Effect of irradiation on the shelf life and nutritional quality of tomato (Solanum Lycopersicon L.) powder

Tomato (Solanum lycoersicon L.) is a major horticultural crop with an estimated global production of over 153 million metric tons. It is the most important fruit vegetable and the second most widely cultivated crop in the world after potato, with a total production of about 141 million tons. In 2009, the average total yield in Ghana was 7.5 Mt ha-1 compared to the achievable yield of 15.0 Mt ha-1. The tomato industry in Ghana for the past decade has been bedevilled by a myriad of problems of which post-havest losses range between 30% and 70% in the major season of production, hence a study was conducted into the preservation of S. lycoersicon L. through drying and packaging to reduce post-havest losses. Two drying methods comprising of solar and freeze drying were employed for three varieties of tomato which are cultivated locally. The methods were compared to determine the more efficient for the three varieties used for the study and the impact of drying and radiation on some physio-chemical properties, microbial load as well as shelf-life of the samples. Evaluation of the packaging material for the dried samples was also carried out. The samples were exposed to gamma radiation at 0 kGy, 1 kGy, 2kGy, 3 kGy. The parameters determined included moisture content, pH, titratable acidity; total soluble solids carotenoids, lycopene, lutein and beta carotene. Microbial analysis carried out included total aerobic mesophilic bacteria count, total coliform count and moulds and yeast using standard methods. Data were analysed using ANOVA. Storage had significant effect (p<0.05) on the pH, TSS, TTA, colour and microbial load of the various varieties used. Irradiation had a significant effect (p<0.05) on pH, colour, microbial quality, lycopene content, beta carotene, and total carotenoid content of the varieties used; however irradiation had no significant (p<0.05) effect on moisture content, total soluble solids and microbial quality of the varieties used. Comparing powders obtained from freeze dried and solar dried tomatoes (Akoma), solar drying emerged as a more efficient method of drying. In Akoma, significant differences (p<0.05) were observed in all the parameters due to the difference in drying methods. Gamma irradiation did not affect (p>00.05) the moisture content, total soluble solids of Akoma variety irrespective of the drying method used. However gamma irradiation had a significant effect (p<0.05) effect on pH, colour, total aerobic mesophilic counts, total coliforms, moulds and yeast, total carotenoid content, lutein and beta carotene. Storage had significant (p<0.05) effect on the colour, total carotenoid content, and lycopene of the powders from the two drying methods. The packaging material used was suitable for the solar dried powder but not the freeze dried powder. Varietal differences (p<0.05) existed between the tomatoes in terms of moisture content, total soluble solids, pH, titratable acidity, colour, total aerobic mesophilic counts, total coliform count and total moulds and yeast counts. (au)