Research On Heating Denaturation And Kinetics Of Whey Protein In Skim Milk

Skim milk powder,as a raw material,is widely used in food industry,and its nutrition value and application properties are affected by whey protein denaturation extent.Preheating stage is a key station of skim milk powder production,but whey protein is easily denatured in the heating conditions that ensuring the required sterilization.This paper studied the influences of heat treatment on whey protein denaturation and analyzed the thermal denaturation kinetics of ?-lactalbumin(?-La)and ?-lactoglobulin(?-Lg)which were the two main components in the whey protein.Specific contents are as follows.WPNI detection standard curve was established by the undenaturation whey protein nitrogen content in per gram sample milk powder.The results of solid samples and liquid samples could be effected by the solid content and total protein content,respectively.In order to avoid the impact of the above two factors on the test result,WPNI detection method was correctied.The new WPNI*detection standard curve was established by the undenaturation whey protein nitrogen content in per gram total protein.A RP-HPLC method was also established to simultaneously detect BSA,?-La and ?-Lg.The detection limit and standard addition recovery rate were conformed to the test requirements,so RP-HPLC was verified a reliable method of quantitative single protein.The denaturation of BSA,?-La and ?-Lg,under 55-95? heating temperature,was analyzed.The denaturation temperature of BSA and ?-La were about 55? and 65?,respectively.The denaturation temperature of ?-Lg was in the range of 60-65?,and 75-80? was the critical controlled temperature.Less than 65? heating,the denaturation value of BSA was available to indicate the denaturation extent of total whey protein.In the rage of 65-85?,?-Lg took the place of BSA,but heating over 85?,?-Lg was replaced by?-La.The correlation(R2 = 0.9622)of p-Lg and whey protein was best in the whole heating process,so ?-Lg was used to indicate the denaturation degree of total whey protein.In addition,casein also should be considered in indicating total whey protein,because it could increase whey protein denaturation speed during heating process.A study was conducted to analyze kinetics of a-La and ?-Lg during 65-95? and the results showed that the reaction order for ?-La and ?-Lg were 0.9 and 1.3,respectively.Based on the reaction order of ?-La and ?-Lg,the kinetic equations to predict protein denaturation trend were as follows:Verify the results of the above two equations showed that the average relative error of the predictive denaturation rate and detective denaturation rate of ?-La and ?-Lg were 9.72%and 8.24%,respectively.Because of the average relative error of the predictive denaturation rate and detective denaturation rate of ?-La and ?-Lg were both less than 10%,the predicted value can reflect the trend of the protein denaturation.