| Rice dreg, a major by-product of rice syrup production with more than 60% protein, is considered a good source for obtaining rice protein. Rice protein has been reported to have a high biological value and low hypoallergenic characteristics. However, the use of rice protein as an ingredient in foods has been limited due to its poor functional properties such as solubility, emulsifying and foaming ability. Limited enzymatic proteolysis is a means of modifying the properties of rice protein, for the peptide generated can not only improve the solubility and emulsifying properties but also exhibit many physiological functions such as high digestion, antioxidant and anti-cancer properties. Thus, rice dreg protein hydrolysate (RPH) may serve as a suitable ingredient for food uses. The objectives of this paper were mainly two-fold:(1) to develop the RPH as a kind of nutritional wall material in microencapsulation of soybean oil/coconut oil blends (7:13, w/w) by spray-drying method; (2) to evaluate the nutritional effects of the resulting microcapsules on the growth and immunity of Sprague-Dawley (SD) rats. The results were shown as in our trails.1. The microencapsulation condition of the blend oils rich in MCFA using a wall system consisting of RPH and maltodextrin (MD) was optimized by response surface methodology (RSM) with the response value of microencapsulation efficiency (MEE), and the optimal conditions were determined as follows:RPH to MD ratio 1:1, core content 27.9%, emulsifier 2.5%, xanthan gum 0.1%, CMC 0.45%, solids concentration 19.2%. Microcapules under the optimized conditions gave rise to the highest MEE, approaching 82.69%.2. The physicochemical properties of the microcapsule under the optimized conditions were investigated. The results were as follows:the moisture content, microencapsulation efficiency and mean particle diameter of the reconstituted emulsion were 2.64%,82.73%and 322.7 nm, respectively. The powdered oil showed good solubility and dispersion. SEM analysis showed that the microcapsules had a regular spherical shape with smooth outer surface and "bee net"-like interior structure which indicated the high MEE of the product with RPH and MD as wall materials. The infared spectrum indicated that the assosication function exists between the protein molecule and the environmental dextrin's hydroxyl, which is good for maintaining the integrity of the microcapsule structure, as to the oil blends, the infrared characterful peaks did not change, which indicated that microencapsulation process had little effect on the core material. Glass transition temperature (Tg) of microencapsulation product by differential scanning calorimetry (DSC) was at 77.16℃which indicated its good storage stability. Thermogravimetric (TG) analysis revealed that the thermal stability of the sample was good at high temperature and the integrative structure could not be damaged during most productions.3. The storage stability of microencapsulation product was investigated by measuring the MEE during storage period and the peroxide value (POV) under the the influence of temperature, oxygen, light, relative humidity. The results showed that the MEE of the sample varied little during 180 days storage time. The POV of the sample increased slowly as the intensity of the temperature, oxygen conditions enhanced, whereas it increased relative rapidly when exposed in light, but it was still much lower compared with that of oil which was not embedded. Microencapsulation product showed low storage stability when relative humidity of the environment >60%, and the POV increased as the intensity of humidity enhanced.4. The effect of xanthan gum addition on physicochemical properties of 2wt% RPH stabilized oil-in-water (O/W) emulsions containing 20%v/v soybean oil was investigated by measuring droplet size, microstructure, creaming profile, viscosity and oxidative stability. In fresh emulsions, addition of xanthan gum at different concentrations did not show any significant effect on the average droplet size. However, emulsion microstructure and creaming profile revealed that the degree of flocculation of the oil droplet is a function of xanthan gum concentration:when xanthan gum=0%, there was no flocculation; when xanthan gum=0.02wt%, there was limited flocculation; when xanthan gum=0.04-0.2wt%, there was extensive flocculation, and when xanthan gum=0.5wt%, there was little or no flocculation. Increase in xanthan concentration led to decrease in creaming index and increase in elastic properties of emulsions. In the presence of 0.5wt% xanthan, the emulsion exhibited a high yield stress, which appreciably inhibited creaming. Lipid oxidation of the emulsions was inhibited by the addition of 0.12-0.5 wt% xanthan.5. Sixty SD rats (21 days'old) in 3 groups were used to evaluate the effects of early-weaned diets with the addition of RPH or RPH as microencapsulation wall materials on growth performance, intestinal absorption and immune, with one group fed with CKdiet after weaning in 28 days'old as a control. Results showed that the slow appetite and growth delayed of early weaning rats were conquered by feeding RPH or MF diets. The growth of rats was promoted in some degree, but the weight change was not significant. Intestinal xylose absorption of rats in early weaning groups was significantly higher than that of the control (P<0.05) for 14 d. In the prophase of the experiment (1-14 d), the contents of sIgA of rats both in MF group and RPH were lower than the control (P<0.05). And in the anaphase of the experiment (15-28 d), there were no significant differences among three groups. |
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