Vacuum impregnated rice as affected by moisture contents and rice varieties

Abstract

Rice is an economical commodity for Thailand. Although it is common to directly consume the rice, its commercial value can be increased through processing, such as vacuum impregnation. Therefore, the aim of this study was to investigate the effect of moisture contents and rice types on the physicochemical properties of vacuum impregnated  rice. Four different rice varieties, including white rice ( Sao Hai ), white glutinous rice ( Kiaw Ngu ), black rice ( Hom Nin ) and black glutinous rice ( Kum Doi Saket ), were cooked  in an electric cooker at different water addition to produce cooked rice with moisture contents of approximately 50 or 60%. The cooked rice was then subjected to vacuum  impregnation at 50 mbar for 10 min in an impregnation solution of saline solution at a ratio of 1:2 for rice and water, respectively, followed by another 10 min period in the solution as a relaxation time. Physicochemical analyses of the impregnated rice showed that different rice varieties and moisture contents of cooked rice significantly affected  hardness, rice volumetric deformation (γ value), volume of rice occupied by impregnation solution (X value), real porosity (e r ), solid gain and water loss (p<0.05). The white glutinous rice with a moisture content of 50.71±0.30% significantly had the highest γ and X values of 1.00±0.64 m 3 /m 3 initial sample and 1.15±0.04 m 3 liquid/m 3 sample, respectively. This rice treatment also significantly possessed the lowest water loss (–94.97±3.06%), whereas  the highest solid gain of 2.45±0.16% was determined in the white rice with a moisture  content of 49.50±0.55%. For the e r value, the lowest value of this parameter (0.022±0.018%) was found in the black glutinous rice with a moisture content of 50.14±0.22%. Finding from this study clearly suggested rice varieties and moisture contents of cooked rice are important parameters in the application of vacuum impregnation.