Quality and safety of sun-dried cassava chips and flour in Kenyan markets and tent solar dried cassava chips

Abstract

Cassava is rich in carbohydrates and is the third most important source of calories in the tropics. However, it poses food safety risks to the consumers due to naturally occurring cyanogenic glucosides and the handling and processing practices employed which may expose it to microbial contamination. This study aimed at determination of the levels of microbiological contamination, cyanide and mycotoxin levels of cassava chips and flour in Coastal (Mombasa) and Nairobi markets and assessment of tent solar drying and size of chips on safety and quality of cassava chips. A comprehensive survey of cassava flour and dried cassava chips in markets in the study sites was carried out and subjected to experimental analysis methods to determine levels of microbial contamination (total viable count, staphylococcus aureus, yeast and mould, total coliforms and E. coli) and chemical (hydrogen cyanide, aflatoxin contamination) and physical analysis (colour). A tent solar drier was also fabricated and used for drying raw cassava and the progress recorded with the dried cassava chips being finally analysed for hydrogen cyanide, moisture content and colour. Thirty six samples of cassava products from Nairobi and Mombasa markets were evaluated; one sample tested positive for E. coli, 87% of cassava flour and 77% of cassava chips samples tested positive for Staphylococcus aureus. The HCN in both the dried cassava chips and cassava flour had levels that were above 10 mg/kg while moisture content was below 12%. Dried cassava chips sold in the markets had low L* values hence less white; with the flours having high L* values indicating very white flours. Three cultivars of cassava (Fumba chai, MH95/0183, MM96/2480) from KALRO-Kakamega farm, were peeled and chopped into 3 thicknesses; 1, 3 and 5 mm. The percentage loss in HCN ranged from 20.2% to 50.1% but the residual HCN was higher than 10 mg/kg. The final MC was below 12% with high L* values hence predominantly white in colour. The 5 mm thick cassava chips exhibited the highest percentage loss of HCN and moisture. This study intimates that the flour in the market may be of good aesthetic quality but unsafe for consumption due to high level of microbial contamination and high residual HCN; also that the tent solar dried cassava chips were good quality: with low moisture content levels and white in colour, but had high residual HCN). It is recommended that farmers and processors are trained on good hygienic practices, adoption of best practices in processing, soaking and washing of cassava raw cassava tubers after chipping and prior to drying. The 5 mm thick chips are recommended on the basis of high moisture as well as high HCN loss.