Intact Watermelon Research Articles

Near infrared light penetration in watermelon related to internal quality evaluation

The interaction between near infrared (NIR) light and the sample is a key factor to take into consideration when developing applications using NIR spectroscopy. The aim of this study was to assess the penetration depth of the NIR light through both intact watermelons and the red flesh of the cut fruit, using an interactance NIR system. The results showed a maximum penetration of between 9 and 11 mm in the assays carried out on intact watermelons and 11 mm in the watermelon flesh. The prediction performance of the different NIR system configurations used were compared by quantifying the SSC in intact watermelons in a non-destructive way. The results obtained for the assay in which the illuminated regions were separated by 28 mm (Distance 4) reported the best results for determination of SSC (%) obtaining an R2cv = 0.73 and RMSECV = 0.39 % and an R2p = 0.81 and RMSEP = 0.30 % when the set of data for that distance was split into calibration and internal validation sets.

Assessment of watermelon maturity using portable new generation NIR spectrophotometers

The non-destructive evaluation of internal maturity in watermelons, which are large fruits with a thick rind, during their development on the vine can be considered as a challenge for the growing sector. Near infrared spectroscopy (NIRS) was used to assess in situ soluble solid content (SSC), the main parameter to establish full maturity, in 249 intact watermelons, of which, 152 had a striped light green rind and 97 a solid dark green rind. Two handheld new generation spectrophotometers were compared for this purpose. Different pre-processing methods and the partial least squares (PLS) regression algorithm were used to build global calibration models and specific calibration models for each one of the two types of watermelon analysed. The results obtained for the global models showed that NIRS is a suitable technology for screening the fruit for maturity, and that the linear variable filters (LVF) sensor is the best equipment for this purpose (SECV = 1.02%; RPDp = 1.36). Moreover, the best results were obtained when different models were used depending on the type of watermelon. Additionally, near infrared (NIR) classification models were developed to discriminate the samples by stage of maturity for each type of watermelon available, using partial least squares discriminant analysis (PLS-DA). The optimum threshold values for the striped light green and solid dark green rind watermelons (0.82 and 0.65, respectively) were displaced from the mean value of the discriminant variable due to the differences in terms of number of samples per class used. A total of 66.4% and 82.2% of the striped light green and solid dark green rind watermelons, respectively, were correctly classified. The results of this study demonstrated the viability of using NIRS technology as a decision-making support tool to measure the maturity of watermelons and to establish the optimum harvest time of watermelons and therefore meet the consumers’ demand for sweet-tasting fruits. Further studies will be needed to improve calibration robustness, and to further interpret outdoor applications in fruits with thick rind.

Oviposition preference and olfactory response of Diaphania indica (Lepidoptera: Pyralidae) to volatiles of uninfested and infested cucurbitaceous host plants

The cucumber moth, Diaphania indica (Saunders) (Lepidoptera: Pyralidae), is a major pest of cucurbitaceous plants. The oviposition preference and olfactory response of larvae, mated and unmated male and female adults to volatiles emanating from uninfested and infested plants of four species of cucurbitaceous host plants and odours of conspecifics were recorded. Also the role of experience in the host finding behaviour of D. indica was evaluated. The experiments were done using a wind tunnel, olfactometer attraction assays and oviposition bioassays. The results reveal that fewer eggs were laid on infested plants than on uninfested plants. Females significantly preferred cucumber over squash, melon and watermelon. Cucurbitaceous plants elicited adults of D. indica to fly upwind followed by landing on the plants. The effect of experience on the olfactory preference of D. indica was dependent on the host plant. Females that had experience of cucumber, squash and melon plants were significantly attracted to the same plant, but not in the case of watermelon. Larvae of this pest were attracted only to volatiles of uninfested cucumber, squash and melon, whereas volatiles of conspecifics, infested plants and intact watermelon did not attract larvae. This study is an initial attempt to investigate the role of volatile infochemicals in the host-finding behaviour of D. indica. These results provide baseline information for the development of new control strategies against D. indica.

Quantification of Lycopene, β-Carotene, and Total Soluble Solids in Intact Red-Flesh Watermelon (Citrullus lanatus) Using On-Line Near-Infrared Spectroscopy.

