Rancimat

Ranceite Rancidity Rancimat system Random access memory Random copolymer Random copolymers... 

Chemical Antioxidant Systems. The antioxidant activity of tea extracts and tea polyphenols have been determined using in vitro model systems which are based on hydroxyl-, peroxyl-, superoxide-, hydrogen peroxide-, and oxygen-induced oxidation reactions (109—113). The effectiveness of purified tea polyphenols and cmde tea extracts as antioxidants against the autoxidation of fats has been studied using the standard Rancimat system, an assay based on air oxidation of fats or oils. A direct correlation between the antioxidant index of a tea extract and the concentration of epigallocatechin gallate in the extract was found (107). 

IV, CCR and oxidation stability are three strictly co-related parameters. As a general rale, the reduction of IV (on the same feedstock) dramatically improves the oxidation stability. On the contrary the distillation step removes the main part of naturally occurring antioxidants. For this reason, even after hydrogenation the Rancimat induction time (as measured according to the EN 14112 standard) of the hydrogenated sample does not fulfill the EN 14214 requirement for oxidation stabihty (6 hours at 110°C), 4 hours being the measured induction period. 

Nevertheless the non-hydrogenated, distilled Tall Oil methylester has a Rancimat induction time lower than 1 hour, demonstrating... 

Oxidative stress Lipid oxidation Oxygen absorption Manometric, polarographic Diene conjugation HPLC, spectrophotometry (234 nm) Lipid hydroperoxides HPLC, GC-MS, chemiluminescence, spectrophotometry Iodine liberation Titration Thiocyanate Spectrophotometry (500 nm) Hydrocarbons GC Cytotoxic aldehydes LPO-586, HPLC, GC, GC-MS Hexanal and related end products Sensory, physicochemical, Cu(II) induction method, GC TBARS Spectrophotometry (532-535 nm), HPLC Rancimat Conductivity F2-iP GC/MS, HPLC/MS, immunoassays... 

Rancimat is an accelerated method to assess oxidative stability of fats and oils. In this test, the sample is subjected to an accelerated oxidative process (by heat in presence of oxygen), where short-chain volatile acids are produced. The acids formed are measured by conductivity. 

Other indices measure a secondary stage of oxidation, such as the anisidine value (ANV), pointing to formation of carbonyl compounds, capable of undergoing condensation reactions with p-anisidine, and the thiobarbituric acid reactive substance (TBARS) pointing to the presence of malondialdehyde (MDA) in particular. In biological systems, TBARS is of widespread use as a measure for the extent of oxidation damage. Another test for stability of oils to oxidation is based on the development of acidity as secondary product, for example, standards using the Rancimat equipment or a similar setup. 

A widespread method for determining the induction period for autoxidation of oils and fats consists of passing a continuous stream of air through the heated sample and collecting the volatile acids evolved in a water trap, where they are determined on a real time basis. The time plot usually presents a flat appearance for a certain period and then takes off in an accelerated manner. This test is the basis of several national and international standards (e.g. AOCS Cd 12b-92—oil stability index" ISO 6886—accelerated oxidation test for oxidative stability of fats and oils ) and the design of the Rancimat equipment, where the end determination is based on conductivity measurements . In addition to oxidation stability as determined by the Rancimat method and POV, which negatively affects virgin olive oil stability, other nonstandard properties were proposed for better assessment of the quality of this oil, namely LC determination of Vitamin E (21), colorimetric determination of total polar phenols and UVD of total chlorophyll. ... 

The ACV is defined as the number of acid equivalents expressed as mg KOH per g of sample. It may be also expressed as percentage (m/m) of a particular fatty acid in a fat or oil. This parameter usually indicates alterations undergone by hydrolysis, and can be determined by direct titration " . The ACV is used as a standard, for example, ISO 660 or lUPAC 2.201 . The acidity of refined oils is always below 1%, whereas that of virgin oils is higher and variable. In cases of extreme oxidation, free carboxylic acids are produced (Scheme 1, Section ll.A.2.c) that contribute to the ACV. This is the operational principle on which the Rancimat equipment for POV determination is based. 

Metrohm, 743 Rancimat , Metrohm Ltd., Herisau, Switzerland (http //www.metrohm.ch). 

Rancimat (Brinkmann holds 3 or 6 sample tubes) or Oxidative Stability... 

NOTE This method relies on either of two commercially available instruments that consist of a means of controlling sample temperature (maintained at 0.1 °C), an air distribution system, conductivity tubes, stoppers and probes, and electronics or software for measuring conductivity and determining induction period. The following steps are generally applicable to both the Rancimat and the Oxidative Stability Instrument however, some variations exist due to differences in hardware and models available. Consult the manufacturer s instructions for additional detail. 

