Studies combining high pressure and thermal treatments to inactivate PME enzymes in orange juice were conducted at The Ohio State University on the ABB Quintus batch high-pressure system shown above. Flow International acquired ABB Pressure Systems in March, 1999. (Source: The Ohio State University)

Continuous ultrahigh pressure (UHP) systems developed by Flow International incorporate several pressure chambers called isolators, driven by 700 MPa (100,000 psi) intensifier pumps and available in capacities up to 215 liters. (Source: Flow International Corp.)

Most refrigerated juice processors avoid the warning label by pasteurizing their products. But pasteurization, like any thermal process, degrades product flavor. Some juice processors prefer to achieve the 5-log reduction through tight sanitation and HACCP, thus retaining full flavor in their products. Others have combined "light" and "ultralight" pasteurization with HACCP to assure 5-log reduction yet minimally impact flavor. Some offer both pasteurized and unpasteurized products. A few even accept the warning label on some products.

FDA's proposed juice HACCP rule of April 1998 -- not yet final at this writing -- would mandate HACCP to achieve the 5-log reduction. To explore how HACCP can be best applied to juice processing, FDA initiated a pilot program with three processors: Ocean Spray Cranberries, Orchid Island Juice Co., and Fresh Samantha, Inc. Ocean Spray and Fresh Samantha pasteurize their juices; Orchid Island produces fresh-squeezed citrus juices.

FDA's proposal does not require pasteurization to achieve the 5-log reduction. "Manufacturers may be able to use other technologies and practices provided their process is validated to achieve a 5-log reduction in the target pathogen," says the agency. "Therefore, reliance on safety performance criteria is a better long-term approach because it provides for the development of new technologies."

New non-thermal technologies with potential for processing juices to retain flavor and extend shelf life include ultra-high pressure (UHP), pulsed electrical fields (PEF), ultraviolet (UV) light, electric pulse and carbon dioxide (CO₂). Over the past several years, intense R&D efforts have aimed at validating and commercializing these technologies. One is now commercial, others are approaching commercialization.

But, should FDA mandate pasteurization, in its final HACCP rule, much of the R&D devoted to non-thermal juice processing may be in vain. Odwalla, Inc., which achieves the 5-log reduction through HACCP but nevertheless "flash pasteurizes" its juices, observes in its July 11 quarterly report "we anticipate that flash-pasteurization will be required."

The continuous ultrahigh pressure system developed by Flow International for juices and other pumpable food products incorporates several isolators, which are sequenced in various stages of operation to maintain a continuous output. Under computer control, juice is sequentially pumped into each isolator, pressurized with water, held for a short time, then pumped to a clean room or aseptic filling station for packaging. (Source: Flow International Corp.)

The promise of high pressure

According to Dr. Edmund Y. Ting, vice-president of R&D at Flow International Corp. (Kent, Wash), 80,000 psi for 30 seconds can achieve a 5-log reduction of pathogens of concern (E. coli O157:H7 and Salmonella) in fresh juices without affecting taste or nutritional values. Flow's isostatic "Fresher Under Pressure" systems include batch systems for packaged products and continuous systems for liquid products such as juices.

Flow announced last March that its earlier agreement to commercialize its UHP technology exclusively with The Minute Maid Co. for juice production had been discontinued, allowing Flow to market its technology to other juice manufacturers. Concurrently, Flow announced orders for UHP systems from Odwalla, Inc. and Fresh Samantha, Inc. (which merged May 3) for producing citrus and vegetable juices and blends, and from the Italian juice producer Ortogel srl for processing orange juice.

Earlier, in May '98, Flow had supplied a pilot UHP system to Mexican juice manufacturer Grupo Jumex, and Jumex has since installed a Flow commercial-scale system. According to a Jumex source, the company is conducting tests at pressures ranging from 44,000 to 73,500 psi for 20 seconds to 1 minute. Jumex hasn't yet determined which juices to commercially produce via UHP, he added, but expects to extend the shelf life of its refrigerated juices by up to 30 days.

Meanwhile, Flow continues working with Minute Maid "to pursue high pressure applications in juice beverages," said Flow President & CEO Ronald W. Tarrant.

Minute Maid has the capability to produce UHP juices, says the company's Dr. Sevugan Palaniappan but -- because its products are distributed nationally -- they must retain quality throughout the distribution cycle. The company thus pasteurizes all of its juices with a high-temperature/short-time process. "You have to get a high level of reduction on the spoilage organisms (which can cause off-tastes) as well as on the pathogens," Palaniappan points out. Fresh-juice processors who can control distribution within a relatively local radius can accept a two-week refrigerated shelf life, but "we want a product that tastes like fresh but can withstand potential refrigeration abuse as well as a thermally-processed product throughout the distribution cycle," he adds. "We've looked at all the new technologies and have tried some of them, but we're still exploring ways to commercialize them."

