The influence of methylcellulose on rheological properties, structure and lipid digestibility of emulsions of pork fat estabilized by soy protein

Soy proteins are commonly used as food emulsifying agents; however, mixed protein-polysaccharide systems improve the functionality of oil-inwater (O/W) food emulsions stabilized only by proteins. Oil-water interfacial adsorption of protein-polysaccharide complexes depends on whether complexation occurs before or after emulsification, as this generates different structures at the interface, which may influence lipid digestibility. Among polysaccharides, methylcellulose (MC) tends to accumulate at the O/W interface due to its high surface activity, providing many technological applications. This study was aimed at determining the effect of MC, added by simultaneous and sequential emulsification methods, on the structure, rheological properties and lipid digestibility of pork lard O/W emulsions stabilized by soy protein concentrate (SPC). Three emulsions (SPC, SPC/MC-sim, SPC/MC-seq) were prepared and compared using confocal laser microscopy, dynamic viscoelastic properties, and in vitro digestion (INFOGEST 3.0 method). MC presence and stage of incorporation affected the emulsion microstructure, as reflected by more spherical, homogeneous and smaller oil droplets. Lipid droplets were entrapped by a protein layer in the SPC emulsion, which was thicker when MC was present, providing greater resistance against environmental stresses during gastrointestinal digestion. MC addition in the SPC-coated oil droplets resulted in a larger linear viscoelastic region without affecting the network rigidity, exerting a delaying effect on the crossover temperature, which was more evident in SPC/MC-seq. The stage of MC incorporation affected the rate and extent of lipolysis, with SPC/MC-seq presenting a lower concentration of free fatty acids, probably because MC, due to its affinity for the O/W interface, hinders the access of lipase to the oil droplet. Decreased extent of lipolysis observed in SPC/MC-seq may be beneficial in the production of animal fat products with reduced fatty aci