Jinjie Zhang

Effects of chitosan, aqueous extract of ginger, onion and garlic on quality and shelf life of stewed-pork during refrigerated storage

Effects of 1% or 0.5% chitosan (CHI), 10% or 5% aqueous extract of ginger, onion and garlic (GOG) and their composite solutions (1% CHI+10% GOG, 0.5% CHI+5% GOG) on quality and shelf life of stewed-pork were evaluated. Microbiological (total bacterial count), chemical (pH, total volatile basic nitrogen (TVB-N), peroxide value (POV), 2-thiobarbituric acid (TBA)) and sensory characteristics were analysed periodically during refrigerated storage at 4 °C for 12 days. CHI and/or GOG treatments retarded the increases in pH, TVB-N, POV, TBA and total bacterial count. CHI showed better antibacteria but weaker antioxidation than GOG. Composite treatment had possible synergistic effect while the high concentration of composite solution (Mix1) had adverse effect on odour and overall acceptance. Mix2, the diluted solution of Mix1, could be a natural promising preservative for the stewed-pork considering the comprehensive effects of antioxidation, antibacteria and sensory quality, which could extend the shelf life for about 5-6 days.

Characterization of unusual proanthocyanidins in leaves of bayberry ( Myrica rubra Sieb. et Zucc.).

Extractable and unextractable proanthocyanidins (EPAs and UEPAs) from leaves of bayberry were characterized. Both EPAs and UEPAs were analyzed by acid catalysis in the presence of excess phloroglucinol. The main cleavage product, epigallocatechin-3-O-gallate-(4β→2)-phloroglucinol, was successfully identified. The EPAs were of the prodelphinidin type. In fact, epigallocatechin-3-O-gallate (EGCG) and traces of epigallocatechin (EGC) were detected as the extension units, but only EGCG was present in the terminal units. All of the compounds exhibited a 2,3-cis configuration, and >98% of them were galloylated. The mean degree of polymerization (mDP) of bayberry leaf EPAs was 6.5, and the most abundant EPAs were the polymers, with mDP values of 9.5-26.7. The UEPAs were highly polymerized prodelphinidins consisting of EGCG and traces of EGC. In addition, EGCG, three EPA dimers, and two trimers were identified. The EPAs and UEPAs consisted mostly of EGCG, which is unusual in the plant kingdom.

Effect of three cooking methods on nutrient components and antioxidant capacities of bamboo shoot (Phyllostachys praecox C.D. Chu et C.S. Chao)

Three cooking methods, namely boiling, steaming, and stir-frying for 5 to 10 min, were used to evaluate the effect on nutrient components, free amino acids, l-ascorbic acid, total phenolic contents, and antioxidant capacities of bamboo shoots (Phyllostachys praecox). Results showed that boiling and stir-frying had a great effect on the nutrient components and they decreased the contents of protein, soluble sugar, and ash, and caused a great loss in the total free amino acids (decreased by 38.35% and 34.86%, respectively). Significant differences (P<0.05) in free amino acids were observed in the samples cooked by different methods. Stir-fried bamboo shoots had a high fat content which increased by 528.57% because of the addition of edible oil. After boiling, the L-ascorbic acid and total phenolic contents were significantly reduced, while steaming increased total phenolic content by 3.98% and stir-frying well-preserved L-ascorbic acid (78.87% of its previous content). Results of the antioxidative property study showed that stir-frying could increase antioxidant capacities of bamboo shoots. It is concluded that stir-frying is more suitable for bamboo shoots because it could obtain the maximum retention of antioxidant capacities.

Participation of cathepsin L in modori phenomenon in carp (Cyprinus carpio) surimi gel

Cathepsin L (Cat L) in carp (Cyprinus carpio) dorsal muscles was purified and its molecular weight determined by SDS polyacrylamide gel electrophoresis (SDS-PAGE) was 36 kDa. Its optimal temperature and pH were 50 °C and 5.5, respectively. The results of the effects of specific substrates, activators and inhibitors on the enzymatic activity showed that Cat L belongs to the family of cysteine proteinases containing thiol. Compared to the control, the gel strength of surimi with the addition of purified Cat L decreased significantly by 24.33% while that of surimi with both purified Cat L and inhibitors increased by 13.7% and 21.6%, respectively, suggesting the participation of Cat L in the modori phenomenon occurring in carp surimi. Both the SDS-PAGE electrophoretic pattern and microstructure figure revealed that Cat L could hydrolyse the main protein in carp surimi and was one of the enzymes involved in the modori phenomenon.

Effect of Different Drying Processes on the Protein Degradation and Sensory Quality of Layú: A Chinese Dry-Curing Grass Carp

Five different drying methods, sun drying, intermittent drying, low-temperature drying at 5°C, low-temperature drying at 15°C, and hot-air drying at 45°C, were comparatively evaluated based on physicochemical properties and sensory properties of dry-cured Layú. Sun drying and intermittent drying Layú showed superior sensory qualities compared with other dried samples. Based on the comprehensive comparison of sensory qualities and safety concerns, intermittent drying Layú was more acceptable compared to other dry-cured Layú and thus was recommended for dry-curing fish products as it could shorten the drying time with relative constant drying rate, increased flavor amino acid content, and fewer safety concerns.