Studies On Effect Of Ultra-high Pressure On Functional Properties Of Chickpea Protein Isolate

Ultra high pressure (UHP) is an innovative technology for food processing, which has many advantages compared to traditional heat treatment. Protein is a major ingredient in food, so it has become an important research object in food science. Chickpea is the second most important pulse crop and accounts for 14% of the production of pulses in the world. Chickpea provides high-quality protein with balanced amino acid composition and nutrition. Effect of UHP on functional properties, structure and hydrolysis of chickpea protein isolate (CPI) has been investigated in order to find out the rules and mechanisms of the change induced by UHP.Analysis by surface hydrophobicity and ultraviolet difference spectra showed that more hydrophobic groups exposed to surface of CPI. Free sulfhydryl group (SHF) determination showed the decrease of SHF leading to create more new disulfides (S-S). Study of conformation by gel filtration, dynamic light scattering and electrophoresis proved the emergence of aggregation of CPI after treatment higher than 300 MPa, while some were dissociated into subunits with small molecular weight and kinetic radius after high pressure processing above 400 MPa.Influence of UHP on functional properties of CPI could be explained by the structural changes induced by UHP. Effect of UHP on solubility, emulsifying ande foaming capacity of CPI were studied, as well as effect of functional properties of CPI in different buffers (phosphate and Tris-HCl buffer) and with certain conditional factors such as pressure intensity, treatment time, pH and ionic strength.Effect of UHP on solubility of CPI in different buffers (phosphate and Tris-HCl buffer) has been investigated at pressures ranging from 100 to 600 MPa. Results showed that solubility of CPI decreased significantly at phosphate buffer pH with pressure intensity above 400 MPa and treatment time longer than 5 min, while ionic strength higher than 0.4 mol/L could effectively prevent the decrease of solubility due to pressurization. In Tris-HCl buffer, effect of UHP on solubility of CPI was not significant under the conditions above.UHP treated CPI displayed much better emulsifying capacity in different buffers. In non-resistent buffer (phosphate buffer), emulsifying activity was significantly enhanced with elevated pressure and prolonged treatment time. Maximum emulsifying activity was achieved at 400 MPa treated for 10 min, while emulsifying stability decreased with pressure higher than 400 MPa and treatment time longer than 10 min. Emulsifying activity improved to different extent at phosphate buffer pH (6.0-8.0) and different ionic strength (0-1.0 mol/L). In resistant buffer (Tris-HCl buffer), the increase of emulsifying activity was consistent with the change in phosphate buffer, while emulsifying stability increased at higher pressure. Foaming property of CPI significantly improved in different buffers. In non-resistent buffer (phosphate buffer), foaming capacity was significantly increased with elevated pressure and prolonged treatment time. Maximum foaming capacity was achieved at 500 MPa treated for 10 min, while foaming stability decreased with pressure higher than 400 MPa and treatment time longer than 10 min. Foaming capacity was enhanced to different extent at phosphate buffer pH (6.0-8.0) and different ionic strength (0-1.0 mol/L). In resistant buffer (Tris-HCl buffer), the increase of foaming capacity was consistent with CPI in phosphate buffer, while foaming stability kept increasing with higher pressure and longer treatment time.CPI hydrolysis by Alcalase orα-chymotrypsin was effectively accelerated after high pressure (above 300 MPa) and heat pretreatment (50-70℃). This increased hydrolysis was due to unfolding of CPI and facilitation of binding of the substrate to the enzyme induced by pressure and heat pretreatment.Kinetic model was used to describe the effect of these two pretreatments on CPI hydrolysis. Results showed that hydrolysis by Alcalase was more sensitive to heat pretreatment as compared to hydrolysis byα-chymotrypsin. However, hydrolysis by Alcalase was less sensitive to pressure pretreatment as compared to hydrolysis byα-chymotrypsin.The rate of hydrolysis by Alcalase orα-chymotrypsin during high pressure treatment (100-300 MPa) was increased dramatically much higher than the rate of hydrolysis after pressure and heat pretreatment. Therefore, hydrolysis under high pressure became an innovative way of enzymatic hydrolysis with high efficiency.