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Humectants have catalytic effect on Maillard reaction.

Humectants, such as sucrose and glycerol, are added to foods to reduce water activity. The idea is to stabilize products from unwanted microbial growth and chemical reactions.

However, on occasion, humectants may actually lower a product's chemical stability. Scientists at Auburn University investigated the catalytic effect of humecants on the Maillard reaction in solution. The acceleration of the Maillard reaction in solution caused by added humectants has not been previously reported. Product development scientists should recognize that the rates of reactions whose mechanisms produce water may be enhanced by humectants added to foods.

As part of their research, the Auburn investigators prepared phosphate buffer solutions (0.2 M) containing 0.2 M glycine and 0.2 M glucose at pH 6.8 to pH 7.7. Using aliquots from the bulk solutions, 2 molal glycerol and 2 molal sucrose solutions were prepared. To correct for any volume displacement caused by the humectants, 14.5% (v/v) and 42% (v/v) of water were added to two additional aliquots. A fifth aliquot with no humectant nor added water served as the control.

The researchers stored the solutions at 25 C. They measured any loss of glucose in duplicate at 10 intervals over nine months. using an enzymatic assay. Browning was measured spectrophotometrically at 420 nm. Glucose loss and browning were modeled using second-order and pseudo-zero order kinetics, respectively.

The rate of the Maillard reaction decreased as scientists added water, which they attribute to reactant dilution. Glycerol and sucrose increased the rate constant for glucose loss, despite reactant dilution by the humectants. At pH 7.7, the rate constants for glucose loss were 3.96 x [10.sup.-5] [(mg per mL).sup.-1][d.sup.-1] for the control, 4.92 x [10.sup.-5] [(mg/mL).sup.-1][d.sup.-1] with added glycerol, and 8.26 x [10.sup.-5] [(mg/mL).sup.-1][d.sup.-1] with added sucrose. Similar, but less dramatic, results were observed for browning rates. The humectants appear to be interacting with the water produced during the initial step of the reaction, shifting their equilibria and accelerating the reaction.

Further information. Leonard Bell, Department of Nutrition and Food Science, Poultry Science Building 101F, Auburn University, Auburn, AL 36849; phone: 334-844-3272; fax: 334-844-3268; email:
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Publication:Emerging Food R&D Report
Date:Feb 1, 2006
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