INTAKE OF ESSENTIAL, TOXIC ELEMENTS AND MICROBIAL LOAD OF SOME LOCALLY CONSUMED RICE IN SOUTHEASTERN NIGERIA

Abstract

Proximate composition and mineral profile of locally cultivated and imported rice obtained from Asaba, Onitsha, Afikpo and Abakalilki in Southeastern Nigeria were assayed in the laboratory using standard techniques. The proximate composition and mineral profile of both local and imported rice were compared. Dietary intakes of the nutrients were computed and compare with dietary reference intake for each element. Microbial analyses of the samples were also conducted. Imported rice was generally richer in protein and fat than the locally cultivated rice varieties probably suggesting fortification of foreign rice or varietal differences. Local rice cultivars had higher carbohydrate, fibre and moisture contents than imported rice. Heavy metal levels (notably As, Cd and Pb) were generally significantly (P<0.05) higher in locally cultivated rice than in foreign rice. Cadmium level was significantly higher (P<0.05) in rice obtained from Onitsha (0.15mg/kg) than any of the imported or locally cultivated rice (0 to 0.01mg/kg). The levels of the toxic elements in both rice cultivars are within the recommended daily intake. Levels of nutrients and essential elements such as potassium, phosphorus, copper, iron, selenium, were significantly higher in foreign rice than their local counterparts. Manganese concentration was significantly lower in foreign rice (4.85 to 5.65mg/kg) than in local (6.73 to 7.59mg/kg). No significant difference (P>0.05) was recorded in the concentration of zinc, sodium and calcium in both local and imported rice varieties. Five bacterial species namely, Escherichia coli, Bacillus cereus, Staphylococcus aureus, Streptococcus bacillus, Streptococcus epididermis and three fungi species namely; Aspergillus niger, Aspergillus flavus and Rhizopus were detected in the various rice samples. The foreign rice brands were generally free from bacterial infection except Thailand rice that was infected with Bacillus cereus. However, they all have Rhizopus infestation probably due to heavy load of Rhizopus spores in the environment. Onitsha and Abakaliki rice brand have the highest bacterial loads of 0.65x105cfu/ml and 0.45x105cfu/ml respectively. Onitsha and Mama Africa have 0.70x103sfu/g and 0.56x103sfu/g fungal loads. The microbial abundance of rice sample observed showed that Bacillus cereus had the highest distribution (57.1%) followed by Staphylococcus aureus (42.9%) Streptococcus bacillus and Streptococcus epididermis had the same distribution of occurrence (14.3%).The findings in this study showed that both the locally cultivated rice and imported rice consumed in southeastern Nigeria contain low levels of toxic elements (Cd, As, and Pb). However, estimated daily intake of the essential macronutrient showed that foreign rice is richer in sodium, calcium, potassium and phosphorus. High moisture content of the local rice may probably be responsible for high microbial load.