Effects of calcium on physical properties and Fourier-transformed infraredspectra of raw and sterilized goat milk

Calcium fortification induces instability of goat milk such as flocculation and sedimentation. The Fourier-transformed infrared (FTIR) spectra could be used as a tool for monitoring such as instability. The objective of this study was to investigate the changes in FTIR spectra, particle size and some properties of raw and sterilized goat milk when stimulated with calcium fortification. Either calcium citrate or calcium phosphate was fortified at 0, 25, 50, 75 and 100% of the recommended daily intake (RDI) per 200 mL of milk samples. For raw goat milk, calcium citrate lowered the pH of goat milk and increased the sediment content. Sterilization lowered the milk pH for both calcium types which can be even lowered when increasing the fortification level. The average particle sizes of raw and sterilized goat milk were 0.543 and 1.063 µm, respectively. The calcium phosphate-treated samples had larger particle sizes than the calcium citrate-treated samples, with particle sizes of 2.603 and 2.242 µm at 50% and 100% RDI, respectively. The sediment of calcium citrate-fortified raw goat milk was correlated with FTIR absorption values in lipid (3000-2800 cm-1 ), protein (1700-1600, 1600-1500 cm-1 ) and phosphate (1100-1000 cm-1 ) regions with correlation coefficients of 0.89, -0.88 and 0.99, respectively. Such correlation was also found with the FTIR absorption values of the sediment of sterilized goat milk. Therefore, goat milk fortification with calcium particularly calcium citrate has resulted in altered FTIR absorption values and correlated to raw and sterilized goat milk’s sediment.