Essential oils against yeasts and moulds causing food spoilage

In foodstuffs with low pH, low water activity, or high carbohydrate content spoilage bacteria are, with some exception, usually not present because this environment is unfavourable for their growth. Food-spoilage yeasts and moulds, however, can grow under these circumstances and cause deterioration of various products, such as fruit and vegetable juices and purees, soft drinks, pickled vegetables, dairy products, bread, dried fruits, sausages. Heat treatment and antiseptic packaging exclude yeast and mould spoilage as long as the packaging is intact. Products that cannot be pasteurized are usually treated with weak acid preservatives: sorbic, propionic or benzoic acid or their salts. However, there is a strong consumers’ demand to avoid or diminish the use of artificial substances in their food. Chemical preservatives also present some problems: it was recently reported that benzene can be formed from benzoic acid in foods by decarboxylating action of some spoilage microorganisms. The use of plant-derived essential oils (EOs) or their components as natural preservatives can overcome these problems. Most EOs are regarded as safe (GRAS) and are accepted by consumers. EOs can be added directly to the food or can be applied in active packaging in vapour phase. Both our experiments and data from the literature showed that EOs and their components increase the lag phases and diminish the maximum cell count in the stationary phase of yeast growth. The colony forming ability of moulds was also reduced or stopped by the EOs. The strong aroma of the EOs can affect the organoleptic properties of the foods but the synergistic combinations of EOs with each other or with other hurdle techniques can reduce this effect. Essential oils represent a natural, effective, and consumer-accepted tool against food spoilage caused by yeast and moulds.