Formation of phenazines, phenoxazines, and benzoxazoles in the browning reactions of o-quinones

Quinone-induced browning is widely produced in foods and is mostly considered a consequence of quinone/nucleophile reactions. However, even in the absence of amino acids or proteins, o-quinones develop browning. In an attempt to better understand the reaction pathways involved in this browning development, this study describes the reactions of 4-methyl-1,2-benzoquinone with alcohols, ammonia, and short chain aldehydes. These reaction mixtures developed browning at 37 °C and the main produced compounds were isolated by semipreparative HPLC and characterized by NMR and MS as phenazines, phenoxazines, and benzoxazoles. A reaction pathway that explains the formation of all these compounds is proposed. The formation of phenazines is responsible, at least partially, for the produced browning, and the formation of benzoxazoles inhibits such browning. Browning development seems to be a consequence of a competition among the reactions of formation of phenazines, phenoxazines, and benzoxazoles, which appear to be produced from a single intermediate.

Addition of olivetol to crackers decreases malondialdehyde content and produces malondialdehyde-olivetol adducts

This study was undertaken to investigate the malondialdehyde-trapping ability by m-diphenols and the consequent decrease of malondialdehyde in foods. Olivetol was added to crackers, which were prepared with wheat flour and either oxidized or fresh sunflower, linseed, and camelina oils. When crackers were prepared with oxidized oils, olivetol-containing crackers contained less malondialdehyde (∼30%) than control crackers. This decrease of malondialdehyde content was parallel to the formation of malondialdehyde-olivetol adducts (250-1300 ng/g). When fresh oils were employed, storage produced more malondialdehyde (300-700%) in control than in olivetol-containing crackers. This decrease of malondialdehyde content was also parallel to the formation of malondialdehyde-olivetol adducts (10-90 ng/g). In both cases, the formation of adducts required the contribution of either formaldehyde or acetaldehyde. Obtained results suggest that olivetol not only removed malondialdehyde, but also short chain aldehydes, therefore contributing to the decrease of the content of these toxic aldehydes in phenolic-enriched crackers.

Carbonyl-trapping by phenolics and the inhibition of the formation of carcinogenic heterocyclic aromatic amines with the structure of aminoimidazoazaarene in beef patties

Carcinogenic heterocyclic aromatic amines (HAAs) with the structure of aminoimidazoazaarene (PhIP, MeIQx, IQ, and MeIQ) are produced by reaction of creatin(in)e, ammonia, and reactive carbonyls (phenylacetaldehyde, acrolein, and crotonaldehyde). In an attempt to provide efficient methodologies for HAA reduction in beef patties, this study: identified phloroglucinol as the most efficient phenolic to reduce HAA formation (76-96% inhibition); isolated and characterized by NMR and MS phloroglucinol/phenylcetaldehyde and phloroglucinol/acrolein adducts; and determined by LC-MS/MS adduct formation in beef patties treated with phloroglucinol. Obtained results suggested that addition of trihydroxyphenols (including phloroglucinol) to beef patties should decrease HAA formation. This was confirmed by both immersing beef patties in apple (or pear) juice before cooking (>90% inhibition) and including wheat bran in patty recipe. All these results confirm the key role of reactive carbonyls in the formation of carcinogenic HAAs and propose carbonyl-trapping as a way for controlling HAA formation in food products.

Malondialdehyde trapping by food phenolics

The reactions between malondialdehyde and 2,5-dimethylresorcinol, orcinol, olivetol, and alkylresocinols were studied in an attempt to investigate both if this lipid oxidation product is trapped by phenolics analogously to other reactive carbonyls and to elucidate the chemical structures of the produced adducts. After being formed, malondialdehyde is both partially fractionated to acetaldehyde and oligomerized into dimers and trimers. All these compounds react with phenolics producing three main kinds of derivatives: 5(or 7)-alkyl-7(or 5)-hydroxy-4-methyl-4H-chromene-3-carbaldehydes, 7-alkyl-9-hydroxy-6H-2,6-methanobenzo[d][1,3]dioxocine-5-carbaldehydes, and 4-(3-formylphenyl)-7-hydroxy-4H-chromene-3-carbaldehydes. A total of twenty-four adducts were isolated by semipreparative high-performance liquid chromatography (HPLC) and characterized by mono- and bi-dimensional nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). Reaction pathways to explain the formation of all these compounds are proposed. Obtained results show that phenolics can trap malondialdehyde producing stable derivatives. The function(s) that such derivatives can play in foods remain(s) to be elucidated.

