Optimization of gamma-aminobutyric acid in three varieties of germinated brown rice using the rotatable central composite design (RCCD) of the response surface methodology (RSM)

Abstract—Gamma-aminobutyric acid (GABA) is one of the bioactive compounds required for nervous health of man especially that of the elderly.  GABA is an inhibitory neurotransmitter in plants and animals. It is present in paddy rice at levels too low for an active functionality in a health food. Germination of paddy rice varieties could increase the concentration of GABA to levels required for human health.  GABA is a non-protein amino acid, it is applied to relieve or prevent non-communicable diseases in man especially among the elderly.  Synthetic has failed to meet the ideal requirement of a good supplement; affordability, safety and availability and renewability. The work was done to improve the content of GABA in Sesalin, Mars, and Vara rice varieties through germination process. The three rice varieties (X₁), were obtained from Ini Local Government Area of AkwaIbom State, Nigeria. Germination of the brown rice was done under the environmental conditions of germination time (X₂), steeping time (X₃), and temperature of steeping water (X₄). The rotatable central composite design (RCCD) of the response surface methodology was deployed (RSM)for the study to identify terms of the models which exhibited optimum levels of GABA concentration, sensory and market attributes of the germinated brown rice (GBR). The experiment revealed that rice variety, steeping time, germination time and their interactions synergistically influenced the germination process. The model of GABA was significant (p<0.05), R²=0.8722 and mean value =16.03µg/100g of the samples. The models for colour, taste and general acceptability of the samples were not significant (p>0.05), but the response surface plots exhibited some effects on the parameters. Optimization process showed that Vara 44 rice variety, sprouting time of 91.42 hr, 0.023 hr, and steeping water temperature of 37^oC produced 906.64ug/100g, 4.53, 4.19, and 7.07 of GABA, colour, taste, and general acceptability of the GBR respectively at 92.80% desirability. More studies are needed using higher values of the independent variables to obtain higher levels of the study responses and education of the consumers on the health benefits of GABA.