INHIBITION OF LISTERIA MONOCYTOGENES BY NATIVE MICROFLORA OF WHOLE CANTALOUPE1

Fresh‐cut cantalcupe has been recalled due to the possible presence of Listeria monocytogenes. Several studies have reported that naturally occurring microflora of vegetable surfaces may be antagonistic to pathogen attachment, growth or survival. To test this possibility for L. monocytogenes and cantaloupes, whole melon were treated with water, ethanol (70%) or chlorine (200 ppm) to reduce the native microflora on the melon surfaces. Treated or untreated melons were immersed in a six strain cocktail of L. monocytogenes (10⁷ CFU/mL) for 10 min and then allowed to dry for 1 h inside a biosafety cabinet followed by storage at 5, 10 and 20C for 15 days. Fresh‐cut pieces prepared from the treated or untreated melons and directly inoculated with L. monocytogenes (3.48 log CFU/g) were stored under the same conditions listed above. Populations of L. monocytogenes and five classes of native microflora were investigated. Growth of L. monocytogenes in sterile or nonsterile rind and fresh‐cut homogenates was also studied. The population of L. monocytogenes recovered from inoculated (10³ to 10⁸ CFU/mL) whole melons given no disinfection treatment or washed with water was significantly less (P < 0.05) than that recovered from melons treated with chlorine or EtOH. In general, populations of L. monocytogenes declined on the surface of treated and untreated whole melons and on fresh‐cut pieces over the 15 days storage period at the temperatures tested. However, the decline in pathogen populations was less rapid in the presence of reduced populations of native microflora. Higher populations of L. monocytogenes were attained in sterile tissue homogenates than in nonsterile homogenates. Addition of yeast and mold to sterile rind homogenates was highly inhibitory to growth and survival of the pathogen. The results of this study indicate that native microflora of whole cantaloupe inhibited attachment to rind surfaces as well as survival and growth of L. monocytogenes on cantaloupe surfaces and homogenized fresh‐cut pieces. Thus, L. monocytogenes recontamination of melons having a reduced level of native microflora following application of a disinfection treatment may be a food safety concern.     

Effect of hydrogen peroxide treatment on microbial quality and appearance of whole and fresh-cut melons contaminated with Salmonella spp

The efficacy of hydrogen peroxide treatment on the inactivation of Salmonella spp. inoculated on the external surface of cantaloupe and honeydew melon was investigated. Salmonella was inoculated onto whole cantaloupe and honeydew melon to a final concentration of 4.65 log(10) CFU/cm(2) and 3.13 log(10) CFU/g, respectively. Inoculated whole melons stored at 5 degrees C for up to 7 days were washed with water, 2.5% and 5% hydrogen peroxide at day 0 and 5. Hydrogen peroxide (2.5% and 5%) treatments of whole melon for 5 min caused a 3 log(10) CFU/cm(2) reduction of the indigenous surface microflora and a 3.0 log(10) CFU/cm(2) reduction in Salmonella spp. on all melon surfaces. The efficacy of the hydrogen peroxide treatments was less when the interval between inoculation and treatment of cantaloupe exceeded 24 h. Unlike cantaloupe fresh-cut pieces, Salmonella was not recovered from fresh-cut pieces prepared from treated whole honeydew melon. Growth of Salmonella occurred in cantaloupe fresh-cut pieces stored at 10 or 20 degrees C, and by 2 weeks, levels reached approximately 1 log CFU/g. A rapid decline in appearance and overall acceptability was observed in fresh-cut pieces prepared from untreated whole cantaloupe. While Salmonella was recovered from fresh-cut pieces from and whole treated cantaloupe, sanitizing the surface of contaminated whole melons with hydrogen peroxide before and after cutting and storage of the fresh-cut pieces at 5 degrees C can enhance the microbial safety and acceptability rating for about 2 weeks after processing.     

