Effect of cooking on functional properties of germinated black glutinous rice (KKU-ULR012)♣️
Thapanan Konwatchara and Araya Ahromrit
pp. 283 - 290
Abstract
The aim of this research was to investigate the changes in functional properties of germinated black glutinous rice
(KKU-ULR012) after cooking. Black glutinous rice grains were obtained from Faculty of Agriculture, Khon Kaen University,
Thailand. The rough grains were soaked for 12 hrs, then germinated for 30 hrs at 35±2°C (95%RH), dried at 45±2°C for 8 hrs,
dehusked and cooked either using a microwave oven or a pressure cooker. The cooked grains were dehydrated in two stages,
85±2°C for 1 hr and 45±2°C for 12 hrs until the final moisture content was 10±2%wb. The antioxidant activity, anthocyanins,
GABA and γ-oryzanol contents, and the microstructure of the dehydrated grains were then characterized. Germination
process induced a 2.55 fold increase in GABA content compared to non-germinated KKU-ULR012. The germinated KKUULR012 gave DPPH value, anthocyanins and -oryzanol contents of 33.74±0.15 mgTrolox/100gdb, 182.89±0.48 mg/100gdb
and 37.72±0.16 mg/100gdb, respectively. Anthocyanins in cooked germinated KKU-ULR012 diminished almost 88-89% after
cooking. The cooking methods employed strongly influenced the antioxidant activity and anthocyanins content that the
pressure cooking tended to prevent loss of anthocyanin content and antioxidant activity. The GABA, γ-oryzanol and anthocyanins contents and antioxidant activity of germinated grains cooked in the pressure cooker were higher than the samples
cooked in the microwave oven (p<0.05). For pressure cooking, the cooked grains gave DPPH, ABTS, anthocyanins and
γ-oryzanol contents of 9.89±0.35 mgTrolox/100gdb, 1.79±0.04 mgTrolox/100gdb, 21.60±0.14 mg/100gdb and 37.16±0.70 mg/100gdb,
respectively. The rice grains cooked by pressure cooking were more moist and sticky than the grains cooked by microwave
cooking. The microstructure examined by SEM showed that the center of the dehydrated cooked rice grain was smooth
indicating starch gelatinization whereas the surface revealed fission of the grain. This study found that germinated KKUULR012 cooked by the pressure method can be one of the native rice varieties that possess a potent source to enhance GABA
and γ-oryzanol contents as well as antioxidant activity.
