Abstract #77

# 77
Improvement of the physicochemical and functional properties of whey protein hydrolysates by conjugation.
Eve M. Mulcahy*1, Daniel M. Mulvihill1, James A. O’Mahony1, 1School of Food and Nutritional Sciences, University College Cork, Cork, Ireland.

Proteins can be modified by enzymatic hydrolysis to alter their functionality. The objective of this study was to determine the effect of conjugation on selected physicochemical functionalities (i.e., solubility and solution clarity/heat stability) of either intact whey protein isolate (WPI) or hydrolysed whey protein isolate (WPH). Conjugation of WPI or WPH (degree of hydrolysis of 8%) with maltodextrin (dextrose equivalent value of 6; MD6) was achieved by heating solutions of 5% WPI or WPH and 5% MD6, initial pH of 8.2, at 90°C for up to 24 h. Samples were taken after 3, 5, 8 and 24 h of heating; the greatest reduction (P < 0.05) in available amino groups (21.0% reduction in AAG, measured by the o-phthaldialdehyde assay) occurred during the first 8 h of heating for WPH-MD6, with a considerably smaller decrease in AAG between 8 and 24 h of heating, which was consistent with the limited (0.8%) reduction of AAG in WPI-MD6 after 8 h. The number of amino groups available to react with the carbonyl groups of MD6 were 55% higher in WPH than in WPI which contributed to a greater extent of conjugation with the former. Unheated WPI had a protein solubility of 87.3% at pH 4.5; WPI-MD6 conjugate solutions (8 h of heating) had a protein solubility of 40.0% at pH 4.5 while WPH-MD6 conjugate solutions (8 h of heating) had enhanced protein solubility of 78.6% at pH 4.5. Unheated WPI increased in turbidity after thermal treatment for 3 min at 85°C, with 40 mM NaCl (48.5% decrease in transmission compared with control) while WPI-MD6 and WPH-MD6 conjugates retained, to a greater extent, solution clarity after heating (3.5 and 0.2% decrease in transmission compared with respective controls). Conjugation of WPH with MD6 resulted in higher levels of conjugation than for WPI and resulted in a conjugate with enhanced functional properties including improved solubility and lower levels of turbidity development in a heated high ionic strength environment compared with unconjugated WPI and conjugated WPI-MD6.

Key Words: conjugation, whey protein hydrolysate, physicochemical functionality