Properties of Low-Fat Yogurt Made from Ultrafiltered and Ultra-High Temperature Treated Milk

Yogurts were made from intermediate-high temperature (100, 110, 120, and 130°C for 4 or 16 s), ultra-high temperature (140°C for 4 or 16 s), and vat heat (82°C for 20 min) treatments of skim milk fortified to 5% protein by either ultrafiltration or the addition of nonfat dry milk (NDM). Whey protein denaturation in heated milks increased with temperature and holding time from indirect plate heating and was highest in vat-heated milks. Whey protein denaturation and yogurt water-holding capacity increased with protein levels in the fortified milks compared to skim milk. Penetrometer gel strength and stirred viscosity in 21 day-old yogurt made from heated ultrafiltered skim milk exceeded those of yogurts made from NDM-fortified skim milk, even though the NDM yogurts contained more solids (13.0 vs 11.4%). Maximum gel strength and viscosity, and least syneresis of yogurts from ultrafiltered and NDM fortified yogurts occurred following intermediate-high temperature treatments of 100°C for 16 s, 110°C for 4 or 16 s, and 120°C for 4 s. There was significantly lower whey protein denaturation at these intermediate-high temperatures compared to UHT or vat heating. Gel strength and viscosity were lower and syneresis greater in yogurts from ultrafiltered or NDM-fortified skim milk following UHT treatment compared to yogurts made with intermediate-high temperature treatments or vat heating. The water-holding capacity of yogurts from fortified milks treated at intermediate-high temperatures was comparable to that of yogurts from vat-heated milks. Fortification by ultrafiltration, to lower total solids (and without use of stabilizers) resulted in yogurt with higher gel strength and viscosity, and reduced syneresis compared to yogurt from NDM fortification. Yogurt prepared by intermediate-high temperature treatment had comparable or better gel strength and viscosity, and reduced syneresis compared to yogurt prepared by traditional vat heating