J. Peter Clark

Nonthermal processing refers to preservation processes other than traditional canning or pasteurization. A good way to see a snapshot of recent research in the area is by reviewing the content of a few of the papers and posters sponsored by the Nonthermal Processing Div. of IFT at the 2010 Annual Meeting July 17–21, 2010, in Chicago. Posters are a particularly convenient way of learning because one can often converse with the authors, and frequently the juxtaposition of papers can lead to serendipitously creative insights.

Operator loads product in flexible packaging into the high-presssure processing system at Sandridge Food.

Getting Novel Processes Approved
Three papers presented at this year’s gathering were based on the recently developed pressure-assisted thermal sterilization (PATS) process, an approach in which high pressure and mild heat are combined to achieve processing temperatures that are customarily used in the preservation (canning) of ambient stable, low-acid food products.

Presenter Larry Keener of International Product Safety Consultants, Seattle, Wash., discussed methodologies for developing process validation data to fulfill U.S. Food and Drug Administration (FDA) low-acid canned food (LACF) filing requirements for shelf-stable foods. Keener’s presentation addressed the procedures, protocols, and methods necessary for securing data that will satisfy regulatory concerns. In particular, the presentation focused on the process for obtaining data that will meet the requirements for an LACF filing involving products manufactured and preserved by PATS.

A case study with inoculated mashed potatoes was the topic in a presentation by Cynthia M. Stewart of Silliker Inc.’s Food Science Center in South Holland, Ill., on microbial validation of the PATS process using Clostridium botulinum spores. By combining heat treatment of the product with pressure application, inactivation of spores and enzymes can be achieved.

This dual process application can no longer be considered nonthermal, but the overall processing times are significantly shorter compared with traditional thermal retorting processes. The PATS process can effectively eliminate microbial presence, both vegetative and spore, while producing a product quality that is superior to that of conventional thermal preservation techniques commonly used today. In the case study, bio-validation was conducted using a three-strain cocktail of C. botulinum spores suspended in mashed potatoes and processed using PATS. The process critical parameters as employed in this work were established as follows: initial product temperature—90°C; minimum process temperature—121°C; minimum applied pressure—690 MPa; and minimum pressurized holding time—3 min.

In another presentation, researchers with the U.S. Army Natick Soldier Center, Natick, Mass., and Framingham State College, Framingham, Mass., reported on a variety of sensory and objective tests over extended shelf life of the new PATS process mashed potato product. Descriptive technical attribute sensory panels were used to monitor quality changes during accelerated storage stress at 38°C. Consumer hedonic panels and a field test by military subjects were also conducted. Changes in organic acid and vitamin C content during processing and storage were monitored by high performance liquid chromatography.

Lethality enhancement of pressure-assisted thermal processing (PATP) of food against Bacillus amyloliquefaciens spores using antimicrobial compounds was the topic of a presentation by researchers from Ohio State University and Kraft Foods. PATP at 500–700 MPa, 90–121°C offers new opportunities to overcome the limitations of conventional canning. The aim of this study was to evaluate the possibility of enhancing PATP lethality against pressure- and heat-resistant spores of Bacillus amyloliquefaciens by sensitizing the spores with selected antimicrobial compounds.

The spore suspensions were treated at 600 MPa and 105°C for 2 min in a high-pressure microbial kinetic tester, and the viable counts were determined after PATP treatment. Among the 20 different compounds tested, lysozyme, SDS, and chitosan were most effective (P<0.05) in increasing the PATP lethality. This research revealed that PATP-induced inactivation of bacterial spores could be enhanced in the presence of certain antimicrobial compounds.

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A study by Louisiana State University researchers examined the influence of low-pressure homogenization on acid tolerance of some dairy bacterial cultures. The objective of this study was to determine the effect of low-pressure homogenization on acid tolerance of Lactobacillus acidophilus, Lactobacillus delbrueckii ssp bulgaricus, and Streptococcus thermophilus. Fat-free milk was autoclaved and individually inoculated at 4°C with the three strains and homogenized at 0, 3.45, 6.90, 10.35, 13.80 MPa for 5 continuous passes. Treating these dairy bacterial cultures to homogenization pressure of 13.8 MPa increased their acid tolerance.

Treating Contaminated Nuts
Disease transmission by foods with low water activity has recently become a major concern in the food industry. Nut products have received significant attention following the recent peanut product disease outbreak. A study presented at the Annual Meeting by Ohio State University researchers investigated the feasibility of decontamination of Salmonella-inoculated in-shell pistachios using hot brining, ozone gas, or combinations of these treatments. Treatment with ozone alone inactivated 1.1–2.2 log Salmonella/g. Hot brining inactivated significantly more Salmonella (P<0.05) than treatment with ozone gas alone (5.7 log/g). The combination of brining and ozone was significantly more effective than either step alone, regardless of the order in which treatments were applied.

Cold plasma is a novel antimicrobial intervention that can eliminate foodborne pathogens on produce. The objective of a research project by Brendan A. Niemira of the U.S. Dept. of Agriculture’s Eastern Regional Research Center was to evaluate the efficacy of short-pulse cold plasma treatments in eliminating Salmonella and E. coli O157:H7 from dry almonds. Three treatment variables were evaluated in a factorial design for each isolate: time, distance, and feed gas. Cold plasma significantly reduced both pathogens on almonds. The greatest reduction observed was 1.34 log cfu reduction of E. coli O157:H7 C9490 after 20 sec of treatment at 6 cm spacing. Longer duration of treatment did not always result in enhanced reductions. In general, nitrogen as a feed gas resulted in a reduced antimicrobial efficacy compared to dry air. These results indicate that short pulses of cold plasma can significantly reduce Salmonella and E. coli O157:H7 on almonds.

