Cereal phenolic compounds and their functionality

Studies have elucidated that secondary metabolites such as phenolic compounds present in wholegrain cereals have antioxidant potential. The antioxidant properties of cereal phenolic compounds have been associated with beneficial health properties such as anti-inflammatory and anti-cancer activities, which has contributed to the interest in cereals as a functional food. Studies of cereal phenolic compounds are often limited to compound identification and investigations of total antioxidant activity. However, the effect of cultivation location on cereal phenolic composition and the contribution of individual compounds to antioxidant activity is rarely considered.
This research investigated the phenolic compounds of cereals grown commercially in Australia with a focus on the impact of cultivation location, functionality as antioxidants and potential as pro-apoptotic agents. Several commercially grown cereals including rice, barley, oats and sorghum were examined. Initial characterisation demonstrated significant variability in phenolic composition amongst the different cereal varieties. Pigmented varieties exhibited greater variability in phenolic content. In rice, numerous unique phenolic compounds were identified in brown, red and purple coloured pericarp varieties. Some of these phenolic compounds contributed to the pericarp colour, hence, colour was observed to be a good indicator of phenolic content and antioxidant activity. In barley and oats, several compounds were identified as having antioxidant activities. These compounds were generally found in all varieties, however, variation existed in the quantity of each compound found in different varieties. Sorghum varieties were different from other pigmented cereals varieties in that pigmentation was not always due to phenolic content.
Phenolic composition of various rice, barley and oat varieties were investigated to determine the impact of cultivation location on composition. It was observed that in all the three cereals examined, total phenolic composition was affected by cultivation location to some degree. However, there were specific phenolic compounds present in some varieties that were relatively stable and unaffected. The variation in phenolic composition caused by growing location was compounded by the impact of genetic variation. These results highlight the importance of understanding the impact of both environment and genetics in determining phenolic composition and ultimately functionality.
The functionality investigated in this research was the apoptotic potential of cereal phenolic extracts on colorectal cancer cells SW480. Varieties that had higher phenolic contents and antioxidant activities also exhibited higher cytotoxicity when incubated with colorectal cancer cells. Red rice (Yunlu29, Black Gora and Lijianghegui), purple rice, black sorghum and brown sorghum exhibited high levels of cytotoxicity at concertation of 500 µg/ ml and higher. Cereal extracts did not exhibit any cytotoxic effects at 500 µg/ ml on normal colon cells FHC. An analysis of the mechanistic pathway elucidated that rice variety Yunlu29 and sorghum varieties Shawaya short black 1 and IS1136 upregulated the p53 protein and potentially instigated the observed caspase activity resulting in activation of effector caspase 3 and 7. The effector caspases are the final stages in the process that results in apoptotic cell death. The findings of this investigation has highlighted the application of cereal phenolic compounds as antioxidants and cancer related apoptotic agents, exhibiting its potential as functional food or food ingredient.