Fresh-Cut Produce Quality: Implications for a Systems Approach
Fresh-cut fruit and vegetables represent an important food segment of interest to growers, processors, retailers and consumers. Fresh-cut products are more perishable than whole produce because they are physically altered from their original state during processing operations. Although they remain in a fresh state, fresh-cut products are living tissues characterized by an accelerated metabolism. Quality in fresh-cut product preparation and distribution is crucial in terms of food safety, quality and environmental impact. Cultivation is still a fundamental part of the supply chain, but the complex market dynamics require detailed knowledge of all stages in the supply chain. In the last 20 years, the fruit and vegetable market has developed a rich array of new products. At the same time, consumers have become more concerned about health and a proper diet (see also Chapters 3 and 5Chapter 3Chapter 5) and have increased the demand for healthy fruit and vegetables and guaranteed products. Globalization has shown that production systems need a new approach that should focus on safety and quality rather than quantity and has shown that a fully integrated and complex supply chain must be able to fulfill the consumers’ needs. This chapter has considered critical points concerning the safety and quality of produce which should be controlled by growers, who represent the first stage in the fresh-cut supply chain, and the technologies used by processors to maintain quality and guarantee safety. An optimal cultivation management on the farm, an efficient and rapid harvesting, proper postharvest handling and storage are key factors that favor the quality of the raw material. Quality raw material enhances processing and final product quality, leading to increased competitiveness in the market for the fresh-cut producer. This, in turn, leads to increased bargaining power of, in particular, processors and retailers.
The market sales of ready-to-use fresh vegetables have grown rapidly in recent decades as a result of changes in consumer attitudes, especially consumption of fresh-cut lettuce and carrot due to their use in prepared salads. Chlorine solutions have been widely used to sanitise fruit and vegetables in the fresh-cut industry. However, the association of chlorine with the possible formation of carcinogenic chlorinated compounds in water has called into question the use of chlorine in food processing. There is a real need to find alternatives for preservation of fresh-cut fruit and vegetables in order to improve the efficacy of washing treatments. Alternatives or modified methods have been proposed, as antioxidants, irradiation, ozone, organics acids, modified atmosphere packaging, whey permeate, etc.; however, none have yet gained widespread acceptance by the industry. For this reason the development of alternatives and markers in order to measure the efficacy of these alternatives are needed.
Factors affecting quality and safety of fresh-cut produce
The quality of fresh-cut fruit and vegetable products includes a combination of attributes, such as appearance, texture, and flavor, as well as nutritional and safety aspects that determine their value to the consumer. Nutritionally, fruit and vegetables represent a good source of vitamins, minerals, and dietary fiber, and fresh-cut produce satisfies consumer demand for freshly prepared, convenient, healthy food. However, fresh-cut produce deteriorates faster than corresponding intact produce, as a result of damage caused by minimal processing, which accelerates many physiological changes that lead to a reduction in produce quality and shelf-life. The symptoms of produce deterioration include discoloration, increased oxidative browning at cut surfaces, flaccidity as a result of loss of water, and decreased nutritional value. Damaged plant tissues also represent a better substrate for growth of microorganisms, including spoilage microorganisms and foodborne pathogens. The risk of pathogen contamination and growth is one of the main safety concerns associated with fresh-cut produce, as highlighted by the increasing number of produce-linked foodborne outbreaks in recent years. The pathogens of major concern in fresh-cut produce are Listeria monocytogenes, pathogenic Escherichia coli mainly O157:H7, and Salmonella spp. This article describes the quality of fresh-cut produce, factors affecting quality, and various techniques for evaluating quality. In addition, the microbiological safety of fresh-cut produce and factors affecting pathogen survival and growth on fresh-cut produce are discussed in detail. Quality of fresh-cut products as affected by harvest and postharvest operations
There is a rising demand for fresh-cut convenience products with high quality and nutritional standards that needs to be met by the fresh-cut industry. It is well known that harvest and postharvest handling of fresh produce has a paramount impact on its quality and storage, although most of the existing literature has focused on these impacts related only to fresh produce that is destined for the final consumers. Indeed, current harvest methods and postharvest technologies have improved fruit and vegetable handling and distribution processes by slowing down physiological processes and senescence. Nonetheless, these technologies and methods may influence the quality of fresh produce as raw material for fresh-cut processing as a result of the dynamic responses of fresh produce to handling procedures and treatments. Here, we review the existing literature on the challenges facing the fresh-cut industry, focusing on the impact of harvest, maturity, and handling of fruit and vegetables on the quality of raw materials, as well as the implications for fresh-cut products. The review also highlights areas for further research with the aim of enhancing the sensorial, nutritional and biochemical quality of such products. © 2018 Society of Chemical Industry.
