FLAVOUR CHANGES IN STRAWBERRIES PACKED IN MODIFIED ATMOSPHERES

The responses of strawberries to high CO₂ and/or low O₂ concentrations have been extensively studied in experimental controlled atmosphere (CA) systems. The main effects of such CA conditions are less decay, firmer texture, and at CO₂ concentrations above 15–20 % also the development of off-flavours. However, only a few have studied the effects of a modified atmosphere (MA) system where the atmosphere is created as a result of the respiration of the fruit combined with the permeability of the packaging material, and the purpose of the present study was to investigate how the flavour of some Danish-grown strawberry cultivars is affected by packing in different MA films.

Ripe strawberries of the cultivars Elsanta, Elvira and Pandora were packed in some commercial MA producing films and stored at 3 °C for 7 days. The content of general strawberry aroma compounds as well as the very volatile compounds ethyl acetate, acetaldehyde and ethanol were measured before and after storage, and the fruit was evaluated sensorily.

Atmospheres developed during storage were 0.5, 1 and 1 % O₂ and 45, 20 and 11 % CO₂ respectively in the different types of film. For all MA stored fruit a very strong off-flavour was developed, and because of the anaerobic respiration the content of acetaldehyde, ethanol, ethyl acetate and other ethyl or acetate esters increased while the content of methyl ester, and hexanal and trans-2-hexenol decreased.

Thus the whole pattern of aroma compounds was changed, but the highest increases were found for ethanol and ethyl acetate and the concentrations of these compounds were most highly correlated to the off-flavour. However, the odour threshold of ethanol is much higher than that of ethyl acetate so ethyl acetate must be regarded as the most important compound in the anaerobic off-flavour of strawberries, and this is also indicated by a strong ethyl acetate note of this off-flavour.