No abstract

Processing starch into resistant starch has many benefits for human health and the food industry. It has been demonstrated that resistant starch (RS) is not hydrolyzed by the amylase enzyme, so it is not absorbed through the small intestine. This has contributed to significantly reducing energy supply to the body without increasing blood sugar. Therefore, the RS has been considered as an essential nutrient to human, especially for obesity, diabetes, and cardiovascular diseases (Homayouni et al., 2013;Cao et al., 2018). Moreover, RS, used as a staple ingredient in many diets and healthy foods exhibits an excellent dietary fiber with superior properties (Yangilar, 2013;Yang et al., 2020).As a proof of concept, resistant starch is classified into five types, in which resistant dextrin (RD) and resistant maltodextrin (RMD) reside to Type-4 as partly hydrolysed starch (Yangilar, 2013). RMD product such as Fibersol-2 or Nutriose has been commercially produced by two important steps: pyrolysis and enzymatic hydrolysis

The silk fibroin solutions were prepared in solvent system of CaCl2. CH3CH2OH. H2O (mole ratio = 1:2:8) followed dialysis against deionized water. The 3% silk fibroin solutions were irradiated under gamma Co-60 source with dose ranging from 0 to 50 kGy at Hanoi Irradiation Centre and bio-activities of the irradiated silk fibroin solutions were investigated with different radiation doses. The results indicated that the antioxidant and antibacterial activities of fibroin were much improved by gamma irradiation. Maximum value of DPPH radical scavenging activity was 70.4% for the solution of silk fibroin irradiated at 10 kGy. Silk fibroin solutions irradiated at doses higher than 10 kGy also exhibited rather high antibacterial activity against E. coli and S. aureus. In order to estimate the applicability of our irradiated fibroin, the silk fibroin solutions were lyophilized to obtain a pure fibroin powder, then their bio-activities were compared with those of commercial silk fibroin (Proteines De Soie/ Zijdeproteine, Bioflore, Canada). Our fibroin powder revealed higher antioxidant and antibacterial activities. The amino acid compositions of our irradiated fibroin were also higher than that of the commercial product. Thus, the irradiated silk fibroin can be used for further application in cosmetic and other related fields.

Low molecular weight (Mw) xanthan was prepared by gamma Co-60 irradiation at both dry and pastelike states. The viscosity average molecular weight (Mv) of the irradiated xanthan gradually decreased with the increase of the radiation dose. Its Mv slowly reduced to 1.8 × 10 3 kDa from 1.1 × 10 4 kDa of non-irradiated xanthan by irradiation at 500 kGy in the solid state, and quickly reduced to 5.3 × 10 2 kDa by irradiation at 50 kGy in the pastelike state. However, the viscosity of the xanthan is still high enough for utilization as a bio-adhesive polymer. Therefore, the low Mw xanthan prepared by gamma irradiation has been studied as the additive to improve the effectiveness of fertilizer. In this study, foliar fertilizers supplemented with xanthan and irradiated xanthan were applied to maize and soybean seedlings. The results suggested that their developments were much increased by the presence of irradiated xanthan compared to initial xanthan, as indicated by the increases of their plant height, root length and fresh biomass.

The motivation of our research is to examine the mutagenic effect of gamma irradiation on cellulase secretion of some filamentous fungi. The spore suspensions of Aspergillus sp. TTG and Trichoderma sp. VTCC were irradiated at dose ranging 0-2500 Gy under gamma Cobalt-60 source at Ha Noi Irradiation Center. The result showed that the survival rate of fungi decreases with the increasing dose. The radiation dose required to kill 90% of the total number of fungal spores (D10) of these strains was about 400 Gy. The viability of Aspergillus sp. TTG and Trichoderma sp. VTCC at 500 Gy were 0.46 % and 0.78%, respectively, while the number of survival spore decreased by 6.5-7.5 Log unit at the dose of 2500 Gy. By screening in PDA medium with the addition of CMC (carboxymethyl cellulose) and Congo red as an indicator of cellulose degradation, hundreds of colonies with higher hydrolysis capacity’s value (HC) compared to the initial strain were observed after irradiation. The colonies expressed the highest cellulose hydrolysis capacity with maximum HC value were obtained at dose range of 700-1500 Gy. It is important to notice the 5 potential mutants including 3 mutants of Aspergillus (TTG-700, TTG-1000 and TTG-1200) and 2 mutants of Trichoderma (VTCC-1000, VTCC-1500) demonstrated the higher CMCase secretion (1.78 – 2.48 times) compared to the wild types. After 5 generations, the enzyme productions of the mutants were fairly stable and there were no differences in growth rates and morphology of each generation. The result of this study is an evidence for using gamma irradiation to improve cellulase production in filamentous fungi.