George P. Rizzi

Chemical structure of colored maillard reaction products

Abstract Visual color in processed foods is largely due to colored products of Maillard or nonenzymic browning reactions. In spite of the longstanding aesthetic and practical interest in Maillard‐derived food coloring materials, relatively little is known about the chemical structures responsible for visual color. In recent years numerous low molecular weight (<500 Da) colored products have been isolated from model Maillard reactions and their structures elucidated. Many colored products appear to be aldolization/dehydration products of sugars which may or may not be attached to proteins or other sources of amino nitrogen. The structures of high molecular weight Maillard pigments are still mostly undefined, but degradative studies have yielded identifiable fragments with chromogenic properties. This report summarizes the current knowledge of colored compounds formed in the Maillard reaction.

A solvent-free synthesis of sucrose polyesters

A solvent-free reaction system is described for making sucrose polyesters (SPE) by interesterification of sucrose and long chain fatty acid methyl esters. The process avoids the usual toxic solvents by using a novel two-stage reaction sequence. In the first stage a 3:1 mole ratio of methyl esters to sucrose is reacted in the presence of potassium soaps to form a one phase melt containing mainly lower esters of sucrose. In the second stage more methyl esters are added and reacted to produce SPE in yields up to 90% based on sucrose. Sucrate ion generated in situ with alkali metal hydrides or Na-K alloy proved to be a superior catalyst for formation of sucrose esters during both stages.

The Strecker Degradation of Amino Acids: Newer Avenues for Flavor Formation

Newer aspects of the Strecker degradation related to foods are examined in terms of currently accepted mechanisms and isolated reaction intermediates. Emphasis is placed on Strecker and Strecker-like reactions between amino acids and lipid oxidation products, and terpenes or o-quinones as potential sources of novel flavor compounds. In addition, reactions are described in which Strecker aldehydes are formed directly from Amadori compounds instead of via amino acid/carbonyl reactions.

Free Radicals in the Maillard Reaction

Abstract This article reviews the study of free radical intermediates in the Maillard reaction from a historical perspective. Early observation of free radicals in biological systems led other workers to discover similar radicals in non‐enzymic Maillard processes such as those observed in foods. Emphasis is placed on a discussion of the chemistry of radical species detected in Maillard systems and their possible relevance to food flavor and color.

The biogenesis of food‐related Pyrazines

Abstract Biogenetically formed pyrazines are important flavor compounds in view of the current industry trend toward all‐natural flavors in foods. Food‐related pyrazines are reviewed and summary data are used as a basis to discuss possible chemical and biochemical mechanisms for their formation.

The Maillard Reaction in Foods

Maillard or non-enzymic browning reactions can play a pivotal role in food acceptance through the ways they influence quality factors such as flavor, color, texture and nutritional value. An overview of Maillard chemistry is presented and an attempt is made to show a chemical basis for the major quality factors.

The Strecker Degradation and Its Contribution to Food Flavor

The Strecker degradation (SD) plays several roles in the formation of flavor compounds in processed foods. Primarily, it is the major pathway for conversion of amino acids’ into structurally related aldehydes of significant flavor value. Also, the SD provides a relatively low energy route for mobilizing amino acids’ nitrogen and sulfur to form ammonia, hydrogen sulfide and many flavor-significant S/N/O-containing heterocyclic compounds. And finally, the SD provides a reduction mechanism for conversion of dicarbonyls into acyloins thereby opening the door to still more diverse flavor compound formation.

An Improved Synthesis of 2′-Hydroxy-3′,4′,6′-trimethoxyacylophenones

Abstract A wide variety of 2′-hydroxypolymethoxyacetophenones and propiophenones, e.g. 1a and 1b are used in the synthesis of flavone and ehromone natural products.1 Repeated attempts to prepare 1a and 1b by reacting 1,2,3,5-tetramethoxybenzene 2 with acetyl or propionyl chlorides and AlCl3 in ether2 gave products which were difficult to purify.3 We traced the problem to ring-ethoxy contaminants which were isolated and tentatively identified as 3a and 3b.

Formation of sulfur-containing flavor compounds from allylic alcohol precursors

Mercaptans and thioethers are well recognized as important components of processed food aromas. Studies performed in a model system demonstrated that flavorous sulfur compounds of this kind can be formed from structurally related alcohols under food processing conditions. Allylic alcohols and furfuryl alcohols are converted to flavor significant mercaptans and thioethers by reaction with sulfur-containing amino acids in water at acidic pH. A mechanism is proposed in which alcohol-derived carbocations attack amino acids or peptides to form flavorous endproducts without involving the Strecker degradation and intermediacy of H2S or alkyl mercaptans.

Formation of flavour compounds in reactions of quinones and amino acids

Abstract Quinone/amino acid reactions relevant for flavour generation were studied in 2-methoxyethyl ether (MEE) (151 °C) and in aqueous (22 °C) model systems. In both systems reaction products were observed resulting from Strecker degradations. In aqueous systems containing p -benzoquinone (BQ) and α-amino acids visibly coloured products including 2-(4-hydroxyphenylamino)-1,4-benzoquinone (HPBQ) (λ max 515 nm) were also formed. With proline and BQ a violet-coloured, highly polar substance was observed (λ max 511 nm) which was tentatively identified as a BQ-induced oxidation product of the predicted Streker intermediate 1-(4-hydroxyphenyl)-2-hydroxypyrrolidine.