Carbonyl-trapping abilities of 5-alkylresorcinols

In an attempt to investigate the carbonyl-trapping abilities of 5-alkylresorcinols, this study describes the role of these compounds in inhibiting the formation of the 2,5-dialkylpyridines (5-ethyl-2-methylpyridine, 5-butyl-2-propylpyridine, and 5-hexyl-2-pentylpyridine) produced by 2-alkenals (crotonaldehyde, 2-hexenal, and 2-octenal) in the presence of ammonia. 5-Alkylresorcinols (as well as orcinol and olivetol) inhibited the formation of pyridines to an extend that depended on the 2-alkenal involved and the reaction conditions. This inhibition was consequence of the trapping of 2-alkenals by the phenolics. Thus, the major adducts produced between the C21:0 alkylresorcinol and crotonaldehyde were isolated and characterized by nuclear magnetic resonance (NMR) and mass spectrometry (MS). These results confirm that, in addition to their free radical scavenging abilities, 5-alkylresorcinols also trap reactive carbonyls. Because trapped carbonyls are involved in the formation of flavors and processing-induced antioxidants, 5-alkylresorcinols might be implied in some of the observed differences between whole and refined grain products.

Formation of heterocyclic aromatic amines with the structure of aminoimidazoazarenes in food products

Thermal food processing has many beneficial consequences, although it also produces some unintentional undesired effects, such as the formation of potentially mutagenic and carcinogenic substances. Among them, the formation of heterocyclic aromatic amines (HAAs) has been related to the declared carcinogenicity of processed meats. In spite of this importance, HAA formation pathways remain mostly unknown, which avoids the design of targeted procedures to inhibit HAA appearance. The objective of this review is to collect information recently appeared that allow advancing in the understanding of how these compounds are produced. Particularly, the possibility that aminoimidazoazarenes are produced similarly to PhIP is discussed, including their formation by cyclizations and oligomerizations of aldehydes and creatinine under usual cooking conditions. Present data suggest that HAA formation might be related to the pool of carbonyl compounds existing in foods, the food carbonylome, which can be controlled by carbonyl-trapping agents, such as amine and phenolic compounds.

Food Processing Antioxidants

Food processing has been carried out since ancient times as a way to preserve and improve food nutritional and organoleptic properties. Although it has some undesirable consequences, such as the losses of some nutrients and the potential formation of toxic compounds, a wide range of benefits can be enumerated. Among them, the increased total antioxidant capacity of many processed foods has been known for long. This consequence has been related to both the release or increased availability of natural antioxidants and the de novo formation of substances with antioxidant properties as a consequence of the produced reactions. This review analyzes the chemical changes produced in foods during processing with special emphasis on the formation of antioxidants as a consequence of carbonyl-amine reactions produced by both carbohydrate- and lipid-derived reactive carbonyls. It discusses the lastest advances produced in the characterization of carbonyl-amine adducts and their potential action as primary (free radical scavengers), secondary (chelating and other ways to prevent lipid oxidation), and tertiary (carbonyl scavengers as a way to avoid lipid oxidation consequences) antioxidants. Moreover, the possibility of combining amino compounds with different hydrophobicity, such as aminophospholipids and proteins, with a wide array of reactive carbonyls points out to the use of carbonyl-amine reactions as a new way to induce the formation of a great variety of substances with antioxidant properties and very variable hydrophilia/lipophilia. All presented results point out to carbonyl-amine reactions as an effective method to generate efficacious antioxidants that can be used in food technology.