| Summary: | 碩士 === 弘光科技大學 === 食品科技所 === 105 === Native starches are widely used in food industry as thickener, colloidal stabilizer, and as agents for gelling, bulking, and water retention. However, much of the modern food processing using native starches are limited by their low thermal stability, extremely high susceptibility to pH changes, rapid retrogradation rate as well as low light transmittance. Chemical modification alters the structure of starch, affects the physicochemical properties of the starch in certain degrees, making it more appropriate for a wider industrial and biomedical applications. There have been accumulating modification methods for starch structure. Up to date, the dual modification of starch with sodium trimetaphosphate (also STMP)/sodium tripolyphosphate (STPP) (= STMP/STPP) and acetic anhydride is still lacking. Whether starch modified as such can be improved to meet certain application, we performed this study.
Results indicated that the optimum data or values for modification were: STMP/STPP (99/1), 0.25 %, reacting at pH 11, 45 oC for 30 min, reaching a peak viscosity 5190 cp. The optimum combination of acetic anhydride (AAn) was 1.0 to 1.5 %, reacting at pH 8.70.02 for 4h, at this point, the peak viscosity reached 5688 cp (for 1% AAn), and 6308 cp (for 1.5 % AAn). The final product exhibited acetyl percentage 0.019 to 0.020 %, the degree of substitution was 0.00072 to 0.00074, and the phosphate content increase from 0.010 % (for unmodified cassava starch, UNC) to 0.017 % (for CEC-1, UNC modified by 0.25 % STMP/STPP (99/1), 30 min, then AAn 1.5 % at pH 8.7 for 4h) and 0.021 % (for CEC-2, UNC modified by 0.25 % STMP/STPP (99/1), 60 min, then AAn 1.0 % at pH 8.7 for 4h). The transmittance (T), gel consistency (GC) and amylose (AmL) contents all decreased by treatments, T decreasing from 84.30.55% (UNC) to 34.750.45% (CEC-1) or 36.200.60% (CEC-2); GC decreasing from 1530.41 mm to 89.00.33 mm or 59.50.50 mm; and AmL decreasing from 20.150.24% to 19.330.35% or 19.270.31%, respectively. The DSC data showed there were only slight changed. The modified starches (CEC-1 and CEC-2) showed better syneresis, but and swelling, and lower solubility than UNC. Morphologically, SEM graphs did not show apparent changed, if any, CEC-1 and CEC-2 were found to have a little more broken granules. X-ray diffraction revealed more 2 sharp peaks appearing in CEC-2 than CEC-1, being more severely than UNC, implicating some microcrystalline structural change after the dual modification with STMP/STPP and AAn. The incorporation of CEC-1 or CEC-2 all showed better storage conditions of the pepper jam than UNC alone. CEC-1 was seen even better in this regard. Conclusively, we have successfully modified the cassava starch by dual treatment with STMP/STPP and AAn, which is more feasible for preparation of the pepper jam.
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