Comparison of 2-acetyl-1-pyrroline production between Aspergillus awamori and Aspergillus oryzae

Abstract

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.