Use ultrafiltered powder from tofu whey to make yogurt.

Tofu whey is a waste byproduct emanating from the processing of tofu. It contains small molecular weight compounds such as isoflavones, saponins and oligosaccharides that are considered functional food ingredients.

The aim of South Korean researchers was to use tofu whey concentrates separated by ultrafiltration (UF) for yogurt production. They found that UF powder could be substituted for skim milk powder without depressing yogurt quality.

In experiments, curd yogurt was prepared from whole milk to which had been added skim milk powder or UF powder. This was fermented with lactic acid bacteria at 37 C for 24 hours. The scientists examined the effects of UF powder on the quality of yogurt in terms of titratable acidity, apparent viscosity, the number of viable cells, volatile compounds and sensory properties. The titratable acidity of all mixtures remarkably increased for the first six hours. The addition of UF powder stimulated acid production.

The apparent viscosity of yogurt with UF powder was lower than that of the control yogurt. The propagation of lactic acid bacteria was stimulated by the UF powder, and the number of cells after 24 hours ranged from 9.11 log colony-forming units per ml to about 9.16 log colony-forming units per ml.

Gas chromatographic analysis detected acetaldehyde, diacetyl, ethanol and organic acids. More volatile compounds were detected in yogurts with the UF powder. Sensory analysis showed that yogurts with UF powder were as acceptable as the control yogurt.

Further information. H. J. Chung, Department of Food Science and Nutrition, Daejin University, 11-1 Seondan-dong, Pocheon-si, Kyunggi-do, 487-711, South Korea; phone: [phone]; fax: [phone]; URL: www.daejin.ac.kr/english.