Chitosan with an initial molecular weight (Mw) of approximately 193 kDa was degraded into about 11.4 and 14.8 kDa by γ-ray irradiation of the solution containing 5% chitosan in 0.2 M acetic acid at 75 kGy and the solution of 5% chitosan in 0.2 M acetic acid supplemented with 1% H 2 O 2 at 10 kGy, respectively. The synergistic degraded chitosan sample with Mw~14.8 kDa was separated into 5 fractions by using ultrafiltration membranes. The analysis results from UV, FTIR, and NMR spectra indicated that the combined treatment of low irradiation dose and low H 2 O 2 concentration did not cause any change in the molecular structure of degraded chitosan fractions. Separated chitosan fractions with Mw > 1 kDa inhibited the growth of Colletotrichum capsici in vitro. While all separated chitosan fractions remarkably enhanced fresh biomass (11-56%) and chlorophyll content (20-92%) of capsicum seedlings. In the field test, the treatment with oligochitosan fractions with Mw in a range of 1-3 kDa (F 2 ) to 3-10 kDa (F 3 ) gained 9.0-11.4% of the fruit yield and reduced 64.8-67.2% of the rate of anthracnose disease outbreak fruits caused by C. capsici. Thus, the F 2 and F 3 fractions in degraded chitosan product are the key fractions for the enhancement of both the growth promotion effect and defense respond activity against the infection of pathogenic Colletotrichum fungi causing anthracnose disease in capsicum.

Gold nanoparticles capped by carboxymethyl chitosan (AuNPs/CM-chitosan) with particle sizes of 5.2–7.3 nm were successfully synthesized by the γ-irradiation of Au3+ solutions. Their characteristics were analysed by transmission electron microscope images, powder X-ray diffraction patterns, UV-visible spectroscopy, and Fourier transform infrared spectra. The antioxidant activity of AuNP/CM-chitosan was time dependent and much higher than that of ascorbic acid at the same concentration. On the other hand, the results of tail vein injection of AuNP/CM-chitosan in mice indicated that this product was not toxic to mice and that AuNPs were mainly distributed in liver tissue, at approximately 77.5%, 6 h after injection. The hepatoprotective activity of AuNP/CM-chitosan was also tested in acetaminophen-induced hepatotoxic mice by oral administration at daily doses of 0.5–2 mg/head. The results indicated that compared to the control, supplementation with 2 mg of AuNPs/head strongly reduced the aspartate aminotransferase and alanine aminotransferase indexes in the blood of the tested mice by approximately 66.5 and 69.3%, respectively. Furthermore, the MTT (3[4,5 dimetylthiazol-2-yl]-2,5-diphenyltetrazol bromide) assay on a liver cancer cell line (HepG2) clearly confirmed strong anticancer activity on HepG2 cells treated with 0.05–0.5 mM AuNPs and the tested cells did not survive after treatment with 0.5 mM AuNPs, while the growth of the normal cell line (L929) has no significant effect at the same treated concentration of AuNPs. The AuNP/CM-chitosan in the present study was synthesized by the γ-irradiation method without using any toxic-reducing chemical and stabilized in a natural biocompatible polymer. The strong antioxidant, hepatoprotective, and anticancer effects of this product may be supported to be used in the biomedical field.

Water-soluble low molecular weight β-glucan (WSLMG) was successfully prepared via γ-irradiation of insoluble β-glucan extracted from brewer’s yeast cell walls. The WSLMG content in an irradiated sample increased as the irradiation dose increased. The WSLMGs with a molecular weight (Mw) of 49, 25, and 11 kDa, obtained at correlative doses of 100, 200, and 300 kGy, respectively, were tested using growth promotion and immune stimulant effects in broilers. Supplementation with 500 ppm WSLMGs not only increased the survival rate (33.3%) and average body weight (40%) but also reduced the feed conversion rate (35.4%) in tested broilers. In addition, WSLMGs enhanced both nonspecific and specific immune components in the blood of supplemented broilers. The WSLMG with Mw ~25 kDa showed the highest effect on the growth performance and immunomodulatory capability in the immune systems of the tested broilers. In conclusion, this product demonstrates substantial promise as an immunostimulant and growth-promoting additive for poultry.