A model for the softening of nectarines based on sorting fruit at harvest by time-resolved reflectance spectroscopy

Time-resolved reflectance spectroscopy (TRS), allows for the complete optical characterization (in terms of the absorption and scattering coefficients) of diffusive media such as fruit, in the spectral range 600–1100 nm, probing a volume to a depth of about 2 cm. The hypothesis was made that the absorption coefficient at 670 nm (μ_a), near the chlorophyll peak, could be an index of fruit maturity at harvest. The aim of this research was to model nectarine softening for fruit of different maturity at harvest, as assessed by μ_a. Nectarine fruit of two sizes (A and B) were picked in 2002, 2003 (cv ‘Spring Bright’) and 2004 (cv ‘Ambra’), measured by TRS at harvest on two opposite sides and ranked by decreasing μ_a averaged per fruit (increasing maturity). Fruit were stored at 0 °C for 3, 10 and 6 days, then at 20 °C for 79, 120 and 117 h in 2002, 2003 and 2004, respectively. Firmness was measured by pressure test (8 mm tip) during shelf life, on two sides of each fruit, and then averaged. Softening at 20 °C followed a logistic model as a function of μ_a at harvest and of time at 20 °C (adjusted R² = 0.85 in ‘Spring Bright’ and 0.75 in ‘Ambra’). The effects of fruit size and cold storage were negligible. The absorption coefficient μ_a explained 13–34% of the variation of firmness. Fruit with different μ_a at harvest softened with the same sigmoidal pattern in time, which was shifted earlier in low μ_a fruit, and later in high μ_a fruit. μ_a accounted for the time shift in softening of individual fruit within the same batch. The value of μ_a can be regarded as an index of the biological age of fruit. By using this model, it is possible to predict individual fruit softening rates at 20 °C.     

Chlorophyll fluorescence for non-destructive measurement of flavonoids in broccoli

Chlorophyll fluorescence (ChlF) by excitation with two radiation beams of different wavelengths can be used for non-destructive quantitation of epidermal flavonoids in leaves. The method was tested on marketable broccoli heads, but including red light (685 nm) and green light (530 nm) in addition to ultraviolet (UV) radiation (382 nm) and blue light (450 nm) for excitation of ChlF. As a reference, the content of flavonoids was measured with high performance liquid chromatography. To induce flavonoids, postharvest treatment during 12 days with various combinations of visible and UV radiation was tried, but the achieved changes in the flavonoid levels were not statistically significant. Instead a large natural variation of flavonoid content among the broccoli heads was used to correlate it with the fluorescence data. It was possible to estimate the content of flavonoids in flower buds by means of ChlF: relative epidermal absorbance of blue light was well correlated with flavonoid content (r = 0.69, p < 0.001). For quercetin alone the correlation was higher (r = 0.77, p < 0.001). On the other hand, relative epidermal absorbance of UV radiation or green light had a much weaker correlation with flavonoid content (r ≤ 0.40, p < 0.05). Within the broccoli heads, flower buds had 15 times higher levels of flavonoids than the floret stalks, which in turn had five times higher contents than the main stem. Repeated ChlF measurements on individual broccoli heads during cold storage could monitor small but significant changes in flower buds, possibly indicating a breakdown of constituents absorbing UV and green light.     

Relationships between internal ethylene and optical reflectance in ripening ‘Antonovka’ apples grown under sunlit and shaded conditions

The feasibility of non-destructive estimation of internal ethylene concentration (IEC) in apple fruit via fruit reflectance using recently developed approaches and a fiber-optics reflectometer was investigated. The relationships between IEC and fruit reflectance in the 400–800 nm range were studied in stored apple (Malus × domestica Borkh., cv. Antonovka) fruit. A strong correlation between IEC and optical reflectance spectra taken from sunlit surfaces of the fruit was detected whereas reflectance of the shaded fruit surface showed a weak correlation with IEC. The increase of the reflectance in the red occurred along with IEC build-up during ripening resulting a strong (r² > 0.80) correlation. By contrast, reflectance in the blue-green part of the spectrum remained low and was negatively (r² ≈ 0.65) correlated with IEC. These observations are consistent with the phenomenon of degradation of chlorophylls which often occurs in parallel with the retention of carotenoids in ripening apple skin. As a result, IEC showed a significant correlation (r² > 0.69; P < 0.001) with the index based on reflectances in the red and blue-green regions of the spectrum (R₆₇₈ ? R₄₈₀)/R₈₀₀. The effects of strong solar light on the relationships between IEC and fruit reflectance are considered. The possibilities and limitations of a non-destructive reflectance-based assay of IEC in apple fruit are discussed.     

