Kinetics of storage losses & sensory characteristics for coextrudates of fish and rice flour

Extrusion cooking of fish and rice flour blends can produce products rich of amino acids, vitamins and minerals. In the present study storage and nutritional kinetics and sensory characteristics of fish and rice flour coextrudates were studied. The process variables used for the development of fish and rice flour coextrudates were barrel temperature (200° C), screw speed (109 rev/min) fish content of feed (44 %) and feed moisture content (39 %). Sorption isotherm drawn at 30° C indicated that the safe a_w levels of the extrudates were 0.4-0.7. The GAB model has described the best the sorption isotherm process and has fitted the best with an r² value of 0.99. Monolayer moisture content based on the GAB model was found to be 0.058 g/g (dry basis). Nutritional and storage characteristics indicated that during the first 15 days of storage a loss of 53.1 % and 50 % of vitamin-A (IU/g) and total tocopherols (%) was observed and whereas the peroxide and free fatty content increased from 46 to 109 mg/kg and 3.8 to 7.7 %. Non-linear model X / X₀= exp(-K × tⁿ) described the best the loss of vitamin-A, and tocopherols and gain in peroxide values and free fatty acid content. The loss of vitamin-A and total tocopherols almost followed the same trend during the complete storage period of 45 days whereas on the other hand the gain in peroxides was more prominent compared to free fatty acid content during the initial 15 days of storage. The ANOVA table indicated that the sensory attributes of the product fried for different times (15-120 sec) were significantly different and the scores of the sensory attributes of the product fried at 15 sec were most acceptable.