Temperature Effect On FT-MIR Spectra Of Milk Powder Products

In this paper, full-cream milk powder and infant formula powder, infantrice cereal and home-made rice powder, soybean milk powder and home-madesoybean powder were used as experimental samples. Experimental results andconclusions are as follows:1. Major components and contents of samplesFT-MIR spectra of samples were acquired by mid-infrared spectroscopy with anAttenuated Total Reflection (ATR) attachment. According to the assignment ofabsorption peaks/bands observed in original spectra, major components of samplesand relative content of each component were able to be identified. The resultsshowed that: the major components in full-cream milk powder and that in infantformula powder were protein, fat and carbohydrate. The content of protein infull-cream milk powder was very similar to that of fat, while the content of fat ininfant formula powder was much higher than that of protein. The contents of proteinin both infant rice cereal and home-made rice powder were obviously higher thanthat of fat. The contents of protein in both soybean milk powder and home-madesoybean powder were slightly higher than that of fat. Contents of major componentsof samples got from experiment were consistent with nutrient content tables given bythe sample manufacturers.2. Changes of absorption peaks of protein and fat with temperatureSpectra of samples under different temperatures (25℃~100℃, set interval as5℃) were acquired, differences among the spectra were compared, and changes ofprotein and fat were concluded. The results showed that: the change trend ofabsorbance of amide bandⅠand amide bandⅡ in3sets of samples were similar,which presenting a contrary trend to the change of absorbance of fat. But the contrarytrend appeared under different temperature regions among3sets of samples.3. Changes of protein secondary structure with temperatureThe second derivative spectra of samples were calculated and used to identifythe secondary structure types of protein in samples. Gauss curve-fitting wasperformed on original spectra to analyze the relative contents of different types of secondary structure. The results showed that: protein in milk powder containedα-helix, β-sheet and β-turn these3kinds of secondary structure, while protein in ricepowder and soybean powder contained random coil additionally. The contents ofdifferent types of protein secondary structure in different samples were not the same,and changed with temperature. With the rise of temperature, reversibletransformations were observed between α-helix and β-sheet, β-turn and random coil.