Study On Solid-state Fermentation Of Polypeptides And Preparation Of Foliar Fertilizer With Them And Nano-Titanium Dioxide

It has always been one of the hot spots of research to find new ways with high added value for recycling agricultural wastes and by-products.As compared with liquid fermentation,solid state fermentation(SSF)has many advantages including higher productivity,simplified operation,low investments,low energy requirements,less water output,better product recovery,etc.In this paper,a series of SSF experiments were conducted by using soybean meal,wheat straw and sugar residues as the main raw materials and a lipopeptide producing bacterium Bacillus amyloliquefaciens XZ-173 as the inoculum for production of polypeptides.Then,the peptide crude extract,trace elements,urea and nano-titanium dioxide were used to made of new fertilizer.The effects of the fertilizers on seed germination and tomato growth were studied.The main findings are as follows:1.Fourier transform infrared spectroscopy(FTIR)analysis of the crude extract from SSF showed that the crude extract had typical functional groups of polypeptides.The peak at 3294 cm-1 was the characteristic absorption peak of N-H stretching vibration in protein.The characteristic absorption peak of the polypeptide(-CONH-)near 2925.78 cm-1 indicated that the powder was polypeptide.A group of amino compounds Ⅰ(C=O)stretching vibration at 1654.88 cm-1 was strong absorption of a-helix structure.A characteristic absorption of N-H bending vibration of amino compound Ⅰ(CNH)amide band was at 1543.54 cm-1.The peak near 1243.82 cm-1 was the characteristic absorption of the amino compound Ⅲ with p-folds.2.Results from analysis by X-ray diffractometer and specific surface area showed that the TiO2 prepared by sol-gel method was nanosized anatase with an average grain size of 22 nm and a specific surface area 60.72 m2/g.3.Substrate screening tests and single-factor experiments were conducted to study the effect of SSF substrate composition,loading capacity,temperature,initial pH,time,water content,and inoculation amount on the yield of polypeptide.Besides,response surface methodology was used to optimize the fermentation factors including nitrogen and carbon sources and their ratios.Results showed:(1)that optimal substrate was composed of 63.03%of soybean meal,33.00%of wheat straw,1.93%of sugar residue,2.04%of yeast extract,with 10.18%(v/w)of inorganic salt solution added;(2)that optimal conditions were 50%of moisture content(adjusted with water at pH 7.5),10%(v/w)of XZ-173 inoculum,pH7.5 and 30℃ for 48h;(3)that the actual yield under these optimal substrates and conditions reached to 110.06 mg/gds,which was much approximate to the forecasted yield 109.85 mg/gds(R2 = 0.9742).4.The seed soaking tests showed that the treatment of the polypeptides-nanoTiO2-micronutrients compound fertilizer had the best effect on germination of tomato seeds as compared with other single factor soaking treatments.After soaking with the compound fertilizer,the biological indexes including germination potential,germination index and vigor index of tomato seeds were significantly improved.5.The polypeptides-nanoTiO2-urea and the polypeptides-nanoTi02-micronutrients compound fertilizers were obtained by preparation of the crude polypeptides and nano-TiO2 and urea or trace element solutions.The results of greenhouse pot experiments showed that the treatment of the polypeptides-nanoTiO2-urea fertilizer applied by spraying or by irrigation was the best for tomato plants as compared with other treatments.The treatment significantly increased the stem diameter,chlorophyll content,biomass and plant height of tomato plants.In conclusion,this study has gained the SSF technological parameters for producing polypeptides from agricultural wastes and by-products;the fertilizers prepared from polypeptides,nano Ti02 and nutrients have significant effect in promoting tomato growth.