Xu Jiachao

Effects of ionic crosslinking on physical and mechanical properties of alginate mulching films.

The effect of different ionic crosslinking parameters on the thickness, radiometric profiles, and mechanical and water vapor permeation (WVP) properties of alginate mulching films was investigated. Crosslinking by Mn(2+), Zn(2+), and Ca(2+) (but not Al(3+)) increased the tensile strength and light transmission and decreased the WVP of the films. Among the films, those crosslinked by Ca(2+) had the greatest tensile strength and exhibited the highest elongation and light transmission. Furthermore, the WVP and light transmission decreased gradually with increasing Ca(2+) concentration, and the maximum tensile strength and elongation were obtained for 2% (w/v) of Ca(2+). However, the WVP of the films increased gradually with increasing crosslinking time, and the elongation saturated after 2 min. These results suggest that alginate films crosslinked by 2% (w/v) calcium chloride for 2 min had the best overall performance and therefore have the potential to be used as entirely biodegradable agricultural mulching films.

Purification and characterization of an alkaline protease from Acetes chinensis

An alkaline protease from Acetes chinensis was purified and characterized in this study. The steps of purification include ammonium sulfate precipitation, ion-exchange chromatography with Q-sepharose Fast Flow, gel filtration chromatography with S300 and the second ion-exchange chromatography with Q-sepharose Fast Flow. The protease was isolated and purified, which was present and active on protein substrates (azocasein and casein). The specific protease activity was 17.15 folds and the recovery was 4.67. The molecular weight of the protease was estimated at 23.2 kD by SDS-PAGE. With azocasein as the susbstrate, the optimal temperature was 55°C and the optimal pH value was 5.5. Ion Ca2+ could enhance the proteolytic activity of the protease, while Cu2+, EDTA and PMSF could inhibit its activity.

Changes of muscle tissue and collagen fibers structure of sea cucumber(Stichipus japonicus)during heated treatment

Sea cucumber Stichopus japonicus has become an important cultivated aquatic species in China in recent years.Previous studies mainly focused on the food sources,nutrition values,biological activity and structure of acid polysaccharide.However,these studies do not have a tissue structural consideration on sea cucumber meat.In this paper,the changes of muscle tissue and collagen fibers structure from S.japonicus during heated treatment were studied,and the variation mechanism was analyzed.The structures of muscle tissue and collagen fibers were observed by a light microscope and a scanning microscope,meanwhile DSC tested the denaturation temperature of sea cucumber.Following were the results.The changes of tissuestructure and collagen fibers after heating treatment were evident.Along with the increasing of heating temperature,the muscle fibers gradually aggregated and cross-linked,forming porous mesh structure.The collagen fiber structure shrunk,accompanied with collagen protein denaturation leading to fibers closely spaced.The changes of collagen fibers structure were more prominent compared with the overall tissue structure.DSC scanning curve of raw S.japonicus meat showed the denaturation temperature was 68.92 ℃.Thermal denaturation of muscle protein during heating treatment resulted in the changes of tissue structure and collagen fibers.

Freshness and texture changes of Lateolabrax japonicus meat during partially frozen storage.

The quality and texture changes of Lateolabrax japonicus meat during partially frozen storage were studied.Tissue structures,texture profile analysis and changes of rheological properties( elastic modulus E0, stress-relaxation time τ1,viscosity η1,rupture strength) ,combined with the total number of bacteria,K value, TVB-N,pH value and sensory scores were determined.The results suggested that the total number of bacteria, K value and TVB-N increased with the extension of storage time,while pH value decreased and then increased.The increasing speed increased with temperature.As the storage time extended,the pores of the myofibril increased,the tissue structure deteriorated,elastic modulus E0 increased,and rupture strength,hardness, springiness,cohesiveness and chewiness decreased,while viscosity η1 and stress-relaxation time τ1 have no significant changes.Compared with that of the refrigerated samples,the shelf-life of partially frozen storage samples could be extended for 20 days.It showed partial freezing could effectively inhibit the activity of enzymes in the meat of Lateolabrax japonicus and the effect of micro-organisms,so that it could alleviate the decomposition of protein.As a result,partial freezing storage is an effective method to extend the storage time of Lateolabrax japonicus.

The hydrolyzation of collagen by fucoidan oligosaccharide’s complex with CeIV

Fucoidan is such a polysaccharide that its hydroxies are easy to combine with lanthanons ion (CeIV) to form complex. This work obtained the complexes of three fucoidan oligosaccharides with different molecular weights F1 (>5000), F2 (1000–5000) and F3 (<1000) by hydrolyzing Oligosaccharide collagen with sulfuric acid. It is found that the fucoidan oligosaccharide F3 can form complex with more CeIV than F1 and F2. Hydrolyzing collagen with the complex was carried out to produce amino acid and peptides. All the three fucoidan oligosaccharide complexes with CeIV (F1, F2, F3) can catalyze by the artificial hydrolytic enzyme, and the activity of the complex of F3 is the highest.