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Content archived on 2022-12-23

Enhancement and Preservation of Quality and Health Promoting Components in Fresh Fruits and Vegetables

Objective

A. BACKGROUND

Current knowledge

Fresh fruits and vegetables (FFV) have both an important nutrition-health and an economic value. According to the new dietary guidelines, FFV are at the fundament of the nutritional pyramid and are, within our global food package, the best carriers of bio-active substances such as vitamins, minerals, dietary fibres, phenolic antioxidants, glucosinolates and other bioactive components. This makes FFV important for our daily nutrition with a suggested intake of 5 servings a day. The relevant nutritional and health promoting effects improve the state of human welfare and reduce the risk of various diseases. Economically, FFV are of importance for many countries worldwide as major import and/or export products. In Belgium, for instance, the international trade (import and export) of FFV in 2000 was between 548,219 and 845,741 tons (Anonymous, 2000).

Currently, up to 23% of the most perishable FFV are lost during their journey through the agri-food chain due to spoilage, physiological disorders, mechanical damage, shrivel and poor external quality (Wilson and Pusey, 1985). In addition, losses that occur during shelf life and food preparation in private homes, catering services and restaurants, are not taken into account in these estimates. Until recently, chemical control was the most important means for prevention of losses in the agri-food chain besides appropriate storage technology (low temperature, controlled atmosphere). However, health risks by chemical contamination of food have accelerated the need to reduce and even eliminate completely the residues on FFV of chemical treatments (fungicides, biocides, preservatives, scald inhibitors etc.). This has set a new trend towards Integrated Crop Management and Organic Farming and has prompted research and industry to develop alternative control methods such as antagonist organisms, induced resistance, natural compounds and physical treatments such as heat, UV, and electron beam.

Quality of FFV generally includes four different aspects:
- Visual quality (colour, absence of skin disorders)
- Organolepic quality (taste, texture, flavour)
- Nutritional or 'convenience' quality
- Hygienic quality (microbiological safety, residues)

Although organoleptic quality has always been of major concern to producers, packers, retailers and consumers, the ubiquitous decrease of nutrients and health promoting substances is currently becoming more relevant by an increasing consumer awareness of the nutritional and safety value of fruits and vegetables. Food and health agencies as well as consumers are increasingly aware of the risk for human health of the accumulation of bacterial and fungal toxins in FFV, infected by various micro-organisms. This has stimulated research on more fundamental aspects of fruit physiology affecting the perceived quality and the health promoting effects of FFV. Metabolomics is a powerful tool for a better insight into the mechanisms determining the responses to interventions like harvest and stresses like storage, as well as to ripening and senescence. Finally, visual quality also plays a very important role in the perspective that it determines the principal consumer demand for FFV. New developments in production, storage and logistic technology are being applied in commercial growing, preservation and distribution of fruits and vegetables, aiming at products with a very good appearance. Some of the most important goals of the agri-food chain are, therefore, (i) to reduce possible losses and (ii) to preserve and enhance the quality and nutritive value accumulated during growth of FFV.

Importance of increasing knowledge

Because of the growing public concern for health and nutrition issues and a pressing request for year round availability of fresh and convenient produce the consumer demand for high quality, high value FFV becomes more and more complex. This creates an inherent need for new developments within the scientific area of horticulture and postharvest technologies to fill in the remaining gaps in measuring and controlling all possible aspects of quality and to understand the specific dynamics of these quality parameters during storage.

Effective chain control with a continuous quality screening is necessary to preserve and enhance this quality and safety of FFV throughout the agri-food chain from the primary producer up to the final consumer. A first area where there is certainly lack of knowledge is that of Integrated Crop Management and Organic Farming. These production systems which are of increasing importance require a corresponding (i.e. environmental friendly) adaptation of the postharvest chain in order not to undo all the work and efforts done in the production phase. Biological and physical treatments may provide a viable alternative to traditional phytofarmaceuticals.

Recent research has elucidated some of the mechanisms behind postharvest quality change and disorders. It is believed that modern methodologies such as metabolic flux analysis and metabolomics which combine traditional physiology with a quantitative approach have a great potential for understanding postharvest phenomena. This is another area which needs to be addressed.

