Effect of X-Ray Treatments on Pathogenic Bacteria,Inherent Microbiota,Color,and Texture on Parsley Leaves

Abstract

This work is a part of systematic studies of the effect of X-ray treatments on fresh produce. The main objective of this investigation was to study the effects of X-ray treatments in reducing the concentration of artificially inoculated Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica, and Shigella flexneri, and inherent microbiota on parsley leaves. The secondary objective was to study the effects of X-ray treatments on color and texture parameters on treated parsley leaves. The Dip-inoculated method was used to inoculate parsley leaves with a mixture of two or three strains of each tested organism at 10⁸ to 10⁹ colony-forming unit (CFU)/mL; the inoculated parsley leaves were then air-dried and followed by treatment with different doses of X-ray (0, 0.1, 0.5, 1.0, and 1.5 kGy) at 22°C and 55–60% relative humidity. Surviving bacterial populations on parsley leaves were evaluated using a nonselective medium (tryptic soy agar) with a selective medium overlay for each bacterium: E. coli O157:H7 (CT-SMAC agar), L. monocytogenes (MOA), and S. enterica and S. flexneri (XLD). Approximately 5.8, 3.1, 5.7, and 5.2 log CFU reductions of E. coli O157:H7, L. monocytogenes, S. enterica, and Shigella flexneri were achieved by treatment with 1.0 kGy X-ray, respectively. Furthermore, the populations of E. coli O157:H7, L. monocytogenes, S. enterica, and Shigella flexneri were reduced to less than the detectable limit (1.0 log CFU/g) by treatment with 1.5 kGy X-ray. Treatment with 1.5 kGy X-ray significantly reduced the initial inherent microbiota on parsley leaves, and inherent levels were significantly (p<0.05) lower than the control sample throughout refrigerated storage for 30 days. No significant differences (p>0.05) in color or texture of control and treated samples with 0.1–1.5 X-ray were observed. The results of investigation indicated that X-ray is an effective technology to eliminate E. coli O157:H7, L. monocytogenes, S. enterica, and Shigella flexneri, and to extend the shelf life of parsley leaves.

Introduction

L eafy green vegetables/herbs are important components of a healthy diet. Parsley is rich in flavonoids (apiin, apigenin, crisoeriol, and luteolin), vitamins (A, beta-carotene, C, E, and B), minerals (potassium, calcium, manganese, iron, and magnesium), and dietary fiber, which helps control blood cholesterol levels, prevents constipation, and protects the body from free-radical mediated injury and from cancers (Kaur and Kapoor, 2001). The World Health Organization, Food and Agricultural Organization, and the U.S. Department of Agriculture all recommend that consumers eat more vegetables to decrease the risk of cardiovascular diseases and cancer (Allende et al., 2006). As a result, the U.S. consumption of fresh produce increased by 27% from 1970 to 1993 (NACMCF, 1999). As produce consumption has increased, there has been a significant increase in the number of foodborne disease outbreaks associated with produce (Corbo et al., 2006). Leafy green vegetables can be contaminated with pathogenic and spoilage bacteria during production from many sources, including irrigation water and manure fertilizers, and during food processing by contaminated equipment and food handlers (Martinez-Sanchez et al., 2006; Mahmoud and Linton, 2008).

In the last two decades, more than 72 foodborne illness outbreaks were associated with the consumption of fresh produce contaminated with norovirus, Escherichia coli O157:H7, Salmonella spp., and other pathogens. For leafy greens, there have been 26 outbreaks attributed to E. coli O157:H7 alone (FDA, 2008). Outbreaks of shigellosis associated with chopped parsley occurred in four states in the United States and in two Canadian provinces in 1998 (Wu et al., 2000). As a result of these outbreaks, more attention has been dedicated to the microbial safety of leafy green vegetables (Martinez-Sanchez et al., 2006). Chlorinated water is widely used to wash and decontaminate produce; however, its effectiveness is limited to 1–2 log colony-forming unit (CFU) reduction for most pathogenic and spoilage bacteria (Virto et al., 2005). Therefore, the food industry is interested in utilizing new effective sanitation technologies in order to meet consumer demands and produce safer raw fruit and vegetables (Allende et al., 2004).

Ionizing radiation has the potential to ensure the safety and quality of leafy greens (Niemira and Fan, 2008). In August 2008, FDA allowed using ionizing irradiation for iceberg lettuce and spinach. The previous studies demonstrated that X-ray can result in very high microbial efficacy (>5 log reduction) for different pathogens on spinach leaves, iceberg lettuce, tomatoes, milk, ready-to-eat shrimp, oysters, and cantaloupe (Mahmoud, 2009a,b,c, 2010a,b, 2012; Mahmoud and Burrage 2009; Mahmoud et al., 2010).

