Agar as a single organogelator in the process of solidification of rapeseed (canola) oil obtained by different manufacturing methods

Abstract

The minimalistic solidified form of oil, herein called hydroleogel, was elaborated via the emulsion oleogelation method by using agar hydrogel, as sole oleogelator. The rapeseed oils, originating from different manufacturing processes, were used as oil phase. The texture and rheological characteristics, weight loss, oil binding capacity, as well as color and appearance once solidified and after 24 h and 48 h of storage were studied. Texture profile revealed the dual dependance – the hardest hydroleogels were formed with 3 % agar and using refined rapeseed (canola) oil showing 14.16 ± 0.28 N and 14.11 ± 0.45 N after 2 h and 48 h, respectively. In contrast, hydrogels formed with cold pressed oil and 3% agar solution had an average of 50% lower hardness compared to the others. The oil retention capacity of the matrix was highest for hydroleogels with 3 % agar and cold pressed oil (98.3 ± 1.4 %), followed by cold pressed and bleached oil (97.0 ± 1.8 %) and refined oil (95.77 ± 2.4 %). The largest weight losses were observed for hydroleogels based on 1 % agar, with the exception of those formed from refined oil where a sub-weight loss of 0.5 % was recorded after 48h. The brightest were hydroleogels with pressed and bleached oil and 1 % (w/w) agar having after 2h the L* parameter equal to 98.95 ± 0.01, while the darkest one was cold pressed and bleached oil with 3 % (w/w) of agar (83.15 ± 0.25). The concentration of agar and the type of rapeseed oils used strongly impacted the physicochemical parameters of agar-based hydroleogels. Rapeseed oil hydroleogels with agar as the only structuring agent - an oleogelator in the composition, are a unique combination of two phases being hydrogel (aqueous phase) and rapeseed oil (oil phase) with promising physicochemical parameters.