Comparative insights into cultivar-dependent nutritional and antioxidant responses to germination across eight rice cultivars

Rice ( Oryza sativa L.) is a major staple crop, and germination is increasingly employed to improve its nutritional and functional quality. However, comparative evidence describing cultivar-dependent biochemical responses under standardized germination conditions remains limited. This study comparatively evaluated physicochemical, nutritional, and bioactive changes in eight rice cultivars: Glutinous Rice 6 (RD6), Red Dok Mali (RDML), Khao Dok Mali 105 (KDML105), Upland, Loi (floating rice), Sanpatong, Yellow 11, and Inpaeng. An optimized protocol involving soaking until the grains reached 40 ± 2% moisture content (wet basis), followed by 48 h of germination, achieved high germination efficiency (>98%) while maintaining grain quality and structural integrity. Germination significantly increased α-amylase activity, reducing sugars, crude protein, free amino acids, and total phenolic content (TPC). Protein enrichment was accompanied by increases in essential and non-essential amino acids, particularly branched-chain amino acids, alanine, glycine, and proline, whereas glutamic acid decreased consistently across cultivars. B-group vitamins (B1, B2, B3, and B6) were elevated after germination. Lipophilic antioxidants increased in most cultivars, with α-tocopherol ranging from 82.4 to 207.3 μg/100 g and γ-oryzanol from 68.3 to 149.4 mg/100 g. TPC (658.9–1,057.1 mg GAE/100 g) and antioxidant capacity improved primarily in non-pigmented cultivars, whereas the pigmented RDML showed limited phenolic enhancement, likely due to soaking-related leaching. Overall, the results demonstrate that nutritional and antioxidant improvements induced by germination are strongly cultivar-dependent , highlighting the importance of cultivar selection and standardized processing conditions for developing value-added germinated rice products.