https://oatao.univ-toulouse.fr/2771/1/joannis-cassan_2771.pdf

Commercial applications of microalgae

Trends in biotechnological production of fuel ethanol from different feedstocks.

Various agricultural residues, such as corn fiber, corn stover, wheat straw, rice straw, and sugarcane bagasse, contain about 20–40% hemicellulose, the second most abundant polysaccharide in nature. The conversion of hemicellulose to fuels and chemicals is problematic. In this paper, various pretreatment options as well as enzymatic saccharification of lignocellulosic biomass to fermentable sugars is reviewed. Our research dealing with the pretreatment and enzymatic saccharification of corn fiber and development of novel and improved enzymes such as endo-xylanase, β-xylosidase, and α-l-arabinofuranosidase for hemicellulose bioconversion is described. The barriers, progress, and prospects of developing an environmentally benign bioprocess for large-scale conversion of hemicellulose to fuel ethanol, xylitol, 2,3-butanediol, and other value-added fermentation products are highlighted.

Hemicellulose bioconversion

Biotechnological potential of agro-industrial residues. I: sugarcane bagasse

In view of rising prices of crude oil due to increasing fuel demands, the need for alternative sources of bioenergy is expected to increase sharply in the coming years. Among potential alternative bioenergy resources, lignocellulosics have been identified as the prime source of biofuels and other value-added products. Lignocelluloses as agricultural, industrial and forest residuals account for the majority of the total biomass present in the world. To initiate the production of industrially important products from cellulosic biomass, bioconversion of the cellulosic components into fermentable sugars is necessary. A variety of microorganisms including bacteria and fungi may have the ability to degrade the cellulosic biomass to glucose monomers. Bacterial cellulases exist as discrete multi-enzyme complexes, called cellulosomes that consist of multiple subunits. Cellulolytic enzyme systems from the filamentous fungi, especially Trichoderma reesei, contain two exoglucanases or cellobiohydrolases (CBH1 and CBH2), at least four endoglucanases (EG1, EG2, EG3, EG5), and one β-glucosidase. These enzymes act synergistically to catalyse the hydrolysis of cellulose. Different physical parameters such as pH, temperature, adsorption, chemical factors like nitrogen, phosphorus, presence of phenolic compounds and other inhibitors can critically influence the bioconversion of lignocellulose. The production of cellulases by microbial cells is governed by genetic and biochemical controls including induction, catabolite repression, or end product inhibition. Several efforts have been made to increase the production of cellulases through strain improvement by mutagenesis. Various physical and chemical methods have been used to develop bacterial and fungal strains producing higher amounts of cellulase, all with limited success. Cellulosic bioconversion is a complex process and requires the synergistic action of the three enzymatic components consisting of endoglucanases, exoglucanases and β-glucosidases. The co-cultivation of microbes in fermentation can increase the quantity of the desirable components of the cellulase complex. An understanding of the molecular mechanism leading to biodegradation of lignocelluloses and the development of the bioprocessing potential of cellulolytic microorganisms might effectively be accomplished with recombinant DNA technology. For instance, cloning and sequencing of the various cellulolytic genes could economize the cellulase production process. Apart from that, metabolic engineering and genomics approaches have great potential for enhancing our understanding of the molecular mechanism of bioconversion of lignocelluloses to value added economically significant products in the future.

Bioconversion of lignocellulosic biomass: biochemical and molecular perspectives

Chlorophyll production from Spirulina platensis: cultivation with urea addition by fed-batch process

Chlorophyll is a pigment used as colorant in the food, pharmaceutical and cosmetic industries. It can be obtained in considerable quantities from Spirulina platensis biomass. In this work, the cultivation of the microalga was done using urea as the nitrogen source by a fed-batch process. The addition of urea was done in four different modes: intermittent addition every 24 or 48 h , continuous addition by exponentially increasing the added mass, and continuous addition by using a constant mass flow rate. The experiments were carried out at three different temperatures: 27° C , 30° C and 33° C and at a constant light intensity of 3.5 klx . The results showed a positive influence of urea in the growth of Spirulina but no effect on the final chlorophyll content of the cultures. Best results were obtained by continuous urea addition in exponentially increasing amount, at 30°C.

An investigation of effect of replacing nitrate by urea in the growth and production of chlorophyll by Spirulina platensis

Hydrolysis of the hemicellulosic fraction of sugarcane bagasse by sulphuric acid was performed in laboratory (25 mL) and semi-pilot (25 L) reactors under different conditions of temperature, time and acid concentration. On the laboratory scale, the three highest recovery yields were obtained at: 140oC for 10 min with 100 mg acid/g dm (yield=73.4%); 140oC for 20 min with 100 mg acid/g dm (yield=73.9%) and 150oC for 20 min with 70 mg acid/g dm (yield=71.8%). These conditions were also used for hydrolysis in a semi-pilot reactor, and the highest xylose recovery yield (83.3%) was obtained at 140oC for 20 min with 100 mg acid/g dm

Acid hydrolysis of hemicellulose from sugarcane bagasse

Influence of inoculum age and concentration in Spirulina platensis cultivation

The influence of light intensity reduction on Spirulina platensis cultivation was investigated, using urea and KNO3 as nitrogen sources. The reduction of light intensity from 5 to 2 klux was studied both on the 9th and the 13th day of cultivation. Increases of up to 29% in the total chlorophyll production were observed for the cultivations with light intensity reduction, in comparison with the cultivations carried out at fixed light intensities.

Sunao Sato

Papers

Chlorophyll production from Spirulina platensis: cultivation with urea addition by fed-batch process

An investigation of effect of replacing nitrate by urea in the growth and production of chlorophyll by Spirulina platensis

Acid hydrolysis of hemicellulose from sugarcane bagasse

Influence of inoculum age and concentration in Spirulina platensis cultivation

Effect of reducing the light intensity on the growth and production of chlorophyll by Spirulina platensis