From field to process: how storage selects toxigenic Alternaria spp. in apples

CÁRDENAS, P.; PAVICICH, MARÍA AGUSTINA; PATRIARCA, ANDREA; FERNÁNDEZ PINTO, VIRGINIA

Freising

Workshop; 2019 ICFM Workshop on "Food- and Airborne Fungi" Challenges for Food Safety and Supply?; 2019

ICFM

Apples are a major crop in Argentina; the main destination of the fruits are export trade, internal commerce and industrialization. Apple fruits are susceptible to fungal contamination in the field as well as in postharvest stage, with the consequent spoilage and severe economic loses; when mycotoxigenic fungi prevail as contaminants, an implicit health risk is associated. Fruits below quality standards for fresh consumption are transferred to by-products, mainly fruit concentrates, which are either exported or used in different local food industries. Before processing, fruits can be stored in refrigerated chambers up to 9 months. Alternaria is the main causal agent of mouldy core (MC), a disease usually unnoticed in the visual inspection performed by apple concentrate industries for the detection of P. expansum blue rot. Given the wide variety of toxic metabolites produced by Alternaria, the incorporation of mouldy fruit to the process line is of concern regarding health risk.The objective of this study was to characterize the apple fruit spoilage mycota and analyse its changes over storage, with special focus on mouldy core disease. Atotal of 240 apples from the Red Delicious variety, grown in Patagonia, Argentina, were collected and analysed; 140 were freshly harvested (H) and 100 had been stored (S) during 9 months in refrigerated chamber (0-3ºC). For fungal isolation, a portion of damaged tissue from the fruit was transferred to Dichloran Cloramphenicol Malt Extract Agar (DCMA) plates. Fruits were disinfected, cut in half, and when mouldy core was detected, it was transferred to DCMA. After incubation at 25ºC for 7 days, fungal genera were identified.From the 140 H apples, 120 (86%) showed external fungal lesions, and only 20 (14%) were undamaged. The incidence of MC was of 34.3% within this group. Penicillium spp. was the most frequent genus (54% infection), and it was mainly isolated from external lesions (43%). Alternaria, the second in frequency (41% infection), was isolated in similar proportions from external lesions (20%) and MC (21%). Other genera were Geotrichum, Rizhopus, Mucor, Nigrospora and Trichoderma (external lesions only), and Cladosporium, Fusarium, and Epicoccum (mostly external, low % of MC). Fungal contamination increased in stored apples (S); only 3/100 were undamaged, 48% had external lesions and 51% MC. Alternaria was predominant (60%), and mainly causing MC (46% infection). Penicillium took the second place, predominantly from external lesions (30%). Cladosporium and Botrytis were the only other genera found in these fruits.Long-term cold storage selected Alternaria and Penicillium over non-toxigenic genera and inverted their frequency of contamination. MC caused by Alternaria spp. increased its incidence during storage. As MC fruits are more likely to be incorporated to the process line, these results suggest a high risk of contamination of apple by-products with Alternaria toxic metabolites.