| As a major component of lotus-seed, starch affects its processing characteristics and nutritional quality largely. The granular, processing, and functional characteristics of lotus-seed were systematically studied in this paper. On the basis, the methods of anti-retrogradation in lotus-seed products were also studied. The results as following: (1) Studied on the granular characteristics of lotus-seed starchThe lotus-seed starch granule has smooth surface, elliptic shape mostly, few of them was round or irregular. The granule have a size range of 3~25μm, and 12μm in average. The granule has obvious eccentric ring veining and polarization cross. The starch possesses 'C' XRD pattern. The content of fat and protein was low. But, it was a specific starch with high amylose content which was above 40%.(2) Studied on molecular characteristics of lotus-seed starchMeasured by high performance liquid chromatography (HPLC) method, the weight average molecular weight and polymerization degree of lotus-seed starch were 1.7×10~6 and 10450 respectively, that of amylose were 6.4×10~5 and 3970, amylopectin were 2.8×10~6 and 17470.Methods of enzymatic debranching combined with gel chromatography were used to investigate the molecular structure of lotus-seed amylopectin. The results showed there were five degree branched chains in an amylopectin molecule, which polymerization degrees were respectively 8, 33, 53, 86, 1116.There were 2 branched chain in the main chain, and only 1-2 in every branched chain. The lotus-seed amylopectin has the longer main chain, the lower branch degree and the shorter branched chain, which was different from the other amylopectin structure.(3) Studied on processing characteristics of lotus-seed starchLotus-seed starch was a restrictive swelling starch. It has lower clarity, more rapid retrogradation, better freeze-thaw stability and lower gel strength. It can be seen from the Brabender viscosity that the lotus-seed starch has a higher gelatinization temperature (77.1℃), better thermostability, stronger retrogradation, weaker cold viscosity stability. The results accorded with its molecular characteristics.Gelatinization and retrogradation dynamics of lotus-seed starch was studied by DSC. The result showed that the initial gelatinization temperature of lotus-seed starch was 64.4℃ and the final temperature was 77.9℃. It was found that gelatinization of lotus-seed starch was a first-order reaction and gelatinization activation energy obtained by Arrhenius equation was 72.97kJ/mol, which was close to that of corn starch. At different temperatures, the degree of retrogradation increased with storage time. It indicated that the retrograde rate under refrigerated conditions was highest, the next was under the room temperature, and the lowest was under the frozen storage temperature. The results calculated by Avrami equation indicated that the retrograde rate stored under refrigerated conditions was 1.6 times higher than that of under the room temperature, and 2.9 times higher than that of under the frozen storage temperature.Modification of lotus-seed starch by food processing indicated that high-pressure homogenization and ultrasonic treatment could decrease the viscosity characteristics and retrograde deposition significantly. But, microwave treatment had few effects; it maybe refer to the higher amylose content of starch. The results suggested that high-pressure homogenization and ultrasonic treatment have a certain application value for manufacturing lotus-seed liquid products (such as lotus-seed juice, lotus-seed paste) certainly.Effect of food emulsifier on stability of lotus-seed starch paste was studied. The results showed that monostearin had highest complexing capacity with lotus-seed starch, followed by sucrose ester, stearyl lactylate and Lecithin in turn. And monostearin had the best stabilizing effect on lotus-seed starch paste.(4) Studied on nutritional characteristics of lotus-seed starchThe content of resistant starch (RS) in crude starch of lotus-seed is lower, just only 3.9-4.2%, which is different from other crude starches. It could obtain the highest content of RS by the condition of 25% starch paste gelatinized at 121℃, retrograded at 4℃. Lotus-seed starch retrograded very quickly. The RS content in starch paste reached up to 38.2% as soon as being cooled, and increased slowly as prolonged the retrogradation time. It could reach up to 41.2% for retrograded 24h (at 4℃). Lotus-seed starch has the commercial value of RS manufacture. Lotus-seed starch has the significant multiplication effect on bifidobacterium, which is close to isomaltooligosaccharide, so lotus-seed starch can be used as a new bifidus factor.Effect of different drying methods on the RS content of lotus-seed was studied. Naturally dry and fresh (quick frozen) lotus-seed were heated by various processing respectively, and its RS content and glycemic index were determined. The results showed that the RS content (in the total amount of starch) of lotus-seed was increased to over 80% after naturally dry, hot air dry, vacuum dry or freeze dry. But microwave dry could decrease the RS content down to 8%. No matter what heating processing could decrease the RS content of naturally dry lotus-seed lightly, but it could maintain a high RS content over 85%. Its glycemic index which inferred from the total starch digestibility was all below 55. So those lotus-seed were in the range of low glycemic index. Heated by various processing could make a great difference in RS content of fresh lotus-seed. The lowest one was 26% when fresh lotus-seed was treated by water cooking after microwave dry (WCMD). It indicated that starch in lotus-seed might be modified by microwave treatment so as to decrease the retrograded rate. So, for the products of lotus-seed with intact shape such as lotus-seed canned, microwave treatment has a certain application value in anti-retrogradation of starch. Fresh lotus-seed and the WCMD fresh lotus-seed were in the range of high glycemic index for its glycemic indexes exceeded 80. It suggested that the microwave dry lotus-seed and fresh lotus-seed were not suitable for diabetic patients. It offer a scientific reference for choosing the processing and eating methods of lotus-seed and exploiting the low glycemic index food of lotus-seed.The effect of various lotus-seed samples on the levels of blood glucose of diabetic rat was studied. The lotus-seed samples included WCMD lotus-seed (high glycemic index), water cooking fresh lotus-seed (middle glycemic index), water cooking naturally dry lotus-seed (low glycemic index), and botulinum cooking fresh lotus-seed (low glycemic index). The results showed that there has a significant effect of different processing on function of lotus-seed to decrease blood glucose of diabetic rat. Except WCMD lotus-seed, the other samples could decrease the fasting blood glucose and improve the glucose tolerance significantly (P<0.05). The antioxidant ability of WCMD lotus-seed in rat' s liver and kidney was also lower than that of other samples. It maybe relate to its higher glycemic index. It was proved that the processing would affect the function of lotus-seed in decreasing blood glucose.(5) Studied on anti-retrogradation of lotus-seed productKinetic model of the firmness change of canning lotus-seed and the effect of anti-retrogradation agent and microwave pre-treatment on product quality was studied. And the mechanism of anti-retrogradation by microwave pre-treatment was discussed also.The results showed that, there is few change in RS content of canning lotus-seed. But, its firmness increased quickly at the beginning of storage, then slowly, and kept in a narrow range. The kinetic equation of firmness change of canning lotus-seed established by Avrami equation was: F=a[1-exp(-kt)]. Sensory evaluation indicated that slight staling flavor of canning lotus-seed appearanced in 30 days at 4℃. Adding some anti-retrogradation agent (trehalose, monostearin, and sucrose ester) could lower the firmness of lotus-seed at a certain extent and delay the appearance time of staling flavor. The optimal combination with 2.0% trehalose, 0.15% monostearin, 0.05% sucrose ester, could lower the firmness of canning lotus-seed about 30%, and delay the appearance time of staling flavor about 90 days. By microwave pre-treatment, the firmness of canning lotus-seed could decrease by 46% again, and staling flavor couldn't be found during one-year's observation period. The technology of microwave pre-treatments combined with anti-retrogradation agent has great commercial application value.
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