J. Verbr. Lebensm. (2010) 5:65–72 DOI 10.1007/s00003-009-0315-6

Journal fu¨r Verbraucherschutz und Lebensmittelsicherheit Journal of Consumer Protection and Food Safety

L E I T T H E M A : H A LT B A R M AC H E N VO N L E B E N S M I T T E L N

Preserving quality of fresh-cut products using safe technologies ´ lez-Aguilar Æ Gustavo Adolfo Gonza J. F. Ayala-Zavala Æ G. I. Olivas Æ ´ lvarez-Parrilla L. A. de la Rosa Æ E. A

Received: 14 April 2009 / Accepted: 4 May 2009 / Published online: 8 August 2009 ¨user Verlag, Basel/Switzerland 2009 Ó Birkha

Abstract Food preservation is critical for keeping the global food supply safe and available for consumers. Food scientists study production and processing to develop new technologies that improve the quality and quantity of healthy food products, with the main objective of increasing food production without affecting food quality and environment, while fulfilling consumer expectations. Nowadays consumers want their food to be fresh, nutritious, safe, and attractive, low priced, and ready-to-eat. That is the case of fresh-cut products; however, maintaining the quality of these products is not an easy task, since minimally processed products experience increased ethylene production and respiration rates, with the consequent lost of quality. New effective and inexpensive technologies to safely preserve the quality of fresh-cut products are needed. In the last

´lez-Aguilar (&)
J. F. Ayala-Zavala Dr. G. A. Gonza Coordinacion de Tecnologie de Alimentos de Origen Vegetal, A.C. Carr. La Victoria Km. 0.6, A.P. 1735, 83000 Hermosillo, Sonora, Mexico e-mail: [email protected] J. F. Ayala-Zavala e-mail: [email protected] G. I. Olivas Centro de Investigacio ´n en Alimentacio ´ n y Desarrollo, A.C. Fisiologı´a y Tecnologı´a de Alimentos de Zona Templada, Cuauhte´moc, Chihuahua, Mexico e-mail: [email protected]

two decades, food scientists have attempted to solve problems in fresh-cut processing and quality preservation, and rapid advances in scientific knowledge on fresh-cut product preservation have been developed. The present review describes the use of emerging technologies such as ultraviolet irradiation (UV-C), edible coatings, active packaging and natural additives, to preserve the quality of fresh-cut fruits; highlighting the areas in which information is still lacking, and commenting on future trends. Keywords UV-C irradiation
Edible coating
Active packaging
Essential oils
Fresh-cut Abbreviations CFU Colony forming unit EOs Essential oils GRAS Generally recognized as safe MJ Methyl jasmonate PAL Phenylalanine ammonia-lyase RH Relative humidity UV Ultraviolet light UV-A Ultraviolet light (315–400 nm) UV-B Ultraviolet light (280–315 nm) UV-C Ultraviolet light (100–280 nm) 1 Emerging techniques applied to preserve fresh-cut fruits and vegetables 1.1 UV-C irradiation

´ lvarez-Parrilla L. A. de la Rosa
E. A ´sicas, Instituto de Ciencias Departamento de Ciencias Ba ´rez Biome´dicas, Universidad Auto ´noma de Ciudad Jua ´rez, Chihuahua, Mexico (UACJ), Ciudad Jua e-mail: [email protected]

Ultraviolet light (UV) is a type of non-ionizing radiation with wavelengths from 100 to 400 nm, which is usually classified into three types: UV-A (315–

