| The influence of the pasting properties of lotus seed starch was important on the quality of lotus seed products and the application of lotus seed starch. The pasting properties, freeze-thaw stability, rheological properties and forming-film properties of lotus seed starch pastes were systematically studied in this paper. And the lotus seed starch was modified by dry heating. The antibacterial effect of lotus seed starch edible coating was studied and coating was applied to fresh-cut fruits storage. The results offer a scientific guidance for the deep processing of lotus seed products and the application of lotus seed starch, and enrich the content of starch-subject research.(1) Studied on the pasting properties of lotus seed starchThe pasting properties of lotus seed starch were investigated by using Brabender viscosimeter. The results showed that the influences of the concentration of starch on the pasting properties of lotus seed starch were significant. It showed a decreasing in the beginning gelatinization temperature, heat and cold stability, an increasing in the peak viscosity and retrogradation with the increase of lotus seed starch concentration. The influence of pH value was also great. The type of viscosity curve changed obviously, however the stability of starch paste was good in neutral or alkaline conditions. It showed an increasing in characteristic values of Brabender viscosity curves, a decreasing in heat and cold stability, an increasing in retrogradation when sucrose, trehalose, glucose, fructose was added respectively. However, the stability of starch paste was improved by high fructose syrup when the addition was 8%. Salt had little effect on the pasting properties of lotus seed starch. And the results showed that the beginning gelatinization temperature, heat and cold stability of lotus seed starch pastes decreased, the peak viscosity greatly increased, while retrogradation changed in different degrees when hydrocolloids were added. The results offer a scientific reference for determining the processing conditions and formulations of lotus seed.(2)Study on the freeze-thaw stability of lotus seed starch pasteThe freeze-thaw stability of lotus seed starch paste was poor. The starch paste after the first cycle had a syneresis of 81.25%. And syneresis increased slightly with additional freeze–thaw cycles. This may be related to the formation of rigidity networks by lotus seed starch molecules due to decanting the free water. Addition of guar gum, xanthan gum or CMC resulted in a reduction of syneresis, and xanthan gum had the best effect. The syneresis after the seventh freeze–thaw cycle reduced to about 50% when adding xanthan gum at 0.5% level. Furthermore, it decreased slightly when the concentration increased to 1%. The effect of carrageenan on the stability of lotus seed starch was not clear. However, sodium alginate had the adverse effect of reducing the stability. The results provide an important significance for improving the freeze-thaw stability of lotus seed starch paste and developing starch based food.(3)Study on the rheological properties of lotus seed starchSteady flow property, dynamic viscoelasticity and in-shear structural recovery of lotus seed starch paste were determined by using a rheometer. The starch pastes exhibited typical time-dependent shear-thinning pseudoplastic and thixotropic behaviour. The yield stress increased with increasing the concentration of lotus seed starch. It suggested that high concentration of starch was difficult to be mixed and need large power. The paste became more pseudoplastic and thixotropic as the concentration of lotus seed starch increased. This is the first study to show that the rheological property of 4% lotus seed starch paste was special, which exhibited composite thixotropic behaviour. It exhibited antithixotropic behavior at high shear rates(γ·>25s-1) and thixotropic behavior at lower shear rates(γ·<25s-1). In-shear structural recovery was also more than 100%. This may be related to 4% lotus seed starch paste in semidilute solutions.All the starch/hydrocolloid mixtures exhibited pseudoplastic behaviour when guar gum (guar), xanthan gum (xan), sodium carboxymethylcellulose (CMC), carrageenan (car) and sodium alginate (alg) was added respectively. Almost upward flow curves and down upward curves overlapped, a few down upward curves were above upward flow curves. So hysteresis loop areas were significantly reduced. This results indicated that starch/hydrocolloid systems enhanced the resistance to shear and the formation of stable shear-induced network. However, different hydrocolloids displayed different effects on the viscosity of mixtures. The yield stress of mixtures was high in the presence of guar or xan, which need large power to stir. While the fluidity of pastes was improved with adding CMC, car and alg