Potential for Development of Tolerance by Penicillium digitatum and Penicillium italicum after Repeated Exposure to Potassium Sorbate

Two strains of Penicillium digitatum and one strain of Penicillium italicum were exposed to various levels of sorbic acid and potassium sorbate, and the MICs were determined. Selected strains of the molds were then repeatedly exposed to subinhibitory levels of the compounds to determine whether increased tolerance might develop. The MIC of sorbic acid (pH 4.75) to P. digitatum was between 0.02 and 0.025%. The MIC of sorbate (pH 5.5) to two strains of P. digitatum and P. italicum was found to be between 0.06 and 0.08%. Increasing levels of sorbate resulted in increasing growth suppression of the molds. Populations of P. digitatum were tested for increased tolerance to sorbic acid, and none was found. Individual molds that started from the same parent colony were examined for increased tolerance to potassium sorbate. Two P. digitatum strains developed no observable increased tolerance, but P. italicum developed a slight increase in tolerance to sorbate. When spores of P. italicum and P. digitatum were exposed to higher levels of sorbate for prolonged times, the fungicidal or fungistatic activity of the inhibitor was dependent upon pH, length of exposure time, level of sorbate, and the mold strain.     

Effect of various salts on the growth and development of Geotrichum candidum,the causal agent of carrot sour rot

This study evaluated the efficacy of ammonium, calcium, potassium and sodium salts as possible alternatives to synthetic fungicides in the control of Geotrichum candidum, the causal agent of sour rot on carrots. In vitro mycelial growth of G. candidum was completely halted by ammonium bicarbonate and carbonate; calcium oxide; potassium benzoate, carbonate and sorbate; sodium benzoate, carbonate and fluoride (2% w/v). Potassium and sodium bicarbonate also reduced mycelial growth by 77.78% and 90.60%, respectively, and the difference between the effects of sodium bicarbonate and the first group of salts was not statistically significant (p < 0.05). With the exception of potassium and sodium bicarbonate, the above‐mentioned salts also halted or strongly reduced arthrospore germination. Potassium bicarbonate, and sodium bicarbonate, acetate and propionate significantly increased conidiation (p < 0.05). Of all the salts tested in vitro, only ammonium bicarbonate and carbonate, calcium oxide and sodium fluoride were toxic to G. candidum. In in vivo studies, all the calcium salts tested (acetate, chloride, citrate, formate, lactate, oxide, propionate and silicate), several of the sodium salts (acetate, bicarbonate, chloride and fluoride) and potassium bicarbonate exhibited both protective and curative activity against G. candidum, significantly reducing the severity of sour rot in comparison to pathogen‐inoculated controls (p < 0.05). Although no curative was observed with ammonium bicarbonate, ammonium carbonate, potassium carbonate, potassium chloride, sodium carbonate or sodium citrate, these salts also demonstrated significant protective activity against sour rot when compared to controls (p < 0.05). In sum, the study findings show that all of the selected salts may be used to control carrot sour rot, except for sodium fluoride, which exhibited phytotoxicity to carrots.     

Biocontrol of green and blue molds in postharvest satsuma mandarin using Bacillus amyloliquefaciens JBC36

In order to control postharvest rot of satsuma mandarin (mandarin) fruits, a new strain of Bacillus amyloliquefaciens JBC36 (JBC36) was isolated from rhizosphere of a mandarin orchard and tested for its suppression of decay due to green and blue molds caused by Penicillium digitatum and Penicillium italicum, respectively, and its mode of action was investigated. In addition, carnauba wax-based and paraffin oil-based coating formulations were developed to increase the control efficacy of the antagonist. The strain JBC36 at 10⁸ CFU mL^?1 inhibited incidence of green and blue molds on wounded mandarin fruits with control efficacies of 88 and 80.2%, respectively. Mycelial growth and spore germination of P. digitatum and P. italicum were strongly inhibited in the presence of JBC36 or antagonistic metabolites. In order to determine antifungal activity, three kinds of antibiotics were isolated by reverse-phase high performance liquid chromatography (RP-HPLC) and identified as lipopeptide families, iturin A, fengycin and surfactin by RP-HPLC and thin-layer chromatography (TLC) analysis. Fengycin was further identified as C16 fengycin A by liquid chromatography/electrospray ionisation-mass spectrometry (LC/ESI-MS) and mass spectrometry/mass spectrometry (MS/MS) analysis. Volatile organic compounds from the antagonist also reduced the mycelial growth of P. digitatum and P. italicum. Carnauba wax-based and paraffin oil-based coating formulations containing 10⁸ CFU mL^?1 of JBC36 efficiently decreased the incidence of green mold with control efficacy of 91 and 80.9%, respectively. Overall, the antagonistic rhizobacterium JBC36 is a promising biocontrol agent for use in preventing postharvest spoilage of mandarin fruits by green and blue molds.     

