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Article

Simultaneous Determination of Hydrolysis and Mutarotation Rates during the Enzymatic Hydrolysis of Lactose

Supporting Info

Daniel M. Jenkins*^†, Michael A. Teruel^†, Jos

I. Reyes-de-Corcuera^§ and Owen Young^#

Room 218, Molecular Biosciences and Bioengineering, University of Hawaii, 1955 East West Rosd, Honolulu, Hawaii 96822; Citrus Research and Education Center, University of Florida, 700 Experiment Station Road, Lake Alfred, Florida 33850; and Food Technology, Auckland University of Technology, 24 Saint Paul Street, Auckland, New Zealand

J. Agric. Food Chem., 2008, 56 (18), pp 8303–8308

DOI: 10.1021/jf801403n

Publication Date (Web): August 20, 2008

* Corresponding author [telephone (808) 956-6069; fax (808) 956-3542; e-mail danielje@hawaii.edu].

†

University of Hawaii.

University of Florida.

Auckland University of Technology.

Abstract

An experiment is described in which a custom-made glucose electrode is used to directly monitor the enzymatic hydrolysis of lactose to glucose. The transient profile of β-d-glucose can be used to simultaneously determine the rate constants for mutarotation and for enzymatic hydrolysis by applying a dynamic nonlinear regression routine. Due to differences in the mutarotation rate constants between lactose and glucose, the β-d-glucose concentration “overshoots” equilibrium under certain conditions, which can be modeled mathematically. This overshoot can be observed reliably and used to quantify the differences in mutarotational equilibria between glucose and lactose. These observations may be important for the analysis of dairy products and commercial lactase preparations and illustrate an unusual kinetic phenomenon caused by intramolecular forces. This approach may also be important for the accurate determination of a variety of oligosaccharides such as glycogen, which tend to be composed primarily of one stereoisomer.

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