UV-B irradiation retards chlorophyll degradation in lime (Citrus latifolia Tan.) fruit

Peel yellowing is a major postharvest problem of lime fruit. Research was conducted to control peel yellowing by UV-B irradiation. Mature green lime fruit were irradiated with UV-B doses at 0 (control), 8.8, and 13.2 kJ m^?2 and then stored at 25 °C in darkness. UV-B treatment at 8.8 kJ m^?2 efficiently delayed the decrease of chlorophyll content. A high level of chlorophyllide a accumulated in mature green fruit and then gradually decreased with the progress of peel yellowing. The chlorophyllide a level was higher in 8.8 kJ m^?2 UV-B-treated fruit than it was in the controls. The pheophorbide a level declined in lime fruit treated with 8.8 kJ m^?2 UV-B, especially during the development of yellowing. In addition, the pheophytin a level increased by 8.8 kJ m^?2 UV-B treatment at the late period of storage. We concluded that UV-B treatment effectively suppressed chlorophyll degradation in mature green lime during storage, which suggests that UV-B irradiation is a usable method for prolonging the postharvest life of lime fruit.     

Studies on classification models to discriminate ‘Braeburn’ apples affected by internal browning using the optical properties measured by time-resolved reflectance spectroscopy

This work aimed at studying the feasibility of time-resolved reflectance spectroscopy (TRS) to nondestructively detect internal browning (IB) in ‘Braeburn’ apples through the development of classification models based on absorption (μ_a) and scattering (μ_s′) properties of the pulp.This research was carried out in two seasons: in 2009, apples were measured by TRS at 670 nm and in the 740–1040 nm spectral range on four equidistant points around the equator, whereas in 2010 apples were measured by TRS at 670 nm and at 780 nm on eight equidistant points.The values of the absorption coefficients measured in the 670–940 nm range increased with IB development. On the contrary, μ_s′780 was higher in healthy fruit than in IB ones. The μ_a780 also significantly increased with IB severity, showing high values when IB affected the pulp tissues compared to the core ones. Also μ_a670 changed with IB development, but it was not able to clearly discriminate healthy fruit from IB ones because its value was also affected by the chlorophyll content of the pulp.The absorption and scattering coefficients were used as explanatory variables in the linear discriminant analysis in order to classify each apple tissue as healthy or IB; then the models obtained were used for fruit classification. The best classification performance was obtained in 2010 using μ_a780 and μ_s′780 and considering the IB position within the fruit: 90% of healthy fruit and 71% of IB fruit were correctly classified. By using all the μ_a measured in the 670–1040 nm range plus the μ_s′780, IB fruit classification was slightly better while healthy fruit classification was worse. The better result of 2010 was due to the increased number of TRS measurement points that allowed better exploration of the fruit tissues. However, the asymmetric nature of this disorder makes detection difficult, especially when the disorder is localized in the inner part of the fruit (core) or when it occurs in spots. A different TRS set-up (position and distance of fibers, time resolution) should be studied in order to reach the deeper tissue within the fruit in order to improve browning detection.     

Data fusion of spectral,thermal and canopy height parameters for improved yield prediction of drought stressed spring barley

