Effect of Microwave Heat on the Nutritional Properties of Infected Red Kidney Beans

Abstract

In this paper, the effect of microwave heat on the nutritional characteristics of affected red kidney beans, i.e., Rajma is studied. Evaluation of crude protein content in microwave heated red kidney beans are carried out using standard Kjeldahl method and Fourier transform infra-red (FTIR) spectroscopy. Red kidney beans affected by Pulse Beetle (Callosobruchus chinensis) have been analyzed throughout the experiments. The heat treatment of the samples is undertaken using a domestic microwave oven at 2.45 GHz. The samples are heated at different microwave powers, such as 90, 270, 450, 750, and 900 W, while the exposure time is varied from 30–90 s. The effective microwave power for maximum disinfestation is found to be 270–450 W at 30–60 s. Most of the red kidney beans are damaged at 900 W for 60 s. Using Kjeldahl method, a constant crude protein level of 22.5 % is obtained for untreated and treated samples at 90–450 W. Crude protein level of red kidney beans is changed at 750–900 W. From FTIR analysis, the absorbance spectrum of carbohydrate peaks is found at 900–1250 cm $^{-1}$ , a moisture peak at 1650 cm $^{-1}$ , and a protein peaks at 2800–3000 cm $^{-1}$ . Statistical analysis of the treated and untreated samples represents the lowest error of 0.0016 at 450 W power level for 60 s. Variances are determined to be the lowest with a value of 270 W and 450 W at 90 s and 60 s. These findings indicate the optimum microwave heat treatment for red kidney beans to retain its protein content.