Melon Rinds Research Articles

Bacterial diversity and composition on the rinds of specific melon cultivars and hybrids from across different growing regions in the United States.

The goal of this study was to characterize the bacterial diversity on different melon varieties grown in different regions of the US, and determine the influence that region, rind netting, and variety of melon has on the composition of the melon microbiome. Assessing the bacterial diversity of the microbiome on the melon rind can identify antagonistic and protagonistic bacteria for foodborne pathogens and spoilage organisms to improve melon safety, prolong shelf-life, and/or improve overall plant health. Bacterial community composition of melons (n = 603) grown in seven locations over a four-year period were used for 16S rRNA gene amplicon sequencing and analysis to identify bacterial diversity and constituents. Statistically significant differences in alpha diversity based on the rind netting and growing region (p < 0.01) were found among the melon samples. Principal Coordinate Analysis based on the Bray-Curtis dissimilarity distance matrix found that the melon bacterial communities clustered more by region rather than melon variety (R2 value: 0.09 & R2 value: 0.02 respectively). Taxonomic profiling among the growing regions found Enterobacteriaceae, Bacillaceae, Microbacteriaceae, and Pseudomonadaceae present on the different melon rinds at an abundance of ≥ 0.1%, but no specific core microbiome was found for netted melons. However, a core of Pseudomonadaceae, Bacillaceae, and Exiguobacteraceae were found for non-netted melons. The results of this study indicate that bacterial diversity is driven more by the region that the melons were grown in compared to rind netting or melon type. Establishing the foundation for regional differences could improve melon safety, shelf-life, and quality as well as the consumers' health.

Simultaneous degradation of chlorpyrifos and profenofos in soils at sublethal concentrations in presence of Eisenia foetida and a native bacterial consortium

The use of organophosphates (OPPs) in agriculture is an environmental problem due to their persistence in the environment, affecting non-target species, including human beings. For this reason, this study evaluated the degradation of chlorpyrifos (CPF) and profenofos (PFF) simultaneously in soils at sublethal concentrations in the presence of Eisenia foetida (EF) and a native bacterial consortium (NBC). For this, we first studied the avoidance behavior of EF to soils contaminated with CPF and PFF by calculating the percentage avoidance response (AR%), finding that EF presents an avoidance behavior to soils contaminated with CPF (6.45 to 65.5 mg/kg) and PFF (2.26 to 112.95 mg/kg) and their mixture, giving values of AR% (+). EF did not show avoidance behavior with AR% (-) values when melon rinds were added as substrate making it feasible to study the degradation of CPF and PFF at concentrations of 65.5 mg/kg and 112.95 mg/kg. EF and NBC showed synergism in degradation, reducing the half-life time from 70 days (CPF) and 50 days (PFF) to 15 days in both cases, with degradation percentages at 28 days of 73.75% for CPF and 71.73% for PFF, with pH being the determining factor in degradation, favoring degradation at pH higher than 7. The study was scaled to real agricultural soils with concentrations of 0.801 and 0.592 mg/kg CPF and PFF, respectively. These concentrations represented an ecological risk with risk quotient values of RQ>1. After the application of EF and NBC, both OPPs were eliminated to non-detectable concentrations. It has been demonstrated that the application of EF and NBC is an effective alternative to be applied in agricultural soils contaminated with OPPs, which would reduce the negative impacts of these toxics on the environment and human beings.

Freeze-Drying Processes Applied to Melon Peel: Assessment of Physicochemical Attributes and Intrinsic Microflora Survival during Storage.

