Effects of heating, aerial exposure and illumination on stability of fucoxanthin in canola oil

Highlights

• Heating promoted the degradation of total, all-trans and 9′-cis fucoxanthin.

• Heating promoted the formation of 13-cis and 13′-cis fucoxanthin.

• First-order degradation or formation kinetics in the absence of air and light.

• Aerial exposure promoted the oxidative degradation of fucoxanthin isomers.

• Illumination promoted the formation of 9′-cis fucoxanthin.

Abstract

The effects of heating, aerial exposure and illumination on the stability of fucoxanthin was investigated in canola oil. In the absence of air and light, the heating caused the degradation of total and all-trans fucoxanthin at all tested temperatures between 25 and 100 °C. The increase of heating temperature promoted the formation of 13-cis and 13′-cis and the degradation of 9′-cis. The degradation and formation reactions were found to follow simple first-order kinetics and to be energetically unfavorable, non-spontaneous processes. Arrhenius-type temperature dependence was observed for the degradation of total and all-trans fucoxanthin but not for the reactions of cis isomers. The aerial exposure promoted the oxidative fucoxanthin degradation at 25 °C, whilst illumination caused the initial formation of all-trans, with concurrent sudden degradation of 13-cis and 13′-cis, and the considerable formation of 9′-cis. The fucoxanthin degradation was synergistically promoted when exposed to both air and light.

Introduction

Fucoxanthin, a marine carotenoid belonging to the xanthophyll class, is abundantly found not only in macroalgae but also in microalgae, and is known to possess diverse health-promoting properties, such as antioxidant, anticancer, anti-inflammatory, antiobesity and antidiabetic activities (Heo et al., 2010, Hosokawa et al., 2009, Yan et al., 1999). These remarkable biological activities may be attributed to its unique molecular structure, in which an unusual allenic bond, a 5,6-monoepoxide and 9 conjugated double bounds are present (Hosokawa et al., 2009, Yan et al., 1999). Since such functional groups are highly susceptible to oxidation and isomerization, fucoxanthin, like other carotenoids, would be prone to degradation during processing and storage as a result of exposure to heat, light, oxygen, metals, enzymes, unsaturated lipids and other pro-oxidant molecules (Achir, Randrianatoandro, Bohuon, Laffargue, & Avallone, 2010). A spectrophotometric analysis by Hii, Choong, Woo and Wong (2010) showed that fucoxanthin was highly unstable when exposed to light and acidic pH, however, to the best of our knowledge, this is the only published study regarding the stability of fucoxanthin.

Thermal processing is one of the most common and effective food preservation techniques and temperature is a key factor influencing the quality of food during storage. Therefore, the thermal stability of carotenoids has been extensively investigated in different types of medium in the presence or absence of air or light, mostly along with the analysis of degradation kinetics, in order to predict their loss during processing and storage. Examples include, β-carotene and lutein in palm olein and Vegetaline® (Achir et al., 2010), lycopene, lutein and β-carotene in safflower seed oil (Henry, Catignani, & Schwartz, 1998), lutein, β-carotene and β-cryptoxanthin in virgin olive oils (Aparicio-Ruiz, Mínguez-Mosquera, & Gandul-Rojas, 2011), lycopene in an olive oil/tomato emulsion (Colle et al., 2010), lycopene in oil-in-water emulsions (Ax, Mayer-Miebach, Link, Schuchmann, & Schubert, 2003), β-carotene in organic solvents (Chen & Huang, 1998), lycopene in hexane (Lee & Chen, 2002), all-trans retinol mixed with microcrystalline cellulose (Manan, Baines, Stone, & Ryley, 1995), lycopene in tomato pulp (Sharma & Le Maguer, 1996), bixin in a water/ethanol solution (Rios, Borsarelli, & Mercadante, 2005) and β-carotene and β-cryptoxanthin in an apple juice (Zepka, Borsarelli, Azevedo, Da Silva, & Mercadante, 2009). The first-order kinetic model and the Arrhenius relationship have been widely adopted to describe the thermal degradation of carotenoids and their temperature dependence, respectively, regardless of the presence of air or light. Heating in the presence or absence of air or light is known to induce not only the degradation of all-trans, cis and total (all-trans plus cis) carotenoids via oxidation or photodegradation, but also the formation of some cis isomers by isomerization, such as 9-cis, 13-cis, or 13, 15-di-cis forms, depending on treatment conditions, medium and type of carotenoids (Aman et al., 2005, Ax et al., 2003; Chen & Huang, 1998; Henry et al., 1998; Lee & Chen, 2002; Manan et al., 1995, Pesek and Warthesen, 1990, Rios et al., 2005; Sharma & Le Maguer, 1996; Shi, Le Maguer, Bryan, & Kakuda, 2003). However, the information on the stability of individual fucoxanthin isomers, influenced by heat, air and light, and on the corresponding degradation kinetics is rarely available.

The objective of this study was to investigate the effects of heating, aerial exposure and illumination on the stability of fucoxanthin, purified from a brown algae, in canola oil. The all-trans isomer and also three cis isomers of fucoxanthin were identified and monitored. Firstly, the kinetics and thermodynamics of the degradation or formation of fucoxanthin isomers were analysed in a temperature range of 25–100 °C in the absence of air and light. Then, the influence of aerial exposure and illumination (300 and 2000 lux) on the kinetics and the concentration-time profiles of fucoxanthin isomers was examined at 25 °C. Canola oil was used as a model solvent phase for fucoxanthin, because the food oil was found to improve the human bioavailability of carotenoids, such as α-carotene, β-carotene and lycopene (Brown et al., 2004).