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I. VAN DER PLANCKEN, Laboratory for Food Technology, Katholieke Univ. Leuven, Dept. of Food and Microbial Technology, 22 Kasteelpark Arenberg, Heverlee, B-3001, Belgium, I. Indrawati, Laboratory for Food Technology, Katholieke Univ. Leuven, Dept. of Food and Microbial Technology, 22 Kasteelpark Arenberg, Heverlee, B-3001, Belgium, A. Van Loey, Laboratory of Food Technology, Katholieke Univ. Leuven, Dept. of Food and Microbial Technology, 22 Kasteelpark Arenberg, Heverlee, B-3001, Belgium, and M. Hendrickx, Laboratory for Food Technology, Katholieke Univ. Leuven, Dept. of Food and Microbial Technology, 22 Kasteelpark Arenberg, Heverlee, B-3001, Belgium. Chicken egg white is extensively used in the food industry, mainly because of its excellent functional properties and nutritional quality. Ovalbumin, the major protein in chicken egg white, in its native form has a low susceptibility to hydrolysis by trypsin and a-chymotrypsin. Ovomucoid is a heat-stable inhibitor of trypsin activity. Our objective was to establish a kinetic model to describe the effect of temperature and pressure on the susceptibility to enzymatic hydrolysis and trypsin inhibition activity of egg white proteins. High-pressure treatment (100-700MPa, 10 to 60° C) was performed in a laboratory scale multivessel high-pressure equipment. The susceptibility to enzymatic hydrolysis was determined using a pH-stat method. A mixture of trypsin and chymotrypsin was used to hydrolyze the pressure pre-treated egg white solutions. The trypsin inhibition activity was determined using N-a-benzoyl-L-arginine-ethyl-ester as a substrate for trypsin. Pressure pre-treatment resulted in an increase of the susceptibility of the egg white proteins to trypsin and chymotrypsin. At lower temperatures, the increase occurred at lower pressures, indicating an antagonistic effect between pressure and temperature. The time-dependent increase in hydrolyzability could accurately be described by a first-order fractional conversion model. The pressure-dependence of the rate constants could be described by the Eyring equation, while the temperature-dependence followed the Arrhenius model. A negative apparent activation energy was obtained, confirming the antagonistic effect between pressure and temperature. Ovomucoid is a rather pressure-stable protein, as pressure treatments of 20 min at 700MPa resulted in less than 10% loss of trypsin inhibition activity at low temperature. At 60° C however, this activity could be reduced to 50% with the same treatment. From a processing point of view, for increasing the hydrolyzability of egg white proteins working at low temperature is interesting as lower pressures are needed and the increase is faster. Little inactivation of ovomucoid occurs at high pressure.
Session 34, Nonthermal Processing: General I
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |