Antifungal features and properties of chitosan/sandalwood oil Pickering emulsion coating stabilized by appropriate cellulose nanofiber dosage for fresh fruit application.

A novel composite edible coating film was developed from 0.8% chitosan (CS) and 0.5% sandalwood oil (SEO). Cellulose nanofibers (CNFs) were used as a stabilizer agent of oil-in-water Pickering emulsion. We found four typical groups of CNF level-dependent emulsion stabilization, including (1) unstable emulsion in the absence of CNFs; (2) unstable emulsion (0.006-0.21% CNFs); (3) stable emulsion (0.24-0.31% CNFs); and (4) regular emulsion with the addition of surfactant. Confocal laser scanning microscopy was performed to reveal the characteristics of droplet diameter and morphology. Antifungal tests against Botrytis cinerea and Penicillium digitatum, between emulsion coating stabilized with CNFs (CS-SEOpick) and CS or CS-SEO was tested. The effective concentration of CNFs (0.24%) may improve the performance of CS coating and maintain CS-SEO antifungal activity synergistically confirmed with a series of assays (in vitro, in vivo, and membrane integrity changes). The incorporation of CNFs contributed to improve the functional properties of CS and SEO-loaded CS including light transmission at UV and visible light wavelengths and tensile strength. Atomic force microscopy and scanning electron microscopy were employed to characterize the biocompatibility of each coating film formulation. Emulsion-CNF stabilized coating may have potential applications for active coating for fresh fruit commodities.

Application of gamma-aminobutyric acid increased the level of phytohormones in Citrus sinensis.

MAIN CONCLUSION: In the current study, we showed that exogenous GABA supplementation increases the endogenous GABA level, several amino acids, and phytohormones in citrus plants, suggesting that GABA works in harmony with phytohormones. Gamma-aminobutyric acid (GABA) plays a key role in cytosolic regulation of pH, controlling of carbon and nitrogen metabolism, and protection against biotic and abiotic stresses. Although it is well-known that GABA is implicated in plant defense and it could act as a signaling molecule, its effect on phytohormones is not completely understood. In this study, we investigated the effect of exogenous GABA on citrus phytohormones using gas chromatography-mass spectrometry. A significant increase in endogenous GABA was observed in GABA-treated plants. The highest increase in GABA was recorded in plants treated with 10 mM 7 days post-treatment. In addition, we observed a moderate increase in several amino acids including glycine, L-alanine, L-proline, L-asparagine, and L-glutamine. The levels of benzoic acid, cinnamic acid, salicylic acid, trans-jasmonic acid, indole acetic acid, indole propionic acid, and abscisic acid were significantly increased in GABA-treated plants compared to the control. The gene expression showed that GABA transaminase (GABA-T) and succinic semialdehyde dehydrogenase (SSADH) were induced in GABA-treated plants, indicating a conversion of GABA to succinate. In addition, the gene expression of the regulatory enzymes of the TCA cycle (malate dehydrogenase and succinic dehydrogenase) was upregulated in GABA-treated plants, indicating an induction of respiration. In agreement with the chemical analysis, the gene expression results showed that most of the genes implicated in the biosynthesis of phytohormones were also upregulated in GABA-treated plants. Our results indicated that GABA works in harmony with phytohormones and suggested that regulation of phytohormones by exogenous GABA could play a key role in reducing plant stress.

cDNA-AFLP analysis reveals the adaptive responses of citrus to long-term boron-toxicity.

BACKGROUND: Boron (B)-toxicity is an important disorder in agricultural regions across the world. Seedlings of 'Sour pummelo' (Citrus grandis) and 'Xuegan' (Citrus sinensis) were fertigated every other day until drip with 10 µM (control) or 400 µM (B-toxic) H3BO3 in a complete nutrient solution for 15 weeks. The aims of this study were to elucidate the adaptive mechanisms of citrus plants to B-toxicity and to identify B-tolerant genes. RESULTS: B-toxicity-induced changes in seedlings growth, leaf CO2 assimilation, pigments, total soluble protein, malondialdehyde (MDA) and phosphorus were less pronounced in C. sinensis than in C. grandis. B concentration was higher in B-toxic C. sinensis leaves than in B-toxic C. grandis ones. Here we successfully used cDNA-AFLP to isolate 67 up-regulated and 65 down-regulated transcript-derived fragments (TDFs) from B-toxic C. grandis leaves, whilst only 31 up-regulated and 37 down-regulated TDFs from B-toxic C. sinensis ones, demonstrating that gene expression is less affected in B-toxic C. sinensis leaves than in B-toxic C. grandis ones. These differentially expressed TDFs were related to signal transduction, carbohydrate and energy metabolism, nucleic acid metabolism, protein and amino acid metabolism, lipid metabolism, cell wall and cytoskeleton modification, stress responses and cell transport. The higher B-tolerance of C. sinensis might be related to the findings that B-toxic C. sinensis leaves had higher expression levels of genes involved in photosynthesis, which might contribute to the higher photosyntheis and light utilization and less excess light energy, and in reactive oxygen species (ROS) scavenging compared to B-toxic C. grandis leaves, thus preventing them from photo-oxidative damage. In addition, B-toxicity-induced alteration in the expression levels of genes encoding inorganic pyrophosphatase 1, AT4G01850 and methionine synthase differed between the two species, which might play a role in the B-tolerance of C. sinensis. CONCLUSIONS: C. sinensis leaves could tolerate higher level of B than C. grandis ones, thus improving the B-tolerance of C. sinensis plants. Our findings reveal some novel mechanisms on the tolerance of plants to B-toxicity at the gene expression level.

