Virgin Oxidation Stability

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 pronounced efficiency of EPDM (POLY) grafted with TPA on the photoageing of the parent polymer is reported on Figure 7. Similar experiment after vulcanisation (not shown) reduced the photo-oxidation rate by a factor 1.5 both for virgin and stabilized films. 

Gutierrez-Rosales, F. and Arnaud, T. (2001) Contribution of polyphenols on the oxidative stability of virgin olive oil. 24th World Congress and Exhibition of the ISF, Berlin, September 2001, Abstracts,... 

Lercker, G., Frega, N., Bocci, F. and Mozzon, M. (1999) Volatile constituents and oxidative stability of virgin olive oils. Influence of the kneading of olive paste. Grasas Aceites, 50, 26-29. 

Comparison of the oxidation stability of virgin oils, reclaimed oils, and S3mthetic lubrication oils. 

Satue, M.T., Huang, S-W. and Frankel, E.N. Effect of natural antioxidants in virgin olive oil on oxidative stability of refined, bleached, deodorized olive oil. J. Am. OH Chem. Soc. 72,1131-1137(1995). 

Velasco, J. and Dobargenes, Oxidative stability of virgin olive oil. Ear. J. Lipid Sci. Technol. 104, 661-676 (2002). 

Gallina-Toschi T et al (2005) Oxidative stability and phenolic content of virgin olive oil an analytical approach by traditional and high resolution techniques. J Sep Sci 28 859-870 Bendini A et al (2009) Stability of the sensory quality of virgin olive oil during storage an overview. Ital J Food Sci 21 389-406... 

Gutierrez F, Jimenez B, Ruiz A, Albi MA. Effect of olive ripeness on the oxidative stability of virgin olive oil extracted from the varieties Picual and Hojiblanca and on the different components involved. J Agric Food Chem 1999 47 121-127. 

Salvador MD, Aranda F, Gomez-Alonso S, Fregapane G (2001) Comicabra virgin olive oil a study of five crops seasons. Composition, quality and oxidative stability. Food Chemistry, 1, 261-21 A. 

DSC was used for samples 1-4 (Table 5.4) at an isothermal temperature of 260 °C. The OIT was determined to be 21.4, 17.8, 14.1 and 8.6 minutes for Samples 1 to 4, respectively. Reprocessed samples exhibit lower OIT values compared with that of the virgin reference samples. The presence of glass fibres in the polyamide matrix seems to decrease the thermo-oxidative stability. 

However, the hydrophilic phenol content in rapeseed oils is low (3-4 pg/g compared to olive oils which contain 40-100 times more hydrophilic phenols) (Koski et al, 2003). When comparing the oxidative stability and minor constituents of cold-pressed low erucic acid rapeseed oils and virgin olive oils, rapeseed oils oxidized more rapidly due to their higher levels of polyunsaturated fatty acids and lower phenol content even though the initial PVs of fresh olive oils were much higher. 

Koski, A., Psomiadou, E., Tsimidou, M., Hopia, A., Kefalas, P, Wahala, K. and Heinonen, M. 2002. Oxidative stability and minor constituents of virgin olive oil and cold-pressed rapeseed oil. Eur. Food Res. Technol. 214 294-298. 

Rohman, A., Che Man, Y. B., Ismail, A., Hashim, P., (2011). Monitoring the oxidative stability of virgin coconut oil during oven test using chemical indexes and FTIR spectroscopy. International Food Research Journal 18, 303-310. 

DSC-OIT appears thus a reliable for detecting stabilizers in virgin polyolefins stabilized with phenolic antioxidants. However, in the case of polymers having previously undergone whether an irradiation or any thermal treatment likely to provoke some thermal oxidation, OIT value expresses... 

Cold-pressed hempseed oil varies from off-yellow to dark green due to the presence of carotenoids and chlorophylls at different levels (Defeme and Pate, 1996 Oomah et al., 2002). While the presence of carotenoids and tocopherols increases the oxidative stability of oil, the presence of chlorophylls increases the risk of oxidation. With high unsaturation levels (see later and Table 11.1.1), virgin hempseed oil was reported to have oxidative stability based on the Rancimat test at 120°C (Matthaus and Briihl, 2008), 1.32h at 110°C (Uluata and Ozdemir, 2012), and 6.4-7.6h at 100°C (Dimic et al., 2009). A slightly better value of 1.35-1.72h at 120°C was also reported (Anwar et al., 2006). Therefore, great care must be taken to prevent oil oxidation. 

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. 

---