Effect of alkalis on konjac glucomannan gels for use as potential gelling agents in restructured seafood products

Four dispersions of 3% glucomannan in water, deacetylated with 5% 0.6 N and 1 N KOH (lots L1 and L2) and 0.6 N and 1 N NaOH (lots L3 and L4) as gelling agents, were evaluated for use in raw restructured seafood products. Several properties (pH, moisture content, water binding capacity, cooking loss and lightness) together with puncture data (breaking force and breaking deformation) were determined after 1 and 10 days of chilled storage at 5 degrees C. All these data were analyzed together with different viscoelastic parameters obtained at small amplitude oscillatory strain (SAOS) after 1 day of chilled storage, showing that L1 and L4 samples were the most suitable gels for incorporation in raw restructured fish products. In both cases the highest stress (sigma(max)) and strain (gamma(max)) amplitude values were found in the linear viscoelastic (LVE) range; however, L1 showed both high strain amplitude and breaking deformation values. Moreover, creep and recovery (transient) data showed that L1 was the most time-stable gel with the highest elasticity and the lowest relaxation exponent (n). L4 gel showed strong rigidity, i.e. the highest values of breaking force and storage moduli (G') and the highest n value, making it less gel-like. Both L1 and L4 gels became significantly less gel-like over 10 days of chilled storage due to the loss of gel strength (S) and a noticeable increase of n. These chilled storage effects were more intense in L4 than in L1. (C) 2011 Elsevier Ltd. All rights reserved.