Influence of Water Activity and System Mobility on Peroxidase Activity in Maltodextrin Solutions

Abstract

Maltodextrins influenced the enzymatic activity in aqueous solutions by affecting the water activity (a w ) and mobility as described by viscosity and T'g. In diluted solutions, viscosity being equal, (1) maltodextrin with dextrose equivalents (DE) of 33 was more effective than glucose in limiting horseradish peroxidase (HRP) activity;(2) an increase in the maltodextrin chain length from DE 33 to DE 8.7 did not further limited enzymatic activity; (3) the maltodextrin with the highest chain length (DE 2.5) determined the highest enzyme inhibition. In general, the increase of molecular weight negatively affected the HRP activity by increasing the viscosity and T'g (decreasing molecular mobility) but it positively affected the a w and, in some cases, this compensated the HRP activity inhibition. In concentrated solutions (apparent viscosity≈40 mPa s) the HRP activity decreased with the increase of the maltodextrin molecular weight, and it showed a dependence on T'g which could be described by a William, Landel and Ferry (WLF)-type equation. On the contrary, in the solution added with the maltodextrin with the highest chain length (DE 2.5) the HRP activity was much higher than that predicted by the WLF-type equation. The maltodextrin with DE 2.5 contains intact starch fragments and in water forms a suspension. In such a discontinuous system, the viscosity in the vicinity of the protein is lower than the bulk viscosity, and thus, the enzyme activity is higher than expected. Moreover, since T'g is a property of the soluble phase, it does not explain the mobility in discontinuous systems.

A review of recent strategies to improve the physical stability of phycocyanin

“…Numerous factors are considered to affect the stability of phycocyanin, including temperature, light, pH, pressure, heavy metal cations, and denaturants ( Berns and MacColl, 1989 ; Kupka and Scheer, 2008 ; Sarada et al, 1999 ). Moreover, studies have highlighted that the water activity, glass transition temperature, and rheology of the system can also influence the stability of phycocyanin ( Neri et al, 2011 ; Neri et al, 2014 ). By elucidating the impact of these factors on phycocyanin stability, it is possible to improve its stability in food and other applications.…”