Evaluation of degradation of pigments formed during garlic discoloration in different pH

The specific chemical bond changes of green pigment formed in garlic discoloration were investigated in our study. Multiple analysis methods were used in the degradation of pigment, including ultraviolet-visible (UV-Vis) spectrophotometry, attenuated total reflection Fourier transform infrared (ATR-FTIR) and Fourier transform infrared near infrared (FT-NIR). Green pigments were treated at 40 °C for 7 days in the pH range of 5.0-8.0. Principal component analysis of the ATR-FTIR and FT-NIR spectra indicated the similarities and differences during pigment degradation. It was found that the degradation degree of green pigments in a solution with pH 5.0 was the lowest. Changes in the absorptions of CO, COO^-, CN, CN, OCOCH, COC, COOH, and NH bonds vibrations are attributed to the decomposition of the pigments. The absorption at 5170 cm^-1 (NH bond first overtone) and 4871 cm^-1 (OCH stretching) correlated to pigment degradation were confirmed by FT-NIR spectra. One proposed pathway of the pigment decomposition was explored.