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P1: SFK/UKS BLBS102-c39 P2: SFK BLBS102-Simpson March 21, 2012 14:20 Trim: 276mm X 219mm Printer Name: Yet to Come 39 Minimally Processed Foods More recent reviews on the technology are Soria and Villamiel (2010) and Chemat et al (2010) Different bacteria exhibit different sensitivities to ultrasonic treatment in different media (Wang et al 2010) Early applications of ultrasound showed relatively low microbial inactivations However, there has been considerable progress in equipment development that has resulted in increased inactivations but typically below logs Application of ultrasound alone is not very effective for microbial inactivation in commercial processing, but the technique can be effective when used in combination with other treatments (Raso et al 1998) Thus, three different techniques, namely thermosonication, manosonication, and manothermosonication have been promoted as a result of the synergistic actions of the different treatments on microbes (Lee et al 2009) Manothermosonication is an emerging technique that combines heat and ultrasound at elevated pressure Based on intensity, amplitude, and time of treatment, manothermosonication can be 6–30 times more effective in killing microorganisms (Bacillus species, Sacchromyces cerevisae) compared to thermal treatment given at same temperature Different enzymes such as POX, lipase, lipoxygenase, protease, and pectin methylesterase have been tested for inactivation by manothermosonication (Demirdoven and Baysal 2009) Manothermosonication has been used to enhance the textural and functional properties of tomato juice and milk proteins (Lopez and Burgos 1995, Vercet et al 2002) Ultrasound has also been used in combination with chlorine, and a strong bactericidal effect was observed (Blume and Neis 2005) Chlorine dioxide, when used with heat and ultrasound, destroyed Salmonella and E coli cells in alfalfa seeds (Scouten and Beuchat 2002) The full potentials of ultrasound in food processing have yet to be tapped There will continue to be progress made on design of improved and efficient equipment Better understanding of the effect of the process on technological and functional properties will be crucial in identifying niche applications of the technology UV Irradiation The nonionizing UV radiation in the wavelength range of 100–400 nm is widely used in food processing The electromagnetic spectrum is classified into three groups, namely UVA (315–400 nm), UV-B (280–315 nm), and UV-C (less than 280 nm) UV-C is particularly used because of its effective germicidal capacity The wavelength of 253.7 nm is known to have the most lethal effect on microorganisms since photons are absorbed most by the DNA of microorganisms at this wavelength (Labas et al 2005) UV light can be generated from various sources The low pressure mercury vapor UV lamps are widely used as reliable and low cost sources of UV light (Ngadi et al 2003) These lamps operate at the nominal total gas pressures of 102–103 Pa and their UV output is in the range of 0.2– 0.3 W/cm (Koutchma 2009) More recently, high intensity lamps with enhanced potential for UV microbial inactivation are being developed Pulsed UV systems (PUV) have been developed and have been shown to be more effective in inactivating bacteria In these systems, alternating current is stored in a capacitor and the energy is discharged through a high-speed switch to form a pulse 755 of intense emission of light of about 100 µs durations Some recent studies have reported application of PUV light for surface treatment of food products such as fresh-cut fruit, meats, and fish (Woodling and Moraru 2005, Ozer and Demirci 2006, Alothman et al 2009, Oms-Oliu et al 2009, Pombo et al 2009) A prime goal of UV application in food processing is to reduce microbial load and achieve high-quality product with improved shelf life while maintaining sensory attributes Some fresh-cut fruits and vegetables such as cantaloupe and fresh-cut melon treated with UV light yield better quality retention, since the treatment was effective in reducing microbial populations (Lamikanara et al 2005, Art´es-Hern´andez et al 2010) The efficiency of the treatment depends on the structure of the fruit surface (Koutchma 2008) A reduction in microbial load was observed in juices from apple, guava, pineapple, and orange when treated with UV radiation (Keyser et al 2008) Application of UV at 24 mW/cm2 on apples inoculated with Salmonella and E coli O157:H7 resulted in 3.3 log reduction (Yaun et al 2004) In order to achieve high microbial inactivation, UV light should be applied for a sufficient time Combination of UV and other minimal processing technologies can be used to improve microbial inactivation efficiency Using modified atmosphere packaging (MAP; high concentrations of carbon dioxide) and UV together significantly reduced microbial population (Art´es et al 2009) Apart from antimicrobial action, UV may also influence the antioxidant activity of fresh-cut fruits and vegetables An increase in the total phenol contents of fresh-cut tropical fruits such as banana and guava (Alothman et al 2009), and enhanced flavonoid and antioxidant levels were observed in blueberries (Perkins-Veazie et al 2008, Wang et al 2009c) when the products were treated with UV irradiation Gomez et al (2010) reported changes in the color and mechanical compression behavior of apple cuts exposed to UV irradiation Treated cuts showed accelerated browning, which the authors attributed to breakage of cellular membranes (plasmalemma and tonoplast) The phenomenon was also used to explain decrease in rupture stress and deformability indices for UV-treated samples during storage This observation is curious as the action of UV on biological cells is