A major problem with fresh orange juice is limited shelf life due to cloud loss caused by the activity of several pectin methylesterase (PME) enzymes. According to studies conducted by Ohio State University (OSU) researchers Dr. Uwe Nienaber and Dr. Thomas H. Shellhammer, high-pressure processing can inactivate spoilage microflora and reduce PME activity without the use of heat. But at least 600 MPa (90,000 psi) must be applied for commercial viability. Pressures of 400 to 600 MPa (60,000-90,000 psi) can be combined with mild heat (less than 50oC) to accelerate PME inactivity. For juice with added pulp, residual activity can be further reduced by thermally treating the pulp before high-pressure treatment.

A current project directed by Dr. V. M. Balasubramaniam and Dr. Peter Slade at the National Center for Food Safety & Technology (NCFST, Summit-Argo, Ill.) aims at developing and validating a HACCP plan for fruit and vegetable juices processed by a Flow semi-continuous (one isolator) UHP system integrated with an aseptic packaging system.

In a continuous (PEF) system, juices flow through a series of treatment zones, each flanked by a high-voltage electrode and a low-voltage electrode. (Source: The Ohio State University)

PEF: commercially feasible?

Research into food applications nevertheless continues, especially at The Ohio State University, where PEF research directed by Dr. Q. Howard Zhang is supported by a consortium including the U.S. Army Natick RD&E Center, NASA, the Electric Power Research Institute, Silliker Laboratories, Nestle, General Mills, Kraft and Tetra Pak.

PEF processing applies high-voltage pulses for just a few microseconds to food placed or flowing between two electrodes. The process destroys both pathogens and spoilage organisms through breakdown or rupturing (electroporation) of cell membranes. Pores become permanent in most vegetative cells treated above 15,000 V/cm, Zhang writes. PEF inactivates bacterial spores by reducing dipicolinic acid, which spores need to germinate. Of three pulse waveshapes evaluated, the square wave is most effective.

OSU is equipped with a real-time microscopic imaging system to observe microbes under PEF; lab-scale batch and continuous PEF systems; and a pilot-scale continuous system integrating PEF with aseptic packaging. In pilot experiments, PEF achieved a 5-log reduction of the pathogen E. coli O157:H7 and its non-pathogenic surrogate E. coli 8739 in apple cider in 143 microseconds at a field strength of 30 kV/cm and average temperature of 25°C (near ambient). Spoilage organisms in orange juice were reduced by 5 logs at a peak field intensity of 40 kV/cm for 60 microseconds. Refrigerated shelf life of fresh orange juice was extended from six to eight weeks.

Zhang believes that PEF is ready for commercial application, and that juices -- as acid, liquid products -- offer the best initial opportunity. OSU is currently constructing a commercial-scale system combining PEF processing with aseptic packaging, Zhang reports. Diversified Technologies, Inc. (Bedford, Mass.) will provide the pulse generator, Tetra Pak (Vernon Hills, Ill.) the aseptic packaging machine in a project funded by the PEF consortium.

Zhang and his team have calculated scale-up for several commercial PEF systems capable of processing juices or pumpable particulated foods at flow rates of 2,000 liters per hour at 35 kV/cm for 50 microseconds. For juices, estimated cost for a co-axial design is $400,000-$600,000; for a co-field design $200,000-$40

A current project at NCFST aims at predicting microbial lethality during PEF processing. Different PEF implementations result in different lethalities to the same microorganism, the researchers point out, indicating that the basic effect of PEF on microbes is not sufficiently understood --"an understanding that is vital if PEF is to be commercialized."

Results of PEF tests conducted at The Ohio State University on apple cider inoculated with the pathogen E. coli O157:H7 and its non-pathogenic surrogate E. coli 8739.

UV light: commercial soon

As reported earlier by FE (Nov., '99), CDF in June '99 filed a food-additive petition with FDA proposing that 21 CFR 179.39 be amended to allow safe use of UV light to reduce pathogens and other microorganisms in juice products. FDA is reportedly expediting petition review.