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400 nm), UV-B (280–315 nm) and UV-C (100–280 nm). UV-C irradiation has its maximum at 254 nm and is, of the three, the one with the highest germicidal action, and the most used for surface decontamination and control of microorganism growth in whole and fresh-cut products (Vicente et al. 2005). Treatment with ultraviolet energy offers several advantages to food processors as it does not leave any residue, and does not have legal restrictions, it is easy to use and lethal to a wide broad of microorganisms, and does not require high economic investment and expensive safety equipment to be implemented (Rivera-Pastrana et al. 2007). Several studies have been published on UV-C as a method to preserve the quality of different fruits and vegetables (Gonzalez-Aguilar et al. 2007; Pombo et al. 2009). Pre-storage application of UV-C reduced chilling injury in pepper (Vicente et al. 2005), delayed senescence yellowing, chlorophyll degradation, and pheophytin accumulation in broccoli (Costa et al. 2006), controlled storage rot in strawberry (Pan et al. 2004; Pombo et al. 2009), reduced pathogen growth and induced disease resistance in the fruit tissue (El Ghaouth et al. 2003; Bonomelli et al. 2004; Pombo et al. 2009). Chilling injury symptoms and deterioration of ‘‘Tommy Atkins’’ mangoes was reduced by UV-C irradiation during storage at 5°C (GonzalezAguilar et al. 2007). In addition, the effect of short UV-C doses (0.4–8.14 kJ m2) on the shelf-life of the fresh processed lettuce has been studied (Allende and Artes 2003). Finding UV-C effective in delaying senescence and deterioration of fresh-processed lettuce during storage. UV-C treatments induced a stress that simulates the production of phenylalanine ammonia-lyase (PAL), an enzyme that plays a key role in the synthesis of phytoalexins, phenolic compounds that improve the resistance of fruits and vegetables to microorganisms (Charles et al. 2008a, 2009). The activation of the secondary metabolism of fresh products enhances the synthesis of phytochemicals with nutraceutical activity (El Ghaouth et al. 2003; Bonomelli et al. 2004). The UV-C treatment-induced phytoalexins have been identified in fresh-cut cantaloupe (Lamikanra et al. 2002) and fresh-cut pineapple (Lamikanra and Richard 2004). Furthermore, it has been shown that the level of enzyme activation correlated positively with disease tolerance induced by UV-C (Bonomelli et al. 2004). In addition to the above physiological effects produced by UV-C light, the most important is the damage to the microbial DNA (Charles et al. 2008b). The use of two-sided UV-C radiation at 1.18, 2.37 or 7.11 kJ m-2 was effective for reducing the

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natural microflora of FC ‘Red Oak Leaf’ lettuce up to 10 days at 5°C, although 7.11 kJ m-2 induced tissue softening and browning after 7 days at 5°C (Allende and Artes 2003). Lado and Yousef (2002) reported that UV-C radiation from 0.5 to 20 kJ m-2 inhibited microbial growth by inducing the formation of pyrimidine dimers which alter the DNA helix and block microbial cell replication. Therefore, cells which are unable to repair radiation damaged DNA die and sub-lethally injured cells are often subject to mutations (Lado and Yousef 2002). 1.2 Edible coatings An edible coating is a thin layer of edible material (hydrocolloid or lipid) applied on the surface of a food product with the purpose of generating a semipermeable barrier to gases, water vapor, and volatile compounds. In fresh-cut products, edible coatings decrease respiration and senescence while protecting the aroma, texture and color of the products throughout storage. The ability of edible coatings to preserve the quality of fresh-cut products may vary depending on the composition and thickness of the coating, type of product, variety and maturity, food surface coverage, and storage conditions. Compounds most commonly used to form edible coatings include chitosan, starch, cellulose, alginate, carrageenan, zein, gluten, whey, carnauba, beeswax and fatty acids. In most cases, additives such as antimicrobials, antioxidants, and nutrients are added to the coating formulation to help preserve the quality of fresh-cut products (Olivas and Barbosa-Canovas 2005; AyalaZavala et al. 2008b). Edible coatings may reduce respiration of fresh-cut products by decreasing the oxygen transmission rate, therefore reducing the internal oxygen concentration. Some coatings have been successfully used to decrease the respiration rate of Fuji apples (zein and whey protein isolate coatings) (Park et al. 1996; Lee et al. 2003), and tomatoes (chitosan coatings) (Liu et al. 2007; Badawy and Rabea 2009; Gonzalez-Aguilar et al. 2009). Fresh-cut products have elevated water transpiration rates (Toivonen and Brummell 2008) which may lead to decreased firmness and metabolic alterations, impacting sensorial and nutritional attributes (Park et al. 1996; Lee et al. 2003). Edible coatings help to decrease water loss of fresh-cut products (RaybaudiMassilia et al. 2008). Methyl cellulose-stearic acid coatings decreased water loss on fresh-cut pears (Olivas et al. 2003); chitosan coatings reduced water

