EFFECT OF GUM ARABIC ON NONENZYMATIC BROWNING OF DEHYDRATED TOMATOES

Abstract

In this study the effect of Gum Arabic (GA) on non-enzymatic browning (NEB) and colour of dehydrated tomato was investigated. Blanched tomato homogenate was treated with different concentrations of Gum Arabic (1%, 2.5%, 5%, 7.5% and 10%) and dehydrated at 80°C by conventional cabinet dryer, stored in dark at room temperature for 1,2,3,4 and 12 months was tested. Blanched tomato treated with 1% sodium metabisulfite and dehydrated thereafter was used for comparison. Colour changes were moitored by using absorbance at 420nm to determine browning index and CIElab system to measure redness, yellowness and lightness. Addition of Gum Arabic decreased browning development in all storage periods, whereas sodium metabisulfite decreased browning over most of the storage periods, only approaching the untreated values at 12 months. Increase in GA concentrations resulted in more decrease of the NEB, up to 7.5%.A minimum concentration of 5% GA was found to be more effective than 1% sodium metabisulfite to retard NEB . Sodium metabisulfite treated samples, showed a significant (P≤0.05) increase in redness (a+) values in all storage periods ranging between 30 to about 39. Lightness (L) value increased in an ascending way with GA concentration to range between 27.5-36 compared with 38.5 for the fresh blanched tomato homogenate. There was no significant difference (P≤0.05) between 5% and 7.5% GA treated sample after dehydration. There was a minor effect, , on the pH of the dehydrated tomato treated with GA (pH ranged between 4.27-4.37) while an increase was observed in pH to reach 5.15 ,when sodium metabisulfite was used. °Brix values increased, for all GA treated samples, from 6.8 to 7.1-8.5 after dehydration and storage. Moisture content and water activity (aw) decreased in GA treated samples to range between (15.3%-7.3%) for moisture content and (0.328-0.2675) for aw.