It's an exciting time for food processors. In response to consumer demand for clean label specialty products, new ingredients, functional foods, alternative sources of protein, bioactive and gut health promoting formulations, and a variety of other market drivers, processors have developed a broad range of novel foods. These products overcome challenges, solve problems, and explore possibilities around the world.
However, this explosion of innovation is taking place in a context where foodborne pathogens such asEscherichia coli,salmonella, zListeria monocytogenesThey continue to cause millions of illnesses each year. Exposure to these pathogens results in health problems ranging from mild to fatal. Products affected by these pathogens include a variety of foods, from fresh fruits and vegetables to meat, poultry, and seafood. Growers, processors, and shippers use advanced environmental controls during cultivation, postharvest washing and sanitizing, and transportation, but ongoing outbreaks highlight the need for additional processing control steps. This article looks at some of the latest advances in nutrition.processing technologies.
Cold plasma: versatile and effective
Cold plasma has become one of the most important new food processing technologies in recent years. Plasma is created by the partial or complete ionization of a gas. Unlike the familiar hot plasmas such as candle flames and welding arcs, the cold plasma discharges used in food processing operate at near room temperature. Effective plasma systems have a sufficient density of reactive products to sanitize food and/or food contact surfaces without heating or damaging the product being treated. Effective against pathogenic bacteria, viruses and parasites, cold plasma has proven to be a flexible and highly effective method of disinfecting surfaces.
Plasmas consist of free electrons, ions, and free radicals. Each has a variable half-life and gives rise to a variety of reaction products. For example, when air or feed gases containing oxygen are ionized, the resulting plasma contains O2+, outside2-, outside3, O, • O, O+, and the−, as well as metastable excited oxygen and ionized ozone. These reaction products interact with the cellular organic compounds of the pathogen, breaking covalent bonds and generating recombination products with cellular nitrogen, hydrogen, oxygen, etc. Cold plasma systems can produce ultraviolet light, with wavelength (and power) ranges defined by pulse frequency and duration, voltage level, electrode gap, and other factors determined. By adjusting the operating controls of the cold plasma system, the type of ultraviolet light emitted can be changed and set to specific wavelength intensities and ratios. In addition, the composition of the cold plasma feed gas significantly affects the chemistry of the resulting plasma. For example, switching from an inert argon or helium based system to a helium/oxygen, argon/oxygen, or air based system can dramatically change the resulting antimicrobial efficacy.
Cold plasma inactivates foodborne pathogens that cause damage to cell membranes, DNA, and other cellular components by reactive chemical species and/or ultraviolet light. Because these antimicrobial modes of action derive from ionized gases and not from the application of exogenous chemical disinfectants, cold plasma is of interest for clean label and organic applications. Because air and electricity are the only inputs for cold plasma, it is attractive as a chlorine-free, low-carbon, and sustainable process. In addition, because direct cold plasma treatment is waterless and non-thermal, it is of particular interest to processors of fresh and minimally processed products.
Plasma activated water: an alternative to chlorine
A variant of cold plasma treatment is that reactive chemical species are trapped in water, either in solution (plasma activated water, PAW) or as discrete fine droplets (plasma activated mist, PAM). For PAW, the plasma is generated and injected into a body of water; in PAM, the water droplets pass through a dielectric barrier discharge or plasma jet. In both cases, the underlying chemistry of the reaction products is such that the shorter-lived products (ultraviolet light, oxygen singlets, etc.) are generally lost on recombination. Longer-lived reaction products (reactive oxygen species, ozone, etc.) are slurried in water and are available for use in applications that mimic traditional chemical sanitizers, but with a non-chlorine composition. While much of the reactivity (and antimicrobial potency) of cold plasma is lost through the capture process, much flexibility is gained by preparing an aqueous disinfectant solution. PAM is applied as is, with a wand, sprayer, or spray system, while PAW can be used as is in a sprayer, drench, or tank, or stored for later use. The shelf life and time-dependent decline in reactivity of PAW are the subject of ongoing investigation, but cold storage of PAW has been shown to significantly extend the shelf life of treated products. This is due to the reduced recombination rates of the reaction products in refrigerated solutions. A new area of research is the capture of plasma reaction products on ice, resulting in bacteriostatic or bactericidal PAW ice. Orders for ice packed fresh produce and transportation of fresh produce and seafood are currently being reviewed.
Although 33 percent of the 95.3 billion eggs produced each year in the United States are processed into liquid eggs or egg whites, most are sold as shell-intact eggs. Raw eggs are a known food safety hazardsalmonellaPollution is a constant concern. Conventional hot water soaking is used on less than 3% of shell eggs in the US A 99.999% (5 log) reduction is achieved during this egg pasteurization process.salmonellain the egg it is relatively slow, taking about 60 minutes at about 59.2°C, to penetrate the albumen (protein). As albumen is sensitive to heat, even a small deviation in the process will cause a loss of egg quality. Coagulant albumin proteins begin to become cloudy and thickened above 59.7°C. Eggs exposed to temperatures above 60°C turn opaque and have the functional properties of a traditional hard-boiled egg, making them unsuitable for baking, cooking, etc.
