Epsilon Archive for Student Projects

Abstract

This study evaluated the structural development of an oat-based yoghurt analogue utilising an oat protein concentrate (OPC: PrOatein, 55% protein). The primary objective was to investigate how combining OPC with pea protein isolate (PPI: Pisane, 83.6% protein), adjusting ionic strength via CaCl2 addition and applying ultrasonication could modulate hydration, interfacial and rheological properties of the system to achieve a desirable protein gel network suitable for yoghurt texture.
Protein dispersions were formulated with varying ratios of OPC and PPI (100:0, 90:10, 75:25) or fortified with 30 mM and 100 mM CaCl2. First, physicochemical attributes with and without ultrasound were analysed including water solubility index (WSI), water holding capacity (WHC), foaming capacity (FC) and emulsifying capacity (EC). The ultrasound effect was evaluated via light microscopy. Second, sonicated milk analogues were created and pasteurised, thereafter inoculated with a commercial yoghurt starter culture and fermented at 40°C. The milk and yoghurt analogues were evaluated rheologically (viscosity and flow curves). The network was analysed via confocal laser scanning microscopy (CLSM).
Light microscopy visually confirmed particle size reduction by sonication, which transformed large, dense aggregates into a finer disperse matrix and increase in WSI and improved interfacial properties. EC was improved with sonication and higher inclusion of PPI.
All formulations exhibited shear thinning (pseudoplastic) behaviour. At neutral pH PPI decreased the viscosity, possibly due to electrostatic repulsion. However, after fermentation viscosity increased, 75:25 (OPC:PPI) blend was the only sample that transitioned from a liquid into an acid induced gel. The sample showed highest shear stress and a distinct yield stress of approximately 24 Pa. The calcium fortified samples induced pre-aggregation (salting out), which hindered network formation and resulted in lower resistance than the non-fortified oat milk and yoghurt. CLSM supported the rheological findings by revealing isolated aggregates in the calcium systems, whereas the 75:25 sample displayed a highly dense, continuous protein network.
These findings demonstrate that the OPC ingredient with gelatinised starch alone was insufficient to form a continuous, yoghurt structure under tested conditions. Instead, including PPI resulted in protein gelation near isoelectric point. Thus, incorporating a threshold concentration of at least 25% PPI in relation to OPC, combined with ultrasonication represents a processing strategy to build structural integrity and enhance physicochemical properties of the OPC.