VISCOGRAPHIC CHARACTERISTICS OF CHEMICALLY MODIFIED CASSAVA STARCHES ASSESSED BY RVA

Resumo

Cassava starch presents technological properties that make it a special raw material for the food industry. Its mild flavor, free of the undesirable “cereal flavor” of corn starch as well as its viscographic pattern during cooking are some of these valued characteristics. In the present work a viscographic study of cassava starch modified with oxidative treatments was made in order to verify the effects of the modifications on the apparent viscosity of the starches during cooking at different pH values. The samples studied were produced by reaction with 0.1N potassium permanganate and 1% lactic acid (LACW) or citric acid (CITW). After a short reaction period the starches were recovered, washed and oven dried. Other cassava starches were considered for comparison, including native (NAT) and sour (SOUR) ones. Also 1% lactic acid treated samples were produced, one oven dried (LACOVW) and another one sun dried (LACSUNW). The viscographic analysis was made in a Rapid Visco Analyser (RVA), with 2g (DM) of starch and 28g of solvent (de-ionized water, 0.2M acetate and 0.2M phosphate buffers at pHs 4.0, 5.0, 6.0, 6.5 and 7.0). The results showed that the chemically oxidized samples (LACW and CITW) as well as the LACSUNW and the SOUR ones presented a related viscographic pattern when studied at the different pH values. These samples had lower viscosity peaks and cooking stability when analyzed at the higher pH values. In the case of LACW and CITW, there was no detectable viscosity at pH 7.0, because the pastes presented high fluidity. The other samples (NAT and LACOVW) did not present this pattern. Their lower viscosity peaks appeared when cooked in the lower pH, which can beexplained by the degradative effect of acidity on the starch macromolecules.

Key words: cassava starch, RVA, oxidized starch