- Email: [email protected]
Preserving fresh fruit quality by low-dose electron beam processing for vending distribution channels
Radiation Physics and Chemistry 168 (2020) 108540
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Preserving fresh fruit quality by low-dose electron beam processing for vending distribution channels
T
Bianca Smith1, Shima Shayanfar2, Rosemary Walzem, Christine Z. Alvarado, Suresh D. Pillai∗ National Center for Electron Beam Research, An IAEA Collaborating Centre for Electron Beam Technology, Texas A&M University, College Station, TX, 77845, USA
A R T I C LE I N FO
A B S T R A C T
Keywords: Electron beam Vending Fruits Bioburden Consumer
Food vending is estimated to be a $20 billion industry in the United States. There is an untapped business opportunity to positively influence nutrition and health by positioning fresh fruits and vegetable items as healthy vending items in vending machines. The hypothesis was that low dose (≤1 kGy) electron beam (eBeam) processing, alone or, in combination with Modified Atmosphere Packaging (MAP) is effective for developing fresh produce-based vending items. Shelf-life, sensory attributes, and consumer acceptability are key metrics for healthy vending items. The experimental objectives were to evaluate low dose eBeam (≤1 kGy) processing alone or along with MAP for red grapes, cherry tomatoes, and strawberries for reducing bioburden, while maintaining sensory attributes and consumer acceptability scores. The eBeam treatment at ≤ 1 kGy alone, or in combination with MAP suppressed bioburden by at least 1 to 2 log units over 21 day refrigerated storage as compared to untreated control samples. eBeam processing did not adversely affect the color or the firmness of the fruits. A consumer taste panel did not find any significant difference (P ≥ 0.05) in acceptability of eBeam processed fruits (compared to untreated samples) in terms of appearance, odor, color, firmness and flavor. Overall, the results suggest that eBeam at low doses (≤1 kGy) alone or in combination with MAP can be a unique approach for developing healthy vending items.
1. Introduction In today's society we are battling nutrition and obesity concerns usually blamed on the lack of time and an abundance of convenience foods. Convenience foods sold via vending machines and convenience stores are particularly high in sugar, sodium, and saturated fat. There is an un-tapped opportunity to improve the nutritional choices available in convenience foods offered through vending machines and in convenience stores. The food vending industry in the US is estimated to be around $20 billion (Pillai et al., 2013). Approximately 23 million children in the U.S. are either obese or overweight because of poor dietary habits (Ogden et al., 2008). Mexico has a 33% adult obesity rate higher than the US (FAO, 2013). A vast majority of school-aged children do not consume the recommended amounts of fruits and vegetables (Overby et al., 2012; Lorson et al., 2009). Thus, there is an untapped business opportunity to positively influence nutrition and health by positioning fruits and vegetable in the vending machine distribution channel, particularly in schools, universities, workplaces, and public areas.
Consumer acceptability, sensory attributes, and extended shelf-life are key quality metrics for healthy vending items (ChangeLab Solutions, 2012; CDC, 2015). Electron beam (eBeam) processing is an FDA approved non-thermal food processing technology that is suitable for processing fresh produce. The FDA has set an upper dose limit of ≤1 kGy for all fresh produce for shelf-life extension applications in the US (FDA, 2014). The underlying hypothesis was that low dose eBeam (≤1 kGy) processing can be used to develop fresh fruit and vegetable based healthy vending items. Additionally, our hypothesis was that consumers will rate eBeam (≤1 kGy) treated items as “acceptable” in specific sensory metrics. The overall objective was to employ eBeam at low doses (≤1 kGy) to document the reduction in the natural bioburden of cherry tomatoes, red grapes, and strawberries and empirically determine the sensory and consumer acceptability scores of the treated fruits. An additional objective was to evaluate the utility of Modified Atmosphere Packaging (MAP) in combination with eBeam processing to reduce the natural bioburden of the fruit samples for healthy vending.
∗
Corresponding author. 418B, Kleberg Center, MS 2472 College Station, Texas, 77843-2472, USA. E-mail address: [email protected] (S.D. Pillai). 1 currently at Nutraceutical Systems International, Austin, TX. 2 currently at Califia Farms, CA, USA. https://doi.org/10.1016/j.radphyschem.2019.108540 Received 19 June 2019; Received in revised form 2 September 2019; Accepted 21 October 2019 Available online 22 October 2019 0969-806X/ © 2019 Elsevier Ltd. All rights reserved.
Radiation Physics and Chemistry 168 (2020) 108540
B. Smith, et al.
2.3. Bioburden analysis
Table 1 The gas composition of the Modified Atmosphere Packaging (MAP) conditions used in the study. Fruit
Oxygen %
CO2%
Nitrogen %
Strawberry Grape Tomato
5 5 5
15 3 0
80 92 95
The eBeam processed and non-eBeam processed (control) samples were stored refrigerated for up to 21 days. The samples were analyzed for Total (aerobic) Plate Counts (TPC) and Yeasts and Molds (YM) on day 0, 1, 3, 7, 14, and 21. However, for reasons of brevity only results from days 0, 7 and 21 are reported. The FDA BAM (Bacterial Analytical Manual) protocols were used (Andrews and Hammack, 2003) were processing the samples and enumeration. Briefly, each 50g sample was aseptically transferred into a sterile stomacher bag with filter containing 450 ml of Butterfield's Phosphate Buffer (BPB) (Sigma Chemical CO, St. Louis, MO). The samples were homogenized for 2 min using a stomacher (Seward 350, London, UK) on the “normal” speed setting. The samples were then serially diluted in BPB and 0.1 mL aliquots were spread plated onto Plate Count Agar for enumeration of TPC and Sabouraud's Dextrose agar (SDA) for YM. All plates were incubated at 28 °C for 5 days prior to enumeration, and the microbial data was expressed as log CFU/g.
2. Materials and methods 2.1. Fruit samples and packaging Red grapes (Vitis vinifera), strawberries (Fragaria ananassa), and cherry tomatoes (Solanum lycopersicum var. cerasiforme) were purchased from a local farmers’ market in College Station, Texas to obtain samples with minimal or no disinfectant washing or other post-harvest processing. The fruit samples were refrigerated until they were apportioned into 50 g sub-samples under aseptic conditions. The 50g samples were placed in polyethylene clamshells (Sambrailo, Santa Maria, CA) for each treatment in triplicate. For the MAP treatment, the clamshells were placed within poly nylon vacuum bags (ULINE, Ontario, CA). The bags were flushed multiple times and filled with the appropriate gas mixture (Praxair, Danbury, CT), and then heat sealed using a commercial sealer (Accu-Seal, San Marcos, CA). The MAP gas mixtures used in this study (Table 1) were based primarily on a previous study (Sandhya, 2010). Two independent experiments were performed on separate days. Each of the experiments was replicated three times.
2.4. Sensory measurements Color Measurements: The surface color of grapes, strawberries and tomatoes, grapes, and strawberries were measured using a Minolta Color Meter (Chroma Meter CR-310, Minolta, Tokyo, Japan). The instrument was calibrated using the white calibration plate (Calibration Plate CR-A43, Minolta Cameras, Osaka, Japan). Color values of L* (lighness-darkness), ± a* (red-green) and b* (yellow-blue) were measured four times for each sample at each sampling time point and the average values were recorded. Texture Analysis: The fruits’ firmness and textural changes between treatments were measured using the texture analyzer (model TA-XT2i, Texture Technologies Corp., Scarsdale, NY). The analysis was performed on the equatorial region of 10 samples. The texture analysis setup parameters are listed in Table 3. The modulus of deformation (N/ mm), force (N), distance (mm) and work to rupture (N.mm) were recorded for all the samples.
2.2. Low dose eBeam processing The packaged samples were transported on blue ice for eBeam processing at the National Center for Electron Beam Research (NCEBR) on the Texas A&M University campus in College Station, Texas. The NCEBR is a USDA-APHIS certified facility to treat fruits and vegetables at low (≤1 kGy) doses. A linear accelerator (15 kW, 10 MeV) was used for delivering the low eBeam doses from top and bottom. Detailed dosemapping studies were initially performed to ensure that the measured doses in the fruit samples were ≤ 1 kGy (Table 2). To achieve the low dose (≤1 kGy), the beam energy was attenuated using a defined number of plywood (total height 25.8 cm) attenuators. The delivered doses were measured using alanine dosimetry and the E-Scan spectrometer (Bruker-BioSpin., Billerica, MA). To ensure accurate dosing with each processing run, “speed checks” were performed on a subset of samples. For each “speed check”, two alanine dosimeters were placed within the fruit on either ends. An X-Acto knife™ was used to create the cavities within the fruit in which the dosimeters (placed in tiny moisture-impermeable, heat-sealed pouches) were placed. It was critically important to measure the dose within the fruit rather than just on the top or bottom of the packages. Two such “speed checks” were used prior to each eBeam processing run. The eBeam processing table's speed was so adjusted to target the eBeam dose as close to 1.0 kGy as experimentally possible but without exceeding 1.0 kGy. All samples were stored on blue-ice prior to and after eBeam processing.
2.5. Consumer acceptability scoring The consumer acceptability studies were performed using procedures approved by the Texas A&M University's IRB procedures (TAMU IRB Protocol # 2012-0463). Thirty- eight untrained volunteers from the university student, staff and faculty community participated in the consumer acceptance portion of this study. The fruit samples were used in consumer acceptance studies no later than 24 h of eBeam processing. Each treatment was assigned a random 3-digit code to reduce bias of sample treatments. Plastic cups were labeled with the random 3-digit numbers in which the fruit samples were placed. The fruit samples were prepared as follows. The strawberries were de-capped and cut into halves. The grapes were removed from the bunch and 2 equal sized grapes were placed in each cup. One cherry tomato was placed in each cup. Each sample was served to the consumer one at a time and they were given salt-less Saltine™ crackers and double deionized water to cleanse their palate in between tastings. The panelists were asked to rate each fruit sample on the following acceptability attributes namely odor, color, flavor and texture using a 9-point hedonic scale ranging from “extremely dislike” to “extremely like”.
