Year: 2005
Type: dissertation
Abstract: Lactic acid bacteria (LAB) are microorganisms that have been used for centuries to prepare and improve storage of food and for ensiling of different crops for animal feed. This thesis explores the possibility of using LAB to inhibit growth of spoilage fungi in food and feed products. LAB isolates, collected from plant material or dairy products, were screened for antifungal activity in a dual culture assay. Strains with antifungal activity were identified and the fungal inhibitory activity was further evaluated. The majority of the identified isolates belonged to the genus Lactobacillus and L. coryniformis was the dominating species. A bioassay-guided isolation method was developed to detect active compounds and Aspergillus fumigatus and Penicillium commune were used as indicator organisms. We identified two cyclic dipeptides, cyclo(L-Phe-L-Pro) and cyclo(L-Phe-trans-4-OH-L-Pro), and 3-phenyl lactic acid as fungal inhibitory compounds from L. plantarum MiLAB 393 and L. coryniformis Si3. Analysis of cell free supernatants indicate that these compounds are also produced by a Pediococcus pentosaceus and a L. sakei strain, together with yet another L. plantarum isolate. One strain, Lactobacillus plantarum L4, also produced the hydroxylated fatty acids 3-hydroxy dodecanoic acid and 3-hydroxy-5-cis-dodecenoic acid. Co-cultivation of L. plantarum MiLAB 393 and Aspergillus nidulans revealed that the fungus was affected both by morphological changes and that the total mass of mycelia was clearly decreased. Protein extracts were prepared from co-cultivated mycelia and changes in protein abundance were detected using two-dimensional differential display. Selected isolates were evaluated for their potential to enhance aerobic storage stability of grass silage. Four LAB strains improved aerobic storage stability and one strain, L. plantarum MiLAB 393, inhibited growth of spoilage yeast effectively. The actual mode of action of the identified compounds in this study has not yet been established. However, it is important to consider that these substances probably act synergistically and that other metabolic products, especially lactic acid, also contributes to the antifungal activity.
Author: Katrin Ström
Language: English
Subfield: Food Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W103579865