Assessment of the Effectiveness of Ginger (Zingiber officinale), Clove (Syzygium aromaticum) and Sodium Benzoate on the Shelf Life of Soymilk

Abstract

The significance of preservatives in food preparations lies in their ability to inhibit or retard the growth of microorganisms which in turn reduces their deteriorative effects on food. The preservative effects at varying concentrations (1%, 3%, 5% v/v) of sodium benzoate was compared with extracts of ginger, cloves and a combination of the two extracts on soymilk at refrigerated temperature. Indices for measurement of shelf life included drop in pH, protein and fat contents, changes in colour and odour, as well as changes in microbial counts. The protein, fat contents and pH decreased more with storage time and these were concentration dependent. The bacterial counts during 25 days of storage ranged from 1.0 x 104 to 6.4 x 105, while fungal counts ranged from 8.0 x 103 to 18.4 x 104. At all concentrations, sodium benzoate exhibited the best preservative effect on the soymilk samples. Reduction in total microbial count was more pronounced in samples treated with clove extract than those treated with ginger extract, while the extracts’ combination exhibited the best preservative effect of all the spice treated samples. The use of ginger as a preservative increased shelf life of soymilk by 7 days, cloves extended shelf life by 10 days, while the combination of the extracts maintained a longer shelf life of 13 days. The bacterial isolates include Bacillus cereus Strain KWS2, Bacillus subtilis strain BTBS, Bacillus amyloliquefaciens strain PJ-5, Bacillus safensis strain SABA5 and Lactobacillus fermentum strain SABA5, while the fungal isolates were Aspergillus niger, Aspergilus fumigatus, Fusarium moniliforme and Saccharomyces cerevisae. The phytochemicals found in ginger and cloves include tannins, phenol, alkaloid, flavonoid, terpenoids, steroids, glycosides, coumarin and saponins, which might be responsible for the antimicrobial properties. The results of the study showed that a combination of ginger and cloves extracts is a better preservative of soymilk than the single extracts, as natural preservatives.