Combined effect of water activity and pH on the growth of food-related ascospore-forming molds
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Racchi et al. Annals of Microbiology (2020) 70:69 https://doi.org/10.1186/s13213-020-01612-6
ORIGINAL ARTICLE
Open Access
Combined effect of water activity and pH on the growth of food-related ascosporeforming molds Irene Racchi1, Nicoletta Scaramuzza2, Alyssa Hidalgo1*
and Elettra Berni2
Abstract Purpose: The contamination of raw materials, packaging, or processing environments by fungal ascospores is a real concern for food industries, where variable rates of spoilage can be reached in pasteurized acidic products such as fruit juices, fruit jams, or soft drinks. The aim of this work was to assess the combined effect of aw and pH on the growth of six isolates from three genera of ascospore-forming molds that may occur in raw materials and in food industrial environments, in order to determine the environmental conditions that prevent the spoilage of pasteurized foods and beverages. Methods: Growth tests were carried out on 60-day-old ascospores from Aspergillus hiratsukae (≡Neosartorya hiratsukae), Aspergillus thermomutatus (≡Neosartorya pseudofischeri), Chaetomium flavoviride, Chaetomium globosum, Talaromyces bacillisporus, and Talaromyces trachyspermus. The tests were performed up to 90 days at 25 °C, using sucrose solutions at different aw (0.85, 0.88, 0.92, 0.95) and pH (3.20, 3.50, 3.80, 4.20, 4.60) values. Growth was characterized by fitting an ordinary logistic regression model to the collected growth data. Results: The explained percentage of the growth/no growth models ranged between 81.0 and 99.3%: aw exerted the largest influence on the growth of all tested species, while pH was significant only for Chaetomium isolates. The minimum conditions for germination and growth were aw 0.92 and pH 3.50 or 3.80, respectively, for C. flavoviride (46 days) and C. globosum (39 days), aw 0.92 and pH 3.20 for T. trachyspermus (13 days), aw 0.88 and pH 3.20 for T. bacillisporus (39 days), and aw 0.88 and pH 3.20 for the two aspergilli (33 and 27 days, respectively, for A. hiratsukae and A. thermomutatus). Conclusions: Most of the spoiling mycetes tested were well-adapted to the formulations considered; therefore, foods strategies aiming to inhibit their growth should explore also the hurdle effect exerted by other factors (e.g., antioxidants, organic acids, oxygen levels). Keywords: Water activity, pH, Growth tests, Talaromyces, Neosartorya, Chaetomium
Introduction About one third of the food produced for human consumption every year is lost or wasted (EU 2016; FAO 2012). Although losses due to microbial contamination or spoilage by bacteria, yeasts, and molds are not welldocumented, this is a real concern for the food industry * Correspondence: [email protected] 1 Università degli Studi di Milano—DeFENS-Facoltà di Scienze Agrarie e Alimentari, Via Giovanni Celoria, 2, 20133 Milano, Italy Full list of author information is available at the end of the article
(Elkhishin et al. 2017). For pasteurized high acidic fruit products, where only some microorganisms can grow, most of the juice processor members
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