Zein Mediated Encapsulation Of Starch Granules And Its Slow Digestion Property

Slowly digestible starch (SDS), as the healthiest component of starch, is able to generate stable blood glucose level, which is important for human health. Zein protein extracted from corn gluten meal is a byproduct from the production of corn starch, and its water insolubility makes it difficult to be used by the body. However, because of its strong hydrophobic nature and excellent ability to form film, zein might be used to control-release drugs or nutritional components. In this paper, zein-starch composite was prepared by different methods and the digestion of the composite was also measured. Furthermore, zein film plasticization and mechanism were also studied. The main research contents are as follows:According to the hydrophobic nature of zein, two methods were adopted to make zein-starch composite. When the cold water was used as phase separation solvent to generate the complex, zein was separated from starch without forming a zein-starch complex. However, when the starch-zein mixture (in ethanol) was added into cold water drop by drop, the complex was formed. When zein was dissolved in ethanol with a concentration of 10%, the complex's structure was most complete and regular, after changing the ratio of zein and starch, we found that the content of the SDS decreased following the increase of starch, and the highest SDS was obtained when the ratio between zein and starch was 1:2. Higher SDS could also be made after adding Tween-80. Overall, the digestion of starch in the complex was indeed reduced, but the ratio of starch in the complex was low. Considering the scale of production, zein-starch complex produced through this method could not meet industrial production requirements.Spray drying method was used to improve the production of the zein-starch complex. Microcapsules were made using the zein as wall material and the starch as core material. SEM results showed that zein as the wall of the microcapsule had formed a regular film coating out of the starch particles and the microcapsules were also shaped regularly. It is found that the size of product decreased when the ratio of starch increased, and when the ratio of wall material and the core material was1:20, the microcapsules were formed by single starch granules, but the starch granule was not coated by zein film completely. Digestion measurement showed the product which was made by zein and starch as 1:6 had an excellent slowly digestion nature. However, digestion measurement showed that the structure of microcapsules was not stable for the product had been destroyed after being shaken in the water for 10min.More experiments were designed to plasticize zein film, research and discussion was also carried out about the plasticization mechanisms. It is found that oleic acid and glycerol could significantly improve the mechanical properties of zein film, and the optimal quantity was 20% (g / g zein); compound plasticized study found that when added 20% mixed solution to plasticize zein film, the best ratio of oleic acid and glycerol was 3:1, whose tensile strength increased 190%, elongation increased 70% compared to non-plasticized zein film. Secondary structure analysis of zein found that, although slight changes could be found in secondary structure after the zein film was plasticized by compound plasticizers, the non-covalent interactions (hydrophobic force and hydrogen bonding) between plasticizers and zein may be the chemical base when the zein film was plasticized.After the wall material of microcapsules was plasticized, the particles are larger comparing with the previous microcapsules and the surface is smoother. RVA analysis indicates that micro-capsule structure can prevent the starch granules to absorb water and swell, small amount of starch which separated out from the microcapsules also showed slowly digestion nature. Animal experiment results also proved the slowly digestion of product, peak time of glucose in blood could be delayed and curve of the blood glucose was more gentle after the mice were fed with microcapsules. At the same time, starch microcapsules were applied into food to study its application, the results show that the starch micro-capsule can shield the raw starch flavor, furthermore, milk with zein coated raw starch can be accepted by consumers.