Storage Stability of Probiotic Soy Yoghurts with Enzyme Hydrolyzed African Breadfruit and Rice Additives

Aims: This study investigated the effect of culture type and storage time on pH, titratable acidity (%Lactic acid), viscosity and syneresis, probiotic viability and sensory properties of probiotic soy yoghurts with enzyme hydrolyzed African bread fruit (HABF) and rice syrup.

Methodology: Three sets of Soy-HABF Yoghurt were formulated by supplementing soymilk with 4% HABF and the addition of enzyme hydrolyzed rice syrup. The formulations were inoculated separately with Bifidiobacterium bifidum and Lactobacillus acidophillus as mono- and co-cultures and fermented at 42 °C for 8 h. Using standard methods, the samples were analyzed after fermentation representing day 1 and on the 5th, 10th, 15th and 20th days of storage at 4⁰ C.

Results: Culture type and the storage time had significant (P≤0.05) effect on physicochemical, probiotic count and sensory properties of the probiotic soy-HABF yoghurt. pH decreased significantly (P ≤ 0.05) with storage time from 4.36 - 4.06, 4.30 – 3.97 and 4.35 - 4.26 for B, L and BL (B. bifidum, L. acidophilus and the co-culture of B. bifidum, and L. acidophilus fermented samples). L. acidophilus had highest pH decrease. Titratable acidity, viscosity and syneresis index increased significantly (P≤0.05) with increase in storage time. Probiotic counts varied from 7.72-6.54 and 8.56 – 7.70 Log CFU/ml for B. bifidum and L. acidophilus respectively in the mono-culture samples B and L and from 7.66 – 5.65 and 7.90 – 6.57 Log CFU/ml for B.bifidum and L. acidophilus in sample BL. Assessors’ degree of likeness for the aroma, appearance, taste and texture of the probiotic soy-HABF yoghurt varied from neither like nor dislike to moderate likeness. The overall acceptability indicated that the L. acidophilus fermented product (sample L) was more acceptable to the assessors within the first 5 days of storage.

Conclusion: This study have shown that B.bifidum and L.acidophillus retained a viability of > log 6 within 15 days of storage. The physicochemical and sensory characteristics of soy/HABF yoghurt were also at optimum within the first 5 days at 4⁰ C.