Impact of shear, heat and pH on the conformation, digestibility and antigenicity of Lactoglobulin

Abstract Text:

Processing induced conformational changes can modulate digestibility of food allergens and their antigenicity. Effects of pH (3, 5, 7), temperature (80, 100, 120 °C) and shear (100, 500 and 1000 s^-1) on conformational changes (monitored by surface hydrophobicity, total thiol content, FTIR and gel electrophoresis) and their relation to antigenicity (determined by indirect enzyme-linked immunosorbent assay) of β-lactoglobulin (β-lg) were investigated. Overall, heating at low pH (3) caused unfolding of proteins, fragmentation by partial acid hydrolysis and thereby exposed β-strands that contributed to appearance of some hidden epitopes resulting in higher antigenicity. Heating at pH 5 and 7 decreased allergenic response due to covalently bonded molecular polymerization and aggregation which destroyed and/or masked some epitopes. Shear alone had no effect on the antigenic response of β-lg but could have an influence in combination with pH and/or temperature. Overall, heating β-lg solutions to 120 °C at pH 5 with shearing (100-1000 s^-1) resulted in minimal antigenicity. Structural modifications of β-lg via denaturation or SS/SH mediated interactions can either enhance or decrease its antigenicity. Based on these results, effects of different pH (3, 5 or 7), temperature (room temperature or 120°C) and shear (0 s^-1 or 1000 s^-1) on gastrointestinal digestibility of β-lg and post digestion antigenic characteristics were further studied. Regardless of pH, unheated β-lg showed resistance to peptic digestion with high antigenic value while it was fairly susceptible to pancreatin with moderate reduction in antigenicity. Heating at 120°C significantly improved both peptic and pancreatic digestion attributed to structural alterations resulted in much lower antigenicity; the level of reduction being pH dependant and lowest antigenicity was recorded at pH 5. High shear (1000 s^-1) slightly reduced digestibility and thereby enhanced antigenicity of unheated β-lg at pH 5 and 7 but reduced at 120°C irrespective of the pH. Thus, treatment at pH 5, 120°C and 1000 s^-1could potentially reduce post digestion antigenicity of β-lg.

Keywords: processing, shear, heat, pH, beta-lactoglobulin, digestibility, antigenicity