Preparation And Inhibitory Effects On PPO And Some Microbe Of Polyoxometalates

Fruit and vegetables are not only a kind of indesipencable food in daily life, but also important processing raw materials in food industry. Although the yield of Chinese fruit and vegetables is the first in the world, the loss rate is up to 25%-30% per year due to imperfect technique in fresh-keeping of fruits and vegetables. Existing freshing-keeping agents for fruit and vegetables have numerous problems, such as drug residue, resistance of pathogenic microorganism. Polyoxometalates (POMs) has gained common recognition in fields of catalysis, medicinal chemistry and biochemistry, but has not been paid enough attention in fresh-keeping of fruit and vegetables. This paper investigated inhibition effects of polyoxometalates on pathogenic microorganism and polyphenol oxodase in order to broaden the application field of polyoxometalates and develop a high effective and low toxic fresh-keeping agent of fruit and vegetables. The research contents are summarizd as follows:(1) The inhibition effects on pathogenic microorganism Escherichia coli, Bacillus subtilis, yeast and Aspergillus niger by three polyoxometalates with diffrecent percentage of vanadium were investigated by disk diffusion method. The results showed that three polyoxometalates produce bacteriostatic effects on above-mentioned microorganism, the best inhibition effects belong toα-PW₁₁V. And the inhibition effects of polyoxometalates are stable with changed temperatue.(2) Four polyoxometalates with different substituted atom number (α-SiW₉V₃,α-SiW₁₀V₂,α-SiW₁₁V, SiW₁₂) against commom bateria (Escherichia coli, Bacillus subtilis, yeast, Aspergillus niger and Penicillium) was studied by disk diffusion method. The results suggest four polyoxometalates have obvious inhibition effects on all the bateria except Penicillium; and the optimal baterial inhibitor is SiW₁₂; the inhibition effects ofα-SiW₁₁V andα-SiW₉V₃ exhibit higher thanα-SiW₁₁V, but both of their effects are no distinct difference. Changes in temperature have not really effective on the compounds.(3) Owing to the value of central atom affecting the properties of polyoxometalates, the inhibition effects of three polyoxometalates PW₁₂(+5), SiW₁₂(+4), BW₁₂(+3) on bacteria were studied by disk diffusion method. The inhibition effects on Escherichia coli and yeast varied regularly as the change of value of central atom under 28℃, the other experimental conditions do not display regularity.(4) The inhibition effects of Na₃PW₁₂O₄₀ on polyphenol oxodase were discussed, with L-DOPA as reaction substrate. The results illustrated that Na₃PW₁₂O₄₀ is a noncompetitive inhititor, and LD₅₀ is 1.68mmol/L. Simple practical experiment selected the excellent fresh-keeping agent is H₃PW₁₂O₄₀·xH₂O. Application of Polyoxometalates in fresh-keeping of fruit and vegetables has board prospect, owing to their inhibition effects on bacteria and polyphnel oxodase.