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Comparing fresh and processed fruits and vegetables as sources of bioavailable phytochemicals
Project Code: N05051
Institute of Food Research Enterprises Ltd
Kroon, P ; Hollands, W; Brett, G; Saha, S; Teucher, B; Needs, P; Bennett, R; Mithen, R
Plants contain a number of chemicals (phytochemicals) that when tested in laboratory models, appear to have the ability to protect cells against damage and against age-related diseases such as cancer and cardiovascular disease. These effects of phytochemicals may partly explain why diets that are rich in fruit and vegetables are beneficial to health.
This project determined the baseline content of specific phytochemicals in several fruit and vegetables which had undergone different levels of processing (fresh or minimally processed foods vs. more extensively cooked/processed). The project also measured the absorption of phytochemicals (i.e. bioavailability) in human volunteers after consumption of standard portions of fruits and vegetables. Bioavailability was determined by measuring the levels of phytochemicals and their metabolites in blood or urine of subjects after consuming each food. In addition, the project investigated whether age affected subject’s ability to absorb phytochemicals, and whether the amount of phytochemicals absorbed from two or more portions was more than from one portion. These questions were investigated through a series of small pilot intervention studies using a randomised crossover study design.
The phytochemical contents of the examined fruit and vegetables were found to depend on variety, the month of purchase and the type processing.
Orange flavanones: Both, Orange fruit and juices were found to be rich sources of flavanones, but levels were significantly higher in fruit. The study found relatively small differences in the amount of flavanones absorbed and excreted by subjects consuming either one large orange or one glass of orange juice.
Effect of age: The study found a trend for lower absorption of the orange flavonoids for older subjects. However, the effect was small and age is probably not an important factor in determining how efficiently flavonoids are absorbed.
Blackcurrant anthocyanins: Fresh and frozen blackcurrant fruits were both found to be rich sources of anthocyanins, but all processed blackcurrant products (e.g. juices, syrups, jams, squashes) contained orders of magnitude lower amounts. This pilot study found that anthocyanins from either blackcurrant fruit or products were very poorly absorbed.
Broccoli sulforaphane: The study examined differences in the amount of sulforaphane absorbed from fresh or frozen broccoli, which was prepared in different ways. Lightly cooked fresh broccoli was found to delivery almost ten times as much sulforaphane than lightly cooked frozen broccoli. Increases in cooking time decreased the sulforaphane content.
Dose-response to strawberry anthocyanins: The excretion of strawberry anthocyanins increased as consumption increased (i.e. a dose-dependant relationship) with no threshold seen within the range of portion sizes tested (100-400g). The excretion was linear up to the maximum intake of 400 g fresh weight of strawberries.
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