Complex coacervation of acid-extracted fiber from butternut squash (Cucurbita moschata) and protein

The ability of acid-extracted butternut squash fiber to form complex coacervates with ovalbumin and gelatin was investigated in this paper. The yield of squash fiber and its galacturonic acid content were approx. 6% and 30% (w/w), respectively. Properties of coacervates prepared with squash fiber and proteins at various mixing ratios were evaluated and compared with coacervates formed with sugar beet pectin extracted under the same conditions. FTIR measurements confirmed that coacervation was a result of electrostatic interactions in pH intervals where fiber and protein were oppositely charged. In general, both observed fibers formed coacervates of higher structure strength with gelatin at lower mixing ratios. Nevertheless, butternut squash fiber proved to be superior to sugar beet pectin regarding the ability to form coacervate with the highest mechanical strength. Storage moduli of coacervates from squash fiber and gelatin at 1:1 and 1:2 mixing ratios were 1.5 and 2 times higher, respectively, compared with moduli of coacervates with sugar beet pectin, while squash based complexes formed at 1:3 mixing ratio exhibited four times higher mechanical stability. In addition, squash fiber-based coacervates with ovalbumin showed the highest stability under simulated gastric conditions resulting in a completely preserved structure in the gastric fluid. More than half of squash fiber:ovalbumin (1:1) coacervate remained intact in the intestinal matrix, thus making it 20% more stable than coacervate with sugar beet pectin.