Functional properties of pea protein hydrolysates in emulsions and spray-dried microcapsules

Abstract

In the present study the impact of partial enzymatic hydrolysis on the functional properties of pea protein isolate (PPI) was investigated. PPI and pea protein hydrolysates (PPH) with various degrees of hydrolysis (DH) were characterised by molecular weight distribution, interfacial activity and dilatational rheology (pendant drop tensiometry) and emulsion properties (oil droplet size and ζ-potential). Their suitability for the microencapsulation of nutritional oils by spray-drying and prevention of hydroperoxide formation during storage was evaluated. Only at very low DH (1%), could stable emulsions be produced using alcalase PPH as emulsifier, most likely due to enhanced bulk aggregation, however the oil droplet size was increased compared to PPI-stabilised emulsions. In contrast, trypsin PPH-stabilised emulsions exhibited smaller oil droplets and an increased surface charge (ζ-potential) with increasing DH in comparison to PPI-stabilised emulsions. Differences observed were reflected in dilatational rheological experiments. Depending on the enzyme used to produce PPH, the dilatational moduli increased and the phase angle decreased (trypsin), i.e. stronger and more elastic interfacial layers were formed, or vice versa (alcalase). The PPI- and trypsin-derived PPH-containing emulsions were stable during atomisation and drying, resulting in high microencapsulation efficiencies (94.5–95.6%). Trypsin PPH exhibited a higher potential than PPI to reduce lipid oxidation of rapeseed oil in spray-dried emulsions during storage as demonstrated by hydroperoxide formation. This effect may be attributed to the altered physical properties of the interfacial film as well as the antioxidative effects of the hydrolysed proteins.