A great interest has recently been focused on lycopene and β-carotene, because of their antioxidant action in the organism. Red-flesh watermelon is one of the main sources of lycopene as the most abundant carotenoid. The use of near-infrared spectroscopy (NIRS) in post-harvesting has permitted us to rapidly quantify lycopene, β-carotene, and total soluble solids (TSS) on single intact fruits. Watermelons, harvested in 2013–2015, were submitted to near-infrared (NIR) radiation while being transported along a conveyor belt system, stationary and in movement, and at different positions on the belt. Eight hundred spectra from 100 samples were collected as calibration set in the 900–1700 nm interval. Calibration models were performed using partial least squares (PLS) regression on pre-treated spectra (derivatives and SNV) in the ranges 2.65–151.75 mg/kg (lycopene), 0.19–9.39 mg/kg (β-carotene), and 5.3%–13.7% (TSS). External validation was carried out with 35 new samples and on 35 spectra. The PLS models for intact watermelon could predict lycopene with R2 = 0.877 and SECV = 15.68 mg/kg, β-carotene with R2 = 0.822 and SECV = 0.81 mg/kg, and TSS with R2 = 0.836 and SECV = 0.8%. External validation has confirmed predictive ability with R2 = 0.805 and RMSEP = 16.19 mg/kg for lycopene, R2 = 0.737 and RMSEP = 0.96 mg/kg for β-carotene, and R2 = 0.707 and RMSEP = 1.4% for TSS. The results allow for the market valorization of fruits.

Accumulation of Weathered P,P′-DDE in Xylem Sap Of Grafted Watermelon

Movement of weathered p,p′-dichlorodiphenyldichloroethane (p,p′-DDE) from contaminated soil to the rhizosphere pore water to the xylem sap of grafted watermelon was studied under green house conditions. p,p′-DDE concentrations in pore water and xylem sap was compared in intact plants, homografted, and compatible heterografts of Cucurbita pepo spp. pepo and Citrullus lanatus plants.An average p,p′-DDE concentrations in pore water of contaminated soil ranged from 0.36 μg/L to 0.55 μg/L and there were no statistically significant among the cultivars. Conversely, the xylem sap p,p′-DDE concentration of heterografted watermelon having a zucchini rootstock and watermelon scion was 71 μg/L and it was greater than intact watermelon plants (0.49 μg/L) but less than that of intact plants of zucchini (141 μg/L). Homografting showed no effect on xylem sap p,p′-DDE concentrations of the identical cultivars. The bio-concentration factors (BCFs) which is an average p,p′-DDE concentration in xylem sap over average p,p′-DDE in pore water were 344, 325, 197, 1.28, and 0.89 for intact plant of zucchini, homografted zucchini, heterografted watermelon, homografted watermelon, and intact plant of watermelon, respectively. Xylem sap p,p′-DDE concentrations of the heterografted watermelon plants were clearly influenced by plant phylogeny and enhanced by the zucchini rootstock compared to intact watermelon plants.

Accumulation of Weathered p,p′-DDTs in Grafted Watermelon

The grafting of melon plants onto cucurbit rootstocks is a common commercial practice in many parts of the world. However, certain cucurbits have been shown to accumulate large quantities of weathered persistent organic pollutants from the soil, and the potential contamination of grafted produce has not been thoroughly evaluated. Large pot and field experiments were conducted to assess the effect of grafting on accumulation of weathered DDX (the sum of p,p'-DDT, p,p'-DDD, and p,p'-DDE) from soils. Intact squash (Cucurbita maxima × moschata) and watermelon (Citrullus lanatus), their homografts, and compatible heterografts were grown in pots containing soil with weathered DDX at 1480-1760 ng/g soil or under field conditions in soil at 150-300 ng/g DDX. Movement of DDX through the soil-plant system was investigated by determining contaminant levels in the bulk soil and in the xylem sap, roots, stems, leaves, and fruit of the grafted and nongrafted plants. In all plants, the highest DDX concentrations were detected in the roots, followed by decreasing amounts in the stems, leaves, and fruit. Dry weight concentrations of DDX in the roots ranged from 7900 ng/g (intact watermelon) to 30100 ng/g (heterografted watermelon) in the pot study and from 650 ng/g (intact watermelon) to 2430 ng/g (homografted squash) in the field experiment. Grafting watermelon onto squash rootstock significantly increased contaminant uptake into the melon shoot system. In the pot and field studies, the highest stem DDX content was measured in heterografted watermelon at 1220 and 244 ng/g, respectively; these values are 140 and 19 times greater than contaminant concentrations in the intact watermelon, respectively. The xylem sap DDX concentrations of pot-grown plants were greatest in the heterografted watermelon (6.10 μg/L). The DDX contents of the leaves and fruit of watermelon heterografts were 3-12 and 0.53-8.25 ng/g, respectively, indicating that although the heterografted watermelon accumulated greater pollutant levels, the resulting contamination is not likely a food safety concern.

