Twin-Screw Extrusion for the Production of Lipid Complexed Pea Starch as a Functional Food Ingredient

Abstract

Canada is a major global producer of pulse products including pulse starch, which notably contributes to a healthy diet. Strategically, Canada is taking steps to research methods of adding greater value to these crop products, and functional foods like resistant starch are particularly interesting. The primary objectives of this study were to develop an effective reactive extrusion process to produce gelatinized lipid complexed pea starches with enhanced enzyme resistance and examine the effects of bulk lipid complexing conditions on physicochemical and functional properties of extruded pea starches. One type of commercially available pea starch, Nutri-Pea, was chosen as the research subject in this study. A number of methods including; Englyst digestion method, differential scanning calorimetry (DSC), infrared spectroscopy (FTIR), contact angle, titrations, residence time distribution (RTD) and rapid visco analysis (RVA) were used to characterize the properties of extruded pea starches. The effects of feed formulation and extrusion conditions on lipid complexing and Englyst digestion profiles were systematically examined on two mixing devices. An extensive kinetics study was conducted on a lab scale twin-screw compounder, DSM-Xplore. The process was then scaled up to produce bulk lipid complexed pea starch on a Leistritz twin-screw extruder. The results showed that lipid complexing and digestion profiles were highly dependent on feed moisture and induced screw shear. Reactive extrusion of pea starches under optimized conditions achieved a significant but moderate increase in either resistant starch (RS) content (from 13.3% to 20.2%) or slowly digestible starch (SDS) content (from 7.85% to 23.3%) compared to their native counterparts. However, RS and SDS content could not be improved simultaneously based on the pea starch and extrusion process in this study. Increased degree of substitution (DS) was found for myristic acid complexed pea starches (nominal DS= ~0.8) when compared to palmitic acid complexed pea starch (nominal DS= ~0.5). Contact angle measurements, FTIR and DSC thermograms confirmed the presence of lipids. Lipid complexed starch films showed increasing hydrophobicity with increasing lipid content. As an alternative product compared to functional foods, the modified starch was considered as a biodegradable film for industrial applications. The material was produced at the highest moisture content for extruded native starch and two concentrations of lipid complexed starch using an intensive screw design. Preliminary results show that increasing lipid content and adding 1% glycerol to samples decreases the force per film thickness required to puncture films. However further investigation is required to determine effect of heat and moisture deformation.