The aim of the study was to compare the effect of the substituent and its position in the aromatic ring on the antioxidant activity of hexanoic acid esters obtained in reactions catalyzed by immobilized lipase B from Candida antarctica. 4-Hydroxybenzyl hexanoate, 2-hydroxybenzyl hexanoate, 4-methoxybenzyl hexanoate, and vanillyl hexanoate were obtained with conversion yields of 50 to 80%. The antioxidant activity of synthesized esters, their alcohol precursors and BHT (Butylated HydroxyToluene) was compared with DPPH (2,2-diphenyl-1-picrylhydrazyl), CUPRAC (cupric ion reducing antioxidant capacity), and CBA (crocin bleaching assay) methods. Furthermore, it was investigated whether the presence of vanillyl hexanoate in a concentration of 0.01 and 0.1% affected the oxidative stability of sunflower and rapeseed oils in the Rancimat test. It was observed that the antioxidant activity of hexanoic acid esters depends on the presence and position of the hydroxyl group in the aromatic ring. The highest activities were found for vanillyl alcohol, vanillyl hexanoate, and BHT. The addition of the ester and BHT significantly extended the induction times of the tested oils, and these compounds exhibited similar activity. Vanillyl hexanoate increased the induction time from 4.49 to 5.28 h and from 2.73 to 3.12 h in the case of rapeseed and sunflower oils, respectively.

The aim of the study was to evaluate the possibility to utilize a fish waste oil issued from the industrial smoking process in nitrogen-limited Yarrowia lipolytica yeast batch cultures. The waste carbon source was utilized by the yeast and stimulated the single cell oil production via an ex novo pathway. The yeast biomass contained lipids up to 0.227 g/g d.m.. Independently from culture conditions, high contents of very long chain fatty acids were quantified in yeast biomass including docosahexaenoic (DHA), eicosapentaenoic acid (EPA), eicosenic and erucic acids. The pH regulation did not influence the cellular lipids yield (0.234 g/g d.m.). Meanwhile, the intensification of the oxygenation of medium by changing the mixing speed (maximum concentration of lipids produced 4.64 g/dm³) and decreasing the amount of inoculum had a positive effect on the culture parameters in waste fish oil medium. Further work on upgradation of the original waste is advisable, especially because the oil indicated high content of polyphenols and lower susceptibility to oxidation than microbial oil derived from control olive oil medium.

Yarrowia lipolytica yeast is a model species of the group of oleaginous microorganisms capable of intracellular lipids accumulation in an amount exceeding 20% of the dry mass. Single cell oil biosynthesis can follow one of two biochemical pathways—de novo accumulation of cellular lipids in medium containing non-lipid carbon sources (including saccharides, glycerol) and ex novo microbial oil synthesis which involves fatty acids uptake from the environment. The mRNA expression of selected genes of de novo and ex novo lipid synthesis pathways was analyzed and correlated with the phenotypically observed features. It was proved that the accumulation yield of storage lipids via ex novo pathway was to some extent dependent on the limitation of the nitrogen source in the medium. It was also proposed that the synthesis of intracellular lipids in lipid-rich medium proceeded mainly via ex novo pathway, although the activity of genes encoding the enzymes of the de novo pathway were not completely inhibited at the stage of transcription by fatty acids present in the medium (e.g., ATP-citrate lyase). Molecular markers of two biosynthesis routes has been outlined and a hypothetical connection point between de novo and ex novo route were indicated.

The purpose of the study was to utilize the waste fish oil after fish smoking process in Y. lipolytica yeast batch cultures in order to assess its valorization to whole-cell biocatalysts with lipolytic properties. Almost 90% of the waste carbon source in medium was used and batch cultures of Y. lipolytica W29 were characterized with biomass yield of 18.59 g/dm³ and lipolytic activity of 53.41 U/g. The yeast biomass was used as a whole-cell biocatalyst in the synthesis of esters of selected phenolic compounds (acetates of 2-phenylethanol, tyrosol (2-(4-hydroxyphenyl) ethanol) and 3-phenyl-1-propanol, and ethyl esters of phenylacetic, 4-hydroxyphenylacetic, 3-phenylpropanoic, and 3-(4-hydroxyphenyl) propanoic acids). Y. lipolytica biomass was able to catalyze esterification of 3-phenylpropanoic acid (conversion of 95% after 24 h), but conversion of other acids to their esters was very weak, and in the case of transesterification of aromatic alcohols with vinyl acetate, conversions were 27%–63% after 24 h. Synthesized esters were tested prior potential activities as food additives. Esters of hydroxylated phenolic compounds showed activity of 2.5 mg/mL against Klebsiella pneumoniae and Citrobacter freundii, exhibited similar antioxidant properties to their precursors, and were better soluble in lipids, which increases the possibility of their use in the food industry.

Waste management solutions including the valorization of waste materials in biotechnological processes is an important issue needing to be explored. A significant amount of waste is being generated by the food industry. In this study, an attempt was made to utilize two fish industry wastes simultaneously—waste brine and post-frying oil from frying fish fillets in Yarrowia lipolytica culture with high single cell oil synthesis yield. Oxygenation in the culture medium had a positive effect on the biosynthesis efficiency of microbial oil, resulting in the highest content of lipids in yeast cells at the level of 0.431 g/g d.m (dry mass). Y. lipolytica yeast preferentially accumulated oleic acid and linoleic acid, and the high content of linolenic acid, valuable from a nutritional point of view, was also found in microbial oil. This study proved that the use of post-frying rapeseed oil gives a chance to obtain valuable storage lipids in Y. lipolytica yeast cells via ex novo biosynthesis pathway. Furthermore, the wastewater stream could be limited using a waste brine as a solvent in medium preparation, but the brine share should not exceed 30% so as not to inhibit yeast cell growth.

Increase in energy demand and limited sources of fossil fuels force the world’s population to seek new energy sources Biodiesel obtained by transesterification of oils with an alcohol in the presence of catalysts is an example of renewable fuel. The aim of the study was to assess the best conditions for enzymatic biodiesel synthesis by direct transesterification of rapeseed cake using Taguchi method. The influence of alcohol (methanol, ethanol, propanol, and butanol), temperature (30–60 °C), C. antarctica lipase B concentration (0.5–2 %), time (6–48 h) and rapeseed cake to alcohol ratio (1:2–1:5) was examined in the synthesis of fatty acid alkyl esters. Optimum conditions for direct enzymatic transesterification of rapeseed cake are: 30 °C, 12 h, 0.5 % of lipase and ethanol in 4:1 ratio to rapeseed cake.