QUALITY ASSURANCE AND SAFETY CONSIDERATION FOR FRESH-CUT PRODUCE
Fresh-cut produce is one of the fastest growing food categories in the United States (U.S.) with annual sales of $12 billion in 2006 (PMA, 2006). Approximately 53 percent of the industry manufactures packaged salads and salad blends, making the quality and safety of lettuce of the utmost importance. Essential to consistent fresh-cut lettuce quality and safety is the function of the Quality Assurance program in the processing plant. Its role is provide the tools for quickly locating and correcting quality or safety issues that might arise during production. (Consumers in the U.S. perceive fresh-cut safety as an entitlement, along with quality.) They expect a fresh-cut product that has met their quality expectations to also be safe to eat. While fresh-cut sales continue to grow at a rapid pace, the biggest challenge for fresh-cut processors is assuring food safety. From 1996 to 2006, 72 foodborne illness outbreaks were associated with the consumption of fresh produce, and of these 25 percent (18 outbreaks) implicated fresh-cut produce (FDA). Thus, fresh-cut processors have made product safety their highest priority. Tremendous effort and expense have gone into developing and implementing effective sanitation and safety programs in the produce supply chain, beginning at the farm level. Vendor-certified programs such as Good Agricultural Practices (GAPs) and Standard Operating Procedures (SOPs) are now required from all fresh produce grower/shipper groups. Fresh-cut processors have developed and follow comprehensive food safety programs, including Good Manufacturing Practices (GMPs), Sanitation Standard Operating Procedures (SSOPs), and Hazard Analysis Critical Control Point (HACCP) programs in their operations.
Quality of fresh-cut products as affected by harvest and postharvest operations
The demand for fresh-cut fruits and vegetables is increasing across the globe, owing to their rich nutritional profile. The nutritional quality and shelf stability of these commodities depend primarily on different pre- and postharvest operations. Various physical and biological agents are emerging due to illegitimate. Pre- and postharvest pose a significant threat to the product quality from farm to fork. The main quality losses take place in terms of color, flavor, texture, and nutritional profile. Unconventional sanitization techniques, advances processing operations help to ensure the safety, nutritious, and keeping quality of fresh-cut fruit and vegetable. The emerging technologies in postharvest services (edible coating, minimal chemical treatment, modified, and controlled packaging) have played a pivotal role in improving the overall quality and shelf life of the fruits and vegetables. This chapter provides the readers with a brief overview regarding the concept of fresh-cut products, the role of pre- and postharvest operations on nutritional quality, fresh-cut processing operations, quality attributes, the strategies to maintain the quality of fresh-cut product, and the existing literature on the subject. The material presented in this chapter would be hugely advantageous for maintaining the pre- and postharvest quality of fresh-cut produce.