Table 2 Example dose distributions on top and bottom of the fruit samples measured during dose-mapping procedures. Stacks of plywood (25.8 cm) sheets were used to attenuate the 10 MeV linac beam energy to achieve doses ≤ 1 kGy. Sample Grape Strawberry Tomato
Dose Top 0.82 0.96 0.84
2.6. Data analysis As mentioned previously, two independent experiments were performed on separate days. Each of these experiments was replicated three times. The microbial data are non-parametric since the natural microbial populations of independent samples were analyzed. The raw microbial data were converted to log10 CFU/50 gm to represent the bioburden in each of the samples that were packaged. Data from the 6
Bottom 0.99 0.98 0.91
2
Radiation Physics and Chemistry 168 (2020) 108540
B. Smith, et al.
Table 3 Parameters employed in the fruit texture analysis. Fruit
Strawberry Grape Tomato
Parameters
Trigger
Pre-test speed (mm/s)
Test speed (mm/s)
Post test speed (mm/s)
Distance (mm)
Data acquisition rate (pps)
Load cell (Kg)
5 5 5
5 1 1
5 5 5
5 5 7
200 200 200
25 25 25
Probe 5 mm spherical 2 mm flat 2 mm flat
Force(N) 0.05 0.05 0.05
tomatoes under both ambient packaging and MAP conditions respectively. The scatter plot data from Day 0 (immediately after eBeam treatment), Day 7, and Day 21 are presented. The grape samples had the lowest initial bioburden levels. Immediately after eBeam processing (Day 0) there was a 0.9 log difference between the TPC counts of the control (untreated) and eBeam processed samples which was significantly different (P < 0.05). Though there was no significant difference between the ambient packaged eBeam and untreated samples at the end of the 21 days study period, there was a significant (P < 0.05) difference between the ambient packaged and MAP packaged samples. This was the case irrespective of whether the grapes were eBeam treated or not. Grape samples stored under MAP conditions had TPC and YM that were for the most part below detection limits (Fig. 1). The ability of MAP conditions to increase shelf-life has been previously reported (Shayanfar, 2013; Mosayyebzadeh et al., 2010; ArtesHernandez et al., 2006; Valero et al., 2008). In the case of strawberries, there was no significant difference between the eBeam treated and untreated samples at the beginning of the study (P > 0.05). However by Day 21, the MAP + eBeam treated samples had significantly lower (P < 0.05) YM counts compared to the untreated samples (Fig. 2).
replicates were combined and presented as column scatter plots values with the median values highlighted. The software, GraphPad Prism (GraphPad Software, Inc.,) was used for data presentation. Samples that had below detection limit (5 × 103 CFU/50g) are represented as 5 × 103 CFU/50g. The eBeam processed and control samples (for both the ambient and MAP conditions) were statistically compared for Days 0 and 21 using the Mann-Whitney test. Statistical analyses were performed using SigmaPlot ver 12. (SigmaPlot, Inc). For the consumer acceptability studies, the data was analyzed using the General Linear Model Procedure in Statistical Analysis System (SAS 9.3, 2001). The mean values are reported, and the differences in the mean values were compared by ANOVA and LSD. The differences in the treatments were considered significant when P < 0.05. 3. Results and discussion 3.1. Bioburden analysis Figs. 1–3 shows the influence that low dose eBeam processing has on the bioburden (TPC and YM) of red grapes, strawberries and cherry
Fig. 1. Scatter plots of the bioburden (total aerobic plate count (TPC) and yeast and molds (YM) counts) on days 0, 7 and 21 after grapes were untreated (control), electron beam (eBeam) treated , Modified Atmosphere (MAP) packaged and MAP packaged+eBeam and stored under refrigerated conditions. The horizontal line represents the median bioburden value based on the 6 replicate samples that are shown. 3
Radiation Physics and Chemistry 168 (2020) 108540
B. Smith, et al.
Fig. 2. Scatter plots of the bioburden (total aerobic plate count (TPC) and yeast and molds (YM) counts) on days 0, 7 and 21 after strawberries were untreated (control), electron beam (eBeam) treated , Modified Atmosphere (MAP) packaged and MAP packaged+eBeam and stored under refrigerated conditions. The horizontal line represents the median bioburden value based on the 6 replicate samples that are shown.
conditions may need further optimization to achieve synergism when combined with eBeam processing. Low dose eBeam processing was not expected to eliminate the microbial bioburden. We have previously shown that a dose greater than 1.0 kGy would be generally required to reduce fungal bioburden by just 90% (Ic et al., 2007). This could possibly explain why the fungal reduction was not as pronounced as that of the TPC. There are recent reports on the efficacy of low dose (between 0.5 kGy and 2.0 kGy) eBeam processing on fruits (Oliveira et al., 2013; Cabo Verde et al., 2013; Kong et al., 2014), These studies further highlight the value of eBeam processing for reducing the bioburden of such fruits to enhance their shelf-life. In the present study, low dose eBeam processed fruits under both ambient and MAP conditions were shown to achieve lower median levels of bacterial and fungal bioburden even after 21 days of storage. The bioburden reduction that can be achieved with eBeam processing can be significant from an economic stand-point. It is estimated that approximately 19 million pounds of fresh fruits are lost annually due to spoilage, of which microbial spoilage plays a major role (Kantor et al., 1997; Brackett, 1994). Barth et al. (2009) has reported that loss of shelf-life results in approximately 30–50% shrinkage of fresh-cut fruits. Thus, using eBeam at low doses to achieve even a 0.5–1.0 log reductions in bioburden could translate to significant economic returns. The ability of 1 kGy eBeam dose to reduce or eliminate microbial pathogens on fresh produce is also worthy of investigation.
Physical evidence of spoilage (i.e. fungal growth) was present on some of the untreated samples on day 21 while the eBeam treated samples did not exhibit such fungal growth (data not included). The synergistic effect of MAP + eBeam processing on fungal loads is evident in the case of strawberries. Combined application of MAP and eBeam synergistically reduced the YM bioburden levels. There was no significant difference (P > 0.05) when the treatments that did not involve eBeam processing were statistically analyzed. This result suggests that the eBeam treatment is effective at controlling fungal populations on strawberries. The ability to retard visible fungal mycelia up to 21 days is noteworthy since strawberries are commodities with limited shelflife. , The use of eBeam technology to increase shelf-life and to eliminate/reduce pathogens is of high value (Yu et al., 1995; Van Calenberg et al., 1999). With regards to tomatoes, there was no statistically significant difference in bioburden between the 1.0 kGy eBeam treated and untreated samples either at the beginning of the study (Day 0) or at the end of 21 days (Fig. 3). These results are in agreement with a previous report (Schmidt et al., 2006). The use of MAP did not offer any advantage in terms of reduced bioburden levels on tomatoes even though Majidi et al. (2014) have previously reported that tomato quality can be maintained better under MAP conditions than just ambient cold storage. Overall, eBeam treatment reduced the median levels of TPC and YM (between 0.5 and 1.0 log units) immediately after processing. During the course of the 21 day refrigerated storage, the eBeam processed grape and strawberry samples showed consistently lower TPC and YM levels under both MAP and ambient-packaged conditions. The results indicate that one should not assume that the combination of MAP and eBeam would always have synergistic effect. In these studies, the synergism was noticed only in the case of strawberries (Fig. 2). These results suggest that the MAP
3.2. Color analysis The synergistic effect of eBeam + MAP on the red color can be observed on the Day14 grape samples (Table 4a). By Day 21, the MAP 4
Radiation Physics and Chemistry 168 (2020) 108540
B. Smith, et al.
Fig. 3. Scatter plots of the bioburden (total aerobic plate count (TPC) and yeast and molds (YM) counts) on days 0, 7 and 21 after tomatoes were untreated (control), electron beam (eBeam) treated , Modified Atmosphere (MAP) packaged and MAP packaged+eBeam and stored under refrigerated conditions. The horizontal line represents the median bioburden value based on the 6 replicate samples that are shown.
Unlike the grape samples, the strawberry samples did not show elevated redness immediately after eBeam treatment (Table 4b). There was no significant difference in the redness at Day 0 (just after eBeam treatment). However, by Day 7, the MAP and eBeam + MAP treated samples were significantly redder than the other samples. Even at Day 21, the MAP (with and without eBeam) stored samples were redder than the non-MAP samples (Table 4b). MAP seemed to have a stronger effect on redness of strawberries than eBeam treatment since these values tended to be higher when subjected to this treatment. The reported L values for different treatments did not indicate any significant difference even at different storage periods. In the case of tomatoes, there was no discernable pattern in the treatment effects of eBeam or MAP on tomatoes redness either immediately after treatment (Day 0) or Day 21 (Table 4c). On Day 21, there was a significant difference in the redness of the eBeam treated
treated and the eBeam + MAP treated grape samples were significantly more red (p < 0.05) than the non-MAP treated grape samples. The effect of eBeam treatment on the grape samples was observed only until Day 7. However, this difference in the redness was not observed after 21 days of storage. At Day 21, the only treatment that had a significant effect was storage under MAP conditions (with or without eBeam). Grapes stored under MAP conditions were significantly redder than samples stored under ambient refrigerated conditions. There was a significant (P < 0.05) difference in the L* values among the different treatments. The samples treated with eBeam were lighter than the other treatment groups in color until the seventh day of storage. However, this value changed over 21 days of storage leading to solely MAP stored grapes to be lighter in color than the other samples, while there was no significant differences (p > 0.05) reported in the other three treatment.
Table 4a Influence of eBeam processing and MAP storage conditions on grape a* (red-green) and L* (whiteness-grey) color values. Treatment Control eBeam MAP eBeam+MAP Control eBeam MAP eBeam+MAP
a* value
L* value
Day 0
Day 7
Day 14
Day 21
7.33 ± 0.57b 12.20 ± 1.59a 9.67 ± 0.66b 10.92 ± 1.72a 25.91 ± 0.70a 31.06 ± 1.17b 27.49 ± 1.74a 25.83 ± 1.77a
9.55 ± 0.83a 10.36 ± 1.11b 9.82 ± 0.30b 8.72 ± 0.31b 26.17 ± 2.29a,b 26.85 ± 0.52a 23.35 ± 0.58b 23.53 ± 0.66b
7.76 ± 0.47a 7.21 ± 0.76a 9.59 ± 1.03a 7.36 ± 0.47b 25.33 ± 1.04a 24.39 ± 7.23a 25.90 ± 0.31a 24.39 ± 0.66a
6.48 ± 0.40b 7.14 ± 0.81b 10.38 ± 0.59a 11.22 ± 1.23a 23.78 ± 0.70a 24.18 ± 1.20a 27.22 ± 0.41b 24.44 ± 0.51a
Mean values shown (n = 4 sample measurements). Means in the same column with different superscript represent statistically significant differences (P < 0.05). 5
Radiation Physics and Chemistry 168 (2020) 108540
B. Smith, et al.
Table 4b Influence of eBeam processing and MAP storage conditions on strawberry a* (red-green) and L* (whiteness-grey) color values. Treatment Control eBeam MAP eBeam+MAP Control eBeam MAP eBeam+MAP
Day 0
a* value
L* value
36.12 38.39 43.25 43.20 45.01 41.29 42.80 44.69
Day 7 ± ± ± ± ± ± ± ±
a
25.44 21.88 32.84 33.11 41.49 46.44 40.41 40.05
9.32 10.32a 8.23a 4.67a 5.23a 9.98a 6.11a 6.58a
Day 14 ± ± ± ± ± ± ± ±
b
6.83 10.80b 13.44a 10.41a 2.60a 8.31a 4.52a 2.71a
27.23 26.78 35.16 36.20 33.89 33.08 39.75 44.90
Day 21
± ± ± ± ± ± ± ±
a
1.49 4.09a 3.60a 9.17a 3.42b 1.79b 3.82b 8.00a
23.17 28.41 37.95 40.77 36.58 39.12 39.60 45.76
10.17b 6.91b 8.36a 8.33a 7.93a 8.39a 6.31a 6.12a
± ± ± ± ± ± ± ±
Mean values shown (n = 4 sample measurements). Means in the same column with different superscript represent statistically significant differences (P < 0.05).
tomatoes compared to the eBeam + MAP treated tomatoes. However, there was no discernable differences in the samples between the other treatments (Table 4c). Vanndy et al. (2008) and Majidi et al. (2014) have reported that MAP conditions delayed the ripening process and thereby reduced redness. Shurong et al. (2006) also found that samples irradiated at doses above 0.5 kGy had a significantly higher red color during days 2 and 4 of storage. This could be due to an increase in lycopene experienced in tomatoes that undergo irradiation. The activation of enzymes for secondary metabolites during eBeam processing has been reported before. Previous studies at our university have shown that mangoes respond to eBeam processing in a dose dependent manner by triggering the phenylpropanoid metabolism (Ryes and Cisneros-Zevallos, 2007; Girennavar et al., 2008). Altogether it can be interpreted that the color in strawberries is not affected by either of the treatment groups, in grapes and tomatoes, eBeam appears to be parameter influencing color. However, beyond seven days of storage, MAP storage influences color more than any other treatment. Nevertheless, the use of eBeam processing at low doses to enhance color via accumulation of phytochemicals can be a value-addition of eBeam processing.
