The Use of Lactic Acid Bacteria Starter Culture in the Production of Nunu, a Spontaneously Fermented Milk Product in Ghana

Abstract

Nunu, a spontaneously fermented yoghurt-like product, is produced and consumed in parts of West Africa. A total of 373 predominant lactic acid bacteria (LAB) previously isolated and identified from Nunu product were assessed in vitro for their technological properties (acidification, exopolysaccharides production, lipolysis, proteolysis and antimicrobial activities). Following the determination of technological properties, Lactobacillus fermentum 22-16, Lactobacillus plantarum 8-2, Lactobacillus helveticus 22-7, and Leuconostoc mesenteroides 14-11 were used as single and combined starter cultures for Nunu fermentation. Starter culture fermented Nunu samples were assessed for amino acids profile and rate of acidification and were subsequently evaluated for consumer acceptability. For acidification properties, 82%, 59%, 34%, and 20% of strains belonging to Lactobacillus helveticus, L. plantarum, L. fermentum, and Leu. mesenteriodes, respectively, demonstrated fast acidification properties. High proteolytic activity (>100 to 150 μg/mL) was observed for 50% Leu. mesenteroides, 40% L. fermentum, 41% L. helveticus, 27% L. plantarum, and 10% Ent. faecium species. In starter culture fermented Nunu samples, all amino acids determined were detected in Nunu fermented with single starters of L. plantarum and L. helveticus and combined starter of L. fermntum and L. helveticus. Consumer sensory analysis showed varying degrees of acceptability for Nunu fermented with the different starter cultures.

Figure 1

Acidification properties of predominant LAB species isolated from Nunu: fast, medium, and slow, when a pH of 0.4 U was achieved after 3 h, 6 h, and 24 h, respectively.

Figure 2

Pattern of proteolytic activities of predominant LAB isolated from Nunu. Good => 100–150 μg tyrosine/mL, fair => 50–100 μg tyrosine/mL, and Poor = 0–50 μg tyrosine/mL.

Figure 3

Exopolysaccharides activities of predominant LAB isolated from Nunu. Good => 100–150 μg/mL, fair => 50–100 μg/mL, and poor = 0–50 μg/mL.

Figure 4

pH of fermenting milk with different starter cultures. Spontaneously fermented (Sp), L. fermentum (Lf), L. plantarum (Lp), L. helveticus (Lh), and L. mesenteroides (Lm), L. fermentum + L. plantarum (Lf + Lp), L. fermentum + L. helveticus (Lf + Lh), L. fermentum + L. mesenteroides (Lf + Lm), L. plantarum + L. helveticus (Lp + Lh), L. plantarum + L. mesenteroides (Lp + Lm), L. helveticus+ L. mesenteroides (Lh + Lm).