Melon peel is recognized as a source of healthy nutrients and oxidant compounds. Being considered a non-edible part with no profit value, large amounts of melon rinds are discharged by fruit industries. Innovative food ingredients with potential health benefits may arise if these parts were conveniently transformed. The objective was to freeze-dry small melon peel cubes to attain a potential edible matrix. An ozone pre-treatment was applied seeking decontamination purposes and quality retention. The effect of these processes was assessed in terms of physicochemical parameters (moisture content, water activity and color), bioactive compounds (total phenolics, vitamin C and chlorophylls) and antioxidant capacity, during 7 weeks of storage at room temperature. Intrinsic microflora (mesophylls, yeasts and molds) were also monitored. Results showed that the freeze-drying process allowed retention of the most bioactive compounds analyzed, except for total phenolic content. In this case, the ozone pre-treatment was important for phenolics preservation. During the storage period, ozonated samples presented a higher content of bioactive compounds. In terms of microflora, the ozone and freeze-drying effects were not significant. Freeze-drying proved to be a suitable preservation method for melon peel. The ozone impact was not relevant in terms of decontamination.

Encapsulated Plant-Derived Antimicrobial Reduces Enteric Bacterial Pathogens on Melon Surfaces during Differing Contamination and Sanitization Treatment Scenarios

This study aimed to quantify survival in Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium isolates on melon rind surface samples achieved by sanitizer treatment under three differing melon contamination and sanitization scenarios. Sanitizing treatments consisted of the plant-derived antimicrobial (PDA) essential oil component (EOC) geraniol (0.5 wt.%) entrapped in the polymeric surfactant Pluronic F-127 (GNP), 0.5 wt.% unencapsulated geraniol (UG), 200 mg/L hypochlorous acid at pH 7.0 (HOCl), and a sterile distilled water wash (CON). The experimental contamination and sanitization scenarios tested were: (1) pathogen inoculation preceded by treatment; (2) the pathogen was inoculated onto samples twice with sanitizing treatment applied in between inoculation events; or (3) pathogen inoculation followed by sanitizing treatment. Reductions in the numbers of surviving pathogens were dependent on the sanitizing treatment, the storage period, or the interaction of these effects. GNP treatment provided the greatest reductions in surviving pathogen counts on melon rinds, but these did not regularly statistically differ from those achieved by HOCl or UG treatment. GNP treatment provided the best pathogen control under differing conditions of pre- and/or post-harvest cross-contamination and can be applied to reduce the risk of pathogen transmission on melon rinds.

Plant-based antimicrobials inactivate Listeria monocytogenes and Salmonella enterica on melons grown in different regions of the United States

The efficacy of plant-based antimicrobials against Salmonella Newport and Listeria monocytogenes on melon rinds was evaluated. Four cantaloupe and 3 honeydew melon varieties grown in Georgia, Arizona, Texas, North Carolina, Indiana and California were tested. Melon rinds (10 g pieces) were inoculated with 5–6 log CFU/10 g rind of S. Newport or L. monocytogenes. Samples were then immersed in 5 % olive extract or 0.5 % oregano oil antimicrobial solution and gently agitated for 2 min. Samples were stored at 4 °C and surviving populations of both bacteria were enumerated at days 0 and 3. Plant-based antimicrobials reduced S. Newport and L.monocytogenes population on all rind samples, regardless of the melon types, varieties or growing locations. Compared to the control, antimicrobial treatments caused up to 3.6 and 4.0 log reductions in populations of Salmonella and L. monocytogenes, respectively. In most cases, plant-based antimicrobial treatments reduced pathogen populations to below the detection limit (1 log CFU/g) at day 3. In general, oregano oil had better antimicrobial activity than olive extract and the antimicrobial treatments were more effective on Salmonella than on L. monocytogenes. The plant-based antimicrobial treatments exhibited better microbial reductions on honeydews than on cantaloupes. These antimicrobials could potentially be used as sanitizers for decontaminating melons.

