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The Impact of Maturity Stage on Cell Membrane Integrity

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The Impact of Maturity Stage on Cell Membrane Integrity Article pubs.acs.org/JAFC The Impact of Maturity Stage on Cell Membrane Integrity and Enzymatic Browning Reactions in High Pressure Processed Peaches (Prunus persica) † § ‡ † ⊥ † Chukwan Techakanon, , Thomas M. Gradziel, Lu Zhang, , and Diane M. Barrett*, † Department of Food Science and Technology, University of CaliforniaDavis, One Shields Avenue, Davis, California 95616, United States § Faculty of Science and Industrial Technology, Prince of Songkla University, Surat Thani Campus, 31 Makham Tia, Muang Surat Thani, Suratthani 84000, Thailand ‡ Department of Pomology, University of CaliforniaDavis, One Shields Avenue, Davis, California 95616, United States ⊥ Department of Applied Biology & Chemical Technology, The Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, China ABSTRACT: Fruit maturity is an important factor associated with final product quality, and it may have an effect on the level of browning in peaches that are high pressure processed (HPP). Peaches from three different maturities, as determined by firmness (M1 = 50−55 N, M2 = 35−40 N, and M3 = 15−20 N), were subjected to pressure levels at 0.1, 200, and 400 MPa for 10 min. The damage from HPP treatment results in loss of fruit integrity and the development of browning during storage. Increasing pressure levels of HPP treatment resulted in greater damage, particularly in the more mature peaches, as determined by shifts in ff transverse relaxation time (T2) of the vacuolar component and by light microscopy. The discoloration of peach slices of di erent maturities processed at the same pressure was comparable, indicating that the effect of pressure level is greater than that of maturity in the development of browning. KEYWORDS: high pressure, 1H NMR, maturity, peaches, enzymatic browning 1. INTRODUCTION suggested by Cantos et al.,9 the importance of cellular integrity High pressure processing (HPP) is a novel advanced process and accessibility of the enzyme to its substrate may be the being extensively studied because of its ability to retain primary factor in the development of enzymatic browning. This study was designed to investigate this hypothesis. In intact products with natural attributes while inducing destruction of 10 microorganisms and modifying enzyme activity. HPP is a plants, PPOs are localized in plastids and remain physically separated from phenolic substrates, which are in the potential alternative method for peach preservation, besides 11,12 canning and freezing, because it can provide a new product with vacuole. However, once the plant loses integrity in its cell novel crispy and aromatic characteristics. The quality of HPP walls and membranes by either cutting, senescence, or physical stress, enzymes and substrates are allowed to mix and the preserved fruits can, however, change during storage due to the 1 ff use of elevated pressure levels, which may induce changes in browning reaction occurs as a consequence. The e ect of HPP on PPOs has been previously studied either in the form of a membrane permeability and trigger loss of subcellular fi 13 compartmentalization. After loss of cellular integrity in fruits, partially puri ed extract or measured directly from the plant material after processing.14 One goal of the current study is to substrates are able to mix with enzymes, as occurs in the case of ff enzymatic browning, which is undesirable to consumers. compare the e ect of HPP on PPOs, both in an extract and as In a large number of fruit and vegetable crops, losses are a found in a plant food matrix. 1 Fruit ripening is an irreversible developmental process that result of postharvest deteriorative reactions, in which fi 15 enzymatic browning reaction causes the second largest quality involves speci c biochemical and physiological attributes. 2 Peaches are a climacteric fruit, in which ripening is associated loss. Enzymatic browning in fruits is initiated by the oxidation fi of phenolic compounds, mainly by polyphenol oxidases with the production of ethylene and a signi cant increase in 3 4 cellular respiration. Ethylene has an important role in all stages (PPOs) with a partial role of peroxidases (PODs). The ff product of this reaction is quinone, which further undergoes of peach ripening; this plant hormone sets o the activity of enzymes responsible for fruit softening, ripening, color nonenzymatic processes to form melanins, brown products on − development, and sugar content.16 19 The ripening process the cut surfaces of fruit that are exposed to oxygen. Most 20 21 studies of enzymatic browning have measured the activity of results in elevated sugar-to-acid ratios, decreases in acidity PPOs and the concentration of their total phenolic substrates and correlated these to the degree of browning, for example, Received: May 18, 2016 − apples5 and peaches.6 8 However, in preliminary studies it was Revised: August 23, 2016 determined they neither correlated well to the difference in Accepted: August 24, 2016 