Effect Of Gelatin Molecular Structure On The Properties Of Fish Oil Emulsions

Fish oil has important physiological functions and the potential to reduce the risk of disease.Due to its unstable double bond,special fishy smell and low solubility,it is difficult to apply in food.It is therefore necessary to develop new dosage forms and formulations(eg droplets)to encapsulate fish oil.Emulsions are thermally unstable systems consisting of water and oil,where one phase exists in the form of droplets in the other.Wrapping fish oil as an oil phase inside the emulsions can effectively improve the storage stability of fish oil and increase its application in food.As a kind of amphiphilic macromolecular protein,gelatin can be used to prepare traditional emulsions directly,or it can be modified to gelatin nanoparticles to prepare Pickering emulsions,and it can also be assembled with polysaccharide to prepare multi-layer emulsions.The different emulsion forms are used in food.There are also different applications in the industry.At present,there is no systematic research on the influence of the molecular structure of gelatin on the properties of emulsions.Therefore,this article mainly focuses on the molecular structure of gelatin to prepare different types of emulsions and compare their characteristics.(1)Preparation of traditional emulsions :We prepared fish oil-loaded gelatin emulsions by a homogenizing method.Subsequently,we explored the effects of preparation and storage factors(gelatin solution p H,homogenizing time,homogenizing speed,and storage temperature)on the emulsions.Our results confirmed the successful preparation of fish oil-loaded gelatin emulsions in liquid and redispersible gel forms.Higher gelatin solution p H,higher storage temperature,and longer storage time would induce the switch from liquid forms to redispersible gel forms.The emulsions mainly consisted of droplets with three different size distributions,which were linearly decreased with the increase of gelatin solution p H and homogenizing time,but were exponentially decreased with the increase of homogenizing speed.Storage temperatures had obviously different effects on the emulsion storage.This work provides a way to encapsulate fish oils in multiple forms of emulsions and provides potential promising application prospective in food beverages,soft sweets,etc.It also provides basic understanding on the formation of gelatin-based emulsions.(2)Pickering emulsions: We first prepared crosslinked gelatin nanoparticles by a secondary desolvation method.We then prepared fish oil-loaded gelatin nanoparticles by homogenization.The results confirmed that cross-linked gelatin nanoparticles and fish oil-loaded gelatin nanoparticles-stabilized Pickering emulsions could be successfully prepared.Pickering emulsions are mainly adsorbed by fish oil-loaded crosslinked gelatin nanoparticles by storage temperatures of different sizes.The storage of the emulsions has significantly different effects.(3)Comparison of properties of traditional emulsions and Pickering emulsions:Traditional emulsions and Pickering emulsions are important delivery systems with different stabilization mechanisms.Generally,it is thought that Pickering emulsions had higher stability compared with traditional emulsions.In this work,gelatin-stabilized traditional emulsions and gelatin nanoparticle-stabilized Pickering emulsions were prepared to compare the long-term stability.Using digital camera,optical microscopy,and confocal laser scanning microscopy,the forms,creaming stability,droplet structure stability,and dilution stability of these two emulsions are compared.The results show traditional emulsions and Pickering emulsions have different stability behaviors.Traditional emulsions have three different forms(liquid,redispersible emulsion gel,unredispersible emulsion gel),whereas Pickering emulsions only have liquid form.Neither traditional emulsions nor Pickering emulsions always showed higher creaming stability,which was dependent on stabilizer concentration and emulsions forms.Droplet sizes were exponentially decreased with the increase of stabilizer concentration.The exponential decrease contains fast decay(“stabilizer-poor”,<.1.0%)regime and slow decay(“stabilizer-rich”,>1.0%)regime.Both traditional emulsions and Pickering emulsions have good droplet structure stability at high stabilizer concentrations(stabilizer is rich,1.0%-4.0%)and show droplet coalescence at low stabilizer concentrations(stabilizer is poor,0.2%-0.5%).Finally,they have similar and good dilution stability.This work provides multiple ways to encapsulate fish oils in multiple form emulsions.Furthermore,it will be beneficial to basic understanding of traditional emulsions and Pickering emulsions.(4)Multilayer emulsions: The development of multilayer emulsions and studying the effects of varying parameters on the storage stability and digestion of multilayer emulsions are of great interest.The purpose of this study was to examine the effects of the interfacial layer number on the storage stability and in vitro digestion of fish oil-loaded multilayer emulsions.Primary,secondary,tertiary,and quaternary multilayer emulsions with the same total thickness of interfacial layer,consisting of gelatin particle and polysaccharides(anionic alginate and cationic chitosan),were prepared using a layer-by-layer electrostatic deposition technique.Then,the microstructure,storage stability,and in vitro digestion of these emulsions were studied.The results demonstrated that the interfacial layer number had an obvious effect on the storage and in vitro digestion of these emulsions.Increasing interfacial layer number increased the emulsion creaming stability during the storage process and increased the emulsion droplet stability against the gastric phase.But,the interfacial layer number in the multilayer emulsions had no obvious effects on the droplet stability against droplet coalescence during the storage process and against the small intestinal phases of gastrointestinal tract models.Moreover,it also had no obvious effect on the sustained FFA release of multilayer emulsions.Further,all the multilayer liquid emulsions could change to stable emulsion gels.This study could advance the fundamental understanding of multilayer emulsions and promote their potential applications.The exploration of these fish oil-loaded liquid emulsions and emulsion gels could result in their potential application in the food industry.