Antifungal Hydroxy Fatty Acids Produced during Sourdough Fermentation: Microbial and Enzymatic Pathways, and Antifungal Activity in Bread

Abstract

Lactobacilli convert linoleic acid to hydroxy fatty acids; however, this conversion has not been demonstrated in food fermentations and it remains unknown whether hydroxy fatty acids produced by lactobacilli have antifungal activity. This study aimed to determine whether lactobacilli convert linoleic acid to metabolites with antifungal activity and to assess whether this conversion can be employed to delay fungal growth on bread. Aqueous and organic extracts from seven strains of lactobacilli grown in modified De Man Rogosa Sharpe medium or sourdough were assayed for antifungal activity. Lactobacillus hammesii exhibited increased antifungal activity upon the addition of linoleic acid as a substrate. Bioassay-guided fractionation attributed the antifungal activity of L. hammesii to a monohydroxy C 18:1 fatty acid. Comparison of its antifungal activity to those of other hydroxy fatty acids revealed that the monohydroxy fraction from L. hammesii and coriolic (13-hydroxy-9,11-octadecadienoic) acid were the most active, with MICs of 0.1 to 0.7 g liter ؊1 . Ricinoleic (12-hydroxy-9-octadecenoic) acid was active at a MIC of 2.4 g liter ؊1 . L. hammesii accumulated the monohydroxy C 18:1 fatty acid in sourdough to a concentration of 0.73 ؎ 0.03 g liter ؊1 (mean ؎ standard deviation). Generation of hydroxy fatty acids in sourdough also occurred through enzymatic oxidation of linoleic acid to coriolic acid. The use of 20% sourdough fermented with L. hammesii or the use of 0.15% coriolic acid in bread making increased the mold-free shelf life by 2 to 3 days or from 2 to more than 6 days, respectively. In conclusion, L. hammesii converts linoleic acid in sourdough and the resulting monohydroxy octadecenoic acid exerts antifungal activity in bread. Sourdough bread has an extended mold-free storage life compared to that of conventionally leavened products (1, 2), and metabolites from specific strains of lactobacilli contribute to the prolonged storage life of sourdough bread (3,4,5). While the fermentation microbiota of traditional sourdough is controlled by the fermentation conditions and the choice of raw materials, the industrial production of sourdough often relies on single strains of lactobacilli with defined metabolic properties (6, 7). To date, cyclic dipeptides, phenyllactic acid, acetic and propionic acids, and short-chain hydroxy fatty acids have been identified as antifungal metabolites of sourdough lactobacilli (8, 9, 10). However, these compounds are either not produced in effective quantities in sourdough fermentations or adversely affect the quality of the product when produced in active concentrations. Cyclic dipeptides, such as 2,5-diketopiperazines, are produced in quantities 1,000-fold below the MIC against molds and are accompanied by bitter or metallic flavors if present in higher quantities (11). Similarly, the amount of phenyllactic acid produced in sourdough is 1,000 times less than the required amount for activity (8,12,13). Cooperative metabolism of Lactobacillus buchneri and Lactobacillus diolivora...

Lactobacillus brevis-based bioingredient inhibits Aspergillus niger growth on pan bread

“…A variety of systems to prevent food spoilage have been investigated mainly because of the consumers demand for natural products instead of chemicals such as food preservatives (Gray and Bemiller, 2003). The current study confirmed the antifungal properties of LAB bioingredients indicating a synergistic role of organic acids (mainly phenyllactic) and proteinaceous compounds in their efficacy, as also previously suggested (Lavermicocca et al, 2000;Gerez et al, 2010;Black et al, 2013;Ryu et al, 2014;Ryan et al, 2011). In addition the influence of the carbon source or acid precursors on the organic acid production by a selected Lactobacillus brevis strain was demonstrated.…”

“…In the latter study a L. brevis strain was selected to produce bioingredients efficient in improve yeast-leavened bread shelf life and its textural properties without affecting the leavening performance of S. cerevisiae (Valerio et al, 2014). The genus Lactobacillus was frequently involved in the antifungal activity of LAB as recently reported by some authors (Stiles, 1996;Gerez et al, 2009Gerez et al, , 2013Ryan et al, 2011;Ryu et al, 2014;Black et al, 2013) and the majority of identified antifungal substances are organic acids, hydroxy fatty acids, hydrogen peroxide, reuterin and proteinaceous compounds. Lactic and acetic acids are the main products of the fermentation of carbohydrates by LAB that generally diffuse through the membrane of the target organisms (Axelsson, 1990) in their hydrophobic undissociated form and then reduce cytoplasmatic pH and stop their metabolic activities.…”

Contribution of volatiles to the antifungal effect of Lactobacillus paracasei in defined medium and yogurt

“…Antifungal lactic acid bacteria (LAB) have been studied in a range of foods and feed like sourdough (Black et al, 2013;Lavermicocca et al, 2000), dairy products (Schwenninger and Meile, 2004) fermented vegetables (Yang and Chang, 2010), and silage (Ström et al, 2002). While most of the efforts have been directed towards finding new potent strains, there is an increasing interest in understanding the antifungal mechanism including the identification and quantification of bioactive compounds produced by these strains.…”

Regioselective Biocatalytic Hydroxylation of Fatty Acids by Cytochrome P450s

“…acting as antibiotic or anti-inflammatory [19]. A range of (R)-α-hydroxy fatty acids (C 14 -C 18 ) has shown antimicrobial activities against plant pathogenic organism such as Vibrio tyrogenuses [39], while (R)-α-and β-hydroxy fatty acids (C 10 -C 12 , and C 14 ) have shown antifungal activity against molds such as Aspergillus fumigatus, Penicillium commune and many more [17,[39][40][41]. Some β-hydroxy fatty acids (e.g.…”