| Jujube(Ziziphus jujuba Mill.)is a kind of plant with high edible and medicinal value,which is the main product of China and has high nutritional value.Jujube can be eaten fresh or processed into ready-to-eat products such as dried jujube,jujube powder,jujube slices,etc.However,in the processing process,only jujube pulp is often used,and jujube kernels are usually discarded as wastes,resulting in waste of resources.Jujube kernel contains more phenolic compounds,and its full utilization can bring its value into play.Jujube powder is a high value-added product,which is convenient to carry and has high nutritional value,but it is easy to absorb moisture and agglomerate.At present,the research on jujube powder mainly focuses on the optimization of drying methods and crushing methods,while there is little research on the improvement of moisture absorption of jujube powder.Therefore,this paper used winter jujube as raw material to prepare jujube powder by superfine grinding technology,and compared the property differences between superfine powder and ordinary powder.In addition,through the static weighing method,the moisture absorption characteristics of different particle jujube powder were explored,and on this basis,the moisture absorption improvement effect of jujube kernels powder on jujube powder was discussed,in order to provide theoretical support for the comprehensive utilization of jujube powder and the development of other jujube products.The main results are as follows:(1)Jujube powder was prepared by ordinary grinding and superfine grinding,and the effects of superfine grinding on physicochemical properties,functional characteristics and structural characteristics of jujube powder were investigated.The results showed that compared with ordinary grinding,superfine grinding could obtain jujube powder with narrow particle size distribution,larger specific surface area and smaller particle size(<30 μm).After superfine grinding,besides water holding capacity and rehydration,the physicochemical properties of jujube powder such as oil holding capacity,soluble solid content,water solubility,swelling capacity,bulk density,angle of repose and sliding angle have been improved significantly.Superfine grinding effectively broke the cell wall of jujube powder and increased the dissolution of nutrients such as protein,water-soluble dietary fiber,total sugar,reducing sugar,total phenol and Vc significantly(P<0.05).There was no significant change in hygroscopicity of jujube powder after superfine grinding,but its antioxidant activity was enhanced significantly(P<0.05).The results of infrared spectroscopy,X-ray diffraction and thermogravimetric analysis showed that superfine grinding did not change the molecular structure,crystal form and thermal stability of jujube powder.(2)To fully understand the moisture absorption characteristics of jujube powder during moisture absorption,In this study,the moisture absorption of jujube powder at 20℃,30℃,40℃ and water activity from 0.112 to 0.946 were measured by staticgravimetric method.The changes of moisture absorption color,adsorption isotherm,thermodynamic properties and sugar substance basis of jujube powder before and after superfine grinding were investigated.The results showed that the browning phenomenon of jujube powder was serious after moisture absorption,and its adsorption isotherm was type Ⅲ.Peleg model was most suitable for describing the adsorption isotherm of jujube powder(E<5%).The net isosteric heat of adsorption and differential entropy decreased exponentially with the increase of equilibrium moisture content of jujube powder,and the superfine powder was lower than that of ordinary powder.The absolute safe moisture content of ordinary powder and superfine powder was about 0.24 g/g and 0.22 g/g respectively.The moisture adsorption process of ordinary powder and superfine powder satisfied entropy-enthalpy compensation theory,and their Gibbs free energy was 1152.80 J/mol and 1184.22 J/mol,respectively,which was an enthalpy-driven non-spontaneous reaction.According to the results of monosaccharide hygroscopic control experiment,the main sugar species in jujube powder was fructose.(3)By preparing jujube powder with different content of jujube kernels powder,and measuring its moisture absorption performance at different humidity levels,the improvement effect of jujube kernels powder on moisture absorption performance of jujube powder was studied.The results showed that jujube kernels powder hardly absorbed moisture,and adding it to jujube powder could effectively reduce the balanced dry basis moisture content of jujube powder,and the higher the content of jujube kernels powder,the lower the balanced dry basis moisture content of jujube powder.Peleg model could be well used to establish the moisture absorption fitting formula of jujube powder containing the influencing factors of jujube kernels powder,and the goodness of fit was 0.9899.The addition of jujube kernels powder could effectively reduce the color difference change of jujube powder during moisture absorption,and reduce the hardness and viscosity of jujube powder during agglomeration.At the same time,the caking degree of jujube powder after moisture absorption decreased significantly after adding jujube kernels powder. |
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