Presence of Phytosterol Oxides in Crude Vegetable Oils and Their Fate during Refining

Abstract

The content of phytosterol oxidation products was determined in samples of crude vegetable oils: peanut, sunflower, maize, palm nut, and lampante olive oils that were intended for refining and not for direct consumption. The 7 alpha- and 7 beta-hydroxy derivatives of beta-sitosterol, stigmasterol, and campesterol and the 7-keto-beta-sitosterol were the principal phytosterol oxides found in almost all of the oils analyzed. In some oils, the epoxy and dihydroxy derivatives of beta-sitosterol were also found at very low levels. The highest total concentrations of phytosterol oxides, ranging from 4.5 to 67.5 and from 4.1 to 60.1 ppm, were found in sunflower and maize oils, respectively. Lower concentrations were present in the peanut oils, 2.7-9.6 ppm, and in the palm nut oil, 5.5 ppm, whereas in the lampante olive oils, only three samples of the six analyzed contained a low concentration (1.5-2.5 ppm) of oxyphytosterols. No detectable levels of phytosterol oxides were found in the samples of palm and coconut oils. Bleaching experiments were carried out on a sample of sunflower oil at 80 degrees C for 1 h with 1 and 2% of both acidic and neutral earths. The bleaching caused a reduction of the hydroxyphytosterol with partial formation of steroidal hydrocarbons with three double bonds in the ring system at the 2-, 4-, and 6-positions (steratrienes). The same sunflower oil was deodorized at 180 degrees C under vacuum for 1 h, and no dehydration products were formed with a complete recovery of the hydroxyphytosterols. A bleaching test with acidic earths was carried out also with an extra virgin olive oil fortified with 7-keto-cholesterol, dihydroxycholesterol, and alpha-epoxy-cholesterol. There was no formation of steratrienes from these compounds, but dihydroxycholesterol underwent considerable decomposition and alpha-epoxycholesterol underwent ring opening with formation of the dihydroxy derivative, whereas 7-ketocholesterol was rather stable

Levels of Phytosterol Oxides in Enriched and Nonenriched Spreads: Application of a Thin-Layer Chromatography−Gas Chromatography Methodology

“…Although both spreads were manufactured by the same producer and presented a similar total fatty acid unsaturation pattern (described in the label), the authors cannot ensure that the same raw materials were utilized for their production; vegetable oils with different quality standards could have actually influenced the trend of phytosterol oxidation and given rise to such a difference on POPs content. It must be also considered that POPs can exhibit different stability depending on the POPs chemical structure and the type of refining process applied to the oils used as raw materials (37). Considering all of these aspects, more research must be performed to elucidate the real source of POPs in this type of food product.…”

Oxysterols formation: A review of a multifactorial process

“…Besides, instead of the ones we analyzed, other oxides could have been formed, such as 6-hydroxy, 20-hydroxy, 22-hydroxy, dienes, trienes… (29,36,63). Moreover, SOPs derived from cholesterol and stigmasterol could have decomposed to form oligomers, polymers and other compounds characteristic of advanced stages of oxidation (29,39), yielding an overall lower balance than for campesterol and sitosterol derived oxides.…”

Oxidation of β-sitosterol and campesterol in sunflower oil upon deep- and pan-frying of French fries

“…In the case of PS compounds, it is also possible that the "gap" partly originates from the formation of steradienes and -trienes, i.e., steroidal hydrocarbons with two or three double bonds in the ring structure. These structures are formed at high temperatures, e.g., through the dehydration of native sterols or 7-ketosterols, with a subsequent subtraction of the OH group from position 3, or through the elimination of water molecules from 7-hydroxysterols (Bortolomeazzi et al 2003;Soupas et al 2005). Moreover, it was mentioned that dimers and polymers are formed under thermal conditions.…”