Yield modelling based on visible and near infrared spectral information is extensively used in proximal and remote sensing for yield prediction of crops. Distance and thermal information contain independent information on canopy growth, plant structure and the physiological status. In a four-years′ study hyperspectral, distance and thermal high-throughput measurements were obtained from different sets of drought stressed spring barley cultivars. All possible binary, normalized spectral indices as well as thirteen spectral indices found by others to be related to biomass, tissue chlorophyll content, water status or chlorophyll fluorescence were calculated from hyperspectral data and tested for their correlation with grain yield. Data were analysed by multiple linear regression and partial least square regression models, that were calibrated and cross-validated for yield prediction. Overall partial least square models improved yield prediction (R² = 0.57; RMSEC = 0.63) compared to multiple linear regression models (R² = 0.46; RMSEC = 0.74) in the model calibration. In cross-validation, both methods yielded similar results (PLSR: R² = 0.41, RMSEV = 0.74; MLR: R² = 0.40, RMSEV = 0.78). The spectral indices R₇₈₀/R₅₅₀, R₇₆₀/R₇₃₀, R₇₈₀/R₇₀₀, the spectral water index R₉₀₀/R₉₇₀ and laser and ultrasonic distance parameters contributed favourably to grain yield prediction, whereas the thermal based crop water stress index and the red edge inflection point contributed little to the improvement of yield models. Using only more uniform modern cultivars decreased the model performance compared to calibrations done with a set of more diverse cultivars. The partial least square models based on data fusion improved yield prediction (R² = 0.62; RMSEC = 0.59) compared to the partial least square models based only on hyperspectral data (R² = 0.48; RMSEC = 0.69) in the model calibration. This improvement was confirmed by cross-validation (data fusion: R² = 0.39, RMSEV = 0.76; hyperspectral data only: R² = 0.32, RMSEV = 0.79). Thus, a combination of spectral multiband and distance sensing improved the performance in yield prediction compared to using only hyperspectral sensing.     

Relationship of IAD index to internal quality attributes of apples treated with 1-methylcyclopropene and stored in air or controlled atmospheres

The research was conducted to evaluate the relationship between I_AD index (index of absorption difference between 670 and 720 nm) values and internal quality attributes of apples treated with 1-methylcyclopropene (1-MCP) and stored in air and controlled atmospheres (CA). Apples of ‘8S6923’ (Aurora Golden Gala™), ‘Fuji’ and ‘Royal Gala’ were tested. The results with Aurora Golden Gala™ show that I_AD index values were maintained at higher levels if the fruit were stored in CA and that 1-MCP had no significant effect on retaining at-harvest values. The I_AD values correlated with chlorophyll a content in the peel (R² = 0.95, P < 0.0001), but not with chlorophyll b content, internal ethylene levels, firmness or titratable acidity. ‘Royal Gala’ apples showed a similar response to Aurora Golden Gala™ apples, showing no correlation between I_AD index values and internal quality attributes of those apples when treated with 1-MCP and/or CA. In contrast, ‘Fuji’ apples showed a relationship between I_AD index value changes and internal ethylene concentrations (R² = 0.67, P < 0.05) and titratable acidity changes (R² = 0.89, P < 0.01), but not firmness. These results suggest that when 1-MCP and/or CA are applied to apples after harvest, that I_AD index values do not consistently correlate to any internal quality attributes other than peel chlorophyll a content.     

Pithy brown core in ‘d’Anjou’ pear (Pyrus communis L.) fruit developing during controlled atmosphere storage at pO2 determined by monitoring chlorophyll fluorescence

Physiological responses and fruit quality of ‘d’Anjou’ pear fruit from five orchard lots were evaluated after cold storage in air or controlled atmospheres (CA) with the O₂ concentration based on assessment of fruit chlorophyll fluorescence (CF) or standard conditions (1.5 kPa O₂). The pCO₂ for all CA fruit was 0.5 kPa. Softening, acid loss, and peel degreening of all lots were delayed at one or more evaluation dates (2, 4, 6, 8 months) by previous storage at the CF pO₂ compared with fruit stored in 1.5 kPa O₂ or in air. Superficial scald developed on fruit previously stored in air but not on fruit stored in a CA. Pithy brown core developed on fruit from all lots stored at the CF pO₂ and on fruit stored at 1.5 kPa in 3 of the 5 lots. Pithy brown core incidence decreased with advanced harvest maturity. Post-storage ethylene and CO₂ production were in most instances lowest for fruit stored at the CF pO₂. A significant relationship between fruit ethanol content and pithy brown core incidence was observed. Results indicate low pO₂ storage based on CF monitoring slows fruit ripening relative to fruit stored at 1.5 kPa O₂, prevents superficial scald development compared with fruit stored in air, however, development of pithy brown core in fruit stored at the CF pO₂ was not accompanied by a change in CF.     

