Synergistic effect of chemical preservatives with ethanol on the microbial shelf life of bread by factorial design

The shelf life, particularly the mould-free shelf life (MFSL) of bread, was evaluated either by adding a conventional chemical preservative or by spraying the surface of bread, in which a chemical preservative was added. As bread making is a complex process and bread is a multicomponent system, the investigation was based on statistical design experiments. Using first-order factorial designs, reliable models were constructed, revealing the effects of some common ingredients of bread (such as salt, sugar, glycerol, potassium sorbate, calcium propionate) and their interactions on the MFSL (optimisation parameter) with and without ethanol surface spraying. The effectiveness of preservation was ranked as potassium sorbate + ethanol > calcium propionate + ethanol > potassium sorbate > calcium propionate. Ethanol addition led to MFSL prolongation of 43.5% and 38.5% compared with MFSL of potassium sorbate and calcium propionate, respectively, when all the factors were fixed to their basic levels.