Zhang Chao-hua

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.

Studies on the fishy odour removal and physicochemical properties of gelatin from Nile tilapia (Oreochromis niloticus) skin.

Nile tilapia (Oreochromis niloticus) aquaculture is expanding throughout the world,most notably in China. According to the statistics of FAO,annual China’s production of tilapia by 2008 had risen to nearly 1.2 million tons,which accounts for about 50% of tilapia production in the world. During processing of tilapia to fillets,large quantities of the by-products such as skin are produced. On one hand,collagen contents in tilapia skins are rich. On the other hand,the bovine spongiform encephalopathy (BSE) episode,as well as religious concerns,has led to intensive research to identify and develop alternatives to mammal-derived gelatin. Therefore,tilapia skin can be a good resource of extracting gelatin. However,gelatin extraction from tilapia skin usually had a strong fishy odour,which would limit its utilization. In order to be applied to food and pharmaceutical industries,some methods must be adopted to make the gelatin odorless. In the present study,methods of active carbon absorption,yeast and lactobacillus fermentation were used to remove fishy odour in the gelatin,in which their roles to diminish fishy odour were compared with each other by sensory analysis. And the effects of active carbon absorption conditions on the transmittance and sensory scores of the gelatin solution were studied by orthogonal experiments. After removing fishy odour,the physicochemical properties of the gelatin were studied and its volatile components were evaluated by simultaneous distillation-extraction (SDE) and gas chromatography-mass spectrometry (GC-MS). Sensory analysis showed that the effects of fishy odour removal of gelatin were significantly different among methods of active carbon absorption,yeast and lactobacillus fermentation (P0.05). Among these methods,the best one was active carbon absorption. The results of orthogonal experiment indicated that the optimal conditions were the ratio of active carbon addition to 5% (w/v) gelatin solution 1.5% (w/v),and incubated at 40 ℃ for 30 min. After removal treatment,fishy odour in the tilapia skin gelatin was barely detectable. The content of crude protein in the gelatin was 91.3% and its gel strength was high up to 301 g. The transmittance of the tilapia skin gelatin solution was higher than before treatment,and the content of water-undissolved matter was diminished. A total of 33 volatile components in tilapia skin gelatin solution before removing fishy odour were detected by simultaneous distillation-extraction (SDE) and gas chromatography-mass spectrometry (GC-MS). The volatile compounds of the gelatin solution were predominantly esters,followed by alcohols,ketones and olefines. After removing fishy odour,a total of volatile components in gelatin solution have been diminished to 26 kinds,which were mainly olefines and ketones. The research shows that active carbon absorption appears as a suitable technique to remove fishy odour in tilapia skin gelatin and to improve their physicochemical properties. So,it can be used for industrial production of fishy odour free tilapia skin gelatin.

Extraction and purification of paralytic shellfish poison from scallop.

HPLC analysis for paralytic shellfish poison (PSP) in shellfish foods has now become a current method in the world,in which PSP standard is necessary. Unfortunately,commercial PSP standard has now become difficult for handling in china,as some purification technique of PSP has not been still breached,and the PSP substance has now been recognized into the list of chemical weapons. Preparing independently some PSP standard is necessary and will be a good way for solving the standard substance problem in china. In this paper,extraction and purification of PSP was discussed,using a poisoned scallop sample as a material. The total toxicity of the crude PSP extract solution was 6 170 MU,while using acid 80% ethanol as an extractant. From the crude extract,PSP was purified via ultrafiltration,Bio-Gel P-2 column chromatography and Bio-Rex 70 column chromatography,and a purified toxin with amount of 2 100 MU was obtained. The result of chromatography showed the toxin mainly contained gonyautoxin group (GTX1-4). HPLC analysis showed that all of the peaks is very sharp and clear,in which the ratio of GTX1,GTX2,GTX3 and GTX4 was 2∶4∶14∶1 (calculated as the ratio of peak area on HPLC),indicating that GTX3 is the major PSP composition in the poisoned scallop sample,and the purified toxin is available using as a standard for HPLC analysis. From the results of experiments,the technique for preparing PSP standard is effective and successful. In the other hand,the stability of the purified toxin was discussed,through comparing the HPLC analysis between the native toxin and that of the one treated with 0.1 mol/L HCl.