Study On The Strip For Detecting Protein Of Milk

Milk protein content is an important index for evaluating the quality of milk.More and more adulteration and watering occurs for getting huge economic interests.Watering of milk lead to the decrease of the protein content,while the Kjeldahl determination was used to detect protein,including all nitrogenous substances,as a national standard method.Illegal traders add ammonium,urea,melamine and other non-protein substances to cover up adulteration and muddle through the detection.Therefore,it is particularly important to find a rapid economic method for the determination of the protein.There are many major methods of measurement of protein content,such as Kjeldahl method,Photometric method,Chromatography,Electrophoresis,Titrimetric method and so on.However,there are some defects in these methods,such as complex operation,expensive equipment,high cost or low sensitivity,unable to distinguish non-protein nitrogen compounds,long detection time,need professional personnel and so on.Paper method transfers the chemical reaction in test tube to the paper reaction,with the emergence of micro instrument which is suitable for the strip,the semi quantitative analysis of strip gradually transformed into precise quantitative.Therefore,a research of portable and easy protein strip has an important significance,simple operation with the portable detection instrument can also meet the needs of quantitative detection.Spectrophotometry is a common method for protein detection.By comparing the linear range,precision,correlation,sensivity,accuracy and other indicators of the Folin-phenol reagent method,biuret method and Comassie brilliant blue method,considering the characteristics of milk samples,make sure to test paper using biuret principle.In this study,the color of the strip was measured by the photoelectric colorimeter.The conditions of preparation and using were optimized with the effect of color rendering,The final production of carrier strips with the thickness of the absorbent paper,soak for 3 times than the standard biuret reagent concentration.Adding 2%Tween 80,0.5%of anhydrous ethanol,and a total of 2%polyvinyl pyrrolidone,soaking for 10 min,drying at 30 min at 60 ?.the strip was immersed in the milk sample for 2s and then reacted at room temperature for 6 min when we use it.In this present study,the strip was used to determine the same concentration of lactal bumin,casein,whey protein and soy protein isolate solution and there's no significant difference between the reflective values.The results indicated that the types of protein had no significant effect on the testing results and the casein was chosen for the preparation of series samples.The standard curve between protein content and reflective value was got and evaluated the testing paper method.The results shows that the relative standard devitation is between 1.71?4.78%and the recovery rate is between 96?97%.The results showed no significant difference with the national standard method by testing the pasteurized milk,milk powder,UHT milk and raw milk.The strip can still be used for 3 months and we need improve stability.The strip prepared has the advantages of simple operation,convenient carrying and fast detection speed.It is accompanied by a self-made portable photoelectric colorimeter which provides a simple means for protein detection for quantitative analysis.