Preparation And Application Of High Internal Phase Water-in-oil Emulsion Gel Of Oleanolic Acid

Solid fats contain too much saturated fatty acids which are unhealthy for consumers,and in traditional production process,there would be some trans-fatty acids(TFAs).In recent years,various countries and regions have successively introduced policies and legislation to prohibit the sale of foods containing trans-fatty acids.Consumers have gradually realized the harm of high-fat diets to human health and the recognition of healthy oils.Food science and industry were in urgent need of new healthy lipid products that could not only solve food safety problems,but also meet nutritional needs.In order to achieve the purpose of improving consumers’ awareness of edible solid fats and expanding the scale of the consumer market.In this regard,the search for natural compound-stabilized water-in-oil emulsion gels to replace traditional solid fats has become an attractive topic in basic research in food science.Oleanolic acid(OA)is a class of pentacyclic triterpenoids,which widely distributed in the leaves,fruits and seeds of plants in nature.OA is a component of a renewable resource,non-toxic,odorless,and has various biological activities such as antioxidant,anti-inflammatory and anti-tumor.At present,it was mainly used in the pharmaceutical industry as an anti-hepatitis drug,and its application in the food field has yet to be developed.Studies had shown that ursolic acid,an isomer of OA,can be used as emulsified particles to stabilize emulsions.Based on this,we deduced that OA also had the potential as an emulsifier to stabilize emulsions.Pickering emulsion gel with vegetable oil as continuous phase was prepared by using OA,which were new method to replace traditional solid fat.It can reduce the intake of saturated fatty acids in traditional solid fat and eliminate the intake of trans-trans fatty acid.In this study,the natural active substance OA was selected as the particle to stable the emulsion.Firstly,the properties of OA were characterized and then to judge the accessibility to stable emulsion.Secondly,OA was used as gelator to prepare emulsion,and the properties of emulsion were also be presented.Lastly,the OA-emulsion was applied as one part of solid fat to produce the cake.The main specific research content and conclusion were showed as below.(1)The relevant properties of OA as stable emulsion particles were determined.Scanning electron microscope,contact angle measuring instrument,nanoparticle size analyzer,polarizing microscope were used to characterize the microscopic morphology,contact angle,particle size and other properties of OA.These determinations could offer the possibility of OA as an emulsion gelator and explain the mechanism of gel formation.The results showed that OA was a rod-like crystal with a length of about 1-20 μm.OA has strong hydrophobicity and has the potential to stabilize W/O-type Pickering emulsion gels.(2)The OA-high internal phase emulsion gel(OA-HIPE)were prepared and researched.The simple emulsion was formed by Canola oil(dispersion phase)and water(continuous phase),and the effects of different additions of OA(geltor)on the properties of emulsion gels were investigated.A common water-in-oil emulsifier,polyglyceryl polyricinoleate(PGPR),was used as a control.The differences in the rheology and stability of the gels were discussed.The formation and stabilization mechanism of HIPE gels were analyzed by confocal laser scanning microscopy(CLSM)and ordinary optical microscopy.The study found that a certain amount of OA could be firmly adsorbed on the oil-water interface.However,an excess of OA could be dispersed in the oil to increase the physical strength of the continuous phase,which can stabilize the high internal phase emulsion and form a gel.CLSM observation confirmed that the formation of W/O type emulsion.Measurement of rheological properties of emulsion gels by using a rotational rheometer.The results showed that when the addition amount of OA increased from 1 % to 5 %,the gel strength of the emulsion was increased.Meanwhile,the yield stress,frequency stability and thixotropic recovery were also increased.Different stability tests of HIPE gels were performed.The results demonstrated that the stability of OA-HIPE gels was positively correlated with the added amount of OA.Under the same addition amount,it was found that the growth rate of OA-HIPE gel’s particle size was smaller than that of PGPR-HIPE after storage for 14 days.Even the former showed better physical stability.The p H stability of the emulsion was investigated by adjusting the p H of the aqueous phase from 3 to 11.It was found that under the condition of p H 3,the OA-HIPE gel had the best emulsion stability.Salt ions were usually considered to hinder the stability of emulsions.However,the stability of OA-HIPE gel was improved after adding salt ions in the research.Meanwhile,the droplet size was significantly reduced,and the stiffness of the emulsion gel was significantly improved.In conclusion,all the stability data showed that OA-HIPE gels were superior to PGPR-HIPE.(3)Application study of oleanolic acid high internal phase emulsion gel.The prepared OA-HIPE gel(with OA addition of 3 %)was used as a structural oil,and cakes with different oil formulations were made to replace the vegetable cream sold in the market,and the texture and sensory evaluations of the cakes were carried out.The microscopic results showed that the prepared cake batter formed a good network structure after adding OA-HIPE gel.Baking loss results showed that cakes prepared with higher moisture content OA-HIPE gel instead of commercial butter had little difference in loss during baking compared to the control,which indicated that the batter had good water holding capacity under this recipe.The texture results have also well verified that cakes prepared with OA-HIPE gel partially or completely substituted for commercially available butter produced samples with different hardness and different chewiness with basically the same elasticity,cohesion and recovery.In conclusion,it was completely feasible to use OA-HIPEs gel to replace part of the oil to prepare cakes.The prepared cakes could catch up with the commercial cakes in terms of appearance and taste,and there was still a lot of room for improvement in terms of flavor,color and smell.In conclusion,OA can be used as a hydrophobic Pickering particle to successfully prepare a high internal phase W/O emulsion gel.The gel strength of the emulsion is positively correlated with the amount of OA added,and has good storage stability and ionic stability.It is feasible to use OA-HIPE gel to replace part of margarine in cake making.Therefore,this study concluded that OA is a kind of Pickering particles with abundant sources,safe and non-toxic,and various biological activities.The method for preparing the OA-HIPE gel is easy to operate,and the formed water-in-oil HIPE gel has excellent properties.It is determined that the stability of OA-HIPE gel has certain advantages compared with commonly used emulsifiers(PGPR),and OA-HIPE gel has the ability to be applied in the food field.The above research is expected to expand the application of OA as a new natural W/O type Pickering emulsion gelling factor,which provides a reference for exploring the field of new food-grade emulsion stabilizers,and also provides hydrogenated vegetable oil products and solid fat products a possible new alternative,which has high reference and innovation in both theory and practice.