| Flaxseed oil is rich in alpha-linolenic acid.Due to the existence of unsaturated fatty acids,it is easy to oxidize and deteriorate during processing and storage,which leads to its limitation in practical application.The microencapsulation of flaxseed oil can enhance its stability and improve product quality.However,the mature technology of microencapsulated flaxseed oil products is rare in the market.Spray drying is widely used in the production of oil microcapsules owing to its short drying time and good quality.Due to the spray drying tower is a completely closed facility,current reports on spray drying are mainly about examining the best process conditions by studying the effects of drying conditions and emulsion components on the product quality,to find out.While the effects of the heat and mass transfer behavior of droplets on the physicochemical properties of obtained particles is rarely studied,which leads to insufficient understanding of the mechanism of drying.The paper adopting Single droplet drying technique(SDD)which could simulate the convection drying environment of spray drying tower,carrying out the drying and rehydration experiments of a single droplet of oil-in-water(O/W)emulsion with gum arabic and whey protein as wall materials and flaxseed oil as core materials under controllable conditions.The drying mechanism of droplets was elaborated by examining the changes of the microscopic morphology,kinetic parameters,wettability of particles during the drying process and discussing oil migration and the formation of surface shell during single drop drying.On this basis,flaxseed oil microcapsules with gum arabian and whey protein as wall material were prepared by spray drying technology in order to investigate the effects of emulsion composition and spray drying conditions on its physicochemical properties and release properties of microcapsules.The data obtained from the experiment is of guiding significance for optimization of microcapsule product quality and studying of drying kinetics model.The results of the study are as follows:Firstly,single droplet drying experiment was carried out to study the effects of drying air temperature,total solids content of emulsion and wall materials on the drying characteristics of droplet.The results show that with the increase of drying air temperature(90 ?,110 ?,130 ?),the drying rate of droplet increased significantly,the time of the first drying stage was shortened,the surface shell formed early,and the dry particles at 130 ? was the largest.When the total solids content of the emulsion increases from 10% to 30%,the surface water content of the droplet decreased,the surface shell formed early,as a result,restraining the particles shrinkage inward and the oil migration transference outward,which ultimately obtained the large particles.Compared with gum arabian emulsion droplets,whey protein emulsion droplets had higher drying rate in the first stage and reached the decreasing drying rate stage firstly,while the drying rate decreased,the total drying time was prolonged,and the morphology of obtained particles was large relatively.Secondly,rehydration experiments was conducted in different drying stages.The formation mechanism of particles surface shell was further studied by examining the effects of total solid content(10%,20%,30%),core wall ratio(1:1,1:2,1:4),wall materials(gum arabic,whey protein)on the wettability of particles.The results showed that the process of the shell formation could be divided into three stages:(1)the density difference between emulsion and water droplet would cause the emulsion to settle quickly to the bottom of the water,indicating that the waterproof shell of the droplet has not formed.(2)the particles and the water droplets merged immediately and collapsed quickly,indicating that soft waterproof shell on the surface of semi-dry particles was formed.(3)the soaking and osmosis of water were an slow process,indicating that the shell of the particles was almost completely formed.With the increase of the total solid content or the decrease of the core wall ratio,the hydrophilicity of the particles increased.The formed particles of whey protein emulsion have poor wettability comparing with gum arabian emulsion.Thirdly,flaxseed oil microcapsules were prepared by spray drying technique.Its basic physicochemical properties and vitro release properties were studied.The effect of formation mechanism of particles surface shell and the migration mechanism of the oil during the drying process on the properties of microcapsules was analyzed.The total solid content increased from 10% to 30%,the soaking time of the powder in water shortening by 5.3 s,the embedding rate increasing.When the core wall ratio decreased from 1:1 to 1:4,the soaking time of the powder decrease,the embedding rate increased from 77.7% to 91.8%,the free fatty acids release amount increased from 89.9% to 94.9%.Compared with the microcapsule powder obtained from gum arabian emulsion,the sizes of the microcapsule powder with whey protein as the wall material were uniform,the surface smooth and spherical,but a few of the particles ruptured,the wettability and embedding effect of the powder poor.The gum arabian shell has better controlled release properties to the oil in the process of simulating digestion in vitro.Due to the oils easy migrate to the surface of the particles during the drying process,the hydrophilicity and embedding rate of the microcapsule powder is reduced,and the release of fatty acids is high at the beginning of the simulated digestive juice,but the final digestion is low. |
PDF Full Text Request