Evaluation of the efficacy of commercial protective cultures to inhibit mold and yeast in cottage cheese.

Biopreservation is defined as using microbes, their constituents, or both to control spoilage while satisfying consumer demand for clean-label products. The study objective was to investigate the efficacy of bacterial cultures in biopreserving cottage cheese against postprocessing fungal contamination. Cottage cheese curd and dressing were sourced from a manufacturer in New York State. Dressing was inoculated with 3 different commercial protective cultures-PC1 (mix of Lacticaseibacillus spp. and Lactiplantibacillus spp.), PC2 (Lacticaseibacillus rhamnosus), and PC3 (Lactic. rhamnosus)-following the manufacturer recommended dosage and then mixed with curd. A control with no protective culture was included. Nine species of yeast (Candida zeylanoides, Clavispora lusitaniae, Debaryomyces hansenii, Debaryomyces prosopidis, Kluyveromyces marxianus, Meyerozyma guilliermondii, Pichia fermentans, Rhodotorula mucilaginosa, and Torulaspora delbrueckii) and 11 species of mold (Aspergillus cibarius, Aureobasidium pullulans, Penicillium chrysogenum, Penicillium citrinum, Penicillium commune, Penicillium decumbens, Penicillium roqueforti, Mucor genevensis, Mucor racemosus, Phoma dimorpha, and Trichoderma amazonicum) were included in the study. Fungi strains were previously isolated from dairy processing environments and were inoculated onto the cheese surface at a rate of 20 cfu/g. Cheese was stored at 6 ± 2°C. Yeast levels were enumerated at 0, 7, 14, and 21 d postinoculation. Mold growth was visually observed on a weekly basis through d 42 of storage and imaged. Overall, the protective cultures were limited in their ability to delay the outgrowth in cottage cheese, with only 8 of the 20 fungal strains showing an effect of the cultures compared with the control. The protective cultures were not very effective against yeast, with only PC1 able to delay the outgrowth of 3 strains: D. hansenii, Tor. delbrueckii, and Mey. guilliermondii. The efficacy of these protective cultures against molds in cottage cheese was more promising, with all protective cultures showing the ability to delay spoilage of at least 1 mold strain. Both PC1 and PC2 were able to delay Pen. chrysogenum and Pho. dimorpha outgrowth, and PC1 also delayed Pen. commune, Pen. decumbens, and Pen. roqueforti to different extents compared with the controls. This study demonstrates that commercial lactic acid bacteria cultures vary in their performance to delay mold and yeast outgrowth, and thus each protective culture should be evaluated against the specific strains of fungi of concern within each specific dairy facility.

Evaluation of the efficacy of commercial protective cultures against mold and yeast in queso fresco.

In this study, we evaluated the efficacy of 3 commercial protective cultures designated PC1 (Lactobacillus spp.), PC2 (Lactobacillus rhamnosus), and PC3 (Lactobacillus rhamnosus) as biopreservatives in queso fresco (QF) against 9 yeast strains (Candida zeylanoides, Clavispora lusitaniae, Debaryomyces hansenii, Debaryomyces prosopidis, Kluyveromyces marxianus, Meyerozyma guilliermondii, Pichia fermentans, Rhodotorula mucilaginosa, and Torulaspora delbrueckii) and 11 mold strains (Aspergillus cibarius, Aureobasidium pullulans, Penicillium chrysogenum, Penicillium citrinum, Penicillium commune, Penicillium decumbens, Penicillium roqueforti, Mucor genevensis, Mucor racemosus, Phoma dimorpha, and Trichoderma amazonicum). All fungal spoilage strains were previously isolated from dairy processing environments. A positive control (C) with no protective culture was included. Fungal spoilage organisms were inoculated on cheese surfaces at an inoculum level of 20 cfu/g, and cheeses were stored at 6 ± 2°C throughout the study. For yeast enumeration, cheeses were sampled on d 0, 7, 14, and 21 postinoculation. Significant inhibition was detected for each yeast strain by comparing yeast counts for each cheese treated with protective culture against the control cheese using one-way ANOVA with Bonferroni correction performed individually at d 7, 14, and 21 postinoculation. Mold growth was visually observed and imaged weekly through 70 d postinoculation. Whereas PC3 inhibited Cl. lusitaniae, Mey. guilliermondii, and Ph. dimorpha, PC2 inhibited the outgrowth of Cl. lusitaniae, D. hansenii, and Ph. dimorpha. Protective culture 1 had the broadest spectrum of efficacy across yeast and molds, delaying spoilage caused by 4 distinct yeast strains (Cl. lusitaniae, D. hansenii, D. prosopidis, and Mey. guilliermondii), and inhibiting visible growth of 2 mold strains (P. chrysogenum and Ph. dimorpha). Results demonstrated that commercial protective cultures vary in performance, as indicated by the breadth of mold and yeast inhibition at both the genus and species level. This study suggests that manufacturers looking into using protective cultures should investigate their efficacy against specific fungal strains of concern.