Acid-Induced Gelation of Caseins Glycated with Lactose: Impact of Maillard Reaction-Based Glycoconjugation and Protein Cross-Linking

Abstract

During food processing or storage, milk proteins can react with reducing sugars via the Maillard reaction (glycation), which may alter their techno-functional properties. The aim of this study was to investigate the relationship between molecular changes of casein occurring during different stages of the Maillard reaction and its acid-induced gelling properties. Therefore, sodium caseinate was heated in a dry state at 60 °C in the presence of lactose and analyzed for structural modifications by determining Amadori compounds (glycoconjugation) indirectly as furosine, the total lysine modification, and the extent of protein cross-linking. For techno-functional characterization, acid-induced gels were prepared by the addition of glucono-δ-lactone and evaluated by measuring pH kinetics during gel formation, gel strength, and water holding capacity. The time to reach pH 4.6 during the gelation process was significantly delayed with increasing extent of the Maillard reaction. Glycation with lactose also led to a significant increase in gel strength and water holding capacity. The increase in gel stability was rather independent from the amount of sugars covalently bound to the proteins during the early phase of the Maillard reaction but strongly correlated to the degree of protein polymerization. Small-and medium-sized casein oligomers, formed during advanced stages of the Maillard reaction, contributed considerably to the formation of stronger gels with higher water holding capacity, whereas a sharp increase in the relative amount of the polymer fraction observed during prolonged crosslinking processes caused a spontaneous destabilization of the gel network. Knowledge about structure−function relationships on a molecular level can provide useful information to control food texture by raw material quality.

Association of Enzymatically and Nonenzymatically Functionalized Caseins Analyzed by Size-Exclusion Chromatography and Light-Scattering Techniques

“…This suggests an enhanced incorporation of casein molecules into the particles of F2 via intermolecular interactions, which are, besides the stabilizing effect of covalent protein cross-linking, further promoted by the Maillard modification. Both casein samples, dry-heated in the presence of lactose, are highly glycoconjugated, containing ∼0.4 mol Amadori products per mol lysine as determined in our previous study . Considering the hydroxyl groups of covalently attached lactose molecules as potent donors as well as acceptors for hydrogen bonds, H-bridges might become more relevant as interaction forces between glycated casein molecules.…”

“…Sodium caseinate was modified with lactose via the Maillard reaction by dry-heating a casein–lactose mixture at a molar ratio of lysine residues to sugar carbonyl groups of 1:1 at 60 °C, a w 0.5 for 36 and 48 h according to the procedure of Hannß et al…”

“…Data processing and integration were performed with Origin 2019 software (OriginLab Corporation). The degree of polymerization (dp) and the relative amounts of oligomeric species were calculated in area-percentages, as previously described . Experiments were performed in duplicate.…”

“…Cross-linking reactions on food proteins can lead to an alternation of their techno-functional properties . The enzymatic cross-linking of casein with microbial transglutaminase [EC 2.3.2.13] (mTG) has already been proven as an effective, technologically applicable tool for the texture stabilization of dairy products. − However, protein polymerization in the course of the Maillard reaction (also referred to as glycation) occurring unintentionally during food production and storage can also influence the texture properties of milk gels, which was recently demonstrated on a molecular level for acid gels of glycated, nonmicellar casein . In contrast to mTG-catalyzed protein cross-linking, which basically produces isopeptide bonds via an acyltransfer between glutamine and lysine residues, the Maillard reaction follows a more complex reaction cascade, yielding a wide variety of different protein-bound reaction products.…”

Understanding the effect of storage temperature on the quality of semi-skimmed UHT hydrolyzed-lactose milk: an insight on release of free amino acids, formation of volatiles organic compounds and browning

“…The higher reactivity of glucose and galactose compared to lactose, as well as the proteolytic side activity of the commercial lactase preparations (LPs), promote MR resulting in products with a shorter commercial shelf-life of 90-120 days at room temperature (Milkovska-Stamenova & Hoffmann, 2017;Naranjo, Gonzales, Leiva, & Malec, 2013;Nielsen et al, 2018). Chemical modifications influence physicochemical parameters of milk and in the case of lactosehydrolyzed milk, glycation alters protein structures and conformation, thus modifying also hydrophobicity and aggregation with consequences on viscosity and gel formation (Hannß, Hubbe, & Henle, 2018).…”