Approximately 1 million tons of waste cooking oils (WCO) are generated in European Union per year. Oftentimes, these oily wastes are discharged through public sewerage systems, increasing the water treatment costs in wastewater treatment plants. The oleaginous yeast Yarrowia lipolytica W29 is used to simultaneously degrade WCO and to produce lipase (market demand is increasing due to its application in the field of bioenergy). A statistical experimental design based on Taguchi method is employed to assess the effect of initial medium pH, WCO, and arabic gum concentration on lipase production. Initial medium pH is found to be the most significant parameter and the interaction between WCO and arabic gum concentration had the highest influence for lipase production. Additionally, the effect of oxygen mass transfer is studied in batch cultures in a stirred tank bioreactor and the maximum lipase activity (12 000 U · L−1) is obtained at kLa of 16 h−1. Simultaneously with lipase production, also lipid‐rich biomass (48% of lipids mass per dry cellular mass), enriched in unsaturated fatty acids (oleic and linoleic acids) is obtained. Practical Applications: In this work it was demonstrated the possibility of replacing an expensive edible oil (olive oil) by a non‐edible oil waste (WCO) for lipase production. Moreover, no more wastes are produced, since whole cells of Yarrowia lipolytica W29 (lipid‐rich biomass), are a potential source for food supplements. Thus, the bioprocess described fulfill the requisites of circular economy: a low cost substrate is used as raw material, added‐value products (lipase and lipid‐rich biomass) are obtained and no further wastes are generated (take‐make‐dispose concept). Waste cooking oils (WCO) are generated from vegetable oils used at high temperatures in food frying. The biological degradation of WCO by the oleaginous yeast Yarrowia lipolytica W29, with concomitant production of added‐value compounds (lipase and lipid‐rich biomass), allows the reduction of pollutant burden of these oily wastes.

Yarrowia lipolytica is a suitable microbial platform to convert low-value hydrophobic substrates into microbial oils and other important metabolites. In this work, this yeast species was used to simultaneously synthetize ex novo lipids and produce citric acid and lipase from animal fat (pork lard) adding higher value to the low-cost fatty substrate. The effect of pH, lard concentration, arabic gum concentration and oxygen mass transfer rate (OTR) on lipids accumulation on Y. lipolytica batch cultures was assessed by an experimental design based on Taguchi method. OTR was by far the most influential parameter in the range of 96mgLh-480mgLh. A bio-modification of initial lipidic substrate was observed and, depending on the nutritional and operational conditions, specialty lipids with specific composition and high added-value were obtained. The unsaturated-to-saturated fatty acids ratio of these microbial lipids is higher than in initial substrate, which indicates that they are more suitable than animal fat for food additives. Moreover, the simultaneous induction of lipase and citric acid by Y. lipolytica growing in animal fat demonstrates that a biorefinery approach may be designed based on animal fat raw material.

The ability of lipolytic yeasts to grow on olive mill wastewater (OMW)-based medium and to produce high-value compounds while degrading this waste, was tested. OMW collected from three-phase olive mills from the North region of Portugal were characterized and used. OMW with COD ranging from 100 g L(-1) to 200 g L(-1) were supplemented with yeast extract and ammonium chloride. Studies of OMW consumption were carried out in batch cultures of Candida rugosa, Candida cylindracea and Yarrowia lipolytica. All strains were able to grow in the OMW-based media, without dilution, to consume reducing sugars and to reduce COD. C. cylindracea was the best strain concerning the lipase production and the reduction of phenolic compounds and COD. For all strains, the phenols degradation was quite difficult, mostly when more easily degradable carbon source is still present in the medium. Among the phenolic compounds tested catechol is the most inhibitory to the cells.

Aims:  To study the cellular growth and morphology of Yarrowia lipolytica W29 and its lipase and protease production under increased air pressures. Methods and Results:  Batch cultures of the yeast were conducted in a pressurized bioreactor at 4 and 8 bar of air pressure and the cellular behaviour was compared with cultures at atmospheric pressure. No inhibition of cellular growth was observed by the increase of pressure. Moreover, the improvement of the oxygen transfer rate (OTR) from the gas to the culture medium by pressurization enhanced the extracellular lipase activity from 96·6 U l−1 at 1 bar to 533·5 U l−1 at 8 bar. The extracellular protease activity was reduced by the air pressure increase, thereby eliciting further lipase productivity. Cell morphology was slightly affected by pressure, particularly at 8 bar, where cells kept the predominant oval form but decreased in size. Conclusions:  OTR improvement by total air pressure rise up to 8 bar in a bioreactor can be applied to the enhancement of lipase production by Y. lipolytica. Significance and Impact of the Study:  Hyperbaric bioreactors can be successfully applied for yeast cells cultivation, particularly in high‐density cultures used for enzymes production, preventing oxygen limitation and consequently increasing overall productivity.