Application of combined methods to prevent fungal spoilage in bakery products.

Once produced, unpreserved bakery products have a very short shelf life at room temperature. The most common causes of deterioration are changes in their texture, in their moisture and spoilage caused by microorganisms, mainly by fungi.

In the last few years, there has been an increasing demand by consumers for products without preservatives. Studies on natural systems with antifungal properties, as well as modified atmosphere packaging, have been regarded as useful alternatives to extend food shelf life without preservatives addition.

The aims of the present work were, firstly, the study of weak acid preservatives addition in fermented dough analogues (croissants) and in sponge cake analogues (magdalenas). On the other hand, the potential of some essential oils for their use as fungal growth inhibitors, in sponge cake analogues has been evaluated. Finally, the suitability of using modified atmosphere packaging in the prevention of sponge cake analogues spoilage has been studied. In all cases, the impact of aw and pH of the products on the efficacy of the treatments has been assessed. Fungal species previously isolated from a representative sample of Spanish bakery products have been used.

It has been observed that weak acid preservatives (potassium sorbate, calcium propionate and sodium benzoate) are not effective at all in the preservation of bakery products of near to neutral pH. On the other hand, the addition of the maximum permited level of potassium sorbate (0.2 %) is effective in controlling fungal spoilage during one month in products with a pH near 4.5 and a water activity below 0.80. However, the same concentration added to a product with a slightly higher pH (5.5) would be only effective for preservation for shorter periods of time. The other two preservatives were even less effective in controlling fungal spoilage at these pH levels.

Simultaneously, antifungal activity of bay, clove, thyme, rosemary, lemongrass and cinnamon leaf essential oils, was detected when added to the culture medium (£ 0,1 %) or to the surrounding atmosphere. However, their subsequent application in sponge cake analogues was not effective.

As an alternative, modified atmosphere packaging was always effective in the prevention of sponge cake analogues fungal spoilage. The use of gas mixtures with high levels of CO2 (near 100 %), as well as the combination of oxygen absorbers with modified atmosphere packaging with gas mixtures or air, were effective to control fungal growth in sponge cake analogues of near to neutral pH and 0.80-0.90 aw.

Finally, potassium sorbate efficacy has been improved by its combination with modified atmosphere packaging with 30 to 70 % CO2.

As a general conclusion, the present work has shown that reduction of water availability enables preservation of bakery products without preservative addition, regardless of their pH value. The use of weak acid preservatives is not effective to prevent spoilage of products of near to neutral pH. However, fungal spoilage of this type of products can be successfully prevented with modified atmosphere packaging.