traditionally attributed to changes in DNA modification Pretreatment of apple cuts blanching or dipping in anti-browning solution were reported as effective in reducing quality changes and maintaining the original color of apple slices after UV treatment Thus, the influence of UV on biological cells may be more complicated as previously thought Improved understanding of the effect may open doors to innovative application of the technology Other Techniques Various other novel techniques, photochemical (intense light pulses, etc.) and nonphotochemical processes are being used for minimal processing of fruits and vegetables Electrolyzed water has been used to disinfect food surfaces The pH of electrolyzed water can be raised or lowered by adding hydroxyl or hydrogen ion concentration Decreased bacterial growth in fresh-cut cabbage was observed when sanitized with slightly acid electrolyzed water (Koide et al 2009) Neutral Electrolyzed Water (NEW) was used to demonstrate the efficacy of NEW over Sodium P2: SFK BLBS102-Simpson March 21, 2012 14:20 Trim: 276mm X 219mm 756 Printer Name: Yet to Come Part 7: Food Processing hypochlorite in inhibiting Listeria monocytogenes, Salmonella, E coli O157:H7, and the bacteria Erwinia carotovora in lettuce and fresh-cut products (Abadias et al 2008) Comparison of bacterial reduction potency of strongly acidic electrolyzed water (SAEW), sodium hypochlorite solution (NaOCl), and slightly acidic electrolyzed water (StAEW) yielded the following order: StAEW > NaOCl > SAEW (Issa-Zacharia et al 2010) The level of implementation of these techniques at commercial scale has been limited QUALITY AND SAFETY CONSIDERATIONS: THE HURDLE CONCEPT Although food safety is critical, it is known that quality is a topof-mind consideration when consumers purchase food products A successful processing technique must therefore not only ensure that the product is safe, it must also maintain appropriate quality attributes that can be acceptable by consumers Thermal treatment is a broad-spectrum antimicrobial process However, novel nonthermal or minimal processing techniques have been developed due to the potential of thermal processing to degrade nutritive quality and functional properties of foods The individual use of most of the new techniques may not provide the inactivation level required for commercial processing Recently, combined inactivation techniques of microorganisms have been widely investigated since a combination of different “hurdles” is a more effective means of inhibiting microorganisms than using each “hurdle” alone (Alakomi et al 2002, Leistner 2000) The hurdle concept is based on the imposition of certain hurdles to restrict the growth of food spoiling microorganisms as illustrated in Figure 39.2 Any microbial inactivation factor can potentially be adapted as a hurdle Nearly 60 potential hurdles have been identified for food preservation The hurdles must be applied in a logical sequence to ensure safety of the food product The resistance of different pathogens should be considered when a hurdle is the lone preservation factor For instance, PEF as well as high-pressure treatment effectively inactivate bacteria and Survival fraction P1: SFK/UKS BLBS102-c39 yeast but are ineffective against bacterial and mold spores and some enzymes Ultrasound is ineffective against wide-ranging pathogens Although heating is the most broad-spectrum inactivation method, cells of Clostridium botulinum are highly resistant even to thermal treatment Moreover, there is an inactivation threshold after which further hurdle application and energy input not inactivate microorganisms or degrade nutritive quality of the treated foods A synergistic relationship between different nonthermal physical and chemical hurdles has been observed for both foods (Fielding et al 1997, Raso et al 1998, Dutreux et al 2000, Heinz and Knorr 2000, Aronsson and Răonner 2001, Fernanda et al 2001) as well as nonfoods liquids (wastes, poultry chiller water, and others) (Liltved et al 1995, Unal et al 2001, Larson and Mari˜nas 2003) Although the simultaneous application of different nonthermal technologies has been shown to have a significant bactericidal effect, thermal treatment may still be required to achieve the level of inactivation of different microorganisms necessary for practical use Thus, combination of thermal treatment with PEF (thermoelectrical treatment), pressure (manothermal treatment), ultrasound (thermoultrasonication), irradiation (thermoradiation), and other hurdles have been reported (Raso et al 1998, Hoover 2000, Aronsson and Răonner 2001, Kim et al 2001, Ohshima et al 2002) Synergistic bactericidal effects have also been observed between heat and ultrasound (Wrigley and Llorca 1992), heat and radiation (Schaffner et al 1989), heat and nisin (Knight et al 1999), high hydrostatic pressure and nisin (Ponce et al 1998), and PEF and nisin (Calder´on-Miranda et al 1999) Some general approaches for understanding hurdle concept can be found in Barbosa-Canovas et al (1998) and Leistner and Gorris (1995) Microbial Stress When microorganisms present in food encounter stress in the form of various hurdles, they undergo homeostasis The organisms try to prevail over inclement conditions caused by hurdles, but metabolic exhaustion due to repair action leads to death of the microorganisms However, when bacteria are under stress, they can become more resistant and synthesize stress shock proteins These proteins play the role of molecular chaperons by folding distorted proteins into a shape that retains the cell functionality under stress (Hightower 1991) But if the food is exposed to different stresses simultaneously, the microorganism generates more shock protein using all the cell energy and dies due to metabolic exhaustion (Leistner 