Proteolysis of burley tobacco-leaf extracts and antioxidant activity of the hydrolysates

Abstract Burley tobacco-leaf protein extracted by alkali and precipitated by acid was hydrolyzed enzymatically, and optimum protease and hydrolysis parameters were determined. Pepsin was best and gave the highest hydrolysis rate (15.55%). As per results of the single-factor test, optimum hydrolysis conditions were: temperature 37 °C, pH 2, and an [E]/[S] ratio of 5%. These hydrolysis conditions were optimized by an orthogonal experiment that rendered the same results as the single factor experiment. The ratio of essential to total amino acids and that of essential to non-essential amino acids contained in the burley tobacco-leaf protease hydrolysate were higher than the FAO/WHO standard values of 0.4 and 0.6, among which hydrophobic amino acid content was the highest, followed by negatively and positively charged amino acid contents. In vitro antioxidant experiments showed that the scavenging rates of DPPH, superoxide anion, and hydroxyl radicals of tobacco-leaf protein hydrolysates were higher than those before hydrolysis. Further, the hydroxyl radical-scavenging rate was the most significant, and total antioxidant capacity was improved. The nutritive value of the burley tobacco-leaf protein hydrolysate improved upon pepsin-mediated hydrolysis, and the antioxidant activity was better. These results provide a theoretical basis for further development and utilization of tobacco protein resources.