Joseph Arul

Antifungal activity of chitosan on post-harvest pathogens: induction of morphological and cytological alterations in Rhizopus stolonifer

The effect of chitosan preparations with different levels of deacetylation and other polyanions on the growth of post-harvest pathogens was investigated. Chitosan markedly reduced the radial growth of all the fungi tested, with a greater effect at higher concentration. Chitosan was more effective than N,O-carboxymethylchitosan, polygalacturonate or d -glucosamine, and its inhibitory activity appeared to increase with the level of deacetylation. In addition to inducing cellular leakage of amino acids and proteins in Botrytis cinerea and Rhizopus stolonifer, chitosan also caused morphological changes in R. stolonifer. The ultrastructural study showed that chitosan caused deep erosion of the cell wall as well as increasing the cell-wall thickness. Although chitosan treatment did not affect chitin distribution in R. stolonifer wall, it stimulated the activities of chitin deacetylase, an enzyme involved in the biosynthesis of chitosan. This may well upset the balance between biosynthesis turnover of chitin, thereby rendering the cell wall more viscoelastic.

Characterization and use of essential oil from Thymus vulgaris against Botrytis cinerea and Rhizopus stolonifer in strawberry fruits

Abstract The essential oils from two clonal types of Thymus vulgaris (Laval-1 and Laval-2) were characterized and tested for antifungal activity. Contents were high in p -cymene, linalool, terpinen-4-ol and thymol which constituted 53.5% and 66.2% of Laval-1 and Laval-2 essential oils respectively. The essential oil volatiles from two clonal types exhibited antifungal activity against Botrytis cinerea and Rhizopus stolonifer , two common storage pathogens of strawberries ( Fragaria ananassa ). The inhibition of B. cinerea and R. stolonifer ranged from 26.5 to 63.5% and 5.5 to 50.5% respectively by oil from Laval-1, when exposed to concentrations of 50 to 200 ppm, while values of 36.9 to 90.5% and 11.5 to 65.8% were observed from oil from Laval-2. The decay of strawberry fruits caused by B. cinerea and R. stolonifer was controlled up to 73.6 and 73.0% respectively by volatiles from maximin concentration of Laval-1, and up to 75.8 and 74.8% from Laval-2. No visual phytotoxic symptoms were noticed for the observed period. Essential oil from Laval-2 exhibited higher antifungal activity which was related to its relatively higher content of antimicrobial compounds.

Potential of induced resistance to control postharvest diseases of fruits and vegetables

Postharvest diseases of fruits and vegetables cause major losses in food production. It is estimated that in the United States, approximately 24% of harvested fruits and vegetables is lost to postharvest spoilage (23). Such estimates are conservative, since they are generally based on assessments made at one point in the food system. No one has evaluated the accvrnuIative postharvest losses of fruits and vegetables that occur during harvesting, processing, storage, transportation, on the grocery shelf. and in homes. In addition, we have no estimates of postharvest losses that occur during food preparation in restaurants and fast-food outlets. In developing countries, where sanitation and refrigeration are lacking or minimal, postharvest losses are even greater, amounting in many cases to aver 50% of the harvested crop (2). Despite the magnitude ofthe problem, plant pathglogists have not given postharvest diseases the priority they warrant, in part because an abundant food supply in developed countries has masked the severity of postharvest losses. Most research has been directed toward improving and protecting crops in the field or greenhouse. This lack of attention is reflected in graduate programs at many universities where little consider-

Intrinsic viscosity–molecular weight relationship for chitosan

The intrinsic viscosity–molecular weight relationship for chitosan was determined in 0.25 M acetic acid/0.25M sodium acetate. Chitosan samples with a degree of acetylation (DA) between 20 and 26% were prepared from shrimp-shell chitosan by acid hydrolysis (HCl) and oxidative fragmentation (NaNO2). Absolute molecular weights were measured by light scattering and membrane osmometry. Size exclusion chromatography (SEC) was used to determine average molecular weights (Mn, Mv, and Mw) and polydispersity. The following Mark–Houwink–Sakurada equation (MHS) is proposed for chitosan of Mw in the range of 35–2220 kDa: The value of the MHS exponent a suggests that chitosan behaves as a flexible chain in this solvent. Examination of MHS constants obtained in this work and those available in the literature with other solvents indicates that a and K are inversely related and that they are influenced by DA, and pH and ionic strength of the solvent.

Effect of pre-harvest chitosan sprays on post-harvest infection by Botrytis cinerea and quality of strawberry fruit

The effect of pre-harvest sprays of chitosan on post-harvest decay and quality of strawberries stored at 3 and 13°C was investigated. Strawberry plants were sprayed with 2, 4 an d6gl 1 , chitosan solutions as the fruit were turning red. A second spray was performed after 10 days. Fruit were picked 5 and 10 days after each spray. Harvested fruit from chitosan sprayed plants were challenged with Botrytis cinerea. Chitosan sprays significantly reduced post-harvest fungal rot and maintained the keeping quality of the fruit compared with control. The incidence of decay decreased with increased chitosan concentration and increased with storage period and temperature. The second spray of chitosan extended the protective effect against decay of fruit from subsequent picks. Fruit from chitosan sprayed plants were firmer and ripened at a slower rate as indicated by anthocyanin content and titratable acidity than berries from non-treated plants. Chitosan sprays were not phytotoxic at all the concentrations tested. Chitosan sprays at 6 gl 1 concentration performed twice, 10 days apart, protected the fruit from decay and kept the fruit quality at an acceptable level throughout the storage period of 4 weeks in fruit stored at 3°C. The protective effect of chitosan sprays was more pronounced for fruit from pick 1 than pick 2. Kinetic data on decay and ripening characteristics provided quantitative evidence that chitosan compensates for higher storage temperature and protects against deterioration of lower quality fruit from the second harvest.

