Abstract

Light transmittance (%T) studies were carried out at 650 nm in several types of starch-based media such as natural tropical and non tropical starch pastes and simplified model media. With natural starch pastes (1% db), the clarity ranged from 8%T (ginger starch) to 79%T (potato starch), with intermediate values for cassava starch (47%T) and waxy maize (35%T). These values depended mainly on the spectrophotometer type, starch concentration, treatment temperature and storage time. In simplified media (treatment at 150°C, acid hydrolysis and DMSO solubilization), all paste (1% db) transmittances were improved and the maximum dispersion (using DMSO) was the main factor influencing the transmittance. In effect, the average values were classified as following: 79.5%T (DMSO) > 64.7%T (HCl 2.2 N hydrolysis) » 54.7%T (heating at 150°C) > 22.8%T (control). Thus, a model was proposed to explain that in a dilute and purified starch paste, the quasi totality of incident light passing through the media was transmitted, which made the medium clear.

Key words: Paste clarity, light transmittance, model, solute, tropical starch.