Glycation of caseinate by fructose and fructo‐oligosaccharides during controlled heat treatment in the ‘dry’ state

Abstract

This paper investigates the controlled heating of caseinate with reducing sugars to produce glycoproteins with improved functionality for use in food. Caseinate was combined with inulin, fructose and a mixture of both inulin and fructose and the lyophilisates heated at a controlled water activity for up to 48 h. Caseinate-glucose and caseinate-lactose glycoconjugates were prepared for comparison. Conjugation between caseinate and fructose occurred readily at 60 • C and 67% relative humidity, modifying up to 75% of the lysine groups of caseinate within 48 h. Moreover, when reconstituted, the caseinate-fructose glycoconjugates showed a dramatic increase in viscosity relative to caseinate 'dry'-heated alone. At 80% relative humidity the reaction proceeded so rapidly that gels containing darkly coloured particulate matter were formed. Incorporation of inulin prevented formation of caseinate-fructose gels, and minimised browning development while still producing moderately viscous solutions. Based on 13 C-NMR, SDS-PAGE and electron microscopy techniques, mechanisms by which inulin modified the reaction have been proposed.

Functional properties of caseinate glycoconjugates prepared by controlled heating in the ‘dry’ state

“…11 As shown in Table 3, the corresponding increases in viscosity were 25-fold, 18-fold and 23-fold, respectively. These results, combined with the results above describing the effect of increasing fructose concentration, show that both the level of glycation and the type of sugar influence the protein viscosity.…”

“…All solutions of protein were lyophilised (−46 • C, 70-90 mtorr, 2-4 days) (Virtis Co. Freezemobile, Gardener, New York, USA) and subsequently preequilibrated to the desired relative humidity (RH) using desiccators containing saturated salt solutions of NaBr (50% RH); CuCl (67% RH) and BaCl (80% RH), as previously described by Oliver et al 11 The pre-equilibrated sample vials were capped, sealed and then heated at 60 • C for up to 120 h. Control experiments were carried out with caseinate without added reducing sugar.…”

“…Glycoconjugates were hydrated and centrifuged, as described previously by Oliver et al 11 Available lysine was subsequently determined on the supernatants using the method of Habeeb. 8 All analyses were performed in triplicate.…”

“…The solutions were then centrifuged (1740 × g, 20 • C, 2 min). 11 The supernatants were analysed in duplicate for soluble protein according to Bradford. 12 Results are expressed as mg mL −1 soluble protein.…”

Modifications of structures and functions of caseins: a scientific and technological challenge

“…On the contrary, glycation with dextran did not improve the rheological properties of caseinate, probably due to the limited extent of the reaction. Similarly, Oliver et al (2006) reported that glycated sodium caseinate with ribose, glucose, fructose, lactose, and inulin have increased viscosities compared to unmodified sodium caseinate with a non-Newtonian behavior. According to these authors, the main cause of increased viscosities was related to an increase of bound water to the glycated proteins.…”