Abstract
Lactic acid fermentation is a natural method of antimicrobial food protection. Antagonistic activity of Lactobacillus sp. bacteria, taking part in this process, is directed mainly against the same or other microorganisms. In this work we determine the impact of the presence of xylitol and galactosyl-xylitol on the antagonistic activity of 60 Lactobacillus sp. strains against indicator molds (Alternaria alternata, Alternaria brassicicola, Aspergillus niger, Fusarium latenicum, Geotrichum candidum, and Mucor hiemalis) and yeasts (Candida vini). We used double-layer method to select antifungal strains of Lactobacillus bacteria and poisoned medium method to confirm their fungistatic properties. Additionally, we examined the inhibition of Alternaria brassicicola by Lactobacillus paracasei ŁOCK 0921 cultivated with xylitol or galactosyl-xylitol directly on wild cherries. The presence of xylitol and its galactosyl derivative led to increase of spectrum of antifungal activity in most of the studied plant-associated lactobacilli strains. However, no single strain exhibited activity against all the indicator microorganisms. The antifungal activity of Lactobacillus bacteria against molds varied considerably and depended on both the indicator strain and the composition of the medium. The presence of xylitol and galactosyl-xylitol in the growth medium is correlated with the antifungal activity of the studied Lactobacillus sp. bacteria against selected indicator molds.
Highlights
Lactic acid fermentation constitutes one of the oldest methods of protecting food from undesirable microflora
First group consisted of 20 strains of L. acidophilus designated as 7, 0840, 0842, 0926–0939, and 0941–0943; second one consisted of 23 strains of L. casei/paracasei: L. casei 0848, 0901–0907, 0909–0911, and 0919, Paris, NCDO206, and L. paracasei 0912, 0913, 0917, 0918, 0920–0922, 0924, and 0985; third group consisted of 13 plantassociated strains: L. plantarum 0981, 0982, 0989, and 0990, L. pentosus 0979 and 0991, L. brevis 0944, 0980, 0983, and 0984, L. helveticus, L. delbrueckii 0854, and L. casei 1020; and the last one consisted of 4 strains isolated from humans: L. casei 0919, L. delbrueckii 0987, L. mucosae 0988, and L. rhamnosus 0908
L. acidophilus, L. casei, L. helveticus, L. paracasei, and L. rhamnosus were incubated at 37∘C under aerobic conditions, the strains isolated from humans at 37∘C in the presence of CO2, and the plant-associated under aerobic conditions
Summary
Lactic acid fermentation constitutes one of the oldest methods of protecting food from undesirable microflora. Lactic acid bacteria (LAB) generate antimicrobial compounds inhibiting the growth of related species and show low antagonistic activity towards fungi, the most widespread food spoilage factors. Our preliminary studies confirmed that polyols (glycerol, lactitol, erythritol, sorbitol, and mannitol) may enhance the antifungal activity of LAB [2]. Some polyols such as sorbitol, xylitol, erythritol, and lactitol are applied in the food industry and benefit human health [4]. The effect of xylitol and its galactosyl derivative on antifungal properties of LAB has not been studied in detail. Galactosyl-xylitol represents a modern prebiotic and can improve condition of gastrointestinal track
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