Effect of thermal treatment on the proteins of amaranth isolates

AVANZA, M.V., AÑÓN, M.C.

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE

Año: 2007 vol. 87 p. 616 - 623

0022-5142

9Abstract: The effect of thermal treatment of proteins from Amaranthus hypochondriacus was studied. Two proteinisolates were obtained from the defatted flour by water extraction at a pH of 9 (A9 isolate) and 11 (A11 isolate),followed by isoelectric precipitation at a pH of 5. Effect of thermal treatment (70 and 90 ◦C, during 3, 5, 10, 15and 30min) on A9 and A11 dispersions were analyzed by differential scanning calorimetry (DSC), polyacrylamidegel electrophoresis, UV spectrophotometry, superficial hydrophobicity and solubility in water. Thermal treatmentinduced the aggregate formation of high molecular mass stabilized by disulfide and non-covalent bond. Thermaltreatment at 70 ◦C produced a 30% denaturation in both, while at 90 ◦C A9 was more denatured than A11 (75%and 55% of denaturation, respectively). An increase in thermal stability was also detected by DSC in A9 treatedat 90 ◦C. The denaturation process was accompanied at short heating times by an increase in UV absorbance andchanges in superficial hydrophobicity. A decrease in water solubility (35–50%, depending on time–temperatureconditions) was also observed for the A9 isolates. The results suggest that the A9 isolates, enriched in a globulinprotein fraction, are more sensitive to thermal treatment than isolates A11 enriched in glutelin protein fraction.The changes shown by both isolates, indeed, could affect their functional properties and could definitely limit theiruse in food products. 2006 Society of Chemical Industry