Effect of processing on the nutritional value of oats (PhD)
The consumption of cereals has been associated with a reduced risk of several chronic diseases such as cancer and cardiovascular diseases such as heart attacks and strokes. The reason for these protective effects is not clear but could be related to the high antioxidant content of these cereals which is primarily dictated by their content of phenolics and various forms of vitamin E or E-vitamers (tocols).
Cereals are most often consumed in the processed state and this processing is likely to have an impact on the content or solubility of these antioxidants. This project examined the effect of industrial processing of oats on their phytonutrients. Oat samples were collected from a commercial processor, extracted with methanol and the soluble antioxidant activity, phenolics content and tocol levels measured. The industrial processing of oat gains to oat flakes resulted in a significant reduction in extractable antioxidant capacity and the content of phenols and tocols. Further processing of the oat flakes was carried out by heating at 180o C and the extractable antioxidant activity again measured. Following this “secondary processing”, antioxidant capacity, phenols and tocols were all significantly increased. To determine whether or not these observations are significant in the diet, a gastrointestinal pH simulated digestion experiment was undertaken on oat grains, oat flakes and the heated oat flakes. The results from this “in vitro” digestion mirrored findings obtained in the methanolic extracts.
The project also examined the effect of this processing on the composition of the material solubilised from oat. Industrial processing, whilst reducing the total level of extractable phenolics, had very little effect on the actual composition of these phenolics. In contrast the secondary processing step resulted in a pronounced change in the phenolics profile of the extracts. Industrial and secondary processing both impacted on the types of Evitamer that were being solubilised. It was interesting to note that in this case there seems to be an increase in the solubility of the α-tochopherol 3 form of vitamin E, the most nutritionally beneficial form of this vitamin and as such this observation may be of significance in terms of nutritional value. These studies have demonstrated the potential benefit of “secondary” processing in the release of antioxidants for the oat samples.
Whether or not this has any actual nutritional benefit remains to be tested. However, phenolics, as well as acting as antioxidants, may also stimulate (or suppress) genes thought to impact on human health. The last stage of the project thus examined the effect of extracts from oat grains, oat flakes and heated oat flakes on the expression of some genes thought to be involved in cardiovascular health. These preliminary results demonstrated an increase in the expression of endothelial nitrous oxide synthase (eNOS). Since the product of this enzyme NO is a vasodilator (acting to reduce blood pressure) this could be beneficial in protection against heart attacks and strokes. Other genes such as endothelin-1, GATA-2 and vascular endothelial growth factor were also effected and again some of these changes could result in improved cardiovascular health. However, these studies have been carried out in cell cultures of Human umbilical vein endothelial cells (HUVEC) and the significance if any for the Human remains to be elucidated.