2-Acetyl-1-pyrroline (ACPY) is a key flavor compound in fragrant rice and widely exploited in food flavoring. It is produced by various microorganisms. This study focused on ACPY production by two fungi (Aspergillus awamori and A. oryzae). The volatile compounds derived from mold cultivation in synthetic medium 18 were identified by Gas chromatograph-mass spectrometer (GC-MS). Seven volatile substances were detected in the liquid culture of A. awamori, i.e. ACPY, one ketone (1-hydroxy-2-propanone), two acids (acetic acid and 4-hydroxybutanoic acid), two alcohols (2,3-butanediol and 2,5-dimethyl-4-hydroxy-3(2H)-furanone) and one saponin glycoside (2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one). Further, 12 volatile compounds were detected in A. oryzae : ACPY, four fatty acids (tetradecanoic acid, n-hexadecanoic acid, octadecanoic acid and oleic acid), one alcohol (1-butanol), two benzenes (ethylbenzene and benzene, 1,3-bis(1,1-dimethylethyl)), three alkanes (pentadecane, heptadecane and 5-methoxy-2,2,6-trimethyl-1-(3-methyl-buta-1,3-dienyl)-7-oxabicyclo[4.1.0] heptane) and one sesquiterpenes (1,6-dimethyl-4-(1-methylethyl)-naphthalene). Both A. awamori and A. oryzae produced the highest amount of ACPY in the stationary phase when cultivated for 72 and 80 h, with the product yield of 0.914 and 1.323 mg/L, respectively. The supplementation with spermidine and spermine resulted in a more than fivefold increase in ACPY production by A. awamori. However, the production of ACPY by A. oryzae was lower when supplemented with spermine or spermidine than without spermine or spermidine. This indicated that the intermediates involved in ACPY production were different between these two species of fungi.
2‐acetyl‐1‐pyrroline (2AP) is a typical food flavour found in aromatic rice, pandan leaf and coconut. Though the extraction from pandan leaf can be made, the amount obtained was low. This research showed the potential 2AP production by Aspergillus awamori and the enhancement occurred in the presence of polyamine supplement. Using different nitrogen sources (2 g/L of putrescine or ammonium sulphate) did not affect cell growth, but existence of putrescine was essential for 2AP production. In addition, supplying polyamine (20 mg/L of spermine, spermidine or putrescine) after 24 h of primary growth led to significant enhancement of cell growth as well as 2AP formation. The dry weight was 7.4 and 6.9 g/L and amount of 2AP was 4.50 and 3.08 mg/L when spermine or spermidine, respectively, was added. As compared to the control, only 6.2 g/L dry weight and 1.51 mg/L 2AP was detected. In contrast, the same medium using ammonium sulphate as the sole N‐source did not produce 2AP. Only when a polyamine (spermine, spermidine or putrescine) was supplied, then small detectable amounts of 2AP were found (1.06, 0.67 and 0.31 mg/L). Furthermore, putrescine was measurable in mycelial cells grown in the medium adding only spermine or spermidine without putrescine, indicating that spermine or spermidine can be converted into putrescine intracellularly. In vitro reaction between crude enzyme, extracted from mycelia, and individual precursors showed that 2AP occurred in the presence of each polyamine. Likewise, 1‐pyrroline was observed as an intermediate for 2AP production, while putrescine was an intermediate found in the reaction flask where the substrate was spermine or spermidine. Thus, in A awamori, polyamine addition resulted in higher production of 2AP.
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