Water potentials and soluble carbohydrate concentrations in tissues of freshly harvested and stored mushrooms (Agaricus bisporus)

Abstract

Abstract The mechanism of water uptake in the cultivated mushroom, Agaricus bisporus was investigated by examining the relationship between total water potential (ψw), component osmotic (ψs) and turgor (ψp) potentials on the one hand and sugar and sugar alcohols concentrations on the other, in different tissues during storage for up to 5 days at 18 and 25°C and 90 and 95% relative humidity. Storage humidity had no effect on tissue water relations in the five tissues examined, although significant temporal changes in water relations over the 5-day storage period were observed. The gills had the highest mean ψw (−1.0 to −1.5 MPa), while the peel had the lowest mean level (−1.5 to −2.5 MPa). The mean turgor potential was approximately +0.5 MPa. Rising ψp often coincided with declining ψs in the upper stipe, inner cap and gill tissue. Sugar (glucose and trehalose) and polyol (mannitol, arabitol, erythritol and glycerol) concentrations in these various sporophore tissues also produced distinct patterns over time. The disaccharide trehalose was present at 5–10 mM concentration throughout the storage period. In contrast, glucose concentrations were highest in the lower stipe tissue immediately after harvesting. The predominant polyol was mannitol (60–100 mM), which decreased in concentration after harvest, for up to 3 or 4 days of storage, depending on the tissue. Glycerol was only present in the gills initially, but concentrations rose significantly in inner cap tissue after 5 days storage. Statistically significant correlations between ψw, its components and sugar/polyol concentrations were found on specific days of storage.