EFFECTS OF DIFFERENT PRESERVATIVES ON THE MICROBIAL, PROXIMATE AND SENSORY COMPOSITION OF TIGERNUT MILK

Abstract

The microbial, proximate, mineral and sensory properties of fresh tigernut milk and preserved tigernut milk were assessed in this study. The milk was produced from tigernut tubers using standard methods. The tigernut milk were preserved using chemical (benzoic acid and sodium metabisulphite) and natural (ginger and Pleurotus ostreatus extracts) preservatives and stored for a period of 5 days under ambient and refrigerated temperatures. The bacterial isolates from the preserved tigernut milk were identified as Staphylococcus aureus, Lactobacillus plantarum, Bacillus subtilis, Lactobacillus vini, Bacillus cereus, Bacillus brevis, Staphylococcus xylosus, Lactobacillus composti and Bacillus pumilus. The tigernut milk sample had varying pH values at both room and refrigerated temperature, tigernut milk without preservative at refrigerated temperature had the highest pH value of 7.02 on day 1 while tigernut milk preserved with Pleurotus ostreatus extract at room temperature had the least pH of 3.12 on day 5. There was a significant increase in the mineral composition of the preserved milk at day 5 compared to day 1 except for tigernut milk preserved with Pleurotus ostreatus extract which was higher on day 1. The result obtained from proximate analysis shows decrease in the moisture, ash, fat, protein, fiber and carbohydrate on day 5 compared to day 1 for both storage conditions. The sensory scores on day 1 shows that the preserved tigernut milk had an overall acceptability rate of 7.25 for both benzoic acid and sodium metabisulphite while on day 5 the acceptability rate for the tigernut milk preserved with natural preservatives was very low with values of 1.75 for tigernut milk preserved with Pleurotus ostreatus extract and 2.00 for tigernut milk preserved with ginger extract on a 9-point hedonic scale. Data from this study revealed that tigernut milk can be preserved with chemical preservatives to extend its shelf life beyond 24hrs and also natural extracts can be used to improve the sensory properties but could not serve as effective preservative.