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Effect of Specific Mechanical Energy on In-Vitro Digestion and Physical Properties of Extruded Rice-Based Snacks

Extrusion cooking is a continuous process commonly used in industry to produce snacks, breakfast cereal and pet foods. It is considered as a high-temperature and short-time cooking process. Processing conditions in an extrusion process have significant effects on physiological properties of the products. Specific mechanical energy (SME) has been proposed to establish the relationship between processing variables and properties of expanded products such as density, expansion ratio, solubility and degree of gelatinization. As a system parameter, SME represents the amount of mechanical energy transferred to the feed material during extrusion, and it can be used to indicate extrusion conditions.

Rice has become an attractive ingredient in the extrusion industry in recent years because of its neutral taste and white color. It has been proposed that rice has a wide range of glycemic index (GI) depending on varieties and types. In this study, the effect of specific mechanical energy (SME) on in-vitro digestion and physical properties of extruded rice-based snacks was investigated.

Whole grains of medium grain brown rice (BR), medium grain sushi rice (SR) and long grain jasmine rice (JR) were extruded to prepare the rice-based snacks using a single screw extruder without additional thermal energy input. SME during extrusion was varied by changing feed moisture content. The feed moisture content (wet basis) was 9.99% - 12.55% for BR, 11.37% - 13.92% for SR and 12.42% - 14.39% for JR, respectively. Six extruded samples of each type of rice with different SME were collected and analyzed.

With the decreasing SME, all three types of rice-based snacks showed significant decreases (p < 0.05) on rapidly digestible starch (RDS) and significant increases (p < 0.05) on slowly digestible starch (SDS). Physical properties, including expansion ratio (ER), bulk density (BD) and fracture energy (FE) were found to be highly correlated to SME.

In conclusion, the results indicated that SME has significant effects on in-vitro digestibility and potentially glycemic index of extruded rice snacks. And in an extrusion process without additional thermal energy input, SME as a system parameter could work as a good indicator of many properties of extrudates such as physical and digestive properties.


Article by Yiming Feng and Youngsoo Lee, from University of Illinois Urbana-Champaign, Urbana, USA.

Full access: http://suo.im/4EnoSZ

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