Advances in public health nutrition rely on the accurate quantification of biologically active constituents of commonly consumed food products. Antioxidants are one particular group of food constituents which are regularly quantified due to their proposed health benefits. Epidemiological studies have shown a reduction in the incidence of disease states such as CVD and cancers when greater amounts of naturally occurring antioxidants are consumed(Reference Agarwal and Rao1). Tomatoes and tomato products have received considerable scientific attention, primarily because they are the major dietary source of the potent antioxidant lycopene and a good source of a variety of other antioxidant carotenoids. Carotenoid bioavailability is increased when tomatoes are processed and therefore, tomato juices may be an excellent source of bioavailable antioxidants(Reference Ryan, O'Connell and O'Sullivan2). In addition to quantifying the total antioxidant capacity (TAC) of produce, it is important to know whether these antioxidants are biologically available after digestion. Therefore, the objective of the present study was to evaluate the TAC of 10 commercially available tomato juices, both value and premium brands, before and after the gastric and duodenal phases of an in vitro digestion. Samples of each juice were subjected to an in vitro digestion procedure involving simulated gastric and duodenal phases. Samples were analysed for TAC before and after the gastric phase, and after the duodenal phase of digestion, using both the ferric ion reducing antioxidant power (FRAP) assay(Reference Benzie and Strain3) and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay(Reference Brand-Williams, Cuvelier and Berset4).
n 3 independent experiments;
* P<0.01=significantly different from same sample prior to digestion, se=standard error, fold change is shown from sample prior to digestion, for the gastric phase (Gas) and duodenal phase (Duo).
The TAC of the analysed tomato juices increased significantly (P<0.01) after both gastric and duodenal phases as measured by the FRAP assay. However, the results of the DPPH assay showed a small increase in TAC after the gastric phase and a small decrease after the duodenal phase. In conclusion, tomato juices show an equivalent or increased TAC following digestion. This study provides the first measurement of tomato juice antioxidants after digestion.
