Fatty acid accumulation in the different fractions of the developing corn kernel
Introduction
Plant oils and animal fats constitute one of the major classes of food product, for the provision of energy and essential fatty acids. Animal sources, such as butter and lard, are characterised by high concentrations of saturated fatty acids. It is well known that a diet rich in saturated fatty acids forms a risk factor for hypercholesterolemia, atherosclerosis and others diseases in humans. In order to reduce the saturated fat content of processed foods, the food industry in developed countries moves progressively from animal fat to vegetable fat sources (Ruiz-Jiménez, Priego-Capote, & Luque de Castro, 2004). The change in consumer preferences is mostly due to consumers demanding food products that combine a pleasant flavour with nutritional benefits. Vegetable oils have a high content of unsaturated fatty acids, which are heart-healthy. The nutritional value of n-3 polyunsaturated fatty acids (PUFA) in the human diet is well recognised, and increased consumption of these fatty acids has been recommended (Department of Health, 1994). The precursor of the n-3 series of long-chain PUFA is the essential fatty acid linolenic acid (C18:3), from which man can synthesise the longer chain PUFA such as eicosapentaenoic acid and docosahexaenoic acid (Elmore et al., 2005). Recently, interest in the PUFA, as health-promoting nutrients, has expanded dramatically.
The intensive research period up to the 1990s, focused on the modification of the fatty acid composition of oilseeds by biotechnology. Information on the fatty acid distribution in seed parts provides a possible way to produce vegetable oils with high additional value. Since, based on the understanding of composition, biosynthetic and metabolic pathways of fatty acids in seed parts it is practically applicable to genetically alter the lipid composition of cells through the alteration of the encoding genes of enzymes that are responsible for lipid synthesis or metabolism. Commercially exploited seeds such as soya and rape have been the subject of many years of breeding programmes to obtain oils with particular fatty acid patterns (Stenberg, Svensson, & Johansson, 2005). Successful advances in plant breeding, such as the elimination of erucic acid from rapeseed, have drastically improved the oil quality. The established limits of fatty acid contents could be used for the detection of fraud of the olive oil with corn oil, at levels of adulteration up to 5% (Christopoulou, Lazaraki, Komaitis, & Kaselimis, 2004). In industry, the use of the oil is determined by the composition of fatty acids, and this is highly dependent on its natural origin. The fatty acid composition of oils from vegetable sources varies depending on plant origin, genetic factors, ripening grade of fruits and specific climatic conditions (Davis and Poneleit, 1974, Velasco et al., 2005). In exploring the role of lipids in cells and tissues, it is useful to know which lipids are present and in what proportions. Furthermore, one of the main objectives of industry is to identify plant matrices rich in some compounds, which have large industrial applications. Thus, Bruni et al. (2002) analysed Ecuadorian Theobroma subincanum seed parts to determine quali-quantitative tocopherol, fatty acids and sterols distributions. A number of studies have been reported concerning the developmental changes in the fatty acid composition of the whole corn kernel (Poneleit and Davis, 1972, Weber, 1969). However, there is limited information on the fatty acid distribution within corn kernel during maturation. The objective of the present research was to monitor the accumulation pattern of fatty acids in the endosperm, germ and pericarp fractions of the corn kernel during maturation. This study seems to be very useful in understanding the source of nutritionally and industrially fatty acids in the corn kernel fractions and for many aspect of vegetable oil production.
Section snippets
Reagents and standard
Methanol, chloroform acetone and pentane, solvents of HPLC grade, were purchased from Panreac Quimica SA. (Barcelona, Spain). Triflorure Bore (BF3) was from Fisher Scientific SA (Loughborough, Spain). Fatty acid standards were acquired from Sigma Aldrich (Madrid, Spain).
Samples
Sweet corn (variety GH2547) was obtained from USA. The sweet corn (Zea mays saccharata) differs from dent corn (Zea mays indentata) by a single recessive gene which prevents some of the sugar to being converted to starch (Bland,
Oil content
Numerous studies reported the developmental changes in the oil content of the maturing whole corn kernel (Harrabi et al., 2007, Weber, 1969). The distribution of the total lipid in the different fractions of mature corn kernel has been examined (Harrabi et al., 2008). In this study, the maturing corn kernels were divided into three parts: germ, endosperm and pericarp. At 20 days after pollination (DAP), the corn kernel was made up mainly of the pericarp (37.1%) and endosperm (52.7%) fractions;
Conclusion
The fatty acid composition showed a different pattern in endosperm, germ and pericarp fractions of the maturing corn kernel. In the endosperm fraction, the early accumulation of oleic acid did not promote its desaturation to linoleic acid, which remained unchanged during corn kernel development. The pericarp fraction accumulated linolenic acid for a longer period and at faster rate than did the germ and endosperm fractions. As a result, at all collection dates the highest levels of linolenic
Acknowledgements
The authors gratefully acknowledge Dr. Hamadi Ben Saleh at INRAT for technical assistance in conducting the culture of corn. They thank Dr. Clem W. Kazakoff and Annick St-Amand for their technical advice.
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