Groundnut Milk Fermentation for Yogurt Production: Physicochemical and Microbial Changes

Abstract

The fermentation of groundnut milk for yogurt production was studied. Groundnut milk was prepared from blended
groundnut seeds. Four types of yogurts: GMYP, GMY1, GMY5 and GMY10 were prepared from groundnut milk by fermentation
with different levels of sucrose; 0, 1, 5 and 10%. The groundnut milk and yogurts were analysed microbiologically and physicochemically
using standard procedures. Freshly processed groundnut milk had a total plate count of 4.8×102 cfu/ml and low mould
(2.8×101cfu/ml) count. No yeasts and coliforms were isolated. Microbial isolates in the groundnut milk include: Bacillus subtilis,
Staphylococcus aureus, Pseudomonas sp, Serratia marcescens, Aspergillus niger and Aspergillus flavus. Physicochemical analysis of
groundnut milk revealed the following: moisture (92.40±0.85 %), protein (2.75±0.02%), fat (3.18±0.05 %), ash (0.51±0.00 %) and
carbohydrate (1.16±0.01 %). The total dissolved solids, titratable acidity and pH were 7.62±0.56 %, 0.15±0.00 % and 6.61±0.01
respectively. The physicochemical properties of fermented groundnut milk yogurts showed the percentage moisture, protein, lipid, ash
and carbohydrate contents were in the range 92.80±0.61-94.81±0.67, 1.87±0.05-2.37±0.12, 1.25±0.05-1.67±0.02, 0.50±0.00-
1.20±0.00 and 0.65±0.02-2.88±0.03 in that order. Yogurts fortified with 5 and 10% sucrose had the lowest pH of 4.30±0.00 and
4.35±0.00 respectively. Acid formation was considerably higher for the fortified yogurt. The final viable cell counts in the yogurts
fortified with 5 and 10 % sucrose (GMY5 and GMY10) were 8.73Log10cfu/ml and 8.85Log10cfu/ml respectively. These high counts
of bacteria with acid production are considered acceptable for a typical yogurt. Production of groundnut milk yogurt is possible with
supplementation with sucrose.