Properties of acid whey as a function of pH and temperature

Compositional differences of acid whey (AW) in comparison with other whey types limit its processability and application of conventional membrane processing. Hence, the present study aimed to identify chemical and physical properties of AW solutions as a function of pH (3 to 10.5) at 4 different temperatures (15, 25, 40, or 90°C) to propose appropriate membrane-processing conditions for efficient use of AW streams. The concentration of minerals, mainly calcium and phosphate, and proteins in centrifuged supernatants was significantly lowered with increase in either pH or temperature. Lactic acid content decreased with pH decline and rose at higher temperatures. Calcium appeared to form complexes with phosphates and lactates mainly, which in turn may have induced molecular attractions with the proteins. An increase in pH led to more soluble protein aggregates with large particle sizes. Surface hydrophobicity of these particles increased significantly with temperature up to 40°C and decreased with further heating to 90°C. Surface charge was clearly pH dependent. High lactic acid concentrations appeared to hinder protein aggregation by hydrophobic interactions and may also indirectly influence protein denaturation. Processing conditions such as pH and temperature need to be optimized to manipulate composition, state, and surface characteristics of components of AW systems to achieve an efficient separation and concentration of lactic acid and lactose.