Shengjun Wu

Using pullulan-based edible coatings to extend shelf-life of fresh-cut ‘Fuji’ apples

Pullulan is a thickener that can form semipermeable films, and glutathione is an effective reducing agent, while chitooligosaccharide has antibacterial activity. In this study, effect of pullulan-based coatings in combination with antibrowning and antibacterial agents (1% pullulan; 0.8% glutathione+1% chitooligosaccharides; and 0.8% glutathione+1% chitooligosaccharides+1% pullulan) on apple slices was investigated during hypothermia storage. Pullulan-coating treatments effectively retarded enzymatic browning, maintained firmness, decreased weight loss, and inhibited microbial growth and respiration rate of apple slices during hypothermia storage compared with that of the control (p<0.05). Results indicate that using pullulan-based coatings in combination with glutathione and chitooligosaccharides is a promising way to extend the shelf-life of apple slices.

Antioxidant activity and antibacterial activity of peach gum derived oligosaccharides.

In this study, peach gum derived oligosaccharides (PGDO) were prepared from peach gum polysaccharides by hydrolysis using hydrogen peroxide (H2O2) under following conditions: time, 8h; temperature, 55 °C; H2O2 concentration, 4% (v/v); and NaOH concentration, 2.0 M. The antioxidant activity and antibacterial activity of PGDO were estimated. There were no significant chemical changes in the backbones of the peach gum polysaccharides treated with H2O2. The PGDO showed high hydroxyl radical scavenging activity (86.12%) and 2, 2-diphenyl-β-picrylhydrazyl radical scavenging activity (91.70%) at the concentration of 100 μg/mL as well as high reducing capacity at the concentration of 50 μg/mL. In addition the PGDO had high antibacterial activity against Bacillus subtilis, Staphylococcus aureus, and Escherichia coli at the concentration of 100 μg/mL.

Effect of chitosan-based edible coating on preservation of white shrimp during partially frozen storage

Chitosan and chitooligosaccharides are preservatives with proven antibacterial activity, while glutathione has antioxidant activity. This study investigated the effects of chitosan coating combined with chitooligosaccharides and glutathione (0.8% glutathione+1% chitooligosaccharides+1% chitosan) on preservation of white shrimp (Penaeus vannamei) during partially frozen storage. Chitosan-based coating treatments effectively inhibited bacterial growth, reduced total volatile basic nitrogen and malondialdehyde, and basically maintained the sensory properties of white shrimp (P. vannamei) during partially frozen storage. Therefore, chitosan-based edible coating combined with chitooligosaccharides and glutathione could be a promising antimicrobial and oxidant method to prevent metamorphism of white shrimp with extended shelf life.

Preparation of peach gum polysaccharides using hydrogen peroxide.

Most polysaccharides cannot dissolve in water but can be hydrolysed using hydrogen peroxide (H2O2) to yield a water-soluble product. This study presents a method of preparing water-soluble polysaccharides from peach gum by hydrolysis using H2O2. Extraction was monitored by the recovery rate. Factors affecting the hydrolysis of peach gum were investigated, and the optimum hydrolysis conditions were determined as follows: time, 8 h; temperature, 55°C; H2O2 concentration, 4% (v/v); and NaOH concentration, 2.0 M. The hydrolysates were filtered, neutralised with HCl, concentrated to ∼20% (w/v), precipitated with 5 volumes of ethanol, freeze-dried, and ground to yield a water soluble and white powder. The polysaccharide content of the product was 97.8%, and the yield was 83.6% (w/w).

Preparation of water soluble chitosan by hydrolysis using hydrogen peroxide.

Chitosan is not soluble in water, which limits its wide application particularly in the medicine and food industry. In the present study, water soluble chitosan (WSC) was prepared by hydrolyzing chitosan using hydrogen peroxide under the catalysis of phosphotungstic acid in homogeneous phase. Factors affecting hydrolysis were investigated and the optimal hydrolysis conditions were determined. The WSC structure was characterized by Fourier transform infrared spectroscopy. The resulting products were composed of chitooligosaccharides of DP 2-9. The WSC content of the product and the yield were 94.7% and 92.3% (w/w), respectively. The results indicate that WSC can be effectively prepared by hydrolysis of chitosan using hydrogen peroxide under the catalysis of phosphotungstic acid.