Pulsed Light and Sonication 
Germicidal ultraviolet (UV) irradiation utilizes the wavelength of 254 nm to limit growth and reproduction of bacteria due to formation of thymine dimers in their DNA. Pulsed light (PL) uses very short and high power pulses of light covering a spectral range from 200–1,100 nm to reduce microbial populations, with UV reportedly having a critical role in inactivation.

The objective of work by two Cornell University researchers who presented during the Annual Meeting was to compare the effectiveness of PL and UV treatments on inactivation of Listeria monocytogenes cells suspended in various liquid media. The results demonstrate that PL treatment can reach the same level of inactivation as UV treatment in a much shorter time, which could represent a significant advantage for commercial food safety applications.

The FDA requires a 5-log reduction in the population of pathogenic microorganism count in juice products. As an alternative to conventional pasteurization, ultrasound in combination with moderate pressure and/or mild heat has been proposed to ensure the food safety and quality of final products. A study by University of Illinois researchers was undertaken to investigate the responses of Escherichia coli to thermosonication (TS), manosonication (MS), and manothermosonication (MTS) treatments in apple cider, and to examine the effects of ultrasonication on product quality. A 5-log reduction was achieved in 1.4 min by MTS, in 2.5 min by MS, and in 3.8 min by TS. MTS may be used as a promising alternative to pasteurization for apple cider. The nonlinear kinetic models may help to determine the treatment times needed for ultrasound treatments to achieve a 5-log reduction in pathogenic microbial counts in juice products.

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Michigan State University researchers reported on their study on the use of low-energy x-rays to inactivate Salmonella on almonds and walnuts. The study’s objective was to quantify the inactivation of Salmonella enteritidis PT30 on the surface of almonds and walnuts, as a function of x-ray dose and product water activity (aw).The computed D10 values (dose required for 1 log reduction) were 0.23, 0.34, 0.46, and 0.36 kGy for almonds and 0.47, 0.50, 0.86, and 0.79 kGy for walnuts at aw values of 0.23, 0.45, 0.64, and 0.84, respectively, with R2 values of 0.83 to 0.97. Based on these findings, Salmonella enteritidis PT30 was most susceptible to irradiation on the driest nuts, however the relationship between resistance and aw was not monotonic. Based on these findings, low-energy x-ray irradiation appears to be a very promising microbial inactivation strategy for products with low water activity.

Ultraviolet Radiation 
A UV device that centrifugally forms a thin film has recently been shown to nonthermally pasteurize grapefruit juice. The objective of a study reported on by a USDA scientist and industry researcher was to determine the nonthermal inactivation of Escherichia coli in liquid egg white using a UV device that centrifugally forms a thin film. Nonthermal UV processing at 9.0 mW/cm2, 450 RPM reduced E. coli in liquid egg white by 5 log. Inactivation increased with increasing UV intensity and decreased with increasing flow rate.

Although space does not permit a discussion of all of them, the fact that the Annual Meeting Scientific Program this year included 30 poster presentations on nonthermal processing techniques attests to the importance of this promising processing technology.

High Pressure Treats Luncheon Meats, Deli Salads
As food safety concerns rise in the global marketplace, commercial applications of high-pressure processing systems to “pasteurize” foods are growing internationally.

Ifantis Group, Athens, Greece, uses high-pressure processing (HPP) to extend the shelf life of its FreshPress product line of luncheon meats, such as smoked pork loin, mortadella, smoked turkey filet, and dry salami. Avure Technologies, Kent, Wash., supplied the HPP system. The packages are clearly distinguished by the new FreshPress label, which announces “ultimate food protection” from “the newest American technology.” The label also refers consumers to a website, www.freshpress.gr, where they can watch a video of an Avure HPP system at work in Ifantis’ state-of-the-art facility in Athens, Greece.

“Consumers, now more than ever, care about food safety,” said Kostantinos Ifantis, CEO. At the same time, they are asking processors for products with fewer or no preservatives, he continued. Partnering with Avure to develop the FreshPress label allowed Ifantis to address both concerns. Since the installation of the HPP system and the launch of the new brand in 2009, Ifantis’ sales of sliced meats are up more than 30%.

Sandridge Food, Medina, Ohio, is using a high-pressure processing system from NC Hyperbaric, Burgos, Spain, to enhance the safety of its deli salads and other chilled foods. The system, which can process up to 15,000 metric tons/year, uses cold water (<45°F) and high pressure (58,000–87,000 psi at 3–5 min) to destroy potential foodborne pathogens and extend product shelf life. The resulting minimally processed product is claimed to have superior appearance, taste, texture, and nutritional value over conventional heat-treated product.

“We have committed to this technology, not only because food safety is our highest priority, but because we firmly believe that foods with fewer preservatives and clean labels are the right thing to provide to the consumers of today,” said Mark D. Sandridge, CEO, Sandridge Food.
—Bob Swientek


by J. Peter Clark, 
Contributing Editor,
Consultant to the Process Industries, Oak Park, Ill. 
[email protected]