No abstract

Carotenoid production from three strains of Rhodosporidium toruloides grown on glycerol was studied. A time-dependent metabolomics approach was used to understand its metabolism on glycerol and mechanism for carotenoid production in three strains during different growth phases (1, 4, 7, and 12 days). Strain CBS 5490 was the highest carotenoid producer (28.5 mg/L) and had a unique metabolic profile. In this strain, metabolites belonging to the TCA cycle and amino acids were produced in lower amounts, as compared to the other strains. On the other hand, it produced the highest amounts of carotenoid and fatty acid metabolites. This indicated that the lower production of the TCA cycle and amino acid metabolites promoted energy and metabolic flux toward the carotenoid and fatty acid synthesis metabolic pathways. This study shows that metabolomic profiling is a useful tool to gain insight into the metabolic pathways in the cell and to shed light on the different molecular mechanisms between strains.

With increasing resource shortage and environmental pollution, it is preferable to utilize materials which are sustainable and biodegradable. Side-streams products generated from the food processing industry is one potential avenue that can be used in a wide range of applications. In this study, the food by-product okara was effectively reused for the extraction of cellulose. Then, the okara cellulose was further employed to fabricate cellulose hydrogels with favorable mechanical properties, biodegrablability, and non-cytotoxicity. The results showed that it could be biodegraded in soil within 28 days, and showed no cytotoxicity on NIH3T3 cells. As a proof of concept, a demostration of wearable and biocompatible strain sensor was achieved, which allowed a good and stable detection of human body movement behaviors. The okara-based hydrogels could provide an alternative platform for further physical and/or chemical modification towards tissue engineering, medical supplies, or smart biomimetic soft materials.

The oleaginous yeast Rhodosporidium toruloides has great biotechnological potential. It accumulates a high amount of lipids which can be used for biofuels and also produces carotenoids which are valuable in the food and pharmaceutical industry. However, the location of these two hydrophobic products in the cell membrane prohibits its efficient harvesting and separation. Here, the transporter Pdr10 was engineered into R. toruloides and cultured in two-phase media containing oil. This enabled the production and in situ export of carotenoids into the oil and concurrent separation from intracellular lipids in the cells. When Pdr10 strain was cultured in the two-phase media, carotenoids and fatty acids yield increased from 1.9 to 2.9 μg/mg and 0.07 to 0.09 mg/mg, respectively. A total of 1.8 μg/mg carotenoids was exported by Pdr10 strain, as compared to 0.3 μg/mg in the wild type. In the Pdr10 strain, the composition of carotenoids and fatty acid it produced also changed. Torulene became the major carotene produced instead of torularhodin. Also, the unsaturated fatty acid C18:2 became the dominant fatty acid produced instead of the saturated C16:0, which was similar to the grape seed oil used in the two-phase media. This indicated that oil was being consumed by the cells, which was supported by the increased intracellular glycerol levels detected by gas chromatography-mass spectrometry (GC-MS). Our approach represents an easy and greener extraction method which could serve to increase the yield and facilitate separation of carotenoids and fatty acids.

Okara is a major agro-waste, generated as a byproduct from the soymilk and tofu industry. Since okara has a high nutritive value, reusing it as a substrate for solid state biofermentation is an economical and environmental friendly option. Rhizopus oligosporus and Lactobacillus plantarum were the probiotic FDA-approved food-grade cultures used in this study. The study revealed that biofermenting okara improves its nutritional composition. It was found that the metabolomic composition (by GC-MS analysis) and antioxidant activity (by DPPH test) improved after the microbial fermentations. Of the two, okara fermented with R. oligosporus showed better results. Further, the metabolites were traced back to their respective biosynthesis pathways, in order to understand the biochemical reactions being triggered during the fermentation processes. The findings of this entire work open up the possibility of employing fermented okara as a potential functional food for animal feed.