【作者】 曾绍校；

【导师】 陈绍军； 郑宝东；

【作者基本信息】 福建农林大学 ， 农产品加工及贮藏工程， 2007， 博士

【摘要】 淀粉作为莲子的主要成分，对莲子的加工特性及营养品质有着重要的影响。本文较为系统的研究了莲子淀粉的颗粒特性、加工特性、功能学特性等品质学特性，并在此基础上研究了莲子深加工产品中淀粉老化抑制的方法。通过实验研究结果如下：（1）莲子淀粉颗粒特性的研究莲子淀粉颗粒表面光滑，大多数淀粉颗粒呈椭圆形，少数为圆形和不规则形，粒径范围在3—25μm，平均粒径为12μm；有明显的偏心环纹和偏光十字；结晶结构属于C型。淀粉颗粒中脂肪和蛋白质含量较低，但直链淀粉含量较高，达40％以上，属于高直链淀粉含量的特异性淀粉。（2）莲子淀粉分子特性的研究高效液相色谱法测得莲子淀粉的重均分子量为1.7×10⁶，聚合度为10450；莲子直链淀粉的重均分子量为6.4×10⁵，聚合度为3970；莲子支链淀粉的重均分子量为2.8×10⁶，聚合度为17470。酶解脱支法结合凝胶色谱法分析表明，莲子支链淀粉有5级分支，平均聚合度分别为8、33、53、86、1116。主链上有2个分支，其它支链上仅有1～2个分支，具有主链较长、分支度较少、支链较短的特点。这与其它来源的支链淀粉分子结构差别较大。（3）莲子淀粉加工特性的研究莲子淀粉属限制型膨胀淀粉，透明度较低，凝沉速度较快；其凝胶具有较强的冻融稳定性和较低的凝胶强度；布拉班德粘度曲线显示，莲子淀粉的糊化温度较高，达77.1℃，热稳定性好，凝沉性强，冷粘度稳定性差，提示其易老化。这与莲子淀粉的分子特性相符合。利用差示扫描量热仪研究了莲子淀粉的糊化和老化动力学，研究表明：莲子淀粉的糊化起始温度为64.4℃，糊化终止温度为77.9℃。莲子淀粉的糊化过程属于一级反应，利用Arrhenius方程求得莲子淀粉的糊化活化能Ea为72.97kJ／mol，与玉米淀粉较接近。在不同温度下，莲子淀粉的老化度随着时间的增加而逐渐提高，其中冷藏条件下的老化速率最大，室温次之，冻藏最小。Avrami方程的计算结果显示，莲子淀粉储存于冷藏条件时的老化速率是室温下的1.6倍，是冻藏条件下的2.9倍。食品加工对莲子淀粉（提取样品）的改性研究表明，高压均质和超声波处理也能显著降低莲子淀粉的特性粘度和返生沉淀量，而微波处理对莲子淀粉的返生沉淀量和特性粘度影响不大，这可能与其高直链淀粉含量有关。提示高压均质和超声波处理在莲子水磨浆制品（如莲子汁、莲蓉）的生产中具有一定的应用价值。研究了食品工业中几种常用的食品乳化剂（单甘酯、卵磷酯、硬脂酰乳酸钠、蔗糖酯）对莲子淀粉糊稳定性的影响。结果表明：单甘酯与莲子淀粉的络合能力最好，其它依次为蔗糖酯、硬脂酰乳酸钠、卵磷酯，单甘酯对莲子淀粉糊具有最好的稳定效果。（4）莲子淀粉功能学特性的研究莲子生淀粉中抗性淀粉（RS）含量较低，仅为3.9～4.2％，这不同于其他来源的生淀粉。在25％的淀粉浓度，121℃温度下糊化后老化产生的RS含量最高，莲子淀粉的老化速度非常迅速，冷却后RS含量即高达38.2％，但随着老化时间的延长，RS含量增加缓慢，老化24h（4℃下）后可达41.2％。莲子淀粉具有制备商用抗性淀粉的价值。莲子淀粉对双歧杆菌具有显著的增殖效应，其增殖效果接近异麦芽低聚糖，可作为新的双歧生长因子。研究了不同干燥方法对莲子（整粒）中RS含量的影响，并将两种莲子形态（自然干燥的干莲和速冻鲜莲）按不同熟化方式进行处理，测定处理后莲子的RS含量以及血糖指数。结果表明：自然干燥、热风干燥、真空干燥和冷冻干燥后的莲子中RS含量大大提高，均达80％（占总淀粉量）以上，而经过微波干燥后RS含量下降至8％（占总淀粉量）。自然干燥的莲子经过熟化处理后，RS含量虽比未处理前稍有下降，但都保持在85％（占总淀粉量）以上的较高水平，从总淀粉消化率推测的血糖指数来看，血糖指数均低于55，属低血糖指数食品。而鲜莲经过不同熟化处理后，RS含量差异较大。其中鲜莲微波干燥后水煮样品RS含量最低，为26％，这大大低于其他处理方式。这说明微波处理整粒莲子时，能使其内部的淀粉发生一定程度的改性，降低了莲子中淀粉的老化率。因此，对于以整粒莲子形态出现的加工产品（如莲子罐头）而言，微波技术在防止淀粉老化方面具有的一定的应用价值。鲜莲、鲜莲微波干燥后水煮样品的血糖指数均大于80，属于高血糖指数食品，这提示糖尿病患者不宜食用经微波干燥的莲子，也不宜生食鲜莲。该研究为合理选择莲子的加工和食用方法及利用莲子开发低血糖指数食品提供了科学依据。研究了微波干燥后水煮样品（高血糖指数），鲜莲水煮样品（中血糖指数），干莲水煮样品（低血糖指数），鲜莲高压蒸煮样品（低血糖指数）对糖尿病大鼠降血糖作用的影响。结果表明：莲子不同的加工方法对糖尿病大鼠的降血糖作用有显著差异，除微波干燥后水煮样品外，其余样品均能显著降低大鼠的空腹血糖并改善其糖耐量（P＜0.05）。微波干燥后水煮样品对大鼠肝肾的抗氧化能力也较其他样品弱。微波干燥后的莲子不具有降血糖作用，这可能与其较高的血糖指数有关。这有力的证明了不同加工方式对莲子的降血糖功能有重要影响。（5）莲子加工产品淀粉老化抑制的研究本文以莲子罐头产品为对象，研究了罐藏莲子硬度变化的动力学模型以及淀粉抗老化剂和微波前处理工艺对产品品质的影响，并探讨了微波前处理抑制淀粉老化的机理。结果表明，莲子制成罐头后，贮藏过程中莲子的RS含量无显著变化，而莲子的硬度先迅速上升，而后渐趋平缓并保持在一定的范围，利用Avrami方程建立罐藏莲子的硬度变化动力学方程为：F=a[1-exp（-kt）]。感官品尝显示莲子罐头在4℃下贮藏30天即出现轻微返生味。添加一定量的淀粉抗老化剂（海藻糖、单甘酯、蔗糖酯），能够不同程度的降低莲子的硬度并延迟返生味的出现，通过正交实验，得出最优组合为海藻糖2.0％，单甘酯0.15％，蔗糖酯0.05％，该组合能使罐藏莲子的硬度(F_max)降低约30％，返生味的产生时间推迟至90天。对莲子进行微波前处理能使罐藏莲子的硬度再降低约46％，改善了产品的口感，并且在1年观察期内未出现返生味。微波前处理结合淀粉抗老化剂的工艺技术具有重大的商业应用价值。更多还原

【Abstract】 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.更多还原