Table 5a Influence of eBeam processing and MAP storage conditions on grape firmness (modulus of deformation) (N/mm). Treatment Control eBeam MAP eBeam+MAP
Day 0 0.70 0.79 0.72 0.62
± ± ± ±
Day 7 a
0.18 0.14a 0.29a 0.13a
0.46 0.50 0.69 0.46
± ± ± ±
Day 14 a
0.14 0.15a 0.14b 0.23a
0.16 0.15 0.19 0.17
Day 21
± ± ± ±
a
0.10 0.08a 0.08a 0.04a
0.18 0.79 1.02 0.26
± ± ± ±
0.09c 0.24b 0.22a 0.13b
Each value is the mean of 9–12 replicate samples ± SD. Means in columns with different superscripts (a, b, c) represent significant difference (P < 0.05). Table 5b Influence of eBeam processing and MAP storage conditions on strawberry firmness (modulus of deformation) (N/mm). Treatment
Day 0
Control eBeam MAP eBeam+MAP
6.27 6.70 7.07 6.62
± ± ± ±
Day 7 1.73a 3.03a 1.10a 1.10a
2.97 3.19 6.40 3.09
± ± ± ±
Day 14 1.73a 1.40a 1.95b 1.09a
1.58 2.13 6.03 2.41
± ± ± ±
Day 21 1.10a 1.68a 1.44b 0.70a
1.84 0.96 3.38 1.56
± ± ± ±
1.44b 2.70c 1.19a 1.95b,c
Each value is the mean of 10 replicate samples ± SD. Means in columns with different superscripts (a, b, c) represent significant difference (P < 0.05).
3.3. Texture analysis Immediately after the eBeam treatment, there was no significant difference in the firmness of either the grape or strawberry samples (Tables 5a and 5b). The effect of MAP on the firmness of the grape samples is observable on Day 7. On Day 21 it is very evident that the control samples were not as firm as any of the other treatments (Table 5a). Though the eBeam treated samples were significantly more firmer than the control samples they were not as firm as just the MAP treated samples. In fact, the eBeam + MAP treatment reduced the firmness of the samples. Neither the eBeam treatment nor the eBeam + MAP treatment had any observable effect on strawberry firmness immediately after treatment on Day 0 (Table 5b). During storage on Days 14 and Day 21, the MAP treatment had a significant effect on strawberry firmness. The MAP treatment maintained the firmness of the strawberries compared to the other treatments even on Day 21. There was no significant effect in the different treatment on the
Table 5c Influence of eBeam processing and MAP storage conditions on tomato firmness (modulus of deformation) (N/mm). Treatment
Day 0
Control eBeam MAP eBeam+MAP
1.42 1.01 1.30 1.08
± ± ± ±
Day 7 0.19a 0.15b 0.21a 0.11b
1.06 0.80 0.83 0.91
± ± ± ±
Day 14 0.23a 0.16b,c 0.16a,c 0.15a,c
0.90 0.70 0.78 0.77
± ± ± ±
Day21 0.27a 0.22a 0.17a 0.11a
1.06 1.01 1.00 0.88
± ± ± ±
0.24a 0.24a 0.12a 0.20a
Each value is the mean of 10 replicate samples ± SD. Means in columns with different superscripts (a, b, c) represent significant differences (P < 0.05).
firmness of tomatoes (Table 5c). One could observe statistical difference between the eBeam treated samples on Day 7. However, by Day 21 there was no significant difference amongst the different treatments.
Table 4c Influence of eBeam processing and MAP storage conditions on tomato a* (red-green) and L* (whiteness-grey) color values. Treatment Control eBeam MAP eBeam+MAP Control eBeam MAP eBeam+MAP
Day 0
a* value
L* value
31.99 38.50 40.11 33.92 36.96 38.87 37.62 39.65
Day 7 ± ± ± ± ± ± ± ±
1.85b 2.52a 0.46a 3.17b 1.45b 1.80a,b 0.66a 2.05a,b
33.24 33.85 33.93 33.02 37.42 36.39 35.10 35.27
Day 14 ± ± ± ± ± ± ± ±
1.42a 1.60a 1.75a 0.73a 0.87a 1.21a,b 1.52b 1.30b
32.07 34.23 33.86 32.94 37.84 36.85 35.54 35.27
± ± ± ± ± ± ± ±
Day 21 1.09a 0.77a 2.10a 3.46a 1.06a 0.32a,b 1.70b 2.39b
31.40 30.81 31.56 35.05 36.73 34.61 36.67 35.39
± ± ± ± ± ± ± ±
3.02ab 3.38b 2.33ab 1.06a 0.73a 2.04b 1.39a,b 0.64a
Mean values shown (n = 4 sample measurements). Means in the same column with different superscript represent statistically significant differences (P < 0.05). 6
Radiation Physics and Chemistry 168 (2020) 108540
B. Smith, et al.
Table 6a Mean values of consumer scores for grapes acceptability 24 h after processing. Treatment
Appearance
Air eBeam MAP eBeam +MAP
7.49 7.29 6.29 7.34
± ± ± ±
Odor a
1.12 1.56a 2.16b 1.43a
6.20 6.17 5.74 5.94
Color ± ± ± ±
a
1.28 1.60a 1.22a 1.57a
7.06 7.37 6.09 7.09
Firmness
± ± ± ±
a
1.78 1.44a 2.12b 1.40a
7.89 7.77 7.43 7.74
± ± ± ±
Flavor a
1.02 1.11a 1.46a 1.63a
7.89 7.60 7.63 7.86
± ± ± ±
1.49a 1.17a 1.31a 1.35a
Means ± SD in column with different superscript (a, b) represent significant differences (P < 0.05). Table 6b Mean values of consumer scores for strawberry acceptability 24 h after processing. Treatment
Appearance
Air eBeam MAP eBeam+MAP
7.29 6.68 7.13 6.32
± ± ± ±
Odor
1.16a 1.38ab 1.82a 1.76b
7.74 7.16 7.24 7.08
Color ± ± ± ±
1.43a 1.13a 2.22a 1.46a
7.61 6.74 7.58 6.39
Firmness
± ± ± ±
1.24a 1.33b 2.16a 1.50b
7.53 6.84 7.00 5.95
± ± ± ±
Flavor
1.33a 1.31a 2.45a 1.72b
7.53 6.45 6.53 6.45
± ± ± ±
1.50a 1.55b 2.48b 1.69b
Means ± SD in column with different superscript (a, b) represent significant differences (P < 0.05). Table 6c Mean values of consumer scores on tomato acceptability 24 h after processing. Treatment Air eBeam MAP eBeam +MAP
Appearance 8.12 7.44 7.52 7.68
± ± ± ±
Odor a
0.97 1.16a 1.61a 1.91a
6.44 6.04 5.96 5.88
Color ± ± ± ±
a
1.45 1.43a 1.51a 1.74a
8.32 7.68 7.68 7.20
± ± ± ±
Firmness a
0.95 1.11a,b 1.55a,b 1.71b
Flavor a
7.32 ± 1.31 6.20ab ± 2.20a 6.36 ± 1.89a,b 5.84 ± 2.62b
7.20 7.32 5.72 6.40
± ± ± ±
1.41a,b 1.31a 1.99c 1.73a,b
Means ± SD in column with different superscript (a, b, c) represent significant differences (P < 0.05).
color. In the case of strawberries, all the treatments scored at 6 (acceptable) or higher for the different attributes. The control samples (stored in air), however, scored significantly (p < 0.05) higher than the other treatment groups in terms of flavor (Table 6b). There was no significant difference in the acceptability scores of the different tomato samples and the eBeam and the control samples scored greater than 7.0 in terms of appearance, flavor, and color. The tomato samples stored under MAP (without eBeam) scored significantly lower compared to the other treatments (Table 6c). Overall, however, the use of eBeam processing either by itself or in combination with MAP did not have a negative effect on the “acceptability” metrics of the consumers involved in this study. There are a number of other studies which have demonstrated that the acceptability of fruits treated with ionizing radiation by consumers is not significantly different from control samples (Yu et al., 1995; Kim and Yook, 2009; Shahbaz et al., 2013).
Modified Atmosphere Packaging provides a protective barrier from moisture loss as well as slowing the respiration rate thereby prolonging the turgidity of the samples. This could explain why the MAP treated samples were more turgid than eBeam+MAP treated samples after prolonged storage. Since we did not normalize the skin firmness data with fruit size or fruit maturity, skin firmness may only partially represent the overall texture of the fruit (Kafkas et al., 2007; Hietaranta and Linna, 1999). The strawberry samples that were treated with eBeam processing exhibited a firmness of 0.96 N/mm on Day 21 (Table 5b). This firmness were significantly (p < 0.05) less than that of the other treatments. A similar result was also reported by Ahmed et al. (1972). Though there was an empirical reduction in firmness this was not observed visually (data not included) and were still within the normal ranges of strawberry firmness of 0.5–1.41 N/mm (Hietaranta and Linna, 1999). Karlidag et al. (2009) have reported that strawberry firmness corresponds to the maturity of the fruit and thus it would be advantageous to evaluate the effects of these treatments on strawberries of similar maturity. It is generally believed that only beyond doses of 2 kGy do fruits exhibit softening. The softening that has been previously observed after higher doses of irradiation has been attributed to changes in pectin (Yu et al., 2006). Softening in fruits has been attributed to pectin breakdown (Caner et al., 2008). Overall, it can be deduced that MAP conditions of the fruits enhanced the firmness which could be linked to reduced respiration and thereby reduced pectin changes associated with softening.