Hyperspectral laser-induced fluorescence imaging for assessing apple fruit quality

Chlorophyll fluorescence is a promising technique for postharvest quality research, and reported studies were mainly based on the fluorescence kinetic analysis method, which has not been quite satisfactory for measuring fruit quality. This paper reports on using a hyperspectral imaging technique for measurement of laser-induced fluorescence from apple fruit for predicting multiple fruit quality parameters. A continuous wave blue laser (408 nm) was used as an excitation source for inducing fluorescence in apples. Fluorescence scattering images were acquired from ‘Golden Delicious’ apples by a hyperspectral imaging system at the instance of laser illumination (0 min) and after 1, 2, 3, 4, and 5 min of illumination. The hyperspectral fluorescence image data were represented by mean, maximum, and standard deviation spectra. Standard tests were performed on measuring fruit skin and flesh color, firmness, soluble solids content, and titratable acid. A hybrid method of combining principal component analysis and neural network modeling was used for developing prediction models to predict fruit quality parameters for each of the six illumination time periods. Fluorescence emission decreased steadily during the first 3 min of illumination and was stable within 5 min. The 0-min fluorescence prediction models had somewhat poorer prediction results for individual quality parameters except skin hue than did the models of longer illumination time. The differences were minimal in the model prediction results from the fluorescence data at 1, 2, 3, 4 or 5 min of illumination. Overall, excellent predictions were obtained for apple skin hue with the correlation coefficient of prediction of 0.94. Relatively good predictions were obtained for fruit firmness, skin chroma, and flesh hue with values for the correlation coefficient being equal to or greater than 0.74 for 1 min of illumination or longer times, and poorer correlations were found for soluble solids content, titratable acid, and flesh chroma. Hyperspectral laser-induced fluorescence imaging is potentially useful for assessing selected quality parameters of apple fruit and further research is needed to improve fluorescence measurement for better prediction of fruit quality.     

NIR spectroscopy for the optimization of postharvest apple management

Apples can be stored for long time under controlled temperature and atmosphere conditions, and therefore, non-destructive and rapid tools are required to assess fruit quality and to monitor changes during the postharvest period. The aim of this study was to evaluate the feasibility of NIR spectroscopy to optimize postharvest apple management and to follow changes in fruit quality during storage. An FT-NIR system operating in diffuse reflectance in the range 12,500–3600 cm⁻¹ was used to evaluate the physico-chemical (dry matter, soluble solids, colour and firmness) and some nutraceutical characteristics (total phenolics, total flavonoids and antioxidant activity) of ‘Golden Delicious’ apples, which were stored for about six months at 1 °C in controlled atmosphere, over two subsequent years. Spectral data were elaborated by PLS regression and LDA classification techniques. Good correlation models between spectral data and chemical and physical parameters were obtained for soluble solids, a* colour coordinate and firmness (0.81 < R² < 0.90 in calibration and 0.79 < R² < 0.89 in cross validation). Even higher correlation values (0.89 < R² < 0.95 in calibration and 0.86 < R² < 0.92 in cross validation) were obtained for indexes correlated to the antioxidant capacity of apples. The classification technique Linear Discriminant Analysis was applied to spectral data, in order to discriminate apples on the basis of storage time. Average correct classification was higher than 93% in validation and close to 100% in calibration, indicating high potential of NIR spectroscopy for the estimation of storage time of apple lots.     

UV-C treatment delays postharvest senescence in broccoli florets

Central broccoli heads (cv. de Cicco) were harvested and treated with UV-C light (4, 7, 10, or 14 kJ m⁻²). All treatments delayed yellowing and chlorophyll degradation at 20 °C but the irradiation dose of 10 kJ m⁻² allowed retaining the highest chlorophyll content yet had lower amounts of pheophytins than every treatment other than 7 kJ m⁻². This dose was selected to analyze the effect of UV-C on postharvest broccoli senescence at 20 °C. The UV-C treatment delayed yellowing, chlorophyll a and b degradation, and also the increase in pheophytins during storage. The activity of chlorophyll peroxidase and chlorophyllase was lower in UV-C treated broccoli. Instead, Mg-dechelatase activity increased immediately after the treatment, but after 4 and 6 d this activity was lower in UV-C treated florets than in controls. Treated broccoli also displayed lower respiration rate, total phenols and flavonoids, along with higher antioxidant capacity. The results suggest that UV-C treatments could be a useful non-chemical method to delay chlorophyll degradation, reduce tissue damage and disruption, and maintain antioxidant capacity in broccoli.     

