PROCESS DEVELOPMENT AND PRODUCT CHARACTERISTICS OF EXTRUDED RICE-SOYBEAN SNACK

ABSTRACT

The eating patterns of Ghanaians are changing due to urbanization, globalization, economic trends, as well as changes in social structure as a result of the increasing number of women working outside the home. These changes in eating patterns include higher consumption of snack foods by all age groups. A snack food is often smaller than a regular meal and normally consumed between meal times. Among cereal-based snacks, wheat and corn are the most popularly used cereals as compared to rice.

Locally grown and milled rice tends to be poorly patronized by consumers in Ghana due to quality defects, so incorporating this low grade rice into a ready to eat snack would provide an avenue for using the commodity which may otherwise be underutilized. This study therefore sought to develop a rice-soybean snack from low grade rice (parboiled or raw form) using extrusion-cooking technology. Rice and partially defatted soy flour blends of composition (75:25-90:10) were obtained based on ratios that were determined using constrained mixture designs for two components. In all twenty formulations were obtained and extruded using an intermeshing co-rotating twin screw extruder at constant screw speed of 1000rpm, barrel temperature of 200oC and a circular die diameter of 4mm. Evaluation of consumer sensory preference was carried out using a 9 point hedonic scale to obtain five most preferred extrudates with high percentage of rice (TMF3 (90% raw Togo Marshall (TM), 10% partially defatted soybean (PDS)); TMF4 (75% raw TM, 25% PDS); TMF5 (82.5% raw TM, 17.5% PDS); PTMF3 (90% parboiled TM, 10% PDS); PTMF4 (75% parboiled TM, 25% PDS)) for further analysis. Physicochemical analysis on the five extrudates showed that increasing amount of partially defatted soybean (PDS) and rice parboiling treatment generally decreased expansion ratio, lightness and increased hardness.

For characterization of proteins, amount of PDS and rice parboiling treatment had a substantial effect on accessible thiols, protein solubility and electrophoretic patterns. Extrudate made using 75% raw rice and 25% PDS (TMF4) showed the least protein digestibility suggesting the presence of antinutritional factor such as trypsin inhibitors. Principal Component Analysis (PCA) was used to discriminate extruded snacks based on odour and taste from data obtained from electronic nose and tongue analysis. Taste characteristics were discriminated based on umami, saltiness, bitterness, sourness and astringency. It was concluded that amount of PDS and rice treatment has a significant effect on the physicochemical properties of the extrudates.