4. Conclusion This study has shown that even low (≤1 kGy) eBeam doses are capable of reducing the microbial bioburden and extending the shelflife (based on microbial bioburden) of high value commodities such as red grapes, strawberries, and cherry tomatoes. The combination of MAP with eBeam processing though not always yielding a synergistic effect did, however, provide significant reduction in bioburden for example in strawberries. A major challenge to allowing a meta-analysis of literature covering the effect of MAP and ionizing irradiation is the variability in the MAP conditions used by different researchers, the produce item(s) that were studied, the specific variety and post-processing performed if any, and most importantly on the type of ionizing radiation employed. Given that the dose rate in eBeam processing is several orders of magnitude greater than cobalt-60-based gamma processing, it is not easy to delineate MAP conditions that are best suited to be used with irradiation processing. Empirical data has to be independently obtained to draw conclusions. Overall, however, the results suggest that MAP storage will have a positive effect on fruit quality over extended
3.4. Consumer acceptability Tables 6a, 6b, and 6c show the consumer acceptability rating of the eBeam treated and other treatments of grape, strawberry and tomato samples. Thirty eight volunteers were involved in the study and the scores are based on a 9 point hedonic scale. The eBeam and eBeam + MAP treated grape samples were rated at 7.0 or higher for appearance, fruit color, firmness and flavor (Table 6a). The MAP stored grape samples scored significantly lower in terms of appearance and 7
Radiation Physics and Chemistry 168 (2020) 108540
B. Smith, et al.
time. Most importantly, the use of eBeam processing either alone or in combination with MAP did not adversely affect consumers ‘acceptability scoring. The ability to reduce bioburden for up to 21 days for highly perishable commodities such as grapes, strawberries and tomatoes will be of value in the development of items for the food vending distribution channels. The ability to reduce re-stocking of vending machines is of high economic value in the vending business. These results demonstrate that the use of eBeam processing either by itself or in combination with MAP conditions will not adversely affect the quality attributes of the fruits in terms of objective and subjective sensory attributes. Since only non-thermal pathogen reduction technologies can be used with fresh produce, these results highlight the value of low dose eBeam processing to reduce the bioburden of potential vending machine items. Overall, eBeam at low doses (≤1 kGy) singly or in combination with MAP can be an approach for developing fresh produce-based healthy vending items.
28 February 2014. FDA, 2014. Code of Federal Regulations Title 21. Title 21, vol. 3 21CFR179.26. http:// www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfCFR/CFRSearch.cfm?fr=179.26 Accessed 2015 April 13. Girennavar, B., Jayaprakasha, G.K., Mclin, S.E., Yoo, K.S., Patil, B.S., 2008. Influence of electron-beam irradiation on bioactive compounds. J. Agr. Chem. 56, 10941–10946. Hietaranta, T., Linna, M.M., 1999. Penetrometric measurement of strawberry fruit firmness: device testing. Hort. Technol. 9, 103–105. Ic, E., Kottapalli, B., Maxim, J., Pillai, S.D., 2007. Beam radiation of dried fruits and nuts to reduced yeast and mold bioburden. J. Food Prot. 70, 981–985. Kafkas, E., Koşar, M., Paydaş, S., Kafkas, S., Başer, K., 2007. Quality characteristics of strawberry genotypes at different maturation stages. Food Chem. 100, 1229–1236. Kantor, L.S., Lipton, K., Manchester, A., Oliveira, V., 1997. Estimating and addressing America's food losses. Food Rev. 20, 2–12. Karlidag, H., Yildirim, E., Turan, M., 2009. Exogenous applications of salicylic acid affect quality and yield of strawberry grown under antifrost heated greenhouse conditions. J. Plant Nutr. Soil Sci. 172, 270–276. Kim, K.H., Yook, H.S., 2009. Effect of gamma irradiation on quality of kiwifruit (Actinidia deliciosa var. deliciosa cv. Hayward). Radiat. Phys. Chem. 78, 414–421. Kong, Q., Wu, A., Qi, W., Qi, R., Carter, J.M., Rasooly, R., He, X., 2014. Effect of electronbeam irradiation on blueberries inoculated with Escherichia coli and their nutritional quality and shelf life. Postharvest Biol. Technol. 95, 28–35. Lorson, B., Melgar-Quinonez, H., Taylor, C., 2009. Determinationts of fruit and vegetable intake in US children. FASEB J. 20, A1008. Majidi, H., Minaei, S., Almassi, M., Mostofi, Y., 2014. Tomato quality in controlled atmosphere storage, modified atmosphere packaging and cold storage. J. Food Sci. Technol. 51 (9), 2155–2161. Mosayyebzadeh, A., Mostofi, Y., Jomeh, Z.E., Nikkhah, M.J., Hajizadeh, H.S., 2010. Effect of modified atmosphere packaging (MAP) with increased levels of O2 on postharvest quality of Iranian 'Shahroodi' table grape. Acta Hortic. (Wagening.) 934, 207–211. Ogden, C.L., Carroll, M.D., Flegal, K.M., 2008. High body mass index for age among U.S. children and adolescents, 2003-2006. JAMMA 299, 2401–2405. Oliveira, M., Pereira, J., Cabo Verde, S., Lima, M.G., Pinto, P., de Oliveira, P.B., Junqueira, C., Marcos, H., Silva, T., Melo, R., Santos, C.N., Botelho, M.L., 2013. Evaluation of potential of gamma radiation as a conservation treatment for blackberry fruits. J. Berry Res. 3, 93–102. Overby, N.C., Klepp, K.I., Bere, E., 2012. Introduction of a school fruit program is associated with reduced frequency of consumption of unhealthy snacks. Am. J. Clin. Nutr. 96, 1100–1110. Pillai, S., Bogran, C., Blackburn, C., 2013. Ionizing irradiation for phytosanitary applications and fresh produce safety. In: Hoorfar, J. (Ed.), Global Safety of Fresh Produce. Wiley-Blackwell, pp. 221–222. Ryes, L.F., Cisneros-Zevallos, L., 2007. Electron-beam ionizing radiation stress effects on mango fruit (Mangifera indica L) antioxidant constituents before and during postharvest storage. J. Agric. Food Chem. 55, 6132–6139. Sandhya, S., 2010. Modified atmosphere packaging of fresh produce: current status and future needs. LWT - Food Sci. Technol. 43, 381–392. Schmidt, H.M., Palekar, M.P., Maxim, J.E., Castillo, A., 2006. Improving the microbiological quality and safety of fresh-cut tomatoes by low-dose electron beam irradiation. J. Food Prot. 69, 575–581. Shahbaz, H.M., Ahn, J.J., Akram, K., Kim, H.Y., Park, E.J., Kwon, J.H., 2013. Chemical and sensory quality of fresh pomegranate fruits exposed to gamma radiation as quarantine treatment. Food Chem. 145, 312–318. Shayanfar, S., 2013. Modified atmosphere packaging for fresh produce. In: Hoorfar, J. (Ed.), Global Safety of Fresh Produce. Wiley-Blackwell, pp. 175–186. https://doi.org/ 10.1533/9781782420279.3.175. Shurong, L., Meixu, G., Chuanyao, W., 2006. Use of irradiation to ensure hygenic quality of fresh pre-cut and balanched vegetables and tofu. In: Use of Irradiation to Ensure the Hygienic Quality of Fresh, Pre-cut Fruits and Vegetables and Other Minimally Processed Food of Plant Origin, Joint FAO/IAEA Program of Nuclear Techniques in Food and Agriculture, Islamabd, Pakistan, pp. 87–105. Valero, D., Guillen, F., Martinez-Romero, D., 2008. A novel active packaging to maintain quality and increase shelf life and safety. Acta Hortic. (Wagening.) 858, 281–286. Van Calenberg, S., Van Cleemput, O., Mondelaers, W., Huyghebaert, A., 1999. Comparison of the effect of X-ray and electron beam irradiation on the microbiological quality of foodstuffs. Food Sci. Technol. Lett. 32 (6), 372—376. Vanndy, M., Buntong, B., Acedo, J.A., Weinberger, K., 2008. Modified atmosphere packaging to improve shelf life of tomato fruit in Cambodia. Acta Hortic. (Wagening.) 804, 453–458. Yu, L., Reitmeier, C.A., Gleason, M.L., Nonnecke, G.R., Olson, D.G., Gladon, R.J., 1995. Quality of electron beam irradiated strawberries. J. Food Sci. 60, 1084–1087. Yu, L., Reitmeier, C.A., Love, M.H., 2006. Strawberry texture and pectin content as affected by electron beam irradiation. J. Food Sci. 61 (4), 844–846.
Acknowledgements We are grateful to Mickey Speakmon, Facility Manager at the eBeam Center for all his efforts and assistance to deliver precise and uniform doses to the samples. This work was supported by the USDA-NIFA Hatch grant H-8708 awarded to Texas A&M AgriLife Research and by the IAEA as part of the IAEA Coordinated Research Project titled, “Use of irradiation for shelf-stable sterile foods for immunocompromised patients and other specific target groups” (CRP-D62009). Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.radphyschem.2019.108540. References Ahmed, E., Dennison, R., Fluck, R., 1972. Textural properties of stored and irradiated tioga strawberries. J. Texture Stud. 3, 80–88. Andrews, W.H., Hammack, T.S., 2003. BAM: food sampling and preparation of sample homogenate. In: Bacteriological Analytical Manual. FDA. Artes-Hernandez, F., Tomas-Barberan, F.A., Artes, F., 2006. Postharvest Biol. Technol. 39 (2), 146–154. Barth, M., Hankinson, T.R., Zhuang, H., Breidt, F., 2009. Microbial spoilage of fruits and vegetables. In: Sperber, W.H., Doyle, M.P. (Eds.), Compendium of the Microbiological Spoilage of Foods and Beverages, Food Microbiology and Food Safety. Springer, pp. 135–183. Brackett, R.E., 1994. Microbiological spoilage and pathogens in minimally processed refrigerated fruits and vegetables. In: Wiley, R. (Ed.), Minimally Processed Refrigerated Fruits and Vegetables. Chapman & Hall, New York. Cabo Verde, S., Trigo, M.J., Sousa, M.B., Ferreira, A., Ramos, A.C., Nunes, I., Junqueira, C., Melo, R., Santos, P.M.P., Botelho, M.L., 2013. Effects of gamma radiation on raspberries: safety and quality issues. J. Toxicol. Environ. Health Part A: 76 (4-5), 291–302. Caner, C., Aday, M.S., Demir, M., 2008. Extending the quality of fresh strawberries by equilibrium modified atmosphere packaging. Eur. Food Res. Technol. 227, 1575–1583. CDC, 2015. Healthy vneding machine initiatives in State facilities. Available at: http:// www.cdc.gov/obesity/stateprograms/pdf/healthy_vending_machine_initiatives_in_ state_facilities.pdf Accessed 2015 April 12. ChangeLab Solutions, 2012. Making change, A guide to healtheir vending for municipalities, ChangeLab Solutions. available at: http://changelabsolutions.org/sites/ default/files/MakingChange_HealthierVending_Guide_FINAL_20120806.pdf Accessed 2015 April 13. FAO, 2013. The state of food and agriculture. Food Agric. Organ U. N. Rome. 2013 Available in: http://www.fao.org/docrep/018/i3300e/i3300e.pdf, Accessed date:
8
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Preserving fresh fruit quality by low-dose electron beam processing for vending distribution channels
T
Bianca Smith1, Shima Shayanfar2, Rosemary Walzem, Christine Z. Alvarado, Suresh D. Pillai∗ National Center for Electron Beam Research, An IAEA Collaborating Centre for Electron Beam Technology, Texas A&M University, College Station, TX, 77845, USA
A R T I C LE I N FO
A B S T R A C T
Keywords: Electron beam Vending Fruits Bioburden Consumer
Food vending is estimated to be a $20 billion industry in the United States. There is an untapped business opportunity to positively influence nutrition and health by positioning fresh fruits and vegetable items as healthy vending items in vending machines. The hypothesis was that low dose (≤1 kGy) electron beam (eBeam) processing, alone or, in combination with Modified Atmosphere Packaging (MAP) is effective for developing fresh produce-based vending items. Shelf-life, sensory attributes, and consumer acceptability are key metrics for healthy vending items. The experimental objectives were to evaluate low dose eBeam (≤1 kGy) processing alone or along with MAP for red grapes, cherry tomatoes, and strawberries for reducing bioburden, while maintaining sensory attributes and consumer acceptability scores. The eBeam treatment at ≤ 1 kGy alone, or in combination with MAP suppressed bioburden by at least 1 to 2 log units over 21 day refrigerated storage as compared to untreated control samples. eBeam processing did not adversely affect the color or the firmness of the fruits. A consumer taste panel did not find any significant difference (P ≥ 0.05) in acceptability of eBeam processed fruits (compared to untreated samples) in terms of appearance, odor, color, firmness and flavor. Overall, the results suggest that eBeam at low doses (≤1 kGy) alone or in combination with MAP can be a unique approach for developing healthy vending items.
