Ekstrakcija masnog ulja i fenola iz semena crne slačice (Brassica Nigra L.) eutektičkim rastvaračima i etanoliza masnog ulja u prisustvu kalcijum-oksida

Abstract

The DESs are prepared based on triethanolamine as an acceptor, and oxalic acid, glacial acetic acid, L-(+)- lactic acid, oleic acid, glycerol, ethylene glycol, propylene glycol, choline chloride or 1,3-dimethylurea, as a donor, in a molar ratio of 1:1 (with acids as donors) or 1:2 (with polyols or amides as donors). The prepared DESs were used to measure physical (density, viscosity, and electrical conductivity) and calculate thermodynamic properties (coefficient of thermal expansion, molar volume, lattice energy, and heat capacity) in the temperature range 293.15–363.15 K at a pressure of 101.3 kPa. The DESs based on polyols and lower carboxylic acids can be used in various chemical and industrial processes at low temperatures. In contrast, for the DES with oleic acid and 1,3-dimethylurea, it is recommended to use at temperatures above 313.15 K. An analysis of the influence of the selected DES, triethanolamine:glycerol (TEOA:G), on yield, physicochemical properties, fatty acid composition, and antioxidant activity of black mustard seed oil, obtained by maceration with trichloroethylene after the pretreatment with the TEOA:G DES and a mixture of trichloroethylene and the TEOA:G DES, was performed. The oil was recovered by cold pressing and maceration with n-hexane and trichloroethylene. The highest oil yield was obtained by the maceration of black mustard seeds with trichloroethylene (31.10 g/100 g), which required twice the volume of trichloroethylene compared to the volume used in the maceration of black mustard seeds after the pretreatment of seeds with the TEOA:G DES in which gave a similar oil yield (29.95±1.20 g/100 g). The oil obtained by the maceration in the presence of the TEOA:G DES has similar physicochemical properties and fatty acid composition but better antioxidant activity than oil obtained by cold pressing. Furthermore, the influence of the use of the DESs TEOA:G, triethanolamine:propylene glycol (TEOA:PEG) and choline chloride:urea (ChCl:U) (molar ratio 1:2) and their mixtures with 25% water or ethanol in the extraction of phenolic compounds from black mustard seeds on the yield of total extractable substances, total phenol content, total flavonoid content and the antioxidant activity of the obtained extracts, were analyzed and compared with the influence of ethanol application as the most commonly used solvent in the extraction of phenolic compounds from plants. Total phenol content and total flavonoid content ranged from 19.9±0.1–32.2±0.2 mg gallic acid equivalents (GAE)/g and 3.9±0.1–7.4±0.3 mg quercetin equivalents (QE)/g, respectively. Black mustard seed extracts obtained with the ChCl:U DES and the mixtures of the ChCl:U or TEOA:G DESs with 25% ethanol showed the best antioxidant activity (IC50 = 100 mg·cm-3). Syringic acid, ellagic acid, gallic acid, caffeic acid, kaftaric acid, kaempferol, rutin, apigenin, taxifolin, vitexin, and hyperoside were identified in the obtained extracts. Finally, the influence of the application of the TEOA:G, TEOA:PEG, triethanolamine:choline chloride (TEOA:ChCl), triethanolamine:1,3-dimethylurea (TEOA:DMU), triethanolamine:ethylene glicol (TEOA:EG), triethanolamine:oleic acid (TEOA:OLK), triethanolamine:menthol (TEOA:M, molar ratio 1:2), and triethanolamine:decanoic acid (TEOA:DEK, molar ratio 1:1) DESs on the heterogeneous alkaline catalyzed ethanolysis of cold-pressed black mustard oil was analyzed. The ethanolysis was performed under the following reaction conditions: temperature of 70 ºC, molar ratio ethanol:oil of 12:1, the DES amount of 20%, and the calcined CaO amount of 10%. Almost all applied triethanolamine-based DESs (TEOA:G, TEOA: PEG, TEOA:ChCl, TEOA:DMU, TEOA:M, and TEOA:DEK) accelerated ethanolysis and provided a high content of fatty acid ethyl esters (FAEE) (≥95.20±0.56%) after 15 min of reaction time compared to the control reaction (without the presence of DES) (23.38±2.8%). The most effective DES was TEOA:ChCl, in the presence of which an FAEE content of 98.46±0.7% was achieved in 1.5 min. At the same time, in the presence of the TEOA:PEG and TEOA:M DESs, an FAEE content higher than 91% was achieved. In the presence of all applied DESs, the final products' separation was faster than the separation after the control reaction. The fastest separation was achieved in the presence of the TEOA:M and TEOA:ChCl DESs (immediately after cessation of mixing and after 1 min, respectively). To evaluate the kinetic parameters of the ethanolysis of black mustard oil catalyzed by calcined CaO in the presence of the TEOA:ChCl DES, a model of the pseudo-first order irreversible reaction and a model of variable order of reaction in relation to triacylglycerols and autocatalytic behavior of ethanolysis reaction were used. The calculated values of the apparent rate constant for both applied models were 0,600–3,219 min-1 and 0,803–3,836 L·mol-1·min-1, respectively while the calculated values of the activation energy were 77.18 kJ/mol and 71.79 kJ/mol, respectively. The physicochemical properties of the obtained biodiesel were within the limit values prescribed by the quality standard (EN 14214 standard).