CDF's UV system was developed by James E. Cruver of Salcor, Inc. (Fallbrook, Calif.), who has a patent pending on the technology. The module encloses a transparent coil of Teflon tubing one inch in diameter with a capacity of seven gallons, surrounded by UV lamps and reflectors. The mercury lamps generate 90 percent of their energy at a wavelength of 253.7 nanometers. As the juice rolls through the tubing it is completely exposed to UV light, which fuses the DNA structure of harmful bacteria to render them incapable of reproduction. Process capacity of one module is 420 gph (7 gpm) at an exposure time of about one minute. Modules can be stacked in series to boost capacity.

Tests conducted by Silliker Laboratories demonstrated that two passes through one module reduced E. coli O157:H7, Listeria monocytogenes and Salmonella by 5 logs each in four different juices -- apple, orange, carrot and mixed vegetable -- without affecting flavor. Log reduction will vary with flow rate and exposure time, Cruver adds, so juice processors may want to achieve some log reduction through HACCP.

A system installed at the National Food Laboratory (Dublin, Calif.) incorporates intensity meters to record intensity over time for validating the process, adds Gene Ruhnke of Sierra West Process & Engineering Co. (Pleasant Hill, Calif.), an affiliate of Salcor. A smaller, bench-scale unit is available at NCFST in Chicago.

According to Dominick Marlia, QA manager at California Day-Fresh, refrigerated shelf life for cold-filled juices is currently five days for neutral pH vegetable juices and 15 days for high-acid fruit juices. "But with our Light Processed System, tests indicate we will be able to double refrigerated shelf life for some of these products," said Marlia. "This will allow us to expand our distribution areas considerably." The process retains nutrients and the natural flavor, texture, color and enzymatic properties of the juices, he adds.

Log reduction depends on type of juice and time of exposure, he continued. "We expect to get 4 logs of reduction with UV, and the additional log through sanitation procedures and HACCP." Once FDA clears the process, CDF will probably first apply it to vegetable juices, "not only to assure the 5-log reduction but also to retain the enzymes," says Marlia. "Pasteurization destroys it all."

Electric pulse commercialized

During project development, microbiological studies demonstrated 7-log reductions of Listeria monocytogenes and Salmonella typhimurium, and a 5-log reduction of E. coli O157:H7 in fresh orange juice. Shelf-life studies show that the process can extend refrigerated shelf life of fresh citrus juice to beyond 60 days. Organoleptic evaluations revealed no change in product taste, color, texture and aroma. Laboratory tests detected no migration of construction materials into the product.

Hardware and pulse parameters were optimized at pilot scale, and commercial-scale tests validated the process. One major objective was to develop a process capable of exemption from FDA's "Threshold of Regulation," and in April 1999 the agency issued a letter of "no objection." The system is currently operated by two undisclosed juice processors: one to treat fresh juices, the other to extend the shelf life of stored juice concentrates.

In April of this year, Robbins applied for a patent on the process, based mainly on its low-energy requirements and how it inactivates microbes. "It's not just applied energy; it's energy applied in a specific fashion," Robbins told Food Engineering. "The waveform is related to the 'couple' between the organism and the medium." Energy is applied to affect only the organism, not the medium, so energy requirements are reduced. Unlike PEF technology, which breaks-down cellular walls, the energy is applied "not to alter the structure of the target organism, but to shut-down its respiration metabolism," he adds.

Design specifications in the patent application include "all the sensors to collect data for process validation," says Robbins. He has formed a new company called Fresh Pulse, Inc. to implement the technology.

CO₂ emerges

Working with the University of Florida, Praxair developed the equipment and continuous process that utilizes CO₂ technology originally patented by UF researchers to inactivate enzymes in fruit juices and licensed to Praxair. The process achieves the 5-log pathogen reduction standard, and an independent sensory panel detected no difference between CO₂-treated and fresh-squeezed orange juice. Tests were conducted on juices inoculated with E. coli O157:H7, L. monocytogenes and S. typhimurium.

The process involves a mixture of CO₂ and juice under pressure, said Dr. Hiraly Shallo, development associate in the Food Applications unit at Praxair. CO₂ alone inhibits microbial growth but does not kill, Shallo explains. "But with pressure, you achieve a more effective reduction step -- not total kill, but a 5-log reduction," she adds. Pressure is applied at less than 10,000 psi, so the process is not a high-pressure system. In a research environment, refrigerated shelf life of fresh juice "at least doubled" from three to six weeks, said Shallo. With proper handling in a production environment, Praxair adds, "we hope to achieve close to 60 days."

Praxair plans a unit which will process 50 gpm at a cost-per-gallon similar to the cost of pasteurization, and with a lower capital cost than a high-pressure system.

IFT evaluates alternative technologies

Is non-thermal "fresh?"