The ever-increasing demand for high quality commodities and the growing importance of internal quality and food safety related quality attributes necessitates the development of novel non-destructive measuring tools. Non-destructive analysis tools hold the potential for online application in grading and process control systems with the fast screening of quality profiles and the possibility to follow one sample in time as a result. There are now many exciting developments in this area, and they need to be addressed as well.

For proper chain management, good and reliable predictive models covering all kind of aspects are necessary to control and optimise the food chain with respect to quality and safety. The traditional empirical models, however useful in dedicated areas, are not suitable to fulfil the need of an integral approach. To this end good, reliable and generic models need to be developed. All knowledge available from practice and research need to be collected and condensed into working and reliable models.

Quality and safety of organic fruit and vegetables

Organic produce are usually claimed to have better internal quality than conventionally produced fruit and vegetables. However, the supporting literature is scarce, and not consistent. Benge et al. (2000) found that, although harvested on the same day, conventional kiwi fruit were generally more mature than organic fruit, as indicated by soluble solids concentrations, but their average firmness did not differ significantly. Despite the differences in maturity, whole fruit softening during storage at 0°C did not differ significantly with production system. However, organic fruit nearly always developed less soft patches on the fruit surface than conventional fruit with the average difference being significant. Typical postharvest handling practices, compared to harvesting directly into trays, did not significantly affect whole fruit softening.

Recentely some concerns have been raised about the safety of organic fruit and vegetables (Moireau-Ria, 1999). However, in a recent study no Salmonella, Campylobacter, E. coli, E. coli, Listeria were found in any of the vegetable samples examined. Aeromonas species were isolated from 34% of the total number of organic vegetables examined. Many (64%) of the organic vegetables examined were "ready-to-eat" after minimal processing, i.e. washing. Although Aeromonas species are frequently detected in organic vegetables, the absence of accepted enteric pathogens was encouraging, and does not support the allegation of organic foods being of high risk due to the farming methods used. In another study, Sagoo SK, et al. (2001) found that only 15 (0.5%) of the examined vegetable samples were of unsatisfactory quality due to Escherichia coli and Listeria spp. (not L, monocytogenes) levels in excess of 10(2) cfu g(-1). The absence of pathogens (L. monocytogenes, Salmonella, Campylobacter and E. coli O157) and the low incidence (1.5%) of E. coli and Listeria spp. associated with these organic vegetables indicates that overall agricultural, hygiene, harvesting and production practices were good. Little is known in the literature about safety of organically produced fruit.

Alternative treatments

Alternative treatments to reduce losses and improve product quality have gained a lot of importance as they match the conditions of biological and integrated farming to reduce the use of pesticides, preservatives and other residues, which may be harmful to the environment. Within the alternative technologies both biological control and physical treatments are distinguished.

With Biological control, antagonistic organisms are applied on the product surface to reduce the microbiological risks through inhibitive action or other modes such as nutrient competition and direct parasitism (Wisniewski and Wilson, 1992; Wilson et al., 1993). This technology meets criticism, however, by the pathological and allergenic potential of the antagonistic organisms and requires the parallel development of biocontrol procedures (Wilson and Pusey, 1995).

A second way to alternatively control losses and quality of horticultural produce is based on the application of physical treatments such as thermotherapie, UV-C radiation and pulsed white light. Thermal treatments are carried out with moist hot air or by dipping in hot water and have been proven effective against chilling injury, ripening, fungal growth, postharvest diseases and insect pests (Couey, 1989; Fallik et al., 1993; Lurie et al., 1993, Marquenie et al., 2002b). To avoid quality loss the temperature must typically be kept below 50°C. UV-C (= 254 nm) treatments are used mainly for surface disinfestations. The mechanism is based on the induction of DNA damage and/or resistance mechanisms against pathogens (Liu et al., 1993; Nigro et al., 1998). The optimal radiation dose and duration is dependent on the type of product and specific cultivar. For strawberry UV-C doses of 0.05 J/cm2 and higher are reported (Marquenie et al., 2002b) Too intense treatments cause damage, discolouration and fast ripening (El Gaouth and Wilson, 1995). Recently, also pulsed light was introduced in the postharvest field. This treatment is based on the use of short light flashes with a high intensity and frequency and is known for the disinfection of packing materials, surfaces and materials. For the optimal treatment of biological material a combination of these treatments offers more possibilities. The sequence of the treatments seems herewith important (Marquenie et al., 2002a).