THE SHELF-LIFE OF MINIMALLY PROCESSED FRESH CUT MELONS

Honeydew and cantaloupe melons were surface sterilized by scrubbing with a hypochlorite solution at low level (200 ppm total available chlorine) and high level (2000 ppm total available chlorine), peeled and cut into “chunks”. Fruit pieces were dipped in a dilute hypochlorite solution (pH 6) of 50 ppm total available chlorine prior to packaging under an atmosphere of 95% N₂ and 5% O₂ and storage at 2.2C. Unwashed and water-washed samples were also prepared as controls. Microbial counts and sensory analyses were monitored during a 20 day storage period. Microbial counts of unwashed and water-washed samples were found to be significantly (p≤0.05) different from the fruits which were chlorine washed initially, and during the storage time. However, increasing the free available chlorine concentration tenfold did not result in any further significant increase in the shelf-life. Rapid decline was observed in all measured microbial and sensory quality factors of unwashed samples during storage. Proper sanitation and production practices along with raw material selection can ensure a shelf-life of 15 days for cantaloupe and honeydew pieces.     

Alternative Sanitizers to Chlorine for Use on Fresh‐Cut “Galia” (Cucumis melo var. catalupensis) Melon

ABSTRACT: Chlorine is commonly used to reduce microbial load in fresh‐cut vegetables. However, the production of chlorinated organic compounds, such as trihalomethanes, which are potential carcinogens, has created the need to investigate the efficiency of nontraditional sanitizers and alternative techniques. The effects of 4 novel sanitizers were tested in fresh‐cut “Galia” melon: chlorine dioxide (ClO₂) at 3 mg/L, peracetic acid (PAA) at 80 mg/L, hydrogen peroxide (H₂O₂) at 50 mg/L, and nisin at 250 mg/L plus EDTA 100 mg/L (nisin + EDTA). A chlorine treatment (NaOCl at 150 mg/L) was used as a control. Pieces of melon were packed in polypropylene trays under passive modified atmosphere (3 to 4 kPa of O₂ and 10 to 11 kPa of CO₂) and stored up to 10 d at 5 °C. Microbial growth, firmness, respiration rate, gas composition, sensory evaluation, color, total soluble solids (TSS), and tritable acidity (TA) were evaluated at days 0, 7, and 10. The novel sanitizers PAA, H₂O₂, and nisin + EDTA, in the studied concentrations, reduced the microbial growth to a more efficient range than chlorine and ClO₂. In addition, those sanitizers delayed softness, did not affect the respiration rate, SST, or AT. The sensorial parameters were kept above the upper limit of marketability and they did not impart an “off flavor.” These sanitizers maintained quality and shelf life of fresh‐cut Galia melon for 10 d of storage at 5 °C. Nevertheless, other concentrations, in particular for ClO_2, could be tested to study an extended shelf life in melon pieces.     

Reducing Salmonella on cantaloupes and honeydew melons using wash practices applicable to postharvest handling, foodservice, and consumer preparation

Washing conditions that included a soak or brush scrub were evaluated for removal of Salmonella from the surface of smooth (honeydew) or complex (cantaloupe) melon rinds. Melon rinds were spot-inoculated onto a 2.5 cm2 area of rind (squares) with approximately 6.0 log(10) CFU/square of an avirulent nalidixic acid-resistant strain of Salmonella typhimurium. Melons were washed by immersion in 1500 ml of water or 200 ppm total chlorine and allowed to soak or were scrubbed over the entire melon surface with a sterile vegetable brush for 60 s. Inoculated sites, uninoculated sites ("next to" sites) that were adjacent to inoculated sites, and sites on the side of the melon opposite (remote sites) the inoculated site were excised and pummeled in a stomacher for 2 min prior to plating onto tryptic soy or bismuth sulfite agar supplemented with 50 microg/ml nalidixic acid. S. typhimurium was reduced on the rind of cantaloupe by 1.8 log CFU/melon after soaking for 60 s in 200 ppm total chlorine, which was significantly better than the 0.7 log CFU/melon achieved with soaking in water. For both water and 200 ppm total chlorine, scrubbing with a vegetable brush was shown to be significantly (0.9 log CFU/cantaloupe) more effective than soaking alone. When honeydew melons were soaked or scrubbed in water, reductions of 2.8 log CFU/melon or >4.6 log CFU/melon (four of five samples), respectively, were observed. However, when water treatments were used, the presence of Salmonella-positive "next to" and remote sites indicated that bacteria were spread from inoculated site on the rind to uninoculated sites either through the rinse water (40-70 CFU/ml of Salmonella) or scrub brush (400-500 CFU/brush). Transfer to other sites occurred more often with cantaloupe than honeydew melons. This transfer was eliminated when 200 ppm total chlorine was used. When 200 ppm total chlorine was used, Salmonella could not be detected in the water or on the scrub brush. For optimal microbial removal in food service and home settings, melons should be scrubbed with a clean brush under running water. However, to ensure the benefits of brushing, instructions for cleaning and sanitizing brushes must also be emphasized. For food service settings where concentration and pH can be adequately measured, the use of chlorinated water may provide additional benefit.     

