(492a) A Study of Some Processing Factors On the Production of Gari (A Fermented Product) From Dehydrated Cassava Chips

Cassava, Manihot esculenta (Crantz) is primarily a source of carbohydrate and contains very little fat or protein. The root starts to spoil after 48 h of harvest (due to physiological changes and microbial activity) unless kept under special storage conditions or must be quickly processed. So far there is no economically feasible technique of storing harvested cassava root for long periods on a large scale except in the form of dry chips. The surplus roots during peak harvest could be dried and stored. When supply of fresh root drops below demand the dry chips from storage could be used to meet the shortage. Dehydrated chips are unfermented dried products of cassava. Drying can be done naturally in the sun or artificially in the oven. Chips are used in animal feed production but some studies have investigated its use as human food ? gari and lafun.

Nigeria is the largest producer of cassava in the world with its production currently estimated at about 49 million tons a year. Cassava plays a vital role in the world food security because of its capacity to yield under marginal soil conditions and its tolerance to drought. With improved technologies annual production is going to increase and there is a need to generate from this crop multiple economic benefits through improved post harvest handling and processing. In addition, the cassava crop is undergoing a transition from a mere subsistent crop to a commercial crop that will be grown in large quantities in plantations. Thus, there is a need to expand its utilization base.

Gari is a dehydrated coarse flour consumed raw or cooked. It is traditionally processed by women and can take 3-5 days. Processing involves peeling, washing, grating, fermenting/pressing, pulverizing and frying. There are several variants of gari in the market reflecting local preference in color (from white to yellow), taste (bland to sour) and texture (smooth to very coarse). Although some work had been done on the conversion of dried cassava chips into gari, the processing conditions utilized are quite different from those employed in this study. An earlier study seeded with fresh cassava mash up to 20%, this work seeded with old liquor and the oven drying temperatures were different. The objective of this work was therefore to study the utilization of cassava chips in the production of gari. The effects of different treatments such as drying method (sun or oven drying), soaking (room temperature for 16hrs and or 45oC for 1hr), fermentation (natural or inoculated with old liquor), and fermentation time (3, 5 and 7 days) on percent yield and physico-chemical properties (swelling capacity, HCN content, pH and moisture content of the gari were determined.

Bitter variety (Manihot esculenta Crantz-TMS 30572) of freshly harvested cassava roots (10-12 months old) obtained from the Teaching and Research farm on the University campus, Ile Ife were used. The matured roots had an average length of 10 ± 2cm, diameter 6.5 ± 2cm and moisture content of 67 ± 6%. Manually peeled, washed, tubers were cut into cylindrical discs of 1.0 ± 0.2mm thickness with a dicing machine. Diced samples were spread thinly on a mesh wire and sun dried (32 ± 2oC) for 4 days while some were dried in the oven at 70oC (to moisture content of about 7.3 ± 0.5%). The dried cassava chips were allowed to cool, packaged in polythene bags, sealed and stored in a cupboard and used within 7 days.

Two rehydrating conditions were used: soaking at room temperature for 16hr or at 45oC for 1hr. The rehydrated chips were grated using a laboratory blender to produce a mash. The mash was divided into two portions. A portion was allowed to undergo natural fermentation in a jute sack while the second portion was seeded with liquor from previous fermentation. Fermentation time varied between 3 and 7 days. The fermented mash was dewatered mechanically, sieved manually to remove fiber and then fryed in a cast iron pan over an open fire with constant stirring. Yield of gari was calculated using the expression: Percentage yield = weight of gari x 100 over weight of fresh peeled roots. The swelling capacity of the gari samples was determined at both room temperature and 100oC while the physico-chemical properties (HCN content, pH and moisture content) were assessed using the AOAC methods. The resulting gari products were subjected to organoleptic evaluation using a 12-man panel based on a 9 point hedonic scale (9 ? like extremely and 1 ? dislike extremely). Coded dried gari granules (from chips) were assessed for texture, colour, odour and overall acceptability. Commercial samples were also coded and tested. All tests were carried out in triplicates and results presented as average readings. t-test was used for comparison and ANOVA where necessary using SPSS package.

Oven dried samples lost more moisture (74%) and exhibited faster drying rates (reaching equilibrium moisture content by day 4) than sun dried samples (68%, 7-8 days). Percent residual cyanide content in the chips reduced with drying time but sun dried chips had greater residual cyanide than oven dried chips. Rehydrating the chips at RT for 16hr resulted in samples having lower residual cyanide content compared to those rehydrated at 45oC. The process of fermentation also contributed to the cyanide reduction by 30-50%. pH of the mash reduced from 6.25 at the beginning of fermentation to 4.32 after 3days with minimal reduction thereafter. The pH of the mash from dehydrated chips was similar to that processed from fresh cassava in the traditional method. Swelling capacity of the gari granules increased with steeping time. Steeping temperature was only significant on the swelling capacity in the first 5min of steeping. Beyond this the effect of steeping temperature was mostly negligible but a few samples recorded lower volumes for prolonged steeping time of 15mins. Results indicated that the longer the fermentation time, the lower the swelling capacity of the resulting products. Yield of gari ranged between 23 and 18% dependent on the processing variables. Prolonged fermentation days decreased % yield while samples seeded with old liquor did not have higher yield than naturally fermented samples. The cyanide content of the final products ranged between 1.79 and 2.02 mg/kg) and was not influenced by the processing variables.

Sensory scores showed that gari from chips had scores in texture similar to those processed traditionally. Gari from chips were darker in color and therefore scored low. Samples from sun dried chips generally had higher scores than oven dried samples. Traditionally processed gari was more acceptable in terms of color, but other attributes such as odour and texture were of comparable acceptance to gari from chips. Gari from chips were darker in color.

The study showed that a good yield of gari can be obtained from sundried chips rehydrated at room temperature and allowed to undergo natural fermentation. However, further investigations are needed to improve on product color for optimal acceptance. This result has great economic implications for rural farmers (because cassava can not be stored for long) and for processors who are limited in production capability.

Key words: cassava chips, gari, yield, physicochemical properties, fermentation, sensory attributes, cyanide content.