Produção de panetone utilizando bactérias ácido láticas e leveduras isoladas de fermento natural liofilizado

Abstract

Natural yeast (sourdough) is a mixture composed of wheat flour and water being fermented by the action of lactic acid bacteria (LAB) and yeasts, used to make some bakery products, such as panettone. Panettone is a product typically marketed in the Christmas period and has a long shelf life, in part due to the pH characteristics and the type of fermentation to which the dough is subjected. The microorganisms involved in the natural fermentation are diverse, with predominant microbiota composed of yeasts and lactic acid bacteria. During their multiplication, these microorganisms produce metabolites able to imprint peculiar sensorial characteristics to the products, as well as to modify physical-chemical characteristics and of stability to the fungal deterioration. The identification of these microorganisms is fundamental to enable studies of interaction between microbial communities, and their isolation and conservation are fundamental for their industrial use as starter yeasts. This doctoral thesis aimed to evaluate the influence of a sourdough composed of lactic acid bacteria and yeasts on the microbiological stability of panettones, aiming to increase the shelf life without the addition of chemical preservatives. To that end, initially the predominant microorganisms in the raw materials (refined wheat flour, wholewheat flour) and sourdough were isolated in the media from Man, Rogosa and Sharpe (MRS) and Sabourand Dextrose Agar (SDA) and were identified through sequencing. Subsequently, some species of microorganisms were selected, based on scientific literature, to evaluate their potential for use in the elaboration of panettones. One of the constraints for large-scale use of these microorganisms is the maintenance of their viability and characteristics over time. Thus, studies were conducted by freeze-drying some isolated microorganisms with different cryoprotectants (sucrose, trehalose, skim milk and sodium glutamate) and evaluated their viability throughout the storage at room temperature. Finally, different formulations were prepared and panettones were elaborated with these freeze-dried microorganisms, which were characterized physicochemistry (instrumental firmness, specific volume, color, moisture, water activity, pH and titratable total acidity), sensorial (check- all-that-apply - CATA, acceptability and purchase intent) and microbiologically (enumeration of molds and yeasts). The predominant microorganisms recovered and identified from the raw materials and freeze-dried sourdough were Saccharomyces cerevisiae, Wickerhamomyces anomalus (Syn. Pichia anomala), Pediococcus pentosaceus, Lactobacillus plantarum and Lactobacillus fermentum. The addition of trehalose promoted a cryoprotective effect on the microorganisms and was more significant for the yeasts. Trehalose provided satisfactory viability rates only for W. anomalus during one year of storage at room temperature. On the other hand, the solutions with 10% of skimmed milk plus 5% of sodium glutamate maintained the highest indexes of cellular stability for Lb. fermentum and W. anomalus during the storage period. The preparation of panettones from selected strains and without artificial preservatives proved to be a more natural and promising alternative in view of the fact that it was well accepted in the sensory field. The panettone made with 50% Lb. fermentum and 50% of W. anomalus presented the best physico-chemical and microbiological characteristics. By the CATA test it was possible to observe a clear distinction between the panettones elaborated with sourdough of those made with commercial yeast. The artisanal panettones proved to be very competitive in comparison to the control and commercial panettones showing more soft throughout the useful shelf life. The commercial panettone showed higher marks in the acceptance test, however it remained stable for only 30 days. Panettones made with sourdough, although presenting conditions susceptible to fungal growth, such as high water activity, did not mold until the 126 days of storage. The use of Lb. fermentum IAL 4541 and W. anomalus IAL 4533 as starters in the production of panettones without artificial preservatives can be considered a promising technological alternative that meets the strong demand of consumers for more natural products.