Effect of nisin in combination with EDTA, sodium lactate, and potassium sorbate for reducing Salmonella on whole and fresh-cut cantaloupet

Nisin (50 microg/ml), EDTA (0.02 M, disodium salt), sodium lactate (NaL, 2%), and potassium sorbate (KS, 0.02%) were tested individually and in various combinations as sanitizer treatments for reducing Salmonella on whole and fresh-cut cantaloupe. Whole cantaloupe and fresh-cut pieces were inoculated with a five-strain cocktail of Salmonella to give 4.76 +/- 0.23 log CFU/cm2 and 3.42 +/- 0.13 log CFU/g, respectively. Inoculated whole melons and fresh-cut pieces were stored at 5 degrees C for 7 days. Washing treatments were applied to inoculated whole melons at days 0, 3, and 7 of storage, and surviving bacterial populations were determined. The effect of the washing treatments on transfer of Salmonella to fresh-cut pieces prepared immediately after treatment was also determined. Directly inoculated fresh-cut pieces were treated at day 0, and surviving bacteria were enumerated at days 0, 3, and 7 of storage. The combination treatments of nisin-EDTA, nisin-NaL, nisin-KS, NaL-KS, and nisin-NaL-KS all resulted in reductions of approximately 3 log CFU/cm2 at day 0 for whole melons. When tested alone, all compounds, along with water washes, were ineffective. After 3 and 7 days of storage, the five combination washing treatments were less effective, resulting in reductions of approximately 2 log CFU/cm2. None of the combination treatments completely eliminated transfer of pathogen survivors to fresh-cut pieces. The combination treatments nisin-NaL, nisin-KS, NaL-KS, and nisin-NaL-KS, but not nisin-EDTA, gave significant (P < 0.05) reductions of Salmonella directly inoculated onto fresh-cut pieces. Washing with nisin-NaL-KS was significantly (P < 0.05) more effective than the other three combination treatments, resulting in a reduction of 1.4 CFU/g. Inhibition by the four effective treatments carried over from day 0 through day 7 of storage, with no increase in the population of Salmonella on the stored fresh-cut pieces. Sensory evaluations indicated that treatment of fresh-cut pieces with nisin-NaL and NaL-KS, but not nisin-KS or nisin-NaL-KS, were acceptable in terms of appearance, odor, and overall acceptability. After the required regulatory approval, treatment of whole cantaloupe with nisin in combination with EDTA, NaL, KS, or NaL and KS and of fresh-cut pieces with nisin-NaL or NaL-KS could help ensure the microbiological safety of fresh-cut cantaloupe.     

