The influence of chemical interesterification on the physicochemical properties of complex fat systems. 3. Rheology and fractality of the crystal network

Chemically interesterified and noninteresterified lard-canola oil (LCO) and palm oil-soybean oil blends ranging from 100% hardstock to 50%:50% hardsto ck/vegetable oil (w/w) were evaluated for hardness index (HI) using cone pe netrometry and viscoelastic properties, such as shear storage modulus G', u sing controlled-stress rheometry. The HI and G' of palm oil decreased upon addition of soybean oil, and chemical interesterification did not affect th e HI or G' of palm oil or palm oil-soybean oil blends. The HI and G' of lar d decreased upon addition of canola oil, while chemical interesterification led to increases in bath the HI and G' of lard and LCO blends. All these e ffects were nonsolid fat content-related, since solid fat content did not c hange substantially upon chemical interesterification. The microstructure o f the fat crystal network in lard and palm oil was quantified theologically using fractal analysis. Chemical interesterification did not affect the fr actal dimension of the fat crystal networks in palm oil or lard (2.82 and 2 .88, respectively). The rheological properties of the macroscopic systems w ere not affected by the spatial distribution of mass within their fat cryst al networks. Moreover, our results suggest that the increases in G' observe d in lard upon chemical interesterification are potentially due to changes in the properties of the particles which make up the network (crystal habit ).