Bioconservation of Packed Bread by Using Antifungal Lactic Acid Bacteria

GEREZ, CARLA LUCIANA; OBREGOZO, MARIANO DAMIÁN; TORINO, MARÍA INÉS; FONT DE VALDEZ, GRACIELA

Madrid, España

Congreso; 13th ICC Cereal and Bread Congress "Cereals Worldwide in the 21st Century: Present and Future"; 2008

Asociación Española de Técnicos Cerealistas (AETC)

Fungal spoilage is the main cause of substantial economic losses in the baking industry. The incidence of moulds in bakery products in the North of Argentina is rather high mainly due to the climatic conditions (warm and wet) and the manufacturing practices. For these reasons, calcium propionate (CP) is commonly used at the highest (0.4%) concentration allowed by the Argentine Alimentary Code. The challenge is to provide new strategies of biopreservation for extending the shelf life of packed bread. In this context, lactic acid bacteria (LAB) are of particular interest; sourdough (a mixture of wheat or rye flour and water fermented by LAB, with or without yeasts) has been reported to have positive effects on wheat bread conservation (Dal Bello et al. 2007). In previous works, the culture supernatants of 95 homo- and hetero-fermentative LAB strains were evaluated for antifungal activity. Only four strains (from sourdough origin) were able to inhibit Aspergillus niger, Penicillium sp. and Fusarium graminearum. In this study, the antifungal LAB strains were evaluated in bread manufacture to develop a ready-to-use starter culture as biopreserver. L. reuteri CRL 1100, L. plantarum CRL 778, L. brevis CRL 796 and CRL 772 were individually inoculated (20% v/v) to a mixture of wheat flour, milk, sucrose and tap water. The mixture (slurry) was fermented under agitation at 37ºC for 72 h; at intervals, samples were withdrawn to determine cell viability, pH, titratable acidity and organic acids. The efficacy of the slurry as biopreserver was evaluated in an experimental model of packed bread, in which water was partially (20-60%) replaced by the slurries. A commercial S. cerevisiae was used as leavening agent. Breads chemically conserved with and without CP were used as control. Loaves were backed (180ºC/45 min) and let cooled at room temperature. The bread loaves were surface sprayed with a conidial suspension of Penicillium sp., packed into polyethylene bags, and stored at 25ºC. The packed breads were observed daily for visible mould growth; the shelf life was defined as the time (in days) for moulds to become visible. Three loaves of each bread type were evaluated in two independent assays. On the whole, the highest antifungal effect in the bread was obtained with 40% slurries that were fermented for 12 h. Differences in the bread shelf life were observed among the LAB strains, best results (5-days conservation) being obtained with L. plantarum CRL 778. In contrast, breads with neither CP nor slurries were spoiled within 2-days. The technological characteristics of the doughs were lost and breads acquired a sharp acid taste at higher (60%) slurries concentrations. The antifungal effect of the slurries was mainly related to the acidifying ability of the LAB and the low pH, which increased the un-dissociated fraction of the organic acid produced in the dough, i.e., lactic (2.3 mmol/kg) acetic (4.0 mmol/kg) and phenyllactic acid (0.02 mmol/kg). The antifungal effect of the L. plantarum CRL 778-slurry was similar to that with 0.3% CP breads. The scaling-up of the CRL778-slurry and the methodology of application in bread manufacture are under study. References  - Dal Bello F, Clarke CI, Ryan LAM, Ulmer H, Schober TJ, Ström K, Sjögren J, Van Sinderen D, Schnürer J, Arendt EK: Improvement of the quality and shelf life of wheat bread by fermentation with the antifungal strain Lactobacillus plantarum FST 1.7. Journal of Cereal Science (2007), 45, 309-318.