RICE PROCESSING METHODS IN NORTHEASTERN NIGERIA: EFFECTS ON NUTRIENTS, PHYTOCHEMICALS AND EATING QUALITY AND PERCEPTIONS

Abstract

This study examined the effects of parboiling and milling on the physical properties, mineral composition, antioxidant and phytochemical profiles, and sensory quality of rice processed in Northeastern Nigeria. Paddy rice from 12 processing sources was evaluated as parboiled and raw rice, with corresponding milled products analysed using standard procedures. Physical properties, minerals (calcium, iron, magnesium, potassium and sodium), antioxidants and phytochemicals, including anthocyanins, phenolic acids, flavonoids, tocopherols, total phenols, oxalates, phytic acid and tannins, were determined. Eating quality was assessed using a 9-point hedonic scale, and data were analysed using ANOVA and Tukey's test at 5% probability. Parboiling improved grain structural integrity, with parboiled milled rice recording bulk densities of 0.80–0.82 g/cm³ and seed weights of 23.00–25.27 g/100 grains, compared with 0.83–0.84 g/cm³ and 22.37–25.37 g/100 grains, respectively, for raw milled rice. Parboiled paddy showed higher mineral retention, with iron reaching 16.84 mg/100 g, magnesium 277.95 mg/100 g, potassium 665.40 mg/100 g, and calcium 296.66 mg/100 g. In milled rice, iron reached 12.01 mg/100 g and potassium 613.97 mg/100 g. Antioxidant concentrations were also higher in parboiled samples, with phenolic acids reaching 462.19 mg/kg in paddy and 410.16 mg/kg in milled rice, while flavonoids reached 190.24 and 163.36 mg/kg, respectively. Parboiled milled rice generally recorded higher sensory scores for appearance, taste, texture, aroma and overall acceptability, although the reported Tukey test indicated no significant differences among sensory means at P < 0.05. Overall, controlled parboiling before milling improved grain integrity and enhanced mineral and antioxidant phytochemical retention while maintaining favourable eating quality. Standardized parboiling, controlled drying and moderate milling are recommended to improve the nutritional and market quality of locally processed rice in Northeastern Nigeria.