respectively. The viscosity of pastes recovered quickly after high shearing in the presence of CMC or alg. While the recovery was induced when the addition of xan or car was lower. Addition of guar was a disadvantage for viscosity recovery, furthermore, the paste became more pseudoplastic as the addition increased. Therefore, effect of shearing on viscosity of starch paste could be reduced by adding suitable type of hydrocolloid at suitable concentration.Dynamic viscoelasticity measurements revealed that G′of lotus seed starch paste was higher than G′′, both of which were increasing with increasing the concentration. The interactions between starch molecules were enhanced, then the sstarch gel structure was stable, indicating predominantly elastic behaviour. The mixtured system also exhibited elastic behaviour after adding hydrocolloid. The mixtured system showed an increasing in G′,G′′with increasing the addition of guar or xan. It had the highest G′when adding CMC, car at 0.5%, 1% level respectively. The mixtured system showed an decreasing in G′,G′′with increasing the addition of alg. It indicated that the hydrocolloids displayed different effects on the viscoelasticity of lotus seed starch.(4) Study on the characteristics of lotus seed starch filmThe influence of starch concentration, glycerol addition and drying temperature on the characteristics of lotus seed starch edible film was investigated and the process was optimized. The results showed that the edible films showed an increasing in tensile strength, a decreasing up to a certain extent in elongation at break, a slightly decreasing in tear strength and a decreasing with slightly fluctuating in water vapor permeability with increasing the concentration of lotus seed starch. It showed a decreasing up to a certain extent in tensile strength, elongation at break and tear strength with increasing the addition of glycerin, which got the highest value when glycerin addition at 1.5%. An increase in water vapor permeability was found with increasing the addition of glycerin. The ideal properties of starch film were not obtained when drying temperature was low or higher, but the drying temperature was moderate. The optimized processing parameters of lotus seed starch edible film by orthogonal experiment was starch concentration 4.0%, glycerol addition 1.5% and drying temperature 80℃. Compared with corn starch films and potato starch films, the better mechanical properties, lower solubility and better water resistance was found in lotus seed starch films. It suggested that lotus seed starch film has a good prospect in application.(5)Study on the modification of lotus seed starch by dry heatingLotus seed starch was modified by dry heating with hydrocolloids. It indicated that the connection of lotus seed starch molecules was improved by hydrocolloids. But the hydrocolloids used in this study displayed different effects on the modification. Therefore, lotus seed starches with different pasting properties could be obtained. The starch pastes exhibited typical time-dependent shear-thinning pseudoplastic behaviour before and after dry heating. The starch pastes after dry heating showed a lot of change in thixotropy, and became antithixotropic. In-shear structural recovery increased, indicating a well capacity of the starch paste to withstand shearing. Dynamic viscoelasticity measurements showed that the G′of lotus seed starch paste after dry heating was higher than native starch. It indicated that internal structure was stable and uneasy to be destroyed after dry heating. Dry heating had no effect on tensile strength of modified lotus seed starch based films, but dry heating with guar gum or CMC increased elongation at break, sodium alginate improved water vapor barrier property greatly. The results provide a scientific reference for making desirable properties of lotus seed starch edible films.(6) Applying lotus seed starch based edible coating on the preservation of fresh-cut fruitsThe antimicrobial properties of lotus seed starch based edible films containing different bacteriostatic agents were evaluated. Then the lotus seed starch films were applied to fresh-cut fruits storage. The results showed that the edible coating had significant inhibitory effects on bacteria such as Staphylococcus aureus, Listeria momocytogenes, Escherichia coli, Salmonella typhimurium when the addition of Nisin was 0.02%, pH value was 7. The browning, softening and growth of microorganisms of fresh-cut pineapple and mango were inhibited with lotus seed starch coating. The quality and safety were maintained. Therefore, the preservation effect of lotus seed starch based edible coating on fresh-cut fruits was good, which was beneficial to expand the comprehensive development and utilization of lotus seed starch.
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