Opposite oleic acid responses to temperature in oils from the seed and mesocarp of the olive fruit

Abstract

Olive oil is mostly extracted from the mesocarp (~95%) of the fruit with the seed (endosperm and embryo, ~5%) containing little oil. There are correlative and manipulative evidence that temperature modulates fruit oil content and fatty acid composition of the oil from the whole fruit (i.e., with no distinction being made between oils derived from each oil-bearing structure) of olive. Notably, oleic acid concentration of olive oil decreases as fruit mean growth temperature increases. This response in the olive fruit is opposite to that documented in annual oil-seed crops such as sunflower and soybean. The objectives of the present study were: i) to compare temperature effects on fatty acid composition of oil derived from seed and from mesocarp; ii) to compare temperature effects on seed and mesocarp dry weights and oil concentrations. To do this, fruiting branches were enclosed in transparent plastic chambers with individualized temperature control. Temperature was manipulated during the seed growth (Period A) and during the second half of mesocarp growth (Period B) subphases. In both periods, the oleic acid proportion in mesocarp oil decreased as temperature increased, and was accompanied by increases of palmitic acid, linoleic and linolenic acids. Mesocarp dry weight did not respond significantly to temperature, but mesocarp oil concentration fell significantly as temperature increased. Seed dry weight, oil concentration and fatty acid composition exhibited responses to temperature during Period A only, with seed dry weight increasing between 20 and 25 °C with a sharp decrease at higher temperature, and oil concentration linearly falling 1.2% per °C. In contrast, seed oil oleic acid percentage increased between 20 and 28 °C, and fell slightly with higher temperature. Palmitic and stearic acids in seed oil increased sigmoidally with temperature, while linoleic acid decreased sigmoidally. Oleic acid percentage showed opposite responses in oil from the seed and the mesocarp. The response of the seed to temperature was similar to those observed in oil from embryos of annual oil-seed crops, although the abrupt fall in palmitic and stearic acid with temperature >25 °C seems to be distinctive for olive seed oil.