Postharvest physiology and metabolomics

Although during storage the metabolic activity of FFV is artificially reduced by means of low temperatures in combination with modified or controlled atmosphere conditions, many metabolic processes still continue. Inproper storage conditions may lead to unbalances in the metabolism and, as a consequence, cause storage disorders. A notable example is brown heart in Conference pears (Lammertyn et al., 2000). Besides storage conditions also mineral and vitamin content of the produce is important. Because of the complexity of the biochemical and physiological phenomea which are involved a quantitative approach would be advantageous.

Metabolic network models have been suggested in the literature to model growth and product synthesis in micro-organisms. Such models are based on the stoecheometry of all relevant biochemical reactions which occur in the cell. Typically a system of algebraic equations is obtained in the unknown intracellullar reaction rates. Such models are believed to be useful to study the postharvest physiology of the produce.

Non-destructive techniques

Recently, several novel non-destructive techniques have been developed to assess organoleptic and visual quality of FFV. Spectroscopic and hyperspectral imaging techniques are based on the reflection, absorption and scattering of electromagnetic radiation with FFV. In this respect, visual and near infrared spectroscopy and hyperspectral imaging have been used successfully for the determination of colour and chemical composition of FFV and have been integrated in the optimal picking date prediction of pipfruit or classification systems of tomatoes (Bellon, 1992; McGlone and Kawano, 1998; Lammertyn et al., 1998; Peirs et al., 2001). Fluorescence Imaging and Laser Scanning Confocal Microscopy are both techniques based on the detection of multiple wavelength fluorescence and enable the evaluation of chlorophyll content and related stress symptoms, colour measurements and wax/surface quality determination (Veraverbeke et al., 2001). Information on the flavour characteristics of FFV can be obtained by means of electronic noses, which provide an aromatic profile composed from the combined response of different molecular sensors (Di Natale et al., Saevels et al., 2001). On line firmness measurements can be carried out by means of the acoustic impulse response technique based on the detection of sound (De Belie et al., 2000). Finally, tomographic techniques such as X-ray-computer-tomography (X-ray CT) and magnetic resonance imaging (MRI) have been used to detect and quantify internal storage disorders in fruit such as pears (Lammertyn, 2001). Other technologies with potential for non-destructive quality analysis such as electronic tongues and biosensors and the extension of these and the previous technologies to other quality attributes (microbiological safety, nutritional quality) need to be investigated.

Modelling

The storage life of some horticultural produce is limited by growth of spoilage or pathogenous micro-organisms. Several attempts have been made toward predictive modelling of the growth of microorganisms inside, or on the surface of, foods as a function of time during refrigerated storage. These models are analytical expressions, such as the Gompertz or the logistic curve (e.g. Zwietering et al., 1991) which exhibit the typical sigmoidal appearance of the bacterial growth curve, or systems of ordinary differential equations (Baranyi et al., 1994). The model parameters typically depend on intrinsic food properties such as pH, aW and chemical compounds such as nitrite, and extrinsic parameters such as gas composition. The empirical sigmoid-like analytical expressions used in predictive food microbiology are attractive because of their simplicity, but nevertheless for several reasons their applicability is limited. Some advances in predictive microbiology include dynamic models with product formation (Nicolaï et al., 1993). Of particular importance is the introduction of uncertainty in predictive microbiology (Nicolaï and Van Impe, 1995), and quantitative risk assessment (Walls and Scott, 1997).

