Determination of phytochemicals in vegetable juices and their effects on postprandial glycaemia

High fruit and vegetable intake correlates well with positive health outcomes and reduced rates of chronic diseases such as cardiovascular diseases, type 2 diabetes, cancers, neurological decline and metabolic diseases. Bioactive phytochemicals such as polyphenols, carotenoids, vitamins, minerals and others present in fruit and vegetables may be at least partly responsible for this effect. The precise mechanisms of action for several groups of compounds, and their potential impacts upon each sphere of health have not yet been fully elucidated. This work provides novel analysis of the total antioxidant capacity and total polyphenol content of 23 commercially available vegetable juices which are available on the UK market, utilising 6 biochemical assays, before and after in vitro digestion. Beetroot juice had the highest total antioxidant capacity and total polyphenol content regardless of the method of analysis, and both measures either increased or remained stable following in vitro digestion. A commercially available beetroot juice shot was selected as a viable method to increase bioactive phytochemical intake in the general population and its carbohydrate and phytochemical profiles were obtained by HPLC and GCMS analysis. The impact of consuming beetroot juice (70 mL) as part of a mixed meal or consuming beetroot juice alone (225 mL) on postprandial glucose and insulin responses was then assessed to investigate a potential role for these phytochemicals in the control of diseases featuring insulin resistance as a primary symptom, such as type 2 diabetes and metabolic syndrome. Consumption of 70 mL of beetroot juice as part of a mixed meal containing a total of 50g available carbohydrate resulted in a significant (P<0.05) reduction in postprandial insulin concentration at 15 minutes compared to a matched control meal. Consumption of 50g available carbohydrate as 225 mL beetroot juice resulted in a significant (P<0.05) lowering of blood glucose in the 0-30 minute segment of the glucose response and a significant (P