Preharvest application of abscisic acid promotes anthocyanins accumulation in pericarp of litchi fruit without adversely affecting postharvest quality

Pericarp colour of litchi fruit is an important quality attribute that determines its market value and consumer acceptance. Plant growth regulators (PGR) such as abscisic acid (ABA) and ethephon are known to play important roles in peel colour development during maturation and ripening of non-climacteric fruits (e.g. grape and litchi). Our aim was to investigate the effects of preharvest application of ABA, ethephon and their combination on pericarp colour and fruit quality of litchi (cv. Calcuttia) and also to assess the potential effects on postharvest performance of fruit. Exogenous application of ABA (150 or 300 mg L⁻¹) at the colour-break stage significantly increased the concentration of total anthocyanins and cyanidin-3-O-rutinoside, the major anthocyanin contributing ∼71–96% of the total anthocyanins, in litchi pericarp compared to ethephon (500 μL L⁻¹). Among different anthocyanins quantified, the relative contribution of cyanidin-3,5-diglucoside to the total anthocyanins was significantly higher in all PGR-treated fruit compared to the control, but the concentration of cyanidin-3-O-glucoside was specifically enhanced by ABA. No significant effect on the concentrations of epicatechin, and quercetin-3-O-rutinoside was observed in response to PGR treatments. Ethephon (500 μL L⁻¹) treatment did not significantly increase the anthocyanin levels in pericarp, but it caused more degradation of chlorophyll pigments than control. Aril quality with regard to firmness, soluble solids and acidity was not significantly affected by PGR treatments, except that ethephon-treated fruit showed significant softening and lower acidity. Postharvest changes in fruit quality attributes including pericarp browning during cold storage at 5 °C for 14 d were mainly related to the storage duration effect, rather than PGR treatment. In conclusion, ABA treatment (150 or 300 mg L⁻¹) at the colour-break stage enhanced anthocyanins accumulation in litchi pericarp without adversely affecting postharvest quality and storage stability for 14 d.     

Effects of 1-methylcyclopropene on ripening of greenhouse tomatoes at three storage temperatures

Tomatoes (Lycopersicon esculentum Mill., cv. Rapsodie) were harvested at the mature green stage and treated with 250 nl l⁻¹ 1-methylcyclopropene (1-MCP) for 24 h at 20 °C. The fruit were then stored for 24 days at 15, 20 or 25 °C at 90–95% relative humidity. Sampling was carried out at 0, 6, 12, 18 and 24 days after treatment. Treatment with 1-MCP delayed ripening as measured by changes in lycopene, chlorophyll, hue angle, polygalacturonase (PG) activity and tissue firmness. Ripening was delayed by 6 days at 25 °C, by 12 days at 20 °C, and by 18 days at 15 °C in 1-MCP-treated fruit. In general, 1-MCP only delayed the onset of ripening-related changes and did not significantly alter final values for measures of firmness, color (hue angle), PG activity, and lycopene and chlorophyll contents at a particular storage temperature. The results suggest that 1-MCP is most effective at delaying ripening of mature-green tomatoes when they are stored near the currently recommended temperature range of 12.5–15 °C.     

Use of chlorine dioxide fumigation to alleviate enzymatic browning of harvested ‘Daw’ longan pericarp during storage under ambient conditions

Pericarp browning reduces both the shelf-life and market value of harvested longan fruit stored at room temperature. Our study investigated the efficiency of chlorine dioxide (ClO₂) fumigation at reducing pericarp browning of longan (Dimocarpus longan Lour.) cv. Daw. Fresh longan fruit were fumigated with 0 (control), 2.5, 5, 10 and 25 mg/L ClO₂ for 10 min, before being packed in cardboard boxes, and stored at 25 ± 1 °C, RH 82 ± 5% for 7 days. Fruit treated with ClO₂ had a lower browning index, but higher hue angle (true color), L* (lightness) and b* (yellowness) values than non-treated fruit. The 10 and 25 mg/L ClO₂ treatments were the most effective at extending shelf-life from 1 to 5 days, compared with the control, by reducing pericarp browning, the activities of polyphenol oxidase (PPO) and peroxidase (POD), disease development and by maintaining the highest total phenolic content. However, quality acceptance of fruit treated with 10 mg/L ClO₂ was higher than fruits treated with 25 mg/L, as determined by odor and flavor. Consequently, ClO₂ fumigation at a concentration of 10 mg/L was considered to be the most effective treatment to reduce pericarp browning of longan, whilst maintaining fruit quality.     

