IMPROVED YOGURT PHYSICAL-PROPERTIES USING ULTRAFILTRATION AND VERY-HIGH TEMPERATURE HEATING

Nonfat yogurt milk was prepared by either ultrafiltration of skim milk and by addition of low-heat, nonfat dry milk powder to skim milk. The se fortification procedures resulted in yogurt milks with 5% total pro tein. The yogurt milks were heat-treated from 100 degrees to 140 degre es C for 4 and 16 s. The milks were also vat-heated at 82 degrees C fo r 20 min. Following yogurt culture inoculation, incubation, and coolin g, the yogurts were tested for gel strength and stirred viscosity afte r 21 d storage. Yogurt prepared from ultrafiltered skim milk had great er gel strength and stirred viscosity values than yogurt prepared with nonfat dry milk-fortified skim milk. These higher values occurred des pite the lower average total solids in ultrafiltered skim milk (11.43 %) than in nonfat dry milk-fortified skim milk (12.98 %). Heat-treatin g yogurt milk at 100 degrees . 110 degrees, or 120 degrees C for 4 or 16 s resulted in yogurts with significantly higher gel strength and vi scosity values than yogurt milk heated to 140 degrees C for 4 or 16 s.