Challenges Facing the Industry and Scientific Community in Maintaining Quality and Safety of Fresh-cut Produce

Fresh-cut produce industry, one of the fastest growing food industries in the United States, has been rapidly expanding in the last two decades. The flourishing of the fresh-cut produce industry is attributable to the high value placed by modern consumers on foods that are fresh, nutritious, and convenient. However, the recent food borne illness outbreaks associated with the consumption of packaged fresh-cut produce have also made bold headline news worldwide. Unlike the intact fruits and vegetables, fresh-cut produce sustains substantial tissue injury during processing, and is thus more susceptible to microbial growth and quality deterioration; unlike traditionally processed food, fresh-cut products consist of living tissues and are processed and marketed as "ready-to-eat" yet without a microbial killing step. In addition, fresh produces grow in the open field, and contamination with human pathogens can potentially occur anywhere from farm to table. These factors reduce the shelf-life of fresh-cut produce and increase the risk of food borne illness. This paper discusses the challenges facing the industry and scientific community. Issues involved in maintaining both quality and safety of fresh-cut produce, their current status and future research directions will be emphasized. INTRODUCTION The fresh-cut produce industry has experienced growth in the vicinity of 10-15% for the past two decades and is projected to continue to grow rapidly along with consumer demand for nutritious, convenient, fresh and flavorful foods (Garrett, 2002; Gorney, 2001; PMA, 2006). The benefit of consuming fresh fruits and vegetables is well documented. Fresh fruits and vegetables are nutritionally important sources of antioxidants including vitamins A, C and E, carotenoids and flavonoids, as well as minerals (McCarthy and Matthews, 1994). Furthermore, there is growing evidence that regular consumption of fresh produce may prevent or reduce the risk of several chronic diseases (Cooper, 2004). However, epidemiological reports have shown that the occurrence of foodborne illness associated with the consumption of fruit and vegetables has increased (Beuchat, 2002; NACMC, 1999; Tauxe et al., 1997). Recently, a number of cases of foodborne illnesses associated with the consumption of fresh and fresh-cut produce have made headline news and negatively impacted the confidence of consumers in fresh produce. Processing of fresh-cut products involves peeling, cutting, washing and sanitizing, drying and packaging. The finished products remain in a minimally processed and fresh state, and ready-to-eat. The International Fresh-cut Produce Association defines fresh-cut products as fruits or vegetables that have been peeled and/or cut into 100% usable product that is bagged or prepackaged. High standards of food quality and safety are essential for sustained industrial growth and fresh-cut product consumption. Many new challenges exist due to the nature of minimal processing: (1) Unlike intact fruits and vegetables, the physical and chemical barriers (skins) provided by the epidermis of produce are removed during preparation of produce for the fresh-cut market. This practice creates the opportunity for the spoilage and/or human pathogenic microorganisms to directly contact the edible portion of produce, thus leading to more rapid product decay and increased health hazards; (2) Fresh-cut fruits and vegetables Proc. IC on Qua]. Manag. Fresh Cut Produce 213 Eds.: S. Kanlayanarat et al. Acta 1-lort. 746, ISI-IS 2007 sustaill substantial tissue injury during processing; the disruption 01 tissue and cell integrity often increases respiration rate, ethylene synthesis, enzymatic browning and (lL\eIopment of physiological disorders (Watada et al., 1996). The damaged plant tissues provide nourished medium for microbial survival and growth (Izumi et al., 2005); (3) unlike traditionally processed food, fresh-cut products consist of living tissues and are processed and marketed as "ready-to-eat" yet without an effective microbial killing step; adding to this challenge is pressure to market "preservative free" fresh-cut products, as licsh-cut processors strive to balance consumer demand for "clean" labels with the need to inactivate or inhibit pathogen growth during distribution (Mermelstein, 2001); and (4) new unforeseen food safety issues have emerged as major concerns in the fresh-cut industry. Consequently, fresh-cut products require special handling during processing, transportation and storage. This review article focuses on the major challenges facing the fresh-cut produce industry and the scientific community, current technologies used to combat the problems, and emerging technologies that hold promise for the future. MODIFIED ATMOSPHERE PACKAGING FOR QUALITY MAINTENANCE Modified atmosphere packaging technology (MAP) is the enabling technology for the blossoming of the packaged fresh-cut produce industry. However, challenges related to the development and applications of MAP remain to be overcome for improved quality and shelf life of fresh-cut produce. MAP decreases oxygen (02) and increases carbon dioxide (CO,) 2 concentrations in the package to create an atmosphere which prolongs the shelf-life offresh-cut produce. The passive changes in package atmosphere are due to the interaction between respiratory 02 uptake and CO 2 evolution of packaged produce, and gas transfer through package fdms (Jacxsens et al., 1999, 2002; Makino, 2001; Schlimme and Rooney, 1994). Film permeability for 0 2 and CO2 should be matched to the respiration rate of the packaged fresh-cut commodity, in order to create a beneficial modified atmosphere inside the package that will reduce metabolic activity, ethylene sensitivity and production, and/or physiological and pathological deterioration during storage (Kim et al., 2003; Luo et al., 2004). The package design must be considered to assure that the materials used will provide adequate oxygen and carbon dioxide transmission for the product. A rapid establishment of a low 02 and/or elevated CO 2 environment, in other words, active MAP, is critical for the prevention of cut surface browning of many fresh-cut vegetables, especially lettuce. This initial atmosphere can be achieved quickly by flushing the package with a gas mixture of pre-determined levels of 0 2 and CO2 . or N2 . Flushing produce packages with a gas mixture, does not usually alter the equilibrium 02 and CO2 concentrations in the headspace, but merely accelerates equilibration. However, some iresh-cut produce appears to present exceptions to this pattern. Kim et al. (2003) found that by adjusting initial oxygen 0 2 levels, CO2 injury could be alleviated, thus minimizing uality loss of lettuce under sub-optimal film OTR conditions. Certain fresh-cut products have either very high respiration rate or require a high axygen level inside the package to maintain the product quality. These products are often nackaged with perforated films because the OTR requirement exceeds the availability of ion-perforated films. However, there have been food safety concerns over the use of perforated films because of the potential transfer of human pathogenic bacteria through the perforations. Since perforated films provide a potential means for contamination of fresh-cut produce, their replacement with high OTR films would be advantageous to alleviate food safety concerns. Packaging design for fresh-cut fruits is different from that for cut vegetables. Due to the need for protection against mechanical injury during handling and transportation, fresh-cut fruits are often packaged in rigid containers, such as clamshells, two piece containers and trays. A major technical issue concerning rigid containers is an insufficient oxygen transmission rate because the containers are made of gas barrier materials and the gas transmission is made through the container lids with limited respiring area.