Purification and Identification of Antifreeze Protein From Cold-Acclimated Oat (Avena sativa L.) and the Cryoprotective Activities in Ice Cream

Antifreeze proteins (AFPs) were extracted from cold-acclimated oat by vacuum infiltration–centrifugation. Ammonium precipitation, ion exchange, and size-exclusion chromatography were used successively to purify the oat AFPs (AsAFPs), and the proteins were identified using matrix-assisted laser desorption/ionization time of flight tandem mass spectrometry. The results showed that an ammonium-sulfate saturation of 50–100 % was optimal for supernatant precipitation. After purification, AsAFP was found to have achieved an electrophoretic purity and its thermal-hysteresis activity was measured at 1.24 °C (15 mg ml−1). The mass fingerprinting and sequencing results indicated the homology of AsAFP and endochitinase. Recrystallization and melting resistance of ice cream were improved by AsAFP (0.1 %). Moreover, the addition of AsAFP (0.1 %) in ice cream increased the glass transition temperature (Tg) from −29.14 to −27.74 °C.