Evaluation of Selected Quality Parameters to Monitor Essential Oil Alteration during Storage

Abstract

This study evaluates a set of analytical parameters to track changes during essential oil storage. On this basis, quality alterations can be monitored.

Impact of different storage conditions on the quality of selected essential oils

“…However, decreasing values due to peroxide degradation into more stable oxidized secondary products have been reported (e.g., Bernhard & Marr, 1960;Haddouchi et al, 2011;Pirilä & Siltanen, 1958), feigning a false state of freshness of the sample analyzed. Considering this fact, conductivity as well as pH assessment has been suggested recently as suitable tools corroborating POV analyses to monitor changes in a range of essential oils during storage (Turek & Stintzing, 2011b). While method development has been based on essential oils stressed by possible worstcase conditions to promote oxidation reactions, the present study investigated the impact of different extrinsic factors in a set of accelerated as well as real term storage conditions.…”

“…Aliquots in amber glass vials were stored at room temperature (23 ± 3°C) in the dark for up to 72 weeks (storage A). On the contrary, aliquots filled in clear glass vials were placed under cool white light imitating daylight (24 h/day, 5000 lx, fluorescent tubes from Osram L36W/840, Osram, Munich, Germany) at either room temperature for up to 24 weeks (23 ± 3°C; storage B) or elevated temperature (38 ± 3°C) for up to 12 weeks representing possible worst-case conditions (storage C; Turek & Stintzing, 2011b). Temperatures were controlled by air conditioning systems and monitored by data loggers collecting data each 30 min (Opus 10 DHI, Lufft, Fellbach, Germany).…”

“…Conductivity together with pH determination was performed after aqueous extraction of the respective essential oil and separation of the polar phase which was then analyzed using InLab® cool (pH value) as well as InLab® 720 (conductivity) electrodes (Mettler Toledo, Schwerzenbach, Switzerland) connected to a combined conductivity/pH meter (SevenMulti, Mettler Toledo, Schwerzenbach, Switzerland) at a reference temperature of 25°C (Turek & Stintzing, 2011b).…”

“…Storage-induced changes of essential oils were monitored at the beginning and after several storage intervals by a set of adequate quality parameters recently established (Turek & Stintzing, 2011b): Briefly, POVs of essential oils were determined potentiometrically as milliequivalents oxygen per 1 kg via sodium thiosulfate titration by an automatic titrator (Titration Excellence Line T90, Mettler Toledo, Schwerzenbach, Switzerland) equipped with an InLab ® Redox Pro platinum electrode (Mettler Toledo, Schwerzenbach, Switzerland) (Turek & Stintzing, 2011b). Conductivity together with pH determination was performed after aqueous extraction of the respective essential oil and separation of the polar phase which was then analyzed using InLab® cool (pH value) as well as InLab® 720 (conductivity) electrodes (Mettler Toledo, Schwerzenbach, Switzerland) connected to a combined conductivity/pH meter (SevenMulti, Mettler Toledo, Schwerzenbach, Switzerland) at a reference temperature of 25°C (Turek & Stintzing, 2011b).…”

“…Nevertheless, only few studies have been performed to comprehensively assess the impact of storage conditions on the stability of essential oils (Braun & Franz, 1999;ElNikeety, El-Akel, Abd El-Hady, & Badei, 1998;El-Wakeil et al, 1986;Fincke & Maurer, 1974;Haddouchi, Chaouche, Lazouni, & Benmansour, 2011;Misharina & Polshkov, 2005;Misharina, Polshkov, Ruchkina, & Medvedeva, 2003;Nguyen et al, 2009;Tóth, 1967), while HPLC was hitherto not addressed in this regard except for quantification of selected hydroperoxides (Hagvall, Sköld, Bråred-Christensson, Börje, & Karlberg, 2008). As the need for comprehensive quality monitoring of essential oils to reveal possible changes upon storage is apparent and important for both sensorial as well as pharmacological reasons, a set of appropriate physico-chemical parameters has been recently established (Turek & Stintzing, 2011b). Amongst them, pH and conductivity analyses have been applied for the first time to track essential oil alteration upon aging.…”