ABSTRACT

Fruits and vegetable juices are proving to be promising carriers for probiotics. The development of these plant-based probiotic beverages is owed to the issues of lactose intolerance and cholesterol content associated with fermented dairy foods. Thus, tigernut was exploited for the development of a functional beverage. The starter cultures employed for this development of functional tigernut milk beverage were Lactobacillus fermentum CS19 and Lactococcus lactis isolated from “Ogi” and Yoghurt respectively. These starter cultures were characterized. They were subjected to Gram Staining and biochemical tests. Their probiotic potentials were determined. They were screened for their acid tolerance, salt tolerance, milk fermentation capacity and antimicrobial activity. Then molecular characterization of the starter cultures was done by DNA extraction and quantification, 16S rRNA amplification, sequencing and phylogenetic analysis. 1.5 x 10⁸ CFU/ml of each identified isolate were encapsulated in gelatin matrix and used for fermentation of the pasteurized milk extracted from the tigernut. There was a control sample which was left uninoculated. The fermentation of the tigernut milk was carried out at 30^oC for 72 hours. The physicochemical and proximate compositions of the tigernut milk samples were determined before and after fermentation. After 72hours of fermentation, the viability counts of the starter cultures were determined and the fermented tigernut milk samples were stored at different temperatures, 4, 28 and 40^oC for 4 weeks. Samples were taken weekly to determine the changes in the physicochemical and proximate compositions of the fermented tigernut milk samples. Effects of storage temperature and storage time of the fermented tigernut milk beverage on viability of the starter cultures: Lactobacillus fermentum CS19 and Lactococcus lactis were evaluated. The sensory properties of the functional tigernut milk product was also evaluated. There was decrease in pH and increase in TTA of the fermented tigernut milk samples with increase in storage time. There was increase in the moisture and protein contents of the fermented samples while decrease in fat and ash contents were observed. However, no fibre was detected after fermentation. Lactobacillus fermentum CS19 had more viability count with value of 1.7x 10¹⁰ CFU/ml than Lactococcus lactis which had 1.9 X 10⁹ CFU/ml viable cells. There was significant reduction in the lactic acid bacteria counts as storage period increased. At the end of the 4weeks, there was reduction by 1.0 X 10⁵ CFU/ml in all counts between the first and fourth weeks, with exception of the samples stored at 40^oC as they had approximately 1.0 x 10⁶CFU/ml reduction. At storage temperature of 4^oC, the samples fermented by Lactobacillus fermentum CS19 and Lactococcus lactis and had viability counts of 1.3 X 10¹⁰ and 1.3 X 10¹⁰ in the first week of storage and reduced to 1.3 X 10⁵ and 1.7 X 10⁵ respectively, in the fourth week. While at storage temperature of 40^oC, the samples fermented by Lactobacillus fermentum CS19 and Lactococcus lactis and had viability counts of 1.7 X 10⁹ and 1.3 X 10⁹ CFU/ml in the first week of storage and reduced to 7.0 X 10³ and 6.7 X 10³ CFU/ml. The tigernut milk sample fermented by Lactobacillus fermentum CS19 had the best sensory acceptability. From this study, despite the encapsulation of the starter cultures, the minimum biovalue of 1.0 X 10⁶ CFU/ml required for beverages to be considered functional was not met at the end of the fourth week of storage. More studies to achieve this are therefore recommended.