Effect of water activity on the stability of freeze-dried oyster mushroom (Pleurotus ostreatus) powder

• Published in: Drying technology Vol. 39; no. 8; pp. 989 - 1002
• Main Authors: Pascual-Pineda, L. A., Hernández-Marañon, A., Castillo-Morales, M., Uzárraga-Salazar, R., Rascón-Díaz, M. P., Flores-Andrade, E.
• Format: Journal Article
• Language: English
• Published: Philadelphia Taylor & Francis 2021; Taylor & Francis Ltd
• Subjects: Adsorbed water; Adsorption; Antioxidants; Color; Dehydration; Entropy; Freeze drying; Harkins-Jura plot; Integrals; Isotherms; Low temperature; Mathematical analysis; Minimum integral entropy; monolayer; Monolayers; Mushrooms; sorption isotherm; Stability analysis; Stability criteria; Surface chemistry; Water activity; Water film; Water spreading
• ISSN: 0737-3937; 1532-2300
• DOI: 10.1080/07373937.2020.1739064

The water spreading pressure was evaluated as a criterion of food stability in the relationship with the monolayer and minimum integral entropy of the water adsorbed on the surface of the freeze-dried Pleurotus ostreatus powder. The monolayer and the thermodynamic functions were calculated from the water adsorption isotherms obtained by a static method at 25, 35 and 45 °C, over a range of water activities from 0.11 to 0.79, and the surface of the powder was investigated using low-temperature nitrogen adsorption. The color parameters (L*, a*, b*), laccase activity and antioxidant capacity of the product were evaluated during storage at different water activities at 25 °C. The maximum color stability occurred in the range of water activity from 0.23 to 0.32, which coincided with the low tendency to contraction or spreading of the water adsorbed on the surface. These values correspond to the water activities of the monolayer and minimum integral entropy due to that the water film was in a condensed phase. The results also showed that the water activity affects the enzyme stability significantly, but slightly the antioxidant capacity of the mushroom during the storage. The study concludes that the analysis of the spreading pressure contributes to determining the more suitable conditions for storage of the dehydrated foods; in addition to that, it has the advantage of being calculated from an isotherm of water adsorption.