Milk Powder And Protein For Rapid Detection Method

Dairy products are the most nutritious food. In recent years, with the growth of dairy products, adulterations in dairy products are becoming more and more popular. Protein adulteration is the popular way. Determination of protein content of milk powder which is constituted by government standard is based on the classical Kieldahl method. This method converts all substances which contain nitrogen into protein nitrogen in principle. Therefore, popular way of protein adulteration is adding hydrolyzed animal proteins, soybean proteins, urea, etc. Another way is artificial dairy products that contain low-protein or non-protein. For example, "Poor Quality Milk Powders Event" in Fuyang City. Dairy products adulterations not only affect market reputation, but also are harmful to people's health. So it is important to develop a high-efficiency, rapid, quantitative detection of adulteration in dairy industry now.This subject was based on the rapid methods of protein determination. Firstly, Bradford and Lowry methods among Spectrophotometric Colorimetry were chosen to analyze protein content of milk powder. Secondly, color reaction between protein content of milk powder and G-250 and Folin-Phenol reagent were established. At the same time, actually determinations of protein content by these methods were compared with that by the Kieldahl method. Thirdly, the interference of popular adulterated substances (e.g. ammonium salt, amino acid, carbohydrate, starch) and the actual effect of determination of adulterated proteins content were identified. Finally, correlation between absorbance and chromatic value of their solution was investigated. It suggested that color difference meter be applied into the determination of protein content.The main conclusions were as follows:(1) Using standard protein or standard sample of milk powder, Bradford method could accurately determine protein content of milk powder;all the results were not significantly different from those obtained by the Kjeldahl method statistically. Furthermore, some popular adulteration did not react with G-250 reagent and not interfere with protein reaction. Therefore, Bradford method was a good, rapid determination of protein content.(2) Only using standard sample of milk powder, Lowry method could accurately determine protein content of milk powder and all the results were not statistically different from those obtained by the Kjeldahl method. But, Lowry was interfered by many substances, it only could be applied into the determination of unadulterated milk powder.(3) Bradford and Lowry method could accurately determine protein content of milk powder which was adulterated with urea. Bradford method was not interfere by fat, so it could accurately determine protein content of milk powder which was adulterated with non-dairy creamer. But the results of Lowry method were a litter higher. G-250 reagent did not react with polypeptide, so it could accurately determine protein content of milk powder which was adulterated with hydrolyzed animal proteins. But Folin-Phenol reagent could bind with polypeptide and change color, the results of Lowry method were a litter higher.(4)Not only Bradford method or Lowry method, correlation between absorbance and chromatic value of their solution was very good. The linearity of chromatic Blue value was the best;the range of variation of chromatic Green value was the biggest. It showed that it was possible to find the relation between solution color information and protein content to simply determination of protein content.In summary, Bradford method can be applied to rapidly determine protein content of milk powder. A kind of commercial kit could be developed to determine protein content on the spot.