Antimicrobial Activity of Kumazasa (Sasa albo-marginata)

The organic solvent extract of Kumazasa leaves (Sasa albo-marginata) showed antimicrobial activity against bacteria, fungi and yeast. Kumazasa at a concentration of 0.2-1.0% showed stronger antimicrobial activity than potassium sorbate or sodium benzoate at the same concentration. Both acidic and phenolic fractions of the extract showed strong antimicrobial activity. Thirty acidic and phenolic compounds were identified by GC and GC-MS analysis. Acetic, propionic, benzoic, phenylacetic, salicylic, 3-hydroxybenzoic and o-anisic acids, and guaiacol, phenol, 4-ethylphenol, xylenol and 4-vinylphenol were the main components. It was estimated that these components play an important role in the formation of the antimicrobial activity of Kumazasa extract.     

Inhibition of penicillium digitatum and penicillium italicum in vitro and in planta with Panomycocin, a novel exo-β-1,3-glucanase isolated from Pichia anomala NCYC 434

Panomycocin, a novel exo-beta 1,3 glucanase, was tested as an antifungal agent against green and blue mold diseases, the most important causes of post harvest decay in citrus fruits. All tested isolates of Penicillium digitatum and Penicillium italicum were susceptible to panomycocin in vitro. Effective panomycocin concentrations for 50% growth inhibition (MIC-2) for P. digitatum and P. italicum were 2 and 1 μg ml⁻¹, respectively. Complete (MIC-0) growth inhibition of all isolates observed at a panomycocin concentration of 16 μg ml⁻¹. Treatment of spores with panomycocin at values lower than the MIC-0 led to slower germ tube elongation and mycelium growth. In tests on fruit, panomycocin at concentrations equal to in vitro MIC-0 value protected lemon fruit from decay.     

Evaluation of Inhibitory Effect of Organic and Inorganic Salts Against Ilyonectria liriodendri,The Causal Agent of Root Rot Disease of Kiwifruit

This study evaluated efficacy of 42 organic and inorganic salts as possible alternatives to synthetic fungicides for the control of Ilyonectria root rot of kiwifruit. Preliminary in vitro tests showed that ammonium bicarbonate, ammonium carbonate, potassium benzoate, potassium sorbate, sodium benzoate and sodium metabisulphite at 2% completely inhibited mycelial growth of the fungus. No significant differences were observed among these salts and disodium EDTA (P ≤ 0.05). However, the ED₅₀, minimum inhibition concentration (MIC), and minimum fungicidal concentration (MFC) values indicated that sodium metabisulphite was more toxic to Ilyonectria liriodendri than these other six salts. Soil bioassays showed that sodium metabisulphite, sodium benzoate and potassium sorbate at 0.25% completely inhibited mycelial growth of the fungus, whereas potassium benzoate reduced the mycelial growth of fungus by 90.30%; however, the differences in inhibitory effects were statistically insignificant (P ≤ 0.05). Moreover, there was no significant difference between 0.1% sodium metabisulphite and 0.5% ammonium carbonate, 0.75% ammonium bicarbonate and 1.5–2.0% disodium EDTA (P ≤ 0.05). Unlike disodium EDTA, complete inhibitory was observed with ammonium carbonate and ammonium bicarbonate at higher concentrations. However, in root bioassays, applications of 2% ammonium bicarbonate, 1.5% ammonium carbonate and 2% disodium EDTA were phytotoxic to kiwifruit seedlings, but 0.25% four other salts were neither phytotoxic to kiwifruit seedlings nor did it adversely affect root length, root fresh weight and root dry weight of seedling. This study also showed I. liriodendri to be capable of growth in both acidic and basic environments. However, while the fungus showed uninhibited growth at pH values of 5–11, growth decreased significantly at both higher and lower pH values (P ≤ 0.05) and was completely inhibited at pH 12.     