Characterization and expression of Cm-AAT1 gene encoding alcohol acyl-transferase in melon fruit (Cucumis melo L.) ‘Hikapel’

Abstract. Wibowo WA, Fatkhurohman MI, Daryono BS. 2020. Characterization and expression of Cm-AAT1 gene encoding alcohol acyl-transferase in melon fruit (Cucumis melo L.) ‘Hikapel’. Biodiversitas 21: 3041-3046. Melon (Cucumis melo L.) is one of the horticulture commodities that have high economic value and its needs increase continuously. Many new melon cultivars have been assembled to produce a higher quality melon. Melon 'Hikapel' developed by the Laboratory of Genetics and Breeding, Faculty of Biology UGM has distinctive character in the form of a strong aroma. This aroma is a complex mixture of various kinds of volatile compound. One of the main determinant compounds is a volatile ester, synthesized by the alcohol acyl-transferase enzyme encoded by the Cm-AAT1 gene. Characterization of Cm-AAT1 began with isolation of melon rinds to get total RNAs. Synthesis cDNA was conducted with oligo-dT primer, followed by detection of Cm-AAT1 using specific primers. A specific band was sequenced to perform phylogenetic tree. Gene expression from 4 melon cultivars, ‘Hikapel’, ‘Hikadi’, ‘Sun Lady’, and ‘Luna’ analysis was performed using relative quantitative Real-Time PCR. The results of this study showed that Cm-AAT1 owned not only by aromatic cultivars ‘Hikapel’ and ‘Hikadi’, but also owned by non-aromatic cultivars ‘Sun Lady’ and ‘Luna’. Phylogenetic analysis shows a high similarity between Cm-AAT1 on 'Hikapel' and 'Hikadi'. Gene expression analysis on 'Hikapel' increases as the process of fruit ripening during the storage period and it is in contrast to 'Hikadi' at decrease when the fruit began to enter the decay process on day 7th. Expression of Cm-AAT1 on ‘Hikapel’ was higher than ‘Hikadi’ at the peak of fruit maturity.

Valorisation of fruit by-products: Production characterization of pectins from fruit peels

The aim of the study is to determine the physical, chemical, structural and thermal properties of the pectins obtained from melon rinds, kiwifruit and pomeganate peels and compared with the pectins obtained from apple and orange peel used in the commercial pectin production process. Pectins extractions from these wastes were performed with citric acid, at 80 °C and 60 min. All pectins, extracted, were found to be high methoxyl pectines. The water holding capacity of the melon rind, kiwifruit and pomegranate peels pectins were lower than the orange and apple peel pectins while the thermal stability of the kiwifruit peel pectin was close to the apple and orange peel pectins. The morphological structures of the extracted pectins showed that they had micro-fractures and hollow openings. The crystallinity of the melon rinds, kiwifruit and pomegranate peel pectins were smilar to orange peel pectin. The result of this study showed that the kiwifruit peel had advantages in terms of commercial pectin production due to its high pectin yield, water holding capacity, esterification degree and thermal stability.

Reducing Transfer of Salmonella and Aerobic Mesophilic Bacteria on Melon Rinds Surfaces to Fresh Juice by Washing With Chlorine: Effect of Waiting Period Before Refrigeration of Prepared Juice

Cantaloupes, honeydew melons and watermelons inoculated with Salmonella cocktail at 4.5 log10 CFU/cm2, 3.810 log CFU/cm2 and 3.2 log10 CFU/cm2, respectively were sanitized with 200 ppm chlorine before rinds removal, cutting and juice preparation. Efficacy of 200 ppm chlorine in reducing transfer of Salmonella, aerobic mesophilic bacteria, yeast and mold, and Pseudomonas from the melon surfaces to freshly prepared fruit juice was investigated including the effect of waiting period before refrigeration of the juices. The melon juice filtrates were refrigerated immediately or stored at room temperature (~22oC) for 3 and 5 h before refrigeration. Average Salmonella bacteria recovered in fresh melon juice prepared from unwashed whole cantaloupes, watermelon and honeydew melons was 1.4 log10 CFU/ml, 0.5 log10 CFU/ml and 0.4 log10 CFU/ml, respectively. Juices from unwashed inoculated melons had the highest bacterial populations and storage at an abusive temperature of 10oC led to proliferation. Holding these juices at room temperature for 5 h before refrigeration allowed Salmonella bacteria to increase by 0.5-0.8 log in cantaloupe juice and 0.3-0.5 log in watermelon and honeydew juices. No Salmonella bacteria was determined in fresh juices prepared from melons washed with chlorinated water. The results of this study showed that washing melons with 200 ppm chlorine before juice preparation and immediately refrigerating the juice will minimize the chances of Salmonella proliferation.