The quality of fresh-cut fruit and vegetable products includes a combination of attributes, such as appearance, texture, and flavor, as well as nutritional and safety aspects that determine their value to the consumer. Nutritionally, fruit and vegetables represent a good source of vitamins, minerals, and dietary fiber, and fresh-cut produce satisfies consumer demand for freshly prepared, convenient, healthy food. However, fresh-cut produce deteriorates faster than corresponding intact produce, as a result of damage caused by minimal processing, which accelerates many physiological changes that lead to a reduction in produce quality and shelf-life. The symptoms of produce deterioration include discoloration, increased oxidative browning at cut surfaces, flaccidity as a result of loss of water, and decreased nutritional value. Damaged plant tissues also represent a better substrate for growth of microorganisms, including spoilage microorganisms and foodborne pathogens. The risk of pathogen contamination and growth is one of the main safety concerns associated with fresh-cut produce, as highlighted by the increasing number of produce-linked foodborne outbreaks in recent years. The pathogens of major concern in fresh-cut produce are Listeria monocytogenes, pathogenic Escherichia coli mainly O157:H7, and Salmonella spp. This article describes the quality of fresh-cut produce, factors affecting quality, and various techniques for evaluating quality. In addition, the microbiological safety of fresh-cut produce and factors affecting pathogen survival and growth on fresh-cut produce are discussed in detail.
Quality and Safety of Fresh-cut Vegetables and Fruits
According to the Produce Marketing Association (PMA, 2014), the U.S. market for fresh-cut vegetables and fruits is estimated at $27 billion annually ($16 billion foodservice and $11 billion retail) with bagged salads representing 61% of the market, other fresh-cut vegetables 27%, and fresh-cut fruit 11%. Fresh-cuts thus account for 16% of total retail produce sales. Postharvest losses of fresh-cut produce are difficult to estimate but given the highly perishable nature of fresh-cuts compared to intact produce, the retail value of fresh-cut produce losses and wastage at all levels may exceed $9-10 billion annually. All previous iterations of this project have worked closely with industry, particularly the United Fresh Produce Association (UFPA; formed in 2006 by the merger of the United Fresh Fruit & Vegetable Association and the International Fresh-cut Produce Association), meeting annually at their convention and helping to plan and contributing to the convention educational program. Participants from previous iterations of S294 have joined with the UFPA’s Food Safety & Technology Council (FSTC) for an all-day meeting before each of our annual project meetings. The approach and objectives for this project were developed with input from the FSTC and approved by that body.
The appearance, convenience, and generally high nutritive value of fresh-cut vegetables and fruits drive sales of fresh produce, but repeat sales of fresh-cuts is dependent upon assurance of its safety and the products having pleasing texture and flavor. The industry primarily relies on established technologies derived mainly from practical experience to maintain visual quality and shelf-life with less consideration of the quality characteristics that drive repeat sales such as good flavor retention, maintenance of an appealing texture (crispness, crunchiness), and increased microbial quality leading to extended shelf stability and food safety. Through interaction with the industry we know that current technologies, especially for fresh-cut fruits, do not provide the shelf stability needed to supply long distance domestic markets with optimum flavor quality.
As a result of physiological and microbial deterioration occurring during storage and marketing of fresh produce, and especially fresh-cut produce, there is a continuing need to develop effective, less-damaging treatments for maintaining the sensory quality (appearance, flavor, texture), nutritional value, and food safety of fresh harvested produce (How, 1990). Most of the sales of fresh-cut produce have been in the vegetable (salad, carrot slice) area (Garrett, 2002) and commercial handling practices for fresh-cut vegetables have been described (Barth et al., 2016). Beginning about a decade ago, research and commercial interest has focused more on fresh-cut fruits and melons (Beaulieu et al., 2004; Beaulieu and Gorny, 2016; Candir, 2017; Kader, 2008; Rojas-Grau and Martin-Belloso, 2008; Soliva-Fortuny and Martin-Belloso, 2003). With over 200 different vegetable and fruit crops with potential for development as fresh-cut products, each with unique physiology and handling requirements, an integrated, scientific approach to research and development including microbiological interactions with these products is critically needed.