Control of green mold and sour rot of stored lemon by biofumigation with Muscodor albus

Control of postharvest lemon diseases by biofumigation with the volatile-producing fungus Muscodor albus was investigated. In vitro exposure to M. albus volatile compounds for 3 days killed Penicillium digitatum and Geotrichum citri-aurantii, causes of green mold and sour rot of lemons, respectively. Lemons were wound-inoculated with P. digitatum and placed in closed 11-L plastic boxes with rye grain cultures of M. albus at ambient temperature. There was no contact between the fungus and the fruit. Biofumigation for 24–72 h controlled green mold significantly, even when treatment began 24 h after inoculation. Effectiveness was related to the amount of M. albus present. In tests conducted inside a 11.7-m³ degreening room with 5 ppm ethylene at 20 °C, green mold incidence on lemons was reduced on average from 89.8 to 26.2% after exposure to M. albus for 48 h. Ethylene accelerates color development in harvested citrus fruit. M. albus had no effect on color development. Biofumigation in small boxes immediately after inoculation controlled sour rot, but was ineffective if applied 24 h later. G. citri-aurantii may be less sensitive to the volatile compounds than P. digitatum or escapes exposure within the fruit rind. Biofumigation with M. albus could control decay effectively in storage rooms or shipping packages.     

Inhibition of green mould in blood orange (Citrus sinensis var. Moro) with salicylic acid treatment

The aim of this study was to find an alternative to synthetic fungicides currently used in the control of devastating fungal pathogen Penicillium digitatum Sacc, the causal agent of green mould disease of blood orange. Antifungal activities of salicylic acid (SA) were investigated against P. digitatum. Treatments consisted of five concentrations (0, 1, 2, 4 and 5?mM). The SA application significantly decreased weight loss percentage and increased life storage of fruits. Also, SA positively affected on post-harvest quality factors including total soluble solids (TSS), titrable acidity, anthocyanin, antioxidant content and pH value. It was observed that treated fruits at a concentration of 5?mM had the highest TSS, titrable acidity, anthocyanin and antioxidant content, and it had the lowest decay and acidity. Thus, these results showed that SA has strong impact on post-harvest decay and fruit quality of blood orange.     

Evaluation of some essential oils as botanical fungitoxicants in management of post-harvest rotting of citrus fruits

During screening of some essential oils against Penicillium italicum, the oils of Mentha arvensis, Ocimum canum and Zingiber officinale were found to exhibit absolute fungitoxic activity against the test fungus. The oils were subsequently standardized through physico-chemical and fungitoxic properties. Practical applicability of the essential oils was observed in control of blue mould rot of oranges and lime fruits caused by P. italicum during storage. The Mentha oil-treated oranges and lime fruits showed enhancement of storage life of 6 and 8 days, respectively. The storage life of Ocimum oil-treated oranges and lime fruits was found to be enhanced by 6 days while in the case of Zingiber oil, it was 4 and 8 days enhancement of shelf life of oranges and lime fruits, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sulla penetrazione di Penicillium digitatum Sacc. e Penicillium italicum Wehmer nei frutti degli agrumi

Summary

The A., with a series of controls and investigations, accomplished on different groups of Oranges and following various forms of artificial infection with Penicillium digitatum and Penicillium italicum, renders evident the different reactions that these moulds have with regard to the resistance of the cuticle and the epidermic and under-epidermic stratums of the peel of the controlled fruits. Moreover the A. confirms that both the P. digitatum and the P. italicum can act as «parasite of injury» and as «parasite of contact».     

Synergy between <Emphasis Type="Italic">Salvia officinalis</Emphasis> L. and some preservatives

The aim of the present study is to investigate the antibacterial activity of Salvia officinalis L. aqueous extracts and its synergistic action with preservatives sodium nitrite, sodium benzoate and potassium sorbate in vitro against selected food spoiling bacteria. Synergy was assessed by the checkerboard assay method and quantitatively represented by the FIC index. Synergistic action was established for aqueous extract/ sodium benzoate, aqueous extract/ potassium sorbate, aqueous extract/ sodium nitrite combinations. Synergy was detected in relation to: Agrobacterium tumefaciens, Bacillus subtilis and Proteus sp. Synergy was established at plant extract and preservative concentrations corresponding up to 1/8 MIC values.     

The effects of Penicillium digitatum and Fusarium oxysporum rots on nutritional content of pawpaw (Carica papaya L.)

Investigations were carried out on the effects of Penicillium digitatum and Fusarium oxysporum on the nutritional value of pawpaw (Carica papaya). Decreases were observed in ash content, phosphorus, sodium, reducing sugars and ascorbic acid levels of fruits infected with P. digitatum, but increases in calcium and potassium content. In fruits infected by F. oxysporium, there were decreases in phosphorus, calcium, sodium ascorbic acid and reducing sugar levels; but the levels of ash content increased. The total protein level increased in the fruits infected with both fungi. These results revealed a reduction in fruit quality.     

