There has been growing interest in the use of microalgae for the production of biofuels, but production costs continue to be too high to compete with fossil fuel prices. One of the main limitations for photobioreactor productivity is light shielding, especially at high cell densities. The growth of the green microalga Chlorella sorokiniana, a robust industrial species, has been evaluated under different trophic conditions with traditional carbon sources, such as glucose and sucrose, and alternative low cost carbon sources, such as carob pod extract, industrial glycerol and acetate-rich oxidized wine waste lees. The mixotrophic cultivation of this microalga with wine waste lees alleviated the problems of light shielding observed in photoautotrophic cultures, improving specific growth rate (0.052 h-1) compared with the other organic sources. The fed-batch mixotrophic culture of Chlorella sorokiniana in a 2 L stirred tank reactor, with optimized nutritional conditions, 100 mM of acetate coming from the oxidized wine waste lees and 30 mM of ammonium, produced an algal biomass concentration of 11 gL-1 with a lipid content of 38% (w/w). This fed-batch strategy has been found to be a very effective means to enhance the biomass and neutral lipid productivity.

The waste materials from the carob processing industry are a potential resource for second-generation bioethanol production. These by-products are small carob kibbles with a high content of soluble sugars (45-50%). Batch and fed-batch Saccharomyces cerevisiae fermentations of high density sugar from carob pods were analyzed in terms of the kinetics of sugars consumption and ethanol inhibition. In all the batch runs, 90-95% of the total sugar was consumed and transformed into ethanol with a yield close to the theoretical maximum (0.47-0.50 g/g), and a final ethanol concentration of 100-110 g/l. In fed-batch runs, fresh carob extract was added when glucose had been consumed. This addition and the subsequent decrease of ethanol concentrations by dilution increased the final ethanol production up to 130 g/l. It seems that invertase activity and yeast tolerance to ethanol are the main factors to be controlled in carob fermentations. The efficiency of highly concentrated carob fermentation makes it a very promising process for use in a second-generation ethanol biorefinery.

BackgroundThe current food system generates about 25 % of total greenhouse gas emissions (GHGE), including deforestation, and thereby substantially contributes to the warming of the earth’s surface. To understand the association between food and nutrient intake and GHGE, we therefore need valid methods to assess diet-related GHGE in observational studies.MethodsLife cycle assessment (LCA) studies assess the environmental impact of different food items. We linked LCA data expressed as kg carbon dioxide equivalents (CO2e) per kg food product to data on food intake assessed by the food frequency questionnaire (FFQ) Meal-Q and validated it against a 7-day weighed food record (WFR). 166 male and female volunteers aged 20–63 years completed Meal-Q and the WFR, and their food intake was linked to LCA data.ResultsThe mean GHGE assessed with Meal-Q was 3.76 kg CO2e per day and person, whereas it was 5.04 kg CO2e using the WFR. The energy-adjusted and deattenuated Pearson and Spearman correlation coefficients were 0.68 and 0.70, respectively. Moreover, compared to the WFR, Meal-Q provided a good ranking ability, with 90 % of the participants classified into the same or adjacent quartile according to their daily average CO2e. The Bland-Altman plot showed an acceptable level of agreement between the two methods and the reproducibility of Meal-Q was high.ConclusionsThis is the first study validating the assessment of diet-related GHGE by a questionnaire. The results suggest that Meal-Q is a useful tool for studying the link between food habits and CO2e in future epidemiological studies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12940-016-0110-7) contains supplementary material, which is available to authorized users.