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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