Autolysis kinetics of <I>Litopenaeus vannamei</I> head

Abstract

This investigation studied the effects of temperature,pH and substrate concentration on the autolysis processing of Litopenaeus vannamei head and the change law of the hydrolysate during the autolysis,a kinetic model of the autolysis reaction process was then established. Our purpose was to monitor autolysis course based on the kinetic model,by which we can not only obtain the anticipative molecular weight autolysate,but also increase protein recovery economically and effectively. The study was conducted to investigate the effects of temperature,pH and substrate concentration on the autolysis process of Litopenaeus vannamei head and the change law of the hydrolysate during the autolysis. The rules of the hydrolysate releasing during the first five hours fitted the first order reaction kinetics: Y = 39.496e -0.391 3x ,KP = -1.146 4Y+59.506,Pe = -0.716 7Y+32.551. It showed a good linear relativity between KP,autolysis hydrolysate under 5 000 u and residual protein. In the course of autolysis,the important factors were temperature,pH and substrate concentration which affect shrimp head autolysis rate. During the autolysis,the value of Ka increased with temperature rising from 40 ℃ to 50 ℃ and reached a peak at 50 ℃,while the value of Ka reduced with temperature rising from 50 ℃ to 60 ℃; the effect of pH and substrate concentration on Ka did not show regularity,the value of Ka reaches a peak at pH9 and substrate concentration 1∶3,respectively. We established an Arrhenius equation LnKa = -13 654/T_k + 41.353 and used it to certify the efficacy of the kinetic model. At the beginning of the autolysis(0-1 h),the hydrolysate above 5 000 u took a greater proportion,the percentage was 58%; the percentage of the hydrolysate under 5 000 u increases rapidly during 2-3 h,and was up to 66.8% at 3 h,the increase trend slowed down at 4-5 h,the percentage was 71.47%. In the course of autolysis (0 h-5 h),the release quantity of most of fatty amino acids increased 2-8 times,the content of aspartic acid is 0.13 mg/100mL after autolysis 5 h while its content was 0.017 mg/100 mL before autolysis; the increase content of glutamic acid followed aspartic acid,the content was 0.17 mg/100 mL after autolysis 5 h and the content was 0.041 mg/100 mL before autolysis; while the contents of heterocyclic amino acids—praline,histidine and the amino acids contain the group of sulphur like cysteine,methionine were stable,the contents of cysteine and proline kept at 0.006-0.009 g/100 mL and 0.07-0.09 g/100 mL,respectively. This paper intended to establish a kinetic model to fit the autolysis of Litopenaeus vannamei head.