Application of residual cyanide concentrations level in processed cassava (Manihot esculenta) to inhibit the growth of spoilage microorganisms in cooked rice (Orysa sativa)

Abstract

Rice (Orysa sativa) is a staple food for human population, providing more than one fifth of the total energy calories consumed worldwide by humans. The shelf life of rice grains when harvested raw milled or unmilled is long. But when it is cooked, it barely lasts for 24hours in storage. The spoilage of rice is due to the presence of different microorganisms such as Bacillus spp and Yeast (Saccharomyces cerevisiae). Cassava has a high cyanide content and it does not get spoilt easily when cooked. In the processing of cassava, there are several methods of fermentation, sun drying, and frying employed to process it to powdery forms ‘Gaari’ and ‘lafun’ and the porridge ‘fufu’ leading to a great reduction in the cyanide contents. The three processed cassava Gaari, Lafun and fufu were obtained from a local market in Akure, Nigeria. Cyanide concentrations before and after cooking these products from (Day 1 to Day 5) were obtained. The cyanide contents equivalents after cooking were prepared and tested for inhibitory effect on spoilage microorganisms isolated from cooked rice. The objectives of this study are to determine the cyanide concentrations in processed cassava (Manihot esculenta) that can inhibit spoilage microorganisms and investigate if the concentration can be added to preserve cooked rice from spoilage. Results obtained showed that Fufu, Gaari and Lafun have residual cyanide contents of 19.63, 10.14 and 7.02mg/kg respectively before cooking and which decreased to 14.94, 4.98 and 4.29mg/kg in day5 after coking. There were no significant correlations between the residual cyanide contents in the cassava products before and after cooking (Sig = 0.947 df =14 p > 0.01). There was a significant inhibitory effect of cyanide concentrations (F_4,20 = 5.307, Sig =0.004 p = 0 < 0.05) on the growth of Saccharomyces cerevisiae, secondary spoilage microorganisms of cooked rice. Cyanide is effective in controlling spoilage microorganisms in rice