Fourier transform infrared spectroscopy (FT-IR) quantification of plasminogen in the presence of casein and whey proteins

摘要: Plasminogen (PG) is the precursor of plasmin in milk and is initially present in much higher concentrations than its activated form, plasmin. Cheese ripening occurs faster as a result of increased milk plasmin levels. Milk plasmin levels can be increased by adding PG activators to milk in order to activate PG. Understanding factors that influence PG concentration in milk is important for developing procedures to control plasmin activity in dairy products. Accurate methods for quantifying PG in the presence of casein proteins are currently unavailable. FT-IR is a good tool for monitoring subtle changes in quantitative, qualitative, physical, and chemical characteristics of constituents present in very low concentrations. The objectives of this study were to quantify PG in the presence of casein and whey proteins using FT-IR spectroscopy. Standard curve solutions were prepared by adding PG (0.08437 mg/ml-2.7 mg/ml) to milk protein solutions: 3%(w/v) sodium caseinate (Alanate 180®), 0.6%(w/v) whey protein concentrate (BiPro®), and 3%(w/v) sodium caseinate+ 0.3%(w/v) b-lactoglobulin solutions. Spectra of pure milk protein solutions and PG in protein solutions were obtained with a FT-IR (Nicolet 670) equipped with a multiple bounce ZnSe-ATR and a MCTA detector. The FT-IR was purged with dry nitrogen during measurements. To determine PG concentration, spectra of protein solutions were subtracted from the protein+ PG spectra, and resulting peak area data were analyzed by the PLS method using TQ software. The correlation coefficients for PLS models developed to predict PG concentration were 0.99. FT-IR is able to quantify PG in solutions …