The effect of high pressure processing on clingstone and freestone peach cell integrity and enzymatic browning reactions Chukwan Techakanon a,b , Gary M. Smith a , Judy Jernstedt c , Diane M. Barrett a, ⁎ a Department of Food Science and Technology, University of California, Davis, One Shields Avenue, Davis, CA 95616, United States b Faculty of Science and Industrial Technology, Prince of Songkla University, Surat Thani Campus, 31 Makham Tia, Muang Surat Thani, Suratthani 84000, Thailand c Department of Plant Sciences, University of California, Davis, CA 95616, United States abstract article info Article history: Received 18 March 2016 Received in revised form 11 December 2016 Accepted 19 December 2016 Available online 21 December 2016 HPP-treated fruits and vegetables may undergo undesirable enzymatic browning reactions due to loss of mem- brane permeability and sub-cellular compartmentalization. Clingstone and freestone peaches were treated from 100 to 500 MPa for 10 min and evaluated for polyphenol oxidase (PPO) activity, color, total phenols, and for cell integrity using light microscopy and 1 H NMR. Significant changes in membrane integrity following HPP above 200 MPa were determined by T 2 shifts in the vacuolar compartment from initial levels of 0.79 (clingstone) or 0.88 (freestone) to approximately 0.60–0.68. Clingstone peaches treated at 300, 400 and 500 MPa showed signif- icant decreases (5, 12 and 7%) in % water of the vacuolar compartment and simultaneous increases in the cyto- plasmic compartment (4, 8 and 5%). Additionally, there was a reduction in the number of viable cells from an initial 57–58% to 0 and 14% in clingstone and freestone peaches, respectively. These results correlated with the development of increased browning. Industrial relevance: Clingstone peaches are firm-textured and therefore are preserved primarily through can- ning, which desirably softens the texture. In this study we evaluated the use of high pressure processing – at a range of MPa levels – for preservation, and found that enzymatic browning took place after 2 weeks in refriger- ated storage if processing occurred above 200 MPa. Analytical tools were developed to follow the onset of the browning, and in future work preventative measures will be studied to minimize this reaction. © 2016 Elsevier Ltd. All rights reserved. Keywords: High pressure processing Membrane integrity 1 H NMR Polyphenol oxidase Peaches Enzymatic browning 1. Introduction High pressure processing (HPP) is a novel food preservation method that is currently receiving the most attention from the food sector, be- cause it is successful in creating products of high nutritional value and sensorial quality. The advantage of this preservation method is that it is not only a microbiologically safe means of providing longer shelf life but also retains the fresh characteristics of products. In general, pressures in the range of 100–600 MPa are used for food preservation (Palou et al., 2000), but these pressures may also result in loss of cell and therefore tissue integrity. In plant-based materials, cell integrity plays an important role in final product characteristics, in par- ticular color and texture. Loss of cell integrity involves increased mem- brane permeability, resulting in opening of subcellular organelles and movement of water and metabolites within the cell. High pressure treatment was previously reported to affect the peach enzymes in- volved in changes in color, polyphenol oxidase activity (Rao et al., 2014) and activity of the enzyme involved in textural changes, pectin methylesterase (Boulekou, Katsaros, & Taoukis, 2010). Undesirable color changes in HPP-processed fruit are a result of enzymatic browning reactions induced by the loss in cell integrity. This loss allows the inter- action between the enzyme, initially located in the plastid of the intact fruit, and its substrates, which are initially located in the vacuole. Color is a primary quality attribute in fruits, therefore enzymatic brow- ning reactions have been a crucial problem in HPP treated fruits e.g. mango puree (Guerrero-Beltrán, Barbosa-Cánovas, & Swanson, 2005), banana puree (Palou, López-Malo, Barbosa-Cánovas, Welti-Chanes, & Swanson, 1999), tomato puree (Sánchez-Moreno, Plaza, De Ancos, & Cano, 2006) and navel orange juice (Polydera, Stoforos, & Taoukis, 2005). The complexity of the browning reaction and its substantial im- pact on food quality has motivated food scientists to explore it at the cel- lular level. Numerous authors have considered that PPO (1,2- benzenediol; oxygen oxidoreductase, EC 1.10.3.1) and phenolic com- pounds are the major factors involved in the enzymatic browning reac- tion (Lee, Kagan, Jaworski, & Brown, 1990; Cheng & Crisosto, 1995; Coseteng & Lee, 1987). However, Cantos, Tudela, Gil, and Espín (2002) observed different results in potatoes, where there was no significant correlation between the degree of browning and any biochemical attri- bute they tested, e.g. PPO, peroxidase or initial phenolic content. These observations led us to the idea that cell integrity and ability of the en- zyme and its substrate to interact may be an important factor control- ling browning reactions. Innovative Food Science and Emerging Technologies 39 (2017) 230–240 ⁎ Corresponding author. E-mail address: dmbarrett@ucdavis.edu (D.M. Barrett). http://dx.doi.org/10.1016/j.ifset.2016.12.011 1466-8564/© 2016 Elsevier Ltd. All rights reserved. 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