| Summary: | 碩士 === 國立屏東科技大學 === 食品科學系所 === 97 === Resistant starches have mainly been categorized into 4 types: RS1, RS2, RS3, and RS4. RS3, generated via starch gelatinization followed by retrogradation, is the most common RS from processing. RS4 is the modified starch through chemical modification. The physicochemical characteristics of RS will depend on the source, structural difference, preparation, and treating condition of starch investigated. This study aims to reveal the differences in structures and characteristics, between gelatinized-retrograded RS3, and RS4 which originated from pregelatinized starch esterified with low molecular weight carboxylic acids. Methods in this investigation include basic physical properties such as enzyme digestibility, water absorption, water solubility, amylose-lipid complexing index, degree of substitution. In addition, differential scanning calorimetry (DSC), rapid viscosity analyzer (RVA), scanning electron microscope (SEM), texture profile analysis (TPA) were implemented for examining the gelatinization, retrogradation, gel structure, etc. Fourier transform infrared specscopy (FTIR) was further utilized for the quantitative characterization of ester bonds formed.
Resistivity to enzyme digestion and heat stability are two primary characteristics for the application of resistant starch. This study utilized hot water bath and autoclave to gelatinize mung bean starch, followed by retrograding the gelatinized starch at 4℃, forming stable double helical amylose and increased its crystallinity (RS3). Esterified starches (RS4) were
prepared by etherifying pregelatinized mung bean starch with low molecular weight carboxylic acids. It was anticipated to create the resistivity to enzyme digestion and heat stability through crosslinkage of ester bonds. The production of RS4 was found to exceed that of RS3 (retrograded starch), and the optimum condition was confirmed as reacted with sodium citrate. Further improvement on RS yield by the combination of physical and chemical treatments. Both water absorption index (WAI) and water solubility index (WSI) decreased upon storage which indicates the advance of retrogradation. WAI/WSI increased as the concentrations of citrate and reaction temperature climbed which were presumable attributed to the increase of hydrophilic ester bonds. Gelatinization of raw mung bean starch was found at 67℃ with 13.7 J/g enthalpy by differential scanning calorimeter (DSC). The peak in DSC thermogram disappears after gelatinization, yet moves to higher temperature zone with slight enhancement of transition enthalpy after retrogradation or esterification, which signifies the enhanced heat stability of resistant starch. The gelatinization temperature by RVA was close to that predicted by DSC, while setback viscosity of retrograded starch increased upon storage yet with a very low continuous viscosity, totally different from that of raw starch. Scanning electron microscope (SEM) confirmed the augmented network structure through gelatinization, but it became more compact through staling or esterification of starch. The network structure of starch gel almost fully disappeared by sodium citrate esterification. Absorption peak at 1728 cm-1 which could be attributed to ester bond was verified by Fourier transform infrared spectroscopy (FTIR), which proved that esterified starch acquires enzyme resistivity by its ester bonds.
In conclusion, RS3 through physical retrogradation, showed quite different characteristics in physicochemical aspects and structural evidences by spectroscopy, from that of RS4 which was chemically esterified. This may have an important effect on the application of these two RS.
|
|---|
