Ester-Producing Mechanism of Ethanol O-acyltransferaseEHT1Gene inPichia pastorisfrom Shanxi Aged Vinegar

The ethanol O-acyltransferaseEHT1is an important element of key signaling pathways and is widely expressed in yeast strains. In this study, we investigated the expression ofEHT1 in the overexpression lines or knockout system ofPichia pastorisusing qRT-PCR and western blotting. The amount of total protein was determined using the Bradford method; the esterase activity was determined using p-nitrophenyl acetate as a substrate, and the production of volatile fatty acids in wild-type, knockout, and over-expression systems was detected using SPME GC-MS. The esterase activity ofEHT1-knockoutP. pastoriswas significantly lower than that in wild type (P<0.01), and the activities of esterase in threeEHT1-overexpressing strains—OE-1, OE-2, and OE-3—were significantly higher than those in wild type (P<0.01). In theEHT1-knockout strain products, the contents of nine volatile fatty acids were significantly lower than those in wild type (P<0.01), and the relative percentages of three fatty acids, methyl nonanoate, methyl decanoate, and ethyl caprate, were significantly lower than those in the other six species in the wild-type and knockout groups (P<0.05). The nine volatile fatty acids in the fermentation products of the overexpressedEHT1 gene were significantly higher than those in the wild-type group (P<0.01). The relative percentages of the three fatty acid esters, methyl nonanoate, methyl caprate, and ethyl caprate, were significantly higher than those in the other six species (P<0.05).EHT1 plays an important regulatory role in esterase activity and the production of medium-chain volatile fatty acids.

Study on Reaction Kinetics of Lipase-Catalyzed Synthesis of Vanillyl Nonanoate in Acetone Media

The reaction kinetics for synthesis of vanillyl nonanoate (VN) by lipase-catalyzed transesterification of vanillyl alcohol and methyl nonanoate in acetone was investigated in this study. The reaction catalyzed by lipase was carried out as follows: A reaction mixture containing given concentration of substrates (1ml) and lipase Novozyme 435 (20mg) in acetone (1ml) was shaken at 30°C for 10min. The initial velocity of the reaction was calculated according to the concentration of VN detected by high performance liquid chromatography (HPLC), and the kinetic equation was obtained by analysis of the double reciprocal plot of initial velocity versus substrate concentration. The data calculated by the kinetic equation were basically in agreement with the experimental data with a correlation coefficient at 0.997. The inhibitory action of methanol (by-product) in the reaction was also investigated and the results indicated that the concentration of methanol influences both slope and intercept of y-axis of the double reciprocal curve, and the lines intersect on the X-axis. These results revealed that this transesterification follows the Ping-Pong reaction mechanism.

Key Aroma Components of a Dry-Cured Sausage with High Fat Content (Sobrassada)

The key aroma components and the lipolysis in a dry cured sausage ‘Sobrassada of Mallorca from black pig’ were studied. Sobrassada was characterized by a fatty acid profile with a high content of monounsaturated fatty acids and by the generation during the curing process of polyunsaturated free fatty acids that were oxidized to generate flavor compounds. Eighty-four different volatile compounds were identified and three of them were for the first time detected in dry sausages (methyl nonanoate, 1-methyl-1H-pyrrole and 2-acetyl pyrrole). Thirty-five different aroma active zones were found. The aroma of sobrassada was not only due to compounds already detected as essential contributors in dry sausages (3-methyl butanoic acid, ethyl 3-methyl butanoate, 2, 3-butanedione and acetic acid) but also to other compounds such as ethyl octanoate, furfural, benzaldehyde, (Z)-2-nonenal, 4-methyl-phenol, delta-hexalactone, heptanoic acid, 2-pentylfuran and 2-acetyl-pyrrole which gave specific aroma notes.

Infuence of MHC on odour perception of 43 chemicals and body odour

The Major Histocompatibility Complex (MHC) is a large gene family that is found in most vertebrates and has an important influence on body odour preference and mate selection in animals. In this research we found, that human leukocyte antigen (HLA) phenotype is strongly connected with the strength and pleasantness of perceived odour of selected chemical compounds found in sweat. Among different chemical classes of compounds tested, the esters of fatty acids such as methyl undecanoate, methyl decanoate, methyl nonanoate, methyl octanoate and methyl hexanoate show strongest connection to HLA. On the other hand, our experiment did not confirm the connection of MHC to the perceived strength and pleasantness of body odour.