2000) Multitarget Preservation of Foods Time, treatment intensity Figure 39.2 Schematic of enhanced microbial inactivation using different hurdles in food processing Hurdle technology emphasizes intelligent combination of various preservation techniques Leistner (1995) proposed concept of multitarget preservation of foods and suggested that different hurdles rather than having an accruing effect may have synergistic action It has been suggested that different preservative factors of variable intensity be used for the synergistic action, instead of using a single high-impact preservative These targets include cell components, enzymes, pH, water activity, redox potential, P1: SFK/UKS BLBS102-c39 P2: SFK BLBS102-Simpson March 21, 2012 14:20 Trim: 276mm X 219mm Printer Name: Yet to Come 39 Minimally Processed Foods etc Barbosa-Canovas et al (1998) suggested that the applicability of multitarget preservation approach is not only limited to traditional methods of food preservation, but also valid for emerging nonthermal technologies like HPP, PEF, etc A lot of new research is being done using newer technologies, which are based upon the central idea of multitarget preservation Limitations of Hurdle Concept Combination of two or more hurdles results in either additive, synergistic, or antagonistic effect Addition and synergism justify the use of hurdle technology but some studies have shown the negative effect of using some hurdle combinations (Jordan et al 1999, Casey and Condon 2002) The antagonistic phenomenon is related to the type of conditions, intensity of preservative action of each hurdle, and the type and nature of food to be minimally processed PACKAGING TECHNIQUES FOR MINMALLY PROCESSED FOODS Map MAP is a method of preserving the fruits and vegetables by changing the composition of the air surrounding the food in a package Different gas mixtures in varying concentrations are used in modifying the atmosphere inside the package Generally, oxygen and carbon dioxide are used for packaging of minimally processed fruits and vegetables, but the potentials of other gases like nitrogen, carbon monoxide, and noble gases (Helium, Argon, and Neon) have also been realized (Sandhya 2010) Higher carbon dioxide and reduced oxygen levels have been found efficient in enhancing the shelf life and preventing the problem of enzymatic browning in fruits and vegetables Generally, 15–20% CO2 has been considered effective in preventing decay in fresh fruits and vegetables In case of meat products, oxygen is used for retaining the red color of oxymyoglobin, but oxygen levels are reduced in other products to prevent oxidative rancidity and spoilage due to microbes Very low oxygen or high concentration of carbon dioxide can initiate anaerobic respiration in the package, which may lead to formation of certain undesirable metabolites, harming the product’s physiology (Soliva-Fortuny and Martin-Belloso 2003) The essential characteristics for MAP packaging material are the gas permeability and water vapor transmission rate Most common packaging materials include polyvinyl chloride, polypropylene, polyethylene, and polyethylene terephthalate (Mangaraj and Goswami 2009) These days, laminates or coextruded films are used for packaging The traditional gas mixture configuration is not enough to prevent the deteriorative reaction if fruits and vegetables get wounded Minimal processing up to some extent is responsible for initiating the tissue damaging Also, the packaging materials used for MAP are prone to some limitations pertaining to textural, color, and permeability changes Hence, as a solution, edible coatings are being seen as potential alternative to the MAP technique (Rojas-Grau et al 2009) The advantages of edible coating are numerous, and con- 757 stantly improvements are being made by incorporating active ingredients like antioxidant, antimicrobials, antibrowning agents, etc Edible coatings have been explained later in the chapter Active and Edible Packaging Active packaging implies incorporation of certain additives that can enhance the shelf life, flavor, texture, etc by interacting with the food product inside the package These additives can be oxygen scavengers, carbon dioxide absorbers or generators, ethanol emitters, ethylene absorbers, and moisture absorbers (Ohlsson and Bengtsson 2002) Antioxidants and antimicrobial compounds are also used in the active packaging Inclusion of chemical or physical additives in packages may become a hindrance for consumer acceptance of packaged foods The development of packaging techniques that use natural materials like edible coating is a potential alternative to the chemicalbased packaging methods Edible coating is applied on the surface of food by spraying, dipping, or brushing Sources of edible coatings are polysaccharides, proteins, and lipids (Lin and Zhao 2007) Edible coatings help reduce water loss and delay ageing by allowing controlled and selective gas permeability through product They are also environmentally friendly as they reduce synthetic packaging waste CONCLUSION Minimally processed foods have become very popular with consumers All the aspects related to minimally processed food, from processing to packaging, are witnessing an unprecedented continuous improvement The combined treatment methods using thermal and nonthermal 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Processed Foods Contreras C et al 20 08 Influence of microwave application on convective drying: effects on drying kinetics, and optical and mechanical properties of apple and strawberry J Food Eng 88 (1):... Final Rule 70(157): 480 57– 480 73 Fellows PJ 1 988 Food Processing Technology, Principles and Practice Elks Horwood, Chichester Fernanda SMM et al 2001 Inactivation effect of an 18- T pulsed magnetic