Formation of pyrochlorophylls and their derivatives in spinach leaves during heating

The changes of chlorophylls and their derivatives during heating of spinach leaves were studied. Chlorophylls and their derivatives were analyzed by high performance liquid chromatography (HPLC) with photodiode-array detection or positive ion fast atom bombardment mass spectrometry (FAB–MS). No chlorophyll derivatives were detected in fresh spinach leaves. The degradations of both chlorophylls, a and b, fit the first-order model, and the rate constant (min−1) by microwave cooking or blanching was greater than that by steaming or baking. The major chlorophyll derivatives formed during baking and blanching included chlorophyll epimers and pheophytins. Pyrochlorophylls a and b were detected in spinach leaves after steaming for 30 min or microwave cooking for 1 min. Pyropheophytins a and b were not formed until steaming or microwave cooking time reached 30 or 5 min, respectively. Steaming favored the formation of pheophytins a and b while microwave cooking favored that of pyrochlorophylls a and b.