Starch Gelatinization as Affected by Lipid

Gelatinization of untreated and defatted corn starch as affected by added elaidinized and non-elaidinized olive oil was investigated. The experimental plan was a 2 x 3 factorial, which included no added lipid as well as elaidinized and non-elaidinized olive oil. The added lipids were used at the level of 6 mg per gram of starch in pastes containing 8 g of starch per 100 ml of liquid. Seven replications were completed. Suspensions were heated in the Brabender Amylograph from 25°C to 92.5°C (45 min) and held at 92.5°C for 15 min. Data taken from each amylogram included: the transition temperature, the temperature of maximum viscosity, viscosity after 45 min of heating and terminal viscosity. Photomicrographs were made of samples of each paste taken before heating and at several stages during heating. Pastes were poured while hot into custard cups and held at room temperature for 24 hr. Penetrability measurements were made on the gels. Viscosity and penetrability data, as well as transition temperature, were subjected to analysis of variance.

Defatting the corn starch resulted in reduced transition temperature (P < 0.01), reduced maximum viscosity (P < 0.01), essentially unaffected terminal viscosity and increased gel strength (P < 0.01). The photomicrographs indicate that possibly the granules of defatted starch swelled more freely and rapidly and showed more implosion that the granules of untreated starch. The greater implosion could explain both lower maximum viscosity and higher gel strength of samples containing defatted starch. The effect of added lipid was limited to increased gel strength and only in the case of untreated starch. The photomicrographs show a possible protective effect of lipid on the granules so that in the presence of lipid, granules were permitted to implode sufficiently but not too extensively and fragmentation did not occur during the holding period. The interaction between starch treatment and lipid was significant (P < 0.01). No clear-cut differences were found between elaidinized and non-elaidinized lipid. Possibly future work should involve the addition of higher concentrations of lipid than used in this study.