Effects Of Different Amino Acids On The Properties Of Potato Starch

In this study, different kinds of amino acid additives, including two neutral amino acids (phenylalanine and methionine), two positively charged (lysine and arginine) and two negatively charged (aspartic acid and glutamic acid), were added into potato starch to investigate the effects of them on the solubility and swelling power of potato starch, The transparency, retrogradation, freezing-thawing stability, color, textural properties, rheological properties and microstructure of potato starch gels were investigated systematically. The purpose of this study was to lay a firm theoretical foundation for the application of amino acids in starch industry. The main content and results of this study were as follows:(1) The effects of different levels of amino acid additives on the solubility and swelling power of potato starch were assessed. It showed that the charged amino acids were able to significantly decrease (P<0.05) the solubility and swelling power of potato starch. The solubility and swelling power decreased gradually with increasing concentration of the charged amino acids. Therefore, the charged amino acids exhibited a large effect on potato starch.(2) The addition of all amino acids was able to decrease the transparency of potato starch paste, especially the charged amino acids. The transparency decreased as the levels of charged amino acids increased.(3) Retrogradation phenomenon was not observed from potato starch gels with phenylalanine and methionine within115h. But the additions of lysine, arginine, aspartic acid and glutamic acid were able to strengthen the retrogradation properties of potato starch paste, and retrogradation properties progressively decreased with increasing concentration of those charged amino acids. Meanwhile, the retrogradation increased with the extention of storage time,.(4) The effects of different amino acids on color of potato starch gels were assessed. It revealed that all amino acids decreased the L*values of potato starch gels, especially the charged amino acids. The addition of lysine significantly increased the a*and b*values.(5) The hardness, springiness, cohesiveness and gumminess of potato starch gels significantly decreased as the levels of charged amino acids increased. The result of gel strength was similar to that of hardness of potato starch.(6) The dynamic rheological analysis revealed that the addition of phenylalanine and methionine had no significant effect on rheological properties. The Gm’(PeakG’) and Gm"(PeakG") decreased with the increasing concentration of four charged amino acids. And the addition of charged amino acids increased Tm’(gelatinization temperature) of potato starch in some degree.(7) The shear stress-shear rate curve of all samples can be preferably expressed by power-law equation (τ=ky"). All samples owned pseudoplastic fluid since the related coefficient (R2) were greater than0.944. In the shear stress-shear rate curve, the lagged areas of four charged amino acids decreased, and it decreased with increasing concentration.(8) The viscosity-shear rate curve showed that all samples present shear-thinning system. And in the same shear rate, the viscosity decreased with the levels of four charged amino acids increased.(9) The scanning electron microscope was used to observe the microstructure of potato starch gels with different amino acids. It showed that the multi-hole structure of potato starch gels was changed into laminated structure as charged amino acids were added.(10) The FT-IR spectrogram showed that the peak width of associated hydrogen bond of potato starch with amino acids increased when compared to potato starch gels, while the other peak had no apparent change, it indicated that the interaction between amino acids did not generated new groups.