Combinations of antimycotics to inhibit the growth of molds capable of producing 1,3-pentadiene

Abstract

Some species of molds are capable of degrading sorbic acid to produce 1,3-pentadiene, a volatile compound with an unpleasant hydrocarbon-like odor. The effectiveness of reduced concentrations of sorbate, in combination with other antimycotics, to control the growth of these molds has not been described. We did a study to evaluate potassium sorbate, sodium benzoate, calcium propionate, disodium ethylenediaminetetraacetic acid (EDTA), and natamycin, alone and in combination, for their effectiveness in preventing the growth of five molds isolated from Parmesan cheese and a lemon-flavored drink subjectively judged to contain 1,3-pentadiene. Growth of Penicillium brevicompactum, Penicillium roqueforti, Paecilomyces variotii, Aspergillus niger, and Cephaloascus fragrans on model agar media containing Parmesan cheese (PRM agar) (pH 5.5) and lemon-flavored drink (LD agar) (pH 2.6) supplemented with antimycotics was studied. All molds grew well at 21 °C on PRM agar containing potassium sorbate (3500 μg/ml), calcium propionate (3000 μg/ml), or natamycin (20 μg/ml). Combinations of potassium sorbate (250–1000 μg/ml), calcium propionate (250–1000 μg/ml), and/or natamycin (10–18 μg/ml) greatly inhibited or prevented growth of molds on PRM agar, indicating their potential as preservative systems at pH values resulting in large percentages of the acids in dissociated forms. Three of the five molds grew on LD agar containing potassium sorbate or sodium benzoate at a concentration of 200 μg/ml. Growth did not occur within 70 days on LD agar containing EDTA (30 μg/ml) in combination with potassium sorbate and sodium benzoate at 50 and 175 μg/ml, respectively, or 175 and 50 μg/ml, respectively. Results of this study show that preservative systems containing a reduced concentration of potassium sorbate, in combination with other antimycotics, particularly natamycin, have potential for controlling the growth of molds thought to be capable of producing 1,3-pentadiene.

Introduction

Raw and pasteurized foods and beverages as well as products subjected to more rigorous thermal processes, e.g., hot-fill beverages, can contain a wide range of molds (Pitt and Hocking, 1997). These molds may grow during the expected shelf life of these products to cause visual spoilage or result in the production of volatile compounds that are offensive to the consumer. Some of the molds known to grow in the presence of potassium sorbate (Bullerman, 1985; Gourama and Bullerman, 1988; Liewen and Marth, 1984) or survive thermal processes commercially applied to foods and beverages (Beuchat and Rice, 1979; Nielsen et al., 1988) can also produce mycotoxins, thereby posing a public health concern.

Growth of some strains of certain species of molds are not always controlled by commonly used antimycotics such as sorbate. Some species of Penicillium isolated from cheese, for example, are capable of growing in the presence of potassium sorbate at concentrations as high as 7100 μg/ml (ca. 5000 μg of sorbic acid/ml) (Marth et al., 1966) and 12,000 μg/ml (Finol et al., 1982). Growth of Penicillium puberulum and Pencillium cyclopium isolated from spoiled cheese is not prevented on yeast extract malt extract (YM) agar containing potassium sorbate at a concentration of 2000 μg/ml (Finol et al., 1982). The potential development of tolerance by Penicillium digitatum isolated from a citrus packing plant after repeated exposure to potassium sorbate has been reported (Schroeder and Bullerman, 1985). Trichoderma harzianum can grow in vegetable spread containing 2500 μg/ml sorbate (Eiroa et al., 1999).

Degradation of sorbate through decarboxylation by some strains of penicillia can result in the accumulation of 1,3-pentadiene, a volatile compound having an odor described as being similar to that of kerosene, acrylic paint, or petroleum products (Marth et al., 1966; Bullerman, 1977; Finol et al., 1982; Liewen and Marth, 1985a, Liewen and Marth, 1985b). Other molds that may also degrade sorbate include Aspergillus, Fusarium, Mucor, Geotrichum, and Trichoderma species (Sofos, 1989; Eiroa et al., 1999). Strains of yeasts belonging to Zygosaccharomyces rouxii and Debaryomyces hansenii are also capable of spoiling sorbate-containing high-sugar foods by producing 1,3-pentadiene (Casas et al., 2004, Casas et al., 1999).

While the control of sorbate-resistant molds and yeasts in some types of foods and beverages may be achievable through the addition of high concentrations of the preservative, the adverse effect of off aromas and off flavors that may result make this approach impractical. Instead, the use of antimycotics other than sorbate, e.g., natamycin (Delves-Broughton et al., 2004), ethylenediaminetetraacetic acid (EDTA) (Shelef and Seiter, 2004), and propionate (Doores, 2004), or a low concentration of sorbate in combination with other antimycotics may be alternatives to prevent or retard the growth of 1,3-pentadiene-producing molds. We undertook a study to evaluate several antimycotics, alone and in combination, for there effectiveness in controlling the growth of five molds isolated from cheese and a lemon-flavored drink containing sorbate which were subjectively judged to contain 1,3-pentadiene.