A comparative study of the characteristics of cross-linked, oxidized and dual-modified rice starches.

Rice starch was cross-linked with epichlorohydrin (0.3%, w/w, on a dry starch basis) and oxidized with sodium hypochlorite (2.5% w/w), respectively. Two dual-modified rice starch samples (oxidized cross-linked rice starch and cross-linked oxidized rice starch) were obtained by the oxidation of cross-linked rice starch and the cross-linking of oxidized rice starch at the same level of reagents. The physicochemical properties of native rice starch, cross-linked rice starch and oxidized rice starch were also studied parallel with those of the two dual-modified rice starch samples using rapid visco analysis (RVA), differential scanning calorimetry (DSC), dynamic rheometry and scanning electron microscopy (SEM). It was found that the levels of cross-linking and oxidation used in this study did not cause any significant changes in the morphology of rice starch granules. Cross-linked oxidized starch showed lower swelling power (SP) and solubility, and higher paste clarity in comparison with native starch. Cross-linked oxidized rice starch also had the lowest tendency of retrogradation and highest ability to resistant to shear compared with native, cross-linked, oxidized and oxidized cross-linked rice starches. These results suggest that the undesirable properties in native, cross-linked and oxidized rice starch samples could be overcome through dual-modification.

Preparation of chitosan oligomers COS and their effect on the retrogradation of intermediate amylose rice starch.

Chitosan oligomers (COS) were obtained by enzymatic hydrolysis and H2O2 oxidative treatment, and then separated into different fractions using ultra-filtration membranes. Each COSM fraction prepared using enzymatic hydrolysis retained its structure, especially the reduced end residue (-NH2 group), and had a peak for molecular weight. On the other hand, each COSH fraction prepared by oxidative treatment had partly damaged -NH2 groups and two peaks for molecular weight. These results indicate that the same COS fractions prepared by the two methods differ in their amino groups and in their molecular weights, though they can both pass through the same size ultra-filtration membrane. The effect of COS on the retrogradation of intermediate amylose rice starch (IA-RS) was also investigated. The 5 k < COSM < 10 k fraction had the best anti-retrogradation ability; the retrogradation ratio of IA-RS with this fraction was reduced by 14.5%, compared to the control, and its relative crystallinity was only 59.69%. 10 k < COSM < 30 k fraction was second best, while the COSM < 5 k fraction had no effect. Therefore, the molecular size of COS determined its anti-retrogradation capability. All COSH fractions from oxidative treatment had no effect on the retrogradation.

Stimulated production of triterpenoids of Ganoderma lucidum by an ether extract from the medicinal insect, Catharsius molossus, and identification of the key stimulating active components.

The medicinal fungus Ganoderma lucidum was inoculated into the media with and without supplementation of medicinal insect extracts to screen stimulators from Chinese medicinal insects for mycelial growth and triterpenoids production in submerged fermentation. The methanol and ether extracts of the tested insects had no significant stimulatory effect on the mycelial biomass production (P > 0.05), and those of H. remigator and Mylabris phalerata markedly inhibited the mycelial growth. However, the ether extract of Catharsius molossus at a concentration of 200 mg l(-1) led to a significant increase in triterpenoids concentration from 231.7 ± 9.77 to 313.7 ± 10.6 mg l(-1) (P < 0.01). Analysis of fermentation kinetics of G. lucidum suggests that glucose concentration in the extract of C. molossus-added group decreased more quickly as compared to the control group from day 2 to day 7 of fermentation process, while the triterpenoids biosynthesis was promoted at the same culture period. However, the culture pH profile was not affected by the addition of the extract. Chemical study of the extract show that cis-9,10-methylenehexadecanoic acid (9,10-MEA) and hexadecanoic acid (especially 9,10-MEA) were the key active compounds of the extract responsible for the stimulatory effect on the triterpenoids production.