Characterization and functional properties of canola protein hydrolysates
Han, Angela Hooi Leng
Functional properties of proteins can be modified by the use of hydrolysis. Canola proteins (Brassica napus) prepared by the protein micellar mass (PMM) method were subsequently hydrolysed by acid, trypsin, chymotrypsin, bacterial and fungal proteases at varying time intervals. Different hydrolysis procedures showed different impacts on the molecular weight distribution, subunit analysis, isoelectric points and protein conformation as well as the surface hydrophobicity. Enzyme treatments cleaved PMM into smaller fragments compared to both acid methods. Some protein aggregation was observed in alternate acid hydrolysates. After hydrolysis with four different enzymes, the resultant hydrolysates showed isoelectric points in the range of 6.2-6.7 whereas all acid hydrolysates from both acid methods had isoelectric points in the range of 4.4-5.7. Fungal and bacterial hydrolysis methods provided the mildest conditions in terms of the enthalpy of denaturation and the thermal denaturation temperature. Overall, T5 had a greater aromatic surface hydrophobicity whereas C20 showed an increased aliphatic surface hydrophobicity. Nitrogen solubility, water holding capacity, fat absorption capacity, emulsion stability, foaming capacity as well as foaming stability of all the hydrolysates were investigated. Hydrolysates treated with chymotrypsin for 20 min (C20) showed the highest nitrogen solubility at pH 4.5 whereas acid hydrolysates of 4 h exhibited the highest solubility at pH 7.0. Hydrolysates prepared by acid hydrolysis for 7 h showed the best water holding capacity whereas chymotrypsin hydrolysates (10 min) exhibited the best fat absorption capacity. Emulsion stability was slightly decreased from the original PMM in most enzyme hydrolysates and mild acid hydrolysates whereas this stability was significantly improved using an alternate acid hydrolysis method. An acid hydrolysate (45) possessed the best foaming capacity whereas the A7 acid hydrolysate showed the best foaming stability. Relationships between moiecular characteristics and functional parameters were established.