| Gelatin is a high-molecular natural polypeptide polymer produced by moderate hydrolysis of collagen.It is widely used in food industry due to its low cost,good biocompatibility,and emulsification.In recent years,the research and application of gelatin-based emulsions become hot spots,and these researches mainly focus on gelatin nanoparticles and gelatin-based Pickering emulsions.The preparation process of nanoparticles usually adopts the anti-solvent method,which involves the use of toxic reagents(like glutaraldehyde and acetone)and cumbersome preparation steps.In addition,the anti-solved method is difficult to use for scale-up production,limiting gelatin’s application in food filed.Emulsions with an internal phase volume fraction greater than 74% are called High Internal Phase Emulsions(HIPEs).In recent years,HIPEs have shown good application prospects in the fields of porous materials,foam and functional factor loading.In this study,aiming at the problems existing in the research of gelatin emulsion,HIPEs were prepared by gelatin microgel technology using type A gelatin as raw material.And for the defect of thermal instability of gelatin emulsion,crosslinking was catalyzed by transglutaminase(TG).The preparation mechanism of highly stable HIPEs was studied and the HIPEs were used for 3D printing and capsaicin embedding,aiming to provide a theoretical basis for the development and application of food grade gelatin-based HIPEs.The specific research contents and conclusions are as follows:(1)One-step homogenization method was used to prepare HIPEs directly stabilized by gelatin,and the effects of gelatin concentration on the properties of HIPEs were studied.The results have shown that,considering energy consumption,the HIPEs were obtained with shear rate at 15,000 rpm for 1 min,and the obtained HIPEs showed a small size and uniform droplet distribution.As the concentration of gelatin increased,the viscosity of the emulsion increased.When the concentration reached to0.5 wt%,a gel-like emulsion could be formed,and the tolerance to shear and centrifugal force of HIPEs was enhanced.After the concentration reached to 1.0 wt%,the oil separation phenomenon after the emulsion experienced a freeze-thaw cycle was improved.When the gelatin concentration increased to 2.0 wt%,the thermal stability of HIPEs increased,but it still could not meet the requirements of high temperature sterilization.Except for the HIPEs stabilized by 0.1 wt% gelatin,the emulsions of the other groups had no obvious droplet coalescence after storage for 70 days,which proved that the HIPEs stabilized by gelatin had good storage stability.The results of the interface behavior study showed that as the concentration of gelatin increased,the rate of gelatin diffusion to the interface gradually increased and the time required was shortened.The rate of gelatin adsorption and rearrangement at the interface also increased,and the stability of the formed interface film increases as well,consistent with the macroscopic properties of gelatin emulsions.The results showed that HIPEs with different properties and stability could be obtained by adjusting the concentration of gelatin to cope with different application scenarios.(2)Aiming at the defects in the thermal stability of gelatin based HIPEs,TG was used to improve the thermal stability of gelatin gels.The effects of TG crosslinking time(0 ～ 4 h)on the properties of gelatin and gelatin-based HIPEs was investigated.The results showed that with the extension of the TG crosslinking time,the melting transition temperature of gelatin increased significantly,the three-phase contact angle increased,and the emulsification of gelatin was enhanced.Thermal stability of gelatin-based HIPEs was significantly improved.TG mainly targeted the catalytic sites of glutamine and lysine,and formed targeted covalent crosslinking within and between gelatin molecules,promoting the formation of intramolecular triple-helical structures and macromolecular aggregates,and increasing intermolecular entanglement.Therefore,a more stable continuous phase structure was formed during the preparation of HIPEs,and the structure remained stable during the heat treatment process.The HIPEs stabilized by gelatin that crosslinked for 4 h still maintained good appearance,small droplet size and high viscosity after sterilization at 121 ℃ for 20 min,which was of great significance for commercial sterilization and storage of emulsions at room temperature.In addition,HIPEs stabilized by gelatin that crosslinked by TG still maintained good freeze-thaw stability,centrifugal stability and storage stability.The results of rheological studies showed that HIPEs stabilized by gelatin crosslinked for 4h showed high viscosity and low frequency dependence.In addition,it showed good printability in 3D printing experiments and fat-soluble pigments further enriched the color of 3D printed products,which could meet consumers’ more diversified needs for food.(3)Capsaicin has a variety of functional properties,but its pungent smell and damage to the gastric mucosa limit its application in food.Gelatin-based HIPEs were used to embed capsaicin,and its application in capsaicin embedded delivery was studied.The results showed that the loading of capsaicin(3 mg/m L)had no significant effect on the droplet distribution and apparent viscosity of gelatin-based HIPEs.The results of the electronic nose showed that compared with the direct dissolution in soybean oil,the HIPEs embedding better concealed the odor of capsaicin,and the concealing effect was enhanced with the prolonged TG crosslinking time.The results of studies on the release of capsaicin in the stomach showed that compared with capsaicin dissolved in free soybean oil,HIPEs embedding effectively reduced the release of capsaicin in the stomach,and TG crosslinking further enhanced the protective effect of embedding.In addition,in vitro static digestion simulation results showed that HIPEs embedding significantly increased the retention rate of capsaicin in the micellar phase in intestinal digestion.In general,HIPEs embedding effectively reduced the irritation of capsaicin on the nasal cavity and gastric mucosa and increased the bioavailability of capsaicin. |
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