Differential metabolism of L–phenylalanine in the formation of aromatic volatiles in melon (Cucumis melo L.) fruit

Studies on the active pathways and the genes involved in the biosynthesis of L-phenylalanine-derived volatiles in fleshy fruits are sparse. Melon fruit rinds converted stable-isotope labeled L-phe into more than 20 volatiles. Phenylpropanes, phenylpropenes and benzenoids are apparently produced via the well-known phenylpropanoid pathway involving phenylalanine ammonia lyase (PAL) and being (E)-cinnamic acid a key intermediate. Phenethyl derivatives seemed to be derived from L-phe via a separate biosynthetic route not involving (E)-cinnamic acid and PAL. To explore for a biosynthetic route to (E)-cinnamaldehyde in melon rinds, soluble protein cell-free extracts were assayed with (E)-cinnamic acid, CoA, ATP, NADPH and MgSO4, producing (E)-cinnamaldehyde in vitro. In this context, we characterized CmCNL, a gene encoding for (E)-cinnamic acid:coenzyme A ligase, inferred to be involved in the biosynthesis of (E)-cinnamaldehyde. Additionally we describe CmBAMT, a SABATH gene family member encoding a benzoic acid:S-adenosyl-L-methionine carboxyl methyltransferase having a role in the accumulation of methyl benzoate. Our approach leads to a more comprehensive understanding of L-phe metabolism into aromatic volatiles in melon fruit.

Effect of native microflora, waiting period, and storage temperature on Listeria monocytogenes serovars transferred from cantaloupe rind to fresh-cut pieces during preparation.

The most recent outbreak of listeriosis linked to consumption of fresh-cut cantaloupes indicates the need to investigate the behavior of Listeria monocytogenes in the presence of native microflora of cantaloupe pieces during storage. Whole cantaloupes were inoculated with L. monocytogenes (10(8)-CFU/ml suspension) for 10 min and air dried in a biosafety cabinet for 1 h and then treated (unwashed, water washed, and 2.5% hydrogen peroxide washed). Fresh-cut pieces (∼3 cm) prepared from these melons were left at 5 and 10°C for 72 h and room temperature (20°C) for 48 h. Some fresh-cut pieces were left at 20°C for 2 and 4 h and then refrigerated at 5°C. Microbial populations of fresh-cut pieces were determined by the plate count method or enrichment method immediately after preparation. Aerobic mesophilic bacteria, yeast and mold of whole melon, and inoculated populations of L. monocytogenes on cantaloupe rind surfaces averaged 6.4, 3.3, and 4.6 log CFU/cm(2), respectively. Only H(2)O(2) (2.5%) treatment reduced the aerobic mesophilic bacteria, yeast and mold, and L. monocytogenes populations to 3.8, 0.9, and 1.8 log CFU/cm(2), respectively. The populations of L. monocytogenes transferred from melon rinds to fresh-cut pieces were below detection but were present by enrichment. Increased storage temperatures enhanced the lag phases and growth of L. monocytogenes. The results of this study confirmed the need to store fresh-cut cantaloupes at 5°C immediately after preparation to enhance the microbial safety of the fruit.