1. Introduction In today's society we are battling nutrition and obesity concerns usually blamed on the lack of time and an abundance of convenience foods. Convenience foods sold via vending machines and convenience stores are particularly high in sugar, sodium, and saturated fat. There is an un-tapped opportunity to improve the nutritional choices available in convenience foods offered through vending machines and in convenience stores. The food vending industry in the US is estimated to be around $20 billion (Pillai et al., 2013). Approximately 23 million children in the U.S. are either obese or overweight because of poor dietary habits (Ogden et al., 2008). Mexico has a 33% adult obesity rate higher than the US (FAO, 2013). A vast majority of school-aged children do not consume the recommended amounts of fruits and vegetables (Overby et al., 2012; Lorson et al., 2009). Thus, there is an untapped business opportunity to positively influence nutrition and health by positioning fruits and vegetable in the vending machine distribution channel, particularly in schools, universities, workplaces, and public areas.
Consumer acceptability, sensory attributes, and extended shelf-life are key quality metrics for healthy vending items (ChangeLab Solutions, 2012; CDC, 2015). Electron beam (eBeam) processing is an FDA approved non-thermal food processing technology that is suitable for processing fresh produce. The FDA has set an upper dose limit of ≤1 kGy for all fresh produce for shelf-life extension applications in the US (FDA, 2014). The underlying hypothesis was that low dose eBeam (≤1 kGy) processing can be used to develop fresh fruit and vegetable based healthy vending items. Additionally, our hypothesis was that consumers will rate eBeam (≤1 kGy) treated items as “acceptable” in specific sensory metrics. The overall objective was to employ eBeam at low doses (≤1 kGy) to document the reduction in the natural bioburden of cherry tomatoes, red grapes, and strawberries and empirically determine the sensory and consumer acceptability scores of the treated fruits. An additional objective was to evaluate the utility of Modified Atmosphere Packaging (MAP) in combination with eBeam processing to reduce the natural bioburden of the fruit samples for healthy vending.
∗
Corresponding author. 418B, Kleberg Center, MS 2472 College Station, Texas, 77843-2472, USA. E-mail address: [email protected] (S.D. Pillai). 1 currently at Nutraceutical Systems International, Austin, TX. 2 currently at Califia Farms, CA, USA. https://doi.org/10.1016/j.radphyschem.2019.108540 Received 19 June 2019; Received in revised form 2 September 2019; Accepted 21 October 2019 Available online 22 October 2019 0969-806X/ © 2019 Elsevier Ltd. All rights reserved.
Radiation Physics and Chemistry 168 (2020) 108540
B. Smith, et al.
2.3. Bioburden analysis
Table 1 The gas composition of the Modified Atmosphere Packaging (MAP) conditions used in the study. Fruit
Oxygen %
CO2%
Nitrogen %
Strawberry Grape Tomato
5 5 5
15 3 0
80 92 95
The eBeam processed and non-eBeam processed (control) samples were stored refrigerated for up to 21 days. The samples were analyzed for Total (aerobic) Plate Counts (TPC) and Yeasts and Molds (YM) on day 0, 1, 3, 7, 14, and 21. However, for reasons of brevity only results from days 0, 7 and 21 are reported. The FDA BAM (Bacterial Analytical Manual) protocols were used (Andrews and Hammack, 2003) were processing the samples and enumeration. Briefly, each 50g sample was aseptically transferred into a sterile stomacher bag with filter containing 450 ml of Butterfield's Phosphate Buffer (BPB) (Sigma Chemical CO, St. Louis, MO). The samples were homogenized for 2 min using a stomacher (Seward 350, London, UK) on the “normal” speed setting. The samples were then serially diluted in BPB and 0.1 mL aliquots were spread plated onto Plate Count Agar for enumeration of TPC and Sabouraud's Dextrose agar (SDA) for YM. All plates were incubated at 28 °C for 5 days prior to enumeration, and the microbial data was expressed as log CFU/g.
2. Materials and methods 2.1. Fruit samples and packaging Red grapes (Vitis vinifera), strawberries (Fragaria ananassa), and cherry tomatoes (Solanum lycopersicum var. cerasiforme) were purchased from a local farmers’ market in College Station, Texas to obtain samples with minimal or no disinfectant washing or other post-harvest processing. The fruit samples were refrigerated until they were apportioned into 50 g sub-samples under aseptic conditions. The 50g samples were placed in polyethylene clamshells (Sambrailo, Santa Maria, CA) for each treatment in triplicate. For the MAP treatment, the clamshells were placed within poly nylon vacuum bags (ULINE, Ontario, CA). The bags were flushed multiple times and filled with the appropriate gas mixture (Praxair, Danbury, CT), and then heat sealed using a commercial sealer (Accu-Seal, San Marcos, CA). The MAP gas mixtures used in this study (Table 1) were based primarily on a previous study (Sandhya, 2010). Two independent experiments were performed on separate days. Each of the experiments was replicated three times.
2.4. Sensory measurements Color Measurements: The surface color of grapes, strawberries and tomatoes, grapes, and strawberries were measured using a Minolta Color Meter (Chroma Meter CR-310, Minolta, Tokyo, Japan). The instrument was calibrated using the white calibration plate (Calibration Plate CR-A43, Minolta Cameras, Osaka, Japan). Color values of L* (lighness-darkness), ± a* (red-green) and b* (yellow-blue) were measured four times for each sample at each sampling time point and the average values were recorded. Texture Analysis: The fruits’ firmness and textural changes between treatments were measured using the texture analyzer (model TA-XT2i, Texture Technologies Corp., Scarsdale, NY). The analysis was performed on the equatorial region of 10 samples. The texture analysis setup parameters are listed in Table 3. The modulus of deformation (N/ mm), force (N), distance (mm) and work to rupture (N.mm) were recorded for all the samples.
2.2. Low dose eBeam processing The packaged samples were transported on blue ice for eBeam processing at the National Center for Electron Beam Research (NCEBR) on the Texas A&M University campus in College Station, Texas. The NCEBR is a USDA-APHIS certified facility to treat fruits and vegetables at low (≤1 kGy) doses. A linear accelerator (15 kW, 10 MeV) was used for delivering the low eBeam doses from top and bottom. Detailed dosemapping studies were initially performed to ensure that the measured doses in the fruit samples were ≤ 1 kGy (Table 2). To achieve the low dose (≤1 kGy), the beam energy was attenuated using a defined number of plywood (total height 25.8 cm) attenuators. The delivered doses were measured using alanine dosimetry and the E-Scan spectrometer (Bruker-BioSpin., Billerica, MA). To ensure accurate dosing with each processing run, “speed checks” were performed on a subset of samples. For each “speed check”, two alanine dosimeters were placed within the fruit on either ends. An X-Acto knife™ was used to create the cavities within the fruit in which the dosimeters (placed in tiny moisture-impermeable, heat-sealed pouches) were placed. It was critically important to measure the dose within the fruit rather than just on the top or bottom of the packages. Two such “speed checks” were used prior to each eBeam processing run. The eBeam processing table's speed was so adjusted to target the eBeam dose as close to 1.0 kGy as experimentally possible but without exceeding 1.0 kGy. All samples were stored on blue-ice prior to and after eBeam processing.
2.5. Consumer acceptability scoring The consumer acceptability studies were performed using procedures approved by the Texas A&M University's IRB procedures (TAMU IRB Protocol # 2012-0463). Thirty- eight untrained volunteers from the university student, staff and faculty community participated in the consumer acceptance portion of this study. The fruit samples were used in consumer acceptance studies no later than 24 h of eBeam processing. Each treatment was assigned a random 3-digit code to reduce bias of sample treatments. Plastic cups were labeled with the random 3-digit numbers in which the fruit samples were placed. The fruit samples were prepared as follows. The strawberries were de-capped and cut into halves. The grapes were removed from the bunch and 2 equal sized grapes were placed in each cup. One cherry tomato was placed in each cup. Each sample was served to the consumer one at a time and they were given salt-less Saltine™ crackers and double deionized water to cleanse their palate in between tastings. The panelists were asked to rate each fruit sample on the following acceptability attributes namely odor, color, flavor and texture using a 9-point hedonic scale ranging from “extremely dislike” to “extremely like”.
