| Rice dregs, a major by-product of rice syrup production, was used to prepare peptides compound by controllabe enzymatic proteolysis method, and the peptides compound was successfully developed as a main wall-material in forming a stable O/W emulsion of a soybean oil/coconut oil blends, and then preparing into microencapsules by spray-drying method. The nutritional effects of peptides compound and microencapsules on small intestinal morphology and somatotrophic axis in Sprague-Dawley(SD) rats were evaluated in this paper, for the purpose of providing technical guide and theory basis for the comprehensive development of rice dregs.1. The limited enzymatic proteolysis of RD was optimized by response surface method with rotatable central composite design and with the response value of degree of hydrolysis(DH) and the extracted yield of protein(YP), and the optimal condition for trypsin was:pH 7.61,52.83℃, trypsin to RD ratio 0.89:1000 (g/g), RD to water ratio 0.17:1(g/ml), and time 2.43h. Under the optimized condition,75.81% protein could be extracted and the hydrolysis degree of protein was 6.94%. The theoretically predictive models obtained by response surface analysis for DH and YP could be described as: Where Y1 and Y2 represent the degree of hydrolysis and protein extraction, x1 is the ratio of trypsin to RD(g/g), x2 is the ratio of RD to water ration(g/ml), x3, x4, and x5 represent pH, temperature(℃) and time(h), respectively. 2. The kinetic mechanism of limited enzymatic proteolysis for RD with trypsin in pH7.6 at 53℃was investigated by pH-stat method. The results showed that the limited proteolysis could be inhibited by the addition of RD while the active sites of trysine were fully binded with substract and soluble peptides, otherwise the hydrolysis rate could be accelerate by the addition of RD. Based on the experimental data, the kinetic models obtained by mathematic deduction method for hydrolysis rate and degree of hydrolysis could be described as:3. The common chemical composition, amino acid compositon and peptides molecular weight distribution of the prepared RD hydrolysate were determined by chemical method and gel exclusion chromatography. The results showed that the hydrolysate was a mixture constituted by 52.2% oligopeptides and 18.7% free amino acids. Based on the reference proteins of egg and cow's milk(FAO/WHO/UNU, 1985), the calculated EAAIs for protein of RD hydrolysate were 0.93 and 0.96, respectively. The Glu and Arg contents in the protein of RD hydrolysate were 180.61,90.61 mg/g, respectively. These results demonstrated that the prepared RD hydrolysate could be a good protrein resource with high quality.4. The effects of spray-drying and freeze-drying processes on the physical and functional properties and protein secondary structure of prepared hydrolysates were investigated. The results showed the nitrogen solubility, emulsifying activities and emulsion stabilities have been remarkably improved after limited hydrolysis, and the surface hydrophobicities and thermal properties of hydrolysate could be significantly effected by drying process. The surface hydrophobicities (pH 7.0) for spray-dried and freeze-dried hydrolysates were 62.633 and 16.725, respectively. The denaturation temperatures and enthalpies of spray-dried and freeze-dried hydrolysates were 98.64 and 88.96℃,25.432 and 20.058 J/g, respectively. FTIR analysis showed that the secondary structure of Amide I band could be obviously influenced, while Amide III band was not significantly influenced by drying process. The main sencondary structure in Amide I band of spray-dried hydrolysate was random coils (47.66%, which was more than freeze-dried hydrolysate by 24.00%), while that of freeze-dried hydrolysate wasβ-sheets(40.06%, which was more than spray-dried hydrolysate by 16.38%). These results indicated that the protein molecule structure could be further stabilized during the freeze drying process and more protein subunits bared during the spray drying process for RD protein hydrolysate.5. To develop the RD protein hydrolysate as a nutritional wall material, the spray-drying method was used in microencapsulating process of the blend oils rich in MCFA. The emulsion system and the spray-drying process parameters were determined through the single factor experiment and orthogonal test. The microencapsulated product was constituted by 25%blend oils as a core materials, whlie the protein hydrolysate and maltdextrin in a ratio of 5:5(w/w) as the wall material. The stable emulsion system was constituted by 3% emulsifers (Tween-80, glyceryl monostearate and sucrose ester being 16:81:3,w/w/w), plus 0.45%CMC and 1% xanthan gum. Afer emulsifying 20 min. at 45℃and double-homeginization with a pressure of 10 MPa, the emultion was spray-dried with inlet and outlet temperatures of 190 and 95℃, respectively. Under the optimumal conditions, the prepared emulsion possessed a good stability and an average granularity of 261 nm, and the final product has a high microencapsulated efficiency up to 83.6%.6. The droplet size distribution, rheological properties, emulsion stababilities and morphology of microcapsules were measured To investigate the influence of wall material compositon on emulsion properties. Results showed that all emulsions exhibited similar viscosities, but emulsions with shell composition of RP:MD=5:4 and 4:5(m/m) were found to be more stable (97.81% and 98.15%, respectively) after water bathing at 60℃for 30 min, and smaller in droplet mean diameter (152.4 and 132.1 nm, respectively) and weaker in surface tension(30.492 and 29.904 mN/m, respectively), and possesed smoother surface morphology and more intact shell, as compared to those with other wall material compositions. 