Cassava fermentation : cassava sour starch in Latin America

Indigenous food fermentations are one of the oldest forms of biotechnology. Fermented foods play an important role in human nutrition on a global level especially in tropical regions. Indeed effective, well-managed fermentation processes facilitate the conservation of agricultural products without requiring energy inputs, whilst improving the digestibility and nutritional quality of certain foods. Also of importance are the organoleptic characteristics produced in foods as a result of fermentation. Cassava, a widely distributed crop, is an important calorie source for about 500 million people. One of cassava's problems is that certain varieties of the crop naturally contain toxic levels of cyanogenic glucosides. Cassava-consuming peoples have developed fermentation techniques to reduce this toxicity to safe levels. This article first describes a number of different fermented cassava foods, then provides a more detailed analysis of a particular example, that of cassava starch fermentation in Latin America. This fermented starch, known as sour starch, is used in the production of typical cheese breads. Lactic fermentation of cassava starch is essential for the acquisition of its breadmaking capacity. The microbial flora involved and the physicochemical changes undergone in processing are detailed here. This traditional fermentation is still poorly controlled at the farm level. Some cassava processors have improved fermentation by inoculating starch with a starter culture taken from previous fermentations. But this practice still produces sour cassava starch of irregular quality. The present study aims at optimizing cassava starch fermentation and developing starter inocula. These starter cultures will facilitate the standardization of product quality and shorter fermentation time. Amylolytic Lactic Acid Bacteria (ALAB) were isolated from traditionally fermented cassava starch. The genetic diversity of 60 purified isolates was evaluated in terms of starch hydrolysis, metabolism of organic acids and protein profile. A selected strain has been tested as experimental inoculum in a cassava starch production unit. Results are very promising as ALAB 20 gave faster obtention of breadmaking capacity than natural fermentation, although the final breadmaking value was the same. As these starter cultures were isolated in their natural ecosystem, they are sustainable and easy to use at the farm level