“…Both biopolymers and low-molecular surfactants can be easily adsorbed at the liquid interfaces (such as "bioliquid-air") with corresponding changes of surface tension (ST) values (Butt, Graf & Kappl, 2006;Kazakov et al, 2000;Khilko, 2014;Voronina, 2017;Zaitsev et al, 2004;Zaitsev, 2016Zaitsev, , 2018. This process is considered to be one of the main mechanisms of the surfactant activity playing a significant role in numerous functions of animals (Miller & Fainerman, 1998;Zarudnaya et al, 2010;Zaitsev et al, 2011b;Zaitsev, 2010Zaitsev, , 2016Zaitsev, , 2018. It is important to highlight that changes of the concentration of biologically active substances (BAS) in biological liquids are influenced by particular periods, for example, growth, development, pregnancy, lactation, and adaptation to changing environmental conditions (stress).…”