Microwave roasting is unique and has gained acceptance in food preparation because of its convenience, efficiency, speed and low operating costs. The microwave heating of a food is caused by molecular friction between electrical dipoles under an oscillating electric field of a specific frequency. The high absorption of microwave energy by water molecules which are the most abundant dipole components in foods, and other dielectric components (salts, fats, and proteins), results in heating of the food [1,2]. Several researchers have studied the effects of microwave heating on food constituents [3]. In fact, microwaves are used by the food industry not only for baking, thawing, drying and warming but also for other applications, such as sterilizing or pasteurizing many food types [4,5]. It is under debate whether food exposed to high temperatures for a short period of time losses fewer heat-sensitive nutrients. In this case the nutritive value of microwave cooked products might be of higher quality than that of traditionally prepared food [2,6]. Microwave ovens are used in a majority of homes (>95% of households in Japan) mainly because consumers appreciate the advantages such as economy, convenience, and savings [7]. However, from time to time consumers are con-cerned by reports [8] that objectionable compounds are produced in microwaved foods.
However, few studies have been published on the alterations that may occur during microwave roasting. Recent work that examined such effects [9,10] did not look at oxidative compounds produced as a consequence of heating. Yoshida et al. [11] demonstrated the effects of microwave heating on the distribution of tocopherols and oxidative quality of the oils in the edible portion of sunflower seeds. Triacylglycerols (TAGs) are the major constituent of total lipids, representing 72 wt-% of the hulls of sunflower seeds. Limited information, however, is available on the effects of microwave heating on the surface lipids of oilseeds, especially TAG molecular species, the main components of the hulls.
The objective of this study was to isolate TAGs from the hulls of sunflower seeds roasted in a domestic microwave oven in order to determine changes in molecular species composition and fatty acid distribution of the TAGs after microwave roasting and to compare the results with those obtained from unroasted sunflower seeds.
2 Methods
Commercially available sunflower seeds (Helianthus annuus L.) used in this work were grown during the summer of 2000 (Aichi, Japan). The seed cultivars (Takii Seed Co, Kyoto, Japan) were selected for uniformity based on