Επίδραση ισοπρενοειδών λιπιδίων και χλωρόφυλλων στην οξειδωτική σταθερότητα ελαίων πλούσιων σε μονοακόρεστα λιπαρά οξέα

Abstract

The role of squalene in a substrate rich in monounsaturated fatty acids, was studied for various addition levels and experimental conditions. Purified olive oil triacyglycerols devoid of prooxidant and antioxidant constituents were used as substrate. A concentration dependent moderate antioxidant activity was found which may be explained by competitive oxidation of the different lipids present. It was found that squalene does not enhance a- tocopherol activity while it reacted very poorly with the free radical DPPH* showing thus no radical scavenging activity. During photosensitized oxidation squalene did not show any activity at all. However it offerred protection to a-tocopherol reducing thus the observed loss. Monitoring of squalene by HPLC during oxidation proved very useful for elucidating its role and revealed the high stability of the molecule.An HPLC methodology was developed for the simultaneous determination of tocopherols, carotenoids and chlorophylls suitable to monitor their fate during virgin olive oil oxidation.. The application of the method in oxidized virgin olive oils indicated that it can help to highlight the effect of these components and their interactions.The analysis of a large number of virgin olive oils from different cultivars and regions all over Greece gave adequate information about their levels and occurrence. The oils were characterized by quite high a-tocopherol content. ^-Carotene was the main carotenoid in the majority of oils while the levels of carotenoids were quite low. Pheophytin a was the main pigment while chlorophylls a and b were found in oils immediately following their production. Virgin olive oil samples, selected on the basis of chlorophyll content and stability, were stored in the dark at room temperature for 24 months or exposed to light. The oxidation was assessed by measurements of peroxide value and K232 while a-tocopherol, and pigments were monitored by HPLC. a-Tocopherol showed considerable changes during autoxidation and its destruction was correlated with the oxidation level of the substrate. Important changes were observed in chlorophylls during autoxidation. Two pheophytin a derivatives were mainly formed. These were tentatively identified as pyropheophytin a and OH-pheophytin a. Their presence could be related to the conditions and duration of storage. The photooxidation of the oils was accompanied by considerable losses in phenolic antioxidants leading thus to quality deterioration. Taking into account the presence of pheophytin a at considerable levels virgin olive oil must be protected from light exposure.The effect of pheophytin a was investigated during photooxidation of olive oil triacylglycerols. The results indicated a concentration dependent prooxidant effect, enhanced by oxygen availability. During autoxidation pheophytin a showed antioxidant activity. This activity was concentration dependent as was evidenced using the Rancimat apparatus (80°C). The antioxidant effect was confirmed with an oven test at 62 °C. During storage at 62°C pyropheophytin a was mainly formed from pheophytin a. The antioxidant activity of pheophytin a could be also attributed to the formation of derivatives exhibiting antioxidant activity.

Σκοποί της- διατριβής- ήταν η- μελέτη TOC- δράσης του- σκουαλενιου,- της- CL τοκοφερόλης^ τωνκαροτενοειδων κοα των χλωροφυλλων στη σταθερότητα λιπαρών υλών πλουσίων σε μονοακορεσταλιπαρα-οξεο-ίΜΑΟί Τα παρθένο ελαιόλαδα (H &νχρησιμοποιηθηκε-ως-(ρΐ)σικα μοντέλα λιπαρής ύληςπλούσιας σε ΜΛΟ που περιείχε ολα τα παραπάνω συστατικά και οι τριακυλογλυκερολες ελαιολάδουμετά- απα απομάκρυνση- πρα/ανηοξειδωτικων- ενο)σεων ως-τα αντίστοιχα μοντέλα προσομοίωσης Η δράση του σκουαλενιου στο μοντέλο εξετάσθηκε σε διαφορετικές συνθήκες αυτοξειδωσης καιφωτοοξειδωσης.- OL μεταβολές- στα υπόστρωμα- μελετήθηκαν- με- περιοδικούς- προσδιορισμούς των πρωτογενών προϊόντων της οξείδωσης, η σταθερότητα των ελαίων εκτιμήθηκε ιιε τη δοκιμή Rancimat καΐ-οι μεταβολές- (ποιοτικες-καιποσατικες)- των μελετωμενων σικιτατικων- με- υγροχρωματογραφικες και φασματοσκοπικές μεθόδους Το σκουαλενιο παρουσίασε αξιοσημείωτη σταθερότητα κατά την αυτοξειδωση καΐ-η- ασθενης-αντιοξεΐδυίτικη- δράση- του αποδόθηκε- στα φαινόμενα της_ανταγωνιστικης Ι οξείδωσης Σημαντικότερη ήταν η συμβολή του κατά τη φωτοευαισθητοποιημενη οξείδωση καθώς παρείχε-προστασία στην-α-τοκοχρερολ,η. Προκεηιενου-να-γΛνεΐ-δυνατη-η-παρα,κολουθηση-τω-V μεταβολών των μελετωμενων συστατικών αναπτυνθηκε μεθοδολογία υγρής χρωματογραφίας υψηλής απόδοσης που επέτρεψε-τοχι ταυτόχρονα προσδιορισμό τοκοφερολών., καροτενοειδων- κανχλωραφυλλων^ EL εξέταση ι ενός μεγάλου αριθμού δειγμάτων έδωσε στοΐγεια για τα επίπεδα της α τοκοφερόλης, καροτενοειδων καιγλωροφυλ>ων- σταΕλληνικο DJEL Απατον προσδιορισμαα-τοκοφερολης-και χρωστικών-προέκυψαν νεα στοινεια για τη συμβολή τους στη σταθερότητα επιλεγμένων δειγμάτων Π Ε. όπως η αντιοξειδωτικη δρα(Π^της-φαιοφυτινης-α-στα σκαταδΐ-Kaua προστατευτικος_ρολος της- α-τοκοφερολης-τασα κατά την αυτοξειδωση οσο και τη ρωτοοξειδωση.