Food Chemistry, Vol. 62, No. 4, pp. 431439, 1998 0 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 030%8146/98 $19.00+0.00
Applications of the Maillard reaction in the food industry
Jennifer M. Ames*
Department of Food Science and Technology, The University of Reading, Whiteknights, Reading RG6 6AP, UK
(Received 6 December1996; accepted 27 February
This paper summarises some recent work concerned with the development of colour and flavour via the Maillard reaction in both aqueous and restricted moisture model systems. High performance liquid chromatography (HPLC) and capillary electrophoresis (CE), both with diode array detection, are discussed for their ability to separate reaction products. The use ofthe diode array data to classify reaction products is presented. The coloured reaction products identified from aqueous sugar-amino acid systems are summarised, and their contribution to the colour of total model systems is considered. The effects of temperature/ time, pH and high pressure on the development of colour and flavour in Maillard model systems are presented. Colour measurement dataand quantitative descriptive analysis (QDA) data are given for a starch-glucose-lysine model system extruded at different feed pH values. The use of a laboratory reaction cell to mimic most of the conditions encountered in the extruder is discussed. Its use to obtain information for the successful prediction of colour development in the extruder is presented. 0 1998 Elsevier Science Ltd. All rightsreserved
INTRODUCTION The Maillard reaction has been used to produce foods that look and taste attractive for thousands of years; for as long as food has been cooked. The modern food industry relies on the application of the Maillard reaction to produce many foods, e.g. coffee and bakery products, that possess the colour and flavour demanded by the consumer. The chemistry underlying theMaillard reaction is extremely complex (Led1 and Schleicher, 1990; Ames, 1992). In 1953, John Hodge published his consolidated scheme (Fig. 1) which summarised the chemical reactions which were understood to comprise the Maillard reaction at that time (Hodge, 1953). The Hodge scheme remains widely used today. In essence, it states that a reducing sugar, such as glucose, condenses with a compoundpossessing a free amino group, such as an amino acid, to give a condensation product. Subsequently, a range of reactions takes place, including cyclisations, dehydrations, retroaldolisations, rearrangements, isomerisations and further condensations, which ultimately lead to the formation of brown nitrogenous polymers and co-polymers, known as melanoidins. Although the Hodge scheme is very useful, it hassome drawbacks. First, the scheme is simply a summary *Fax: 0118 931 0080; e-mail: firstname.lastname@example.org 431
of the reactions that take place. Secondly, in the intervening years, a vast amount of research on the Maillard reaction has been undertaken (e.g. Eriksson, 1981; Waller and Feather, 1983; Fujimaki et al., 1986; Finot et al., 1990; Labuza et al., 1994; Ikan, 1996; O’Brien etal., in press). More recent work has established that other important pathways, not accounted for by the Hodge scheme, also exist. For example, Namiki (1988) has shown that a free radical route operates, especially at high pH. In both the food and medical fields, the central importance of the Amadori rearrangement product (ARP), which is implied by the Hodge scheme, has been questioned (Edwards andWedzicha, 1992; Fu et al., 1994, Wedzicha et al., 1994). Nursten (1986) gave a list of 12 symptoms of the Maillard reaction. Probably, the most important, as far as the food manufacturer is concerned, are the formation of colour and discoloration, the formation of flavours or off-flavours, the production of compounds with antioxidant activity, the reduction in nutritional value, and the formation...