Control of alternaria black spot in persimmon fruit by a mixture of gibberellin and benzyl adenine,and its mode of action

In Israel, alternaria black spot (ABS) disease, caused by Alternaria alternata, is the main postharvest factor that reduces quality and impairs storability of persimmon fruit Diospyros kaki cv. Triumph. The fungus infects the fruit in the orchard and remains quiescent until harvest, or renews its development just before harvest, following rain or high humidity; it then preferentially colonizes the stem-end of the fruit. Recent findings suggest the importance of ethylene and respiration during early fruit growth as factors influencing maturity, crack development, and occurrence of ABS in the stem end of the fruit. We tested the effects of the growth regulator Superlon, a mixture of gibberellin (GA₄₊₇) and benzyl adenine (BA), applied at 40 μg mL⁻¹ once a month during three consecutive months, on fruit physiological responses during growth and on ABS occurrence during storage at 0 °C. Superlon treatments during the early stages of fruit growth, i.e., starting 40 days after fruit set (daf), applied once monthly during three consecutive months, inhibited ethylene and CO₂ production in the stem end. Treatments applied starting 100 daf enhanced cell proliferation under the fruit cuticle. Regardless of application timing, Superlon delayed chlorophyll degradation, and reduced fruit cuticle cracking and ABS susceptibility during the late stages of fruit growth and during storage. Present results suggest that the phytohormone, acting as a modulator of host physiological responses that result in delayed fruit maturation, is a main factor in enhanced resistance to ABS at harvest and during storage.     

Evaluation of the use of sulfur dioxide to reduce postharvest losses on dark and green figs

Postharvest diseases limit the storage period and market life of fresh figs (Ficus carica L.). The objective of this work was to determine the effect of sulfur dioxide (SO₂) applied by fumigation and/or by dual release SO₂ generating pads on postharvest decay and quality retention of ‘Black Mission’ and ‘Brown Turkey’ (dark skin), and ‘Kadota’ and ‘Sierra’ (green skin) figs. A protocol for the computer-controlled application of gaseous SO₂ has been developed which allows the application of very low specific concentration × time products of SO₂ and simultaneous monitoring of the application progress. In vitro tests with important fungal, yeast and bacterial postharvest pathogens plated on Petri dishes and exposed to a SO₂ concentration × time product (C × t) of 100 (μL/L) h at different temperatures showed fewer survived at 20 °C than at 0 °C. Therefore, fumigations were carried out at 20 °C in the rest of the experiments. The evaluation of different SO₂ concentration × time products showed that a product of 25 (μL/L) h provided the best compromise between decay control and fruit injury. The performance of SO₂ fumigations on warm or cold fruit, its combination with SO₂ generating pads, and the use of repeated fumigations during cold storage were also evaluated. All the SO₂ treatments tested reduced the percentage of decay, extending the market life of fresh figs. However, in some cases, the use of SO₂ generating pads increased the incidence of skin bleaching. Fumigation of warm fruit at 25 (μL/L) h of SO₂ reduced populations of Alternaria and Rhizopus spp. growing on the fig surface. The treatment was more effective against Rhizopus spp. than against Alternaria spp. Contamination of fruit by Botrytis spp. and Penicillium spp. was also reduced by SO₂. In conclusion, results showed that SO₂ can be a potential tool to control postharvest rots and therefore increase the market life of fresh figs.     

Papaya endoxylanase biochemical characterization and isoforms expressed during fruit ripening

