Mercè Torres

Analysis of underivatizated patulin by a GC-MS technique.

An alternative approach based on the use of gas chromatography-mass spectrometry (GC-MS) is used to confirm the presence of patulin in apple juice. In the gas chromatography (GC) methods previously described, derivatization of patulin was always necessary in order to achieve good chromatographic detection. The use of electronic pressure control (EPC) and on-column injection avoids the need for patulin derivatization and allows a sensitive analysis of patulin. A detection limit of 4 microg/liter in apple juice can be attributed to the method.

Fumonisin producing capacity of Fusarium strains isolated from cereals in Spain

A total of 147 Fusarium spp., predominantly from the section Liseola were isolated from cereals in Catalonia, Spain. Fusarium moniliforme was the predominant species (85.7%) isolated from these grains. Other species·included Fusarium sporotrichoides , Fusarium heterosporum , Fusarium tricinctum , Fusarium poae , Fusarium anthophilum and Fusarium subglutinans . The ability of these isolates and species to produce fumonisin B1 and B2 was assessed on moist sterile corn. This showed that about 34% of the strains from the section Liseola produced both fumonisin B1 and B2 although the quantities varied considerably. One isolate of F. subglutinans was demonstrated to produce both fumonisin B1 and B2.

Bactericidal and fungicidal activity of Aspergillus ochraceus metabolites and some derivatives

The bactericidal and fungicidal activities of aspyrone and asperlactone, secondary metabolites of Aspergillus ochraceus, and some aspyrone derivatives were studied. In general, aspyrone exhibited better activity than asperlactone or aspyrone derivatives. The inhibition patterns of the assayed compounds were different. Helminthosporium monoceras was the tested mould most inhibited by the studied compounds. The comparative study of the activity of the different compounds showed that the epoxy group seems to be necessary for activity against some micro-organisms.

Lipase activity of resting cells of Aspergillus flavus after solvent washing; memory effects from endogenous substrate arising from the original growth medium

Aspergillus flavusresting cells were washed with solvents of different polarity for 2, 6, and 24 h and then suspended in isooctane containing either oleic acid and 1-propanol or 1-propanol alone. Propyl oleate and propyl linoleate were produced in all experiments after 24 h due to the presence of residual fatty acids originating from the sunflower oil used for growing the mycelium. After 24 h washing, most solvents produced a 70 to 90% decrease in lipase activity and a 0 to 99% decrease in the amount of residual acids. 0.7 M 1-propanol in hexane was the best washing solvent among all those assayed (93% remaining activity, 0.3% residual oleic acid).

Preparation of (S)-1-Halo-2-octanols Using Ionic Liquids and Biocatalysts

Preparation of (S)-1-chloro-2-octanol and (S)-1-bromo-2-octanol was carried out by the enzymatic hydrolysis of halohydrin palmitates using biocatalysts. Halohydrin palmitates were prepared by various methods from palmitic acid and 1,2-octanediol. A tandem hydrolysis was carried out using lipases from Candida antarctica (Novozym® 435), Rhizomucor miehei (Lipozyme IM), and “resting cells” from a Rhizopus oryzae strain that was not mycotoxigenic. The influence of the enzyme and the reaction medium on the selective hydrolysis of isomeric mixtures of halohydrin esters is described. Novozym® 435 allowed preparation of (S)-1-chloro-2-octanol and (S)-1-bromo-2-octanol after 1–3 h of reaction at 40 °C in [BMIM][PF6].

A Survey of aflatoxins and aflatoxigenic Aspergillus flavus in corn-based products from the Spanish market

The natural occurrence of aflatoxins B1, B2, G1 and G2, incidence of Aspergillus flavus, and capacity to produce aflatoxins by A. flavus isolates, were investigated in 100 corn-based samples from Spain destined for human and animal consumption. Only one sample for animal consumption and none for human consumption were found to be contaminated with aflatoxins B1 and B2. The levels of contamination were 0.15 micrograms/g of B1 and 0.08 micrograms/g of B2. Of 43 isolate of A. flavus, only 4 were aflatoxin producers.