Behavior of Listeria monocytogenes inoculated on cantaloupe surfaces and efficacy of washing treatments to reduce transfer from rind to fresh-cut pieces

Attachment and survival of Listeria monocytogenes on external surfaces (rind) of inoculated cantaloupe, resistance of the surviving bacteria to chlorine or hydrogen peroxide treatments, transfer of the pathogen from unsanitized and sanitized rinds to fresh-cut tissues during cutting and growth, and survival of L. monocytogenes on fresh-cut pieces of cantaloupe were investigated. Surface treatment with 70% ethanol to reduce the native microflora on treated melon, followed by immersion in a four-strain cocktail of L monocytogenes (10(8) CFU/ml) for 10 min, deposited 4.2 log10 CFU/cm2 and 3.5 log10 CFU/cm2 of L monocytogenes on treated and untreated cantaloupe rinds, respectively. L. monocytogenes survived on the treated or untreated cantaloupe rinds for up to 15 days during storage at 4 and 20 degrees C, but populations declined by approximately 1 to 2 log10 CFU/cm2. Fresh-cut pieces prepared from inoculated whole cantaloupes stored at 4 degrees C for 24 h after inoculation were positive for L. monocytogenes. Washing inoculated whole cantaloupes in solutions containing 1,000 ppm of chlorine or 5% hydrogen peroxide for 2 min at 1 to 15 days of storage at 4 degrees C after inoculation resulted in a 2.0- to 3.5-log reduction in L. monocytogenes on the melon surface. Fresh-cut pieces prepared from the sanitized melons were negative for L. monocytogenes. After direct inoculation onto fresh-cut pieces, L. monocytogenes survived, but did not grow, during 15 days of storage at 4 degrees C. Growth was evident by 4 h of storage at 8 and 20 degrees C. It is concluded that sanitizing with chlorine or hydrogen peroxide has the potential to reduce or eliminate the transfer of L. monocytogenes on melon surfaces to fresh-cut pieces during cutting.     

Use of hydrogen peroxide in combination with nisin, sodium lactate and citric acid for reducing transfer of bacterial pathogens from whole melon surfaces to fresh-cut pieces

Hydrogen peroxide (2.5%) alone or hydrogen peroxide (1%) in combination with nisin (25 microg/ml), sodium lactate (1%), and citric acid (0.5%) (HPLNC) were investigated as potential sanitizers for reducing Escherichia coli O157:H7 or Listeria monocytogenes populations on whole cantaloupe and honeydew melons. Whole cantaloupes inoculated with E. coli O157:H7 and L. monocytogenes at 5.27 and 4.07 log10 CFU/cm2, respectively, and whole honeydew melons inoculated with E. coli O157:H7 and L. monocytogenes at 3.45 and 3.05 log10 CFU/cm2, respectively, were stored at 5 degrees C for 7 days. Antimicrobial washing treatments were applied to inoculated whole melons on days 0 or 7 of storage and surviving bacterial populations and the numbers transferred to fresh-cut pieces were determined. At days 0 and 7 treatment with HPLNC significantly (p<0.05) reduced the numbers of both pathogens, by 3 to 4 log CFU/cm2 on both types of whole melon. Treatment with HPLNC was significantly (p<0.05) more effective than treatment with 2.5% hydrogen peroxide. While fresh-cut pieces prepared from stored whole melons were negative for the pathogens by both direct plating and by enrichment, fresh-cut pieces from cantaloupe melons treated with 2.5% hydrogen peroxide were positive for both pathogens and pieces from honeydew melons were positive for E. coli 0157:H7. The native microflora on fresh-cut melons were also substantially reduced by HPLNC treatment of whole melons. The results suggest that HPLNC could be used to decontaminate whole melon surfaces and so improve the microbial safety and quality of fresh-cut melons.     

Effect of cutting and storage on sensory traits of cantaloupe melon cultivars with extended postharvest shelf life

Fresh cut cantaloupe melons (Cucumis melo L var reticulatus) from fruits with extended postharvest shelf life were analysed for changes in their volatile aroma compounds and polygalacturonase activity during storage. The total volatile aroma contents and the number of volatile compounds in fruits with extended shelf life were significantly less than those present in the traditional shelf life cultivar Mission. Esters were the major volatile compounds present in the fruits, and their concentrations decreased considerably with storage of the cut fruit for 24 h at 4 °C. Polygalacturonase activity was detected from measurements of the hydrolytic release of reducing groups after storage of the cut fruit for 3 days. Enzymatic activity decreased thereafter in all fruits. The results indicate a lack of correlation between the postharvest shelf life of whole cantaloupe and that of fresh cut fruit. © 2003 Society of Chemical Industry     

