29D-24 |
Effect of temperature-time treatments on phytase activity in cowpea flour |
N. S. AFFRIFAH, Dept. of Food Science & Technology, Univ. of Georgia, 1109 Experiment St., Melton Bldg., Griffin, GA 30223-1797 and M. S. Chinnan, Department of Food Science and Technology, University of Georgia, 1109 Experiment St., Melton Bldg., Griffin, GA 30223-1797. The hard-to-cook defect of legumes including cowpeas is a major constraint which limits their consumption and production. The development of the defect is a complex mechanism which is still under investigation with most results suggesting the involvement of the phytase enzyme. Understanding the inactivation of the enzyme in the seed would be of practical value in designing process treatments aimed at prevention. To determine the effectiveness of heat treatments in inactivating phytase in cowpeas. The study followed a 6 x 4 factorial design (temperature – 50, 60, 70, 80, 90, 100 and time – 5, 10, 15, 20). Finely ground cowpea flour was thinly dispersed into an aluminum foil pouch and heated between two aluminum plates held at the specified temperature and time followed by rapid cooling on ice. The enzyme was extracted with 0.05M Tris-HCl (pH 7). The residual enzyme activity was determined by incubating at 37°C with sodium phytate and measuring the amount of inorganic phosphate produced. The enzyme was found to be quite stable to heat with 78% of its activity being retained after subjection to the highest temperature and time combination. Additionally, most of the treatment combinations resulted in an improvement of the measured activity. Overall, the residual activity ranged from 78% to 122%. Contrary to expectations, a bimodal effect of temperature was observed at all heating times such that increasing temperature resulted in two distinct phases of increased phytase activity with an intermediate region of decline in activity. The uncharacteristic response of phytase to increasing temperature may be indicative of the complexity of the underlying mechanisms of the hard-to-cook defect. The results from this study can help in designing experiments to systematically evaluate as well as modify strategies for prevention of legume hardening.
Session 29D, Food Engineering: Thermal processes
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