Investigation On The The Effects Of Different Antioxidants On The Physicochemical Stability And In Vitro Digestibility Of Lipids Of Protein-Stabilised Oil-In-Water Emulsion

Protein-stabilized emulsion has been widely used in food industry. However, The visual creaming could be produced by poor physical stability of emulsions, while the lipid oxidation of emulsion may seriously influence the flavor, even promoting the formation of toxic substances that were harmful to human health. The effects of various antioxidants on physicochemical stability and in vitro digestibility of lipids of the emulsions were investigated. The main results were as follows:1.The effects of whey protein concentration(0.45%~3.60%) and ionic strength(250 mmol/L NaCl) on the interfacial property,physical and oxidative stability of emulsions were investigated. The results showed that increasing whey protein concentration lead to decrease in the particle size, creaming index, peroxide value(POV) and thiobarbituric acid reactive substances(TBARS), and increase in interfacial protein concentration, viscosity and potential. Addition of 250 mmol/L NaCl contributed to increase in the particle size, creaming index, interfacial protein concentration, potential,viscosity, POV and TBARS values of the emulsions. These findings indicated that the physical and oxidative stability of the emulsions could be improved by increasing the interfacial protein concentration or decreasing ionic strength.2. The effects of naringin in the range of 0.05 mg/m L ~ 0.4 mg/mL on the physical and oxidative stability of emulsions stabilized by native and heat-denatured whey protein were investigated. The formation of whey protein–naringin complex was verified by the fluorescence spectra. The whey protein–naringin complex had little effect on the physical stability of emulsions,but positive influence on the oxidative stability of emulsions. The ability of the whey protein to suppress the primary oxidation of emulsions enhanced after heat treatment,while the ability to delay the secondary oxidation of emulsions decreased.3. The effects of naringin in the range of 0.05mg/m L ~ 0.2mg/m L on the physical and oxidative stability of emulsions stabilized by native and heat-denatured whey protein were investigated. The formation of whey protein–naringin complex was verified by the fluorescence spectra. In the case of heated whey protein emulsion, the oil-water interface could be competitively adsorbed by naringin particles to form protein–naringin complex, which resulted in the extraordinary improvement of physical and oxidative stability. However, compared to the heated group, as the native whey protein was just inclined to form unstable whey protein–naringin complex due to the fact that naringin particles were supposed to mainly adsorb outside protein layer, thus the stability of native whey protein emulsions showed no distinct improvement.4. Moreover,the effects of ascorbyl palmitate(lipophilic), rutin(amphiphilic), ferulic acid(hydrophilic) on the stability and in vitro digestibility of lipids of different protein-stabilized ?- carotene emulsions were investigated. The results showed that the three antioxidants had little effect on the physical stability of sodium caseinate and whey protein isolate stabilized emulsions, but remarkable influence on the soy protein-stablized emulsion in the order:rutin>ferulic acid>ascorbic palmitate>blank.The rate of ?-carotene degradation significantly accelerated as the storage temperature increases. The three antioxidants could not suppress ?-carotene degradation in whey protein-stabilized emulsions,especially under the condition of 60 ?, ferulic acid and ascorbic acid palmitate even accelerated the degradation of ?-carotene. Degradation of ?-carotene could be inhibited by ferulic acid and rutin in sodium caseinate-stabilized emulsion at all the three temperatures(30 ?, 45 ?, 60 ?).However, the antioxidants could not hinder ?-carotene degradation in the emulsions stabilized by soy protein isolate at 30 ? and 45 ?, but could enhance the stability of ?-carotene in the emulsions at 60 ? in the order: rutin> ferulic acid> ascorbic palmitate> blank. The negative potential of the emulsions significantly reduced after digestion,which meant the decreased physical stability of emulsions.Ferulic acid and ascorbic acid palmitate could delay the digestion rate of sodium caseinate-stabilzied emulsions and emulsions stabilized by soy protein isolates respectively, while rutin enhanced the digestion rate of whey protein-stabilzied emulsion. Three antioxidants could suppress the ?-carotene decomposition of the protein-stabilzied emulsions during digestion at different levels, in which rutin exhibited the best ability to stabilize ?-carotene followed by ferulic acid, ascorbyl palmitate.