Evaluating food additives as antifungal agents against Monilinia fructicola in vitro and in hydroxypropyl methylcellulose–lipid composite edible coatings for plums

Abstract

Common food preservative agents were evaluated in in vitro tests for their antifungal activity against Monilinia fructicola, the most economically important pathogen causing postharvest disease of stone fruits. Radial mycelial growth was measured in Petri dishes of PDA amended with three different concentrations of the agents (0.01-0.2%, v/v) after 7 days of incubation at 25 °C. Thirteen out of fifteen agents tested completely inhibited the radial growth of the fungus at various concentrations. Among them, ammonium carbonate, ammonium bicarbonate and sodium bicarbonate were the most effective while sodium acetate and sodium formate were the least effective. The effective agents and concentrations were tested as ingredients of hydroxypropyl methylcellulose (HPMC)-lipid edible coatings against brown rot disease on plums previously inoculated with M. fructicola (curative activity). 'Friar' and 'Larry Ann' plums were inoculated with the pathogen, coated with stable edible coatings about 24h later, and incubated at 20 °C and 90% RH. Disease incidence (%) and severity (lesion diameter) were determined after 4, 6, and 8 days of incubation and the 'area under the disease progress stairs' (AUDPS) was calculated. Coatings containing bicarbonates and parabens significantly reduced brown rot incidence in plums, but potassium sorbate, used at 1.0% in the coating formulation, was the most effective agent with a reduction rate of 28.6%. All the tested coatings reduced disease severity to some extent, but coatings containing 0.1% sodium methylparaben or sodium ethylparaben or 0.2% ammonium carbonate or ammonium bicarbonate were superior to the rest, with reduction rates of 45-50%. Overall, the results showed that most of the agents tested in this study had significant antimicrobial activity against M. fructicola and the application of selected antifungal edible coatings is a promising alternative for the control of postharvest brown rot in plums.

Effect of Hydroxypropyl Methylcellulose-Beeswax Composite Edible Coatings Formulated with or without Antifungal Agents on Physicochemical Properties of Plums during Cold Storage

“…Finally, potassium sorbate (PS), sodium methylparaben (SMP), or sodium ethylparaben (SEP) (Merck KGaA, Darmstadt, Germany) were added to the emulsions under magnetic agitation to achieve final concentrations of 1% PS or 0.1% SMP or SEP in the coating formulations. These antifungal agents and their concentrations had been previously selected as the most effective in controlling brown rot on inoculated plums [8]. Viscosity and pH values of the emulsions were measured with a viscosimeter (Visco Star Plus R, Fungilab S.A., Barcelona, Spain) and a pH-meter (Consort C830 multiparameter analyzer, Turnhout, Belgium), respectively.…”

“…By protecting fruit from postharvest decay caused by deleterious microorganisms, these coatings provide extra functions beyond retarding fruit dehydration and reducing fruit respiration rate and ethylene production. Compounds as essential oils, organic and inorganic acids and their salts, and other permitted food additives or generally recognized as safe (GRAS) compounds have been preferred as active ingredients of antifungal edible coatings for fruits and vegetables [8][9][10][11][12]. These coatings are of particular interest for fruits that are not peeled for consumption and have emerged as an important alternative to the use of synthetic chemical fungicides for postharvest disease control.…”

“…In previous studies, we evaluated a wide variety of common food preservatives (mineral salts, organic acid salts, paraben salts, and other GRAS compounds) as ingredients of HPMC-BW edible coatings against brown rot disease caused by Monilinia fructicola on artificially inoculated plums [8].…”

State of the Art of Antimicrobial Edible Coatings for Food Packaging Applications

“…Different biopolymers, such as proteins, lipids, polysaccharides or their combinations, have been used as carriers to produce edible coatings with antimicrobial properties (Figure 1) [5][6][7][8]. They can be directly extracted from biomass and easily processed to get films to be used as coatings to control gas exchange, moisture permeation or oxidation processes in food while also reducing the microorganism's growth.…”

Starch-Based Coatings for Preservation of Fruits and Vegetables

“…The increasing restrictions on the use of agrochemicals imposed by many countries and the growing consumer demand for high quality, minimally processed fresh food products have intensified the search for new preservation methods and technologies. The use of edible coatings (ECs) has emerged as an effective and environmentally-friendly alternative to extend their shelf life [4] and protect them from harmful environmental effects. Such films, applied as coatings, can create semipermeable barriers to gases and water vapour, reducing respiration these molecules during coating formation can affect the thickness of the film [3].…”