AbstractsChemistry

Commercial lipases, from porcine pancreas (PPL), Candida rugosa (CRL) and Thermomyces lanuginosus (Lipozyme TL IM), were investigated in term of their efficiency for the hydrolysis of safflower oil (SO) for the liberation of free linoleic acid (LA), used as a flavor precursor. Although PPL showed a high degree of hydrolysis (91.6%), its low tolerance towards higher substrate concentrations could limit its use for the SO hydrolysis. On the other hand, Lipozyme TL IM required higher amount of enzyme and additional reaction time to achieve its maximum degree of SO hydrolysis (90.2%). CRL was found as the most appropriate biocatalyst, with 84.1% degree of SO hydrolysis. The chromatographic analyses showed that the CRL-hydrolyzed SO was composed mainly of free LA. Using selected sources of LA as substrates, including pure LA (100%) and commercial (67%) LA as well as SO and its hydrolyzed product, the synthesis of linoleic acid hydroperoxides (HPODs) by lipoxygenase (LOX) and their recovery were carried out. The conversion of pure and commercial LAs resulted in insignificant differences in HPODs yield of 69.7 and 68.9%, respectively. However, there was a significant difference in the HPODs yield, obtained from the SO (2.0%) and that from the hydrolyzed SO (58.0%), in comparison to that from the pure LA. The ratios of the different forms of 9- and 13-HPOD isomers were insignificantly different for the sources containing free LA. Using the optimized conditions, HPODs yield was 85.9 and 74.0% for the commercial LA and the hydrolyzed SO, respectively. The presence of selected dehydrogenases, including alcohol dehydrogenase (ADH-YL) and aldehyde dehydrogenase (ALDH-YL) of Yarrowia lipolytica JMY 861, and their potential role in the synthesis of flavor compounds were investigated. The experimental findings showed that using the reduced form of nicotinamide adenine dinucleotide (NADH) as cofactor, the ADH-YL activity in-vitro was 6-fold higher than that with the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH); however, the results indicated the absence of any ALDH-YL activity. The in-situ hexanal reduction was achieved within 70 min of reaction, with 95.4% of relative n-hexanol concentration. The optimum pH of 6.7 for the biomass production of Y. lipolytica was shown to favor the hexanal reduction over the n-hexanol oxidation. The chromatographic analyses indicated the conversion, in-situ, of HPODs into volatile C6-compounds, mainly 2-hexanone, hexanal, 3-hexanol and 2-hexenol, after 60 min of HPODs addition to the yeast cells suspension. The stability of ADH-YL was investigated in the presence of selected chemical additives, including glycerol, potassium chloride (KCl) and mannitol where that prepared in 2.5% (w/v) mannitol remained stable up to the sixth week of storage. The NADH cofactor exhibited a greater affinity for the commercial purified ADH than that for the ADH-YL. Using the living cells (in-situ) of Y. lipolytica and their endogenous lyophilized enzymatic extract (in-vitro), the inhibition of…