Effects of dog rose and watercress extracts on control of green mould decay and postharvest quality of orange fruits.

Minimum inhibitory concentration (MIC) and IC50 values and total phenolics of dog rose fruits were 72.5-80 µL mL(- 1), 130 µg mL(- 1) and 5.7 mg GA g(- 1), respectively. The Fashand watercress population and dog rose extracts exhibited mycelia growth inhibition values of 45.08% and 37.12%, respectively. The results of in vivo study indicated that the treatment of inoculated fruits with both methanol extracts especially the watercress plant extract considerably controls the citrus fruits decay (Penicillium digitatum) up to 73%. In conclusion, methanol extracts of dog rose fruits and especially watercress plant had the potential to be used against citrus green mould and even for the improvement of postharvest quality of orange fruits.

Stevia rebaudiana Bertoni as a natural antioxidant/antimicrobial for high pressure processed fruit extract: processing parameter optimization.

Response surface methodology was used to evaluate the optimal high pressure processing treatment (300-500 MPa, 5-15 min) combined with Stevia rebaudiana (Stevia) addition (0-2.5% (w/v)) to guarantee food safety while maintaining maximum retention of nutritional properties. A fruit extract matrix was selected and Listeria monocytogenes inactivation was followed from the food safety point of view while polyphenoloxidase (PPO) and peroxidase (POD) activities, total phenolic content (TPC) and antioxidant capacity (TEAC and ORAC) were studied from the food quality point of view. A combination of treatments achieved higher levels of inactivation of L. monocytogenes and of the oxidative enzymes, succeeding in completely inactivating POD and also increasing the levels of TPC, TEAC and ORAC. A treatment of 453 MPa for 5 min with a 2.5% (w/v) of Stevia succeeded in inactivating over 5 log cycles of L. monocytogenes and maximizing inactivation of PPO and POD, with the greatest retention of bioactive components.

Cell wall modifications and ethylene-induced tolerance to non-chilling peel pitting in citrus fruit.

Non-chilling peel pitting (NCPP), a storage disorder resulting in the formation of depressed areas in the peel of many citrus cultivars, is reduced by ethylene treatments. We hypothesized that this effect may be associated with biochemical changes of cell wall components. Therefore, we extracted cell wall material from albedo and flavedo tissues of 'Navelate' oranges stored in air, conditioned with ethylene (2µLL(-1)) for 4 days and subsequently transferred to air, or continuously stored in an ethylene-enriched atmosphere (2µLL(-1)). Uronic acids and neutral sugars were extracted into five fractions enriched in specific wall polymers namely water-, CDTA-, Na2CO3-, and 1 and 4M KOH-soluble fractions. Pectin insolubilization was found in control fruit at long storage times. Ethylene treatments, alleviating NCPP, increased polyuronide solubility in the albedo and had a slight effect on the flavedo. Ethylene-treated fruit showed greater content of water-soluble neutral sugars and a larger proportion of hemicelluloses readily extractable with 1M KOH, with a concomitant reduction in the 4M KOH-soluble fraction. This suggests that the protective role of ethylene on NCPP is associated with an increased solubilization of the wall of albedo cells.

Tree size and flowering intensity as affected by nitrogen fertilization in non-bearing orange trees grown under Mediterranean conditions.

'Lane Late' orange trees. Five nitrogen (N) rates were used in a randomised block design with three replicates. The 180 g N tree(-1) over three years led to the greatest canopy width (176 cm) and volume (2,697 dm3). The greatest rate applied (720 g N tree(-1) in the three years) led to the largest flower yield. Nitrogen concentration in the flowers significantly increased with fertilizer N, and also with the flowering period up to the 23rd day, declining thereafter. Flower yield was strongly correlated (r = 0.99, p < 0.001) with flower N concentration. Nutrient composition of flowers and of mature leaves from the spring flush was compared. Significant correlations were found for N (r = 0.47, p < 0.01), P (r = -0.49, p < 0.01), K (r = 0.44, p < 0.05) and Ca (r = 0.87, p < 0.001), suggesting that flowers can be used as a tool to diagnose the nutritional status of trees. Canonical analysis (with N treatment as dummy-variables) showed strong relationships between canopy width and N, which were greater at the larger rates of fertilizer application, and strong and inverse relationships between K and Mg, also with the greatest N rates.

Structural basis of the rind disorder oleocellosis in Washington navel orange (Citrus sinensis L. Osbeck).

Oleocellosis, a physiological rind disorder of citrus fruit, is an unattractive surface blemish caused by phytotoxic effects of released rind oils. The development of oleocellosis in Washington navel orange (Citrus sinensis L. Osbeck) was examined by following a time sequence of surface symptoms and microscopic rind changes. The two natural causes of oleocellosis were simulated: mechanical damage to the fruit and transfer of rind oil between fruit. Mechanical fruit injury resulted in rupture of the epidermis above oil glands. Released surface oil appeared to infiltrate the rind via the ruptured epidermis resulting in rapid degeneration of cortical, but not epidermal, cell contents. Oil application to the rind surface produced a more severe blemish than did mechanical damage. The oil appeared to diffuse through the cuticle causing degeneration of the contents of all cell layers, including the epidermis. Loss of membrane integrity was detected within 30 min, followed by cell content degeneration and cell collapse. The resulting blemish, characterized by rind collapse and darkening, developed substantially within 3 d and was attributed to the cellular damage.