E:Food Engineering & Physical Properties Inactivation of Vibrio parahaemolyticus in Hard Clams (Mercanaria mercanaria) by High Hydrostatic Pressure (HHP) and the Effect of HHP on the Physical Characteristics of Hard Clam Meat Gabriel K. Mootian, George E. Flimlin, Mukund V. Karwe, and Donald W. Schaffner Abstract: Shellﬁsh may internalize dangerous pathogens during ﬁlter feeding. Traditional methods of depuration have been found ineffective against certain pathogens. The objective was to explore high hydrostatic pressure (HHP) as an alternative to the traditional depuration process. The effect of HHP on the survival of Vibrio parahaemolyticus in live clams (Mercanaria mercanaria) and the impact of HHP on physical characteristics of clam meat were investigated. Clams were inoculated with up to 7 log CFU/g of a cocktail of V. parahaemolyticus strains via ﬁlter feeding. Clams were processed at pressures ranging from 250 to 552 MPa for hold times ranging between 2 and 6 min. Processing conditions of 450 MPa for 4 min and 350 MPa for 6 min reduced the initial concentration of V. parahaemolyticus to a nondetectable level (<10 1 CFU/g), achieving >5 log reductions. The volume of clam meat (processed in shell) increased with negligible change in mass after exposure to pressure at 552 MPa for 3 min, while the drip loss was reduced. Clams processed at 552 MPa were softer compared to those processed at 276 MPa. However, all HHP processed clams were found to be harder compared to unprocessed. The lightness (L ∗ ) of the meat increased although the redness (a ∗ ) decreased with increasing pressure. Although high pressure-processed clams may pose a signiﬁcantly lower risk from V. parahaemolyticus, the effect of the accompanied physical changes on the consumer’s decision to purchase HHP clams remains to be determined. Keywords: clams, high hydrostatic pressure, postharvest treatment, shellﬁsh, Vibrio parahaemolyticus Practical Application: Shellﬁsh may contain dangerous foodborne pathogens. Traditional methods of removing those pathogen have been found ineffective against certain pathogens. The objective of this research was to determine the effect of high hydrostatic pressure on V. parahaemolyticus in clams. Processing conditions of 450 MPa for 4 min and 350 MPa for 6 min reduced the initial concentration of V. parahaemolyticus to a nondetectable level, achieving >5 log reductions. Introduction Increased consumers demand for minimally processed, safe, fresh, and nutritious products, has revolutionized food process- ing. The emphasis now is on nonthermal food processing meth- ods that retain the natural ﬂavor, color, and nutritional value of food without compromising on their safety and shelf-life stability (Hendrickx and Knorr 2002). An example of a nonthermal food processing technology is high hydrostatic pressure (HHP) process- ing. HHP has been used to process fruit juices, meat products, and shellﬁsh in the United States, Europe, and Japan (Sun 2005). HHP has particularly generated interest within the shellﬁsh industry be- cause of its ability to shuck shellﬁsh without damaging the meat (He and others 2002). Shellﬁsh are ﬁlter-feeding organisms that may accumulate bac- terial and viral pathogens from contaminated waters (DePaola MS 20121244 Submitted 9/8/2012, Accepted 11/1/2012. Authors are with Dept. of Food Science, School of Environmental and Biological Sciences, Rutgers, The State Univ. of New Jersey, 65 Dudley Rd., New Brunswick, NJ 08901-8520, USA. Direct inquiries to author Schaffner (E-mail: schaffner@aesop.rutgers.edu). and others 1990; Lees 2000). Consumption of raw contaminated shellﬁsh has been implicated in shellﬁsh-borne gastroenteritis (Potasman and others 2002). Depuration and relaying are the postharvest treatments tradi- tionally used by the shellﬁsh industry but have been found inef- fective against pathogens such as Vibrio spp. and norovirus. This makes the consumption of raw shellﬁsh a potential health haz- ard (Croci and others 2002). HHP has been reported to inac- tivate viral and Vibrio pathogens in oysters making HHP an al- ternative postharvest treatment method (Calik and others 2002; Kingsley and others 2007; Kural and Chen 2008a; Kural and others 2008b). HHP on the other hand has been reported to change the tex- ture and color qualities of food. In fruits and vegetables, HHP has been shown to cause loss of ﬁrmness in cherry tomatoes due to simultaneous activity of pectin methylesterase (PME) and polygalacturonase (PG), where PG depolymerizes pectin that has been demethylated by PME (Oey and others 2008). High-pressure treatment preserves the color of fresh fruits and vegetables. Spec- trophotometric analysis of pressure-treated orange juice and straw- berry juice showed color was not signiﬁcantly affected by HHP (Oey and others 2008). C  2013 Institute of Food Technologists R  doi: 10.1111/1750-3841.12014 Vol. 78, Nr. 2, 2013  Journal of Food Science E251 Further reproduction without permission is prohibited