The main objective of this study was to investigate the reduction of E. coli O157:H7, Listeria monocytogenes, Salmonella enterica, and Shigella flexneri on artificially inoculated parsley leaves using X-ray treatments. The second goal was to study the effect of X-ray on the inherent microbiota counts of parsley leaves during storage at 5°C for 30 days. The third goal was to study the effect of X-ray on the color and texture of treated parsley leaves using Hunter colorimeter and Instron texture machines, respectively.

Materials and Methods

Parsley

Fresh parsley leaves (during a day after being harvested) were purchased at a local supermarket (Pascagoula, MS) the day before the experiments and stored at 5°C until use.

Bacterial strains and growing conditions

Four bacteria mixtures were used, including (1) a three-strain mixture of E. coli O157:H7 (C7927, EDL933, and 204P); (2) a three-strain mixture of Listeria monocytogenes (Scott A, F5069, and LCDC 81-861); (3) a three-serotype mixture of Salmonella enterica (Salmonella Poona, Salmonella Montevideo, and Salmonella Typhimurium); and (4) a two-strain mixture of Shigella flexneri (ATCC 9199 and ATCC 12022). These strains were selected based on their prevalence in produce, association with produce foodborne outbreaks, and for their resistance to antimicrobial treatments (Mahmoud et al., 2008). All bacterial strains were obtained from ATCC or from our personal culture collection. Bacterial strains were grown in Tryptic Soy Broth with 0.6% Yeast Extract (TSBYE; Difco–Becton Dickinson, Sparks, MD) and incubated at 37°C for 24h prior to use. Three or two strains of each bacterium were mixed with an equal volume (5 mL each) to give approximately 10⁷ to 10⁹ CFU/mL.

Inoculation of parsley leaves

The dip-inoculated method was used to inoculate parsley leaves (10 g leaves/100 mL inoculation solution), separately, with a mixture of two or three strains of each tested organism (approximately 8–9 log/mL). The parsley leaves were drained (for 30 s) to remove the extra inoculation solution then air-dried at 22°C for 30 min (to allow bacterial attachment; it was obvious that the 30-min drying, after draining, was enough to dry the parsley leaves to the normal status prior to the dip inoculation) in the biosafety cabinet prior to X-ray treatments.

Treatment of inoculated parsley leaves with X-ray

Specific irradiation doses (0.1, 0.5, 1.0, and 1.5 kGy) were generated using the RS 2400 industrial cabinet X-ray irradiator (Rad Source Technologies, Alpharetta, GA) according to Mahmoud (2009a). The X-ray doses in the treatment chamber were determined using a dosimeter (Rad Source Technologies). Inoculated parsley leaves were placed into plastic clamshell containers (size, 7″×5″×2″; Monte Package Company, Riverside, MI), wrapped in PVC film (AEP Industries Inc., South Hackensack, NJ), inside the exposure chamber. Samples were treated with 0.1, 0.5, 1.0, and 1.5 kGy X-ray at 22°C and 55–60% relative humidity. At each examined dose, samples were pulled from the exposure chamber for microbial enumeration to determine surviving cell populations.

Microbial enumeration

Two controls were used; an uninoculated and untreated control was used to determine background microbiota and pathogen levels if they were present. An inoculated and untreated control was used for comparisons with inoculated-treated samples. Both controls, as well as the inoculated and treated parsley leaves samples (10 g), were mixed with 90 mL of 0.1% sterilized peptone water in a sterile 200-mL stomaching bag (Fisher Scientific, Pittsburgh, PA) and homogenized for 2 min using a Stomacher 80 Lab-blender (Stomacher 400; Seward, London, UK). Serial 10-fold dilutions were prepared in 0.1% peptone water (Difco– Becton Dickinson). Surviving bacterial populations on parsley leaves were evaluated using a nonselective medium (tryptic soy agar [TSA]) for 6 h (it was important to use TSA for 6 h to support the injured cells after treatment with X-ray) (McCarthy et al., 1998) with the appropriate selective medium overlay for each bacteria: for Escherichia coli O157:H7 (Cefixime Potassium Tellurite Sorbitol–MacConkey Agar [CT-SMAC]), for Listeria monocytogenes (Modified Oxford Agar [MOA]), and for Salmonella enterica and Shigella flexneri (xylose lysine deoxycholate agar [XLD]). Plates were then incubated for an additional 18 h at 37°C. Colonies were counted, and the results were expressed as log CFU/g.