An egg pasteurization process that uses radio frequency (RF) energy effectively inactivatessalmonellamaintaining the quality of the eggshell (Figure 1). The eggshells are in direct contact with curved electrodes that emit radiofrequency energy through the albumin. This resistance-capacitance circuit of the coupled albumen and yolk generates heat within the eggs (due to internal electrical resistance), while the dielectric nature of the eggshell generates series capacitance. The external RF field results in the production of uniform resistive heat from the electrical fields maintained within the egg due to the dissipation of the applied power. The net effect is that the HF process heats the egg from the inside out, as opposed to traditional hot water immersion, which heats the egg from the outside in.salmonellait dies while the albumin remains essentially unchanged. Process controls include adjustment of applied voltages and control of the gap between the electrodes and the box. These operational controls ensure uniform internal heating, which is further enhanced by rotating the egg and applying a jet of water to the shell to increase electrical contact. This system generates and reduces an outside temperature of the casing of 38 °Csalmonellato 99.999% in less than 20 minutes. The resulting pasteurized shell eggs showed little or no effect on yolk height or color, foaming, egg shelf life, color or integrity, and other factors of egg functionality and quality. Baking trials confirmed the suitability of these HF-pasteurized eggs for growth in cakes and other experimental baked goods.
Chlorine Dioxide Gas - Packaging Solution
chloroxide (ClO2) is an increasingly popular disinfectant. Applied as an aqueous solution, ClO2It can reduce bacterial pathogens on food and food contact surfaces by more than 99.99 percent. When used in gaseous form, ClO2It can inactivate pathogens in hard-to-reach places on fruits and vegetables. ClO2The gas is generally formed by the reaction of the sodium chlorite salt with an organic acid. Due to the lower production of trihalomethanes or chloramines, it is considered a more environmentally friendly alternative to washing with sodium hypochlorite or calcium hypochlorite. aqueous ClO2It is generated on demand, injected into the water to make the sanitizing solution, which is then used for rinsing, soaking, or washing. When used for fumigation or product treatment, ClO2The gas is generated and used in the plant. Gaseous ClO packaging applications2involve reacting the precursors and injecting the resulting ClO2in the bag or container before closing/sealing. While this is effective in the short term, subsequent degradation of ClO2requires initial concentrations (eg at the time of closure) high enough to cause sensory and qualitative deterioration of the food product.
Efforts to develop alternative means of generating ClO22Inside the packaging were bag-shaped booklets containing the precursor chemicals. Although these approaches showed the potential of this approach, the first prototypes began to generate the ClO2Gas immediately after sealing the moisture-laden bag. This resulted in an excessive initial concentration (with the possibility of undesirable sensory effects) which decreased to an insufficient late concentration (with limitations related to biostatic and/or biocidal activity). A more recent system for generating ClO2 in containers uses a multilayer "sticker" consisting of individual laminated layers of pectin or gelatin, each saturated with the reactive precursors: the organic acid and sodium chlorite salt. Separated by one or more layers of inert gelatin, the entire assembly is sandwiched in protective outer layers of inert gelatin. The label is storable and inactive in high humidity conditions and remains inside the package. if ClO2when gas is desired, a mechanical force is applied which breaks the gelatin layers separating the reactive layers; The precursors are mixed, allowing the normal reaction to occur with the acid, chlorite salt, and moisture in the container. ClO gas2therefore, it is released as needed at a user-specified time after pooling. With further process optimization, for example through multiple layers, higher precursor concentrations and thicker reagent layers, the operating mechanics require ClO2Production can be tailored to individual product requirements. As this technology evolves, tags can be customized to control release rate and/or duration, peak concentration, facilitated sequential releases, or other parameters for ClO usage.2Gas on demand during transportation, distribution or at the point of sale.
Pulsed Electric Fields: Production Enhancers
Pulsed electric field (PEF) processing uses high-intensity electric fields that operate in the range of 20 to 80 kV/cm and pulse rapidly (1 to 100 milliseconds). The main antimicrobial mode of action of PEF is electroporation, in which depolarization of the cell membrane opens holes in the lipid bilayer. This changes the concentration of ions in the membrane and leads to uncontrolled permeation of the membrane, which is fatal. Process effectiveness is determined by process conditions such as electric field strength, pulse width, frequency and duration, total treatment time, and input power. Equally important are the temperature, the flow rate, the holding time and the general properties of the treated feed (conductivity, pH value, conductivity, particles, etc.).
As a food processing technology, PEF has been used in liquid foods, such as juices and liquid eggs, to kill suspended foodborne pathogens. When processing solid foods, the product is fed between PEF electrodes in a liquid levitation conveyor system. One application is the pretreatment of roots and tubers (eg white potatoes, sweet potatoes, cassava, beets, carrots, etc.) for further processing into French fries, chips, and other starchy products. Plant cells are electroporated by PEF to release intracellular compounds in addition to reducing sugars. This change reduces the degree and tendency of excessive browning during frying. The same type of sugar release phenomenon can be used to increase the extraction of sugars and nutrients from beet fibers, skins, and stalks. With related developments, PEF has been evaluated to improve the shelf life and preservation of semi-liquid food products and to improve the extraction of bioactive and nutraceutical cellular components such as antioxidants, essential oils, and algae proteins.
Advanced food processing technologies such as those described in this article will enable increased safety and quality in a variety of foods and formulated food products, as well as new applications in product development and process optimization. Many of these technologies have a specific set of raw materials for which they are most efficient or cheapest to use. Applicable product criteria may include foods with a specific moisture content, desired shelf life, or composition. Combined, these advanced technologies, used in synergistic protocols with each other and with gentle heat, broaden the spectrum of pathogens effectively targeted. Consumer education and marketing will be a critical factor in consumer acceptance of new and unfamiliar technologies. With effective applications across all major product lines to address serious food safety challenges, advanced food processing technologies can protect consumer health and offer new opportunities for producers and processors.
The author thanks Drs. Olanya and Sudarsan for their reviews of this article in preparation. Mention of trade names or trade products in this article is for specific information only and does not imply endorsement by the United States Department of Agriculture (USDA).
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Brendan A. Niemira, Ph.D., is the Director of Research for the USDA Food Safety and Intervention Technologies Research Unit.