The solubility of potato proteins from industrial potato fruit juice as influenced by pH and various additives

The effects of pH and various additives on the precipitation and (re)solubility at pH 7 of potato proteins from industrial potato fruit juice (PFJ) were studied. The use of various strong and weak acids did not result in differences in protein precipitation, which on average occurred to a maximum of 60% of total protein at pH 3. Weak acids did, however, result in precipitates with a higher resolubility at pH 7 compared with strong acids. At pH 5, addition of FeCl3 or ZnCl2 increased both precipitation and resolubility compared with the situation without additives. The largest increases in both precipitation and resolubility were achieved using organic solvents at pH 5 as an additive, resulting in a maximum precipitation and maximum resolubility at pH 7 of 91 and 83% of total protein respectively. The results described in this study lead to the hypothesis that precipitation and resolubilisation of potato proteins from PFJ are not determined by their isoelectric pH but by their interactions with low‐molecular‐weight components.