12 January - 20 June 2016

Wine grape pomace may increase dietary fibre and stability of yogurts and salad dressings

23 Jan 13

Wine grape pomace, the residual seed and skin from winemaking has been found to be a source of antioxidant dietary fibre (ADF). The concept of an antioxidant dietary fibre was first proposed by Saura-Calixto in 1998.  It was noted that a ADF should meets the criteria of 1g of ADF having DPPH free radical scavenging capacity equivalent to 50 mg of vitamin E and dietary fibre content higher than 50% dry matter from natural constituents of the material.   Grape fibres have been found to reduce blood pressure and efficacy in lipid profiles.  It is thought that this is due to the combined effect of dietary fibre and antioxidants. A study published in Food Chemistry by Zhao et al. has investigated the feasibility of fortifying wine grape pomace (WGP) as the source of dietary fibre and polyphenols in yogurt and salad dressing.  The scientists evaluated three different forms of WGP; dried whole grain pomace (WP), pomace liquid extract and freeze dried liquid extract.   These were added at 1, 2, or 3g to 100 g yogurt samples. The yogurt was stored at 4oC and on days 1, 7 and 14  was evaluated for dietary fibre content, and quality, including pH, peroxide value, total phenolic content and antiradical scavenging activity.  It was also analysed for lactic acid percentage, viscosity and syneresis.   Measures of WGP were also added to two types of commercial salad dressing, a creaming dressing and a liquid type dressing.  These were stored and evaluated the same way as the yogurts.  The products were also assessed by twelve panellists.  Only the products fortified with the WP were evaluated, as the scientists found that the WP had the highest amount of ADF.  Zhao et al report that based on their results, the best received products were 1% (w/w) WP fortified yogurt, 0.5 (w/w) fortified Italian dressing and 1% WP fortified Thousand Island dressing.  WGP from Pinot Noir grapes was found to not only increase dietary fibre and total phenolic content but also delay lipid oxidation during storage. However the products fortified with the liquid extract and freeze dried liquid extract were found to have the most similar physiochemical properties to the control.  Zhao et al note that during storage the total phenolic content and the DPPH radical scavenging activity of the samples decreased, and state that further investigation is therefore needed into mechanisms and methods of retention.

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