Acid-Induced Aggregation and Gelation of Bovine Sodium Caseinate-Carboxymethylcellulose Mixtures

MARÍA EUGENIA HIDALGO; BIBIANA D. RIQUELME; ESTELA M. ALVAREZ; JORGE R. WAGNER; PATRICIA H. RISSO

Food Industrial Processes- Methods and Equipment

Intech Publisher

Lugar: Rijeka; Año: 2012; p. 75 - 88

Bovine sodium caseinate (NaCAS) is a dairy ingredient in which casein is the major proteincomponent, involving the co-existence of predominantly sub-micellar species with a smallamount of supramolecular assemblies. It is widely spread in food industry owing to itsexcellent functional and nutritional properties. Carboxymethylcellulose (CMC) is a typicalanionic polysaccharide and has been widely used as a stabilizer in food products, for example inacidified milk drinks. Protein/polysaccharide/water mixtures are frequently used in the foodindustry as thickening agents for low or zero fat product. The interaction of proteins withpolysaccharides in solution could influence in a positive or negative way, depending on thecolloidal system in question, the functionality of the protein and, therefore, the food properties.Milk can be acidified by the addition of glucono-δ-lactone (GDL), which slowly hydrolyzes togluconic acid with a resulting reduction in pH 4. In this work, conformational, aggregating andgelling behaviors of NaCAS aqueous solutions were studied when different quantities of CMCwere added.The mixtures were thermodynamically compatible at all evaluated NaCAS:CMC ratios,without phase separation. In the presence of CMC, takes place the formation of mixed microparticles that grow in average size as CMC proportion increases. Surface hydrophobicity diminished as NaCAS:CMC ratios became lower. The acid aggregation, induced by addition of GDL, shows two well-defined steps. At the beginning, a slow phase with a decrease of average size of protein particles is observed. The second step presents a sharp increase in the average size of particles due to formation of colloidal aggregates (aggregation time, tag) that grow until they reach a limit value, i.e., a fractal dimension of aggregates. As CMC proportion rises, the aggregation and gel times of NaCAS:CMC mixtures increasedand the pH at which these processes begin decreased, reveals a stabilizing effect of CMC. Thedegree of compactness diminished when the CMC proportion increased. This effect can belinked to protein conformational changes in the presence of CMC that lead to a decrease ofsurface hydropobicity, which difficult to establishment of hydrophobic interactions. The gelsalso showed lower elasticity at CMC:NaCAS high ratios. Therefore, it is possible to obtain acidgels with different textures varying the protein:polysaccharide proportions due to the formationof micro particles of different size and surface hydrophobicity.