Ji Hongwu

裂殖壶菌 Schizochytrium sp. 20888产DHA培养条件优化

目的为了优化裂殖壶菌产DHA的培养条件，提高油脂中DHA含量。 方法采用单因素试验和正交设计试验方案，针对分批培养时间、培养基碳、氮源的种类和浓度以及培养温度开展试验，采用重量法测定生物量、采用索氏提取法测定油脂总量，采用气相色谱法测定油脂DHA含量，考察培养条件对细胞油脂DHA含量的影响。 结果最适培养时间为4 d，培养温度23 °C，最优碳氮源组成为(g/L)：葡萄糖65、甘油80、蛋白胨6、酵母粉4和谷氨酸钠8。 结论裂殖壶菌Schizochytrium sp. 20888在葡萄糖和甘油组成的复合碳源和由蛋白胨、酵母粉和谷氨酸钠组成的复合氮源的培养基中可以得到最优的DHA产量，细胞DHA含量能达到33.68%。

Isolation and identification of ACE inhibitory peptides from the autolysis product of shrimp head(Litopenaeus vannamei)

Shrimp head is susceptible to autolysis under certain conditions,the protein in it is degraded into soluble protein,peptides and amino acids,and some peptides are active peptides which can inhibit the ACE enzyme activity.At present,many ACE inhibitory peptides derived from food protein have been developed.In the present study,two ACE inhibitory peptides(Tyr-Pro and Leu-Pro/Ile-Pro)were highly purified from the shrimp head(Litopenaeus vannamei)autolysate by extra fine membrane and a series of column chromatographies.In the first autolysis solution of shrimp head was consecutively extracted through extra fine membrane with molecular weight cut-offs(MWCO)at 8,5,3 ku,respectively.The active results shown that filtrate through MWCO at 3 000 u had the highest ACE inhibitory activity.The crude filtrate through MWCO at 3 ku was purified by Sephadex G-25 gel chromatography,SP Sephadex C-25 anion-exchange chromatography as well as Sephadex G-15 gel chromatography,respectively.After that,the ACE inhibitory activity of purified filtrate almost increased by 8 times(IC50=0.19 mg/mL)that of crude filtrate.The high active collected fraction from Sephadex G-15 gel chromatography was carried out by RP-HPLC(High-Performance Liquid Chromatography)twice for the further purification and two kinds of dipeptide were obtained,and the identification of dipeptide by mass spectra showed that they were Tyr-Pro and Leu-Pro/Ile-Pro,and the molecular weight was 279 u and 229 u,respectively.

Autolysis kinetics of Litopenaeus vannamei head.

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.