Effect of ozone processing on anthocyanins and ascorbic acid degradation of strawberry juice B.K. Tiwari a , C.P. O’Donnell a , A. Patras a,b , N. Brunton b , P.J. Cullen c, * a Biosystems Engineering, UCD School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland b Ashtown Food Research Centre, Ashtown, Dublin 15, Ireland c School of Food Science and Environmental Health, Dublin Institute of Technology, Dublin 1, Ireland article info Article history: Received 29 May 2008 Received in revised form 7 July 2008 Accepted 28 August 2008 Keywords: Anthocyanin Ascorbic acid Colour Ozone Strawberry juice abstract Strawberry juice samples were ozonated with processing variables of ozone concentration (1.6–7.8% w/w) and treatment time (0–10 min). Effects of processing variables on anthocyanins (P3G), ascorbic acid (AA) and colour values (L * , a * , and b * ) were determined. Significant reductions in anthocyanin content (98.2%) and ascorbic acid (85.8%) were observed at an ozone concentration of 7.8% w/w and a treatment time of 10 min. The changes in lightness (L * ) values and total colour difference (TCD) values were fitted well to zero-order kinetics, whereas, a * , b * followed first-order kinetics. P3G and AA were fitted to first order and fraction conversion models. The rate constants for L * , a * , b * and TCD were linearly correlated with ozone concentration, whereas, P3G and AA were exponentially related. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Fruit juices are increasingly promoted and consumed due to their reported nutritional claims. Strawberries are known for their high levels of micronutrients and phytochemical compounds (Tulipani et al., 2008). Recent studies have shown the potential benefits of anthocyanins from edible berries in human health and disease prevention. These include cardiovascular disorders, advancing age-induced oxidative stress, inflammatory responses and diverse degenerative diseases (Zafra-Stone et al., 2008). Ber- ries such as cranberries, blueberries, strawberries and raspberries contain significant amounts of non-nutritive phytochemicals including polyphenols which are reported to reduce cancer risk (Duthie, Duthie, & Kyle, 2000). Pelargonidin-3-glucoside (P3G) is the major anthocyanin found in strawberries and is responsible for the bright red colour of fresh strawberries (Francis, 1989). Anthocyanins may degrade due to various factors including pH, light, oxygen, enzymes, ascorbic acid and thermal treatment (Cemeroglu, Velioglu, & Isik, 1994; Jackman, Yada, Tung, & Speers, 1987; Wang & Xu, 2007). Thermal degradation of anthocyanins has been studied for blackberry (Wang & Xu, 2007), sour cherry (Cemeroglu et al., 1994), raspberry (Ochoa, Kesseler, Vullioud, & Lozano, 1992), pomegranate (Martí, Pérez-Vicente, & García-Vigu- era, 2001) and strawberry (Skrede, Wrolstad, Lea, & Enersen, 1992; Garzon & Wrolstad, 2002). Anthocyanin stability may also be influenced by other fruit components, especially the interac- tion with ascorbic acid, resulting in mutual degradation as re- ported in strawberry and blackcurrant products (Skrede et al., 1992). The interaction of ascorbic acid with anthocyanin pig- ments results in the degradation of both compounds and a de- crease in product colour and nutritional quality through oxidation or condensation of ascorbic acid directly with anthocy- anin pigments (Markakis, Livingston, & Fellers, 1957). Degradation of anthocyanins or ascorbic acid in the presence of ozone could be due either to direct reaction with ozone or indirect reaction because of secondary oxidants. The direct reaction is de- scribed by the Criegee mechanism (Criegee, 1975) where ozone molecules undergo 1,3-dipolar cycloaddition with double bonds present, leading to the formation of ozonides (1,2,4-trioxolanes) from alkenes and ozone with aldehyde or ketone oxides as decisive intermediates, all of which have finite lifetimes (Criegee, 1975). This leads to the oxidative disintegration of the ozonide and forma- tion of carbonyl compounds, while oxidative work-up leads to car- boxylic acids or ketones. To facilitate the preservation of unstable nutrients many juice processors have investigated alternatives to thermal pasteurisa- tion, including unpasteurised short shelf life juices with high retail value. This trend has continued within the European Union. How- ever, within the US, recent regulations by the FDA have required processors to achieve a five-log reduction in the numbers of the most resistant pathogens in their finished products. This rule comes after a rise in the number of food borne illness outbreaks and consumer illnesses associated with consumption of untreated 0308-8146/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2008.08.085 * Corresponding author. Tel.: +353 1 4027595. E-mail address: pjcullen@dit.ie (P.J. Cullen). Food Chemistry 113 (2009) 1119–1126 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem