Abstract:
The chemical compounds used as preservatives in fruit juices have been associated with many health problems. Hence, it is imperative to find safer alternatives from natural sources such as plants. This study assessed Moringa oleifera and Xylopia aethiopica extracts for their preservative potential in fruit juice based on their phytochemical contents, antioxidant activities and anti-yeast properties. Qualitative phytochemical analysis showed that M. oleifera extracts contained alkaloids, tannins, saponins, glycosides, terpenoids and flavonoids but the water extracts lacked alkaloids. The same phytochemicals, except terpenoids, were also found in all X. aethiopica extracts. The antioxidant activity determined using 2, 2- dipheny- 1- picrylhydrazyl (DPPH) and the total phenolic content expressed as Gallic Acid Eqivalent (GAE/g), indicated that the plant extract with the highest antioxidant activity (IC50) also had the highest total phenolic content (GAE/g). The methanol extract of M. oleifera had IC50 of 48.09 μg/mL and GAE/g of 110.0 mg while the acetone extract of X. aethiopica had IC50 of 19.10 μg/mL and GAE/g of 173.2 mg. The agar dilution assay was used to evaluate the anti-yeast activity of the extracts in vitro against fruit juice spoilage yeasts. The methanol extract of M. oleifera had the strongest anti-yeast activity and was specifically fungicidal against the CY0757 and IGC4242 strains of Zygosaccharomyces bailii and Wickerhamomyces anomalus. The acetone and water extract were poor growth inhibitors. All M. oleifera extracts showed stimulatory activity on Yarrowia lipolytica which has been reported as beneficial in biofuel production. The best anti-yeast activity for X. aethiopica was shown by the methanol extract which was fungicidal against Zygosaccharomyces bailii IGC4242 and Cryptococcus laurentii. The acetone extract of X. aethiopica exerted inhibitory activity against most of the yeasts. The water extract showed the least bioactivity. The anti-yeast activity of plant extracts in fresh grape and orange juice showed microbial overgrowth in the untreated fruit juices used as controls, indicating the presence of contaminants in treated fruit juices. The Hoechst 33342 and propidium iodide dual staining procedure showed that M. oleifera extracts were not cytotoxic on normal Vero cells. The water extract of X. aethiopica also did not show toxicity on the cells. The methanol and acetone extract were, however, very toxic on the cells. This study demonstrates that although M. oleifera and X. aethiopica extracts have limited potential as natural preservatives in fruit juice, the growth stimulatory activity of M. oleifera extracts on Y. lipolytica may be useful in biofuel production and this requires further investigation.
