Modelling the combined effect of temperature, pH and aw on the growth rate of Monascus ruber, a heat-resistant fungus isolated from green table olives

Abstract

Aims: Growth modes predicting the effect of pH (3AE5-5AE0), NaCl (2-10%), i.e. a w (0AE937-0AE970) and temperature (20-40°C) on the colony growth rate of Monascus ruber, a fungus isolated from thermally-processed olives of the Conservolea variety, were developed on a solid culture medium. Methods and Results: Fungal growth was measured as colony diameter on a daily basis. The primary predictive model of Baranyi was used to fit the growth data and estimate the maximum specific growth rates. Combined secondary predictive models were developed and comparatively evaluated based on polynomial, Davey, gamma concept and Rosso equations. The data-set was fitted successfully in all models. However, models with biological interpretable parameters (gamma concept and Rosso equation) were highly rated compared with the polynomial equation and Davey model and gave realistic cardinal pHs, temperatures and a w . Conclusions: The combined effect of temperature, pH and a w on growth responses of M. ruber could be satisfactorily predicted under the current experimental conditions, and the models examined could serve as tools for this purpose. Significance and Impact of the Study: The results can be successfully employed by the industry to predict the extent of fungal growth on table olives.

Effect of Temperature, pH and Water Activity on <i>Penicillium digitatum</i> Growth

“…These results are concordant with that published by Neumeyer's team [28] who established that Pseudomonas growth rate is unaffected by pH in the range pH 5.4 to 8.6. Similar results have been reported for fungi growth [5] [11] [12], in general, when pH interval studied is around of optimal pH range for microorganism growth, not significant lineal or interactive effects were found regardless of acids nature (acetic, lactic, phosphoric, citric or hydrochloric acids) used to adjust pH. Otherwise, significant effects were reported when pH range studied is far of optimal region for growth when potassium citrate [13] was used to buffering media in a pH range of 2.8 to 3.3.…”

Use of Gradient Plates To Study Combined Effects of Temperature, pH, and NaCl Concentration on Growth of Monascus ruber van Tieghem, an Ascomycetes Fungus Isolated from Green Table Olives

“…Finally, the temperatures were 25, 30, and 35°C, which are common storage temperatures, particularly during the summer. Lower temperatures (e.g., 20°C) were not selected because fungal growth is slow (12), and consequently, growth would take longer to be detected on the plates. This could probably cause a problem in the gradient plate technique owing to diffusive breakdown of the gradients due to prolonged incubation (8).…”

“…The surviving ascospores can grow at low oxygen tension during storage, resulting in significant spoilage which is not confined to mycelium on the surface of the olives but also softens the fruit and increases the pH of the product. Ascospore germination depends on pH, NaCl concentration, and storage temperature (12). An effective way to study the simultaneous effect of these parameters on fungal growth is with gradient plates, which yield overall trends of combined variables on growth.…”

Modelado del Efecto de la Temperatura, Actividad de Agua y pH sobre el Crecimiento de Rhizopus oryzae

“…El crecimiento de los hongos presenta también esta diversidad de curvas de crecimiento, y el modelo de Baranyi ha sido usado también para ajustar las curvas de crecimiento de estos microorganismos (Meletiadis et al, 2001;Panagou et al, 2003). Y aunque el diámetro de las colonias no necesariamente representa la verdadera naturaleza del crecimiento de los hongos, es la forma más simple y directa de medir el crecimiento (Gibson y Hocking, 1997).…”