Angélique Fontana

Continuous alcoholic fermentation of sucrose using flocculating yeast. The limits of invertase activity

SummaryAt high flow rates, the continuous alcoholic fermentation of sucrose in a laboratory fermenter with internal cell recycle, using a strongly flocculating yeast can be limited by the substrate hydrolysis. This system is sensitive to glucose catabolic repression and to mineral deficiency. The release of invertase activity in the medium is negligible. From theoretical and experimental considerations, the hydrolysis rate is imposed by diffusionnal limitations in the biomass particles. Nevertheless, ethanol productivities as high as 68 g/L.h can be reached, without biomass retention problems. A better understanding of the basic phenomena involved in floc formation and evolution is required to control reactor performances.

Diffusivity measurement in a flocculating yeast layer

The diffusion of small molecules (sugars and alcohols) through a dense layer of flocculating yeast has been studied and compared to the theorical value calculated from parameters such as porosity and yeast density. Lactose, ethanol and methanol were chosen as model molecules. In comparison with water, the diffusion rate of lactose is divided by three. Alcohols which cross the cell envelope diffuse relatively faster than lactose which was assumed not to penetrate the cells. An increase of the lactose diffusion rate is observed when the yeast are heat killed.

Analysis of neutral lipids from microalgae by HPLC-ELSD and APCI-MS/MS.

A method was developed to analyze neutral lipids through the use of three triglycerides, four free fatty acids, six di- and four mono-glycerides standards by high performance liquid chromatography (HPLC) normal phase coupled with either with evaporative light scattering detector (ELSD) or with mass spectrometry (MS) operating in atmospheric pressure chemical ionization (APCI) mode. The method was applied to the determination of the neutral lipid fraction from a Botryococcus braunii race A (B. braunii) culture. This method led us to identify neutral lipids synthesized by B. braunii in a single analysis within 45min through HPLC-APCI-MS/MS technique.

Fructose syrups and ethanol production by selective fermentation of inulin

Jerusalem artichoke is a favorable substrate for inulin or fructose syrup production. The sugar content and the fructose ratio of inulin depend on various factors, particularly on the date of harvest. Incomplete fermentation of extracts by selected yeasts allows the production of inulin with increased fructose content. The yeast strains (Saccharomyces cerevisiae, S. diastaticus...) are chosen for their ability to ferment sucrose and inulin small polymers, but not easily inulin large polymers. A good increase in the fructose ratio and a good yield in residual sugars can be obtained with the better strains. After fermentation and acid or enzymatic hydrolysis, extracts from “early” and “late” harvested tubers lead to syrups of good quality containing up to 95% and 90% of fructose respectively. This fermentative enrichment process is competitive with others (for example, chromatographic enrichment), is appropriate to raw extracts, simplifies the purification steps, and also permits the simultaneous benefit of production of by-products in the form of ethanol and yeast (in addition to the pulps). Unhydrolyzed inulin polymers with high fructose content can be recovered by this selective fermentation.

Influence of aeration and [rho0] mutation on the structure of the cell walls of Saccharomyces cerevisiae and S. diastaticus

The structure of the cell walls of Saccharomyces cerevisiae and S. diastaticus wild strains and mutants [rho0] was studied after growth of the cells in aerobiosis and without aeration. Transmission electron microscopy observations of the walls showed that in respiratory deficient cells the external region, corresponding to the phosphopeptidomannan layer, was altered, while the inner zone corresponding to the wall matrix was less damaged. Chemical analysis of the purified walls as well as of pronase extracted heteropolyosides revealed in the mutants [rho0] and in the cells grown without aeration, but to lesser extent, an enhanced synthesis of phosphopeptidomannans. These polymers were, however, less phosphorylated and their apparent molecular mass was lower than those of phosphopeptidomannans extracted from wild strains grown under aerobiosis. The chemical analysis of the wall and of wall residues provides results consistent with the transmission electron micrographs. It is suggested that in respiratory deficient cells, there is a lack of a mitochondrial function which controls the synthesis of the wall phosphopeptidomannans.

Effect of post-harvest treatments on the occurrence of ochratoxin A in raw cocoa beans

Abstract Cocoa beans are the principal raw material for chocolate manufacture. Moulds have an important place in the change in the quality of cocoa beans due to their role in the production of free fatty acids and mycotoxins, namely ochratoxin A (OTA). This study investigated the impact of the key post-harvest treatments, namely the fermentation and drying methods on OTA contamination of raw cocoa beans. Analytical methods for OTA detection were based on solid–liquid extraction, clean-up using an immunoaffinity column, and identification by reversed-phase HPLC with fluorescence detection. Of a total of 104 randomly selected cocoa samples analysed, 32% had OTA contents above 2 µg kg–1. Cocoa sourced from pods in a bad state of health had a maximum OTA content of 39.2 µg kg–1, while that obtained from healthy pods recorded 11.2 µg kg–1. The production of OTA in cocoa beans increased according to the pod-opening delay and reached 39.2 µg kg–1 after an opening delay of 7 days after harvest, while 6.1 and 11.2 µg kg–1 were observed when pods were opened after 0 and 4 days. OTA production also seemed to depend considerably to the cocoa fermentation materials. When using plastic boxes for bean fermentation, the OTA production was enhanced and reached an average OTA content of about 4.9 µg kg–1, while the raw cocoa treated in banana leaves and wooden boxes recorded 1.6 and 2.2 µg kg–1 on average respectively. In parallel, the OTA production was not really influenced by either the mixing or the duration of the fermentation or the drying materials.

Microbiological safety of flours used in follow up for infant formulas produced in Ouagadougou, Burkina Faso

The prevalence of diarrheal diseases in children aged from 6 to 24 months in Burkina Faso is 38%. These diarrheas may be due to the consumption of contaminated weaning food. Therefore, the microbiological quality of follow up infant flours used as supplement foods is a key-point to reduce children diseases. In this study, the microbiological safety of locally-produced infant flours was investigated. One hundred and ninety-nine (199) samples were collected mainly in retails outlets and in Recovery and Nutrition Education Centers. According to the Burkina Faso regulations, microbiological analyses were carried out for Total Aerobic Mesophilic Flora (TAMF), thermotolerant coliforms, Salmonella spp. and yeasts/molds. The bacterial and fungal isolates were identified using phenotypic and genotypic methods and the study of the production of mycotoxins was carried out from the fungal isolates. In collected samples, the TAMF count ranged from 0 to 1.8 × 106 CFU/g with a total average of 6.3 × 104 CFU/g. About 2% of the samples had a microbial load exceeding the standards (105 CFU/g). No Salmonella spp. was isolated in the final infant flours. However, the presence of Enterobacteriaceae (Klebsiella spp. Enterobacter spp. and Cronobacter spp.) was detected and molecular characterization revealed also the presence of fungal species of the genus Aspergillus spp., Penicillium spp. and Fusarium spp. Some of these species were found to produce aflatoxins, ochratoxin A and fumonisins, which are potential carcinogenic toxins. These results demonstrated the need for a preventive approach based on the application of Hazard Analysis Critical Control Point in the food industry to ensure food safety of infant flours in Burkina Faso.