Nestrukturirani modeli mliječno-kiselog vrenja

To describe a microbial process, two kinds of models can be developed, structured and unstructured models. Contrary to structured models, which take into account some basic aspects of cell structure, their function and composition, no physiological characterization of cells is considered in unstructured models, which only consider total cellular concentration. However, in spite of their simplicity, unstructured models have proven to accurately describe lactic acid fermentation in a wide range of experimental conditions and media. A partial link between cell growth and production, namely the Luedeking and Piret model, is mostly considered by the authors. Culture pH is the main parameter to be considered for model development. Acidic pH leads to inhibitory concentrations of undissociated lactic acid, the main inhibitory component, which causes cessation of growth and then production. On the other hand, pH control at optimal value for LAB growth allows to overcome product inhibition (by the total lactic acid produced or its undissociated part); hence nutritional limitations have to be considered for model development. Nitrogen is mainly involved in cessation of growth, owing to the fastidious nutritional requirements of LAB, while lactic acid production ceased when carbon was exhausted from the medium. The lack of substrate inhibition when usual concentrations of carbon substrate are used should be noted.Da bi se opisao mikrobni proces, upotijebljeni su strukturirani i nestrukturirani modeli. Strukturirani modeli uzimaju u obzir strukturu, funkciju i raspored stanica, a nestrukturirani ne uzimaju fiziološka svojstva, već samo ukupnu koncentraciju stanica. Ipak, usprkos njihovoj jednostavnosti, nestrukturirani modeli precizno opisuju mliječno-kiselo vrenje u različitim eksperimentalnim uvjetima i na raznim podlogama. Autori najčešće koriste Luedekingov i Piretov model, koji opisuje djelomičnu vezu između rasta stanica i proizvodnje mliječne kiseline. U razvoju ovoga modela najčešće je pH-vrijednost glavni parametar. Pri niskoj pH-vrijednosti nastaju inhibicijske koncentracije nedisocirane mliječne kiseline, što zaustavlja rast mliječno-kiselih bakterija, a time i proizvodnju mliječne kiseline. Taj se inhibicijski učinak može prevladati održavanjem optimalne pH-vrijednosti, ali pritom treba uzeti u obzir utjecaj hranjivih tvari na rast mliječno-kiselih bakterija. Nedostatak dušika je najčešći uzrok inhibicije mliječno-kiselih bakterija, jer im je prijeko potreban za rast, dok nakon iscrpljivanja ugljika iz podloge prestaje proizvodnja mliječne kiseline, što se može izbjeći korištenjem odgovarajućih koncentracija ugljika

Biodegradation by bioaugmentation of dairy wastewater by fungal consortium on a bioreactor lab-scale and on a pilot-scale

International audienceA fungal consortium including Aspergillus niger, Mucor hiemalis and Galactomyces geotrichum was tested for the treatment of dairy wastewater. The bio-augmentation method was tested at lab-scale (4 L), at pilot scale (110 L) and at an industrial scale in Wastewater Treatment Plants (WWTP). The positive impact of fungal addition was confirmed when fungi was beforehand accelerated by pre-culture on whey (5 g/L lactose) or on the dairy effluent. Indeed, chemical oxygen demand (COD) removal yields increased from 55% to 75% for model medium, diluted milk. While after inoculation of an industrial biological tank from a dairy factory with the fungal consortium accelerated by pre-cultivation in a 1000 L pilot plant, the outlet COD values decreased from values above the standard one (100 mg/L) to values in the range of 50-70 mg/L. In addition, there was a clear impact of fungal addition on the 'hard' or non-biodegradable COD owing to the significant reduction of the increase of the COD on BOD5 ratio between the inlet and the outlet of the biological tank of WWTP. It was in the range of 451%-1111% before adding fungal consortium, and in the range of 257%-153% after bio-augmentation with fungi. An inoculated bioreactor with fungal consortium was developed at lab-scale and demonstrated successfully at pilot scale in WWTP

Absorption and biodegradation of toluene: Optimization of its initial concentration and the biodegradable non-aqueous phase liquid volume fraction

International audienceDi (2-EthylHexyl) Phthalate (DEHP) was selected as a biodegradable organic solvent to be implemented in a two-phase partitioning bioreactor (TPPB) dedicated to remove a model hydrophobic volatile organic compound (VOC), toluene. In a first step, the absorption capacity of toluene in the selected organic solvent was examined according to the partition coefficients H. In a second step, toluene biodegradation in DEHP by non-acclimated activated sludge was carried out for different volume fractions of DEHP in water and five different toluene concentrations (4.3, 43, 106, 212 and 430 mg l−1). Toluene showed high affinity for DEHP with H = 0.99 Pa m3 mole−1. Both toluene and DEHP were completely consumed for 4.3 mg l−1 (initial toluene concentration) and a volume ratio of 0.1% DEHP in water. For an initial toluene concentration of 106 mg l−1 and a volume ratio of 0.1%, total toluene consumption and 87% DEHP degradation yield were obtained after seven days of incubation

