Application of raisin extracts as preservatives in liquid bread and bread systems.

Interest in natural ingredients with multifunctions in food has led to the investigation of the antimicrobial activity of raisins, a traditional baking ingredient. Water and 60% ethanol extracts, and raisin juice concentrate (RJC, a commercial food ingredient) were assessed for their ability to inhibit the growth of ropy-bread-causing Bacillus species. The ability of these additives and raisin paste were tested for antifungal activity in liquid bread model system and bread. In the liquid bread model, concentrations as low as 20 and 36 mg crude extract or RJC per gram media significantly (P < 0.05) reduced the populations of B. licheniformis and B. subtilis, respectively. A significant reduction in the population of Aspergillus flavus and Penicillium chrysogenum was achieved at 80 and 470 mg crude extract per gram media, respectively. Bread formulas containing 7.5% of a water extract (equivalent to 70 mg extract per gram dough) or RJC (70 mg/g dough) produced bread that had equivalent mold-free shelf life. The mean mold-free shelf life of the bread containing 7.5% water extract was 18.1 +/- 3.3 d at room temperature while the negative control was mold free for 9.4 +/- 2.4 d. The antifungal efficacy of the extracts in bread was equivalent to 0.24% calcium propionate in 21 d of storage. Doubling the concentration of the extract did not improve the mold-retarding property in bread. The bread containing raisin paste, the percentage of which in dough was equivalent to 15% raisin extract, exhibited a stronger antifungal activity than did the extracts in bread.