1‐Methylcyclopropene effects on temporal changes of aroma volatiles and phytochemicals of fresh‐cut cantaloupe

BACKGROUND: Orange‐fleshed cantaloupe melons have intense aroma and flavor but are very perishable during storage life. Fresh‐cut processing enhances ethylene‐mediated quality losses. Post‐cutting 1‐methylcyclopene (1‐MCP) application to fresh‐cut cantaloupe was evaluated for its effects on quality attributes, phytochemical content and aroma volatiles. RESULTS: Fresh‐cut cantaloupe (Cucumis melo var. cantalupensis ‘Fiesta’) cubes treated with 1.0 µL L^?1 of 1‐MCP for 24 h at 5 °C, packaged in vented plastic clamshells and stored under normal atmosphere at 5 °C for 9 days, preserved their soluble solids, total phenolics, total carotenoids and β‐carotene contents, but significant softening occurred. A significant increase of non‐acetate esters and a decrease of aldehydes occurred during storage. Most quality attributes of fresh‐cut cantaloupe were unaffected by the treatment with 1‐MCP. 1‐MCP‐treated fresh‐cut cantaloupe accumulated higher levels of propyl acetate, 2‐methylbutyl acetate, methyl butanoate, methyl 2‐methyl butanoate, methyl hexanoate, 2‐methylbutyl alcohol and phenethyl alcohol, and lower levels of benzyl alcohol and heptanal than untreated controls. CONCLUSION: Post‐cutting treatment with 1‐MCP affected nine of the flavor‐important volatiles, particularly those derived from the amino acids isoleucine and phenylalanine, but had no practical effect on phytochemicals or other quality attributes. © 2012 Society of Chemical Industry     

Synergistic antibacterial effect of nisin,ethylenediaminetetraacetic acid,and sulfite on native microflora of fresh white shrimp during ice storage

This study aims to investigate the effectiveness of using nisin, ethylenediaminetetraacetic acid (EDTA), and sulfite alone or in combination in reducing Vibrio parahaemolyticus, Salmonella enterica, and Pseudomonas fluorescens in broth and native microflora on raw Pacific white shrimp during ice storage. Nisin (50 ppm), EDTA (20 mM), alone or in combination were used to test on the growth of V. parahaemolyticus, S. enterica, and P. fluorescens in broth. Nisin (50 ppm), EDTA (20 mM), sodium metabisulfite (1.25 and 0.625%), ice; alone or in combination were used on shrimps during 1°C storage for 10 days. Microbial and chemical changes were analyzed during shrimp storage. First, the combination of nisin and EDTA exhibited antibacterial effects against V. parahaemolyticus, S. enterica, and P. fluorescens in broth. Second, in shrimp preservation, the combination of nisin, EDTA, and sulfite at a low dose of 0.625% exhibited higher antimicrobial activity than did a high dose of sulfite (1.25%). Based on aerobic bacteria counts, psychrotrophic bacteria, and TVB-N, shrimp treatment with combination of nisin, EDTA, and low-dose sulfite were still acceptable within 10 days of storage. Based on our findings, nisin and EDTA can be used to reduce uses of sulfite for shrimp preservation in the future.     

Effect of vacuum-steam-vacuum treatment on microbial quality of whole and fresh-cut cantaloupe

