Plant-based food materials are increasingly utilized as constituents of a healthy and sustainable human diet. Many plant-based side streams contain high levels of linoleic acid (LA) in their lipids. In the work described in this thesis, a bioprocess was developed for bioconversion of plant LA to health-beneficial conjugated linoleic acid (CLA). The materials used were oats, sunflower oil and two side streams of plant oil processing, soy okara and camelina meal. The core reaction of the process is microbial isomerization of LA to a c9,t11 isomer of CLA. Prior to isomerization, liberation of LA from plant lipids as free fatty acid is necessary for the microbial catalysis. For this, a process step was developed in which plant material was supplemented with non-heat treated oat flour containing naturally occurring lipolytic activity and the hydrolysis was carried out at low water activity. By adjustment of the lipolysis time, the amount of free LA entering the isomerization stage could be controlled. The isomerization reaction was performed by Propionibacterium freudenreichii in aqueous plant slurries at pH 8.0–8.5. The precultivated, non-growing cells rapidly produced CLA in the tested materials and the highest production rates were observed in okara slurries. Thus, the antimicrobial action of free LA was probably attenuated by components of the heterogeneous plant slurry which in part made the use of higher initial free LA levels possible. The rates of CLA production, final concentrations of CLA and amounts in total lipids were at least equal to or even higher than have earlier been reported for milk-based microbial isomerizations. Of the tested materials, camelina meal also contained high amount of α-linolenic acid (α-LNA). α-LNA was hydrolyzed into free fatty acid and isomerized simultaneously with LA into conjugated α-linolenic acid (α-CLNA). The predominant isomer produced was c9,t11,c15-CLNA.CLA was recovered and concentrated from the isomerization slurries by lowering the pH to 5.5, which resulted in adherence of the free fatty acids to easily separable particulate material. Free CLA, as other free fatty acids, may cause decreased palatability of foods. In the present study this problem was resolved for the first time by a second fermentation step using a selected yeast strain as an esterification agent. Thereby, the free CLA produced in the isomerization stage was re-esterified in yeast neutral lipids. It is anticipated that the process developed will have general applicability for producing value-added bioactive food ingredients from a wide variety of plant materials.
|Translated title of the contribution||Kasviperäisten elintarvikemateriaalien ja -sivuvirtojen bioprosessointi konjugoidun linolihapon rikastamiseksi niihin|
|Publication status||Published - 2020|
|MoE publication type||G5 Doctoral dissertation (article)|
- conjugated linoleic acid
- plant material
- side stream