Research On Optical Rapid Measurement Of Protein Content In The Milk Powder

Nowadays, facing ever-increasing quality problem of milk powder, more andmore people have realized that it is important to supervise timely the quality of milkpowders. The main quality problem of dry milk is that the protein content is too lowto reach the standard of official requirement. Routine chemical methods for proteindetermination are slow and expensive, which can't satisfy the requirement of modernquality control. It is urgent to develop a simple and fast determining method. In thepaper two optical methods, near infrared diffuse reflectance spectroscopy and dyebinding method, are compared.Near infrared diffuse reflectance spectroscopy has been used widely on foodanalyzing for its obvious advantages such as high speed, simultaneous non-destructivemeasurement of a number of constituents. The fundamental research on quantitativeanalysis of protein content in dry milk is performed on Nicolet Fourier near infraredspectrometer with diffuse reflectance spectroscopy. Experimental condition andsampling method are carefully selected. Two kinds of pretreating methods, SNV andMSC, are discussed which can effectively remove the multiplicative interferences ofscatter, sampling dense and particle size. PLS calibrations are performed on milkpowder with the whole band. The correlation and RMSEP of the model with SNVpretreatment is 0.98 and 0.43%, respectively. The correlation and RMSEP of themodel using selected 11 wavelengths to reduce the calculation of modeling is 0.95and 0.68%, respectively.Dye binding method measure protein content of dry milk by colorimetricdetermination of unbound Acid Orange 12 dye with the advantage of fast, accurateand low cost. The visible spectrum of Acid Orange 12 is analyzed. According to theresult of experiment, the procedure that firstly dissolves powdered milk in distilledwater can provide more accurate modeling result than that without the dissolvingprocedure. It is feasible by measuring the Absorbance of Acid Orange 12 at 483nm todetermine the protein content of milk powder. A single beam protein analyzer isdesigned using monochromatic LED as light source and photocell as detector. In thispaper, the whole system is introduced including amplifying circuit, A/D conversion,Single-Chip Microcomputer control system. The stability of the instrument is about0.12%. The analyzer is calibrated using milk powder with protein determined byKjeldahl method. The correlation and standard deviation of the model is 0.994 and0.22%, respectively. Therefore, the home-made device can meet the requirement ofthe protein measurement..