Abstract
Diversified mixed confectionery waste streams were utilized in a two-stage bioprocess to formulate a nutrient-rich fermentation media for microbial oil production. Solid-state fermentation was conducted for the production of crude enzyme consortia to be subsequently applied in hydrolytic reactions to break down starch, disaccharides, and proteins into monosaccharides, amino acids, and peptides. Crude hydrolysates were evaluated in bioconversion processes using the red yeast Rhodosporidium toruloides DSM 4444 both in batch and fed-batch mode. Under nitrogen-limiting conditions, during fed-batch cultures, the concentration of microbial lipids reached 16.6–17 g·L−1 with the intracellular content being more than 40% (w/w) in both hydrolysates applied. R. toruloides was able to metabolize mixed carbon sources without catabolite repression. The fatty acid profile of the produced lipids was altered based on the substrate employed in the bioconversion process. Microbial lipids were rich in polyunsaturated fatty acids, with oleic acid being the major fatty acid (61.7%, w/w). This study showed that mixed food side-streams could be valorized for the production of microbial oil with high unsaturation degree, pointing towards the potential to produce tailor-made lipids for specific food applications. Likewise, the proposed process conforms unequivocally to the principles of the circular economy, as the entire quantity of confectionery by-products are implemented to generate added-value compounds that will find applications in the same original industry, thus closing the loop.
Highlights
The concept of the circular economy is emerging as a worldwide strategy to transit from the current linear economy model of production and consumption to efficient resource exploitation [1,2]
Free Amino Nitrogen (FAN) concentration was measured with the ninhydrin colorimetric method, whereas inorganic phosphorus (IP) concentration was analyzed by the ammonium molybdate spectrophotometric method
Conversion of starch to glucose reached more than 95% when an initial concentration of 50 g·L−1 of Mixed food for infants (MFI) was applied
Summary
The concept of the circular economy is emerging as a worldwide strategy to transit from the current linear economy model of production and consumption to efficient resource exploitation [1,2]. Within this framework, bio-economy encompasses the holistic valorization of renewable resources towards the development of biorefinery concepts and bioprocessing schemes to produce high value-added products. The production of highly unsaturated microbial lipids has gained the attention of many researchers, as they could be widely employed in functional food formulations, eliciting high nutritional composition [3].
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