Development and Experimental Validation of a Predictive Model for Puffability of Gelatinized Rice.

Abstract

This investigation was performed to determine the extent to which selected endogenous parameters of rice effect the puffing of rice. The objectives were (1) to measure selected physicochemical properties of a variety of rice samples, (2) to identify where possible those parameters influencing the puffing of gelatinized rice, and (3) to develop and validate regression equations for the prediction of puffing. Under laboratory conditions designed to simulate closely an industrial rice processing environment, 113 samples of several varieties and types of rice were milled. The resulting head rice was analyzed for selected physicochemical properties. The quantitative interrelationships of several of these properties were established. Empirical models were developed for predicting the hardness of milled rice and the puffing of gelatinized, dried rice. The physical properties of length, width, area, and volume were determined for each of the head rice samples. Hardness was determined as was amylose and protein content and reaction in dilute alkali for each sample. The samples were cooked in excess water, air dried, and puffed in hot oil. Predictive models were developed using multiple regression techniques on a randomly selected subset of 83 samples. Each model was validated using the remaining 30 samples by comparing the predicted values for load and expansion to those actually observed. Hardness could be predicted for 67% of the holdout samples to within (+OR-)10% of the observed value using rough rice moisture content, percent head rice yield, and area-volume ratio. Expansion was accurately predicted within (+OR-)10% of the observed value for over 70% of the holdout samples using protein content, alkali spreading value, and rough rice moisture content. Long grain samples categorically expanded to a greater degree upon puffing than did either medium or short grain samples. Three varieties of medium grain rice, Nato, Brazos, and Vista, were found to expand comparably to long grain samples. This fact, coupled with higher yields and slightly lower cost per pound of medium grain varieties when compared to long grain varieties should maintain the incentive for industrial buyers to keep buying medium grain rice.