Heat induced conformational changes of whey proteins in model infant formulae: effect of casein and inulin

RODRÍGUEZ-ARZUAGA M.; AÑÓN M.C; ABRAHAM A.G

Conferencia; 11th NIZO Dairy Conference: Milk Protein Functionality. Papendal, The Netherlands. 8-11 October 2019.; 2019

Milk infant formula (IMF) and cow milk have compositional differences, such as whey protein-to-casein and protein-to-lactose ratios and presence of components with prebiotic function. Whey proteins (WP) are sensitive to heat-induced denaturation and aggregation, which could have techno-functional and nutritional implications. This study investigated how the presence of casein and inulin, at ratios relevant to IMF processing, affect the heat-induced conformational changes of WP.Model systems were prepared as aqueous dispersions of WPI (WP; 1.8%) alone or with calcium caseinate (CAS; 1.2%) and/or inulin (INUL; 1.5%), and heated for 30min at 66, 70 or 75ºC. Protein solubility, ATR-FTIR, SDS-PAGE, DSC and protein particle size (PPS) by dynamic light scattering (DLS) were analyzed on the unheated (UH) and heated systems.Results showed that solubility of WP system decreased significantly when heated at 75ºC (Fig.1). Heat treatment (HT) of WP induced protein denaturation and aggregation as evidenced by DSC (Table 1), SDS-PAGE and DLS. Under non-reducing conditions, SDS-PAGE of WP showed a band of high molecular weight that decreased with temperature due to aggregation. PPS increased from 258 (UH) to 932nm (75ºC). FTIR spectra showed higher proportions of intermolecular β-sheet structures.CAS addition reduced protein solubility but did not modify WP denaturation temperature (Td). WP-CAS solubility increased with HT. PPS was constant with HT (UH=323±20 nm; 75ºC=288±18 nm) and less intermolecular β-sheets were obtained by FTIR. These results suggested that CAS inhibited WP aggregation.INUL did not affect solubility nor PPS but increased Td. HT did not modify WP-CAS-INUL solubility, in spite of the high denaturation degree determined by DSC. The high solubility of CAS after HT and interaction between CAS and WP could explain this result.It can be concluded that casein and inulin inhibit heat-induced aggregation and denaturation of WP, respectively. This study provided information relevant to the IMF production.