| At early stages of kiwi fruit development, the thick peel limits the occurrence of contamination by Penillium spp., however, the peel became thin and soft during ripening, making the fruits more vulnerable to contamination by fungi and patulin. To overcome these challenges, better approaches to patulin control are needed to assure kiwi fruit quality and safety. Biological adsorption, especially yeast adsorbent has recently been considered the most effective strategy for the management of patulin in food industry. However, the process of yeast adsorption is complex, and no specific analysis has been performed to confirm the adsorption mechanism. Thus, further studies on patulin adsorption from the microscopic viewpoint are needed. In this study, twelve yeast strains were investigated, and different patulin adsorption capability strains were selected for adsorption mechanisms study. Furthermore, a new biological safety, easily separation and recovery, core-shell structure magnetic adsorbent was prepared based on yeast cell adsorption behavior simulation. The main research contents and results were as follows:(1) In order to research patulin adsorption capabilities of different yeast strains and evaluate the application value of yeast cells in fruit juice industry, twelve inactivated yeast strains were prepared to research their characteristics, biomass, patulin adsorption capabilities and juice flavor maintenance capabilities. The results showed that the biomass and patulin adsorption capability were strain differences. N-10 strain showed a best performance on biomass and patulin adsorption along the testing strains, while L-3p and B-2p strains were the weakest. Furthermore, yeast cells application research indicated that the quality and flavor of kiwi fruit juice was without any change except color and luster better than before, and the results indicated that yeast cells could adsorb patulin from kiwi fruit juice efficiently.(2) Candida tropicalis N-10 was selected to conduct the adsorptive selectivity assay, using acidic aqueous solution, clear kiwi fruit juice and cloudy kiwi fruit juice as medium solution, the patulin adsorption results showed a nonspecific adsorption on yeast cells. The effects of initial patulin concentration, temperature, incubation time and adsorbent addition were assessed in acidic aqueous solution and clear kiwi fruit juice, the results indicated that with adding yeast cells 500 μg into 10 mL of 200 μg/L patulin acidic aqueous solution for 48 h at 45°C, the maximum patulin adsorption capacity was 3.85 mg/g; with adding yeast cells 150 mg into 10 mL of 200 μg/L patulin kiwi fruit juice for 36 h at 45°C, the maximum patulin adsorption capacity was 11.55 μg/g. After adsorption kinetic and isotherm study, yeast cells adsorption behavior were found following pseudo-first-order reaction kinetics, and equilibrium experiments fit the Langmuir isotherm model. The investigation revealed that patulin adsorption is a spontaneous endothermic physic-sorption behavior.(3) Four different patulin adsorption capability yeast cells(N-10, WLS-38, 7# and B-2p) were selected to investigate the active adsorption sites, their active cells, inactive cells, cell wall damaged cells and cell wall lacked cells were used to conduct patulin adsorption assay, the results indicated that patulin adsorption more likely occurs through surface adsorption than metabolism or enzymatic reaction, cell wall was the main region of patulin adsorption. Cell wall, serving as the first barrier against exposure to patulin, and its composition and physical structure were studied,the results showed that patulin adsorption capability was mainly determined by the insoluble 1,3-β-glucan content, which forms the backbone of the network. The adsorption process could be considered as the embedment of a free patulin into a three-dimensional network structure. The patulin adsorption capability increased with increasing network density.(4) Three different ratio of core and shell components of magnetic chitosan were prepared by simulating yeast cell core-shell structure, the superior magnetic chitosan was selected for further characterization and conduct the patulin adsorption behavior assay based on the adsorbents granular morphologies, adsorbents recoverability and patulin adsorption efficiency. The results revealed that magnetic chitosan with the ratio of Fe3O4 particles to chitosan is 1:1 was the superior patulin adsorbent, it was well coated and nearly superparamagnetic as confirmed by FTIR and magnetic analysis. Patulin adsorption study showed that with adding 100 mg magnetic chitosan into 10 mL 200 μg/L patulin contaminated kiwi fruit juice for 9 h at 35°C, patulin adsorption capability reached the maximum of 19.4 μg/g. Also, its paulin adsorption behavior followed pseudo-second-order process and was fitted well with Langmuir isotherm model.(5) Since magnetic chitosan were potential representatives as patulin adsorbents, their toxic effect should be determined. HepG2 and BGC-823 cells were used to evaluate the cytotoxicity of magnetic chitosan, the results showed that the cell viability still higher than 85% even when the input of magnetic chitosan concentration increasing to 10,000 times of residue amount. Furthermore, acute toxicity evaluation on mice was conducted and the results suggested that the magnetic chitosan was non-cytotoxic, and had no toxic response or histopathological changes on mice. Finally, magnetic chitosan application research indicated that the quality and flavor of kiwi fruit juice was without any change except color and luster better than before. This furnished an excellent paulin adsorbent for its great potential application in juice processing industry. |
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