Carotenoids in staple foods and their interaction with other essential nutrients.

Abstract

Carotenoids are responsible for a large proportion of the red, orange and yellow pigments found in nature. Their value in natural systems extends beyond that of colour, as they are precursors to vitamin A, antioxidants and important in eye health. The aim of the studies presented here was to identify useful sources of carotenoids in staple foods and their interactions with other nutrients. The potential for improving carotenoid nutrition in wheat is the initial focus of the presented work. Colorimetry using the CIE L* a* b* method was identified as a useful tool for fast identification of lutein concentration in durum wheat and both lutein and provitamin A concentration in bread wheat. A further study on the effect of storage conditions on colour and carotenoid concentration showed that in wheat stored as grain an increase in temperature from 5°C to 35°C resulted in a large decrease in B* value, lutein and B-carotene concentration. However, in wheat stored as flour, a greater decrease in B* value and carotenoid concentration was caused by storage for 6 months, regardless of temperature. In addition to grains, fruit and vegetables are important in diets of developed populations. Commonly consumed fruit and vegetables were analysed to identify useful sources of lutein and zeaxanthin, involved in the prevention of age related degeneration of sight. The leafy green vegetables parsley, kale and spinach were the best source of lutein isomers, with total lutein concentrations of 110, 95 and 90 mg/kg respectively. The greatest concentration of zeaxanthin isomers was found in spinach and parsley with total zeaxanthin concentrations of 3.9 mg/kg and3.7 mg/kg respectively. Zeaxanthin concentration was not related to food type nor was the zeaxanthin to lutein isomer ratio. In the final study the effect of lutein on iron uptake and metabolism in chickens was investigated. Four treatment diets were compared for the response in haemoglobin concentration including high concentrations of supplemental β-carotene and lutein and low concentrations of lutein from a supplement and wheat. Birds on the high supplemental lutein diet had haemoglobin concentrations equal to those on the β-carotene diet, and above that of birds on the other diets. Hepatic iron stores were not significantly different between birds on the different diets indicating that remobilization of hepatic stores was not the cause of the increase in haemoglobin concentrations. The increase in haemoglobin concentration resulting from an interaction between dietary iron and lutein determined here, has the potential to decrease the incidence of iron deficiency anaemia world-wide. Further studies are necessary however to endorse the results of this preliminary study, determine the optimal time period and the dose response effect, and to confirm that the interaction is present in humans. This thesis represents a valuable contribution to the understanding of the relationships between colour and carotenoid concentration in wheat. Furthermore, this study has investigated for the first time the interaction between lutein and iron bioavailability in an animal model. Iron deficiency affects populations world wide and an increase in the bioavailability of this essential nutrient due to an interaction with one of the most abundant carotenoids has the potential to dramatically reduce this insidious problem.