Studies On The Physicochemical Properties And Preparation Technology Of Fern Root Resistant Starch

Occupying the proportion of about 35% in fern root, the starch is its main composition. Some researches have shown that fern root starch not only can strengthen our bodies, but also it has the function of preventing and killing cancers. Therefore, there is a vast range of prospects for exploiting fern root starch. With a view to that, the paper makes a systematic investigation of the physicochemical properties and the molecular structure of fern root starch, and deeply illustrates the best technology of making fern root resistant starch through autoclaving. The main results are as follows:1. Physicochemical properties of fern root starchComparing with corn and potato starches, the granule shape, crystal type, retrogradation properties, rheological properties and gelatinization properties of fern root starch were studied by scanning electron microscope, X-ray diffraction, spectral photometer, Brabender viscosimeter and differential scanning calorimetry.Fern root starch contained little water, and the contents of its ashes, proteins, and fats were between those of com and potato starches. It consisted of 10.29%±0.17% of water, 0.31 %±0.03% of ashes, 0.09%±0.01% of crude protein and 0.22%±0.02% of fat. Most of fern root starch granules were oval, and a few of them were round and polygon in shape, which were smooth and of no cracks. The granules were around 7～28μm in diameter, and their average diameter was 14μm. The granules had a clear malte cross, most of which appeared cross-shaped, but some of which appeared X-shaped in the center. The crystalline pattern of fern root starch was C type.Comparing with corn and potato starches, fern root starch was less transparent. Its freeze-thaw stability and solubility were between them. Deposited for seven hours, fern root starch paste had little sedimentation. The degree of retrogradation value was greater than that of potato starch, and smaller than that of corn starch. The starch concentration of the paste had great influence on its retrogradation value.The higher the temperature was, the lower the apparent viscosity of fern root starch paste becomed. Affected by certain shearing force, the apparent viscosity of fern root, corn and potato starch pastes would decrease as the shearing time increases. Appearing a kind of pseudoplastic fluid, they belong to shearing dilution system. Shearing dilution of fern root starch paste was weaker than that of corn and potato starches. The Brabender viscosity analyses of starch pastes indicated that the peak viscosity of fern root starch was obviously higher than that of corn starch, and a little lower than that of potato statch. Moreover, it had the property of good heat and cold paste stability. DSC thermograms of fern root starch showed that the gelatinization temperature, being from 58.94℃to 71.73℃, was slow ,and enthalpy, being 12.86 J/g, was lower than those of potato and corn starches.Being not easy to break, the surface of fern root starch gelatinization was not very brittle. Its inside was not very hard, but was elastic and of high viscosity. Affected by outside forces, fern root starch gelatinization was easy to return the original form.2. Molecular structure of fern root starchBeing in the proportion of 25.38 %, the amylose content of fern root was more than that of corn starch, which was in the proportion of 20.33 %.The fractionation of amylose and amylopection, and their purity were affected by the blending speed of dispering starch in base solution, the velocity of separating amylose from saline solution, centrifugal speed and temperature.Highly pure amylose and amylopectin can be successfully separated from fern root starch by means of 1-butanol and re-crystallization for 8 times and 5 times. The molecular weights of fern root amylose and amylopectin is smaller than those of corn starch.Theλ_max of starch-iodine complexes of fern root amylose and amylopectin were 640nm and 547nm respectively. Being 0.91 and 0.13 respectively, the blue values were in the corresponding range, which indicated that fern root amylose and amylopectin were of high-purity.3. Preparation technology of fern root resistant starchIn resistant preparation, the yield of fern root resistant starch was somewhat influenced by starch concentration, autoclaving temperature, pH value, autoclaving time and retrogradation time. The results of three-factor and two-dimensional revolving orthogonal combinatorial design showed that the subsequence of influence was like this: starch concentration>pH values >autoclaving time. The optimum of preparation process for fern root resistant starch was as follows: starch concentration being 28.7%, its pH being 7.8, the starch had been heated for 38minutes at 121℃,then retrograded for 24 hours at 4℃, and the yield was 10.94%.On the optimized conditions, starch concentration being 27.05 %～28.02%, pH being 7.48～8.00, autoclaving time being 29.68min～36.27min, the possibility reached above 8.5% of the fern root resistant starch's yield was 95 %.