Use of dielectric-barrier discharge (DBD) cold plasma for control of bread spoilage fungi

Bread is a greatly consumed bakery product worldwide. Unfortunately, it is an optimal substrate for fungal contamination and deterioration (aw > 0.95), commonly caused by the genera Penicillium, Paecilomyces, and Aspergillus, resulting in significant economic losses. Traditional conservation methods, such as the use of calcium propionate, are rejected by some consumers, leading to investment in alternative methods, such as the use of cold plasma. This study aimed to verify the effectiveness of dielectric-barrier discharge (DBD) cold plasma in inhibiting the growth of bread spoilage fungi. The species Penicillium sumatrense (ML1), Penicillium roqueforti (FML125), Penicillium paneum (FML126), Paecilomyces variotii (FML112), Aspergillus niger (ML2) were used. To assess the effect of plasma on fungi, they were inoculated into swabs, stainless steel coupons, and then small plugs were taken directly from the fungal culture and pan bread slices. All strains were inoculated into swabs and pan bread slices, but only the ML1 strain was used for experiments with coupons and plugs. Regarding the swabs of all strains (System I, 50 W/15 min), in addition to the milder treatments on the plug (System II, 50 W/2.5, 5, 10, and 20 min) and all treatments of ML1 strain coupons (System II, 200 W/15 min, 10 W and 8 W/2.5 and 1.5 min), the cold plasma presented fungistatic properties, delaying mycelial growth from 8 to 30 days and reducing the fungal population by 2.24 log when compared to controls. By analyzing the 200 W treatment with the longest exposure (5, 10, and 20 min) on the plug, plasma showed fungicidal action, completely inactivating mycelial growth. Regarding the pan bread slices, plasma System III, when applied for 45 min, reduced strains FML126 and FML112 by 1 log, FML125 and ML2 by 2 logs, and ML1 by 7 logs, demonstrating potential for use as a control method in the baking industry.