Fabrication And Stability Of Milk Protein-triglyceride Nanoemulsions

One of the most important factors affecting emulsion stability is the choose of emulsifiers.Emulsifiers currently used in the food industry can be synthetic,but more of them are natural emulsifiers such as phospholipids,proteins,polysaccharides and so on.In recent years,the function of milk protein as emulsifiers are rising more and more attention and it can be quickly adsorbed on the new oil-water interface during emulsification.Casein and whey protein isolates from milk are widely used in the food and beverage industry.Tripolyglycerol monostearate(PGFE)is a low molecular weight synthetic emulsifier with good dispersion,emulsification and defoaming ability.It is classified as a GRAS substance by FDA and can be completely digested and absorbed by the human body.In this thesis,three main milk proteins(casein and its commonly used sodium salt,sodium caseinate,whey protein isolate)were selected and mixed with a small molecule emulsifier PGFE to prepare food grade peppermint oil nanoemulsions.In recent years,there has been increasing interest in the preparation of new materials containing essential oils.As one kind of essential oil,peppermint oil has been used in many fields.Over the past years,nano-encapsulation technology has become a new choice for its addition in food formula.It not only protects bioactive substances in essential oils from direct exposure to various environmental factors,but also produces new types of performance improvements with good application prospects.β-carotene has a wide range of applications in the food industry,such as food coloring,feed additives,and fragrances.Moreover,dietary β-carotene is the main source of vitamin A,which has great benefits for skin,mucous membranes,immune system and vision.The main goal of this study is to prepare a high-stability nanoemulsion by using a mixture of milk protein and PGFE emulsifiers,broaden the application range of milk protein emulsion,and load the functional components peppermint oil and β-carotene.At the same time,by studying its stability and sensory characteristics,we hope to explore a new type of functional emulsion products.The addition of milk protein can significantly reduce the surface tension of nanoemulsions stabilized only by PGFE.Casein-PGFE emulsion has lower surface tension,smaller particle size and higher viscosity.All emulsions show shear thinning phenomenon.The peppermint oil nanoemulsions with three suitable concentrations of milk protein and PGFE show good particle size,PDI and potential stability during storage for 21 days at room temperature.All the emulsions remain stable at the end of storage.The instability mechanism of the emulsion is mainly caused by creaming and coalescence,and the PGFE/casein composite emulsion has a better stability index than others.All emulsions exhibit good ionic stability and freeze-thaw stability,and the addition of milk protein increases the absolute zeta potential of the emulsion at high salt ionic strength.In addition,the composite emulsifier nanoemulsion also has good neutral and alkaline stability,but has low resistance to acidic environments.Comparing two preparation methods of β-carotene peppermint oil solution(low temperature and long-time heating combined with ultrasonic and high-temperature short-time heating),it was found that the nanoemulsions prepared by the latter show higher β-carotene retention rate,smaller droplet size and PDI during high-temperature storage.When the mixing ratio is less than 0.5,PGFE-casein-stabilized β-carotene peppermint oil nanoemulsion have a single,narrow particle size distribution and exhibit good physical stability.Based on the Herschel-Bulkley model,β-carotene nanoemulsions are found to be pseudoplastic fluid with n<1.Sensory analysis found that electronic tongue can distinguish small differences between all the different samples by the difference in taste.It is indicated that electronic sensory evaluation is a convenient and effective sensory evaluation method.The identification and evaluation of flavor emulsion can be achieved by different data processing methods.