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Fungal spoilage remains a challenge facing the industry with 5 – 10% of food wasted annually. This decreases manufacturers’ profitability and threatens the sustainability of the industry. It also negatively impacts consumer experience. Some mold strains have the ability to produce toxic mycotoxins endangering consumers health. Post-pasteurization contamination can occur in many stages limiting the effectiveness of pasteurization in preventing spoilage. Adding to that, consumers are increasingly looking for “clean labels” out of health consciousness. In my thesis, I focused on investigating the antifungal potential of protective cultures as well as lactose oxidase as bio-preservatives in dairy products. For protective cultures, cottage cheese and queso fresco were inoculated with 3 different commercial protective cultures (designated PC1 of Lactobacillus spp., PC2 of Lb. rhamnosus & PC3 of Lb. rhamnosus) following manufacturer recommended dosage. A positive control with no protective culture was included. Nine genera of yeast (Candida zeylanoides, Clavispora lusitaniae, Debaryomyces hansenii, D. prosopidis, Kluyveromyces marxianus, Meyerozyma guilliermondi, Pichia fermentans, Rhodotorula mucilaginosa, and Torulaspora delbrueckii) and eleven species of mold were included in the study (Aspergillus cibarius, Aureobasidium pullulans, Penicillium chrysogenum, P. citrinum, P. commune, P. decumbens, P. roqueforti, Mucor genevensis, M. racemosus, Phoma dimorpha, and Trichoderma amazonicum). All strains were previously isolated from dairy processing environment and were spotted on cheese surface at a rate of 100 CFU. Samples were stored at refrigeration temperature (6± 2 °C). Yeast levels were enumerated at 0, 7, 14 &21 days post-inoculation. Significant inhibition (p<0.05) was determined individually for each yeast strain by comparing yeast counts for each protective culture treatment against control cheese using one-way analysis of variance (ANOVA) with Bonferroni correction performed individually for at time point 7, 14- and 21-days post-inoculation. Mold growth was visually observed on cottage cheese and queso fresco for 42- and 72-days post-inoculation respectively and imaged. Results showed that commercial lactic acid bacteria varied in performance based on breadth of mold and yeast at both genus and species level, and thus each protective culture maybe ideal against specific strain taking into consideration food matrix factors impacting fungal growth. For lactose oxidase (LO), we did screening of LO antifungal activity using two different enzyme concentrations (1.2 and 12 g/L) against five Penicillium spp. strains (Penicillium chrysogenum, P. citrinum, P. commune, P. decumbens, and P. roqueforti) on set-yogurt stored at 21± 2 °C for 14 days. Through day 14, mold growth was only observed on wells with no LO for all Penicillium spp. strains. Based on this finding, we decided to detect the minimum inhibitory level of LO using four enzyme levels (0.12, 0.48, 0.84 and 1.2 g/L) each Penicillium spp. strain. For P. chrysogenum, P. citrinum, and P. roqueforti, minimum inhibitory level was detected as 0.48 g/L LO. P. commune was inhibited at higher level detected as 0.84 g/L LO. P. decumbens results suggest that it was the most sensitive among tested Penicillium spp. strains showing inhibition at LO level as low as 0.12 g/L. Comparing pH values of different LO levels (0.12, 0.48, 0.84, 1.2 and 12 g/L) on set-yogurt to control with no lactose oxidase at day 14 of storage at 21± 2°C, significant difference (p<0.0001 for each respective comparison) was detected. Nonetheless, we expect slower rate of reaction and lower impact on pH under refrigerated conditions over set-yogurt shelf life. Overall, our results suggest potential antifungal efficacy of LO against common spoilage organisms in dairy product with residual lactose and relatively low-pH.
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Food science; Lactose oxidase; Biopreservation; Fresh Cheese; Fungal Spoilage; Protective cultures; Yogurt
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Alcaine, Samuel David
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Novakovic, Andrew Milovan
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Food Science and Technology
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M.S., Food Science and Technology
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Master of Science
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dissertation or thesis
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