EVALUATION OF THE USE OF XANTHAN GUM AND CHITOSAN IN THE FORMATION OF EDIBLE COATING MATERIALS

Abstract

Researches in food preservation have evolved into use of edible polysaccharide products in the coating of perishable fruits. The most utilized polysaccharide is xanthan gum. In this study, xanthan gum and chitosan were used in composite coating materials, and the effects on the preservation and nutritional quality of tomato fruit were evaluated. Films obtained from xanthan gum and chitosan were prepared in varying proportions; 90:10, 92.5:7.5, 95:5, 97.5:2.5, 100:0. Films obtained from the mixture of xanthan gum and chitosan in the above proportions were analyzed for mechanical properties (Young’s modulus, elongation at break, strain at break, load at break, stress at break and energy at break). Using the elongation at break and Young’s modulus as reference parameters, the films with the following proportions of xanthan-chitosan; 90:10, 95:5, 97.5:2.5 were further evaluated for barrier properties (thickness, solubility in water, oxygen permeability and water vapour permeability) and optical properties (opacity and colour parameters). The xanthan gum-based films brought about changes in thickness, water vapor permeability and solubility of films but did not change significantly (p ≤ 0.05) the oxygen permeability. Film obtained from the mixture of xanthan gum and chitosan (95:5) was used as the coating material. Fresh tomato fruits were coated with the film, and dried at room temperature (25±2 o C). The coated and uncoated tomato fruits were collected daily and examined for microbial analysis, texture, weight loss, pH, nutritional and phytochemical (beta carotene, ascorbic acid and lycopene) constituents; and antioxidant properties (ABTS, DPPH and hydroxyl scavenging, metal chelating and ferric reducing antioxidant power). The results showed that xanthan and chitosan composite coating delayed the deterioration and shrinking of tomato fruits. The study also showed a gradual reduction in the levels of phytochemicals determined in the tomato and the antioxidant activities from day 1 to 13, the coated tomato fruits had sustained levels of the phytochemicals compared to the uncoated tomato. The study concluded that the coating film decelerated the deterioration rate of the tomato fruit; retaining the phytochemicals and antioxidant properties than in the uncoated tomato fruits.