Food Biochemistry and Food Processing

24

Nonenzymatic Browning of Cookies,

Crackers, and Breakfast Cereals

M. Villamiel

555

Introduction
Available Lysine
Furosine
Hydroxymethylfurfural
Color
Fluorescence
Acrylamide
Maltulose
References

INTRODUCTION

Cereal-based products such as cookies, crackers, and
breakfast cereals represent a predominant source of
energy in the human diet, especially for children
consuming cereal derivatives for breakfast meals.
Cookies, crackers, and breakfast cereals can be
manufactured by means of traditional processes or
by extrusion cooking. In general, during convention-
al treatment of flour products (generally, tempera-
tures close to 200°C or higher for several minutes),
more intense processing conditions are applied as
compared with the extrusion process (González-
Galán et al. 1991, Manzaneque Ramos 1994, Huang
1998). Extrusion cooking is a well-established in-
dustrial technology with a number of food applica-
tions since, in addition to the usual benefits of heat
processing, extrusion has the possibility of changing
the functional properties of food ingredients and/or
of texturizing them (Cheftel 1986). In the extruder,
the mixture of ingredients is subjected to intense
mechanical shear through the action of one or two
rotating screws. The cooking can occur at high tem-

peratures (up to 250°C), relatively short residence

times (1–2 minutes), high pressures (up to 25 MPa),

intense shear forces (100 rpm), and low moisture con-

ditions (below 30%). In addition to the cooking step,

cookie, cracker, and breakfast cereal manufacture

involves toasting and/or drying operations (Cheftel

1986, Camire and Belbez 1996, Huang 1998).

During these technological treatments, due to the

elevated temperatures and low moisture conditions

used, different chemical reactions such as the non-

enzymatic browning can take place. Nonenzymatic

browning includes the Maillard reaction and cara-

melization. The products resulting from both reac-

tions depend on food composition, temperature,

water activity, and pH and both reactions can occur

simultaneously (Zanoni 1995).

The Maillard reaction that occurs between reduc-

ing sugars such as glucose, fructose, lactose, and

maltose and free amino groups of amino acids or

proteins (usually the epsilon-amino group of lysine)

is favored in foods with high protein and reducing

carbohydrate content at intermediate moisture con-

tent, temperatures above 50°C, and a pH in the range

from 4 to 7. Caramelization depends on direct degra-

dation of carbohydrates due to heat, and it needs

more drastic conditions than the Maillard reaction;

thus, at temperatures higher than 120°C, pH lower

than 3 or higher than 9, and very low moisture con-

tent, caramelization is favored (Kroh 1994).

In addition, other chemical reactions that can

occur during processing of these products may af-

fect the extent of the nonenzymatic browning. Thus,

starch and nonreducing sugars such as sucrose can

Food Biochemistry and Food Processing

Edited by Y. H. Hui

Copyright © 2006 by Blackwell Publishing