Residue of dates from the food industry as a new cheap feedstock for ethanol production

International audienceSyrup resulting from date by-products constitutes a favorable medium for yeast development, owing to its sugar composition; it was hence tested for ethanol production. Three yeasts, Saccharomyces cerevisiae, Zygosaccharomyces rouxii and Candida pelliculosa, were selected for ethanol production on dates syrup. In batch fermentation, the ethanol concentration depended on the initial sugar concentration and the yeast strain. For an initial sugar concentration of 174.0 ± 0.2 kg m−3, maximum ethanol concentration was 63.0 ± 0.1 kg m−3 during S. cerevisiae growth, namely higher than the amounts achieved during Z. rouxii and C. pelliculosa growth, 33.0 ± 2.0 kg m−3 and 41.0 ± 0.3 kg m−3 respectively. Contrarily, only Z. rouxii was able to grow on 358.0 ± 1.0 kg m−3 initial sugar amount, resulting in 55.0 ± 1.0 kg m−3 ethanol produced

Enzymatic degradation of Congo Red by turnip (Brassica rapa) peroxidase.

Pas de DOI. Info bibliogr : http://www.znaturforsch.com/ac/v67c/67c0429.pdfInternational audienceThe enzyme peroxidase is known for its capacity to remove phenolic compounds and aromatic amines from aqueous solutions and also to decolourize textile effluents. This study aims at evaluating the potential of a turnip (Brassica rapa) peroxidase (TP) preparation in the discolouration of textile azo dyes and effluents. An azo dye, Congo Red (CR), was used as a model pollutant for treatment by the enzyme. The effects of various operating conditions like pH value, temperature, initial dye and hydrogen peroxide concentrations, contact time, and enzyme concentration were evaluated. The optimal conditions for maximal colour removal were at pH 2.0, 40 degrees C, 50 mM hydrogen peroxide, 50 mg/l CR dye, and TP activity of 0.45 U/ml within 10 min of incubation time. Analysis of the by-products from the enzymatic treatment by UV-Vis and IR spectroscopy showed no residual compounds in the aqueous phase and a precipitate of polymeric nature

Potrošnja ugljika i proizvodnja metabolita tijekom rasta plijesni Geotrichum candidum i Penicillium camemberti u podlozi s glukozom i aminokiselinama

Amino acids had previously been characterized based on their ability to be assimilated as carbon sources by Penicillium camemberti and Geotrichum candidum. For each microorganism, three groups of amino acids have been characterized, leading to four different metabolic behaviours. To describe those recorded during P. camemberti growth on an amino acid and glucose, an unstructured model had previously been developed, based on the sequential consumption of both carbon substrates; glucose first, followed after its exhaustion by the selected amino acid. Only the part of the amino acid assimilated as a carbon source for cellular biosynthesis was considered in the model, which had to be deduced from the total amino acid consumption. To avoid the use of such an indirect parameter, ammonium was considered in this work, which was produced after amino acid deamination and corresponded to the release of the excess nitrogen, since amino acids contain excess nitrogen in relation to their carbon content in fungi. The model, therefore, involved substrate carbon consumption, ammonium production, as well as biomass yield on the carbon substrate, YX/S, and biomass yield on the produced ammonium, YX/P. The model proved to describe satisfactorily the various metabolic behaviours recorded during P. camemberti and G. candidum growth on an amino acid and glucose.U ispitivanju su upotrijebljene aminokiseline prethodno okarakterizirane kao izvor ugljika za rast plijesni Geotrichum candidum i Penicillium camemberti. Za svaki su mikroorganizam karakterizirane tri skupine aminokiselina, čija se asimilacija odvija kroz jedan od četiriju različitih metaboličkih puteva. Prethodno je razvijen nestrukturirani model rasta P. camemberti u podlozi s aminokiselinom i glukozom, temeljen na potrošnji ugljika iz glukoze, pa nakon iscrpljivanja glukoze iz odabrane aminokiseline. U izračunu je modela uzet samo dio aminokiseline, asimiliran kao izvor ugljika pri biosintezi stanica plijesni, dobiven oduzimanjem dijela aminokiseline asimiliranog kao izvor dušika od ukupne potrošnje aminokiselina. Kako bi se izbjegla upotreba ovakva indirektnog parametra rasta, u model je uključena količina amonijaka dobivenog deaminacijom aminokiselina, koja odgovara količini oslobođenog dušika. Tako je naposljetku model obuhvaćao potrošnju ugljika, proizvodnju amonijaka, prinos biomase YX/S izračunat prema potrošnji ugljika i prinos biomase YX/P dobiven na osnovi količine proizvedenog amonijaka. Takav model uspješno opisuje različite metaboličke puteve asimilacije aminokiselina tijekom rasta P. camemberti i G. candidum u podlozi s aminokiselinom i glukozom

