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Application of lactose oxidase to control Pseudomonas spp. and delay age gelation in UHT milk.

V. K. Rivera Flores

Abstract:

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Application of lactose oxidase to control Pseudomonas spp. and delay age gelation in UHT milk.
V. K. Rivera Flores*, T. A. DeMarsh, S. D. Alcaine. Cornell University Ithaca, NY.

Shelf-stable milk is consumed worldwide, and this market is expected to continue growing. One quality challenge for UHT milk shelf life is age gelation, which can be caused by bacterial heat-stable proteases (HSP) synthesized during the raw milk storage period before heat processing. Some Pseudomonas spp. are HSP producers and their ability to grow well at refrigeration temperature make them important spoilage organisms to control for UHT processors. Previous work from our group showed that lactose oxidase (LO), a commercial enzyme that produces hydrogen peroxide and lactobionic acid from lactose, can control bacterial growth in raw milk. In this research, we investigated the ability of LO to control HSP producer outgrowth and thus prevent, or delay, age gelation in UHT milk. Six strains of Pseudomonas spp. were selected based on their ability to synthesize HSP and used as a cocktail to inoculate both raw and sterile milk at a level of 1 � 105 cfu/mL. Samples were treated with and without LO, incubated for 3 or 4 d at 6�C, and monitored for cell count and pH. A heat treatment was applied after the incubation period, and particle size analysis and visual inspection were used to monitor gelation from HSP activity. Coagulation assessment -analyzed using Tukey's HSD test- showed that in sterile milk, a LO treatment [0.12 g/L] was significantly different from the control (P < 0.05). In raw milk, however, a LO treatment of 0.24 g/L was needed to prevent gelation. The test was scaled up to 18.9 L pilot plant batches of raw milk, which were challenged with the Pseudomonas spp. cocktail, and treated with LO [0.24 g/L] for 3 d. Batches were then processed with a MicroThermics UHT unit, and bottles monitored for gelation at room temperature. Significant difference in particle size between the sample treated with LO and the control was observed as early as one month after processing (P < 0.05). These results demonstrate that LO can be used to prevent age gelation in UHT milk induced by HSP-producing Pseudomonas spp., representing an opportunity to improve quality and reduce post-production losses in the shelf-stable milk market sector.

Keywords: lactose oxidase, age gelation, UHT milk.

Biography: Viviana K. Rivera Flores holds a B.Sc. in Food Engineering from Guayaquil, Ecuador. During her first years of professional experience, she worked at AB InBev, where she focused on the implementation of quality standards and the planning and execution of beer production. Viviana is now studying a Ph.D. in Food Science and Technology in the Dairy Fermentations Laboratory under the mentorship of Dr. Samuel Alcaine at Cornell University. Her research focuses on improving waste-driven sustainability along the dairy supply chain through dairy fermentations, as well as, on the use of enzymatic agents to minimize post-production losses.