritional quality of sour-milk.