Assessment of the nutritional quality of lactic acid bacteria fermentation of tiger nut (cyperus esculentus) milk for yoghurt production
This study investigated the technological and bio-preservative properties of lactic acid bacteria (LAB) as starter culture in the fermentation of tiger nut milk for highly nutritive yoghurt production. It also evaluated the shelf life, sensory attributes and nutritional qualities of tiger nut yoghurt produced with LAB strains. These were with a view to obtaining a relatively less expensive yoghurt rich in dietary nutrients. Tiger nuts and Sorghum bicolorsamples were purchased at Sabo market, Ile-Ife, Osun State, Nigeria.S. bicolor grains were steeped in water for ogi production for 5 days to isolate LAB and from yoghurt samples.The LAB were obtained and purified by successive subculturing on MRS agar and subjected to biochemical test. Gram positive and catalase negative isolates wereconfirmed as LAB. Tiger nuts were sorted, washed, milled and sieved to obtain the milk. The LAB strains with desirable properties were selected as potential starter for this study. The tiger nut milk extract was divided into 3 portions for fermentation. One was fermented with Lactobacillus plantarum while the second was fermented with Lactobacillus fermentum and the third fermented spontaneously. Physicochemical properties such as pH, titratable acidity, proximate and anti-nutritional factors were monitored in the raw tiger nut, tiger nut yoghurt using standard procedures. Sensory and organoleptic evaluation of the starter produced yoghurt were assessed by a panel of 50 consumers of yoghurt and the nutritional properties was compared with commercially sold yoghurt by proximate analysis. A total of 47 LAB were isolated from the samples and identified as L. plantarum,L. acidophilus, L.fermentum, L. casei, L. pentosus, L. cellobiosus, L. lactis,and S. thermophilus. The technological properties showed L. plantarumfrom sorghum and L. fermentumfrom yoghurt as the best starter and they showed high exopolysaccharide production and positive bacteriocin production against test isolates (S. aureus ATCC 43300 and E.coli NCIB 86). Diacetyl, lactic acid and hydrogen peroxide production ranged from 0.42 - 0.53 g/L, 11.90 -18.1 g/L and 0.34 - 0.70 g/L respectively. There was a reduction in the anti-nutritional factors in the raw tiger and fermented yoghurt (phytate 65 - 05 mg/100g, protease inhibitor 0.3 - 0.00 mg/100g; tanins 35 - 05 mg/100g). The microbial load of LAB ranged from 3x106- 3x108 cfu/mL during fermentation while the enzymatic activities of the starters varies. The nutritional analysis of the raw and fermented tiger nut yoghurt showed an increase in the protein content 6.6 - 15.2 mg/g; ash content 3.7 - 8.3 mg/g; riboflavin 0.09 - 3.01 mg/g, niacin 3.5 - 6.5 mg/g and thiamine 0.19 - 4.19 mg/g. The organoleptic assessment showed the starter mediated yoghurt had prolonged shelf life when compared with the spontaneous fermented yoghurt. This study concluded that Lactobacillus plantarum and Lactobacillus fermentum could be used asstarter culture to improve the nutritional composition and extend the shelf life of tiger nut yoghurt.