Antioxidant Activity Of Modified Whey Protein And Walnut Oil Microcapsules Preparation

Whey protein isolate proteins (WPI) belong to the full price protein, easy to digest and absorb, with high nutritional value.It were widely used in infant formula. Whey protein by moderate modification can further improve or to improve their functional properties, food taste, texture, stability, extending shelf life of the product and expand its application in the food. The effective use of the whey has important means. In this study. the whey protein isolate was modified by six small molecule sugars. Filter out a whey isolate protein glycation product which has strong antioxidant capacity that as a raw material to prepare walnut oil microcapsules. It can effectively prevent the oxidation of the walnut oil. It appears for the development of walnut oil products towards convenience, nutrition and function. It also make walnut oil coming into high-quality, stable and high nutritional raw materials. At the same time, it provides a new way for the development and utilization of whey protein isolate.Using WPI, xylose, glucose, fructose, sucrose, maltose, and lactose as Maillard reaction raw materials, study the effect of carbohydrate types and mixture ratio on browning degrees of Maillard reaction products (MRPs). The antioxidant activity of the MRP was also determined. The results showed that the MRPs of WPI-Xylose systems under the conditions of2:1protein-to-xylose ratio had the highest browning degree. The MRPs of WPI-Xylose systems revealed strong reducing capacity, inhibition of lipid peroxidation, DPPH·radical scavenging activity, and hydroxyl free radical scavenging under the conditions of2:1protein-to-xylose ratio. Characteristics and antioxidant property of the conjugates of whey protein and six types of saccharides under various conditions of pH were studied by means of the moist-heating glycosylated reaction. It was shown that the absorbances at420nm and294nm of the six glycosylated proteins were significantly different after glycosylated reaction under the pH3-9(P<0.05). Meanwhile, In addition to conjugate of WPI-Scruose, the free amino group contents of other six glycosylated conjugates decreased significantly (P<0.05).And the reducing power, DPPH radical scavenging activity, hydroxyl radicals scavenging and Inhibition of lipid peroxidation were greatly improved except the conjugates of WPI-Scruose,with the increasing of pH. The conjugate of WPI-Xylose had the best antioxidant property among all the conjugates, and had stronger reducing power than Vc under the condition of pH7-9. SDS-PAGE analyses indicated formation of cross-linked proteins that large molecular mass was produced from WPI-X systems. Results analyzed by FT-IR indicated that the amide I, II and III bands of WPI from WPI-X and WPI-G systems were changed by the Maillard reaction. CD spectroscopy showed that β-sheet (β-turns and random coil were increased while the α-helix was decreased after the WPI-G and WPI-X systems aqueous solution was heated.Modification of whey protein isolate and gum arabic were used as wall material which could form a firm by complex coacervation at the surface of the walnut oil. The microcapsules of walnut oil were immobilized by transglutaminase (TG-H). The final products were dehydrated by freeze-drying. The preparation conditions and immobilization conditions were evaluated by the oil-in- rate of microcapsules. The results indicated that the optimum preparation conditions were as follows:walnut oil dosage0.6mL, modified whey protein isolate20mL, gum Arabic6%. pH4.5, stirring speed300r/min. The optimal immobilization conditions:immobilization pH6.0, the immobilization time of10h, the immobilization temperature of10℃, transglutaminase enzyme dosage of25U/g of gum arabic. The final oil-in-rate could reach84.15%. In the storage process, the microcapsules could delay walnut oil peroxide value increase.Physical property was studied. The moisture was7.09±0.03%; The density was0.13±0.01g.mL; The repose angle was45°±0.5°。 The color was light brown, the smell was pure SEM observation of modified whey protein isolate and gum arabic to form a gel film, will dissolve the walnut oil close coated. Microcapsules nonpositive circular, the grain sizes of10μm or less. Thermal gravimetric analysis (TGA) shown that the weightlessness was dramatically after450℃. It might be the cohesion composite wall material disintegration, and the oils evaporated quickly.The presence of time test of walnut oil microcapsules in artificial gastric and intestinal fluid showed that microcapsules existed in the artificial gastric juice shorter and existed in the artificial intestinal fluid longer, it had a good sustained release and enteric.