Dairy Foods II: Cheese

Our objective was to develop a rapid method for measuring fat, protein, solids, and salt content of Cheddar cheese using a mid-infrared (MIR) transmittance analysis. Currently, quality assurance is done using near-infrared (NIR). For MIR analysis, Cheddar cheese (about 9 g) was blended with a sodium metasilicate solution (about 85 g). Cheese was blended to a uniform particle size (about 3 to 4 mm). The blended cheese (4°C) was added to a sodium metasilicate solution at 60 to 65°C in a stainless steel blender jar, 3 drops of a silicone based antifoam were added, and the mixture was blended for 15 s at low speed followed by 45 s at high speed. The blended sample was poured into a 60-mL snaplid plastic vial and placed in a 40°C water bath before analysis using a MIR milk analyzer. An infrared spectra and conductivity reading were collected for each sample. Measurement of fat and protein were done using traditional wavelengths used for milk analysis. Salt measurement was a combination of infrared traditional wavelengths and conductivity. Total solids was determined by a summation of fat, protein, and salt. Reference values for cheese solids were determined directly by forced air oven drying and salt was determined by a silver nitrate titration (Volhard method). The same solution of cheese/sodium metasilicate analyzed on the MIR was analyzed using Mojonnier ether extraction and Kjeldahl total nitrogen to obtain reference values for fat and protein content. Calibration slope and intercept adjustment for each component were done using linear regression. Standard error of predictions (SEP) for fat, protein, solids, and salt were generally less than 0.20. Typical SEP values for NIR for cheese fat, moisture, and protein are >0.3. MIR analysis of cheese may offer a more accurate alternative to NIR testing for routine quality control testing in a cheese factory, while reducing the amount of reference chemistry testing required to achieve a good calibration relative to that of NIR.