Effect of photochemical treatment in the preservation of fresh tomato (Lycopersicon esculentum cv. Capello) by delaying senescence

Abstract The effect of hormic dosage of ultraviolet radiation in delaying the senescence of tomato was investigated. Mature-green tomato fruit (var. Capello) were irradiated with ultraviolet light (UV-C, 200–280 nm) corresponding to 0, UV–3.7×103 J m−2 and UV-24.4×103 J m−2, and were stored at 16°C, under high relative humidity for a period of 35 days. Attributes of senescence such as weight loss, color, texture, respiration rate, ethylene production and putrescine were monitored periodically throughout the storage period. A dose of UV-3.7×103 J m−2 was found to be beneficial (hormic) in delaying ripening and senescence, while the higher dose impaired ripening and caused abnormal browning, manifested as sun-scalding of the fruits surface. The development of color and softening of tissue were significantly retarded during storage in response to the treatment with the hormic dose (UV-3.7×103 J m−2). In addition to a delay in the climacteric response by at least 7 days, the respiration rate and ethylene production of the treated fruit were also reduced. The delay in senescence was attributed in part, to the maintenance of a high level of putrescine (antisenescence agents exerting opposite physiological effect to ethylene). The results suggest that photochemical treatment may have potential for preservation of fresh fruit and vegetables.

Ultrastructural and cytochemical aspects of the effect of chitosan on decay of bell pepper fruit

Effect of chitosan treatment on the infection process of bell pepper fruit by Botrytis cinerea was investigated at the ultrastructural level. In inoculated control tissues, fungal colonization proceeded rapidly, causing extensive degradation of host walls and middle lamellae. Such alterations were also observed over walls distant from invading hyphae. In chitosan-treated tissue, however, fungal cells were mainly restricted to wound cavities and ruptured epidermal cells. Host walls, even when appressed against invading hyphae, appeared well preserved and showed no sign of alteration. While in inoculated control tissues, invading hyphae appeared normal, the fungal cells detected in chitosan-treated tissue displayed various degrees of cellular disorganization from wall loosening to protoplasm degradation. Structural host defence responses such as formation of wall appositions and plugging of intercellular spaces with fibrillar material were frequently observed in chitosan-treated tissues. Such structure reacted intensely with an Aplysia gonad lectingold complex, indicating the presence of pectic residues.

Biochemical and cytochemical aspects of the interactions of chitosan and Botrytis cinerea in bell pepper fruit

Abstract The effect of chitosan on the necrotrophic growth of Botrytis cinerea in bell pepper fruit was investigated. In control tissue, massive fungal colonization was followed by extensive degradation of the pectin component of host walls and middle lamella. Reduction of pectin labelling was also observed in walls distant from invading hyphae. In contrast, cellulose breakdown was limited to small wall areas closely appressed against the pathogen. The disruption of host walls and the reduction of pectin labelling appeared to parallel levels of cell-wall-macerating enzymes isolated from B. cinerea -infected tissue. High levels of polygalacturonase and trace amounts of cellulase were detected in B. cinerea -infected tissue. In chitosan-treated tissue, the preservation of pectin binding sites and the intense and regular cellulose distribution over host walls, suggested that chitosan might have prevented the maceration of host tissue by B. cinerea . Chitosan not only was effective in reducing the production of polygalacturonases by B. cinerea , but also caused severe cytological damage to invading hyphae. This may, in part, explain the limited ability of the pathogen to colonize tissues in the presence of chitosan.

Effect of organic and inorganic salts on the growth and development of Fusarium sambucinum, a causal agent of potato dry rot

Potato dry rot, caused by Fusarium sambucinum , is a major postharvest disease of economic significance worldwide. Postharvest application of thiabendazole to control dry rot is becoming less effective since many strains of F. sambucinum have become resistant to this fungicide. Thus, alternative control strategies are needed. In vitro studies showed that several salts (0.2 M) inhibited completely mycelial growth and spore germination of F. sambucinum. Among these salts, sodium benzoate, sodium metabisulfite, potassium sorbate, trisodium phosphate and aluminium salts were fungitoxic. In vivo studies showed that aluminium chloride in curative application and sodium metabisulfite, sodium carbonate and sodium bicarbonate in preventive application significantly reduced the development of dry rot in potato tuber. Results from this study demonstrate that selected salts can be used to control potato dry rot.

Fragmentation of chitosan by microfluidization process

Fragmentation of chitosan in 0.1 M acetic acid (HAc) by microfluidization was investigated. The degree of fragmentation was followed by viscometry and size exclusion chromatography. The chemical structure of chitosan and its fragments was examined by elemental analysis and 1H NMR spectroscopy. Fragmentation of chitosan was affected by pressure or intensity of turbulence, exposure time, and hydrodynamic parameters such as molecular weight and polymer concentration in solution; but temperature had only a negligible effect. Chain scission increased bi-linearly with pressure, increased with molecular weight of chitosan but decreased with its concentration. Continuous microfluidization appeared to be more effective in fragmentation than volume pass mode. Molecular weight distribution of fragments was narrower than that of the original polymer indicating that large macromolecules were preferentially fragmented. Degree of acetylation of fragments increased when 0.1 M HAc was used as solvent for chitosan but not in 0.04 M HCl. The fragmentation of chitosan by microfluidization process was described by a parametric model relating chain scission to mechanical action and hydrodynamic parameters of the polymer. It was concluded that microfluidization can be a useful method for moderate fragmentation of chitosan.