Two extracellular enzymes (MsP1 and MsP2) capable of efficient beta-carotene degradation were purified from culture supernatants of the basidiomycete Marasmius scorodonius (garlic mushroom). Under native conditions, the enzymes exhibited molecular masses of approximately 150 and approximately 120 kDa, respectively. SDS-PAGE and mass spectrometric data suggested a composition of two identical subunits for both enzymes. Biochemical characterisation of the purified proteins showed isoelectric points of 3.7 and 3.5, and the presence of heme groups in the active enzymes. Partial amino acid sequences were derived from N-terminal Edman degradation and from mass spectrometric ab initio sequencing of internal peptides. cDNAs of 1,604 to 1,923 bp, containing open reading frames (ORF) of 508 to 513 amino acids, respectively, were cloned from a cDNA library of M. scorodonius. These data suggest glycosylation degrees of approximately 23% for MsP1 and 8% for MsP2. Databank homology searches revealed sequence homologies of MsP1 and MsP2 to unusual peroxidases of the fungi Thanatephorus cucumeris (DyP) and Termitomyces albuminosus (TAP).

The formation of a green or beany off-flavor during storage of legume protein extracts limits their application in foods. Pea protein extracts were submitted to lactic acid fermentations to improve the flavor by either reducing off-flavor formation or by masking undesirable green notes. The aroma profiles of untreated pea protein extract (PPE) and fermented pea protein extract (PPEF) were compared to each other and to a commercial whey protein as a benchmark. Kinetic measurements of n-hexanal and n-hexanol formation were used as an indicator for progressing lipid oxidation and storage stability. The nonfermented and fermented pea protein extracts showed a shelf-life comparable to the commercial whey protein reference. Volatiles were identified and quantified using dynamic headspace sampling with subsequent coupled TDS-GC-MS and TDS-GC-olfactometry flavor dilution analysis. A total of 18 odorants with dilution factors equal to or higher than 100 were determined in PPE an d 17 in PPEF. Altogether, 23 highly odor-active compounds were identified according to their mass spectra, odor impressions, linear retention indices, and standard substances in PPE and PPEF, among them n-hexanal, 1-pyrroline, dimethyl trisulfide, 1-octen-3-one, 2,5-dimethyl pyrazine, 3-octen-2-one, -damascenone, and guaiacol. The fermentation considerably amended the aroma profile of pea protein preparations resulting in a reduction or a masking of undesirable flavors

No abstract

To biotechnologically produce norisoprenoid flavor compounds, two extracellular peroxidases (MsP1 and MsP2) capable of degrading carotenoids were isolated from the culture supernatants of the basidiomycete Marasmius scorodonius (garlic mushroom). The encoding genes were cloned from genomic DNA and cDNA libraries, and databank homology searches identified MsP1 and MsP2 as members of the so-called "DyP-type" peroxidase family. Wild type enzymes and recombinant peroxidases expressed in Escherichia coli were employed for the release of norisoprenoids from various terpenoid precursor molecules. Carotenes, xanthophylls, and apocarotenals were subjected to the enzymatic degradation. Released volatile products were characterized by GC-FID and GC-MS, whereas nonvolatile breakdown products were analyzed by means of HPLC-DAD and HPLC-MS. C13 norisoprenoids together with C10 products proved to be the main volatile degradation products in each case.

No abstract