D-value determination

A first-order kinetic model (linear model) was used to analyze the data for log of surviving organisms per treatment dose (Mahmoud et al., 2007). The D-values (X-ray dose required for a 90% reduction) were determined using survival data for 0, 0.1, 0.5, 1.0, and 1.5 kGy X-ray during treatment. D-value analyses were performed using Microsoft Excel for Microsoft Windows XP (Microsoft, Redmond, WA).

Effect of X-ray on the inherent microbiota count of parsley leaves during storage at 5°C for 30 days

Fresh parsley leaves were used for this microbiota counts study. The untreated (control) parsley and the samples treated with the lowest (0.1 kGy) and highest (1.5 kGy) X-ray were packaged separately into plastic clamshell containers (Monte Package Company), wrapped in PVC film (AEP Industries Inc.), and stored at 5^OC for 30 days. Samples were withdrawn from the refrigerator at 0, 5, 10, 15, 20, 25, and 30 days, and microbiota counts were determined.

The microbiological analyses for aerobic mesophilic bacteria, for aerobic psychrotrophic bacteria, and for yeast and mold were examined, according to Mahmoud et al. (2007). For each determination, 25-g samples of parsley leaves were homogenized for 2 min using a Stomacher 80 Lab-blender (Stomacher 400; Seward) with 225 mL of sterilized 0.1% peptone water (Difco Laboratories, Sparks, MD). Serial dilutions (10⁻¹ to 10⁻⁶) were prepared from the homogenate with 0.1% sterilized peptone water. For mesophilic counts, 0.1/1.0 mL of each dilution was plated onto TSA and incubated at 37°C for 24 h. For psychrotrophic counts, 0.1/1.0 mL of each dilution was plated onto TSA and incubated at 5°C for 10 days. For yeast and mold counts, 0.1/1.0 mL of each dilution was plated onto acidified potato dextrose agar (PDA; Difco–Becton Dickinson) and incubated at 25°C for 5 days. Viable counts were expressed as log CFU/g.

Effect of X-ray on the color and texture of parsley leaves

Parsley leaves were treated with 0.1, 0.5, 1.0, and 1.5 kGy X-ray at 22°C and 55–60% relative humidity. At each examined dose, samples were pulled from the exposure chamber for instrumentally quality analysis. The color was evaluated using the Hunter (L*, a*, and b*) colorimeter values (LabScan XE Hunter Colorimeter; Hunter Associates Laboratory, Inc., Reston, VA). The texture was also measured by a puncture test using an Instron 4944 (Instron, Norwood, MA). The instrumental settings and operations were accomplished using the software Bluehill Materials Testing Software (Bluehill 3, version 3.13, 2010; Instron). On the test day, parsley leaves were punctured with a cylindrical probe (10 mm diameter). Crosshead speed was set at 50 mm/min. Force-distance curves were obtained from the puncture tests, and texture was taken as the force (N) required to puncture parsley leaves (20 g of parsley leaves were placed in 5×5 cm Instron puncture room) for a distance of 4.8 cm.

Statistical analysis

All experiments were replicated three times using two samples of parsley leaves per experiment for a total of six data points per treatment. Data were pooled, and the mean values and standard deviations were determined. Differences between samples were determined using a Student's t-test, with Microsoft Excel (for Microsoft Windows XP) and were considered to be significant when p<0.05.

Results and discussion

Inactivation of E. coli O157:H7, L. monocytogenes, S. enterica, and Shigella flexneri on parsley leaves by X-ray