Besides microbial growth, other quality attributes and texture in particular may change adversely during storage. Kinetic models have been used successfully to describe changes of texture related properties of fruits and vegetables, e.g. texture of Elstar apples during storage (Tijskens et al., 1997). De Smedt et al. developed a dynamic model for describing mealiness development in apple (2002). Modelling of changes of gas composition in MA packages is also an active research area (e.g. Hertog et al., 1997). Whereas most models which are produced so far are lumped and, hence, consist of systems of ordinary differential equations, it has been recognised that in many cases the distributed nature of some processes must be taken into account. This is for example the case when gas transport related storage disorders are considered, such as brown heart in pears (Lammertyn et al., 2002).

European dimension

The Action is in full compliance with the common characteristics for research projects as defined in to the CAP reform of 1992 and described in document "Relevance or research proposals to community policies: The Common Agricultural Policy (CAP) - The Common Fishery Policy (CFP)" (available at http:/cordis.europa.eu/)

- Multidisciplinary research approach. This Action involves various areas including production of FFV, postharvest technology, physiology, physics, engineering, biochemistry, mathematical modelling and plant pathology. There is currently no research team in the world, let alone in Europe, which has sufficient expertise in all these areas.
- Socio-Economic aspects. It is expected that the proposed project will lead to reduced losses and an increased amount of premium FFV which would command a higher price. This will contribute to the economic well-fare of European growers, cooperatives, wholesalers and retailers.
- Application aspects. The field of agri-food chain is gaining more and more importance throughout Europe. CORDIS actually reports 14 projects dealing with this subject that are funded by EU. The results and output of these projects will help to define and to refine the optimal conditions for preserving, storing and distributing FFV through the agri-food chain. Within this European framework, the COST Action will enhance and favour exchange and dissemination of scientific knowledge, acquired by EU and national funded projects, through the organisation of workshops, symposia, round table meetings and through the publication of the proceedings.
- Food safety and nutrition. Food safety and nutritional value are of paramount importance. Because the trade in FFV nowadays has a global dimension, it is clear that the European-wide framework that is provided by the COST system is required.

Reason for COST Action

This Action is justified on the ground that the agri-food chain fails up to now to supply FFV fully responding to the quality, nutritive value and safety as requested by the consumers and defined by the food and health agencies. Two aspects in particular are relevant in fulfilling these objectives:

(1) Enhancing the knowledge available in the agri-food chain by improving the dissemination of information and exchange of scientists
(2) Implementing technological developments and innovations

Both aspects are not very developed within the agri-food chain but are basic for contemporary management of the agri-food chain, oriented towards consumer and market satisfaction. A rather limited amount of knowledge is available in literature about the impact of the various technologies applied for protecting, storing, packing, disinfecting and shipping on the safety, nutritive value and on the overall quality of FFV as perceived by the consumers. Moreover, this information is hardly structured, and therefore very difficult to apply in practice. Due to the broad range of activities and its multidisciplinary character, the agri-food chain would gain substantially from a European co-operation, for covering and applying all available and relevant topics that are essential for an adequate understanding of the complex phenomena underlying the life and behaviour of FFV.

B. OBJECTIVES AND BENEFITS

Objectives

The main objective of this Action is to enhance and preserve fruit quality, safety and the amount of nutritional and functional components in fresh fruits and vegetables in an integrated approach from orchard to consumer with special attention to organic growing.

This objective can be further specified in the following sub-objectives:

- Improvement of quality and uniformity of fruit quality at harvest
- Evaluation of the effect of integrated postharvest systems on biochemical and physical processes
- Further adaptation of postharvest systems
- Improvement of the management of postharvest chains to provide healthier, safer and more nutritious fruit and vegetables of the required overall quality
- Evaluation of new strategies (including definition and measuring technology) to assess quality, safety and value of fruit and vegetables

These objectives can only be successfully achieved in an integrated and cooperative way with special attention going to the dissemination of results. This requires:

- A review of the state of the art within the participating countries, through an inventory of the ongoing postharvest research
- The promotion of an exchange of available knowledge and further co-operation on a European scale based on ongoing national programmes and projects between the research institutions and the industry
- Stimulation of new national and European programmes and projects

