Microbiological and Nutritional Assessment of Starter-Developed Fermented Tigernut Milk

Abstract

Fermented tigernut milk (FTM) was prepared from three different varieties (fresh yellow, big and small dry brown) of tigernut ( Cyperus esculenta ) obtained from Bodija market, Ibadan, Oyo state. Fifty two microbial isolates were obtained from FTM at different fermentation times, 32 of which were on MRS agar, 12 on nutrient agar and 8 on malt extract agar. Lactic acid bacteria were identified as Lactobacillus plantarum (LP), Lactococcus lactis (LC), Lactobacillus brevis , Lactococcus cremoris , Lactobacillus bulgaricus and Lactococcus thermophilus (LT). The non-LAB identified includes E. coli , Bacillus species and Proteus species while the yeasts include Saccharomyces cerevisiae and Candida kefyr . Lactic acid bacteria were found to predominate the total microflora of the FTM with their count ranging between 2.0 × 10 4 cfu/ml to 2.0 × 10 8 cfu/ml. Microbiological examination revealed that the FTM was safe for consumption as non-LAB counts were below the limit of acceptance which is 2.0 × 10 5 cfu/ml for dairy milk by Codex Alimentarius Commission. The quantity of lactic acid produced by the LAB isolates ranged between 0.86 g/l - 2.86 g/l while that of hydrogen peroxide ranged between 0.16 g/l - 0.51 g/l. Starter cultures were selected based on predominance of isolate, physiological characteristics, quantity of lactic acid and hydrogen peroxide production. The tiger nut varieties were fermented with the following starter combinations LP, LP/LC, LP/LC/LT, LP/LT while the fifth was spontaneously fermented. The nutritional, chemical and sensory properties of the starter fermented tiger nut milk were evaluated. The highest protein content (24.80%) was obtained in FTM with mixed cultures of LP/LC/LT while the least (3.00%) was obtained in spontaneously fermented milk. There was a significant difference in the FTM varieties. The highest fat content (9.40%) was obtained in spontaneously fermented tiger nut milk while the least (3.40%) was found in FTM with mixed cultures of LP/LC/LT. Fermentation decreased the pH and increased the lactic acid of the starter developed FTM, while sensory evaluation test showed that the FTM with mixed cultures of LP/LC/LT was highly acceptable. In conclusion, an excellent and acceptable FTM can be produced using treatments which comprise of pasteurization at 90° for 15 minutes, fermentation at 45℃ for 18 hours using mixed cultures of Lactobacillus plantarum , Lactococcus lactis and Lactococcus thermophilus .