Preserving quality of fresh-cut products

loss on peeled litchi (Dong et al. 2004) and sliced mango (Chien et al. 2007), carrageenan coatings avoided water loss on sliced banana (Bico et al. 2009) and alginate coatings prevented water loss on freshcut apple (Lee et al. 2003; Fontes et al. 2007), papaya (Tapia et al. 2007), pear (Oms-Oliu et al. 2008a), and melon (Oms-Oliu et al. 2008b). Chitosan coatings decreased texture loss on freshcut papaya (Gonzalez-Aguilar et al. 2009), alginate coatings preserved the texture of peach (Maftoonazad et al. 2008), and gluten coatings protected the texture of strawberry (Tanada-Palmu and Grosso 2005). Broccoli retained its firmness after the application of zein-oleic acid coating (Rakotonirainy et al. 2001), while fresh-cut apple firmness was preserved by the use of alginate coatings (Olivas et al. 2007), and also by a combination of whey protein isolate and hydroxyl propyl methyl cellulose (Perez-Gago et al. 2005). Changes in color of fresh-cut products can be prevented by the use of edible coatings by their ability to decrease oxygen transmission rate and their potential to act as carriers of antioxidants, such as ascorbic acid, citric acid, oxalic acid, cysteine, 4-hexylresorcinol, and N-acetylcysteine. Browning of fresh-cut apples has been prevented or reduced by (1) carrageenan and whey protein coatings containing ascorbic, citric and oxalic acid (Lee et al. 2003), (2) whey protein-beeswax coatings containing ascorbic acid, cysteine and 4-hexylresorcinol (Perez-Gago et al. 2006), (3) alginate and gellan coatings containing n-acetylcysteine (Tapia et al. 2007), and (4) alginate coatings containing ascorbic acid (Olivas and Barbosa-Canovas 2008). The color of fresh-cut pears was preserved by methyl cellulose coatings containing ascorbic acid (Olivas et al. 2003), and alginate and gellan coatings containing N-acetylcysteine and glutathione (Oms-Oliu et al. 2008b). 1.3 Active packaging Active packaging is defined as a system in which the package interacts with the product or the headspace, in order to maintain the nutritional and sensory quality, fresh-like appearance, and safety of products (Appendini and Hotchkiss 2002; Ayala-Zavala et al. 2008b). Headspace artifacts were the first antimicrobial active packaging commercialized in the market, in the form of sachets that are enclosed in the interior of the package or attached to it. They can be divided in two groups: indirect and direct antimicrobial activity. Headspace artifacts with direct antimicrobial activity include antimicrobial volatile

