Effect of polyamine on growth, intermediates and 2‐acetyl‐1‐pyrroline formation by Aspergillus awamori

Abstract

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.