Masayo Miura

Identification of Blue Pigment Formed in a D-Xylose-Glycine Reaction System.

D-Xylose (1 M), glycine (0.1 M), and sodium hydrogencarbonate (0.1 M) were dissolved in aqueous 60% ethanol at pH 8.1 and left at 26.5°C for 2 days in a dark room under nitrogen displacement. Blue pigment was isolated and purified from the blue solution by anionic exchange and gel filtration chromatographies. Blue pigment which was designated Blue-M1 (blue Maillard reaction intermediate-1) was identified as 5-{[1,4-(dicarboxymethyl)-5-(2,3-dihydroxypropyl)-2-pyrrolo[3,2-b]pyrrolyl]methine}-1,4-(dicarboxymethyl)-2-(1,2,3-trihydroxypropyl)-pyrrolo[3,2-b]pyrroly-lium. Blue-M1 is supposed to be a dimer of yellow colored pyrrolopyrrole-2-carboxaldehyde compounds. Blue-M1 that reacts readily to yellow compounds has a polymerizing activity, suggesting it is an important Maillard reaction intermediate through the formation of melanoidins.

Kinetic Analysis of the Inhibition by Melanoidin of Trypsin

The inhibition by melanoidin of trypsin was investigated in a kinetic approach. Melanoidin was prepared by the Maillard reaction between D-glucose and glycine, and BANA was used as a substrate. The inhibition was found to follow a non-competitive mode with a Ki of 5.8% and to be exerted through an electrostatic interaction between melanoidin and trypsin. Approximately 20% of the activity of trypsin survived even at a greatly increased concentration of melanoidin. The inhibiting mechanism of melanoidin might be due to an allosteric effect, which was probably different from a proteinaceous inhibitor such as ovoinhibitor diminishing trypsin-activity completely. The melanoidin molecule was thought to trap a great number of trypsin molecules, binding them and reducing their activity.

Inhibiting effect of browned processed foods on trypsin

Inhibition of proteases was examined in browned foods including soy pastes, soy sauces, fish sauce, sauces, teas, coffees, and others in association with melanoidin, a Maillard product, which had been found to be a potent inhibitor of trypsin. Most of the foods were effective in restraining trypsin activity based on hydrolysis of N-α-benzoyl-DL-arginine-p-nitroanilide, while being ineffective on chymotrypsin except for black tea and cola. Especially, teas were noted for their strong inhibitory effect on trypsin. The color intensity of the foods in terms of optical density at 400 nm appeared not to correlate with the extent of inhibition except for soy sauces.

A Tentative Measurement of Brown Pigments in Various Processed Foods.

A tentative method for measuring brown pigment in food was proposed and applied to 25 items of commercial browned foods. The principle was based on the assumption that any brown pigment with general absorption in the visible wave-length spectrum is quantitatively equivalent to melanoidin prepared from a model system of the Maillard reaction. The spectral curve for general absorption was represented by the equation dE/dλ=-kE (E, absorbance; λ = wave length; k = constant > 0), of which the value k w as found to correlate with the molecular weight and the molar extinction coefficient and to serve as an empirical parameter for the measurement of brown substances in different foods.