Supplementary Antimold Activity of Phosethyl AL, A New Brown Rot Fungicide for Citrus Fruits

Phosethyl Al (= Aliette) is a new and promising postharvest fungicide against brown rot of citrus fruits. Its effectiveness in controlling green mold (Penicillium digitaum), the major citrus fruit pathogen, was studied on artificially inoculated fruit and compared with that of sodium o-phenylphenate (SOPP) and thiabendazole (TBZ). In vitro and in vivo experiments have shown that phosethyl Al is capable — although to a lesser extent than SOPP and TBZ — of inhibiting growth of P. digitatum and reducing the incidence of decay of citrus fruits, caused by a wild-type, and apparently also by a benzimidazole-resistant strain of this fungus. The influence of times of treatment and modes of application (including temperature and duration of treatment, rinsing of the fruit) on the effectiveness of phosethyl Al, SOPP and TBZ in controlling green mold was studied and discussed. It is concluded that, under conditions of natural infection, phosethyl Al can be used for the postharvest control of Phytophthora-caused brown rot without any apparent increase in the incidence of green mold in the treated fruits.     

Effect of potassium sorbate,sodium benzoate,and sodium nitrite on biosynthesis of cyclopiazonic and mycophenolic acids and citrinin by fungi of the <Emphasis Type="Italic">Penicillium</Emphasis> genus

The effect of potassium sorbate, sodium benzoate, and sodium nitrite used as preservatives in the food industry in the production of such mytotoxins as citrinin cyclopiazonic and mycophenolic acids by the contaminating fungi Penicillium citrinum, P. commune, and P. brevicompactum, respectively, was investigated. It was shown that the effect of preservatives used at concentrations relevant to the food industry on the synthesis of mycotoxins depended on the species-specific biochemical and physiological features of the cultures. The growth of P. brevicompactum was inhibited to the highest degree by sodium nitrite and potassium sorbate, and the growth of P. commune was so inhibited by sodium benzoate. It was established that the introduction of 0.015% sodium nitrite into the medium resulted in 1.3- and 1.4-fold reductions of the production of citrinin and mycophenolic acid, respectively, while the production of cyclopiazonic acid did not change in comparison with the control. The introduction of 0.015% sodium benzoate caused a more than 1.5-fold increase of the concentration of citrinin, cyclopiazonic, and mycophenolic acids, and the addition of 0.02% potassium sorbate increased the production of cyclopiazonic and mycophenolic acids by 1.7 and 2.6 times, respectively.     

Effectiveness of various food preservatives in controlling the outgrowth of Byssochlamys nivea ascospores

Potassium sorbate, sodium benzoate, sulfur dioxide, and diethylpyrocarbonate (DEPC) were tested for their effectiveness in preventing the outgrowth ofByssochlamys nivea Westling ascospores. Sulfur dioxide was the most inhibitory of the test antimycotics, complete inhibition of colony formation occurring in acidified (pH 3.5) potato dextrose agar containing 50 ppm of the preservative. Complete inhibition ofB. nivea ascospore outgrowth in grape juice stored for 60 days was noted in the presence of 300 ppm sulfur dioxide, 400 ppm potassium sorbate, and 600 ppm DEPC. Growth was observed in grape juice containing 1000 ppm sodium benzoate. The presence of up to 100 ppm potassium sorbate in grape juice during heat activation appears to have a stimulatory effect on breaking dormancy, while the other test preservatives at this concentration decrease the heat resistance ofB. nivea ascospores. The time elapsed between heat shock and exposure to DEPC or sodium benzoate is critical with respect to the sensitivity of ascospores to these preservatives.     

Production of environmentally safe biocides from essential oils having antimicrobial activity

Different liquid formulations of anise, coriander and black cumin essential oils were used for preparing some biocides. The prepared formulations were tested for their antimicrobial activity against some post-harvest pathogenic microorganisms. The tested microorganisms were Fusarium oxysporum (Dray rot of potato), Alternaria alternata (Black rot of tomato), Penicillium italicum, P. digitatum, (Blue and green rot of orange, respectively), Botryitus cinerea (Gray rot of strawberry) and Erwinia carotovora (Soft rot of potato).The results revealed that the different formulations showed a complete inhibition effect on the growth of most of the tested microorganisms. Also, the antimicrobial activity of the formulated essential oils did not affect the formulation process compared with the original oil.     

