Science - June 6, 2019

Sunflower seed more useful if cold-pressed

Anja Janssen

The residue of sunflower oil production, known as oil cake or press cake, usually goes to the livestock feed industry at present. PhD student Dimitris Karefyllakis thought of a way of using it to make useful food ingredients for human consumption.

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Sunflower oil cake is rich in protein and therefore an interesting waste product for food production. One use for the protein could be to stabilize food products. The standard method of extracting protein from waste products is to first dissolve it at a low acidity level (a pH of over 8). The problem is, however, that oil cake made of sunflower seeds is also rich in natural antioxidants known as phenols. At such low acidity levels, these form dark-coloured compounds with the proteins, and these compounds are not as good at stabilizing food products. Removing the phenols from the oil cake beforehand is difficult and expensive, says Karefyllakis. He knew, however, that phenols and proteins do not form these problematic compounds in a neutral, watery environment (a pH of 7). This gave him the idea of just leaving the phenols in the protein mixture and only using water to dissolve the proteins. With this method he arrived as a mild and more sustainable way of processing the sunflower seeds.

Producers of sunflower oil often press the oil at temperatures of over 100 degrees, and later use the organic solvent hexane to squeeze the last bit of oil out of the cake. Karefyllakis first pressed most of the sunflower oil out of the seeds at a low temperature (below 45 degrees). He then mixed the oil cake with water, thus dividing it in two parts: a soluble part with proteins, phenols and a residue of oil, and an insoluble part with a lot of fibre. 

Sunflower proteins are good stabilizers, but they worked even better in combination with the phenols
Dimitris Karefyllakis, PhD student

The researcher tested the stabilizing properties of the protein part of the oil cake. And what did he find? ‘Sunflower proteins are good stabilizers, but they worked even better in combination with the phenols. My emulsions became even more stable,’ says Karefyllakis.

The oil yield from cold pressing is 20 per cent lower than the yield from hot pressing. But Karefyllakis sees sufficient compensation for that in the fact that the protein mixture can now be used in foods. He also made a surprise discovery: ‘Some of the oil in the protein part turned out to be present in its original form, as oleosomes.’ These can be used in products like vegan milk substitutes or as carriers of bioactive ingredients.

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