Oxidative stability of fatty acid alkyl esters: a review.

Abstract

The purpose of this study was to investigate and to process the current literary knowledge of the physico-chemical properties of vegetable oil raw used for biodiesel production in terms of its qualitative stability. An object of investigation was oxidative stability of biodiesel. In the study, we focused on the qualitative physico-chemical properties of vegetable oils used for biodiesel production, oxidative degradation and its mechanisms, oxidation of lipids, mechanisms of autooxidation, effectivennes of different synthetic antioxidants in relation to oxidative stability of biodiesel and methods of oxidative stability determination. Knowledge of the physical and chemical properties of vegetable oil as raw material and the factors affecting these properties is critical for the production of quality biodiesel and its sustainability. According to the source of oilseed, variations in the chemical composition of the vegetable oil are expressed by variations in the molar ratio among different fatty acids in the structure. The relative ratio of fatty acids present in the raw material is kept relatively constant after the transesterification reaction. The quality of biodiesel physico-chemical properties is influenced by the chain length and the level of unsaturation of the produced fatty acid alkyl esters. A biodiesel is thermodynamically stable. Its instability primarily occurs from contact of oxygen present in the ambient air that is referred to as oxidative instability. For biodiesel is oxidation stability a general term. It is necessary to distinguish ‘storage stability' and ‘thermal stability', in relation to oxidative degradation, which may occur during extended periods of storage, transportation and end use. Fuel instability problems can be of two related types, short-term oxidative instability and long-term storage instability. Storage instability is defined in terms of solid formation, which can plug nozzles, filters, and degrade engine performance. Biodiesels are more susceptible to degradation compared to fossil diesel because of the presence of unsaturated fatty acid chain in it. The mechanisms of oxidative degradation are autoxidation in presence of atmospheric oxygen; thermal or thermal-oxidative degradation from excess heat; hydrolysis in presence of moisture or water during storage and in fuel lines; and microbial contamination from contact with dust particles or water droplets containing fungi or bacteria into the fuel. The oxidation of lipids is a complex process in which unsaturated fatty acids are reacted with molecular oxygen by means of free radicals. The radicals react with lipids, and cause oxidative destruction of unsaturated, polyunsaturated fatty acids, therefore, known as lipid peroxidation. The factors such as heat, oxygen, light, and some metal ions, especially iron and copper, also play a significant role in creating oxidation. Oxidative products formed in biodiesel affect fuel storage life, contribute to deposit formation in tanks, and they may cause clogging of fuel filters and injection systems. The volatile organic acids formed as secondary by products of the oxidative degradation, may stimulate corrosion in the fuel system. Poor stability can lead to increasing acid numbers, increasing fuel viscosity, and the formation of gums and sediments. In general, antioxidants can prevent oxidation. Biodiesel, because it contains large numbers of molecules with double bonds, is much less oxidatively stable than petroleum-based diesel fuel. Oxidation stability is the important parameter to determine the storage of biodiesel for longer period of time. Biodiesel samples were evaluated according to methods on the base of kept in contact with pure oxygen at elevated temperatures and pressures. The results show that the performance antioxidants variation is observed for biodiesel. The most commonly used primary synthetic antioxidants

Comparison of Meat Oxidative Stability Free-Rearing and Farm-Rearing Pheasants

“…It is a three-carbon dialdehyde that can exist in various forms depending on the pH value. Cyclic peroxides, biclyclic endoperoxides, and hydroperoxyl are some of its major precursors (Lima et al, 2013;Amaral et al, 2018). MDA is important for industry and scientific research since it can be used to determine lipid peroxidation through the TBARS test (Thiobarbituric Acid Reactive Substances), the most widely used assay to assess the effects of lipid oxidation on meat and meat products (Min and Ahn, 2005;Amaral et al, 2018).…”

“…Cyclic peroxides, biclyclic endoperoxides, and hydroperoxyl are some of its major precursors (Lima et al, 2013;Amaral et al, 2018). MDA is important for industry and scientific research since it can be used to determine lipid peroxidation through the TBARS test (Thiobarbituric Acid Reactive Substances), the most widely used assay to assess the effects of lipid oxidation on meat and meat products (Min and Ahn, 2005;Amaral et al, 2018). Another important secondary oxidation products are the volatile compounds responsible for the off-odor and off-flavor such as propanal, hexanal and pentanal (Barriuso et al, 2013;Lorenzo et al, 2013;Guyon et al, 2016;Cunha et al, 2018).…”

Oxidative Stability of Chicken Meat After Use of Oregano Essential Oil

“…Free radicals cause oxidative deterioration of biomolecules such as membrane lipids, nucleic acids and proteins and antioxidants are defined as molecules that can prevent or delay oxidation of an oxidizable substrate, in this line (Halliwel and Whitemann, 2004). The mechanisms of oxidative degradation can be autoxidation in presence of atmospheric oxygen (Angelovič et al, 2015). Oxygen is a major component affecting lipid oxidation in meat as it reacts with unsaturated lipids to form lipid peroxides in a process of oxygen uptake and double bonds rearrangement.…”

Effect of eugenol, neridol and piperine feed supplement on the thigh muscle fat profile of broiler chickens

“…We have followed this study for ongoing research at the Slovak University of Agriculture in Nitra, published by Tkáčová et al (2015), which states, on the basis of the oxidative stability results of chicken meat, that the natural feed component has its justification. This issue requires however, further research.…”