Genetics of Flavonoid, Carotenoid, and Chlorophyll Pigments in Melon Fruit Rinds

External color has profound effects on acceptability of agricultural products by consumers. Carotenoids and chlorophylls are known to be the major pigments of melon (Cucumis melo L.) rinds. Flavonoids (especially chalcones and anthocyanins) are also prominent in other fruits but have not been reported to occur in melons fruit. We analyzed the pigments accumulating in rinds of different melon genotypes during fruit development. We found that melon rind color is based on different combinations of chlorophyll, carotenoids, and flavonoids according to the cultivar tested and their ratios changed during fruit maturation. Moreover, in "canary yellow" type melons, naringenin chalcone, a yellow flavonoid pigment previously unknown to occur in melons, has been identified as the major fruit colorant in mature rinds. Naringenin chalcone is also prominent in other melon types, occurring together with carotenoids (mainly β-carotene) and chlorophyll. Both chlorophyll and carotenoid pigments segregate jointly in an F(2) population originating from a cross between a yellow canary line and a line with green rind. In contrast, the content of naringenin chalcone segregates as a monogenic trait independently to carotenoids and chlorophyll. Transcription patterns of key structural phenylpropanoid and flavonoid biosynthetic pathway genes were monitored in attempts to explain naringenin chalcone accumulation in melon rinds. The transcript levels of CHI were low in both parental lines, but C4H, C4L, and CHS transcripts were upregulated in "Noy Amid", the parental line that accumulates naringenin chalcone. Our results indicate that naringenin chalcone accumulates independently from carotenoids and chlorophyll pigments in melon rinds and gives an insight into the molecular mechanism for the accumulation of naringenin chalcone in melon rinds.

BIOFILM FORMATION BY SALMONELLA SPP. ON CANTALOUPE MELONS**

ABSTRACT The ability of two strains of Salmonella to form biofilms on whole cantaloupe melons was investigated. Ten microliters of bacterial suspensions was spot‐inoculated onto cantaloupe melon rinds in pre‐marked areas, and the cantaloupe melons were held at either 10 or 20C. Biofilm formation was monitored using scanning electron microscopy on excised portions of the cantaloupe melon rind at 2, 24, 48, 72 and 144 h postinoculation. Micrographs indicated that biofilm formation occurred rapidly following introduction of cells (2 h at 20C) onto the cantaloupe melon rind. A fibrillar material was visible after just 2 h at 20C, and cells were embedded in extracellular polymeric material after 24 h at either temperature. These results indicate that a human pathogen is capable of forming a biofilm on plant tissue and that biofilm formation may be responsible for the increased recalcitrance of bacteria to aqueous sanitizers.

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 cm 2 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 μg/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.

On-Farm and Postharvest Processing Sources of Bacterial Contamination to Melon Rinds

Multistate and international foodborne illness outbreaks, particularly involving cantaloupe and often involving rare Salmonella spp., have increased dramatically over the past 13 years. This study assessed the sources and extent of melon rind contamination in production fields and at processing and packing facilities. In the spring of 1999, cantaloupe (Cucumis melo L. [reticulatus group] cv. Cruiser) sampled from two sites in the Rio Grande River Valley showed that postharvest-processed melon rinds often had greater plate counts of bacterial contaminants than field-fresh melons. Cantaloupe in the field had 2.5 to 3.5 log CFU g−1 rind total coliforms by aerobic plate counts, whereas washed melons had 4.0 to 5.0 log CFU g−1. In the fall of 1999, coliforms on honeydew melons (C. melo [inodorous group] cv. Honey Brew) ranged from 2.6 to 3.7 log CFU g−1 after processing, and total and fecal coliforms and enterococci never fell below 2.5 log CFU g−1. A hydrocooler at another site contaminated cantaloupe rinds with up to 3.4 log CFU g−1 total and fecal enterococci; a secondary rinse with chlorinated water incompletely removed these bacteria. Sources of coliforms and enterococci were at high levels in melon production soils, especially in furrows that were flood irrigated, in standing water at one field, and in irrigation water at both sites. At one processing facility, wash water pumped from the Rio Grande River may not have been sufficiently disinfected prior to use. Because soil, irrigation water, and process water were potential sources of bacterial contamination, monitoring and management on-farm and at processing and packing facilities should focus on water quality as an important control point for growers and packers to reduce bacterial contamination on melon rinds.