Papaya fruit ripening processes involve the coordinated action of several hydrolases that causes cell wall degradation. Endoxylanase participates in xylan or arabinoxylan modifications and its importance has been related to papaya softening. However, endoxylanase has been not fully characterized biochemically and kinetically. Semipurified endoxylanase from ripe ‘Maradol’ papaya fruit had an optimal temperature from 45 °C to 50 °C, a pH optimum of 5.5 against Remazol brilliant blue-xylan (RBB-Xylan) and enzymatic activity remained stable during 36 h at 45 °C. The activation energy of the enzyme was 25.5 kJ mol⁻¹, and the V_max at 32, 37 and 42 °C was 788.9, 888.9 and 1085.6 μg kg⁻¹ s⁻¹, respectively. The K_m did not change as a function of temperature and was measured as 1.8 g L⁻¹ and was within the range reported for other xylanases. Total proteins were extracted from color-break, half-ripe and ripe fruit. A pre-endoxylanase at 63.9 kDa was identified in the color-break fruit and an active endoxylanase at 32.5 kDa that was only found in ripe fruit, when the highest enzymatic activity was obtained. Immunodetection on two-dimensional gel electrophoresis (2DE) protein blots showed three isoforms of the pre-endoxylanase at color-break and ripe stages and, four isoforms in ripe fruit that were absent in color-break fruit. The biochemical and kinetic characteristics of the endoxylanase are crucial to our understanding papaya fruit softening.     

Blueberry leaf extracts incorporated chitosan coatings for preserving postharvest quality of fresh blueberries

The phenolic compounds in blueberry (Vaccinium spp.) fruit and leaf extracts (BLE) were determined based on HPLC analysis. Antimicrobial assays against Staphylococcus aureus, Listeria monocytogenes, Salmonella typhimurium and Escherichia coli, as well as fungi isolated from the rotting blueberry fruit were conducted. The effects of chitosan coating incorporating different concentrations of BLE on the quality of fresh fruit during postharvest storage at 2 ± 1 °C and 95 ± 2% relative humidity (RH) for 35 d and then at room conditions for 3 d were also investigated. Five different coating treatments were applied including 2% (w/v) chitosan coating (T1), 2% (w/v) chitosan coating containing 4% (w/v, T2), 8% (w/v, T3), or 12% (w/v, T4) BLE, and 2% (w/v) chitosan coating containing 12% BLE plus modified atmosphere packaging (MAP at 3 kPa O₂ + 12 kPa CO₂) (T5). A sample of blueberries dipped into distilled water was used as control (T0). BLE had a greater variety of phenolic compounds than fruit extracts with syringic acid the highest concentration (0.259 ± 0.003 g kg⁻¹), but the total phenolic content in BLE was lower (P < 0.05) than in fruit extracts. BLE showed good antimicrobial activity against all tested microorganisms, with a minimum inhibition concentration from 25 to 50 g L⁻¹. The 2% chitosan coating that incorporated 8% or 12% BLE showed some degree of decreasing decay rate of fruit compared with the control, and the coating with BLE plus MAP had more effective control of fruit decay. All treated samples maintained higher total phenolic content and radical scavenging activity than the control. This study suggested that chitosan coating incorporating BLE can be employed to extend shelf-life and maintain high nutritional value of fresh blueberries during postharvest storage.     

Control of Neofabraea alba by plant volatile compounds and hot water

Fumigation by plant volatile compounds and hot water treatment were tested in vitro and in vivo for their activity against Neofabraea alba (anamorph Phlyctema vagabunda), the cause of lenticel rot in apple fruit. In vitro trials with volatile compounds showed a consistent inhibition of pathogen growth by carvacrol, trans-cinnamaldehyde, citral and trans-2-hexenal, while (?)-carvone, hexanal, p-anisaldehyde, 2-nonanone and eugenol showed progressively lower inhibition. The greatest inhibition of mycelial growth was demonstrated by carvacrol (effective doses for 50 and 95 inhibition [ED₅₀ and ED₉₅] = 5.9 and 17.0 μL L^?1, respectively; minimum inhibitory concentration [MIC] = 36.9 μL L^?1) and of conidial germination by trans-2-hexenal (ED₅₀ and ED₉₅ = 4.1 and 6.9 μL L^?1, respectively; MIC = 9.2 μL L^?1). Hot water showed a complete inhibition of conidial germination in vitro after 10, 2 and 1 min of exposure at 40, 45 and 50 °C, respectively, and a complete inhibition of mycelial growth after 20 min of exposure at 75 °C. Among the volatile compounds tested, only 25 μL L^?1 of carvacrol slightly reduced fungal infection on artificially infected apples (11.4% efficacy). Hot water treatment at 45 °C for 10 min showed high efficacy in the control of lenticel rot on apples. Reduction of infection was 80% in artificially inoculated fruit (cv Golden Delicious) and 90% in naturally infected fruit (cv Pink Lady) after 90 and 135 d of storage, respectively.