Fatty acid composition of edible oils derived from certified organic and conventional agricultural methods

Abstract

The objective of this study is to compare the fatty acid composition of commercially available edible oils derived from certified organic and conventional agricultural methods. A total of 59 certified organic and 53 conventional oils were purchased from retail markets in Sydney, Australia. Organic and conventional products were matched for comparison according to the description of production methods, labelled total fat content, brand name (wherever possible), and country of origin. Total fat was extracted and the fatty acid composition of the oils was determined by gas chromatography. No consistent overall trend of difference in the fatty acid composition was observed between organic and conventional oils. Saturated (SFA), monounsaturated (MUFA) and polyunsaturated (PUFA) fatty acids were all significantly different between types of oil (P < 0.001 in all three), and each had significant interaction between type and production method (P = 0.002, P < 0.001 and P < 0.001, respectively) indicating that organic and conventional oils differed in these components in an inconsistent fashion. Despite this, there were large differences particularly between MUFA and PUFA components in specific pairs of oils, especially in sunflower and mustard seed oils. The absence of an overall difference in the fatty acid composition of organic and conventional oils does not support the tenet that organic foods are of a higher nutritional quality than their conventional counterparts.

Introduction

Organic agricultural practices aim to enhance biodiversity, biological cycles and soil biological activity so as to achieve optimal natural systems that are socially, ecologically and economically sustainable. Although there is no recognised worldwide standard for organic agriculture, a number of international organisations have developed basic frameworks against which organic production methods can be measured. The International Federation of Organic Agriculture Movements (IFOAM) has established standards for organic production, labelling, and certification procedures to be enforced by national organic associations (Australian Certified Organic, 2006). The Food and Agriculture Organization (FAO)/World Health Organization (WHO) (1999) Codex Alimentarius Commission has produced guidelines as a first step towards official international harmonisation of the requirements for organic products in terms of production and marketing standards, inspection arrangements and labelling requirements.

Consumer studies indicate that one of the primary reasons for purchasing organic food is the perception that it conveys nutritional advantages over conventional products (Bourn and Prescott, 2002, Magkos et al., 2003, Shepherd et al., 2005, Williams, 2002). Reviews of the literature, however, have demonstrated few and inconsistent differences in the nutrient composition of organically produced foods compared to foods that have been produced by conventional methods (Bourn and Prescott, 2002, Magkos et al., 2003, Woese et al., 1997). Comparisons between studies are made difficult by the large variability in study design and methodology (Woese et al., 1997, Worthington, 2001). Nonetheless, there are indications that many organic food varieties have a lower nitrate content (Bourn and Prescott, 2002, Magkos et al., 2006, Siderer et al., 2005, Worthington, 2001) and a higher vitamin C content (Magkos et al., 2003, Williams, 2002, Worthington, 2001) than their conventional counterparts.

A small number of studies have reported on the effect of agricultural methods on the fatty acid composition of meat and dairy products. Milk produced through organic practices has been shown in some instances to contain higher amounts of alpha-linolenic acid (ALA) (Bergamo et al., 2003, Ellis et al., 2006, Fievez and Vlaeminck, 2006, Jahreis et al., 1996) and conjugated linoleic acid (CLA) (Bergamo et al., 2003, Fievez and Vlaeminck, 2006, Jahreis et al., 1996); while other reports demonstrated no clear effect of local management practices on the presence of ALA (Toledo, Andrén, & Björck, 2002) or CLA (Ellis et al., 2006, Toledo et al., 2002). Organic milk has been found to contain a lower n−6:n−3 fatty acid ratio when compared with conventional milk (Ellis et al., 2006, Wong et al., 2006). The fat quality of lamb is reported to reflect differences in the fatty acid composition of the animal feed rather than a specific metabolic impact of the production method (Nürnberg et al., 2006) and steers raised by organic or conventional methods showed no difference in the fatty acid composition of muscle tissue (Walshe, Sheehan, Delahunty, Morrissey, & Kerry, 2006). Organic chicken breast, based on a sample of 2 chickens, is reported to have lower ALA and higher linoleic acid (LA) compared to 2 conventionally produced chickens (Jahan, Paterson, & Spickett, 2004).

There is limited research comparing the effect of production methods on the fatty acid composition of edible oils. Perretti, Finotti, Adamuccio, Della Sera, and Montanari (2004) reported that the fatty acid composition of sunflower seed oil was unaffected by the method of production, whereas Gutierrez, Arnaud, and Albi (1999) found that the oleic acid concentration tended to be higher and the level of LA lower in organic compared to conventional virgin olive oil. The objective of the present analysis is to compare the fatty acid composition of a range of commercially available certified organic and conventionally produced edible oils.