h i g h l i g h t sMedium pH for the lipid and carotenoid production by R. toruloides is different. A dual step pH control fed-batch strategy improved the yeast products production. The oxygen played a crucial rule in the yeast carotenoid synthesis. t r a c tThe optimal medium pH to produce biomass and fatty acids by the red yeast Rhodosporidium toruloides NCYC 921 is 4.0, and to produce carotenoids is 5.0. Based on this difference, a dual-stage pH control fed-batch cultivation strategy for the enhancement of lipids and carotenoids production by this yeast was studied. The results showed that when the yeast growth phase was conducted at pH 4.0, and the products accumulation phase was conducted at pH 5.0, biomass, total fatty acid and total carotenoid productivities were significantly improved comparing with the yeast fed batch cultivations carried out at fixed medium pH (4 or 5). Under dual-stage pH control conditions, the biomass, carotenoids and lipids productivities attained 2.35 g/L h, 0.29 g/L h and 0.40 g/L h, respectively. It was also observed that the oxygen played a major role in the yeast carotenoid production.

The effect of the culture medium pH (3.5-6.0) on the carotenoid and lipid (as fatty acids) production by the yeast Rhodosporidium toruloides NCYC 921 was studied. Flow cytometry was used to evaluate the yeast's physiological response to different culture medium pH values. The yeast biomass concentration and lipid content were maxima at pH 4.0 (5.90 g/L and 21.85 % w/w, respectively), while the maximum carotenoid content (63.37 μg/g) was obtained at pH 5.0. At the exponential phase, the yeast cell size and internal complexity were similar, at different medium pH. At the stationary phase, the yeast cell size and internal complexity decreased as the medium pH increased. At the exponential phase, the proportion of cells with polarized membranes was always high (>80 %) but at the stationary phase, the proportion of yeast cells with depolarized membranes was dominant (>65 %) and increased with the medium pH increase. The results here reported may contribute for yeast bioprocesses optimization. For the first time, multiparameter flow cytometry was used to evaluate the impact of medium pH changes on the yeast cell physiological status, specifically on the yeast membrane potential, membrane integrity, cell size and internal complexity.

Carob pulp syrup (CPS) was used as carbon source to produce carotenoids from Rhodosporidium toruloides. To increase the carbon concentration in the growth medium aiming at the carotenoid production improvement, the CPS was concentrated and two different total sugar (TS) concentrations (195.6 g/L and 548.7 g/L) were studied. CPS 195.6 g/L TS contained 4.1 g/L and 0.7 g/L of hydroxymethyl furfural (HMF) and furfural, respectively. CPS 548.7 g/L TS contained 17.7 g/L of HMF and 1.2 g/L of furfural, respectively. > 42% of metabolically active cells (with intact membrane and enzymatic activity) were detected throughout the course of the yeast cultivation on CPS 195.6 g/L TS. On the contrary, the proportion of metabolically active cells was always below 28% during the yeast cultivation on CPS 548.7 g/L TS. Nevertheless, the maximum carotenoid content and productivity (0.42 mg/g and 0.43 mg/Lh, respectively) were obtained when using CPS 548.7 g/L TS.

Brewery wastewater has been proposed as an attractive low-cost substrate for microbial lipid production for oleaginous yeast and microalga with promising results. For each liter of beer produced, from 3 to 10 L of wastewater are generated which can be used as culture medium for autotrophic or heterotrophic metabolism. This strategy allows reducing the culture medium cost, as well as obtaining high lipid contents and other high value compounds which can make the process profitable. Additionally, the use of industrial effluents/wastes as substrates for microbial growth can be a strategy to treat them based on the circular economy rules. This review presents the different brewery wastewater treatment strategies using oleaginous yeast and microalga pure and mixed cultures for the concomitant wastewater treatment and lipids/carotenoids production so far reported, highlighting the benefits/disadvantages of such strategies and comparing their performance in terms of wastewater treatment, lipids and carotenoids production between pure and mixed cultures performance. Graphical Abstract

No abstract

In this study, secondary brewery wastewater (SBWW) supplemented with sugarcane molasses (SCM) was used for SBWW treatment with concomitant lipid and carotenoid production by the yeast Rhodosporidium toruloides NCYC 921. In order to improve the biomass production, ammonium sulfate, yeast extract and urea were tested as nitrogen sources. Urea was chosen as the best low-cost nitrogen source. A fed-batch cultivation was carried out with SBWW supplemented with 10 g L −1 of sugarcane molasses as carbon source, and 2 g L −1 of urea as nitrogen source. A maximum biomass concentration of 42.5 g L −1 was obtained at t = 126.5 h and the maximum biomass productivity was 0.55 g L −1 h −1 at t = 48.25 h. The maximum lipid content was 29.9 % w/w (DCW) at t = 94 h of cultivation and the maximum carotenoid content was 0.23 mg g −1 at 120 h of cultivation. Relatively to the SBWW treatment, after the batch phase, 45.8 % of total Kjeldahl nitrogen removal, 81.7 % of COD removal and 100 % of sugar consumption were observed. Flow cytometry analysis revealed that 27.27 % of the cells had injured membrane after the inoculation. This proportion was reduced to 10.37 % at the end of the cultivation, indicating that cells adapted to the growth conditions.

No abstract

A new process for co-extraction and separation of fatty acids and carotenoids from Rhodosporidium toruloides NCYC 921 biomass in order to achieve full exploitation of the yeast lipidic fraction is described. A saponification of the wet yeast biomass was performed using a potassium hydroxide solution (1.1 M) in ethanol 96%, at 65 °C for 180 min. In the carotenoid extraction step, a biphasic system with an organic:aqueous phases ratio of 0.49 mL/mL and a water content of 18.9% (w/w) was used. In the presence of an acid catalyst, the fatty acid fraction was esterified into fatty acids ethyl esters. The yeast biomass downstream processing allowed reaching a fatty acid and total carotenoids recovery yields of 91.0% and 85.2%, respectively. The process reported here takes advantage of various components of the yeast biomass, therefore maximizing the value derived from the biomass feedstock, with a minimal environmental impact within the frame of circular bioeconomy.