María C. Maldonado

Production of pectinesterase and polygalacturonase by Aspergillus niger in submerged and solid state systems

Production of pectinesterase and polygalacturonase by Aspergillus niger was studied in submerged and solid-state fermentation systems. With pectin as a sole carbon source, pectinesterase and polygalacturonase production were four and six times higher respectively in a solid state system than in a submerged fermentation system and required a shorter time for enzyme production. The addition of glucose increased pectinesterase and polygalacturonase production in the solid state system but in submerged fermentation the production was markedly inhibited. A comparison of enzyme productivities showed that those determined for pectinesterase and polygalacturonase with pectin as a carbon source were three and five times higher by using the solid state rather than the submerged fermentation system. The productivities of the two enzymes were affected by glucose in both fermentation systems. The membranes of cells from the solid state fermentation showed increased levels of C18:1, C16:0 and C18:0 fatty acids. Differences in the regulation of enzyme synthesis by Aspergillus niger depended on the fermentation system, favoring the solid state over the submerged fermentation for pectinase production.

Catabolite repression of the synthesis of inducible polygalacturonase and pectinesterase byAspergillus niger sp.

The synthesis of pectinesterase (PE) and polygalacturonase (PG) by a strain ofAspergillus niger isolated from rotten lemons was repressed by glucose, even in the presence of the inducer. The production of both enzymes started again once the sugar was used up, or when the mycelium was washed free of glucose and incubated in a glucose-free medium containing the inducer; this proved the reversibility of the repression mechanism. The effect of glucose was also tested in the absence of transcription. The results obtained suggest that repression occurs at the translational level.

Purification and characterization of invertase from Aspergillus niger

Invertase produced by a strain of Aspergillus niger showed the following main characteristics: maximum activity at 60°C, pH 5.0; Km with sucrose as substrate, 0.0625mm; Vmax 0.013 mol/min; and free energy 9132 cal/mol. The metal ions and p-chloromercuribenzoate (PCMB) acted as inhibitors respectively.

Production of pectinases byAspergillus sp using differently pretreated lemon peel as the carbon source

SummaryAspergillus sp strains from decaying lemons were tested for extracellular pectinase production, testing differently pretreated lemon peel as the carbon source instead of pectin. It was found that the production of extracellular polygalacturonase was about the same and that of pectinesterase substantially higher when unwashed fresh lemon peel was used instead of pectin. The culture filtrate obtained showed a clarifying capacity similar to that of a commercial pectinase preparation, but the vitamin C of the juice was less affected by the treatment.

Purification and characterization of pectinesterase produced by a strain ofAspergillus niger

After an 88-fold purification, pectinesterase produced by a strain ofAspergillus niger, isolated from rotten lemons, showed the following main characteristics: maximum activity at 45°C, pH 5; Km, with pectin as substrate, 1.01 mg/L; ΔG*, 4750 Cal/mol. Polygalacturonic acid and methanol acted as competitive and non-competitive inhibitors, respectively. The activity of the enzyme was impaired by MgCl2 and stimulated by NaCl.

Chemicals and lemon essential oil effect on Alicyclobacillus acidoterrestris viability

Alicyclobacillus acidoterrestris is considered to be one of the important target microorganisms in the quality control of acidic canned foods. There is an urgent need to develop a suitable method for inhibiting or controlling the germination and outgrowth of A.acidoterrestris in acidic drinks. The aim of this work was to evaluate the chemicals used in the lemon industry (sodium benzoate, potassium sorbate), and lemon essential oil as a natural compound, against a strain of A.acidoterrestris in MEB medium and in lemon juice concentrate. The results pointed out that sodium benzoate (500–1000–2000 ppm) and lemon essential oil (0.08–0.12–0.16%) completely inhibited the germination of A. acidoterrestris spores in MEB medium and LJC for 11 days. Potassium sorbate (600–1200 ppm) was more effective to inhibit the growth of the microbial target in lemon juice than in MEB medium. The effect of sodium benzoate, potassium sorbate and essential oil was sporostatic in MEB and LJC as they did not affect spore viability.

Purification of Peptides from Bacillus Strains with Biological Activity

One of the greatest causes of loss in the food industry is postharvest diseases of fruits and vegetables (Vero Mendez & Mondino, 1999). According to U.S.A. estimations this loss reaches 20 25% whereas in developing countries the losses are often more severe due to inadequate storage and transportation facilities (Sharma et al., 2009), but loss has generally been considered to be approximately 10% to 40% depending on packinghouse technology (Vero et al, 2002).

Aislamiento, identificación y sensibilidad a antifúngicos de hongos patógenos y no patógenos del limón

Resumen Numerosas especies de hongos filamentosos se aislaron de limones provenientes de diferentes plantaciones en la provincia de Tucuman, Argentina. Se adaptaron las tecnicas recomendadas por el National Committe for Clinical Laboratory Standards, Subcommitte of Antifungal Susceptibility (EE.UU.), para estudiar el efecto de tres concentraciones de los antifungicos imazalil, guazatina, SOPP y tiabendazol sobre los hongos: Fusarium oxysporum, Fusarium moniliforme, Aspergillus niger, Aspergillus clavatus, Aspergillus flavus, Geotrichum candidum, Rhizopus sp, Penicillum sp, Penicillum digitatum y Mucor sp. Todas las cepas fueron resistentes al tiabendazol. Los otros fungicidas tuvieron una accion diferente para cada cepa. Se ensayo una mezcla de SOPP (5%), imazalil (100 ppm) y guazatina (350ppm) y se demostro un efecto sinergico en Rhizopus sp que es resistente a cada antifungico en forma individual. Mucor sp fue el unico hongo resistente a los cuatro antifungicos ensayados y a la mezcla mencionada.

Preliminary Study and Improve the Production of Metabolites with Antifungal Activity by A Bacillus Sp Strain IBA 33

Bacillus sp strain IBA 33 metabolites, isolated from decaying lemon fruits, were evaluated for the control of pathogenic and non-pathogenic fungi (Penicillium digitatum, Geotrichum candidum, Penicillium expansum, Aspergillus clavatus, Aspergillus flavus, Aspergillus niger, and Fusarium moniliforme). These metabolites were recovered from Landy medium (LM) without aminoacids. In order to optimize metabolites production the LM was modified by adding different concentrations and sources of amino acids and carbohydrates at different culture conditions. Bacillus sp strain IBA 33 metabolites efficacy to control fungi were evaluated with in vitro and in vivo assays. A. flavus growth inhibition was 52% with the metabolites of Bacillus sp strain IBA 33 recovered from LM (MBLM) in vitro assays. MBLM supplemented with 0.5% glutamic acid, inhibited the growth of P. digitatum, G. candidum, A. clavatus, A. niger and F. moniliforme by 65%, 88.44%, 84%, 34% and 92% respectively. The highest inhibition of P. expansum was 45% with MBLM supplemented with 0.5% aspartic acid. Similar results were obtained in vivo assays. These results showed that Bacillus sp strain IBA 33 metabolites specificity against fungi depended on the composition of the LM.

Methanol utilization by a strain of Aspergillus niger: influence on the synthesis and activity of pectinases

During the production of pectinases by a strain of Aspergillus niger isolated from rotten lemons, methanol was liberated into the medium due to the cleavage of the pectin molecule used as the carbon source. The methanol was subsequently consumed by the microorganism but neither the synthesis nor the activity of pectinesterase and polygalacturonase was affected. Although not studied in detail, the mechanism involved in the utilization of methanol is similar to that described for methylotrophic yeasts.