EFFECTS OF SELECTED LEAF EXTRACTS AND ORGANIC ACIDS ON THE MICROBIAL AND STORAGE QUALITIES OF SOME FRUIT JUICES

Abstract

Fruit juices play major roles in the diet of human beings. They may help to reduce the risk of numerous chronic diseases known to be initiated by long term inflammation. However, since fresh fruit juices cannot be kept for long time because of their high perishability, this study aims at evaluating the effects of selected leaf extracts (Ocimimum gratissimum Linn., Cymbopogan citratus Linn. and Anthocleista djalonensis Linn.) and organic acids (citric, lactic, acetic and benzoic) on the microbial and storage qualities of selected fruit (watermelon, orange, pineapple and apple) juices stored at ambient temperature (30±2 oC) using standard techniques. The phytochemical constituents of the selected leaf extracts and the nutritional composition of the preserved juices were also investigated using standard methods. The extracted fruit juices were preserved with different concentrations of the hot aqueous extract of the selected plant leaves ranging from 5.0% w/v to 40.0% w/v and organic acids concentrations which ranged from 0.2%v/v to 0.5%v/v. Prior to the treatment of the fruit juices, the microbial types and loads were determined, so also the physicochemical parameters such as pH, titratable acidity, mineral contents, vitamin types and values and organic acids profile. The total viable bacterial count (TVB) for orange juice without any preservative ranged from 7.91±0.08 log10 cfu/ml to 8.11±0.01 log10 cfu/ml while it ranged from 7.70±0.01 log10 cfu/ml - 8.08±0.01 log10 cfu/ml for watermelon juice. The TVB count of pineapple juice ranged from7.75±0.02 log10 cfu/ml - 7.97±0.02 log10 cfu/ml while, it ranged from 7.41±0.01 log10 cfu/ml to 7.82±0.02 log10 cfu/ml for apple juice. The fungal counts of orange juice ranged from 2.29±0.03 log10 sfu/ml – 3.22±0.02 log10 sfu/ml, watermelon juice from 2.17±0.02 log10 sfu/ml – 2.91±0.01 log10 sfu/ml, pineapple juice from 2.77 ±0.01 log10 sfu/ml – 3.44 ±0.02 log10 sfu/ml and apple juice from 3.13±0.01 log10 sfu/ml – 3.79 ±0.02 log10 sfu/ml during storage at 30±2 oC for 72 hours. Seven bacterial types, four yeasts species and three moulds species were isolated from the different fruit juices during the storage. The bacterial species are Acinetobacter indicus, Bacillus cereus, Staphylococcus aureus, Corynebacterium sp, Micrococcus luteus, Bacillus thuringiensis and Bacillus subtilis, the yeasts are Saccharomyces cerevisiae, Candida tropicalis, Candida krusei and Pichia kudriavezeii while the moulds are Aspergillus aculeatus, Curvularia lunata and Curvularia aeria. Out of the leaf extracts used as preservative, hot aqueous extract of O. gratissimum (40% w/v) significantly (p≤0.05) reduced the microbial load of the selected fruit juices stored at 30±2oC for 240 hours. The total viable bacterial counts of watermelon, orange, pineapple and apple juices treated with Ocimum gratissimum (40% w/v) ranged from 1.43±0.03 log10 cfu/ml to 2.17±0.01 log10 cfu/ml, 2.09±0.02 log10 cfu/ml to 2.23±0.03 log10 cfu/ml, 1.83±0.02 log10 cfu/ml to 2.24±0.01log10 cfu/ml and 2.04±0.03log10cfu/ml to 2.63±0.02log10 cfu/ml respectively while the fungal load of the juices ranged from 1.20±0.02 log10 sfu/ml to 1.55±0.02 log10 sfu/ml, 0.00 log10 sfu/ml to 1.45±0.04log10 sfu/ml, 0.00 log10 sfu/ml to 1.04±0.01 log10 sfu/ml and 0.00 log10 sfu/ml to 1.31±0.01 log10 sfu/ml. Out of the organic acids used, citric acid (0.5% w/v) significantly (p≤0.05) reduced the microbial load of the selected fruit juices stored at 30±2 oC for 240 hours. The total viable bacterial counts of watermelon, orange, pineapple and apple juices treated with citric acid (0.5% w/v) ranged from 2.00±0.01 log10 cfu/ml to 2.14±0.02 log10 cfu/ml, 1.16±0.02 log10 cfu/ml to 1.70±0.05 log10 cfu/ml, 1.93±0.00 log10 cfu/ml to 2.30±0.00 log10 cfu/ml and 1.80±0.11 respectively while the fungal load of the juices ranged from 0.00 log10 sfu/ml to 2.12±0.02 log10 sfu/ml, 0.00 log10 sfu/ml to 1.98±0.00 log10 sfu/ml, 1.19±0.00 log10 sfu/ml to 2.29±0.01 log10 sfu/ml and 0.00 log10 sfu/ml to 2.04±0.01 log10 sfu/ml. O. gratissimum (40% w/v) leaf extract was the best to maintain the nutrients in pineapple juice than 0.5% citric acid. It improved the vitamin, proximate and mineral compositions of pineapple juice during storage. It is suggested that, the hot aqueous extract of O. gratissimum leaf (40% w/v) extract be exploited as a natural preservative to extend the shelf life of pineapple juice at ambient temperature of 30±2 oC for a maximum of 240 hours