Daniel F. Farkas

Antimicrobial effect of water‐soluble chitosans with high hydrostatic pressure

Abstract Two commercially available water‐soluble chitosan salts, chitosan lactate and chitosan hydroglutamate, were examined for antagonistic effect against Escherichia coli V517, Staphylococcus aureus MF‐31 and Saccharomyces cerevisiae 15. Significant inactivation of each population was evident within 2 min of incubation with Chitosan. S. cerevisiae was the most sensitive of the microorganisms examined. Concentration effects varied but chitosan hydroglutamate was usually the more effective of the chitosans for inactivation of these microorganisms. Application of high hydrostatic pressure (2,380 atmospheres) to chitosan‐treated cultures of E. coli V517 or S. aureus MF‐31 resulted in additional inactivation but an amplified or synergistic effect was not found.

Ultra-high pressure pasteurization of fresh cut pineapple

Ultra-high pressure (200, 270 and 340 MPa), temperature (~4, 21 and 38°C), and time (5, 15, 40 and 60 min) combinations were evaluated as a means to extend the shelf-life of fresh cut pineapple chunks. Cut pineapple obtained from an industrial processor was packed in heat-sealed polyethylene pouches. Triplicate samples were temperature adjusted and treated in an Autoclave Engineers IP2-22-60 isostatic press. Surviving bacteria and total yeast and mold counts were determined using plate count agar (PCA) and acidified potato dextrose agar (PDA), respectively. At the highest pressure (340 MPa) and 15 min, decimal reductions measured by growth on PCA were 3.0 (~4°C), 3.1 (21°C) and >2.5 (38°C). Pressure treated pineapple pieces had PCA counts < 50 colony forming units (CFU)/g. At 270 MPa and 15 min, greater than two decimal reductions were observed only at 38°C. Exposure to pressures of 200 MPa resulted in about one decimal reduction in PCA counts for all temperature and time combinations tested. PDA counts followed a similar behavior for all pressure treatments.

Comparison of static and step-pulsed ultra-high pressure on the microbial stability of fresh cut pineapple

Fresh cut pineapple cubes inoculated with 104–5 CFU g−1Saccharomyces cerevisiae were packed in heat-sealed polyethylene pouches and subjected at ambient temperature to static and step-pulsed ultra-high pressure (UHP) treatments. Static treatments included 100 and 9000 s at 270 MPa and 9000 s at 340 MPa. Step-pulsed pressure treatments included 100, 300 and 600 s at 0–270 MPa using 0·5-s and 10-s pulses. Inoculated treated and untreated samples were held at 4°C for 60 days. Bacteria and yeast counts were determined using plate count agar and yeast extract peptone dextrose agar, respectively. Static treatment at 270 and 340 MPa for 9000 s resulted in <240 CFU g−1 yeast and bacteria counts for up to 60 days. Step-pulsed pressure treatments for 100 s at 0–270 MPa using 0·5-s (200 pulses) and 10-s pulses (10 pulses) were more effective than a 100-s static 270-MPa treatment. Step-pulsed pressure treatments (300 and 600 s) using 0·5-s pulses (600 and 1200 pulses) and 10-s pulses (30 and 60 pulses) were as effective as 9000-s static pressure treatments at 270 and 340 MPa. This storage study confirmed the superiority of step-pulsed over static pressure treatments.

Pathogenic Psychrotolerant Sporeformers: An Emerging Challenge for Low-temperature Storage of Minimally-processed Foods

Sporeforming bacteria are a significant problem in the food industry as they are ubiquitous in nature and capable of resisting inactivation by heat and chemical treatments designed to inactivate them. Beyond spoilage issues, psychrotolerant sporeformers are becoming increasingly recognized as a potential hazard given the ever-expanding demand for refrigerated processed foods with extended shelf-life. In these products, the sporeforming pathogens of concern are Bacillus cereus, Bacillus weihenstephanensis, and Clostridium botulinum type E. This review article examines the foods, conditions, and organisms responsible for the food safety issue caused by the germination and outgrowth of psychrotolerant sporeforming pathogens in minimally processed refrigerated foods.

Evaluation of Batch and Semicontinuous Application of High Hydrostatic Pressure on Foodborne Pathogens in Salsa

The effects of high hydrostatic pressure (HPP; 545 MPa) on strains of Escherichia coli O157:H7, Listeria monocytogenes, enterotoxigenic Staphylococcus aureus, and nonpathogenic microorganisms were studied in tomato-based salsa. Products were evaluated for the survival of the inoculated pathogens following HPP treatment and after storage at 4 degrees C and 21 to 23 degrees C for up to 2 months. Inoculated samples without HPP treatment, stored under the same conditions, were also evaluated to determine the effects of the acid environment of salsa on the survival of inoculated strains. None of the inoculated pathogens were detected in the HPP-treated samples for all treatments throughout the storage period. Inoculated pathogens were detected in the non-HPP-treated samples stored at 4 degrees C after 1 month, with L. monocytogenes showing the highest level of survivors. In the non-HPP-treated samples stored at 21 to 23 degrees C, E. coli and S. aureus were not detected after 1 week, but L. monocytogenes was detected in low levels. Studies with nonpathogenic strains of the pathogens were conducted at Oregon State University using HPP treatments in a semicontinuous production system. The nonpathogenic microorganisms (E. coli, Listeria innocua, Listeria welshimeri, and nonenterotoxigenic S. aureus) were inoculated together into a feeder tank containing 100 liters of salsa. Microbiological results of samples collected before HPP treatment and from the aseptic filler were similar to those obtained for the pathogenic strains. No survivors were detected in any of the HPP-treated samples.

A Short History of Research and Development Efforts Leading to the Commercialization of High-Pressure Processing of Food

The history of the development and commercialization of high hydrostatic pressure processing of foods includes groups in Japan, Europe, and the United States. This narrative focuses on early research and development commercialization efforts starting in 1984 in the Department of Food Science at the University of Delaware, Newark, Delaware. Research efforts expanded in 1990 as a joint program among the University of Delaware, the Department of Food Science and Technology at Oregon State University, and the US Army Combat Feeding Directorate at the Natick Soldier Research, Development and Engineering Center, Natick, Massachusetts. Activities of an industry-university High Pressure Consortium, managed by Marcia Walker and D. Farkas, at Oregon State University, helped commercialization by providing a focus for research, development, technology transfer, regulatory challenges, and solutions. The plan was to develop the use of high hydrostatic pressure into a profitable, new food processing technology that provided safe, fresh-tasting, convenient foods, with an extended shelf life.