Isolation of Antifungal Lactic Acid Bacteria from Food Sources and Their Use to Inhibit Mold Growth in Cheese

<p>A large amount of cheese is lost every year due to mold contamination. Biopreservation, which is the use of biological entities (microbes) and their metabolites to suppress microbial spoilage instead of chemical preservatives has lately gained increasing interest. Lactic acid bacteria (LAB) have the potential for use in biopreservation, because they are safe to consume and naturally exist in many foods. In this study, fifteen strains of lactobacilli isolated from dairy products, vegetables, and fermented pickles were tested by agar overlay assay for their anti-mold activity. Six strains grown on MRS agar showed strong inhibitory activity against a target mold (<em>Penicillium</em> sp. at 10⁵spores/ml) isolated from the surface of Cheddar cheese. The isolates were identified by biochemical tests using API CHL50 strips. Five strains were identified as <em>Lactobacillus plantarum</em>, and one strain as <em>Pediococcus pentasaceus</em>. Well-diffusion method was used to demonstrate anti-mold activity in <em>concentrated </em>cell-free supernatants. Supernatants from all strains showed inhibition of the target mold (indicator). The anti-mold compound(s) produced by all the strains was heat-resistant (100^o C for 15 min). Supernatants from 5 strains retained the anti-mold activity when the pH was adjusted to 6.8 ± 0.2, while one strain DC2 isolated from cheese lost its anti-mold activity at that pH. Temperature of incubation of cultures affected anti-mold activity. The optimum was 37^o C. Very little or no inhibition was noted when cultures were incubated at either 10 or 55 °C.</p> <p>A preliminary study of applying anti-mold lactobacilli in Cheddar cheese was completed. Anti-mold LAB was added to the cheese milk as <em>an adjunct</em> to give 10⁵ cfu/ml. After 1-week and 1-month ripening, mold (10~20spores) was added on to the surface, and the cheese was wrapped loosely. The appearance of the mold on cheese surface was monitored. Mold was not present on the 1-week old cheese “NB in milk” until the 6^th day after the control cheese (made without strain NB) showed signs of mold. The 1-month old cheese “NB in milk ” extended the shelf life 17 days longer than the control cheese.</p>

Name thesis:degree_name

MS in Agriculture - Dairy Products Technology

Discipline thesis:degree_discipline

Dairy Science

Year dc:date.available

2011

Author dc:creator

• Zhao, Dan

Contributors dc:contributor

• Nana Y. Farkye

• antifungal lactic acid bacteria
• cheese
• biopreservative
• mold
• Agriculture

Identifier

10.15368/theses.2011.99

OAI identifier oai:identifier

oai:digitalcommons.calpoly.edu:theses-1574