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Selective survival of dairy cultures to high-pressure processing by leveraging freeze-drying and encapsulation.

M. McGillin



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Selective survival of dairy cultures to high-pressure processing by leveraging freeze-drying and encapsulation.
M. McGillin*, S. Alcaine. Cornell University Ithaca, NY.

High-pressure processing (HPP) is an increasingly adopted non-thermal treatment for food products. Although effective at inactivating vegetative cells, spores can survive and potentially germinate, hence the need for additional hurdles to address them. Biopreservation utilizes select food-grade microbes to inhibit the growth of undesired microbes. Furthermore, in many low acid foods, such as dairy, a subsequent selective culture activity is desired. Currently, adding desirable microbes to a food matrix before HPP inactivates them. A potential way to circumvent this issue is to maintain the cultures in a desiccated, spore-like state, which enables them to resist the damaging effects of HPP. For application in a high moisture food, an encapsulation system that maintains desiccation prior and during HPP, followed by rehydration post-HPP is required. To evaluate the survival of desiccated cultures to HPP treatment, cell counts of freeze-dried lactic acid bacteria (LAB) cultures (HPP-FD-LC) and hydrated LAB cultures (HPP-LC) were compared. There was approximately a 7.5 log difference between HPP-FD-LC (6.27 � 108 cfu/mL) and HPP-LC (3.29 cfu/mL) post-HPP (600 MPa, 3 min, 5�C), demonstrating the role desiccation plays in HPP survival. To delay the hydration of the HPP-FD-LC in a high-moisture food matrix, the cultures were encapsulated in cocoa butter (33�C) by homogenization before HPP, resulting in cocoa butter encapsulated freeze-dried cultures (CB-FD-PC). A response surface model was generated to optimize homogenization factors of temperature, speed, and duration. Analysis of the model determined the optimal factors to be 4000 rpm for 3 min at 33�C. The only significant factor (α < 0.05) proved to be the starting temperature, demonstrating a relationship between lower temperatures and higher viability. Future work will determine the rate of rehydration of the encapsulated cultures within a high-moisture food matrix (i.e., skim milk), to establish the processing window in between introducing the encapsulated cultures into the food matrix and the HPP treatment.

Keywords: high-pressure processing, protective cultures, encapsulation.