The conditions on the cut surface of fresh-cut products, with the presence of water and compounds that can be used for nutrition, are ideal for growth of microbes. Unfortunately, as produce consumption has increased in the U.S. in recent years, so has the number of produce-related outbreaks of foodborne illness. Produce-related outbreaks accounted for 12.3% of all reported foodborne outbreaks from 1990 to 2007, compared to only 0.7% in the 1970s (AFF, 2010, Sivapalasingam et al., 2004). More recently, about 24% of all foodborne illnesses from 2004 to 2013 were due to fresh produce (more than any other category; CSPI, 2015). Between 1996 and 2008, lettuce/leafy greens (32.9%), tomatoes (17.1%), and melons (15.9%) comprised two-thirds of produce-related outbreaks (Gravani, 2009). Pathogens of primary concern are Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes, and Norwalk-like viruses. From 1996 to 2006, 72 foodborne illness outbreaks were associated with fresh produce consumption with 18 of these connected to fresh-cut produce (FDA 2008). The economic yearly losses due to acute foodborne illness are estimated to be $152 billion, with $39 billion of this loss associated with fresh, processed, and canned produce (Scharff, 2010). The continuing nature of such produce-related outbreaks represents a threat to further increases in per capita consumption due to lowered confidence in the microbial safety of the product by the consuming public. Such outbreaks can also be very costly to growers, processors, shippers and restaurants.
It is very difficult to ascertain the efficacy of control measures for food safety as there are no direct measures of the effectiveness of intervention strategies on the rate of occurrence of foodborne illness in the general population. Instead, model systems are used to test the effectiveness of intervention strategies at selected stages of the processing chain. The hope is that by identifying and implementing numerous control strategies along the processing chain that were found to be effective in model systems, that the resulting net risk reduction will effectively reduce the real risk of foodborne illness. There are a number of opportunities to address food safety concerns as part of this project. Quality and safety concerns often overlap. For example, efforts to reduce spoilage organisms should also impact pathogenic organisms, since conditions that support spoilage organism growth also support human pathogen survival/proliferation. Removing damaged produce prior to production will reduce the risks associated with pathogen colonization of wounds.
The Food & Drug Administration (FDA) in collaboration with the USDA and the Centers for Disease Control (CDC) issued a series of guidelines in 1998 (since updated) referred as Good Agricultural Practices (GAPs) to reduce the risk of foodborne diseases from fresh fruits and vegetables (U.S. FDA, 2008). Since that time, indicative of the importance of fresh fruit and vegetable food safety and security research, USDA has emphasized the enhancement of safety and security in its strategic planning and created the Food Safety and Quality National Education Initiative (FSQ), Special Research Grants for Food Safety, the Food Safety Institute of the Americas, and the National Food Integrated Safety Initiative. Members of S294 have been actively involved in all of these programs and many also are involved in extension food safety programs. The Food Safety Modernization Act of 2011, currently being implemented, “…aims to ensure the U.S. food supply is safe by shifting the focus from responding to contamination to preventing it.” (https://www.fda.gov/food/guidanceregulation/fsma/).
In order to ascertain food safety risks involving fresh and fresh-cut produce, it is critical to be able to determine the survival and persistence of viable or infectious human pathogens under environmental conditions occurring in produce handling and processing facilities, on harvested crops, and on intact or fresh-cut products. Therefore, methods for detection and enumeration of target microbes, including bacteria and viruses, are of core relevancy to this project. Approaches for detection and enumeration of microbes on fresh produce can play an important role in mitigation of fresh produce-associated spoilage or foodborne disease, as well, providing decision makers with timely and actionable data, especially on the presence of human pathogens in these products (Brehm-Stecher et al., 2009). These data could help guide interventions such as: refusal of contaminated product from the field, cessation of processing for line or equipment sanitation, destruction of contaminated product held in inventory pending testing results, or product recall. Due to the relatively short shelf lives of most types of fresh and particularly fresh-cut produce, rapid methods for detection and enumeration are of special relevance to the goals of this work.
Integration of physiological, pathological, food safety, and instrumental and sensory quality measurement concepts is essential for developing the most effective handling procedures and innovative, new technologies for maintaining quality and shelf stability, and safety of fresh-cut products. This multistate project is structured to foster the cooperation and collaboration among AES, ARS and other scientists in multiple disciplines that is necessary to accomplish such outcomes. Much experimental work is needed to optimize and integrate new and emerging treatments in diverse fresh-cut products. This fact supports the proposed integrated approach of having parallel projects in different states and of focusing the research into specific areas of importance. Alternative and emerging technologies for maintaining the quality and shelf stability of fresh-cut produce are being introduced at a rate that often precludes thorough evaluation of instrumental and sensory quality attributes, and their impact on product nutritional value, microbial quality and food safety. To do so, a multidisciplinary approach as proposed herein is needed to optimize the new and emerging treatments.
