P effectively reduced the populations of native microflora onfresh blueberries, a reduction which persisted throughout thestorage period of the study. This is thefirst study that investigatesthe CP-induced inactivation of potential spoilage microorganismson blueberries while considering its effect on the quality. Duringstorage at 4C, APC on the untreated control demonstrated a steadylogarithmic growth, while treatments all treatments seconds andlonger demonstrated APC suppression of approximately 0.8e1.6 logCFU/g after 1 day (Fig. 2). After 7 days in 4C storage, all CP treat-ments demonstrated at least 1.5 log CFU/g lower APC whencompared to the control. CP has demonstrated its effectiveness inreducing human pathogens, such asE. coliO157:H7,Salmonella,Listeria monocytogenes,Staphylococcus aureus, andShigellaspp.(Niemira, 2012a). The capability of CP as a postharvest sanitationprocess was demonstrated in this study by the logarithmicreduction immediately after treatment, and sustained suppressionof bacterial counts. Many methods for removing pathogens, as wellas minimizing their effect on quality of treated produce, have beeninvestigated. Other nonthermal inactivation technologies such as,UVc, ultrasound, and ozone, can require 20e60 min of exposure toachieve significant log reduction of pathogenic and spoilage mi-croorganisms (Bialka and Demirci, 2007; Birmpa et al., 2013). Theefficacy of electrostatic sprays of electrolyzed oxidizing water, UVlight, ozone, and a combination of ozone and UV light in inacti-vatingE.coliO157:H7 was studied on blueberries (Kim and Hung,2012). The combination of ozone and UV light significantly inacti-vated more microorganisms on the calyx of blueberries than UVlight alone, or ozone treatments alone, indicating a synergistic ef-fect (Kim and Hung, 2012). Research suggests that the antimicrobialmechanism of CP derives primarily from the production of UV,ozone, and other reactive chemical products (Niemira, 2012a). Theeffect of CP on the visual appearance, surface color, compressionfirmness, and total anthocyanins was measured immediately aftertreatment. Based on visual inspection, blueberries did not displayany signs of gross physical damage compared to the control for CPtreatments shorter than 60 s. For longer treatments, damage wasnoted as rupturing and bruising of the skin and wilting of the se-pals. Compressionfirmness was also significantly impacted after60 s of CP treatment (Fig. 3). Softening of the blueberries was theresult of mechanical damage and/or temperature rise (Fig. 4) ob-tained during treatment. Some berries exhibited a noticeablyincreased reflectance of the cutaneous wax after 45 s, consistentwith temperature rise. Blueberries were treated with 7 cfm ofambient air to ensure uniform CP treatment; however, this turbu-lent airflow also facilitated collisions between the blueberries andthe glass surface of the jars. A trend towards reduction incompressionfirmness was noted when blueberries were treatedwith 7 cfm of ambient air alone, with significant reduction after90 s (Fig. 3). It is likely that cutaneous damage observed at thelonger treatment times was a result of the berries' contact with theglass walls of the containers used. Further optimization of thisFig. 2.Aerobic plate counts of blueberry after cold plasma treatment and during storage at 4C. Results represent the mean (n¼6)±the standard error. * indicates (P<0.05) logreduction compared to the control, immediately after treatment.A. Lacombe et al. / Food Microbiology 46 (2015) 479e484481
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