| Rana chensinensis ovum(RCO)is the main waste/by-product during the process of traditional Chinese medicine,Oviductus Ranae(OR),which is a unique biological resource.It is rich in protein,unsaturated fatty acid,phospholipids,trace elements,free amino acids and other nutrients,which can be used as a natural high-quality and cheap nutritional food raw material.At present,the research on the application and development of RCO is not deep enough,and the scientific and technological content is not high,resulting in insufficient utilization of RCO resources.Due to improve the application potential of RCO in food,enhance its commercial and added value,this study aimed to develop new preparations using the two main nutritional components in RCO,and explore the application potential in bioactive substances delivery.First of all,this work focused on the preparation of self-assembled RCO protein nanoparticles(RNPs)for use as stabilizers,and analyzed the effects of three acidifiers,including hydrochloric acid(HCl),D-glucono-δ-lactone(GDL)and citric acid(CA),on the physicochemical properties and structure of the prepared RNPs.The effects of homogenization,filtration and centrifugation on the properties of RNPs were compared.The appearance and microscopic differences of RNPs prepared by different acidifiers were analyzed by photography and scanning electron microscopy(SEM).Meanwhile,particle size,zeta potential and autofluorescence spectrum demonstrated that different acidifiers affected the structure and conformation of RNPs.In addition,the interaction between the RNPs during the p H cycle was further analyzed by Fourier transform infrared spectroscopy(FTIR),indicating that there was self-assembly between RNPs.The results indicated that RNPs-CA showed the good performance as an acidifier.Compared with the RNPs prepared by HCl and GDL,RNPs-CA had the smallest particle size and the most charge,which was an ideal Pickering emulsion stabilizer.Secondly,in order to explore the potential application of RNPs in the health food industry,the functional properties,stabilization and antioxidant activities of soybean protein isolate,zein,whey protein and ovalbumin nanoparticles prepared by p H cycling method were analyzed and compared.Various properties and functions of RNPs were studied through experiments on particle size,zeta potential,long-term stability and antioxidant activity.In general,RNPs prepared by p H cycling method showed significant advantages in functional properties,long-term stability,stability and antioxidant activity.RNPs held great promise in meeting the demand for "surfactantfree" Pickering emulsion with adjustable interface structure.It can be used not only as a stabilizer for Pickering emulsion,but also as an antioxidant to effectively delay or inhibit oxidation processes,and had a broad application prospect in the field of drugs,cosmetics and health foods.Then,in order to realize the comprehensive stereoscopic exploitation of RCO resources,a new Pickering emulsion system was constructed using the prepared RNPs and its own bioactive Rana chensinensis ovum oil(RCOO).Pickering emulsion with different RNPs concentrations and oil volume fractions were prepared by high-speed homogenization technology.The results of particle size,zeta potential and long-term stability observation showed that when the oil phase volume fraction was constant,the RNPs concentration increased,the particle size decreased,and the emulsion stability increased.When RNPs concentration was constant,the oil phase volume fraction increased in the range of 30%-60%,the particle size increased,and the emulsion stability decreased.In addition,the emulsion showed great storage stability during 30-day observation.The microstructure of RNPs stabilized Pickering emulsion was observed by CLSM.The colocalization of RNPs and RCOO distribution in the fluorescently labeled emulsion indicated that the resulting emulsion successfully integrated the oil and RNPs.The droplets were round in shape,and closely connected.RNPs was firmly adsorbed on the oil-water interface,forming O/W Pickering emulsion.Rheometer was used to analyze the rheological properties of Pickering emulsion.All emulsion showed that storage modulus(G’)was greater than the loss modulus(G"),indicating that Pickering emulsion formed a gel-like network structure.At the same time,the data showed that higher oil phase volume fraction and RNPs concentration contributed to the formation of gel-like network structure.In the lipid oxidation experiment,the Lipid hydroperoxide(LH)was used as the primary oxidation index and malondialdehyde(MDA)was used as the secondary oxidation index.The results showed that the degree of lipid oxidation was affected by the concentration of RNPs.The higher the concentration of RNPs,the lower the content of LH and MDA,indicating that higher RNPs concentration was conducive to the antioxidant effect of emulsion.For the first time,RNPs was creatively used as a stabilizer to encapsulate RCOO,and the two main active parts of RCO were used to prepare a new Pickering emulsion,which can bring high added value and high commercial value to RCO.Finally,in order to explore the application potential of the novel Pickering emulsion in delivering bioactive substances,quercetin was taken as an example,the Pickering emulsion with RNPs concentration of 2% and oil volume fraction of 50%was used to load quercetin,and the storage stability,thermal stability,UV stability and degradation characteristics of the emulsion system were further studied.The results showed that the physical barrier formed by RNPs at the oil-water interface helped the quercetin encapsulated in Pickering emulsion maintain a high retention rate when exposed to heat,UV and long-term storage.Compared with bulk oil,Pickering emulsion can release more free fatty acids during the simulated intestinal digestion process,effectively improving the bioavailability of quercetin.This work shows that the constructed novel Pickering emulsion shows great potential in improving the stability and bioaccessibility of bioactive substances.The results of this work could broaden our current understanding of edible Pickering emulsion,provide valuable information for the design of food-grade carriers for packaging,protection and transport of bioactive substances,and provide reference basis for practical applications in the pharmaceuticals,cosmetics,and health food. |
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