Reduction of inoculated E. coli O157:H7, L. monocytogenes, S. enterica, and Shigella flexneri on parsley leaves after treatment with 0.0, 0.1, 0.5, 1.0, and 1.5 kGy X-ray is shown in Table 1. Population reductions of the tested pathogens were greater with increasing X-ray doses, as expected. Approximately 3.1, 0.9, 2.0, and 1.8 log CFU/g reduction of E. coli O157:H7, L. monocytogenes, S. enterica, and Shigella flexneri were achieved by treatment with 0.1 kGy X-ray, respectively. Treatment with 0.5 kGy X-ray significantly reduced the populations of E. coli O157:H7, L. monocytogenes, S. enterica, and Shigella flexneri by 5.2, 2.0, 4.4, and 3.4 log CFU/g, respectively. The populations of E. coli O157:H7, L. monocytogenes, S. enterica, and Shigella flexneri were significantly (p<0.05) reduced by 5.8, 3.1, 5.7, and 5.2 log CFU/g, respectively, after treatment with 1.0 kGy X-ray. Furthermore, the populations of E. coli O157:H7, L. monocytogenes, S. enterica, and Shigella flexneri were significantly (p<0.05) reduced to less than the detectable limit (1.0 log CFU/g) by treatment with 1.5 kGy X-ray. E. coli O157:H7 was the most sensitive pathogen to X-ray treatment. The D-value of E. coli O157:H7 was 0.50 kGy compared with 0.96, 0.52, and 0.58 kGy for L. monocytogenes, S. enterica, and Shigella flexneri on parsley leaves, respectively. These findings are in the same trend as those reported by Mahmoud et al. (2010), who reported that the D-values (kGy) of inoculated E. coli O157:H7, L. monocytogenes, S. enterica, and Shigella flexneri on spinach leaves were 1.1, 1.0, 1.2, and 0.96 kGy X-ray, respectively. Previous studies have also shown that Gram-negative bacteria were more sensitive than Gram-positive bacteria to different treatments (Rhee et al., 2003). The doses needed to reduce E. coli O157:H7, L. monocytogenes, S. enterica, and Shigella flexneri, by 5 log reduction, on parsley leaves were similar to those needed for other produce. Mahmoud (2010a) found that more than a 5 log CFU reduction of E. coli O157:H7, L. monocytogenes, S. enterica, and S. flexneri was achieved with 2.0 kGy X-ray on shredded iceberg lettuce. Similar reductions were obtained for the same pathogens on spinach leaves (Mahmoud et al., 2010).

Table 1.

Changes of Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica, and Shigella flexneri Populations (log CFU/g) on Parsley Leaves After Treatment with X-Ray Irradiation

	Treatments
Bacteria	0.0 kGy	0.1 kGy	0.5 kGy	1.0 kGy	1.5 kGy
E. coli O157:H7	8.3±0.1^a	5.2±0.1^b	3.1±0.1^c	2.5±0.3^c	ND
L. monocytogenes	6.8±0.2^a	5.9±0.1^b	4.8±0.2^c	3.7±0.4^d	ND
Salmonella enterica	8.8±0.2^a	6.8±0.1^b	4.4±0.3^c	3.1±0.1^d	ND
Shigella flexneri	8.7±0.2^a	6.9±0.1^b	5.3±0.1^c	3.5±0.3^d	ND

Mean values with different letters in same row are significantly different (p<0.05).

ND, not detectable (<1.0 log CFU/g).

This study revealed that X-ray has a stronger inactivation effect on tested pathogens than other sanitizer agents and technologies applied on leafy green vegetables. Karapinar and Gönül (1992) used different washing solutions to reduce artificially inoculated Y. enterocolitica on fresh parsley. Dipping the parsley containing 10⁷ CFU/g Y. enterocolitica into 40% (v/v) vinegar led to 3 log₁₀ cycles reduction. Pirovani et al. (2001) reported that treatment of spinach leaves with chlorinated water (125 ppm free chlorine) reduced Salmonella by a 1.4 log CFU reduction. Akbas and Olmez (2007) reported that dipping of iceberg lettuce in citric acid or lactic acid solutions of 0.5% and 1.0% for 2 or 5 min resulted in reducing of E. coli and L. monocytogenes by 1.2–2.8 log CFU/g. Changa et al. (2007) reported that treatment of inoculated lettuce (10⁷ CFU/g of E. coli O157:H7 and Salmonella enterica) with commercial vinegar containing 5% acetic acid for 5 min reduced the population of both bacteria by 3 log CFU. Less than a 1.0 log CFU reduction was observed with commercial vinegar containing 0.5% acetic acid for 5 min. Hadjok et al. (2008) studied the efficacy of ultraviolet (UV) light combined with hydrogen peroxide to inactivate Salmonella spp. on lettuce. By using the optimized parameters (1.5% H₂O₂, UV dose of 37.8 mJ cm⁻²), the Salmonella were reduced by 4.0 and 2.8 log CFU reduction on the surface and internal of lettuce leaves, respectively. Guentzel et al. (2008) reported that dipping lettuce leaves for 10 min in electrolyzed water (at 100 and 120 ppm total residual chlorine) reduced bacterial counts of Escherichia coli by 0.2 log CFU. Zhang and Farber (1996) found that aqueous chlorine dioxide (5 ppm) was only capable of reducing L. monocytogenes on lettuce by 1.7 log CFU/g.

