Effect of drying lactic fermented uji (an East African sour porridge) on some carboxylic acids Calvin Onyango, 1 * Michael W Okoth 2 and Samuel K Mbugua 2 1 Kenya Industrial Research and Development Institute, PO Box 30650, Nairobi, Kenya 2 Department of Food Technology and Nutrition, College of Agriculture and Veterinary Sciences, University of Nairobi, PO Box 29053, Nairobi, Kenya Abstract: Maize, ®nger millet, cassava, maize±®nger millet and cassava±®nger millet ¯ours were fermented and sun-, cabinet-, or drum-dried. Total titratable acidity (TTA), ®xed acidity (FA), pH and carboxylic acids were determined. The TTA of the non-fermented ¯ours ranged from 0.22%(w/w) lactic acid in cassava to 0.36%(w/w) lactic acid in the maize±®nger millet composite. After fermentation the TTA ranged from 3.26%(w/w) lactic acid in cassava±®nger millet to 4.54% in maize-®nger millet while FA ranged from 2.86% in cassava±®nger millet to 4.26% in cassava and maize±®nger millet. Fermentation decreased the pH from about 5.5 to 3.7±4.1. Drying did not change the pH but TTA decreased by 20±60%. Acetic acid levels in the fermented slurries varied from 0.80 to 0.95 mg per 5 mg while those of hexanoic acid varied from 0.9 to 1.8 mg per 5 mg. Propionic acid was absent in the fermented slurries. Acetic and formic acids were completely lost when the fermented slurries were dried. On average hexanoic acid losses on drying varied from 33% in maize to 91% in cassava fermented slurries. These losses were not signi®cantly in¯uenced by the drying system. In sensory evaluation panellists could not detect ¯avour loss as a result of drying. # 2000 Society of Chemical Industry Keywords: uji; fermentation; drying; carboxylic acids INTRODUCTION Uji, a thin starchy porridge, is usually prepared from suspensions of maize, sorghum, millet or cassava ¯ours and is normally preferably consumed sour after lactic acid fermentation and sweetening immediately after boiling. The product contains 85±90% water and is usually eaten with a spoon. The product is consumed widely in East Africa and there are many ethnic variations to the same basic drink. 1 The most common uji preparations involve mixtures of either maize and sorghum or millet ¯ours, or cassava and sorghum or millet ¯ours. Traditional milling of the cereal grains does not involve dehulling and degermination pro- cesses. Whereas whole milled ¯ours are more nutri- tious because of their high extraction rates they deteriorate quickly and develop a bitter and rancid ¯avour. Also the whole milled ¯ours are coarsely ground resulting in a product with a coarse and gritty mouthfeel. Lactic fermented and dried products based on cereals such as kishk of Egypt, trahanas of Turkey and Greece and gari of Nigeria are on the other hand reported to have keeping qualities in excess of a year without deterioration. 2,3 These products are reported to be non-hygroscopic, are well balanced nutritionally and conserve their natural ¯avour qualities. Lactic fermentation of uji involves mixed cultures such as Lactobacillus plantarum, L fermenti, L buchneri, L cellobiosus, Pediococus acidilactici and P pentocaceus. 4,5 These cultures are involved in the generation of the appropriate uji natural ¯avour compounds; and their characteristic rapid production of lactic acid inhibits the growth of undesirable coliform and pathogenic bacteria. Carboxylic acids contribute signi®cantly to both volatile and non-volatile ¯avour compounds in fer- mented cereal and root crops. 6±9 In all these fermenta- tions lactic acid was the main non-volatile acid while acetic, butyric, pyruvic, succinic, isobutyric and propionic constituted the volatile acids. Other com- pounds that have been identi®ed in fermented cereal and root crop slurries are esters, branched alcohols and aldehydes. 2,8,9 The carboxylic acids lower the pH of the uji slurries to 3.5±4.0 while simultaneously raising the total titratable acidity to 0.6% (w/w) lactic acid equivalent. 5 The carboxylic acids and the general ¯avour pro®le of lactic fermented starchy porridges are bound to be in¯uenced by the microbial pro®le and fermentation conditions such as time, temperature redox potential and moisture content of the fermenta- tion slurry. The drying process of fermented uji is aimed at improving its shelf-life. However drying is bound to contribute to losses of the carboxylic acids due to their different volatilities which in turn can in¯uence the ¯avour pro®le of the dried lactic fermented uji. Andah and Muller 10 and Nout et al 11 reported varying degrees of losses of carboxylic acids on drying (Received 25 April 2000; accepted 31 May 2000) * Correspondence to: Calvin Onyango, Kenya Industrial Research and Development Institute, PO Box 30650, Nairobi, Kenya Contract/grant sponsor: University of Nairobi # 2000 Society of Chemical Industry. J Sci Food Agric 0022±5142/2000/$30.00 1854 Journal of the Science of Food and Agriculture J Sci Food Agric 80:1854±1858 (online: 2000)