Expected benefits

The COST Action will improve the management of the agri-food chain by using the existing knowledge and by promoting and integrating new research projects resulting in extended postharvest life and quality of FFV. Where year-round supply from individual countries is not possible, different regions in Europe can supplement each other. Thus southern regions can fill the gap in, e.g. pear production by the northern countries. In this way the European market will be enlarged and this will have a beneficial effect on product prices and on the diet of the European consumers. Thus the economic advantage will be the increase of sales due to widening of the market also beyond the European borders and improvement in product quality. The economic impact on agribusiness will be very relevant due to the large amount of the production of FFV in all the European countries.

Generally, by multidisciplinary co-operation between different scientific and technological fields such as postharvest technology, physiology, physics, engineering, biochemistry, mathematical modelling and plant pathology, this Action will result in a reinforcement of research efforts, strengthening the links between postharvest research groups and industries within and between the different EU countries. The Action will also provide favourable conditions for the establishment of national and especially European projects aiming at increased quality, healthiness, and safety for the consumer.

More specifically, identifying and analysing the major problems of integrated food chains will stimulate environmentally friendly production systems of fruit. Postharvest scenarios will be further improved leading to a better preservation of quality. The existing knowledge of individual links and participants will be integrated by a quantitative, modelling approach, which will support a better management of the chain and which will facilitate the identification of remaining gaps in required knowledge. Better management of the chain, in turn, leads to better fulfilment of consumer expectations and a safer produce.

C. SCIENTIFIC PROGRAMME

Five main directions of research can be discerned within the postharvest field:

1) Improvement of the agri-food chain in terms of quality, healthiness and safety
2) Postharvest physiology and metabolomics: the interaction of postharvest scenarios with biochemical and physiological aspects and processes
3) Alternative methods for increasing shelf life and safety
4) Non-destructive methods for quality assessment
5) Modelling as a tool for integration and management of the whole chain

In the first field the improvement of the agri-food chain will be aimed for. This will require a better understanding of the magnitude and causes of variation in quality of FFV at harvest, a further improvement in storage scenarios and postharvest treatments, and an extension of datasets on development and decay of quality along the chain.

The second field focuses on the understanding of the response of biochemical and physiological processes to different postharvest scenarios in order to evaluate their effects on storage life, on the content of bioactive components (vitamins, phenolics), etc.

Micro-organisms cause an economic loss of fruit and vegetables but also constitute a potential health hazard by the toxins they produce. Among consumers there is a growing awareness for this kind of food safety and health issues, which not only imposes a need for an increased microbiological safety but also for a chemical and residue free control of the problem, especially within the field of organic and integrated farming. The development of alternative approaches to characterise and minimise microbiological growth will, therefore, be the subject of a third field of research.

Next to alternative treatments, also non-destructive technologies have gained importance in the process of quality assessment and control throughout the agri-food chain. These technologies have better potential for online application and allow fast screening of intact fruit. In the fourth field of this Action, more attention will be drawn towards the development and integration of new and existing non-destructive tools.

The fifth field, eventually, will deal with the establishment of a modelling framework. Modelling will provide an important generic view on the chain as a whole (supporting management decisions) for each of the mentioned aspects and can define areas where further or more detailed research or data are required.

All these fields will be dealt with in five corresponding working groups (WG), which will be further described below. Interactions between these different working groups will be established by using the non-destructive tools developed in WG4 for the quality improvement in WG1. Next, these improvements will be evaluated in a biochemical and molecular approach in WG2 and in the microbiological control of WG3. Finally all previous working groups will interact with WG5 where all results will be integrated in a modelling approach to define gaps in knowledge and develop recommendations and decision support systems.

The scope of the Action is limited to fresh, unprocessed fruit and vegetables. Also minimally processed FFV will not be considered.

Working group 1: Improvement of the agri-food chain in terms of quality, healthiness and safety

Introduction

Enhancement of the overall FFV quality serves the dual aim of better fulfilling consumer demands and increasing the product value to lift the economic revenues of horticulture above the average for all partners in the agri-food chain.

