Study On Preparation And Properties Of Modified Rapeseed Albumin (Napin) From Ultrasonic-assisted Extraction

In this paper,rapeseed albumin（napin）was prepared from traditional hot pressing rapeseed meal by ultrasonic-assisted technique.The main components of ultrasonic-assisted extracted napin（UEN）and traditional water-extracted napin（TEN）were determined and compared,respectively.Then the functional properties and physicochemical characteristics of napins were measured and studied the relationship between those,effects of ultrasounic-assisted on protein modification were analyzed.The antioxidant activity in vitro of napins was discussed preliminarily.Finally,the acute toxicity of napin could create a theoretical basis for its application in food industry.1.Preparation of napin by ultrasonic-assisted extraction.The extraction process of napin from defatted rapeseed meal using ultrasound-assisted was optimized.Effects of liquid/meal ratio,extraction time,ultrasonic temperature and ultrasonic power on napin extraction yield were studied.The components of UEN were measured and compared with those of TEN.The results indicated that dissolution rate of napin had significantly increased by ultrasonic-assisted extraction.The optimal extraction conditions were as follows:liquid/meal ratio was 18:1,extraction time was 62 min,ultrasonic temperature was 42℃and ultrasonic power was 80 W.The one-time extraction rate of napin was up to75.75%.The protein content of UEN was 82.3%and impurity content was lower than TEN.With the full range of amino acids,amino acid composition（AAC）of napin was balanceable and complied with the FAO/WHO recommendation pattern.2.Study on the functional properties of napins.The functional properties of napins were determined as function of p H and temperature,and compared with those of soybean protein isolates（SPI）.The study found that solubility of UEN was slightly reduced than TEN and reached its lowest point at p H 5 and 10;oil-holding capacity of UEN was significantly enhanced and reached highest at 60℃,the oil-holding capacity began to decline after 70℃;emulsifying properties of UEN showed relative improvement and was consistent with the trend of solubility;foaming properties were related to solubility,foaming stability of UEN was increased while foaming capacity showed decreased.Compared to determination results of SPI,napins showed stronger oil-holding,foaming and emulsifying capacity.3.Analysis of physicochemical characteristics of napins.Structure of napins were determined by scanned using UV-Vis,FT-IR,fluorescence and SEM;physicochemical properties,including relative molecular mass,-SH,disulfide bonds,surface,thermodynamic properties,particle size,were measured.Compared to TEN,UV absorption band of UEN shifted to short wavelength（blue shift）,infrared absorption peak of amide and associating hydroxyl region were changed,fluorescence emission wavelength and intensity were all changed,surface shape of protein grain became smaller;UEN had the same relative molecular mass,increased content of free sulfhydryl groups,reduced content of disulfide bonds,smaller average particle size,and the surface hydrophobicity index of UEN was increased,thermal denaturation temperature of UEN became higher and the heat enthalpy was decreased.Thus can be inferred that ultrasonic-assisted extraction had changed secondary and tertiary structure of napin but may had no effect on the primary structure.4.Preliminary discussion about antioxidant activity of napins.The antioxidant activity in vitro of two kinds of napins was measured by various antioxidant assays,including DPPH radical scavenging,hydroxyl radicals（·OH）scavenging,superoxide anion radical（O₂^-·）scavenging,ferric reducing power and inhibitory ability of linoleic acid oxidation.The results showed that two kinds of napins had certain antioxidant activity in vitro,and the antioxidant activity of napin was significantly increased after ultrasonic-assisted extraction（P<0.05）.The ability of the free radicals scavenging activity was:DPPH·>·OH>O₂^-·.The ferric reducing capacity showed a good linear relationship with concentration of protein.The inhibition of linoleic acid oxidation of UEN was enhanced and inhibition rate was could be up to 36.5%at 7 d.5.Evaluation of acute toxicity of ultrasonic-assisted napin.Acute toxicity of ultrasonic-assisted napin was evaluated by intragastric administration in mice.The pre-experiment indicated that the median lethal dose(LD₅₀)was unable to measured.Then observed for 14 consecutive days after intragastric administration in mice with maximum dose(20 g/kg·d^-1)one-time.The medicated mice didn’t die,growth rate of body weight and food intake had no distinctly difference with the control group.After dissected,the main organs of mice did not show pathological changes.There were no significant difference between organ coefficients among all groups.The results indicated that ultrasonic-assisted napin had no obvious toxicity.Napins can be used as additives or nutrition enhancer applied in food industry.