7. The glass transition properties of microencapsulates were characterized by differential scanning calorimetry(DSC) and their oxidative stabilites was evaluated basing on the peroxide values(POVs) by Schaal oven accelerated storage test. The wall material was based on RP and 16.7-77.8% MD and/or MS replacement of RP. Results showed that the glass transition temperature (Tg) of microencapsulate were lowered by the increase of RP but heightened by the addition of MD and/or MS, the glass transition enthalpies of microencapsulates could be generally decreased by increasing MS content but increased with increasing MD proportion, and the glass transition cooperativity of shell constituents could be enhanced by the addition of MS. TG-DTG analysis results showed that the degradation temperature of blend oils was retarded from 270℃to above 300℃. During the accelerated storage period, oxidative stabilites of the core oils were exponentially decreased for the encapsulates with the shell compositions of MS:MD:RP=2:2:2,1:4:1 and 4:1:1, while the oxidative stabilites of the encapsulates with a higher portions of RP hydrolysate as shell compositons were gradually improved. The POVs of the encapsulates were kept in the induction stage after 7 days'storage period.8. The secondary structure of the protein and molecule structure of oils in the core of encapsulates were characterized by optical information of fourier transform infrared spectroscopy(FTIR). Results showed that the secondary structure of protein exhibited a significant change tendency from P-sheets to a-helixes during the spray drying process, accompanied by a decrease of random coils and an increase inβ-turns. However, the conversion into random coils in amide I band could be attenuated by the increasing MD content in shell, and that in amide III band could be reduced by the increasing MS content in shell. After 6 months'storage period at 60℃, the molecule structure of protein was more stable in the shell with a relative higher portion of RP, the stable secondary struture of protein tended into less stable structures in the shell with a relative higher content of carbohydrate, meanwhile, the unsaturated double bonds of core oils have been broken down, and turned into C=O, which was contributed to the decreased proportion of unsaturated fatty acids in the core oils. 9. Sixty Sprague-Dawley rats(3weeks old) in 3 groups were used to evaluate the effects of protein from RD(RD) or its hydrolate (RD-H) on growth performance, blood chemical compositions, serum hormone, small intestinal morphology, and somatotrophic axis, with one group on soybean protein(SB) diet as a control. Compared with the control, the recovery and growth of impaired villus in the small intestine could be ameliorated by rice proteins that from RD or RD-H diets, and the feed conversion efficiency and growth performance could also be improved by rice proteins that from RD or RD-H diets. Blood analysis indicated that the protein metabolim status of SD rat body could be improved by RD-H diet, athought the body was still in the adaptive phase to the RD-H diet, as compared to RD and SB diets. Serum IgG concentration has no significant difference among three groups. The growth levels of organs were not influenced by the diets with addition of RD or RD-H. Real-time RT-PCR analysis showed that, the hepatic expression level of GHR mRNA in SD rats fed with RD-H diet was higher than those fed with RD or SB diets for 7 d, the hepatic (except for 28 d) and muscular expression of IGF-1 mRNA in SD rats were enhanced by RD-H diet as compared to RD or SB diets for 7 d and 28 d, and the muscular expressiong of GHR mRNA was not different among the three groups throughout the experiment. These results suggested that diet with addition of RD-H could be helpful for the growth status improvement of post-weaned SD rats.10. Sixty Sprague-Dawley rats(3weeks old) in 3 groups were used to evaluate the effects of early-weaned diets with additon of RD-H or RD-H as microencapsulate shell materials on growth status, small intestinal morphology and somatotrophic axis, with one group weaned on SB diet on 28 d as a control. Results showed that the growth performances of rats early-weaned on RD-H or MF diets on 21 d were not lower than those in the control. The level of serum UN in rats fed on RD diet was lower than those both of RD-H group and the control for 14 d(p<0.05), and there were no significant difference among three groups for 28 d. The serum concentrations of IL-2, IgG and Insulin were similar to each other among three groups. The serum GH concentrations of rats in early-weaned groups were significantly higher than that of the control (p<0.05) for 14 d. Though their bodies still in the stress state, the serum GH concentration of rats fed on RD-H diet was remarkably higher than that in MF group (p<0.05). The growth levels of organs were also similar among three.groups. For the control, the small intestine morphosis was still in the recovery stage on 14 d. Real-time RT-PCR analysis showed that the hepatic and muscular expression of IGF-1 mRNA of SD rats fed with RD-H diet was slightly higher than that in MF group (p>0.05), but significantly higher than that in the control (p<0.05) for 14 d. The hepatic expression of FAS mRNA of SD rats fed with RD-H or MF diet was significantly higher than that in the control for 28 d (p<0.05). These results indicated that diets of MF or RD-H could put the weaning age of SD rats forward 7 days.11. A 28-day metabolic test was conducted with 4×4 Latin square design and tweenty Sprague-Dawley rats(28d old) were used to evaluate the nutrition values of proteins from RD, RD-H or MF, with a control of soybean protein. Compared with the control, the nitrogen retention in body and the digestion and absorption of dietary fat were significantly improved by rice proteins from RD, RD-H or MF diets(p<0.01), and the average daily nitrogen depositions for SB, RD, RD-H and MF diets were 0.538,0.590, 0.605 and 0.625g, respectively. The digestion and absorption of dietary protein and fat were not influenced by the limited proteolysis of RD or emulsifying process of oil in vitro(P>0.05).
|
PDF Full Text Request