Growth and fumitremorgin production by Neosartorya fischeri as affected by food preservatives and organic acids

The effects of potassium sorbate, sodium benzoate, sulphur dioxide and citric, malic and tartaric acids on growth and fumitremorgin production by a heat-resistant mould, Neosartorya fischeri , cultured on Czapek yeast autolysate agar (CYA) were studied over a 32-day incubation period. Colonies were examined, and extracts of agar and mycelia were analyzed for mycotoxin content using high performance liquid chromatography (HPLC). Growth of N. fischeri always resulted in production of the fumitremorgins verruculogen and fumitremorgin A and C. Growth on CYA (pH 3.5) was highly repressed by potassium sorbate and sodium benzoate; 75 mg/1 completely inhibited germination of ascospores. Sulphur dioxide was less inhibitory; growth occurred on CYA containing 100 but not 200 mg/1. Growth of N. fischeri was significantly reduced when the pH of CYA was reduced from 7.0 to 4.5 to 3.5 to 2.5. Citric, malic and tartaric acids promoted growth and fumitremorgin production when supplemented to CYA (pH 2.5). These observations indicate that growth and fumitremorgin production by N. fischeri are influenced by pH and type of acid present and can be controlled by small amounts of preservatives.     

Potential of a new strain of Bacillus subtilis CPA-8 to control the major postharvest diseases of fruit

Biocontrol potential of Bacillus subtilis strain CPA-8 was tested against the main postharvest diseases of orange, apple and stone fruit. Previously, CPA-8 growth was characterized and its antifungal activity in vitro determined against Botrytis cinerea, Monilinia laxa, M. fructicola, Penicillium digitatum, P. expansum, and P. italicum. In vivo activity against these pathogens was tested by treating fruits with cells, endospores or cell free supernatants. CPA-8 treatments cannot control decay caused by P. digitatum and P. italicum on oranges. The higher concentrations of CPA-8 studied were effective in controlling B. cinerea on apple, showing grey mold incidence from 70 to 12.5% in comparison with 100% in the control. However, in general, CPA-8 treatments were not effective in controlling P. expansum. The best results of CPA-8 treatments were obtained in stone fruit against M. laxa and M. fructicola where most treatments resulted in brown rot incidence of 0% compared with 70 and 90% in the control. Based on these results, cultures, cells and cell free supernatants at different concentrations were tested against M. laxa and M. fructicola on stone fruit. Most bacterial concentrations were effective in controlling M. laxa and M. fructicola as well as or better than Serenade® Max, in some treatments showing brown rot incidences of 0% in comparison with 100% of control. Bacterial populations of CPA-8 were maintained stable or increased up to 2-log inside wounds, showing the ability of the bacteria to colonize injured tissues. Experimental evidence suggests that B. subtilis CPA-8 has biocontrol potential for control of postharvest disease on several fruit types.     

Effect of sorbic acid and potassium sorbate on growth ofBacillus cereus andBacillus subtilis in rice filling of Karelian pasty

Summary The Karelian pasty is a perishable bakery product: the pH of the rice filling is approximately 6.60 and the a_W=0.98. Contamination after baking was shown to be the most important reason for microbial spoilage. The rice fillings of the pasties were artificially contaminated by spores ofBacillus cereus andB. subtilis, and growth at room temperature was followed.B. cereus was totally inhibited by an addition of 0.20% sorbic acid or 0.40% potassium sorbate.B. subtilis was totally inhibited by an addition of 0.10% sorbic acid or 0.26% potassium sorbate. An addition of 0.10% sorbic acid to the filling before baking is recommended. This level of addition does not alter the organoleptic quality of the pasty but is a considerable safety factor for Karelian pasty production.     

Comparison of anti-Vibrio activities of potassium sorbate, sodium benzoate, and glycerol and sucrose esters of fatty acids.

The effects of fatty acids and their glycerol and sucrose esters, potassium sorbate, and sodium benzoate on growth of Vibrio parahaemolyticus in laboratory media at pH 6.7 were evaluated. The minimum concentrations at which inhibition by esters of glycerol could be detected were lowest for monolaurin (5 microgram/ml) and monocaprin (40 microgram/ml); these concentrations were lower than those observed for inhibition by lauric and capric acids, respectively. Inhibitory action of sucrose caprylate was detected at 40 microgram/ml, whereas sucrose caprate was effective at 100 microgram/ml; sucrose esters of lauric, myristic, and palmitic acids were ineffective at 100 microgram/ml. Potassium sorbate and sodium benzoate inhibited growth at concentrations as low as 30 and 300 microgram/ml, respectively, and enhanced the rate of thermal inactivation of V. parahaemolyticus at slightly higher concentrations. Fatty acid esters of glycerol and sucrose offer potential as perservatives for slightly acid or alkaline low-fat foods which do not lend themselves to the full antimicrobial action of traditional food preservatives such as potassium sorbate and sodium benzoate.