Partial characterization of ice structuring proteins from winter wheat and their functionality in frozen foods.

摘要

The freezing properties of sucrose solutions containing ice structuring proteins (ISPs) from cold-acclimated winter wheat extract (AWWE) were evaluated. Neither significant ice nucleation nor thermal hysteresis activity in unpurified AWWE were detected (P>0.05). Ice crystal growth was significantly reduced with the addition of more than 0.05% total protein from AWWE to sucrose solutions quiescently frozen. The ISP activity in reducing ice recrystallization increased with ISP concentration until reaching a plateau after adding 0.13% total protein from AWWE (74% ISP activity), representing a surface coverage of 9 mg protein/m 2 ice. Retardation of ice crystal growth was also observed in ice cream model solutions quiescently frozen (44% ISP activity).; In heat shocked ice cream, ice recrystallization rates were significantly reduced (P≤0.05) by 46% with the addition of 0.0025 and 0.00375% total protein from AWWE. Adding the AWWE before pasteurization increased its activity by 17%, probably due to a more homogeneous distribution of the ISPs in the mix. With the total removal of stabilizer, the activity of ISP was reduced by 52%. A remarkably smoother texture for ice creams containing ISPs after heat-shock storage was evident by sensory evaluation.; Additionally, ISPs from AWWE were concentrated and partially characterized. The most active ISP fraction was precipitated after adding 60 to 95% of ammonium sulfate followed by dialysis or ultrafiltration. Approximately 80% of the total protein in this fraction comprised a protein with a molecular weight close to 6 kDa, implying that considerable ISP activity may come from it. Further separation procedures by size-exclusion and ion exchange chromatography suggested that at higher concentrations the small molecular weight proteins present in the most active ISP fraction agglomerate in aggregates of higher molecular weight. Electrophoresis patterns from AWWE and non-AWWE suggest that ISPs may be always present in the extract but the cold acclimation increases the activity of them. No protein glycosylation was identified in the proteins present in the raw extracts. To reduce the concentration of other solids, AWWE was concentrated by ultrafiltration and its activity was retained.