Impact of germinated Tubtim Chumphae rice flour substitution on the functional, nutritional, and sensory properties of cookies

• Germinated TTC rice flour enhanced water and oil absorption capacity. • Increasing substitution reduced amylose and RVA pasting viscosities. • Higher substitution darkened cookies and reduced hardness and spread. • Fifty percent substitution achieved optimal sensory quality and GABA. This study investigated the functional, nutritional, and sensory effects of substituting wheat flour with germinated Tubtim Chumphae (TTC) rice flour in cookie formulations. Composite flours were prepared at five ratios—0:100, 25:75, 50:50, 75:25, and 100:0 (germinated TTC flour: wheat flour, w/w)—and cookies were produced accordingly (T0, T25, T50, T75, T100). Substitution with germinated TTC rice flour significantly reduced amylose content and pasting viscosities, while increasing water solubility, water absorption, and oil absorption capacities, reflecting germination-induced modification of starch structure. Cookies with higher TTC levels showed progressive decreases in lightness, hardness, crispness, and spread ratio, alongside greater redness attributable to intrinsic anthocyanins. Among all treatments, T50 demonstrated the most balanced technological and sensory performance, yielding the highest overall acceptability. Nutritionally, T50 cookies contained markedly higher γ-aminobutyric acid (GABA; 3.73 mg/100 g) than the T0 control (0.23 mg/100 g), with modest increases in moisture and fat but reductions in protein, carbohydrate, and caloric values. Overall, T50 was identified as the optimal substitution level, demonstrating that germinated TTC flour can enhance GABA content while maintaining desirable sensory and functional qualities in cookie applications.