Minimally processed fruits and vegetables have a limited shelf life because of deterioration caused by spoilage microflora and physiological processes. Cutting may increase microbial spoilage of fruits through transfer of microflora on the outer surfaces to the interior tissue. The objectives of this study were to use the vacuum-steam-vacuum (VSV) process to reduce indigenous spoilage microflora on the surface of cantaloupes and to investigate the effects of such treatments on transfer of spoilage microflora from the cantaloupe surface to the fresh-cut melon during rind removal and cutting. Whole cantaloupes were treated in the VSV processor, and fresh-cut pieces prepared from treated and control samples were stored at 5 and 10 degrees C for up to 9 days. Presence and growth of mesophilic bacteria, yeasts and molds, and Pseudomonas spp. were determined in fresh-cut samples during storage. Texture and color (CIE L*, a*, and b*) also were measured during storage. VSV treatment resulted in a 1.0-log reduction of aerobic mesophilic bacteria, a 2.0-log reduction of yeasts and molds, and a 1.5-log reduction of Pseudomonas spp. on cantaloupe surfaces. VSV treatment significantly reduced transfer of yeasts and molds and Pseudomonas spp. from whole cantaloupe surface to fresh-cut pieces during preparation (P < 0.05). Texture and color of the fresh-cut pieces prepared from the VSV-treated whole melons were similar to those of the controls. The results of this study indicate that the use of the VSV process to reduce the surface populations of yeasts and molds and Pseudomonas spp. on whole cantaloupes will reduce subsequent transfer of these microbes to fresh-cut pieces and enhance the microbial quality of the fresh-cut product.     

Comparison of calcium lactate with chlorine as a washing treatment for fresh‐cut lettuce and carrots: quality and nutritional parameters

The efficacies of calcium lactate and chlorine washing treatments of fresh‐cut lettuce and carrots were compared during storage at 4 °C over 10 days. The gas composition of packages, colour, enzyme activity, texture, sensory attributes, microflora and levels of ascorbic acid and carotenoids were evaluated at 1, 3, 7 and 10 days. Calcium lactate treatment was not significantly different to chlorine treatment (p < 0.05) in terms of maintaining colour, texture and acceptability of fresh‐cut lettuce and carrots during the entire storage period. The washing treatments did not affect levels of ascorbic acid of fresh‐cut lettuce or carrots. Carotenoid levels were higher in calcium lactate‐treated carrots than chlorine‐treated samples at the end of storage. Mesophilic, psychrotrophic and lactic acid bacteria counts were not significantly different between treatments for both vegetables. Copyright © 2005 Society of Chemical Industry     

Effect of Processing Under Ultraviolet Light on the Shelf Life of Fresh-Cut Cantaloupe Melon

ABSTRACT: The effect of processing cantaloupe melon under ultraviolet-C (UV-C) radiation on storage properties of the cut fruit at 10 °C was compared with post-cut UV-C fruit treatment and the untreated control. Cutting fruit under UV-C light induced a hypersensitive defense response that resulted in increased accumulation of ascorbate peroxidase relative to the other 2 treatments. Fruit processed under UV-C radiation had the lowest esterase activity throughout the storage period. Lipase activity was higher in post-cut treated fruit than fruit processed under UV-C light and the control fruit. Lipase activity, however, decreased rapidly in fruit processed under UV-C and was undetectable after 7 d of storage. Human sensory aroma evaluation indicates reduced rancidity, and instrumental texture measurements suggested improved firmness retention in fruit cut under UV-C radiation. The treatment also reduced respiration during cut fruit storage. UV-C was effective in reducing yeast, mold, and Pseudomonas spp populations in both treatments. Fresh-cut pieces from whole melon cut under UV light had lower populations of aerobic mesophilic and lactic acid bacteria relative to the control and post-cut treated pieces. Results indicate that while post-cut application of UV improved shelf life of cut cantaloupe melon, cutting fruit under UV-C radiation further improves product quality.     

Emulsion Stabilized with Starch Octenyl Succinate Prolongs Nisin Activity Against Listeria Monocytogenes in a Cantaloupe Juice Model

Food safety related to fresh and fresh‐cut produce, such as cantaloupe, is a great challenge in the food industry. Various processing technologies, including the use of antimicrobial materials, have been applied to reduce pathogens. Nisin, an antimicrobial peptide, shows strong inhibitory activity against Listeria monocytogenes (LM); however, it suffers from quick depletion in foods. In this study, the protective effect of starch octenyl succinate (starch‐OS) stabilized emulsion on nisin was evaluated in a cantaloupe juice model. Results showed that the proteolytic enzyme in cantaloupe juice caused nisin depletion, and the adsorption of nisin in emulsion led to considerable protection of antimicrobial activity. After 1, 3, and 6 d of incorporation with cantaloupe juice, the size of LM inhibitory ring were 7.64, 7.60, and 2.97 mm, respectively for emulsion formulations, whereas it reduced from 3.60 mm to a negligible level for nisin‐alone. This study showed the potential of using carbohydrate colloidal systems to prolong the efficacy of antimicrobial materials.     