Effect of treatment with X-ray on the inherent microbiota on treated parsley leaves during storage at 5°C for 30 days

Vegetables, including parsley, are generally colonized by a wide variety of microorganisms, including bacteria, yeasts, and fungi, which cause spoilage (Lindow and Brandle, 2003). Changes in the microbiota (mesophilic, psychrotrophic, and yeast and mold) on parsley leaves were evaluated during storage at 5°C for 30 days (Tables 2 –4). Treatment with 0.1 kGy significantly (p<0.05) reduced the initial populations of mesophilic bacteria, psychrotrophic bacteria, and yeast and mold counts on parsley leaves from 4.3, 4.6, and 2.7 log CFU/g to nondetectable (ND) level, 4.3 CFU/g, and ND level, respectively. In this study, psychrotrophic bacteria were more resistant than mesophilic bacteria at low dose (0.1 kGy); however, mesophilic bacteria showed more resistance than psychrotrophic bacteria at high dose (1.5 kGy). These results are in agreement with those obtained by Dogbevi et al. (1999).

Table 2.

Changes in the Psychrotrophic Bacterial Counts (log CFU/g) of Treated Parsley Leaves with X-Ray During Storage at 5°c for 30 Days

	Treatments
Storage time (days)	Control	0.1 kGy	1.5 kGy
0	4.6±0.29^a	4.3±0.29^a	ND
5	5.0±0.05^a	4.4±0.29^a	ND
10	5.4±0.10^a	4.5±0.15^a	ND
15	5.5±0.05^a	4.7±0.15^a	3.2±0.10^b
20	6.2±0.10^a	4.9±0.05^b	3.2±0.52^c
25	6.8±0.15^a	5.3±0.05^b	3.4±0.05^c
30	8.8±0.05^a	7.9±0.05^a	5.0±0.25^b

Mean values with different letters in same row are significantly different (p<0.05).

ND, no detectable survivors (<1.0 log CFU/g).

Table 3.

Changes in the Mesophilic Bacterial Counts (log CFU/g) of Treated Parsley Leaves with X-Ray During Storage at 5°c for 30 Days

	Treatments
Storage time (days)	Control	0.1 kGy	1.5 kGy
0	4.3±0.30^a	ND	ND
5	4.5±0.10^a	2.9±0.05^b	2.3±0.05^b
10	5.0±0.00^a	3.8±0.20^b	2.4±0.05^c
15	5.2±0.05^a	4.6±0.15^a	2.7±0.10^b
20	5.3±0.15^a	4.8±0.12^a	2.8±0.15^b
25	6.3±0.20^a	5.0±0.10^b	2.9±0.06^c
30	7.0±0.05^a	6.0±0.15^a	3.0±0.10^b

Mean values with different letters in same row are significantly different (p<0.05).

ND, no detectable survivors (<1.0 log CFU/g).

Table 4.

Changes in the Yeast and Mold Counts (log CFU/g) of Treated Parsley Leaves with X-Ray During Storage at 5°c for 30 Days

	Treatments
Storage time (days)	Control	0.1 kGy	1.5 kGy
0	2.7±0.10^a	ND	ND
5	2.9±0.11^a	ND	ND
10	3.7±0.05^a	2.4±0.35^b	ND
15	3.8±0.47^a	3.0±0.15^a	ND
20	5.2±0.15^a	3.4±0.12^b	ND
25	5.7±0.12^a	3.5±0.17^b	1.7±0.33^c
30	6.0±0.10^a	4.4±0.06^b	3.2±0.41^c

Mean values with different letters in same row are significantly different (p<0.05).

ND, no detectable survivors (<1.0 log CFU/g).

The aerobic plate counts of fresh produces are reported to range from 10³ to 10⁹ CFU/g (Szabo et al., 2000). Treatment with 1.5 kGy significantly (p<0.05) reduced the initial populations of mesophilic bacteria, psychrotrophic bacteria, and yeast and mold to less than the detectable limit (1.0 log CFU/g), as shown in Tables 2 –4, respectively.

