Efficacy of sodium bicarbonate and chlorine based sanitizers on postharvest microbial load and quality attributes of packaged tomato fruits

The high potential of tomato production is not realized in Kenya due to various factors in the value chain such as high postharvest losses estimated to be 40-50%. These losses are as a result of many factors including poor postharvest handling, lack of storage facilities and deteriorative agents such as postharvest diseases. Microbial decay alone accounts for 15% of the postharvest losses. Some of the methods and treatments used to manage microbial decay are costly and unhealthy. In this study, sodium bicarbonate (baking soda) which is a low cost sanitizer was evaluated for its effectiveness to manage fungal rots in comparison with the commonly used chlorine based sanitizers. The fungus was isolated on potato dextrose agar media (PDA). The mature green tomato fruits were wounded (4 wounds, 3mm deep near stem end) and artificially inoculated with a spore suspension of 106 conidia/ml of Alternaria alternata. Different sanitization treatments were then applied to control the fungal rots. The treatments included 30,000 ppm sodium bicarbonate solution; 150 ppm chlorine solution; 200 ppm NaOCl solution; water and untreated samples which served as a negative control. The fruits were then air dried and either packaged into special modified atmosphere packaging (MAP) bags or left unpackaged. The treated fruits were then stored under ambient room conditions (Temp 25 ± 10 °C and RH 65± 5%). Physical parameters (color, percentage weight loss, firmness, wilting index), biochemical parameters (total soluble solids and total titratable acidity) and microbial analysis (spore count and disease severity index) were determined. The results showed that sodium bicarbonate whether packaged or unpackaged significantly (P<0.05) reduced deterioration compared to chlorine based sanitizers and control as evidenced by the number of live spores. Although deterioration of wounded fruits was more rapid compared to the unwounded ones, application of Na2CO3 sanitizers slowed down deterioration. Therefore sodium bicarbonate can be recommended as a low cost and healthier sanitization option for tomatoes.