Preparation of oligosaccharides from Chinese yam and their antioxidant activity

In the present study, the oligosaccharides from Chinese yam were prepared by hydrolysis with hydrogen peroxide (H2O2), which can cleave the glycosidic bonds in polysaccharides. The hydrolysis conditions were optimised by using a central composite design (CCD) as follows: reaction time 4.02 h, temperature 84.35 °C, and H2O2 concentration 2.46%, under which the yield of Chinese yam derived oligosaccharides (CYOs) reached 11.73%, which was consistent with the predicted yield by analysis of the results of CCD (11.89%). The CYOs products were partially characterised by chemical component and Fourier transform infrared spectrum. The CYOs scavenged hydroxyl radical by 89.05% at the concentration of 100 μg/mL, indicating that the CYOs may be a viable option for use as a food antioxidant.

Cellulase-assisted extraction and antioxidant activity of the polysaccharides from garlic

In the present study, the polysaccharides were prepared from garlic by using a cellulase-assisted extraction method and the antioxidant activity of garlic polysaccharides (GPs) was evaluated. To improve the yield of GPs, the influences of the several factors such as extraction time, temperature, pH, and cellulase amount on the extraction efficiency were studied. The optimal conditions for extraction of GPs were determined as follows: time, 80 min; temperature, 45 °C; pH, 5; cellulase amount, 8000 U/g. Under the optimised extraction conditions, the yield of GPS reached up to 35.34%. The GPs product exhibited strong antioxidant activity including hydroxyl radical scavenging activity, 2,2-diphenyl-β-picrylhydrazyl radical scavenging activity, and reducing power. The results suggest that the GPs could be used as potential antioxidants.

Preparation of chitooligosaccharides from Clanis bilineata larvae skin and their antibacterial activity

Clanis bilineata larvae are widely consumed in China. In this study, chitooligosaccharides were prepared from C. bilineata larvae skin by demineralisation, deproteination, washing, drying, deacetylation, hydrolysis using commercial α-amylase, filtration, setting the preparation at approximately 15% (w/v), precipitation with 6 volumes of ethanol, and drying at 60°C for 2 h. The optimal hydrolysis conditions were determined as follows: pH 5.5; temperature, 55°C; enzyme amount, 40 mg/(g chitosan); reaction time, 4 h. The Fourier transform infrared spectra revealed that chitooligosaccharides with a degree of polymerisation in the range of 2-8 were the main component of the resulting product, with the chitooligosaccharide content and yield being 95.8% and 96.2% (w/w), respectively. The resulting product showed high antibacterial activity compared with the original chitosan.

Effect of trehalose on Lateolabrax japonicus myofibrillar protein during frozen storage

The effect of trehalose on the denaturation of weever (Lateolabrax japonicus) myofibrillar protein during frozen storage at -18 °C for 90 d was investigated. Trehalose (2.5-10 g dry weight) was added to 100 g of myofibrillar protein, and changes in the Ca(2+)-adenylpyrophosphatase (ATPase) activity, solubility, sulfhydryl content, and unfrozen water content of myofibrils were examined during frozen storage. Ca(2+)-ATPase activity and myofibrillar protein solubility decreased gradually during frozen storage at -18 °C upon addition of trehalose. By contrast, Ca(2+)-ATPase activity and myofibrillar protein solubility in the control group dropped drastically during the first 45 d of storage and then further decreased gradually for up to 90 d of storage, indicating a biphasic denaturation pattern. Trehalose addition significantly increased sulfhydryl and unfrozen water contents in the myofibrillar protein of the treatment groups compared with that of the control group (p<0.05) during frozen storage at -18 °C.

Preparation and antioxidant activity of the oligosaccharides derived from Laminaria japonica

Hydrogen peroxide (H2O2) can degrade polysaccharides and has bleaching effect. In this study, the oligosaccharides derived from Laminaria japonica were prepared by hydrolysis with H2O2 and their antioxidant activity was investigated. The optimal hydrolysis conditions were determined as follows: reaction time 24h, reaction temperature 75°C, and H2O2 concentration 4%. Under the optimum conditions, the maximum yield of the oligosaccharides reached 17.65%, which was higher than that of aqueous extraction, and at the same time, the maximal decoloration rate reached 79.85%. The oligosaccharides sample contained 94.82% sugar, of which the average degree was approximately 8, and showed light green. The oligosaccharides derived from L. japonica showed high hydroxyl radical scavenging activity (91.31%) at the concentration of 100 μg/mL.