PREDICTIVE MODELING AND GROWTH MODELS OF AEROBIC MESOPHILIC BACTERIA ON FRESH-CUT LETTUCE BY HYPOCHLORITE-WASHING

Response surface methodology was used to evaluate the effect of three selected factors (chlorine concentration, washing time and water‐to‐lettuce ratio) on reducing aerobic mesophilic bacteria on fresh‐cut lettuce. According to statistical analysis, the model established was effective in predicting the reduction of aerobic mesophilic bacteria on fresh‐cut lettuce by washing with chlorine. In addition, best‐fit Gompertz‐modified models were described to evaluate aerobic mesophilic bacteria growth on fresh‐cut lettuce during storage at 0, 4 and 25C, respectively. The final load of aerobic mesophilic bacteria and shelf life of fresh‐cut lettuce could be predicted in various storing temperatures with the growth models.     

ATP bioluminescence assay for estimation of microbial populations of fresh-cut melon

Estimation of microbial numbers in foods by conventional microbiological techniques takes days, so there is a need for faster methods that can give results in minutes. Research was undertaken to investigate the use of bioluminescent ATP determination and a firefly luciferase assay to estimate the initial population of aerobic mesophilic bacteria on fresh-cut melons immediately after preparation and during storage at 5 or 15 degrees C for up to 12 days. Populations of aerobic mesophilic bacteria on fresh-cut cantaloupe prepared immediately from unsanitized whole melons averaged 3.42 log CFU/g, corresponding to an ATP value of 5.40 log fg/g. Populations for fresh-cut honeydew prepared from unsanitized whole melon averaged 1.97 log CFU/g, corresponding an ATP value of 3.94 log fg/g. Fresh-cut pieces prepared from cantaloupe or honeydew melons sanitized with either chlorine (200 ppm free chlorine) or hydrogen peroxide (2.5%) had similar ATP values: 3.1 log fg/g (corresponding to bacterial counts 1.7 log CFU/g) for cantaloupes and 2.6 log fg/g (corresponding to bacterial counts of 0.48 CFU/g) for fresh-cut honeydew. Positive linear correlations for ATP concentrations and microbial populations were found for fresh-cut cantaloupe (R2 = 0.99) and honeydew R2 = 0.95) during storage at 5 degrees C for up to 12 days. ATP values in fresh-cut melons inoculated with either aerobic mesophilic bacteria or yeast and mold were significantly higher (P < 0.05) than control values and parallel total plate counts on plate count agar. Results of this study indicate that the bioluminescent ATP assay can be used to monitor total microbial populations on fresh-cut melon after preparation and during storage for quality control purposes to establish specific sell-by or consume-by dates.     

EFFECT OF PRECUT SANITIZING DIP AND WATER JET CUTTING ON QUALITY AND SHELF‐LIFE OF FRESH‐CUT WATERMELON1

Abstract Whole watermelons were dipped in water or hypochlorite solution, and then cut with a knife or water jet. Cut melons were stored at 4C for up to 14 days and tested for color, texture, pH, soluble solids, weight loss, and bacterial counts. Sanitizing dip and cutting method had no effect on pH or soluble solids. Sanitizing dip had no effect on color, texture, or weight. Water jet‐cut melon pieces were darker, knife‐cut pieces were softer and showed higher weight loss. Aerobic plate counts for all treatments increased by up to 5 log cycles during storage. A precut sanitizing dip resulted in about a two log cycle reduction in initial aerobic and about a one log cycle reduction in initial coliform bacterial counts.