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Leaf extract of Syzygium Guineense can preserve tomato fruits

By Olubunmi Ogah-Fasuan (Food Microbiologist)
Syzygium guineense fruiting branch B. Wursten

A fruit is the edible part of a mature ovary of a flowering plant. Fruits could also be described as the succulent or fleshy covering of a nut which is pulpy, often juicy in character. As they were developed from the flower of a plant; they consist of ripened seed or seeds with some tissues attached. Fruits play a vital role in human nutrition by supplying the necessary growth factors such as vitamins and essential minerals in human daily diet and that can help to keep a good and normal health.

In developing countries, losses of fruits and vegetables during post- harvest fluctuate between 20% atnd 50%. Tomato is a particular example of fruits which quickly get spoilt due to its high sugar content after it has ripened. It has been estimated that 20-50% of tomato fruits harvested for human consumption are lost through microbial spoilage. Other losses result from damage by dynamic stresses during transit and through rough handling during loading and unloading.

For centuries, plants have been appreciated for their antimicrobial or medicinal activity. Syzygium guineense (water berry tree), a dense, leafy forest tree around 30 meters high; bark flaky, grayish-white; leaves broadly lanceolate, opposite, entire to the branch; fruit ellipsoid drupe, purplish in color. This plant has wide application in African traditional medicine.

The methanolic extract of S. guineense leaves had been reported to have antibacterial activity against Escherichia coli, Bacillus subtilis and Shigella sonnei. The ethanolic extracts of stem bark of Syzygium guineense showed molluscicidal activity. Triterpenes with antibacterial activity against Escherichia coli, Bacillus subtilis and Shigella sonnei were isolated from a methanol leaf extract, the most active being arjunolic acid and asiatic acid.

The objective of a research carried out during my Masters Degree programme at the Federal University of Technology was to determine the preservative efficacy of S. guineense leaf extracts on fresh and stored tomato fruits. The leaf extract, carried out using ethanol, was tested on both fungal and bacterial population on the tomatoes. And though there were significant effects on both sets of organisms, there were some interesting findings.

The microbial population of preserved tomato samples was significantly increased at both storage conditions, though the population of fungi increased more at a higher temperature. The acidity and moisture contents of tomato samples favoured the growth of fungi and are associated with their greater predisposition to fungal spoilage. Also, the higher load of fungi compared to the bacteria in the treated samples under the two environmental conditions may be connected to the antimicrobial activity of the extract since the extract had a better inhibitory effect on the bacteria than fungi. There was a general increase in total bacteria count of the stored tomato which may be due to favorable conditions which allowed the multiplication of the microorganisms.

There were however other results as well.

There was significant difference between the total acidity of the treated and even the control tomato samples kept under different environmental conditions during the storage period. Although the pH value of the stored tomato samples increases during the storage period, there was slight reduction in the pH of S. guineense ethanolic extract-treated tomato samples.

The outcome of the proximate analysis also revealed that the treated tomato showed a lower considerable loss in the moisture, crude fiber and carbohydrate contents compared to the controlled samples under varied environmental conditions. There was significant decrease in the Sodium, Calcium and Magnesium contents of all the preserved tomatoes, except the treated samples that had an increase in the percentage of Calcium.

Conclusively, the results of this study suggested that the crude extracts of S. guineense leaves could serve as alternative preservative agent to chemical preservatives, which have been under criticism for a long time. Further studies should be done to evaluate the biosafety of S. guineense using laboratory animals and determine the bioactive compounds found in the extracts of S. guineense leaves.





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