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The growth and survival of the psychrotroph Penicillium spinulosum in paperboard was studied along with the wicking characteristics of ultra-pasteurized milk to understand sporadic fungal contamination of ultra-pasteurized, extended shelf life milk products. Previous research has indicated paperboard packaging as a potential source for the fungal contamination. Migration from paperboard to ultra-pasteurized skim milk during a 60-day shelf life, was investigated by inoculating condia (spores) into sterilized paperboard squares (57.2 by 57.2 mm) made from ultra-pasteurized milk cartons. Test-squares were sealed on three sides and inoculated at 3.2, 6.4, 9.5 and 12.7 mm from the uncoated (unskived) edge. The surrounding milk was tested for the presence of the fungus. Penicillium spinulosum was detected in 84% of samples at 3.2, 72% at 6.4, 50% at 9.5, and 28% at 12.7 mm from the uncoated edge. Survival in paperboard was investigated in sealed paperboard test-squares incubated in ultra-pasteurized skim milk at 7°C every 10 days up to 60 days. Penicillium spinulosum survived in the interior of paperboard for the entire incubation period. Survival was also measured on all test-squares for which P. spinulosum was not detected in the surrounding milk in the migration study. Penicillium spinulosum was detected in 94.4% of all negative samples. The wicking characteristics of ultra-pasteurized skim and whole milk were measured in four boards from gable-top cartons for ultra-pasteurized milk products. Test-squares were sealed on 3 sides and incubated in ultra-pasteurized skim or whole milk at 7°C. Wicking distances were measured every 10 days up to 60 days. A significant interaction was seen between the types of paperboard and milk. It is most likely that P. spinulosum at all inoculation distances had access to milk as a source of nutrition by day 40 in the migration study. / Master of Science

Orientador: Salvador Massaguer Roig / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-05T11:20:00Z (GMT). No. of bitstreams: 1 Busani_SilviaFatimaBorges_D.PDF: 12953590 bytes, checksum: f4928b1a7cba5073da7384ea057dda79 (MD5) Previous issue date: 2005 / Doutorado / Doutor em Tecnologia de Alimentos

The initial aim of this work was to evaluate processing conditions for extended shelf life (ESL) milk to have a shelf life at refrigeration temperature of 60 d. Milk was processed on a pilot-scale ultra-high-temperature processing plant and evaluated for microbial and sensory quality over 60 d at 7°C storage. Results of this study showed that lower process temperatures were preferable to minimize cooked flavors and that the minimum safe processing temperature was 134°C for 4 s as determined by the destruction of bacterial spores in the processed milk. Consumer preference panel results indicated that consumers preferred milk processed at 134°C for 4 s (those recommended in this study for ESL processing) to commercial UHT milk although there was a slight preference for pasteurized milk. The critical sensory characteristic of the processed milk was a cooked flavor, which decreased with lower processing temperature and shorter storage time; however, a significant increase in flavors that could be associated with lipolytic activity was also noted. This study highlighted deficiencies in existing methods for determining heat-stable bacterial products in thermal-processed foods. No rapid, sensitive assay for detection of heat-stable spores or lipases in milk exists. If such assays were available, it would allow processors to determine Lipase activity and bacterial spore counts before processing and direct raw milk with low spore counts and low lipolytic activity into long-shelf-life products. To this end, assays to rapidly quantitate spores and lipolytic activity in milk were developed. The lipase assay relies on the hydrolysis of p-nitrophenyl caprylate liberating a yellow color that is detected using reflectance colorimetry. The assay is sensitive to 5 mUnits/ml and is linearly correlated to spectrophotometry (r2 = 0.93) and release of titratable free fatty acids (r2 = 0.92 to 0.97). An immunocapture, enzyme-linked immunoassay coupled with a fluorescent detection system was developed for and resulted in a prototype spore assay using Bacillus stearothermophilus spores. This organism was selected because it is extremely heat resistant, is commonly found in milk, and is associated with spoilage of milk and milk products. The assay was able to quantitate spores down to 103 cfu/ml in milk and other products in about 1.5 h. Other detection limits could be set if needed.