Abstract
The study was conducted to evaluate the preservative potentials of essential oils (EOs) of Piper guineense, Xylopica aethiopica and Tetrapleura tetraptera in mixed fruit juice and determine their antioxidant capacity. The preservative effect at varying concentrations was evaluated using S. cerevisiae, S. aureus and B. cereus as test isolates. The antioxidant properties were determined using 1,1- diphenyl-2-picrylhydrazyl (DPPH) and ferric ion reducing power assay (FRPA) methods. Concentrations (10 and 5%) of P. guineense and X. aethiopica EOs reduced the number of S. cerevisiae by one log cycle on the 10th day of storage, while 3.3% reduced it by one log cycle after 14 days. The 10% concentration produced a log cycle reduction in the growth of S. aureus and B. cereus on the 12th day. However, 5% concentration reduced the growth of B. cereus by one log cycle on the 14th day. T. tetraptera had the largest amounts of vitamin A (544.41 iu/100 mL), phenol (1.81%) and flavonoids (0.45%). P. guineense had the highest value for vitamin E (37.03 iu/100 mL). X. aethiopica EO produced the highest scavenging activity (46.04%), while P. guineense EO produced the strongest reducing power activity (38.64%). The EOs can act as natural preservative in mixed fruit juice. Their inclusion in such products can improve the products thereby serving as functional foods/beverages, and thus can reduce the risks of cancer formation and chronic diseases in humans. Key words: Mixed fruit juice, preservation, microbial isolates, essential oils, antioxidant ability.
Highlights
There has been an increase in the consumption of unpasteurized fruit juices and minimally processed fruit products in recent times (Estrada et al, 2013)
Concentrations (10 and 5%) of P. guineense and X. aethiopica essential oils (EOs) reduced the number of S. cerevisiae by one log cycle on the 10th day of storage, while 3.3% reduced it by one log cycle after 14 days
Pure cultures of S. aureus and B. cereus were obtained from the laboratories of Federal Medical Centre, Owerri, Imo State, Nigeria, while Saccharomyces cerevisiae was isolated from spoilt fresh fruit juice
Summary
There has been an increase in the consumption of unpasteurized fruit juices and minimally processed fruit products in recent times (Estrada et al, 2013) This increase is due to the high nutrient content of the juice and their freshness (Rathnayaka, 2013). Several fresh fruit products are not normally heat processed and do not contain preservatives, they can be contaminated and spoiled by various microorganisms especially fungi and bacteria. These fruits are very good substrates that support their growth where they cause.
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