RHEOLOGICAL AND TEXTURAL PROPERTIES OF GOAT’S MILK AND MIXTURE OF GOAT’S AND COW’S MILK FRUIT YOGURT

Abstract

Yogurt rheological and textural parameters are known to have an important impact on food quality and acceptability. The paper includes the determination of the viscoelastic and textural parameters of goat's milk and cow's milk yogurt in terms of physico-chemical indices and technological properties. Two series of yogurts were prepared: series I of goat's milk and cow's milk 50:50 (5 samples) and series II of 100% goat's milk (5 samples), adding the aronia, strawberries, raspberries, peaches using classical technology. Texture parameters with higher values were obtained for yogurt of first series due to the presence of casein fractions specific to cow's milk. Added fruits to yogurt have had a positive impact on texture indices, due to contained hydrocolloids that confer thickening, stabilizing, gelling and emulsifying properties to food products. Due to the organic acids contained in fruits, the pH of yogurt is lower, so the voluminosity of casein micelle increases at lower pH value due to increased hydration, possitivly influensed the viscosity parameters. Manufacture of yogurt from goat's milk and cow's milk induced stronger yogurt gel (series I), due to a higher content of α casein in cow's milk compared to goat's milk. The viscoelastic characteristics of yogurt samples, show that G′ is higher than G′′ during the entire frequency range. The added fruits to yogurt influence the viscoelastic parameters more through some components present in their composition: The higher dry matter content in the yogurt samples with the addition of aronia, respectively indicates the higher values for the parameters G' and G'', namely for the yogurt of the second series.

Keywords

• yogurt
• rheological parameters
• textural parameters
• casein fractions
• heat treatment of yogurt
• starter cultures of yogurt
• dairy gels