Prediction of Total Soluble Solid Content in Intact and Cut Melons and Watermelons Using near Infrared Spectroscopy

There is currently a growing tendency for fruit to be classified and marketed in accordance with quality criteria. One parameter used to evaluate quality in melons and watermelons is total soluble solid content, measured by invasive analytical methods which are incompatible with current quality-assurance requirements for individual pieces of fruit. Use of near infrared (NIR) reflectance spectroscopy as a nondestructive technique for measuring total soluble solid content could therefore be of considerable interest to the fruit and vegetable sector. The present study assesses the use of a NIR diode array spectrometer for estimating total soluble solid content (°Brix) in intact and cut melons and watermelons. NIR calibration models were developed using two sets for each fruit, a 2006 set ( N = 158) and a 2007 set ( N=415) for melon samples and a 2006 set ( N=77) and 2007 set ( N = 183) for watermelon samples, grown in El Ejido (Almeria, Spain). The predictive ability of the calibrations developed were greater for cut fruit ( SECV= 0.60°Brix, r2 = 0.88, RPD=2.94 in melons and SECV = 0.49 °Brix, r2 = 0.85, RPD=2.50 in watermelons) than for intact fruit (SECV = 0.98°Brix, r2 = 0.76; RPD=2.05 in melons and SECV= 0.93°Brix, r2 = 0.65, RPD = 1.69 in watermelons). This study demonstrates the value of NIR spectroscopy for grading cut melons and watermelons, intact melons and possibly intact watermelon fruits into categories of high, medium and low levels of sweetness.

Measurement of soluble solids content in watermelon by Vis/NIR diffuse transmittance technique

Watermelon is a popular fruit in the world with soluble solids content (SSC) being one of the major characteristics used for assessing its quality. This study was aimed at obtaining a method for nondestructive SSC detection of watermelons by means of visible/near infrared (Vis/NIR) diffuse transmittance technique. Vis/NIR transmittance spectra of intact watermelons were acquired using a low-cost commercially available spectrometer operating over the range 350~1000 nm. Spectra data were analyzed by two multivariate calibration techniques: partial least squares (PLS) and principal component regression (PCR) methods. Two experiments were designed for two varieties of watermelons [Qilin (QL), Zaochunhongyu (ZC)], which have different skin thickness range and shape dimensions. The influences of different data preprocessing and spectra treatments were also investigated. Performance of different models was assessed in terms of root mean square errors of calibration (RMSEC), root mean square errors of prediction (RMSEP) and correlation coefficient (r) between the predicted and measured parameter values. Results showed that spectra data preprocessing influenced the performance of the calibration models. The first derivative spectra showed the best results with high correlation coefficient of determination [r=0.918 (QL); r=0.954 (ZC)], low RMSEP [0.65 degrees Brix (QL); 0.58 degrees Brix (ZC)], low RMSEC [0.48 degrees Brix (QL); 0.34 degrees Brix (ZC)] and small difference between the RMSEP and the RMSEC by PLS method. The nondestructive Vis/NIR measurements provided good estimates of SSC index of watermelon, and the predicted values were highly correlated with destructively measured values for SSC. The models based on smoothing spectra (Savitzky-Golay filter smoothing method) did not enhance the performance of calibration models obviously. The results indicated the feasibility of Vis/NIR diffuse transmittance spectral analysis for predicting watermelon SSC in a nondestructive way.

Total Sugar and Maturity Evaluation of Intact Watermelon Using near Infrared Spectroscopy

In this study, a near infrared spectroscopy (700–1100 nm) measurement technique was used to evaluate the internal quality of watermelons non-destructively. A spectrometer and near infrared ray emitting diode were designed and developed to evaluate the internal quality parameters such as total sugar content and maturity of intact watermelons. A relationship was found between the maturity of intact watermelon and the diffuse transmittance spectra. The total sugar content was calculated from the second derivative spectral values at four selected wavelengths. The verification correlation coefficient and standard error of prediction values were 0.81 and 0.42 Brix% respectively.

