Abstract
Protein hydrolysates are complex mixtures of peptides of different chain length produced from purified protein by enzymatic hydrolysis. The efficiency of the hydrolysis is defined by a global value known as hydrolysis degree (HD), which is the fraction of peptide bonds cleaved in the treated protein. Hydrolysates, showing a similar value of HD, may differ in the composition (free amino acids, dipeptides, tripeptides and/or oligopeptides) and in their absorption kinetics. It is well known that protein hydrolysates containing mostly di- and tripeptides are more rapidly absorbed than those based on longer peptides. Novel methodologies have been investigated in order to control the extent of the enzymatic hydrolysis as well as the quality of the produced hydrolysates. Among them, non-thermal technologies, such as High Hydrostatic Pressure (HHP) and Pulsed light (PL), modify the conformational structure of proteins. Proteolysis can be modulated if it is conducted in combination with these technologies which are able to change the availability of peptide bonds exposed to the enzymatic action. The work aimed at investigating the effects of the combination of these two technologies on the hydrolysis kinetics of a target protein: Bovine Serum Albumin (BSA). BSA protein (5 mg/mL) in sodium phosphate buffer (50 mM, pH =7.5) was treated with PL and HHP at different processing conditions, namely pressure level and treatment time in the case of HHP and treatment time and energy input in the case of PL. The two technologies were applied in different orders: HHP or PL treatment followed by non-thermal assisted hydrolysis; HHP and PL assisted hydrolysis; HHP and PL treatment followed by thermal hydrolysis. Chymotrypsin and trypsin (E/S ratio = 1/10) were used to hydrolyze the BSA protein solutions.
The experimental data demonstrate that both HHP and PL treatments are able to cause protein unfolding. Higher pressure level and prolonged times in HHP processes as well as higher number of pulses and lower distances from the lamp in PL treatments enhance protein hydrolysis. The combination of PL and HHP treatments is suitable to increase the extent of BSA proteolysis with chymotrypsin and trypsin. The highest value of the hydrolysis degree is observed when HHP assisted hydrolysis and PL assisted hydrolysis are applied in sequence.
