Effect of heating on the stability of grape and blueberry pomace procyanidins and total anthocyanins

Fruit by-products are rich sources of procyanidins and anthocyanins known for potential health benefits. Freeze dried blueberry pomace and grape pomace were heated in a forced air oven at 40, 60, 105, and 125 °C for 72, 48, 16, and 8 h respectively, to study the stability of procyanidins and total anthocyanins. Heating decreased procyanidin concentrations significantly (p < 0.05) in both blueberry and grape pomace, except when heated at 40 °C for 72 h. Reduction occurred when heated at 60 °C or above with no further reduction when heating temperature increased from 105 to 125 °C. Heating also affected total anthocyanin contents in both grape and blueberry pomace with no significant (p > 0.05) loss when heated at 40 °C. Total anthocyanin loss was highest at 125 °C for both blueberry (52%) and grape pomace (70%). Results suggested that while heating at lower temperatures for up to 3 days may not be detrimental, heating at higher temperatures for more than 8 h results in considerable loss of both the compounds.