Table 2 Example dose distributions on top and bottom of the fruit samples measured during dose-mapping procedures. Stacks of plywood (25.8 cm) sheets were used to attenuate the 10 MeV linac beam energy to achieve doses ≤ 1 kGy. Sample Grape Strawberry Tomato
Dose Top 0.82 0.96 0.84
2.6. Data analysis As mentioned previously, two independent experiments were performed on separate days. Each of these experiments was replicated three times. The microbial data are non-parametric since the natural microbial populations of independent samples were analyzed. The raw microbial data were converted to log10 CFU/50 gm to represent the bioburden in each of the samples that were packaged. Data from the 6
Bottom 0.99 0.98 0.91
2
Radiation Physics and Chemistry 168 (2020) 108540
B. Smith, et al.
Table 3 Parameters employed in the fruit texture analysis. Fruit
Strawberry Grape Tomato
Parameters
Trigger
Pre-test speed (mm/s)
Test speed (mm/s)
Post test speed (mm/s)
Distance (mm)
Data acquisition rate (pps)
Load cell (Kg)
5 5 5
5 1 1
5 5 5
5 5 7
200 200 200
25 25 25
Probe 5 mm spherical 2 mm flat 2 mm flat
Force(N) 0.05 0.05 0.05
tomatoes under both ambient packaging and MAP conditions respectively. The scatter plot data from Day 0 (immediately after eBeam treatment), Day 7, and Day 21 are presented. The grape samples had the lowest initial bioburden levels. Immediately after eBeam processing (Day 0) there was a 0.9 log difference between the TPC counts of the control (untreated) and eBeam processed samples which was significantly different (P < 0.05). Though there was no significant difference between the ambient packaged eBeam and untreated samples at the end of the 21 days study period, there was a significant (P < 0.05) difference between the ambient packaged and MAP packaged samples. This was the case irrespective of whether the grapes were eBeam treated or not. Grape samples stored under MAP conditions had TPC and YM that were for the most part below detection limits (Fig. 1). The ability of MAP conditions to increase shelf-life has been previously reported (Shayanfar, 2013; Mosayyebzadeh et al., 2010; ArtesHernandez et al., 2006; Valero et al., 2008). In the case of strawberries, there was no significant difference between the eBeam treated and untreated samples at the beginning of the study (P > 0.05). However by Day 21, the MAP + eBeam treated samples had significantly lower (P < 0.05) YM counts compared to the untreated samples (Fig. 2).
replicates were combined and presented as column scatter plots values with the median values highlighted. The software, GraphPad Prism (GraphPad Software, Inc.,) was used for data presentation. Samples that had below detection limit (5 × 103 CFU/50g) are represented as 5 × 103 CFU/50g. The eBeam processed and control samples (for both the ambient and MAP conditions) were statistically compared for Days 0 and 21 using the Mann-Whitney test. Statistical analyses were performed using SigmaPlot ver 12. (SigmaPlot, Inc). For the consumer acceptability studies, the data was analyzed using the General Linear Model Procedure in Statistical Analysis System (SAS 9.3, 2001). The mean values are reported, and the differences in the mean values were compared by ANOVA and LSD. The differences in the treatments were considered significant when P < 0.05. 3. Results and discussion 3.1. Bioburden analysis Figs. 1–3 shows the influence that low dose eBeam processing has on the bioburden (TPC and YM) of red grapes, strawberries and cherry
Fig. 1. Scatter plots of the bioburden (total aerobic plate count (TPC) and yeast and molds (YM) counts) on days 0, 7 and 21 after grapes were untreated (control), electron beam (eBeam) treated , Modified Atmosphere (MAP) packaged and MAP packaged+eBeam and stored under refrigerated conditions. The horizontal line represents the median bioburden value based on the 6 replicate samples that are shown. 3
Radiation Physics and Chemistry 168 (2020) 108540
B. Smith, et al.
Fig. 2. Scatter plots of the bioburden (total aerobic plate count (TPC) and yeast and molds (YM) counts) on days 0, 7 and 21 after strawberries were untreated (control), electron beam (eBeam) treated , Modified Atmosphere (MAP) packaged and MAP packaged+eBeam and stored under refrigerated conditions. The horizontal line represents the median bioburden value based on the 6 replicate samples that are shown.
conditions may need further optimization to achieve synergism when combined with eBeam processing. Low dose eBeam processing was not expected to eliminate the microbial bioburden. We have previously shown that a dose greater than 1.0 kGy would be generally required to reduce fungal bioburden by just 90% (Ic et al., 2007). This could possibly explain why the fungal reduction was not as pronounced as that of the TPC. There are recent reports on the efficacy of low dose (between 0.5 kGy and 2.0 kGy) eBeam processing on fruits (Oliveira et al., 2013; Cabo Verde et al., 2013; Kong et al., 2014), These studies further highlight the value of eBeam processing for reducing the bioburden of such fruits to enhance their shelf-life. In the present study, low dose eBeam processed fruits under both ambient and MAP conditions were shown to achieve lower median levels of bacterial and fungal bioburden even after 21 days of storage. The bioburden reduction that can be achieved with eBeam processing can be significant from an economic stand-point. It is estimated that approximately 19 million pounds of fresh fruits are lost annually due to spoilage, of which microbial spoilage plays a major role (Kantor et al., 1997; Brackett, 1994). Barth et al. (2009) has reported that loss of shelf-life results in approximately 30–50% shrinkage of fresh-cut fruits. Thus, using eBeam at low doses to achieve even a 0.5–1.0 log reductions in bioburden could translate to significant economic returns. The ability of 1 kGy eBeam dose to reduce or eliminate microbial pathogens on fresh produce is also worthy of investigation.
Physical evidence of spoilage (i.e. fungal growth) was present on some of the untreated samples on day 21 while the eBeam treated samples did not exhibit such fungal growth (data not included). The synergistic effect of MAP + eBeam processing on fungal loads is evident in the case of strawberries. Combined application of MAP and eBeam synergistically reduced the YM bioburden levels. There was no significant difference (P > 0.05) when the treatments that did not involve eBeam processing were statistically analyzed. This result suggests that the eBeam treatment is effective at controlling fungal populations on strawberries. The ability to retard visible fungal mycelia up to 21 days is noteworthy since strawberries are commodities with limited shelflife. , The use of eBeam technology to increase shelf-life and to eliminate/reduce pathogens is of high value (Yu et al., 1995; Van Calenberg et al., 1999). With regards to tomatoes, there was no statistically significant difference in bioburden between the 1.0 kGy eBeam treated and untreated samples either at the beginning of the study (Day 0) or at the end of 21 days (Fig. 3). These results are in agreement with a previous report (Schmidt et al., 2006). The use of MAP did not offer any advantage in terms of reduced bioburden levels on tomatoes even though Majidi et al. (2014) have previously reported that tomato quality can be maintained better under MAP conditions than just ambient cold storage. Overall, eBeam treatment reduced the median levels of TPC and YM (between 0.5 and 1.0 log units) immediately after processing. During the course of the 21 day refrigerated storage, the eBeam processed grape and strawberry samples showed consistently lower TPC and YM levels under both MAP and ambient-packaged conditions. The results indicate that one should not assume that the combination of MAP and eBeam would always have synergistic effect. In these studies, the synergism was noticed only in the case of strawberries (Fig. 2). These results suggest that the MAP
3.2. Color analysis The synergistic effect of eBeam + MAP on the red color can be observed on the Day14 grape samples (Table 4a). By Day 21, the MAP 4
Radiation Physics and Chemistry 168 (2020) 108540
B. Smith, et al.
Fig. 3. Scatter plots of the bioburden (total aerobic plate count (TPC) and yeast and molds (YM) counts) on days 0, 7 and 21 after tomatoes were untreated (control), electron beam (eBeam) treated , Modified Atmosphere (MAP) packaged and MAP packaged+eBeam and stored under refrigerated conditions. The horizontal line represents the median bioburden value based on the 6 replicate samples that are shown.
Unlike the grape samples, the strawberry samples did not show elevated redness immediately after eBeam treatment (Table 4b). There was no significant difference in the redness at Day 0 (just after eBeam treatment). However, by Day 7, the MAP and eBeam + MAP treated samples were significantly redder than the other samples. Even at Day 21, the MAP (with and without eBeam) stored samples were redder than the non-MAP samples (Table 4b). MAP seemed to have a stronger effect on redness of strawberries than eBeam treatment since these values tended to be higher when subjected to this treatment. The reported L values for different treatments did not indicate any significant difference even at different storage periods. In the case of tomatoes, there was no discernable pattern in the treatment effects of eBeam or MAP on tomatoes redness either immediately after treatment (Day 0) or Day 21 (Table 4c). On Day 21, there was a significant difference in the redness of the eBeam treated
treated and the eBeam + MAP treated grape samples were significantly more red (p < 0.05) than the non-MAP treated grape samples. The effect of eBeam treatment on the grape samples was observed only until Day 7. However, this difference in the redness was not observed after 21 days of storage. At Day 21, the only treatment that had a significant effect was storage under MAP conditions (with or without eBeam). Grapes stored under MAP conditions were significantly redder than samples stored under ambient refrigerated conditions. There was a significant (P < 0.05) difference in the L* values among the different treatments. The samples treated with eBeam were lighter than the other treatment groups in color until the seventh day of storage. However, this value changed over 21 days of storage leading to solely MAP stored grapes to be lighter in color than the other samples, while there was no significant differences (p > 0.05) reported in the other three treatment.
Table 4a Influence of eBeam processing and MAP storage conditions on grape a* (red-green) and L* (whiteness-grey) color values. Treatment Control eBeam MAP eBeam+MAP Control eBeam MAP eBeam+MAP
a* value
L* value
Day 0
Day 7
Day 14
Day 21
7.33 ± 0.57b 12.20 ± 1.59a 9.67 ± 0.66b 10.92 ± 1.72a 25.91 ± 0.70a 31.06 ± 1.17b 27.49 ± 1.74a 25.83 ± 1.77a
9.55 ± 0.83a 10.36 ± 1.11b 9.82 ± 0.30b 8.72 ± 0.31b 26.17 ± 2.29a,b 26.85 ± 0.52a 23.35 ± 0.58b 23.53 ± 0.66b
7.76 ± 0.47a 7.21 ± 0.76a 9.59 ± 1.03a 7.36 ± 0.47b 25.33 ± 1.04a 24.39 ± 7.23a 25.90 ± 0.31a 24.39 ± 0.66a
6.48 ± 0.40b 7.14 ± 0.81b 10.38 ± 0.59a 11.22 ± 1.23a 23.78 ± 0.70a 24.18 ± 1.20a 27.22 ± 0.41b 24.44 ± 0.51a
Mean values shown (n = 4 sample measurements). Means in the same column with different superscript represent statistically significant differences (P < 0.05). 5
Radiation Physics and Chemistry 168 (2020) 108540
B. Smith, et al.
Table 4b Influence of eBeam processing and MAP storage conditions on strawberry a* (red-green) and L* (whiteness-grey) color values. Treatment Control eBeam MAP eBeam+MAP Control eBeam MAP eBeam+MAP
Day 0
a* value
L* value
36.12 38.39 43.25 43.20 45.01 41.29 42.80 44.69
Day 7 ± ± ± ± ± ± ± ±
a
25.44 21.88 32.84 33.11 41.49 46.44 40.41 40.05
9.32 10.32a 8.23a 4.67a 5.23a 9.98a 6.11a 6.58a
Day 14 ± ± ± ± ± ± ± ±
b
6.83 10.80b 13.44a 10.41a 2.60a 8.31a 4.52a 2.71a
27.23 26.78 35.16 36.20 33.89 33.08 39.75 44.90
Day 21
± ± ± ± ± ± ± ±
a
1.49 4.09a 3.60a 9.17a 3.42b 1.79b 3.82b 8.00a
23.17 28.41 37.95 40.77 36.58 39.12 39.60 45.76
10.17b 6.91b 8.36a 8.33a 7.93a 8.39a 6.31a 6.12a
± ± ± ± ± ± ± ±
Mean values shown (n = 4 sample measurements). Means in the same column with different superscript represent statistically significant differences (P < 0.05).
tomatoes compared to the eBeam + MAP treated tomatoes. However, there was no discernable differences in the samples between the other treatments (Table 4c). Vanndy et al. (2008) and Majidi et al. (2014) have reported that MAP conditions delayed the ripening process and thereby reduced redness. Shurong et al. (2006) also found that samples irradiated at doses above 0.5 kGy had a significantly higher red color during days 2 and 4 of storage. This could be due to an increase in lycopene experienced in tomatoes that undergo irradiation. The activation of enzymes for secondary metabolites during eBeam processing has been reported before. Previous studies at our university have shown that mangoes respond to eBeam processing in a dose dependent manner by triggering the phenylpropanoid metabolism (Ryes and Cisneros-Zevallos, 2007; Girennavar et al., 2008). Altogether it can be interpreted that the color in strawberries is not affected by either of the treatment groups, in grapes and tomatoes, eBeam appears to be parameter influencing color. However, beyond seven days of storage, MAP storage influences color more than any other treatment. Nevertheless, the use of eBeam processing at low doses to enhance color via accumulation of phytochemicals can be a value-addition of eBeam processing.