Acylation of Chiral Alcohols: A Simple Procedure for Chiral GC Analysis

The use of iodine as a catalyst and either acetic or trifluoroacetic acid as a derivatizing reagent for determining the enantiomeric composition of acyclic and cyclic aliphatic chiral alcohols was investigated. Optimal conditions were selected according to the molar ratio of alcohol to acid, the reaction time, and the reaction temperature. Afterwards, chiral stability of chiral carbons was studied. Although no isomerization was observed when acetic acid was used, partial isomerization was detected with the trifluoroacetic acid. A series of chiral alcohols of a widely varying structural type were then derivatized with acetic acid using the optimal conditions. The resolution of the enantiomeric esters and the free chiral alcohols was measured using a capillary gas chromatograph equipped with a CP Chirasil-DEX CB column. The best resolutions were obtained with 2-pentyl acetates (α = 3.00) and 2-hexyl acetates (α = 1.95). This method provides a very simple and efficient experimental workup procedure for analyzing chiral alcohols by chiral-phase GC.

Reactive Extraction of the Acylglycerides Present in Various Materials using Rhizopus oryzae Resting Cells

We carried out reactive extractions at moderate temperatures using Rhizopus oryzae resting cells and various solid materials containing different proportions of vegetable oil. Our methodology allows for free fatty acids and either methyl or solketal fatty esters to be prepared in moderate to high yields. Moreover, the process can be carried out in either a solvent or a solvent-free system. In a solvent-free system, the final yield can be increased if easily ground solid material is used. The water present in each material and the solvents used has an influence on the results.

Raw and waste plant materials as sources of fungi with epoxide hydrolase activity. Application to the kinetic resolution of aryl and alkyl glycidyl ethers

Abstract The by-products of olive oil production can be used as sources of microbial strains. Penicillium sp., Aspergillus terreus, Penicillium aurantiogriseum, Aspergillus tubingensis and Aspergillus niger were selected on the basis of their epoxide-hydrolyzing activity towards racemic rac-glycidyl phenyl ether. We studied the effect on enzymatic activity of adding styrene oxide to the growth medium. It induced the biosynthesis of epoxide hydrolases and reduced cell growth. The resolution capacity of the five fungi was tested on rac-glycidyl phenyl ether, rac-benzyl glycidyl ether, rac-1,2-epoxyhexane and rac-1,2-epoxyoctane. The resolution of rac-glycidyl phenyl ether by A. niger, rac-benzyl glycidyl ether by P. aurantiogriseum and A. terreus, rac-1,2-epoxyhexane by A. tubingensis and rac-1,2-epoxyoctane by A. terreus provided (S)-3-phenoxy-1,2-propanediol (45.1% yield, 51.4% ee), (R)-3-benzyloxy-1,2-propanediol (40.8% yield, 43.3% ee), (S)-3-benzyloxy-1,2-propanediol (45.4% yield, 45.6% ee), (R)-1,2-hexanediol (70.4% yield, 24.4% ee) and (R)-1,2-octanediol (21.4% yield, 27.5% ee), respectively. The (R)-enantiopreference of the epoxide hydrolases from P. aurantiogriseum is unprecedented.

Entrapment in polymeric material of resting cells of Aspergillus flavus with lipase activity. Application to the synthesis of ethyl laurate

The lipase activity of resting cells of Aspergillus flavus was improved by entrapment in various polymeric acrylates (PAAFs). Commercially available ethyl acrylate, butyl acrylate and ethyl methacrylate, and acrylates synthesized from 1,3-dichloropropan-2-ol were used as monomers for the in situ polymerization. The cells were physically entrapped via free-radical-polymerization in aqueous medium or by bulk polymerization. The percentage of resting cells immobilized in the polymers was assessed by analysing the ergosterol content. Bulk polymerization with ethyl methacrylate allowed the greatest incorporation ratio, with 85% of entrapped biocatalyst. Entrapped resting cells were used to prepare ethyl laurate, achieving yields of up to 98%. The specific activity (r) of PAAFs was determined using a batch reactor and a packed-bed reactor (PBR). The highest r was observed for the resting cells entrapped in poly(ethyl methacrylate) using PBR. These results demonstrate that entrapped resting cells of A. flavus can be used to prepare commercial products.