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Virginia Sea Grant funded research

The Effect of High Hydrostatic Pressure Processing on Microbial Quality, Shelf-life Extension, Drip Loss, and Physical Characteristics of Oysters (C. virginica and C. ariakensis)

George Flick, Stephanie Penn (Va Tech)

The overall objective is to determine the feasibility of implementing high hydrostatic pressure (HPP) technology for processing oysters, Crassostrea virginica and Crassostrea ariakensis. This objective will be achieved through the application of various strategies assessing how HPP processes affect selected chemical, biological, and physical composition parameters of the oysters. Summer and winter oysters will be subjected to various pressures, times, and temperatures to determine: (A) the effect(s) on color, yield, drip loss (bleed rate), appearance, microbial populations, and shelf-life after processing and refrigerated storage; electron microscopy studies will be performed to determine cellular damage resulting from the HPP treatments; (B) the effect of season and packing media on bleed rate during refrigerated storage; (C) the effect(s) of post-harvest holding times and HPP process schedules on release of the adductor muscle from the shells; (D) the identification of barotolerant microorganisms; (E) the contribution of barotolerant microorganisms toward spoilage and shelf-life; (F) the characterization of oyster waste water from various HPP processes; (G) the processing efficiencies of hand shucking vs. HPP shucking ; (H) the potential for Virginia processors to implement the technology either independently or through formation of a cooperative; and (I) the project results will be disseminated to stakeholders.

Gulf and East coast oysters (as well as C. ariakensis) oysters will be processed during the winter and summer at varying times, pressures, and temperatures. The effect on color will be determined with a Minolta Color Meter. Oysters will be shucked by hand or with the assistance of a knife to determine the effects of varying process schedules on yield. High hydrostatic pressure processed oysters will be stored at two temperatures (0° and 4° C) and examined after storage (0, 3, 6, 9, 12, 18, and 20 days) for drip loss, microbial populations, and physical appearance (using AOAC/BAM procedures). Microbial populations surviving HPP treatments will be enumerated using two fastidious media (Chopped Meat and Brain Heart Infusion Agar containing salt to assist in the recovery of injured and halophilic organisms). Transmission and scanning electron microscopy studies will be determined and photographs taken to record the changes. Oysters will be held at approximately 40° F (4.4° C) varying times, temperatures, and pressures to determine thels. Microorganisms surviving the various HPP processes will25-Jan-2008e) using the Sherlock Microbial Identification System. Microbial isolates surviving the HPP treatments will be inoculated into andDate --> The samples will be stored and smelled by trained panelists a C to determine which microorganisms contribute to spoilage. This information will enable one or more HPP process schedules to be identified that will extend shelf-life and maintainby professional oyster shuckers and individuals having no experience in oyster shucking will help determine whether inexperienced individuals could be employed in firms where HPP technology is utilized. Results of the project will be presented to representatives of the Virginia oyster industry to determine whether individual firms or an industry cooperative will implement the technology. Results of the project will be disseminated to stakeholders through trade publications, refereed journals, and industry and professional society conferences.

This project is urgently needed before the Gulf and East coast oyster industry can seriously consider investment in high hydrostatic pressure technology. The technology has been successfully implemented for half-shell Gulf coast oysters but not for shucked oysters. There has been only limited information published on the effects of high hydrostatic pressure processing on oysters and those publications have only included two species, Crassostrea gigas and Ostrea edulis, neither of which is present on the Gulf and East coasts. The published papers did not investigate important aspects of oyster processing such as shelf-life extension (which is important to Gulf and East coast processors especially during the Thanksgiving and Christmas seasons); post-processing drip loss; increased process efficiency; identification of barotolerant microorganisms and their contribution to quality and safety; and optimum processing schedules. Also, microbiological studies did not consider the use of resuscitation media or added salt.