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Seven different types of starch based fat substitutes were used for the production of set-style yogurt from reconstituted skimmed milk powder. The yogurt milks contained 14. 0-15.8% total solids, 7.3-9.1% carbohydrates, 5.3-5.6% protein and 1.0-1.2% ash. The fat content of all the batches was 0.1% except the control (1.5%), which was made with anhydrous milk fat. Yogurts made with P-Fibre 150 C and 285 F contained 0.5 and 1.1% fibre respectively. Decrease in whey syneresis and increase in firmness in all the yogurts were observed during 20 days' storage at 5°C. Yogurt made with P-Fibre 150 C had the least amount of whey syneresis. Scanning electron microscopy and transmission electron microscopy revealed subtle differences in the microstructure of set-style yogurts due to the different starch based fat substitute used. 'Spikes' and 'hair' like structures were evident around the casein micelles in the milk base. They were lightly stained when compared with the caseins. Their detection in the yogurt was very difficult and only P-150 C and P-285 F substitutes were visualized whereas the others could not be detected even when their concentration was increased to 5%. Yogurt made with Lycadex' 100 was more porous and had slightly larger void spaces filled with milk serum. The use of a higher concentration (5%) of.fat substitutes increased the firmness, but impaired the flavour and mouth feel of the yogurts.

Low calorie yogurts were manufactured from reconstituted skimmed milk powder using microparticulate whey protein (Simplesse 100® in wet and dry form) as a fat substitute. They were compared with yogurt containing anhydrous milk fat (AMF 1·5%). The quality of whey protein based yogurts (at a 1·5% level of addition) was high and similar to that of the control samples containing AMF. However, serum separation was higher and firmness was lower for yogurts containing microparticulate whey protein than for those containing AMF. This difference between yogurt containing AMF and microparticulate whey protein was most marked when microparticulate whey protein (ie, wet type) was incorporated on an equivalent dry matter basis to AMF. The sensory panel identified significant differences (p<0·05) between products containing AMF and microparticulate whey protein only in terms of sour odour and perceived serum separation.

The effect of a protein based fat substitute (Simplesse@ 100) incorporated at a 1.5% level (wlw) in set-style yogurt on its microstructure, syneresis and firmness was compared with the effect of anhydrous milk fat (AMFj used at the same concentratiofir. The fat substitute was used in both commercial forms available, ie, as a dry or a wet ingredient. The yogurt bases consisted of reconstituted skimmed milk powder including the added ingredients and contained 14.3-15.5% total solids. Electron microscopy revealed that homogenization of A M F produced fat globules which interacted with milk proteins present in the yogurt base and thus the fat became an integral part of the yogurt microstructure. Similar integration was observed with the fat substitute, the particles of which (0.1-3 pm in diameter) were found to be parts of the casein micelle chains or spanned adjacent chains. These chains were found to be somewhat shorter (no statistical assessment was carried out) in the yogurts made with the fat substitute in wet or dry forms than in the yogurt made with A M F . Yogurts with the fat substitute were softer than the yogurts containing A M F , although their composition was similar except for the fat which was replaced with the fat substitute. Vol48, No 4 November 19% JoLir.mil of tlic Sociery of Duir?. Technology

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