lightness in stored HPP treated peaches. Therefore, as Published: August 24, 2016 © 2016 American Chemical Society 7216 DOI: 10.1021/acs.jafc.6b02252 J. Agric. Food Chem. 2016, 64, 7216−7224 Journal of Agricultural and Food Chemistry Article (due to decreases in malic and citric acid), changes in ground TA.XT2 Texture Analyzer (Stable Micro Systems Ltd., Surrey, UK): color of the skin, and an increase in volatile compounds.22 (1) maturity 1 (M1), which was 50−55 N; (2) maturity 2 (M2), 35− 40 N; and (3) maturity 3 (M3), 15−20 N. The three maturity stages, Measurement of respiration rate, ethylene, sugar, and acid all − involve destructive evaluation; however, the use of firmness as a M1 M3, were harvested at 312, 314, and 316 days after blossom formation, respectively. Approximately three peaches per maturity maturity indicator can be nondestructive. All of these changes stage per processing replicate were hand peeled and cut into create desirable fruit characteristics and make peaches more approximately 3 cm thick slices before being vacuum packed in palatable to the consumer. Fruit maturity is one of the most polyethylene bags (4 mil vacuum pouches, Ultrasource, North Kansas important factors associated with the quality of the final City, MO, USA). Each bag contained three peach slices of the same processed product; therefore, selecting the right maturity stage maturity, classified by firmness, one from each of three different fruits, is critically important and processors need to be concerned with all of which were to be analyzed using the same analytical method. this. However, very few researchers have focused on the effect Peach extracts taken from each maturity stage were vacuum packed in 23,24 polyethylene bags of approximately 2 mL. On each replicate day of of fruit maturity on the quality of HPP treated products. fi This study, therefore, explores methods to measure changes in processing, six packages (one for each of the ve analytical methods plus a control) for each of the three maturity levels were processed at cell integrity of fruits from different initial maturities following 1 each of the three pressures: 0.1, 200, and 400 MPa. The same fruit was the high pressure process. Nuclear magnetic resonance ( H analyzed for all analytical parameters, for example, difference in NMR) water proton relaxometry is a nondestructive measure- lightness, the paramagnetic study using NMR, PPO activity, total ment that detects physiological changes of water in a sample. phenols, and light microscopy. The control sample was unprocessed This method has undergone continuous development and has sliced peaches in a vacuum package (approximately 0.1 MPa). All of been applied in a wide range of plant studies, for example, plant the packaged samples were kept at ambient temperature (22 ± 2 °C) freezing,25 HPP treated strawberries,26 tomato pericarp for 30 min prior to HPP treatment. ripening,24 and identification of black heart in pomegranates.27 2.2. High Pressure Processing (HPP). The packages containing − three different maturity stages of peaches were processed at 0.1 The proton spin spin (T2) relaxation time is usually in the range of seconds to milliseconds on the 1T aspect system. The (control group was at a standard atmosphere, 101.3 kPa or 0.1013 ff MPa), 200, and 400 MPa for 10 min in a high pressure processing unit value is related to properties of water in di erent locations in (2L-700 Lab system, Avure Technologies Inc., Kent, WA, USA). The the tissue, to total water content in both free and bound form, pressure levels used in this experiment were justified on the basis of 28 and to the interaction of water with macromolecules. In plant the rupture of the plant cellular membranes at 200 MPa and the cells, the plasmalemma (membrane surrounding the cytoplasm) inactivation of microorganisms at 400 MPa, both of which were and tonoplast (membrane surrounding the vacuole) provide observed in preliminary experiments. The high pressure unit had a 2.0 the primary control of permeability between their compart- L vessel, and 600 MPa was the maximum pressure level; the pressurizing medium was water. The initial high pressure unit ments. Once cell damage occurs as a consequence of high ° pressure treatment, decompartmentalization of membranes is temperature (Ti) was approximately 23 C. The maximum temper- 29 ature in the high pressure chamber depended on the target pressure triggered, leading to an increase in cell permeability. This ° ff and was 28 and 32 C for the treatment at 200 and 400 MPa, induces an exchange of water between di erent cell compart- respectively. In each operation, there will be a come-up (approximately ments. The increased water exchange rate will facilitate 2 and 4 min for 200 and 400 MPa, respectively) stage, a constant intercellular water transport. The degree of membrane damage pressure stage for 10 min, and a decompression stage. At the end of can therefore be determined by observing changes in the water the holding period, pressure is released to atmospheric pressure within proton relaxation behavior (T2) of the vacuolar and other a few seconds.
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