Concurrent effects of parboiling and milling/hand-pounding on the physical, chemical, and phytochemical properties of six common Bangladeshi rice varieties

This study aimed to evaluate the physical, chemical, and phytochemical properties of six widely consumed rice varieties in Bangladesh namely Gandha, BRRI Dhan84, Bina Dhan17, Bangabandhu Dhan100, Badshah Bhog, and Katari Bhog. The objective was to determine how parboiling and processing methods such as hand-pounding and huller machine milling affect nutritional quality, functional properties, and food safety. Four processing categories were assessed for each variety: hand-pounded parboiled, hand-pounded raw, huller-milled parboiled, and huller-milled raw. Physical analyses showed that parboiling reduced cooking time (12.14-36.29 minutes), while hand-pounded rice had higher swelling capacity (1.43-3.91 g/g). Huller-milled rice required greater force to break (19.6-43.56 N). Chemical analyses indicated that hand-pounding increased protein, fat, and ash content, whereas machine milling raised moisture and carbohydrate levels. Amylose content ranged from 18.53% to 40.52%, with the highest levels in machine-milled raw rice. Thiamine (0.31-3.59 ppm) and mineral retention (iron, manganese, copper, zinc) were greatest in hand-pounded parboiled rice. However, some hand-pounded samples contained heavy metals (chromium, cadmium, lead) above recommended safety limits. Phytochemical analyses revealed that Badshah Bhog had the highest total phenolic content (33.26–315.65 mg GAE/100 g), while Gandha exhibited the highest total flavonoid content (16.53–45.28 mg QE/100 g) and antioxidant activity (13.8%–55.54%). Hand-pounded samples consistently demonstrated superior phytochemical values. In all, no single rice variety or processing method optimizes all nutritional and safety parameters. These findings provide important guidance for consumers and industry in selecting rice based on cooking qualities, nutritional value, and health-related needs.