Table 5a Influence of eBeam processing and MAP storage conditions on grape firmness (modulus of deformation) (N/mm). Treatment Control eBeam MAP eBeam+MAP
Day 0 0.70 0.79 0.72 0.62
± ± ± ±
Day 7 a
0.18 0.14a 0.29a 0.13a
0.46 0.50 0.69 0.46
± ± ± ±
Day 14 a
0.14 0.15a 0.14b 0.23a
0.16 0.15 0.19 0.17
Day 21
± ± ± ±
a
0.10 0.08a 0.08a 0.04a
0.18 0.79 1.02 0.26
± ± ± ±
0.09c 0.24b 0.22a 0.13b
Each value is the mean of 9–12 replicate samples ± SD. Means in columns with different superscripts (a, b, c) represent significant difference (P < 0.05). Table 5b Influence of eBeam processing and MAP storage conditions on strawberry firmness (modulus of deformation) (N/mm). Treatment
Day 0
Control eBeam MAP eBeam+MAP
6.27 6.70 7.07 6.62
± ± ± ±
Day 7 1.73a 3.03a 1.10a 1.10a
2.97 3.19 6.40 3.09
± ± ± ±
Day 14 1.73a 1.40a 1.95b 1.09a
1.58 2.13 6.03 2.41
± ± ± ±
Day 21 1.10a 1.68a 1.44b 0.70a
1.84 0.96 3.38 1.56
± ± ± ±
1.44b 2.70c 1.19a 1.95b,c
Each value is the mean of 10 replicate samples ± SD. Means in columns with different superscripts (a, b, c) represent significant difference (P < 0.05).
3.3. Texture analysis Immediately after the eBeam treatment, there was no significant difference in the firmness of either the grape or strawberry samples (Tables 5a and 5b). The effect of MAP on the firmness of the grape samples is observable on Day 7. On Day 21 it is very evident that the control samples were not as firm as any of the other treatments (Table 5a). Though the eBeam treated samples were significantly more firmer than the control samples they were not as firm as just the MAP treated samples. In fact, the eBeam + MAP treatment reduced the firmness of the samples. Neither the eBeam treatment nor the eBeam + MAP treatment had any observable effect on strawberry firmness immediately after treatment on Day 0 (Table 5b). During storage on Days 14 and Day 21, the MAP treatment had a significant effect on strawberry firmness. The MAP treatment maintained the firmness of the strawberries compared to the other treatments even on Day 21. There was no significant effect in the different treatment on the
Table 5c Influence of eBeam processing and MAP storage conditions on tomato firmness (modulus of deformation) (N/mm). Treatment
Day 0
Control eBeam MAP eBeam+MAP
1.42 1.01 1.30 1.08
± ± ± ±
Day 7 0.19a 0.15b 0.21a 0.11b
1.06 0.80 0.83 0.91
± ± ± ±
Day 14 0.23a 0.16b,c 0.16a,c 0.15a,c
0.90 0.70 0.78 0.77
± ± ± ±
Day21 0.27a 0.22a 0.17a 0.11a
1.06 1.01 1.00 0.88
± ± ± ±
0.24a 0.24a 0.12a 0.20a
Each value is the mean of 10 replicate samples ± SD. Means in columns with different superscripts (a, b, c) represent significant differences (P < 0.05).
firmness of tomatoes (Table 5c). One could observe statistical difference between the eBeam treated samples on Day 7. However, by Day 21 there was no significant difference amongst the different treatments.
Table 4c Influence of eBeam processing and MAP storage conditions on tomato a* (red-green) and L* (whiteness-grey) color values. Treatment Control eBeam MAP eBeam+MAP Control eBeam MAP eBeam+MAP
Day 0
a* value
L* value
31.99 38.50 40.11 33.92 36.96 38.87 37.62 39.65
Day 7 ± ± ± ± ± ± ± ±
1.85b 2.52a 0.46a 3.17b 1.45b 1.80a,b 0.66a 2.05a,b
33.24 33.85 33.93 33.02 37.42 36.39 35.10 35.27
Day 14 ± ± ± ± ± ± ± ±
1.42a 1.60a 1.75a 0.73a 0.87a 1.21a,b 1.52b 1.30b
32.07 34.23 33.86 32.94 37.84 36.85 35.54 35.27
± ± ± ± ± ± ± ±
Day 21 1.09a 0.77a 2.10a 3.46a 1.06a 0.32a,b 1.70b 2.39b
31.40 30.81 31.56 35.05 36.73 34.61 36.67 35.39
± ± ± ± ± ± ± ±
3.02ab 3.38b 2.33ab 1.06a 0.73a 2.04b 1.39a,b 0.64a
Mean values shown (n = 4 sample measurements). Means in the same column with different superscript represent statistically significant differences (P < 0.05). 6
Radiation Physics and Chemistry 168 (2020) 108540
B. Smith, et al.
Table 6a Mean values of consumer scores for grapes acceptability 24 h after processing. Treatment
Appearance
Air eBeam MAP eBeam +MAP
7.49 7.29 6.29 7.34
± ± ± ±
Odor a
1.12 1.56a 2.16b 1.43a
6.20 6.17 5.74 5.94
Color ± ± ± ±
a
1.28 1.60a 1.22a 1.57a
7.06 7.37 6.09 7.09
Firmness
± ± ± ±
a
1.78 1.44a 2.12b 1.40a
7.89 7.77 7.43 7.74
± ± ± ±
Flavor a
1.02 1.11a 1.46a 1.63a
7.89 7.60 7.63 7.86
± ± ± ±
1.49a 1.17a 1.31a 1.35a
Means ± SD in column with different superscript (a, b) represent significant differences (P < 0.05). Table 6b Mean values of consumer scores for strawberry acceptability 24 h after processing. Treatment
Appearance
Air eBeam MAP eBeam+MAP
7.29 6.68 7.13 6.32
± ± ± ±
Odor
1.16a 1.38ab 1.82a 1.76b
7.74 7.16 7.24 7.08
Color ± ± ± ±
1.43a 1.13a 2.22a 1.46a
7.61 6.74 7.58 6.39
Firmness
± ± ± ±
1.24a 1.33b 2.16a 1.50b
7.53 6.84 7.00 5.95
± ± ± ±
Flavor
1.33a 1.31a 2.45a 1.72b
7.53 6.45 6.53 6.45
± ± ± ±
1.50a 1.55b 2.48b 1.69b
Means ± SD in column with different superscript (a, b) represent significant differences (P < 0.05). Table 6c Mean values of consumer scores on tomato acceptability 24 h after processing. Treatment Air eBeam MAP eBeam +MAP
Appearance 8.12 7.44 7.52 7.68
± ± ± ±
Odor a
0.97 1.16a 1.61a 1.91a
6.44 6.04 5.96 5.88
Color ± ± ± ±
a
1.45 1.43a 1.51a 1.74a
8.32 7.68 7.68 7.20
± ± ± ±
Firmness a
0.95 1.11a,b 1.55a,b 1.71b
Flavor a
7.32 ± 1.31 6.20ab ± 2.20a 6.36 ± 1.89a,b 5.84 ± 2.62b
7.20 7.32 5.72 6.40
± ± ± ±
1.41a,b 1.31a 1.99c 1.73a,b
Means ± SD in column with different superscript (a, b, c) represent significant differences (P < 0.05).
color. In the case of strawberries, all the treatments scored at 6 (acceptable) or higher for the different attributes. The control samples (stored in air), however, scored significantly (p < 0.05) higher than the other treatment groups in terms of flavor (Table 6b). There was no significant difference in the acceptability scores of the different tomato samples and the eBeam and the control samples scored greater than 7.0 in terms of appearance, flavor, and color. The tomato samples stored under MAP (without eBeam) scored significantly lower compared to the other treatments (Table 6c). Overall, however, the use of eBeam processing either by itself or in combination with MAP did not have a negative effect on the “acceptability” metrics of the consumers involved in this study. There are a number of other studies which have demonstrated that the acceptability of fruits treated with ionizing radiation by consumers is not significantly different from control samples (Yu et al., 1995; Kim and Yook, 2009; Shahbaz et al., 2013).
Modified Atmosphere Packaging provides a protective barrier from moisture loss as well as slowing the respiration rate thereby prolonging the turgidity of the samples. This could explain why the MAP treated samples were more turgid than eBeam+MAP treated samples after prolonged storage. Since we did not normalize the skin firmness data with fruit size or fruit maturity, skin firmness may only partially represent the overall texture of the fruit (Kafkas et al., 2007; Hietaranta and Linna, 1999). The strawberry samples that were treated with eBeam processing exhibited a firmness of 0.96 N/mm on Day 21 (Table 5b). This firmness were significantly (p < 0.05) less than that of the other treatments. A similar result was also reported by Ahmed et al. (1972). Though there was an empirical reduction in firmness this was not observed visually (data not included) and were still within the normal ranges of strawberry firmness of 0.5–1.41 N/mm (Hietaranta and Linna, 1999). Karlidag et al. (2009) have reported that strawberry firmness corresponds to the maturity of the fruit and thus it would be advantageous to evaluate the effects of these treatments on strawberries of similar maturity. It is generally believed that only beyond doses of 2 kGy do fruits exhibit softening. The softening that has been previously observed after higher doses of irradiation has been attributed to changes in pectin (Yu et al., 2006). Softening in fruits has been attributed to pectin breakdown (Caner et al., 2008). Overall, it can be deduced that MAP conditions of the fruits enhanced the firmness which could be linked to reduced respiration and thereby reduced pectin changes associated with softening.
