Multiple Techno-Functional Characteristics of Leuconostoc and Their Potential in Sourdough Fermentations

Abstract

In this study, the potential of Leuconostoc as non-conventional sourdough starter cultures was investigated. A screening for antifungal activities of 99 lactic acid bacteria (LAB) strains revealed high suppression of bakery-relevant moulds in nine strains of Leuconostoc with activities against Penicillium sp., Aspergillus sp., and Cladosporium sp. Mannitol production was determined in 49 Leuconostoc strains with >30 g/L mannitol in fructose (50 g/L)-enriched MRS. Further, exopolysaccharides (EPS) production was qualitatively determined on sucrose (40 g/L)-enriched MRS agar and revealed 59 EPS positive Leuconostoc strains that harboured dextransucrase genes, as confirmed by PCR. Four multifunctional Lc. citreum strains (DCM49, DCM65, MA079, and MA113) were finally applied in lab-scale sourdough fermentations (30 °C, 24 h). Lc. citreum was confirmed by MALDI-TOF MS up to 9 log CFU/g and pH dropped to 4.0 and TTA increased to 12.4. Antifungal compounds such as acetic acid, phenyllactic and hydroxyphenyllactic acids were determined up to 1.7 mg/g, 2.1 µg/g, and 1.3 µg/g, respectively, mannitol up to 8.6 mg/g, and EPS up to 0.62 g/100 g. Due to the observed multifunctionalities and the competitiveness in the natural flour microbiota present in sourdoughs, non-conventional LAB genera such as Leuconostoc seem promising for application in sourdough-based bakery products.

Potential of a Techno-Functional Sourdough and Its Application in Sugar-Reduced Soft Buns

“…The selection of those two LAB were based on their functional activities, which are as follows: Lc. citreum DCM65 was previously described by Müller et al [26] as a multifunctional lactic acid bacterium due to its antifungal activities against molds belonging to the genera Cladosporium and Penicillium, mannitol production, and EPS forming functionalities during sourdough fermentation. Additionally, Lpb.…”

“…Bacterial cultures were prepared as described by Müller et al [26] with the following modifications: 10 mL of a food grade medium (30 g/L vegetable peptone broth (Oxoid), 20 g/L dehydrated wheat syrup (Meurens Natural S.A., Herve, Belgium), 10 g/L maltose, 0.05 g/L manganese sulfate (Roth, Karlsruhe, Germany), and 0.5 g/L magnesium sulfate (Roth, Karlsruhe, Germany) was inoculated with one colony of a fresh culture and incubated at 30 • C for 17 h. The strains of the co-culture were incubated as single cultures in a separate tube. The sourdough was prepared by mixing tap water and wheat flour (W550 obtained from Stadtmühle Schenk AG, Bern, Switzerland) 1:1, saccharose (1.5%) and fructose (1.5%), followed by inoculation with 1 × 10 7 CFU/g of pure culture of Lc.…”

“…Fructose, mannitol, acetic acid, and lactic acid were analyzed in sourdough before (t 0 ) and after (t 24 ) fermentation by high performance liquid chromatography (HPLC) as described by Quattrini et al [36] and Müller et al [26]. Samples were diluted 1:5 with double distilled water and incubated for 3 h at 80 • C. Then, the samples were centrifuged (5000× g, 4 • C, 5 min, Sigma Laborzentrifugen GmbH, Osterode am Harz, Germany) and the supernatants were diluted 1:1 with 7% perchloric acid followed by storage overnight at 4 • C. Again, the samples were centrifuged as mentioned above and sterile filtered (0.2 µm) prior to HPLC analysis on an Agilent 1260 system (Agilent, Santa Clara, CA, USA) using a Rezex RPM monosaccharide PB + 2 column (300 × 7.8 mm, Phenomenex, Torrance, CA, USA) and a guard column (Carbo-Pb; Phenomenex, Torrance, CA, USA) coupled to an RI detector (1260 RID G1362A, Agilent, Santa Clara, CA, USA, temperature set to 50 • C) to quantify mannitol and fructose using double distilled water as an eluent with a flow rate of 0.6 mL/min at a temperature of 85 • C. Lactic and acetic acids were quantified using a ROA-Organic Acid H+ column (150 × 4.6 mm, Phenomenex, Torrance, CA, USA) and a guard column (Carbo-H, Phenomenex, Torrance, CA, USA) using 0.005 M sulphuric acid as eluent with a flow rate of 0.2 mL/min at 25 • C. Of each sample 5 µL was injected.…”

“…Bacterial exopolysaccharides (EPS) are described for their positive impact on bread qualities, such as decreasing the crumb firmness [22]. Dextran, an EPS consisting of α-(1→6)-linked glucopyranosyl units, can be produced by LAB species of the genera Weissella [23] and Leuconostoc [24][25][26] when sucrose is metabolized. Amylases, used in bakery products to soften the bread crumb due to degradation of starch to smaller molecules, such as dextrin [27], may be replaced by amylolytic LAB, such as strains C5 or OB8 of Lactiplantibacillus (Lpb.)…”

“…plantarum [28][29][30]). Furthermore, LAB were also described as producing antifungal metabolites including organic acids (acetic, lactic, and phenyllactic acid) [26,31], fatty acids [32], or cyclic dipeptides [33]. Yet, these LAB antifungal activities are not fully understood, however, synergistic effects were described for mold inhibition, for example, in bread application by Axel et al [34] under acidic conditions.…”