Related, Current and Previous Work
A search of the CRIS database revealed an absence of multistate project(s) or coordinating committees concerning fresh-cut vegetables and fruits, and collaborative participation involving plant physiologists, food scientists, and microbiologists working together. This multistate project is needed in order to provide coordination and collaboration among scientists working in this field if duplication of effort is to be avoided and the available time and resources are to be effectively applied. In this way, more effective approaches that are globally applicable to different fresh-cut products may be efficiently developed and utilized.
A. Critical Review of Previous Project Accomplishments
This proposal is for a replacement project to S-294, Postharvest Quality and Safety in Fresh-cut Vegetables and Fruits (2011-16), which has resulted in numerous collaborative activities including multiple federally funded grants with multistate collaboration. The project members developed information on postharvest treatment and storage effects on the nutritional value of fresh-cut products; standardized methods for subjectively evaluating postharvest quality-related changes; developed or evaluated new tools, treatments and cultivars to improve the quality and safety of fresh-cut vegetables and fruits; developed new information on the contamination and attachment of microbes to fresh-cut product as well as developing novel approaches to microbial control; developed standard practices for recovery, inoculation, detection, and enumeration of human microbial pathogens on produce; and elucidated the physiological processes underlying both positive and negative quality changes associated with fresh-cut processing.
The new project will emphasize standardization of microbiological procedures and instrumental and subjective methods for sensory quality analysis and flavor-based shelf life measurement and emerging treatments and techniques for assuring fresh-cut quality; similarly, we will consider physiological processes that control quality changes in fresh-cut products. We will develop standard protocols for evaluation of the efficacy of sanitizers and the appropriateness of experimental protocols for microbiological challenge studies with fresh-cut produce. New sanitizers, natural product antimicrobials, and physical treatments to control microbes will be tested. Because of the potential for treatment interactions between vegetable and fruit tissues and microbes, we plan on close coordination between microbiologists and plant/food scientists in all of the above activities.
B. Fresh-cut Product Quality
Pre-harvest conditions that stress the plant will affect the quality and shelf-life of the postharvest crop (Monselise and Goren, 1987; Nigh, 1990). Knowledge of these conditions is important for assessing postharvest potential of fresh-cut products (Blacharski et al., 2001; Borve and Sekse, 2000; Gorny et al., 1998; Kim et al., 1993). The maturity of fruits and vegetables intended for fresh-cut processing is a critical factor determining potential quality and shelf life (Bai et al., 2009; Beaulieu, 2005, 2007; Beaulieu et al., 2004; Soliva-Fortuny et al., 2002, 2004). Integration of cultivar selection, pre-harvest and postharvest conditions and treatments is needed to obtain the best possible quality of the marketed fresh-cut product (Beaulieu and Lea, 2003).
Understanding the components of eating quality involves comparison of instrumental with sensory analysis (Beaulieu and Baldwin, 2002; Jordán et al., 2001a,b; Plotto et al., 2000; Schieberle and Hofmann, 1997). Detailed sensory analysis is required on fresh-cut produce treated in various applications that potentially affect flavor and textural attributes and impact overall eating quality. Many attempts at measuring texture have used sensory analysis coupled with instrumental measurements (Abbott et al., 1984; Beaulieu et al., 2004; DeBelie et al., 2002; Drake, 1962; Harker et al., 2002; Mohamed et al., 1982; Szczesniak, 1963; Vickers, 1981; Vickers and Bourne, 1976; Vincent, 1998). There are no generally accepted definitions of textural attributes applicable to fresh-cut products, sensory scale anchors, or methods for their measurement (Fillion and Kilcast, 2002; Harker et al., 1997). The proposed project will include study of practical methods for measuring flavor and texture of fresh-cut vegetables and fruits, and relating to sensory measurements using modern multivariate statistical techniques.