4. Conclusion This study has shown that even low (≤1 kGy) eBeam doses are capable of reducing the microbial bioburden and extending the shelflife (based on microbial bioburden) of high value commodities such as red grapes, strawberries, and cherry tomatoes. The combination of MAP with eBeam processing though not always yielding a synergistic effect did, however, provide significant reduction in bioburden for example in strawberries. A major challenge to allowing a meta-analysis of literature covering the effect of MAP and ionizing irradiation is the variability in the MAP conditions used by different researchers, the produce item(s) that were studied, the specific variety and post-processing performed if any, and most importantly on the type of ionizing radiation employed. Given that the dose rate in eBeam processing is several orders of magnitude greater than cobalt-60-based gamma processing, it is not easy to delineate MAP conditions that are best suited to be used with irradiation processing. Empirical data has to be independently obtained to draw conclusions. Overall, however, the results suggest that MAP storage will have a positive effect on fruit quality over extended
3.4. Consumer acceptability Tables 6a, 6b, and 6c show the consumer acceptability rating of the eBeam treated and other treatments of grape, strawberry and tomato samples. Thirty eight volunteers were involved in the study and the scores are based on a 9 point hedonic scale. The eBeam and eBeam + MAP treated grape samples were rated at 7.0 or higher for appearance, fruit color, firmness and flavor (Table 6a). The MAP stored grape samples scored significantly lower in terms of appearance and 7
Radiation Physics and Chemistry 168 (2020) 108540
B. Smith, et al.
time. Most importantly, the use of eBeam processing either alone or in combination with MAP did not adversely affect consumers ‘acceptability scoring. The ability to reduce bioburden for up to 21 days for highly perishable commodities such as grapes, strawberries and tomatoes will be of value in the development of items for the food vending distribution channels. The ability to reduce re-stocking of vending machines is of high economic value in the vending business. These results demonstrate that the use of eBeam processing either by itself or in combination with MAP conditions will not adversely affect the quality attributes of the fruits in terms of objective and subjective sensory attributes. Since only non-thermal pathogen reduction technologies can be used with fresh produce, these results highlight the value of low dose eBeam processing to reduce the bioburden of potential vending machine items. Overall, eBeam at low doses (≤1 kGy) singly or in combination with MAP can be an approach for developing fresh produce-based healthy vending items.
28 February 2014. FDA, 2014. Code of Federal Regulations Title 21. Title 21, vol. 3 21CFR179.26. http:// www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfCFR/CFRSearch.cfm?fr=179.26 Accessed 2015 April 13. Girennavar, B., Jayaprakasha, G.K., Mclin, S.E., Yoo, K.S., Patil, B.S., 2008. Influence of electron-beam irradiation on bioactive compounds. J. Agr. Chem. 56, 10941–10946. Hietaranta, T., Linna, M.M., 1999. Penetrometric measurement of strawberry fruit firmness: device testing. Hort. Technol. 9, 103–105. Ic, E., Kottapalli, B., Maxim, J., Pillai, S.D., 2007. Beam radiation of dried fruits and nuts to reduced yeast and mold bioburden. J. Food Prot. 70, 981–985. Kafkas, E., Koşar, M., Paydaş, S., Kafkas, S., Başer, K., 2007. Quality characteristics of strawberry genotypes at different maturation stages. Food Chem. 100, 1229–1236. Kantor, L.S., Lipton, K., Manchester, A., Oliveira, V., 1997. Estimating and addressing America's food losses. Food Rev. 20, 2–12. Karlidag, H., Yildirim, E., Turan, M., 2009. Exogenous applications of salicylic acid affect quality and yield of strawberry grown under antifrost heated greenhouse conditions. J. Plant Nutr. Soil Sci. 172, 270–276. Kim, K.H., Yook, H.S., 2009. Effect of gamma irradiation on quality of kiwifruit (Actinidia deliciosa var. deliciosa cv. Hayward). Radiat. Phys. Chem. 78, 414–421. Kong, Q., Wu, A., Qi, W., Qi, R., Carter, J.M., Rasooly, R., He, X., 2014. Effect of electronbeam irradiation on blueberries inoculated with Escherichia coli and their nutritional quality and shelf life. Postharvest Biol. Technol. 95, 28–35. Lorson, B., Melgar-Quinonez, H., Taylor, C., 2009. Determinationts of fruit and vegetable intake in US children. FASEB J. 20, A1008. Majidi, H., Minaei, S., Almassi, M., Mostofi, Y., 2014. Tomato quality in controlled atmosphere storage, modified atmosphere packaging and cold storage. J. Food Sci. Technol. 51 (9), 2155–2161. Mosayyebzadeh, A., Mostofi, Y., Jomeh, Z.E., Nikkhah, M.J., Hajizadeh, H.S., 2010. Effect of modified atmosphere packaging (MAP) with increased levels of O2 on postharvest quality of Iranian 'Shahroodi' table grape. Acta Hortic. (Wagening.) 934, 207–211. Ogden, C.L., Carroll, M.D., Flegal, K.M., 2008. High body mass index for age among U.S. children and adolescents, 2003-2006. JAMMA 299, 2401–2405. Oliveira, M., Pereira, J., Cabo Verde, S., Lima, M.G., Pinto, P., de Oliveira, P.B., Junqueira, C., Marcos, H., Silva, T., Melo, R., Santos, C.N., Botelho, M.L., 2013. Evaluation of potential of gamma radiation as a conservation treatment for blackberry fruits. J. Berry Res. 3, 93–102. Overby, N.C., Klepp, K.I., Bere, E., 2012. Introduction of a school fruit program is associated with reduced frequency of consumption of unhealthy snacks. Am. J. Clin. Nutr. 96, 1100–1110. Pillai, S., Bogran, C., Blackburn, C., 2013. Ionizing irradiation for phytosanitary applications and fresh produce safety. In: Hoorfar, J. (Ed.), Global Safety of Fresh Produce. Wiley-Blackwell, pp. 221–222. Ryes, L.F., Cisneros-Zevallos, L., 2007. Electron-beam ionizing radiation stress effects on mango fruit (Mangifera indica L) antioxidant constituents before and during postharvest storage. J. Agric. Food Chem. 55, 6132–6139. Sandhya, S., 2010. Modified atmosphere packaging of fresh produce: current status and future needs. LWT - Food Sci. Technol. 43, 381–392. Schmidt, H.M., Palekar, M.P., Maxim, J.E., Castillo, A., 2006. Improving the microbiological quality and safety of fresh-cut tomatoes by low-dose electron beam irradiation. J. Food Prot. 69, 575–581. Shahbaz, H.M., Ahn, J.J., Akram, K., Kim, H.Y., Park, E.J., Kwon, J.H., 2013. Chemical and sensory quality of fresh pomegranate fruits exposed to gamma radiation as quarantine treatment. Food Chem. 145, 312–318. Shayanfar, S., 2013. Modified atmosphere packaging for fresh produce. In: Hoorfar, J. (Ed.), Global Safety of Fresh Produce. Wiley-Blackwell, pp. 175–186. https://doi.org/ 10.1533/9781782420279.3.175. Shurong, L., Meixu, G., Chuanyao, W., 2006. Use of irradiation to ensure hygenic quality of fresh pre-cut and balanched vegetables and tofu. In: Use of Irradiation to Ensure the Hygienic Quality of Fresh, Pre-cut Fruits and Vegetables and Other Minimally Processed Food of Plant Origin, Joint FAO/IAEA Program of Nuclear Techniques in Food and Agriculture, Islamabd, Pakistan, pp. 87–105. Valero, D., Guillen, F., Martinez-Romero, D., 2008. A novel active packaging to maintain quality and increase shelf life and safety. Acta Hortic. (Wagening.) 858, 281–286. Van Calenberg, S., Van Cleemput, O., Mondelaers, W., Huyghebaert, A., 1999. Comparison of the effect of X-ray and electron beam irradiation on the microbiological quality of foodstuffs. Food Sci. Technol. Lett. 32 (6), 372—376. Vanndy, M., Buntong, B., Acedo, J.A., Weinberger, K., 2008. Modified atmosphere packaging to improve shelf life of tomato fruit in Cambodia. Acta Hortic. (Wagening.) 804, 453–458. Yu, L., Reitmeier, C.A., Gleason, M.L., Nonnecke, G.R., Olson, D.G., Gladon, R.J., 1995. Quality of electron beam irradiated strawberries. J. Food Sci. 60, 1084–1087. Yu, L., Reitmeier, C.A., Love, M.H., 2006. Strawberry texture and pectin content as affected by electron beam irradiation. J. Food Sci. 61 (4), 844–846.
Acknowledgements We are grateful to Mickey Speakmon, Facility Manager at the eBeam Center for all his efforts and assistance to deliver precise and uniform doses to the samples. This work was supported by the USDA-NIFA Hatch grant H-8708 awarded to Texas A&M AgriLife Research and by the IAEA as part of the IAEA Coordinated Research Project titled, “Use of irradiation for shelf-stable sterile foods for immunocompromised patients and other specific target groups” (CRP-D62009). Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.radphyschem.2019.108540. References Ahmed, E., Dennison, R., Fluck, R., 1972. Textural properties of stored and irradiated tioga strawberries. J. Texture Stud. 3, 80–88. Andrews, W.H., Hammack, T.S., 2003. BAM: food sampling and preparation of sample homogenate. In: Bacteriological Analytical Manual. FDA. Artes-Hernandez, F., Tomas-Barberan, F.A., Artes, F., 2006. Postharvest Biol. Technol. 39 (2), 146–154. Barth, M., Hankinson, T.R., Zhuang, H., Breidt, F., 2009. Microbial spoilage of fruits and vegetables. In: Sperber, W.H., Doyle, M.P. (Eds.), Compendium of the Microbiological Spoilage of Foods and Beverages, Food Microbiology and Food Safety. Springer, pp. 135–183. Brackett, R.E., 1994. Microbiological spoilage and pathogens in minimally processed refrigerated fruits and vegetables. In: Wiley, R. (Ed.), Minimally Processed Refrigerated Fruits and Vegetables. Chapman & Hall, New York. Cabo Verde, S., Trigo, M.J., Sousa, M.B., Ferreira, A., Ramos, A.C., Nunes, I., Junqueira, C., Melo, R., Santos, P.M.P., Botelho, M.L., 2013. Effects of gamma radiation on raspberries: safety and quality issues. J. Toxicol. Environ. Health Part A: 76 (4-5), 291–302. Caner, C., Aday, M.S., Demir, M., 2008. Extending the quality of fresh strawberries by equilibrium modified atmosphere packaging. Eur. Food Res. Technol. 227, 1575–1583. CDC, 2015. Healthy vneding machine initiatives in State facilities. Available at: http:// www.cdc.gov/obesity/stateprograms/pdf/healthy_vending_machine_initiatives_in_ state_facilities.pdf Accessed 2015 April 12. ChangeLab Solutions, 2012. Making change, A guide to healtheir vending for municipalities, ChangeLab Solutions. available at: http://changelabsolutions.org/sites/ default/files/MakingChange_HealthierVending_Guide_FINAL_20120806.pdf Accessed 2015 April 13. FAO, 2013. The state of food and agriculture. Food Agric. Organ U. N. Rome. 2013 Available in: http://www.fao.org/docrep/018/i3300e/i3300e.pdf, Accessed date:
8