Standardized Yield Factors and Grain Hydration in Sri Lankan Indica Rice Varieties: Applications in Nutritional Assessment and Contaminant Exposure

• Standard cooking of 100 g Indica rice takes 13.26 ± 2.60 minutes • Grain hydration % increases significantly during washing and cooking • Raw-to-cook % weight gain was 200.74 ± 16.73 and correlated with grain-length • Yield factor was 3.01, 100 g raw Indica rice produced 301 ± 17 g cooked rice • Yield factor heterogeneity influenced contaminant assessment in rice such as Cd The quantification of nutrients, anti-nutrients and contaminants in foods is significantly influenced by water content in food matrices. Accurate transformation of nutrient and contaminant data from raw to cooked foods requires reliable yield factors, yet variety-specific data for rice remain limited. This study developed and validated a standardized domestic cooking procedure for 25 Sri Lankan Indica rice varieties to establish yield factors (YF) applicable to nutritional assessment and contaminant exposure calculations. Rice samples underwent standardized cooking using a 1:2.25 rice-to-water ratio with complete water absorption. Hydration percentage (%H), weight gain (%WG), and YF were quantified at raw, washed, and cooked stages using lyophilization and comprehensive statistical analysis including ANOVA, post-hoc testing, and Monte-Carlo simulation. Hydration increased significantly from 5.96 ± 0.30% (raw) to 19.13 ± 1.82% (washed) to 47.52 ± 2.80% (cooked) ( p <0.001). Weight transformation showed a consistent threefold increase with YF of 3.01 ± 0.17, corresponding to 200.74 ± 16.73% weight gain. Parboiled varieties required significantly longer cooking times (15.32 ± 2.11 vs 11.53 ± 1.18 minutes, p <0.001) and exhibited reduced water absorption. Monte-Carlo simulation indicated coefficient of variation <10%, meeting analytical validation criteria. Application to cadmium exposure assessment demonstrated that the current Codex standard of 0.4 mg kg -1 for raw rice translates to 0.133 (0.128-0.140) mg kg -1 in cooked rice, enabling daily cadmium intake estimation of 0.067 - 0.119 mg person -1 day -1 for Sri Lankan adults. These validated protocols provide essential conversion factors for precise dietary exposure calculations with broad applicability across rice varieties and cooking methods.