Laubli, M.W and Bruttel, P.A.(1986) Determination of the oxidative stability of fats and oils comparison between the active oxygen method and the rancimat metho lm. Oil Chem. So,c.63 792-795. 

Rancimat induction Lag in lipid oxidation in a stream of air at relatively high temperature (90-130 °C) Anese and Nicoli446... 

FIG. 9 Sunflower oil stability (induction time (IT) sample/IT control) under Rancimat (110°C) conditions and in the presence of ground Echinacea (0.05-1%) E. purpurea herb (EPH) and root (EPR), and E. angustifolia herb (EAH) and root (EAR). 

Dry clean tanshen rhizomes were powdered and extracted with hexane for three days at room temperature. The hexane solution was kept overnight and then filtered. After removal of the solvent a residue was obtained which was separated into seven colored fractions by column chromatography with silica gel. Miltirone was isolated by preparative tic from fraction 1 (light red) using hexane ethyl acetate (4 1) followed by benzene-acetone (20 1). The product obtained was recrystallized from ethylacetate, m.p. 100-101°C. Its structure was confirmed by mass spectrum, NMR, IR and UV spectra which agree quite closely with those of Ho et al [76], Miltirone showed antioxidant behavior comparable to that of the commonly used phenolics BHT and BEA [77], The antioxidant activity of miltirone in lard at 100°C was determined with a Rancimat. Miltirone and other related compounds may have the potential of being used as natural antioxidants in food and cosmetics. 

The Biodiesel Stability (BIOSTAB) project, supported by the European Commission, was initiated in 2001 to establish clear criteria and analytical methods for the monitoring biodiesel fuel stability (Various, 2003 Prankl, 2002). The resulting unified method, EN 14112 (Anon., 2003c) established a means for measuring oxidative stability utilizing the Rancimat or oxidation stability instruments. This test method was essentially developed from standards employed in the fats and oils industry to measure isothermally the induction period for oxidation of fatty derivatives. At present, both biodiesel fuel standards ASTM D 6751 (Anon., 2007a) and EN 14214 (Anon., 2003b) include an oxidative stability specification based on measurement by method EN 14112. 

TABLE 1.11. Rancimat induction peroid (RIP = OSI) during a 12-month period of storage of RME with and without TBHQ and pyrogallol. 

An earlier study (Stavinoha and Howell, 2000) examined the effects of TBHQ and a-tocopherol on oxidative stability of SME from four different sources by non-isothermal P-DSC in static (zero air-purge) mode. P-DSC curves were analyzed by measuring the OT where P = 2000 kPa, initial temperature = 25 °C, and (S = 5°C/min. Results for two of the SME samples showed that addition of 2000 ppm a-tocopherol increased OT by -20 °C while addition of 2000 ppm TBHQ increased OT by -30 °C. Addition of the same concentration of a-tocopherol and TBHQ to the other two SME samples increased OT by -30 °C and -40 °C, respectively. Interpretation of these results suggested TBHQ was more effective at increasing relative resistance to oxidation of SME than a-tocopherol, a conclusion that was in accordance with those by Mittelbach and Schober (2003) for the isothermal Rancimat method. 

Lacoste, F., and Lagardere, L. 2003. Quality Parameters Evolution During Biodiesel Oxidation Using Rancimat Test. Eur. J. Lipid Sci. Technol., 105,145-155. 

Oxidation Stability (OSI or Rancimat) has been introduced in many ways. In EN14214 it exists as OSI and as a maximum acceptable Iodine Value, or maximum level of linolenic acid or of poly-unsaturated fatty acids. Oxidation stability is of importance when it comes to polymerization and oxidation during storage as well as during use in the engine. Oxidation is directly related to the presence of unsaturated bonds in the FAME, and probably because of this the EN 14214 includes a cap on Iodine Value. 

Uitrasound irradiation of an edibie oii (particuiariy direct irradiation of the sample) causes fast oxidation of biophenois present and produces a rancid smell as a result, mainly with easiiy oxidized oiis such as those from sunfiower [73]. Ultrasound energy allows Rancimat times from 129 h to be reduced to 50 min therefore, the overall time required for the determination of oil stability, even for highly stable virgin olive oils, is less than 1 h. 

Figure 7.13 shows the oxidative stabiiity of virgin oiive oiis from diverse oiive varieties. Figure 7.14 exposes the exceiient correiation of the US method with the oonventionai Rancimat method, and the drastic reduction in operating time (from, for exampie, 129 h to 50 min [74]). 

Figure 7.14. Comparison of the results of the US-assisted and conventional Rancimat methods (Reproduced with permission of Eisevier, Ref [74].)...

---