Preparation Of Kiwifruit Polypeptide And Its Antibacterial Activity

The kiwifruit contains many biologically active substances and has great potential for applications.Polypeptides have very important in topic of higher research value.However,there are few studies on kiwifruit’s polypeptides.In this paper,a preliminary and more comprehensive study was conducted on picking fresh kiwifruit as a research object,providing a certain reference for the future improvement of actual application value of kiwifruit and in-depth study of polypeptides.The main findings are:1.Using the characteristics of chemical substances,the components of kiwi fruit were initially extracted,analyzed and then identified.The resultants materials were proteins,polypeptides,polysaccharides,triterpenoids,organic acids and other few components were also initially detected in kiwifruit.The presence;2.Ultrasonic water extraction method was used to optimize the extraction process of proteins in the fresh kiwifruit.The experimental results showed that when ultrasonic was power 200 W,extraction temperature was 50 ℃,pH value was 8.0,extraction time was 1h,water ratio was 15:1,and proteins extraction rate recorded at peak was55.13%.3.Enzymatic hydrolysis of the prepared kiwifruit proteins as raw materials,the type of the best hydrolase was selected as neutral protease,and then the enzymolysis process was optimized through experiments,that is: the amount of neutral protease was added at 3%,the substrate protein contents in the hydrolysate was 16 mg/ml,and the pH value was 8.0.In a water bath at 55 ℃,the hydrolyzed protein was obtained after hydrolysis for 5 h.The highest peptide content was 62.24%.4.Due to the different molecular weight of the polypeptide solution,ultrafiltration was performed to obtain polypeptides of different molecular weights.According tothe experimental results,the optimal ultrafiltration conditions were as follows: The optimal ultrafiltration condition for the ultrafiltration membrane with a molecular weight of 10000 Da was ultrafiltration.The time was 45min/time,the temperature of the enzymolysis solution was 40℃,the pressure was 0.10 MPa,and the initial pH of the hydrolysate can be maintained.At this time,the maximum ultrafiltration efficiency can be reached to 60.41%;and the ultrafiltration membrane with a molecular weight of 5000 Da can be obtained.The ultrafiltration time is 75min/time,the enzymolysis temperature didnot exceed the membrane tolerance temperature beyond 50℃,the operating pressure was 0.10 MPa,and the pH of the enzymolysis solution also maintained the initial pH value.At this time,the ultrafiltration efficiency of the polypeptide solution can be as high as 59.32 %;5.By separating and purifying the polypeptides,two polypeptides with different molecular weights were obtained.The antibacterial activity of three antibacterial components was tested,including kiwifruit proteins,were tested and it was concluded that kiwifruit polypeptides have strong antibacterial activity against bacteria.Among them,polypeptides with a molecular weight below 5000 Da have the highest antibacterial activity,followed by polypeptides with a molecular weight of 5000Da-10000 Da,and kiwifruit has almost no antibacterial activity.