2.7.1. Water Absorption Index, Water Solubility Index

CPP as well as all extruded samples were milled using a coffee mill (M55, Petra Electric, Ense, Germany), and then sieved to particle size between 0.07 and 0.14 mm. Sieved powders were dried in a vacuum dryer (VT 5042 EK, Heraeus, Hanau, Germany) at 40 °C and 8 mbar. The water solubility index (WSI) and water absorption index (WAI) were determined according to Anderson [36] with slight modifications. Sieved powders (0.5 g) were added to 19.5 g of demineralized water, and the suspensions were mixed for 1 min (REAX top, Heidolph Instruments GmbH & Co. KG, Schwabach, Germany). The samples were shaken at 200 min⁻¹ (Orbital shaker Incubator SI 50, Stuart, Staffordshire, United Kingdom) for 24 h at room temperature (about 25 °C) and centrifuged at 4600× g for 50 min at 20 °C (Rotanta 460 R, Andreas Hettich GmbH & Co. KG, Tuttlingen, Germany). After separation, the wet precipitates were weighed directly, whereas the supernatants were dried for 72 h at 80 °C (T-6060 Heraeus, Hanau, Germany) before weighing. WAI and WSI were calculated according to the following Equations (2) and (3):

Analyses were performed in triplicate.