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compounds such as sulfur dioxide (Ozdemir and Floros 2004), ethanol (Vermeiren et al. 2002; Ozdemir and Floros 2004), organic acids and EOs (Cha and Chinnan 2004; Ozdemir and Floros 2004; Ayala-Zavala et al. 2008b). Recently, Ayala-Zavala et al. (2008a, b, c, d) described a cyclodextrin essential oil microcapsule that could be used as a headspace artifact to increase the shelf-life of fresh-cut products. In this study, it was hypothesized that internal moisture can be the driving force that released the antimicrobial compound from the complex. Reports showed that the inclusion complexes b-cyclodextrin-hexanal (1.1 lL hexanal/L) and b-cyclodextrin-acetaldehyde (0.12 lL acetaldehyde/L) were effective against Alternaria alternata, Colletotrichum acutatum and Botrytis cinerea (Almenar et al. 2007). A sachet containing different concentrations of 2-nonanone (2.5, 5 and 10 lL), volatile compounds that are naturally found in strawberry fruit, impregnated in alumina as adsorbent solid was developed, studied and finally incorporated as a part of the active packaging system. The final package increased the shelf-life of wild strawberries, delayed fungal decay and maintained the overall quality of the fruits (Almenar et al. 2007). It has to be remarked that among the different kinds of active packages, headspace artifacts have been successfully used to preserve fresh products, even industrially. Another type of antimicrobial active packaging artifacts are those in which the antimicrobial compound is embedded in the bulk polymer and it has to migrate to the surface in order to interact with the microorganism. Different natural and synthetic polymers have been used as carriers; a review on this subject has been recently published (Tripathi and Dubey 2003; Ayala-Zavala et al. 2008b; Fisher and Phillips 2008). Low density polyethylene films incorporated with 1% antimicrobial agents of Rheum palmatum extract, Coptis chinensis extract and Ag-substituted inorganic zirconium matrix, were applied to modified atmosphere packaging of 200 g of fresh strawberries. The antimicrobial low density polyethylene film retarded the growth of total aerobic bacteria, lactic acid bacteria and yeast on the fruits and resulted in significantly lower decay (Chung et al. 1998). There are few examples of antimicrobial packages in which the antimicrobial compound has been immobilized into the polymer by ionic or covalent bonds. In order to attach the antimicrobial, the presence of functional groups in both the polymer and antimicrobial is necessary. Nevertheless, application of this kind of packaging in fresh fruits and

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vegetables has not been reported to our knowledge. Silver zeolite is the most used immobilized antimicrobial, especially in Japan (Lopez-Rubio et al. 2004). Other immobilized antimicrobials include peptides, enzymes, polyamines and organic acids (Appendini and Hotchkiss 2002; Lopez-Rubio et al. 2004; Buonocore et al. 2005). The main inconvenience of this kind of active packaging is that, in order to inhibit the microorganism growth, direct contact between the fresh produce and the polymer is necessary. In this context the design of wrapping films could be desirable to ensure the beneficial effect of maintaining the quality of fresh fruits and vegetables.

2 Emerging additives applied to fresh-cut fruits and vegetables Research actions on the effect of several natural additive compounds have been undertaken, evaluating their mode of action, activity, toxicology, and effect on sensorial, biochemical and physiological properties of the treated fresh-cut product, all aimed at fulfilling consumer demands of healthy and safe products with excellent quality. Therefore, considerable research has been recently directed toward the development of effective natural food preservatives. 2.1 Natural additives with antimicrobial and flavoring potential Natural antimicrobial compounds are a re-emerging alternative to fresh-cut products preservation (Corbo et al. 2009). The antimicrobial power of plants and herb extracts has been recognized for centuries, and mainly used as natural medicine. Plant volatiles have been widely used as food flavoring agents, and many are generally recognized as safe (GRAS). Several essential oils (EOs) such as oils of garlic, cinnamon, thyme, oregano, clove, basil, coriander, citrus peel, laurel, ginger, rosemary and peppermint, among others, have been studied as antimicrobial natural products against both bacteria and molds (Burt 2004; Burt et al. 2005; Ayala-Zavala et al. 2008c, d; Corbo et al. 2009). The inherent aroma and antimicrobial activity of EOs are related commonly to the chemical configuration of the components, to the proportions in which they are present and to interactions between them, affecting their bioactive properties (Fisher and Phillips 2008). Considering the complex mixture of EOs constituents is difficult to attribute the antimicrobial mode of action to one specific mechanism, being reported several targets in