Physiological properties of fresh‐cut watermelon (Citrullus lanatus) in response to 1‐methylcyclopropene and post‐processing calcium application

AbstractSeedless watermelon (Citrullus lanatus Thunb. Mansfeld, cv. Millionaire) fruit were exposed to 10 µL L−1 1‐methylcyclopropene (1‐MCP) or air for 18 h. Afterward, the fruit were processed into placental‐tissue pieces, treated with calcium dips (20 g kg−1 CaCl2) or deionized water, and stored in vented containers for 7 days at 10 °C. At intervals during storage, fresh‐cut placental tissue was monitored for respiration, ethylene production, firmness, electrolyte leakage, total soluble solids, titratable acidity and microbial growth. Ethylene production was below detection in fresh‐cut placental tissue, consistent with the low ethylene production in intact watermelon fruit. Respiration rates were significantly enhanced in response to tissue processing, and continued to increase throughout the 7 days of storage. Tissue derived from 1‐MCP‐treated fruit showed enhanced 1‐aminocyclopropane‐1‐carboxylate synthase (ACS, EC 4.4.1.14) activity, suppressed respiratory rates and undetectable levels of 1‐aminocyclopropane‐1‐carboxylate oxidase (ACO) activity during storage. Post‐processing calcium dips (CaCl2) had little influence on ACS activity relative to tissue not receiving calcium, but significantly enhanced ACO activity and maintained firmness of fresh‐cut tissue throughout storage. The data collectively support the conclusion that 1‐methylcyclopropene treatment of intact watermelon fruit is alone unlikely to benefit the storage duration of fresh‐cut watermelon. Copyright © 2005 Society of Chemical Industry

Influence of Storage and Sanitizing Protocols on the Physiology of Fresh-Cut Watermelon

Fresh-cut watermelon cubes stored at selected temperatures within the range of 1.1 to 14.5 °C had decreasing quality shelf life corresponding with increasing temperature. At lower temperatures there was a random occurrence of chilling injury symptoms in some cubes that was associated with the section of watermelon from which the cubes were cut. Cubes removed from the top side of the intact watermelon fruit were more susceptible to chilling injury than cubes from other sectors of the fruit. Sanitizing cubes with chlorine (40 μL·L–1) or ozone (0.04 μL·L–1) solutions caused an initial reduction in microbial count but during storage the effect diminished and became insignificant compared to controls. Overall quality was lower in cubes receiving aqueous sanitizing treatments, possibly due to mechanical injury occurring during centrifugation to remove excess solution. Overall quality of cubes exposed to UV light (≈250 nm for 1–5 min) was better than cubes receiving aqueous sanitizing treatment. The effectiveness of UV treatment in reducing microbial load was dependent on the amount of cube surface exposed to the light. The results emphasize the importance of preventing microbial contamination during processing of fresh-cut watermelon.

514 Influence of Storage and Sanitizing Protocols on the Physiology of Fresh-cut Watermelon

Fresh-cut watermelon cubes stored at selected temperatures within the range of 1.1 to 14.5 °C had decreasing quality shelf life corresponding with increasing temperature. At lower temperatures there was a random occurrence of chilling injury symptoms in some cubes that was associated with the section of watermelon from which the cubes were cut. Cubes removed from the top side of the intact watermelon fruit were more susceptible to chilling injury than cubes from other sectors of the fruit. Sanitizing cubes with chlorine (40 ul/l) or ozone (0.04 μL/L) solutions caused an initial reduction in microbial count, but, during storage, the effect diminished and became insignificant compared to controls. Overall quality was lower in cubes receiving aqueous sanitizing treatments, possibly due to mechanical injury occurring during centrifugation to remove excess solution. Overall quality of cubes exposed to UV light (≈250 nm for 1 to 5 min) was better than cubes receiving aqueous sanitizing treatment. The effectiveness of UV treatment in reducing microbial load was dependent on the amount of cube surface exposed to the light. The results emphasize the importance of preventing microbial contamination during processing of fresh-cut watermelon.

Discrimination of Internal Quality in Intact Watermelons Using Auto-Correlation Function of Vibration

Discrimination of Internal Quality in Intact Watermelons Using Auto-Correlation Function of Vibration