Sugar-amine browning

Figure 1. Sugar-amine Maillard browning reactions Two pathways to melanoidins and byproducts. (Reprinted with permission from ref. 12. Copyright 1967 Avi Publishing.)...

Mixtures of various sugars with amines were refluxed in ethanol for 10 min. The reddish-brown mixtures were developed on silica gel TLC plates and sprayed with 2,4-dinitrophenylhydra-zine (2,4-DNP). As shown in Fig. 9, a particular spot at around Rf 0.7 was observed immediately after the spraying in every case, and an additional spot was also detected in the cases of ti-butylamine and cyclohexylamine. These spots agreed well in Rf... 

Figure 12. Polyamide fluorescence production in sugar-amine browning. Conditions Water activity 1.0, 80 °C, sugar, 0.02 M and dipped and dried plate. Key O, blank A, glyceraldehyde 0, xylose and , arabinose.

Figure 13. Possible structures of the fluorophore in sugar-amine browning. (Reproduced from Ref. 11. Copyright 1972, Institute of Food Technologists.)...

Possible Chemical Nature of the Sugar-amine Fluorophore In sugar-amine browning, the relative amount of the fluorophore is usually low. Adhikari and Tappel found 130 pmoles per mole of glucose based on an assumption of an amino-imino-propene moiety (11). The relative amount of acid reducing power is usually much higher (28). But of course it cannot be assumed, no matter how simple the system, that the polymer-bound fluorophore and reducing power reside in the same molecule. 

We have reported here on comparison of the sugar-amine browning fluorescence with oxidative lipid-derived fluorescence to bring out the similarities and differences of the two emissions. The sugar-amine browning fluorescence can also be studied within an antioxidant-containing medium to assess browning potential of the system. 

Analytical applications of the malonaldehyde and Maillard fluorescent product formation to assessment of abuse status of oxidizing oils, relative effectiveness of antioxidants, and sugar-amine browning potential are available. 

Figure 1. Amadori rearrangement of glycosylated proteins. Integration of known reactions leading to browning in sugar-amine systems. (Reproduced from Ref. 101. Copyright 1953, American Chemical Society.)...

Because of their significant electrophilic character, aldehydes are often unstable and will react with nucleophiles. For example, a common reaction of aldehydes is the formation of a hemiaminal with amines. If the amine is a primary amine, the hemiaminal can dehydrate to form an imine as shown in Figure 21. The reaction of aldehydes with primary and secondary amines is a well-studied reaction pathway because it is a common reaction pathway of reducing sugars and amino acids, and this reaction pathway is known as the Maillard reaction (40). In the case of amino acids and sugars, this reaction leads to discoloration, or browning. This reaction will be discussed in greater detail in the Amines-Maillard Reaction section. 

Methylcyclopentenolone has a strong caramel-like, maple-like or licorice-like aroma (31j, and was found in browned, dehydrated orange juice at the 1 ppm level (43). Its synergistic flavor effect with other compounds, such as 5-methyl-2-furfural and N-ethylpyrrole- 2-carboxyaldehyde, was reported (43). Although it is present at levels five times below its threshold value, it still impacts on the heat-abused flavor of dehydrated orange juice. This ketone probably results from amine-assisted sugar degradation (45). 

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