Study On The Processing Technique And Characteristics Of Lotus-root Starch And Super-fine Whole Lotus-root Powder

Nelumbo nucifera Gaertn is a kind of hydrophilous economy-crop which can provide ample nutrition such as starch,vitamin,Fe,Ca and alkaloid et al.But after harvested lotus root tends to get browning. Many inhibitors and drying methods were studied to protect fresh-cut lotus root from browning during experiments.The production of super-fine whole-lotus-root powder can keep much of the nutrition and be benefit to the store and conveyance of the lotus root.The study of super-fine whole-lotus-root powder's functional characteristic provided the theoretic base for structure,pasting and retrogradation characteristics, and the results can be the guidance for application of super-fine whole-lotus powder in food industry.The results as following:(1) The study of protecting fresh-cut lotus root from browningThe best inhibitor combination is:citric acid 0.15%,vc 0.15%,dl-malicacid 0.25%and L-cysteine 0.15%,combined with 60℃water dipping during the production to control browning.(2) The study of drying methods on fresh-cut lotus rootThe fresh-cut lotus root are drying with hot-air drying,microwave drying,microwave+hot-air drying and vacuum freezing drying.The qualities of products are evaluated comprehensively by drying rate, starch-iodine-blue,TW and the ability of water retention.The results show that hot-air drying is the best method to preserve the quality of lotus root.And the best technological drying condition is 70℃,the speed of wind is 0.3m/s and the quantity is 40g.Under this condition,the mathematical drying model equation MR＝0.857412114exp(-0.050102613t)(R~2＝0.96537) has been established.The results show that there is little difference between the speculated results and the calculated outcomes,so the mathematical model equation established on these date can be applied to describe the process of hot-air thin layer drying for fresh-cut lotus roots. (3) The preparation of lotus root starch and super-fine whole-lotus root powderWe get the lotus root starch with the method of extracting with water.The drying slices of lotus root are crushed to get the meal and then transferred to the super micron-milling equipment to gain the finer powder.And the powder is separated to three grades according to their size.The output of each sample is that the percent of 1-starch,1-100,1-200,1-300 is 3.23%,34.3%,47.0%,15.3%each;the percent of 2-starch, 2-100,2-200,2-300 is 3.71%,30.2%,47.6%,19.4%each;the percent of 3-starch,3-100,3-200,3-300 is 2.64%,35.3%,38.7%,and 22.1%each.(4)The study on the structure of lotus root starch and super-fine whole-lotus root powderThe shape and the structure of lotus starch and different sizes of super-fine whole-lotus powder are studied with optical microscope,scanning electron microscope,polarizing microscope and X-ray diffraction.The results show that most of the lotus starch particles are club-shaped and the size are about 40μm and a few of them are elliptic or circular and the size are about 10-25μm,and all of them present apparent ring and their center is on the end of particle.The intrinsic structure of lotus root starch is almost destroyed during super-fine smashing.Little intact starch can be observed,the damaged starch attached to other fragments to form small groups.Otherwise the size of whole-lotus root powder is getting smaller after super-fine smashing,even smaller then starch.The polarization cross is clear and the club-shaped starch shapes"X",but elliptic and circular starch shape vertical or declining cross and some of them are in the shape of"X",Most lotus starch structure of super-fine whole-lotus powder is destroyed,only a few"X"or fragmentary"X"and cross can be seen.Lotus starch exhibits a B-type in X-ray diffraction pattern,but after super-fine smashing which exhibits an A-type in X-ray diffraction.With the sizes of the super-fine whole-lotus powder getting smaller,the intention of diffraction apex falls and the extent of crystal minishes and the extent of non-crystal spreads.The crystal degree of each sample is that the percent of 1-starch,1-100,1-200,1-300 is 35.77%,25.61%,23.77%,21.81%each,the percent of 2-starch, 2-100,2-200,2-300 is 32.30%,28.72%,24.28%,22.49%each,the percent of 3-starch,3-100,3-200,3-300 is 32.96%,28.94%,26.48%,25.76%each.The 80%of the size distribution of each sample is that 1-starch, 1-100,1-200,1-300,2-starch,2-100,2-200,2-300,3-starch,3-100,3-200,3-300 is among 19.652μm-73.045μm,8.473μm-135.541μm,8.7μm-88.907μm,7.395μm-56.966μm,18.74μm-66.371μm, 14.07μm-213.55μm,7.895μm- 63.463μm,7.433μm-53.244μm,17.616μm-76.813μm,9.979μm-202.63μm, 7.196μm-56.888μm,7.444μm-53.697μm each.(5) The study of paste characteristic of lotus root starch and super-fine whole-lotus root powderThe results show that the changing direction of viscosity of different size of whole-lotus root powder is similar to the same sort of lotus root starch under varied conditions.The gelatinization temperature of super-fine whole-lotus powder is higher than the lotus root starch due to the complicated component and the reciprocity of each other.The energy needed to gelatinize of super-fine whole-lotus powder is fewer than the lotus root starch because that the structure of starch in whole-lotus powder has been destroyed during super-fine smashing.The super-fine powder is more soluble than the starch.The solubility of different size of super-fine powder is that 300 mesh＞200 mesh＞100 mesh.The swelling power of super-fine powder is better than starch.The swelling power of different size of super-fine whole-lotus powder is that 100 mesh＞200 mesh＞300 mesh.The freezing-thawed stability of lotus starch is much better than super-fine powder.The freezing-thawed stability of different size of super-fine whole-lotus powder is that 100 mesh＞200 mesh＞300 mesh.The viscosity of super-fine whole-lotus root powder is lower than lotus root starch while its stability is better than the starch.The viscosity stability of different size super-fine whole-lotus root powder under high temperature and low temperature are both 100mesh＜200mesh and 300mesh,there is little difference between 200 mesh and 300 mesh.Lotus root starch can gel when the concentration is above 6%while the super-fine whole-lotus root powder can gel only when the concentration is above 11%.The intensity of starch gel is higher than super-fine whole-lotus root powder while the springness is on the contrary.(6) The study of retrogradation of lotus root starch and super-fine whole-lotus root powderThe results show that the paste's euphotic ratio of lotus root starch and super-fine whole-lotus root powder fall during placement.And the paste's euphotic ratio of super-fine whole-lotus root powder is lower than that' of lotus root starch.Comparing with lotus root starch,the super-fine whole-lotus root powder paste more easily incline to delaminate,and the sedimentation rate is getting faster with the size getting smaller.Both the starch-iodine-blue and the decomposeing percent of paste and gel of lotus root starch and the super-fine whole-lotus root powder decline during the placement.The explanation is that the content of dissociated starch are getting fewer during the placement in the paste and gel and the retrogradation is processing slowly.The gel's intensity is getting stronger and it's springiness gets lower during placement.The innovations of this paper as following:(1) Four drying methords have been applied for fresh-cut lotus root,and the parameters of hot-air drying are optimized.We work over the producing technics about super-fine whole-lotus root powder and gain the production.(2) The physical and chemical characteristics,granule structure and functional characteristics of lotus root starch and super-fine whole-lotus root powder are studied systemicly for the first time at home.And the research affords the academic foundation for their application in the food insustry.