During storage, the microbiota on parsley leaves gradually increased for untreated and treated samples; however, treated samples maintained microbial populations at a significantly lower level compared to the untreated control. Treatment with 1.5 kGy X-ray maintained the population of mesophilic, psychrotrophic, and yeast and mold under the detectable limit for 0, 10, and 20 days storage, respectively. These results are in agreement with previous studies (Mahmoud, 2010a,b; Mahmoud et al., 2010). These results show the same trend as obtained by Zhang et al. (2006), who reported that aerobic mesophilic bacteria on fresh-cut lettuce irradiated with 1.0 kGy gamma rays was reduced by 2.4 log CFU. The limited shelf life of fresh processed produce is one of the greatest problems faced by commercial marketers (Soliva-Fortuny and Martin-Belloso, 2008). The other benefit of irradiation besides ensuring the produce safety is in increasing the shelf-life of those products where shelf-life is limited by microbial action. The recommended limit for yeast and mold counts in vegetables is 5 log CFU/g so as to guarantee sensory quality (Allende et al., 2006). Taking this limit into account, the shelf life of parsley leaves was prolonged from 15 days for the control to more than 30 days for the treated sample with 1.5 kGy X-ray at 5°C and 90% RH. These results show the same trend as previous results obtained by Mahmoud (2010b), where the shelf life of tomatoes was prolonged from 6 days for the control to 20 days for the sample treated with 1.5 kGy X-ray at 22°C. Mahmoud (2010a) reported that the shelf life of shredded iceberg lettuce leaves was prolonged from 6 days for the control, to 12 days and more than 30 days for the treated sample with 0.1 and 2.0 kGy X-ray at 4°C. Mahmoud et al. (2010) found that treatment with X-ray significantly reduced the initial inherent microbiota on spinach leaves and inherent levels were significantly (p<0.05) lower than the control sample throughout refrigerated storage for 30 days at 4°C.

Effect of treatment with X-ray on the color and texture of parsley leaves

Besides microbiological analyses, control and X-ray treated samples were also submitted to the evaluation of some quality parameters (Tables 5 and 6). Changes in the color of parsley leaves were monitored by measuring lightness (L*), red–greenness (a*), and blue–yellowness (b*) by the Hunter colorimeter directly after treatment with X-ray (Table 5). Treatment with X-ray did not significantly (p>0.05) affect the color. The values of L*, a*, and b* ranged were 21–22.8, −9.5 to 9.8, and 22.2–23.521, respectively. Changes in the texture (firmness) of parsley leaves were monitored by measuring the maximum load needed for parsley samples (25 g) using Instron 4944 machine directly after treatment with X-ray (Table 6). Treatment with X-ray did not significantly (p>0.05) affect the texture. The maximum loads were 68.8, 68.0, 67.2, 8.3, and 67.0 Newton (N) for samples treated with 0.0, 0.1, 0.5, 1.0, and 1.5 kGy X-ray, respectively. These results are in agreement with those obtained by Mahmoud (2012).

Table 5.

Changes in the Color (Hunter Parameters) of Treated Parsley Leaves with Different X-Ray Doses

Treatment (kGy)	L^*	a^*	b^*
0.0	21.0±2.1	−9.5±2.1	22.3±3.0
0.1	21.1±3.0	−9.0±2.7	22.8±2.3
0.5	21.2±3.2	−9.8±2.6	23.3±3.3
1.0	22.8±2.8	−9.7±1.6	22.2±1.7
1.5	21.8±4.2	−9.4±1.8	23.5±3.2

No significant differences (p>0.05) between samples were detected. L^* , lightness; a^* , red-greenness; b^* , blue-yellowness.

Table 6.

Changes in the Texture (by a Puncture Test Using an Instron 4944) of Treated Parsley Leaves with Different X-Ray Doses

Treatment (kGy)	Maximum load (Newton)
0.0	68.8±1.8
0.1	68.0±1.0
0.5	67.2±1.0
1.0	68.3±1.7
1.5	67.0±1.2

No significant differences (p>0.05) between samples were detected.

Conclusion

In conclusion, this study is in line with our previous studies regarding the effects of X-ray irradiation on different fresh produce. The actual data of X-ray irradiation on each produce will be valuable information for future application by the produce industry. Furthermore, this is the first report that describes the effects of X-ray treatments on inoculated E. coli O157:H7, L. monocytogenes, S. enterica, and Shigella flexneri, on inherent microbiota, and on the color and texture of parsley leaves. This study indicated that X-ray treatment was very effective against the tested pathogenic bacteria and inherent microbiota, and did not negatively affect the color or texture of treated parsley leaves. The results obtained from the microbiological and quality studies indicate that X-ray irradiation could be used for preserving parsley quality and extending shelf life.

Footnotes

Acknowledgments

This paper is a journal article of the Mississippi Agriculture and Forestry Experiment Station.

Disclosure Statement

No competing financial interests exist.

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