Effect of thermal treatment of the proteins of amaranth isolates

AVANZA MARÍA VICTORIA; AÑÓN MARÍA CRISTINA

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE

Año: 2007 vol. 87 p. 616 - 623

0022-5142

Abstract: The effect ofthermal treatment ofproteins from Arnaranthus hypochondriacus was studied. Two protein isolates were obtained from the defatted flour by water extraction at a pH of 9 (A9 isolate) and 11 (All isolate), followed by isoelectric precipitation at a pH of 5. Effect of thermal treatment (70 and 90°C, during 3, 5, 10, 15 and 30min) on A9 and All dispersions were analyzed by differential scanning calorimetry (DSC), polyacrylamide gel electrophoresis, UV spectrophotometry, superficial hydrophobicity and solubility in water. Thermal treatment induced the aggregate formation of high molecular mas s stabilized by disulfide and non-covalent bond. Thermal treatment at 70°C produced a 30% denaturation in both, while at 90°C A9 was more denatured than All (75% and 55% of denaturation, respectively). An increase in therrnal stability was also detected by DSC in A9 treated at 90°C. The denaturation process was accompanied at short heating times by an increase in UV absorbance and changes in superficial hydrophobicity. A decrease in water solubility (35-50%, depending on time-temperature conditions) was also observed for the A9 isolates. The results suggest that the A9 isolates, enriched in a globulin protein fraction, are more sensitive to therrnal treatment than isolates All enriched in glutelin protein fraction. The changes shown by both isolates, indeed, could affect their functional properties and could definitely limit their use in food products.