G. A. Gonza ´lez-Aguilar et al.

the microbial cell. It seems that they may cause deterioration of cell wall, damage to cytoplasmic membrane, damage to membrane proteins, leakage of cell contents, coagulation of cytoplasm, depletion of proton motive active sites, inactivation of essential enzymes, and disturbance of genetic material functionality (Burt 2004; Ayala-Zavala et al. 2008b; Gutierrez et al. 2008). Methyl jasmonate (MJ) is a natural compound widely distributed in plants. It was first detected as a sweet fragrant compound in Jasminum essential oil ´lez-Aguilar et al. 2006). and other plant species (Gonza MJ is known to regulate plant development and response to environmental stress (Demo et al. 2005; Yao and Tian 2005), affecting many biochemical and physiological reactions in the tissue of whole and fresh-cut fruits and vegetables and extending shelf-life of whole and fresh-cut tomatoes, mangoes, guavas, ´lez-Aguilar et al. 2006). and strawberries (Gonza Several devices have been designed to control ethanol release in the headspace of packed fruit (Kalathenos and Russell 2003). Ayala-Zavala et al. reported that ethanol treatment in conjunction with MJ increased antioxidant capacity, volatile compounds, and post-harvest life of strawberry fruit, as well as extended shelf-life of fresh-cut tomatoes (Ayala-Zavala et al. 2005, 2008c). Plotto et al. concluded that ethanol vapor applied for 20 h, prior to processing whole mangoes, did not delay ripening; however, shorter time of exposure (10 h) suppressed fruit ripening (Plotto et al. 2006). For the application of natural antimicrobial and flavoring compounds such as fresh-cut fruits and vegetables preservatives, the sensorial impact should be considered (Ayala-Zavala et al. 2008a). Several fresh-cut fruits and vegetables that generally are associated with herbs, spices or seasonings would be the least affected by this phenomenon; however, new combination of flavors can be considered based in consumer studies (Baranauskiene et al. 2005). Even the most healthful foods are not routinely accepted and regularly consumed if they have poor sensory properties according to the consumer point of view (Park et al. 2005). In this context, the right combination of a given natural antimicrobial and flavoring volatile, used also as a fresh-cut product preservative, could increase consumer acceptability. 2.2 Natural additives with anti-browning and texturizer potential Complexing agents entrap or form complexes with the substrates of the enzyme polyphenol oxidase or

Preserving quality of fresh-cut products

with reaction products. Some of the complexing agents are cyclic nonreducing oligosaccharides of six or more D-glucose residues. Some researchers have observed that b-cyclodextrin has low water solubility and, in some experiments with apples, was not effective or not consistent in controlling browning (Lamikanra 2002). Alvarez-Parilla et al. compared the polyphenol oxidase inhibitory effect of b-cyclodextrin, 4-hexylresorcinol, and methyl jasmonate in red delicious apple; the inhibitory strength was higher for 4-hexylresorcinol followed by b-cyclodextrin, and then methyl jasmonate. There was also a dual synergistic effect between b-cyclodextrin and 4-hexylresorcinol (Alvarez-Parilla et al. 2007). Jeon and Zhao evaluated ten different honeys from floral sources and their anti-browning effect on freshcut apples. The apples were vacuum impregnated in 10% honey solutions and the color was monitored for 10 days during storage at 4°C and 80% RH. The Wildflower and Alfalfa honeys significantly inhibited browning discoloration, although there was an initial reduction of lightness as a result of the color from honey. A honey with light color may be preferred to be used as an anti-browning agent for fresh-cut apples (Jeon and Zhao 2005). Song et al. used rhubarb juice as a natural antibrowning agent for fresh-cut apple slices. They found that juices at 20% concentration containing 67 mg/100 g of oxalic acid inhibited browning (Song et al. 2007). Yoruk and Marshall investigated the mode of inhibition of oxalic acid on polyphenol oxidase and determined that - by binding with copper to form an inactive complex - it reduces catechol–quinone product formation (Yoruk and Marshall 2003). Oxalic acid was a more potent inhibitor of polyphenol oxidase compared with other structurally related acids. Other compounds, such as benzoic and cinnamic acids, are polyphenol oxidase inhibitors but have been found not to give prolonged protection along storage time (Lamikanra 2002). 2.3 Fortificants Vitamins and minerals, called micronutrients, play a very important role in our health even though they only make up a very small part of the foods we eat each day. Diets which do not contain adequate amounts of vital micronutrients often result in deficiency diseases, including blindness, mental retardation, and reduced resistance to infectious diseases, depending on the particular micronutrient. In this context, several additives with possibility to be applied as

