Development of a rice starch-based coating with antioxidant and microbe-barrier properties and study of its effect on tomatoes stored at room temperature

Tomatoes coated with rice starch-based edible coating formulation containing coconut oil and tea leaf extract were studied for the effect of coating on biochemical changes during storage for 20 days. Addition of lipid and tea leaf antioxidant extract in starch/glycerol coating solution improved the surface integrity of films but decreased the solubility and stability of the films and coating solutions. Starch retrogradation was reduced and amylose-lipid complexation occurred on addition of coconut oil as suggested by Differential Scanning Calorimetry. After 20 days of storage, weight loss was 1.78% less for starch/glycerol/lipid (S/G/L) coated and 3.53% less for starch/glycerol/lipid/antioxidant (S/G/L/A) coated tomatoes as compared to control. Titratable acidity was 0.262 +/- 0.007% and 0.337 +/- 0.003% and pH was 4.62 +/- 0.013 and 4.27 +/- 0.015 for control and S/G/L/A coated tomatoes, respectively. TSS (degrees Brix) increased with storage in all samples but S/G/L/A coated tomatoes exhibited 0.5 degrees Brix less TSS than the control. Reducing sugars and ascorbic acid increased with storage initially and thereafter decreased later on with control showing maximum fall and S/G/L/A and S/G/L recording lowest fall, in that order. Coconut oil and tea leaf extract in the edible coating clearly delayed ripening effects on tomatoes. The coconut oil and tea extract also exhibited microbe-barrier property. (C) 2012 Elsevier Ltd. All rights reserved.