Epsilon Archive for Student Projects

Abstract

This study explores the incorporation of yeast lipids into complex food products, using a pea protein emulsion gel as a model system. Some yeast strains can produce lipids up to 80% of their weight, and these lipids could have the potential to replace use of vegetable oils, as a less resource-intensive alternative. Rhodotorula toruloides CBS14 is one such yeast strain, that also produces brightly coloured antioxidants, carotenoids. The potential for the use of these in food was explored through texture, stability and colour measurements in this study.
The yeast oil was extracted from the dried biomass using hexane extraction and emulsified into a protein slurry, and then heated to form a gel. Rapeseed oil was used as a control. Texture Profile Analysis was used for textural measurements of the gels where hardness, springiness and cohesiveness were used as the textural parameters. Colour was measured using a Konica Minolta CR-400 , and lipid oxidation was used as a shelf life indicator and measured through TBARS. Gel syneresis was measured after 7 days through weight difference due to driploss.
The yeast oil samples created a thick, spreadable emulsion with a bright orange-pink colour before gelation, compared to the rapeseed oil gel that was thinner and pourable, with a pale beige colour. After gelation the yeast oil gels displayed more air bubbles than the rapeseed oil gels, indicating more incorporated air in emulsification, or less dispelled air during subsequent centrifuging. The yeast oil gels were significantly harder than the rapeseed oil control, and cohesiveness was slightly lower, however the difference was not statistically significant. The colours of the gels are clearly different from each other with a ΔE of 26,9, but no significant change occurred in the samples from day 2 to day 7 (ΔE < 2,6). The yeast oil gels were more red, yellow and darker than the rapeseed oil samples as expected. Lipid oxidation did not differ significantly in any of the samples after 7 days. The yeast oil gels displayed significantly less syneresis (1,1-1,8% ) than the rapeseed oil gels (11,3-11,5%) after 7 days.
The results in this study indicate that yeast oil from R. toruloides has potential as a food ingredient. It seems to have potential in replacing some colourants, stabilisers and emulsifiers in emulsified protein gel products. Repeat measurements over longer time is needed for any conclusions as to antioxidant effect on lipid oxidation in the yeast oil.