Abstract
This work evaluates the possibility of applying enzymatic beech wood (Fagus sylvatica) hydrolysate as a feedstock for Chlorella sorokiniana growth, and fatty acid and pigment production. Beech wood solids were pretreated with NaOH at high temperature to partially remove xylose and Klason lignin, and enable production of glucose during subsequent enzymatic hydrolysis. Neutralized wood enzymatic hydrolysate containing glucose (TGP-Enz10), was tested on Chlorella growth during heterotrophic cultivation and compared with microalgae growth in a medium containing synthetic glucose (TGP). Results show that enzymatic hydrolysate enabled Chlorella growth in the dark for biomass, fatty acid and pigment production due to the presence of glucose, although the productivity obtained was smaller, if compared to heterotrophic cultivation in a synthetic TGP medium. Partial growth inhibition and diminished productivity in wood hydrolysate supplemented Chlorella culture was due to the presence of neutralized citrate buffer. Neutralized citrate buffer (TGP-Cit10) was found to partially inhibit heterotrophic growth and also strongly suppress mixotrophic growth in Chlorella culture. This buffer was also shown to alter fatty acid composition and to slightly affect ChlTotal/CarTotal ratio during heterotrophic cultivation. Heterotrophic Chlorella cultivation with TGP-Enz10 showed that wood enzymatic hydrolysate can constitute a potential feedstock for microalgae cultivation, although the composition of the buffer used during enzymatic hydrolysis should be taken into consideration.
Highlights
Microalgae are photoautotrophic microorganisms, capable of using light energy to fix CO2 and discharging O2 as a waste product during photosynthesis [1]
Beech wood material contained 44% ± 2 glucose, 17% ± 1 xylose and 20% ± 1 Klason lignin as it was determined in our previous report, where wood particles were subjected to a diluted acid (3%)
Alkaline pretreatment with the use of NaOH was reported as an effective method to remove hemicellulose and Klason lignin from birch [17], cedar [18] and eucalyptus [18,19] wood, resulting in the increase in cellulose exposure and improvement of cellulose conversion to glucose during enzymatic hydrolysis [18,19]
Summary
Microalgae are photoautotrophic microorganisms, capable of using light energy to fix CO2 and discharging O2 as a waste product during photosynthesis [1]. Microalgal cells contain valuable biocompounds, such as fatty acids and pigments, which can find applications in many branches of industry [2]. High amounts of microalgal biomass are necessary to produce target biocompounds from microalgae in a feasible process [3]. High microalgae biomass concentrations can be achieved during mixotrophic or heterotrophic cultivation. During mixotrophic or heterotrophic cultivation, microalgae growth can be supported with organic carbon such as glucose, resulting in high microalgal biomass productivity [4]. Glucose can be obtained from cellulose, a carbohydrate polymer found in lignocellulosic materials, upon hydrolysis with the use of cellulosic enzymes [5].
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