Thermal Oxidation Analysis of Forage Turnip (Raphanus sativus L. var. oleiferus Metzg.) Oil

Abstract

The seed of the R. sativus L. has around 40-54 % of its weight in oil, extracted by mechanical pressing. The resulting cake retains around 7.5 % of its own weight in oil and has a high nutritional value, in addition to high palatability as cattle feed [1].It is known, however, that lipids can undergo chemical changes during storage and/or processing, such as hydrolytic rancidity and oxidative rancidity, compromising the quality of the oil [3]. These oxidative processes constitute one of the most important technical problems when working with oils. Rancidity can be observed through the production of free fatty acids and shortchain organic acids from double bond oxidation [4]. As a result, properties such as the acid value and density are altered [3,4]. As an alternative to traditional methods of analysis, such as titrimetric analyses, techniques based on optical analyses are gaining interest in the scientific community as analytical tool for the analysis and quality control of oils [5,6]. Recent studies have shown that the breakup of the carbon chains of triacylglycerols when they are subjected to oxidation, alters the optical properties of the oils, causing changes in the absorption of radiation at two characteristic wavelengths, 232 and 270 nm [7,8]. These alterations provide relevant information on the initial and final stages of oxidation. The degradation of oil also results in changes in the molecular emission profile, causing the appearance and/ or extinction of some bands of fluorescence [9]. In this context, this work monitored the thermal oxidation process of the oil from the oilseed R. sativus based on the analysis of its density, acid value and induction period, in addition to tracking the oil's degradation process based on spectroscopic techniques to assess the molecular absorption in the ultraviolet and visible region and its molecular fluorescence.Abstract In this work, the composition of fatty acids and the oxidative stability of the oil from Raphanus sativus L. var. oleiferus Metzg. are presented and analyzed with the Rancimat method, and by absorption and molecular fluorescence spectroscopy. The gas chromatography showed that the content of unsaturated fatty acids was 90.27 ± 6.10 %, with a predominance of oleic (C 18:1), linoleic (C 18:2), erucic (C 22:1), linolenic (C 18:3) and eicosenoic (C 20:1) acids. The induction period determined by the Rancimat method was 48.0 ± 1.0 h. In addition, the thermal degradation of the oil was monitored through its acid value, density, UV-Vis absorption and molecular fluorescence, and here we show the potential applicability of emission spectroscopy for R. sativus oil oxidation studies.

Thermogravimetric Approach for Assessing the Oxidation Level of a Biodiesel Sample

“…As observed, the peak at 232 nm grows as a function of exposure area, whereas the peak at 270 nm increases slightly with the exposure area. This result indicates that an increase in conjugated dienes, as a result of degradation of unsaturated mono-alkyl esters, 24 confirms higher levels of oxidation with increased exposure area. Accordingly, the accelerated oxidation test achieves the objective and provides different oxidation states.…”

Drought tolerance in potential oilseed plants for biofuel production

“…The oil of both species is rich in erucic acid, which is not suitable for use in food applications but important as industrial crops to produce lubricants, polymers, pharmaceuticals items (Lalas et al, 2012;Chammoun et al, 2013) and biodiesel (Wazilewski et al, 2013). The biodiesel produced of the crambe and turnip forage oils have higher composition of fatty acids and fatty alcohols which confer a higher oxidative stability (Oliveira et al, 2015;Zhu et al, 2016) and a similar energetic conversion, compared to soybean oil (Wazilewski et al, 2013), demonstrating its great potential for biodiesel feedstock production. In addition, the use of vegetable oils instead of diesel is of great environmental importance for ensuring power generation with reduced gas emission (Rosa et al, 2014).…”

“…In Brazil, R. sativus and C. abyssinica are winter crops and can be cultivated in the off-season of soybean and corn crops (Carlsson et al, 2014;Oliveira et al, 2015), which corresponds to the dry period. The frequent exposure to water deficits compromises the growth and development of plants and, consecutively, the crop production (Liu et al, 2011).…”

Fluorescence Spectroscopy Applied to Monitoring Biodiesel Degradation: Correlation with Acid Value and UV Absorption Analyses

“…Our previous works have shown that the acidification of vegetable oils reflects on the changes in the absorbances at 232 and 270 nm with direct impact on the emission profile [ 15 , 16 ]. However, the optical behavior is still not completely understood for biodiesel, especially for unconventional vegetable sources studied here (from Raphanus sativus L. and Sesamum indicum L. seeds).…”