First, this will require a thorough evaluation and detailed description of the consumer demands and requirements on food quality through consumer and sensory panels. After translation of these aspects into measurable quality attributes such as concentration of health promoting substances, sugar content, firmness, etc., new strategies can be developed to optimise these quality aspects determining the overall appreciation of FFV. In this approach, the growing importance of integrated and organic production will be accounted for.

Second, weak points in the agri-food chain with respect to quality, as determined in the first part, will be identified and specific approaches towards quality enhancement in the different stages of the chain will be defined. In the production phase different production methods will be considered with special emphasis on the specific contributions of organic production versus traditional production. At harvest, a lot of research has already been carried out to determine the optimal picking dates of different products. Further research will focus on the optimisation of these dates with the introduction of new measurement technologies. In the postharvest part of the chain, quality enhancement will be obtained mainly by optimisation of storage conditions both in cold storage with the introduction of for example dynamic storage conditions and during shelf life by means of for instance special packaging. Together with the development of novel and/or alternative postharvest treatments this will lead to an optimal preservation of product quality and potential for year round supply of fresh produce.

In a third and last part the results and improvements obtained by different specialised research groups in different parts of the agri-food chain will need to be applied, disseminated and integrated into an overall approach covering the whole process. This will require full cooperation between different research groups in joint projects on further research and newly developed exchange programs or workshops for implementation of results.

Objectives

- To determine the required quality of selected fruits and vegetables as defined by consumers
- To translate required quality at consumption into required quality at preceding points in the chain
- To compare different production systems, including organic systems, in their effects on quality and content of healthy substances at harvest and along the chain
- To stimulate the development of scenarios of optimum harvest date and postharvest methods that increase the level of health beneficial functional components and flavour in particular, and preserve quality in general

- To study the distribution of quality in the plant with the perspective

(a) of increasing uniformity of quality and stimulating the level of quality
(b) of designing harvesting systems that result in grading into more uniform lots each with a distinct and particular quality
(c) sorting for (internal) quality on the basis of previously established relations between easily measurable characteristics and the target characteristic.

- To study pre- and postharvest treatments that improve the production and preservation of quality both, in the store and during shelf life with special attention for the quality of organic fruit and vegetables

Deliverables

- At least one workshop on improvement of the agri-food chain in terms of quality, healthiness and safety
- A survey of organic production systems in different EU countries
- A report on optimal picking dates of organic fruit
- A report on quality issues of organic FFV
- Consumer studies in different EU countries for selected FFV

Working Group 2: Postharvest physiology and metabolomics: the interaction of postharvest scenarios with biochemical and physiological aspects and processes

Introduction

Since there is an increasing awareness of consumers with respect to the presence of bioactive compounds such as nutrients, aromatics and health promoting compounds, it is of major importance to increase the knowledge about biosynthesis and metabolism of these compounds in FFV and to study their preservation along the agri-food chain. Common postharvest procedures (cold storage, postharvest treatments, controlled and modified atmospheres) have until now been optimised with respect to a general "quality" maintenance, almost exclusively based on external quality in all its aspects, like, e.g. colour, shape and the absence of disorders impairing the appearance of the produce. Optimisation has been conducted to obtain the longest economic lifetime of the produce, without considering internal quality attributes like taste and aroma. Very little is known, however, about the effects of such procedures on the biochemical and physiological processes that occur in fruit and vegetables and on the metabolism of its functional components. By an integrated biochemical and physiological approach it will be possible to elucidate the characteristics of such components during postharvest life of produce and the application of different technological procedures. This will constitute a knowledge platform for further optimisation of postharvest procedures (type of storage, duration) with respect to the presence of bioactive compounds (vitamin C, aromatics), and the control of internal storage disorders (browning) which are often affected by the bioactive compound concentration, without neglecting marketing and sensory quality.

In order to focus the project, the emphasis will be put on the metabolism of vitamin C and E and the physiology of cell wall degradation. Special attention will be paid to the more quantitative modelling approach of metabolomics and metabolic flux analysis to analyse

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