Characterization of the off-flavor from Pichia pastoris GS115 during the overexpression of an α-l-rhamnosidase.

The off-flavor of Pichia pastoris strains is a negative characteristic of proteins overexpressed with this yeast. In the present study, P. pastoris GS115 overexpressing an α-l-rhamnosidase was taken as the example to characterize the off-flavor via sensory evaluation, gas chromatography-mass spectrometer, gas chromatography-olfaction, and omission test. The result showed that the off-flavor was due to the strong sweaty note, and moderate metallic and plastic notes. Four volatile compounds, that is, tetramethylpyrazine, 2,4-di-tert-butylphenol, isovaleric acid, and 2-methylbutyric acid, were identified to be major contributors to the sweaty note. Dodecanol and 2-acetylbutyrolactone were identified to be contributors to the metallic and plastic notes, respectively. It is the first study on the off-flavor of P. pastoris strains, helping understand metabolites with off-flavor of this yeast. Interestingly, it is the first study illustrating 2-acetylbutyrolactone and dodecanol with plastic and metallic notes, providing new information about the aromatic contributors of biological products. IMPORTANCE: The methylotrophic yeast Pichia pastoris is an important host for the industrial expression of functional proteins. In our previous studies, P. pastoris strains have been sniffed with a strong off-flavor during the overexpression of various functional proteins, limiting the application of these proteins. Although many yeast strains have been reported with off-flavor, no attention has been paid to characterize the off-flavor in P. pastoris so far. Considering that P. pastoris has advantages over other established expression systems of functional proteins, it is of interest to identify the compounds with off-flavor synthesized in the overexpression of functional proteins with P. pastoris strains. In this study, the off-flavor synthesized from P. pastoris GS115 was characterized during the overexpression of an α-l-rhamnosidase, which helps understand the aromatic metabolites with off-flavor of P. pastoris strains. In addition, 2-acetylbutyrolactone and dodecanol were newly revealed with plastic and metallic notes, enriching the aromatic contributors of biological products. Thus, this study is important for understanding the metabolites with off-flavor of P. pastoris strains and other organisms, providing important knowledge to improve the flavor of products yielding with P. pastoris strains and other organisms. ONE-SENTENCE SUMMARY: Characterize the sensory and chemical profile of the off-flavor produced by one strain of P. pastoris in vitro.