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fresh-cut fruit and vegetable preservatives could be contemplated. Most fruits and vegetables contain low amounts of some important vitamins and minerals, such as vitamin E, calcium, and zinc. For example, 100 g of raw apple (with skin) contains only 0.18 ± 0 mg of vitamin E, 6 ± 0.34 mg of calcium, and 0.04 ± 0.004 mg of zinc, according to the USDA Natl. Nutrient Database for Standard Reference. Only 8.0% of men and 2.4% of women in the United States met current recommendations for vitamin E intake from food sources (Maras et al. 2004). Instead, vitamin E supplements are consumed daily by more than 35 million people in the United States (Traber 2004). Leonard et al. showed that the bioavailability of vitamin E from vitamin E-enriched foods is much greater than that of an encapsulated supplement (Leonard et al. 2004). Along with increased consumption of fresh-cut apples due to their convenience, fresh-like taste, and consumers’ awareness of their health benefit, fresh-cut apples enriched with vitamin E or other bioactive compounds would be a good choice to develop functional foods and to provide opportunities for increasing intake of these nutraceuticals. Food fortification has been applied with success in both developed and developing countries to address and prevent micronutrient deficiencies. Due to varying eating habits and type of deficiency disease, the food vehicle, the micronutrient added, and the amounts that are added would not be the same for each country. 2.4 Probiotics Probiotics are live microorganisms that transit the gastro-intestinal tract and, in doing so, benefit the health of the consumer (Tannock et al. 2000). Several members of the genera Lactobacillus and Bifidobacterium have gained recognition as probiotic bacteria because of their various therapeutic health benefits, mainly resistance to enteric pathogens, anti-colon cancer effect, immune system modulation, and allergies. The addition of probiotics to obtain functional edible films to treat fresh-cut fruits has been reported (Tapia et al. 2007). Fresh-cut apple and papaya cylinders were successfully coated with 2% (w/v) alginate or gellan film-forming solutions containing viable Bifidobacteria. Upon culture, Bifidobacteria added to the film-forming solutions yielded viable populations of B. lactis Bb-12 in the order of 9.93 and 9.67 log10 CFU/g for the gellan or alginate coatings, respectively. Immediately after coating (day 0), viable

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counts of B. lactis Bb-12 on the coated papaya pieces were 6.89 and 7.52 log10 CFU/g for alginate or gellan, respectively, while for coated apple pieces the values were 7.91 and 7.78 log10 CFU/g for alginate or gellan, respectively. This represents approximately a 2-logcycle decrease compared to the concentration of the original film-forming solution; this drop was caused by dilution effects. Bifidus population remained viable and constant during the 10-day storage period at 2°C. The survival and maintenance of B. lactis Bb-12 in the alginate- or gellan-based edible coatings on both fresh-cut papaya and apples may be regarded as satisfactory, as their values remained between 6 and 7 log10 CFU/g. In order to confer health benefits to humans, the viable count of Bifidobacteria at the time of consumption should be 106 CFU/g (Samona and Robinson 1991). It is also important for manufacturers and retailers to be able to confirm the viable count of these organisms in Bifidus-containing products.

3 Concluding remarks Considering the increasing demands of consumers and the fresh-cut fruit processors, as well as environmental preservation, the use of safe emerging technologies and additives based on natural compounds could be an alternative in the preservation of fresh-cut fruits and vegetables. Future research should be focused on optimization of the industrial application, the influence of temperature and food matrix on the functional activity in order to find optimal doses of these compounds, and to evaluate toxicological activity, as well as assessing sensorial and overall quality of fresh-cut fruit. All these studies will be useful to understand the possible mode of action of the additives, and will allow offering producers a practical method to preserve fresher, more natural foods containing less artificial preservatives, maintaining an increasing quality of fresh-cut fruits and vegetables.

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