Seed Thermal Fingerprint and Oilseed Storage Risk

Application of biophysical fingerprints and evaluation of seed chemical composition to predict and overcome underperformance of seeds during low temperature storage and recovery.

Thermal fingerprint of dry Helianthus annuus (sunflower) seeds showing lipid melting with a main peak centred at -35°C.

Seeds with oil contents greater than about 18% of their dry weight, i.e. that of soybean, are considered to be potential commercial oilseeds. For example, sunflower, tea, citrus and papaya. Extracted oils are major commodities with palm kernel oil accounting for 4% of global vegetable oil consumption. The commodity values of coconut, sunflower seed and palm oil were around $1.3k, $1.7k and $1k per metric ton, respectively (http://www.indexmundi.com, 2011). Besides these agricultural crop species, wild species in the genera Allanblackia and Jatropha are being domesticated for their various oil-related products, including for bio-energy. Many other oilseeds of value in sustainable livelihoods remain to be discovered and explored.

An interesting challenge with respect to the seed conservation of these species is that many of them store poorly under dry cold conditions, including at -20°C. This may result in a loss of viability within months to a few years, e.g. coffee and papaya. In contrast, most citrus species studied need to be cryopreserved and this was the preferred storage option for coffee seeds. It is not clear if all oily seeds originating from temperate, sub-tropical and tropical regions will show reduced viability in storage at cold temperature. However, our screening study initiated in 2009 on 18 species of the Asteraceae (sunflower family) has revealed about 25% with a putative storage problem at -20°C. Based on a review of oil content data for >100 species in the family, we estimate that 86% could be classified at oilseeds. On the basis that there are about 23,000 species in the family, and if the proportion at risk during storage reflects our first study, then c. 5000 species in the family may show relatively poor performance in the bank. This raises the question as to the frequency of such a response in other families. We have evaluated a similar number of species from the Brassicaceae in collaboration with the Spanish National Genebank and Universidad Politecnica de Madrid. As with Asteraceae, our results on Brassicaceae reveal significant variation in thermal fingerprints between family members, as judged by differential scanning calorimetry. We seek to establish whether thermal fingerprints can be used to identify seeds at higher risk of storage stress, including in the Malvaceae, Euphorbiaceae and Cactaceae. In addition to lipid content, we are determining fatty acid composition using GC-MS.This project is part of the Research theme 'Frozen Planet'.

The outputs of the project are being published in peer-reviewed journals, with the work on Asteraceae and Brassicaceae due to appear in 2012. Two post-doctorate level staff from overseas, one PhD student and a handful of MSc and college-based sandwich course students and work experience students have been involved part-time in this project.