THE MICROSTRUCTURE OF SET-STYLE, NATURAL YOGURT MADE BY SUBSTITUTING MICROPARTICULATE WHEY-PROTEIN FOR MILK-FAT

The effect of a protein based fat substitute (Simplesse(R) 100) incorp orated at a 1.5% level (w/w) in set-style yogurt on its microstructure , syneresis and firmness was compared with the effect of anhydrous mil k fat (AMF) used at the same concentration. The fat substitute was use d in both commercial forms available, ie, as a dry or a wet ingredient . The yogurt bases consisted of reconstituted skimmed milk powder incl uding the added ingredients and contained 14.3-15.5% total solids. Ele ctron microscopy revealed that homogenization of AMF produced fat glob ules which interacted with milk proteins present in the yogurt base an d thus the fat became an integral part of the yogurt microstructure. S imilar integration was observed with the fat substitute, the particles of which (0.1-3 mu m in diameter) were found to be parts of the casei n micelle chains or spanned adjacent chains. These chains were found t o be somewhat shorter (no statistical assessment was carried out) in t he yogurts made with the fat substitute in wet or dry forms than in th e yogurt made with AMF. Yogurts with the fat substitute were softer th an the yogurts containing AMF, although their composition was similar except for the fat which was replaced with the fat substitute.