HEAT TREATMENT AND STORAGE EFFECTS ON TEXTURE CHARACTERISTICS OF MILK AND YOGURT SYSTEMS FORTIFIED WITH OILSEED PROTEINS

Abstract

ABSTRACTCOW'S milk systems fortified to 15.0% and 18.0% total solids with nonfat dry milk (NDM), peanut flour (PF) or soy protein isolate (SPI) were heated at 70, 80, 85, and 90°C for 30 min. Protein content ranged from 6.4% for NDM milk to 10.0% for SPI milks at 18.0% total solids. All milks exhibited pseudoplastic flow behavior at 4°C. Consistency index (K), or apparent viscosity (Q) at shear rate of unity, of PF and SPI milks was generally higher than that of similarly processed NDM milk. Increased total solids and increased heat treatment more dramatically increased the K value for oilseed milks than for NDM milk. Storage (10 days at 4°C) increased K value of SPI milk heated at 80°C or above. Stirred viscosity of yogurt prepared from PF milk heated at 85°C was lower than that of similarly processed NDM and SPI yogurt. Increased total solids increased all yogurt texture data for NDM yogurt, penetration work data for PF yogurt and stirred viscosity data for SPI yogurt. Texture data were maximal with heating at 80–85°C for NDM yogurt and with heating at 90°C for SPI and PF yogurt. Yogurt texture data increased with storage in NDM systems heated at 85°C or above and in SPI systems heated at 90°C.