Effect of homogenization pressure, lipid content, and emulsifier content on the rheological properties of yogurt

Abstract

The interaction of high pressure homogenization lipid hics. content, and surfactant on the rheological properties of yogurt were evaluated. NFDM, cream, and a nontoxic emulsifier (Tween 20) were combined to obtain samples with of 0% and 2% fat and Otto and 0.5% Tween 20 at 1 1% Milk Solids Not Fat (MSNF). A HBDVIII Brookfield rheometer with vane spindles was used. to obtain rheological measurements. Static and dynamic yield stress was determined using the vane method. Values for the flow behavior index (n), consistency coefficient (K), and structural parameter (1) were determined from samples measured at 5, 10 , 30 , 50 , 100, 150, 180, and 200 RPM for 15 minutes at 4OC. Protein load on the milk fat globules was determined by the difference between the protein in the milk and the protein remaining in the serum after centrifugation relative to the surface area of the milk fat. Increasing homogenization pressure caused particle size to decrease and protein load on the milk fat particle to increase. The difference was more apparent between samples homogenized at 30 Mpa and 60 Mpa than for samples homogenized at 60 Mpa and 90 Mpa. Samples homogenized at 60 Mpa had a higher yield stress than samples homogenized at 90 Mpa. Samples containing 2% fat had a higher viscosity and consistency coefficient than samples containing 0% fat. The area of hysteresis loops was greater for samples containing 2% fat and the flow behavior index (n) was smaller for samples that contained fat indicating greater structural breakdown in the samples with fat. between 20 adsorbed to the fat globule and displaced milk proteins causing a decrease in protein load and a weakening of the yogurt structure in samples containing 2% fat. The gel strength of samples with 0% fat was also decreased by addition of between 20 to the sample. The formation of a complex between Tween 20 and p-lactoglobulin probably caused the weaker structure of the gels. The vane method was compared to penetrometry for measurements of gel strength. Significant differences in gel strength were detected by both methods on unstirred 2% fat and nonfat samples. Only the vane method could detect significant differences (gel strength between treatments in the stirred samples.