Parallel plate

To analyze the dynamic viscoelastic properties of the PIs, they were subjected to an in situ gelation, similar as described by van Berlo et al.[22] (link). Frozen PIs were thawed under cold running tap water and directly chopped on ice for 30 s in a small chopper (Black and Decker®, China), followed by adding 2 % (w/w) of NaCl and then chopping the sample for two more minutes to create a homogenous paste. For the analysis, 1–2 g of the paste (n = 1) was loaded on a dynamic rheometer (Paar Physica, Rheometer MCR 300, Anton Paar GmbH, Austria). A parallel-plate (Anton Paar GmbH, Austria) with a 25 mm plate diameter and a 1 mm plate gap as well as an oscillating mode was used to identify the viscoelastic properties. To prevent evaporation, the exposed edge of the sample was covered with mineral oil. The in situ gelation was done in three steps in a viscoelastic region (1% strain, 0.1 Hz frequency). First, the temperature increased from 20 °C to 90 °C at a constant heating rate of 5 °C/min, after which the highest temperature was held for 30 min, before ramping the temperature down to 20 °C at a constant cooling rate of 5 °C/min.

The rheological properties of goat milk and goat yogurts were measured using a Physical MCR301 rheometer equipped with a parallel plate of 50 mm diameter (Anton Paar, Graz, Austria) at 25 °C. Samples were gently placed between parallel plates with a gap set at 1.0 mm. The apparent viscosities of the goat milk and yogurts samples were measured with a gradually increasing shear rate from 0.01 to 100.0 s⁻¹ to obtain the flow curve. Viscoelastic properties were determined by frequency sweep test, which performed with a frequency ramp from 0.1 to 10 Hz at a constant strain of 0.5% (within linear viscoelastic region). The test was performed in triplicate for each sample.