Production of fermented soymilk and its preservation using essential oils from the leaves of Hoslundia opposite

Fermented Soymilk (FSM), a protein rich beverage is highly prone to microbial contamination. Its preservation is therefore key to its availability and safety. Soymilk was prepared by aqueous extraction of soybeans and allowed to ferment spontaneously. Samples of FSM were treated with leaf essential oil of Hoslundia opposita (LEOHO) at 5% and 10% (v/v) and stored at ambient temperature. The organoleptic, pH and microbiological qualities of the samples were evaluated periodically during storage. The protein content was significantly (p<0.05) improved by fermentation from 8.18±0.06% to 12.62±0.12%. Compared to the untreated, samples treated with LEOHO had higher sensory ratings. The pH of the samples decreased from 6.9 to 5.7 during fermentation; and further to 4.9 during storage. Overall, the bacterial load was significantly (p<0.05) reduced (up to 80.04%) during storage; while the fungal load was reduced to zero immediately after fermentation. The bacterial isolates were Bacillus wiedmannii FSL W8-016, Micrococcus luteus NCTC 2665, Lactobacillus algidus M6A, Lactobacillus sakei NBRC 15893, Lactobacillus apodemi ASB1, Shigella sp., Staphylococcus aureus and Escherichia coli, while the fungi were Candida parapsilosis IQMustafa31, Penicillium citrinum, Aspergillus flavus and Fusarium verticilloides. All the bacterial isolates were sensitive to LEOHO with zone of inhibition ranging from 10.00±1.00mm to 46.33±1.53mm. This study shows that LEOHO was effective in preserving the sensory and nutritional value as well as reducing the microbial population of FSM. LEOHO is therefore recommended as preservative to increase the shelf life of FSM.