Ethanol vapour pressure in bakery products

Ethanol is a common ingredient in formulated foods, naturally present or added in liquid form in order to achieve the desired sensorial properties. In many complex foods this volatile compound could also serve interesting technological functions, as well as extending their shelf-lives, owing to its capacity to inhibit or reduce the rate of microbial growth. At the European level there are no known restrictions regarding the use of ethanol in foods as a preservative, while in Italy, current regulations allow its addition as an anti-moulding agent in pre-packed bread, at a maximum concentration of 2% on a dry weight basis. This research studied the effect of water activity (a w) and water content on the ethanol vapour pressure of sliced white bread, previously equilibrated at various a w values and with 2% ethanol added. Different a w values were obtained by both rehydration from previously freeze-dried bread, and dehydration from the fresh product. The results showed that both a w and moisture affected the vapour pressure of ethanol as a consequence of water–solute and ethanol–solute interactions in the matrix. These interactions varied according to the modality of equilibration (desorption or absorption) at a given a w. The results are discussed in terms of ethanol activity (ae), computed as the ratio between the ethanol vapour pressure in bread and the vapour pressure of pure ethanol at the same temperature. This index, analogous to a w, proved to be useful in evaluating the ‘freedom’ of the ethanol present in a food matrix to be released in the vapour phase.