Starch Comprehensive Modification Process And Development And Factory Design Of Antibacterial Starch

The aim of this thesis is to prepare low-substitution acetate esterified starch from tapioca starch and to synthesize acetate esterified graft starch by reacting acetate esterified starch with isophorone diisocyanate(IPDI)and polyhexamethyleneguanidine hydrochloride(PHMG)and to evaluate its antimicrobial properties.We focused on the preparation process of acetate esterified starch and acetate grafted starch,characterized the morphological structure and properties of acetate esterified starch and its grafted starch using infrared,Xray diffraction and scanning electron microscopy techniques,and tested the antibacterial properties of the modified starches.Based on this,a plant with an annual capacity of 2500 tons of acetate esterified grafted starch with excellent antimicrobial properties was designed,and the main conclusions are as follows:(1)Preparation process and characterization of acetate esterified starchBased on the single-factor experiments,the optimal process optimized by orthogonal experiments was: starch milk concentration of 35%,at pH=8.5,reaction temperature of30 ℃,reaction time of 2 h,and addition of 10% acetic anhydride(as a percentage of the dry starch mass),which could yield acetate esterified starch with a degree of substitution of 0.0994.In this process,the improvement effect of two catalysts on the degree of substitution and reaction time was compared,when 4% N,N-carbonyl diimidazole(CDI)was added as catalyst and the reaction time was 0.5 h,the product with the degree of substitution of 0.1144 could be produced,and the degree of substitution was increased by27.25%;when 4% potassium persulfate(KPS)was added as catalyst and the reaction time was 0.5h,the product with the degree of substitution of 0.1042 was obtained,and the degree of substitution was increased by 15.90%.However,there was no synergistic effect when both were added to the reaction system at the same time.The comparison of the IR spectra of the acetate esterified starch and the original starch showed that the peak viscosity of the acetate esterified starch was significantly higher compared with the original starch due to the successful introduction of acetyl groups.x-ray diffraction patterns showed that the acetate esterified starch had characteristic diffraction peaks at 15°,17°,18° and 23°,and still maintained the starch A-type crystal structure.Scanning electron microscopy images showed that the granule morphology of starch did not change after the acetate esterification reaction.(2)Preparation process and characterization of acetate grafted starchThe process parameters of the graft modified starch were: IPDI reacted with PHMG at 120 ℃ for 1 h and then reacted with starch at 60 ℃ for 3 h.The grafting rate of PHMG to starch reached 28.43%.The IR spectra showed that the bond of IPDI and PHMG was successfully grafted on the acetate starch,and the acetyl structure of the acetate starch did not change.x-ray diffraction spectra showed that the grafted starch only showed diffusion peaks at 20°,indicating that the grafted starch was an amorphous polymer.Compared with the original starch,the grafted starch showed lower pasting temperature and higher transparency.(3)Antibacterial properties of acetate grafted starchThe samples of raw starch,acetate grafted starch,raw starch blended with PHMG and raw starch blended with potassium sorbate were selected for comparison,and the antibacterial effect of acetate grafted starch was investigated.The results of the inhibition circle method showed that: the acetate grafted starch produced inhibition circles,which confirmed its obvious inhibitory effect on Escherichia coli and Staphylococcus aureus,and Staphylococcus aureus was more sensitive to it and the inhibition effect was stronger.And the results of shaking flask method showed that the inhibition effect on bacteria was stronger as the grafting rate increased,and when the grafting rate was 28.43%,the inhibition rate of acetate grafted starch on E.coli was 90.24% and on S.aureus was 94.45%.On this basis,the effect of water washing on the inhibition rate of acetate grafted starch was investigated: after 10 times of water washing,the inhibition rate of acetate grafted starch on E.coli only decreased by 3.04% and that on S.aureus only decreased by 2.95%,indicating that PHMG is firmly fixed on the starch through chemical bonding and the inhibition effect is long-lasting,which is a kind of acetate grafted antibacterial starch with development prospects.(4)Plant design for 2,500 tons per year of acetate esterified antibacterial starchAccording to the general principles of food plant design,a plant with an annual capacity of 2500 tons of acetate esterified antibacterial starch was designed.After material accounting,equipment selection,drawing the general layout of the plant,process flow diagram,workshop layout diagram,the economic benefits were calculated.The total original investment of the plant is 18.86 million yuan,the annual production cost is 25.68 million yuan,the total annual sales can reach 45 million yuan,the annual net profit of the enterprise is 13.47 million yuan,and the payback period is 2.40 years.