Umjetna inteligencija i matematičko modeliranje kinetike sušenja prethodno obrađenih cjelovitih plodova marelice

This study involved monitoring and modelling the drying kinetics of whole apricots pre-treated with solutions of sucrose, NaCl, and sodium bisulphite. The drying was performed in a microwave oven at different power levels (200, 400, and 800 W). Two artificial intelligence models were used for the prediction of drying time (DT) and moisture ratio (MR): artificial neural network (ANN) and an adaptive neuro-fuzzy inference system (ANFIS). On the other hand, the MR prediction was also done with 21 semi-empirical models, one of which we created. The results showed that the drying time decreased with the increase in microwave oven power for the three treatments. The treatment with NaCl was the most suitable for our work. The correlation coefficients of drying time (0.9992) and moisture ratio (0.9997) of ANN were high compared to the ANFIS model, which were 0.9941 and 0.9995, respectively. Among twenty semi-empirical models that were simulated, three models were fitted to our study (Henderson & Papis modified, Henderson & Pabis, and Two Terms). By comparing the three models adapted to our work and the model that we proposed, as well as ANN for MR prediction, it was observed that the model that we created was the most appropriate for describing the drying kinetics of NaCl-treated apricot. This solution opens the prospect of using this potential model to simulate fruit and vegetable drying kinetics in the future.Ovim istraživanjem obuhvaćeno je praćenje i modeliranje kinetike sušenja cjelovitih plodova marelice prethodno obrađenih otopinama saharoze, natrijeva klorida i natrijeva bisulfita. Sušenje je provedeno u mikrovalnoj pećnici pri različitim snagama (200, 400 i 800 W). Za predviđanje vremena sušenja (DT) i omjera vlage (MR) primijenjena su dva modela umjetne inteligencije: umjetna neuronska mreža (ANN) i prilagodljivi sustav neizrazitog zaključivanja zasnovanog na neuronskoj mreži (ANFIS). S druge strane, za predviđanje MR-a upotrijebljeno je 20 postojećih poluempirijskih modela te jedan koji su autori izradili sami. Rezultati su, kod sve tri primijenjene obrade, pokazali redukciju vremena sušenja s povećanjem snage mikrovalne pećnice. Tretman otopinom natrijeva klorida pokazao se najpogodnijim. Koeficijenti korelacije ANN modela za vrijeme sušenja (0,9992) i omjer vlage (0,9997) bili su viši nego kod ANFIS modela (0,9941 i 0,9995). Za dvadeset primijenjenih polu-empirijskih modela, tri modela pokazala su se podudarnim s rezultatima ovog istraživanja (modificirani model Hendersona i Pabisa, model Hendersona i Pabisa te model dvaju pojmova). Uspoređujući tri spomenuta modela i model predložen u ovom radu, kao i predviđanje MR-a ANN-om, uočeno je da je model predložen u radu najprikladniji za opisivanje kinetike sušenja marelice tretirane otopinom natrijeva klorida. Takvi rezultati ukazuju da bi se predloženi model potencijalno mogao ubuduće primjenjivati za simulaciji kinetike sušenja voća i povrća

Enhancement of the biodegradability of a mixture of dyes (methylene blue and basic yellow 28) using the electrochemical process on a glassy carbon electrode

International audienceThe coupling of an electrochemical process with a biological treatment for the degradation of methylene blue (MB) and basic yellow 28 (BY28) considered separately or in mixture on a glassy carbon electrode was examined in this study. It was shown that color removal efficiency and mineralization yield of MB, BY28, and their mixture increased with the working potential and decreased with the initial dye concentration. The optimal conditions were found to be E=2.4V/SCE, [MB](0)=50mg L-1, [BY28](0)=50mg L-1, pH=2, T=25 degrees C, and =600rpm, which led to 100% color removal after 120 and 240min of reaction time for BY28 and MB, respectively. Under these optimal conditions, the mineralization yield of BY28, MB, and their mixture (50mg L-1 of each dye) was close to 59, 57, and 54% within 360min of reaction time, respectively. The biological oxygen demand (BOD5)/chemical oxygen demand (COD) ratio increased substantially after 360min of pre-treatment from 0.04 to 0.27 for the dyes mixture. Microbial degradation was therefore performed for the pre-treated mixture solution and the results showed significant mineralization yield leading to an overall dissolved organic carbon decrease of 78% for the coupled process. It was therefore shown the presence of residual refractory compounds at the end of the culture which was illustrated by the decrease of the BOD5/COD ratio (0.045) obtained for the final solution. However, biodegradability was improved after a recycling of the solution in the electrochemical oxidation pre-treatment during 180min leading to a BOD5/COD ratio of 0.73