7.13.1 Minimally processed products and MAP
One of the fastest growing trends in food retailing is that in ready prepared foods. In the fresh produce sector, this is observed in growing sales of so-called fresh cut or minimally processed salads. New developments are having to be made in MAP to prevent the rapid deterioration which occurs once fresh produce has been cut open (Day, 1996; Day and Gorris, 1993). Up to now, the development of new MAP solutions has remained something of an art, with selection based on trial and error. Attempts to put MAP design onto a more theoretical basis have led to a number of models being developed. However, the general applicability of these models has been limited by the complexity of the systems involved (Kader et al., 1989). With the continued expansion in computing power available, eventually models which can be used successfully to predict suitable MAP solutions will be developed.
These developments in MAP will be accelerated by the commercial availability of films for so-called 'active packaging', for example, polymer films which become more permeable to respiratory gases at higher temperatures (Day and Gorris, 1993). Packaging may include components which remove aroma or off-flavours, scavenge O2, ethylene or water vapour or emit CO2 or other preservative vapours (Robertson, 1991; Wills et al., 1998). Novel gas combinations such high O2, argon or neon may have useful applications in this field (Day, 1996).
7.13.2 On-line technologies for non-destructive grading and shelf-life evaluation
Another market of growing importance is the 'ready-to-eat' market where the consumer is led by the product label to expect a fully ripe fruit for immediate consumption. To guarantee good eating quality while minimising post-harvest losses, the development of robust non-destructive quality testing equipment for use on packing lines is required. This type of equipment will also be used for the detection of external and internal defects, thus reducing labour costs in the packhouse.
The physical science behind many non-destructive techniques for evaluating internal quality of fresh produce such as the use of near infrared, X-ray scattering, acoustic resonance, etc. is well understood (Chen and Sun, 1991). The goal of turning the science into technologies which can be applied commercially within the fresh produce sector has proved somewhat elusive. Flavour factors such as sugar content may eventually be routinely measured using near infrared (Peiris et al., 1999). Aroma profiles of fruits may be assessed using electronic nose technology based on polymer arrays which are sensitive to volatile compounds (Russell, 1995). At the time of writing, the response time of this equipment is too slow to be of practical use, that is, it is in the order of minutes rather than seconds. Some of this additional information could be incorporated on to labels applied on-line, perhaps indicating the expected shelf-life and percentage sugar content of each individual product.
Machine vision applications for the detection of external blemishes are rapidly making progress towards commercialisation (Tillett, 1991; Yang, 1992). Among the novel techniques being developed for the non-destructive detection of internal defects are computer-aided X-ray tomography and nuclear magnetic resonance (NMR) imaging. These are based on the measurement of differences in tissue density or proton mobility respectively and can be used, for example, to detect cavities or tissues disruption caused by insects, disease development or developmental disorders (Wills et al., 1998).
In many countries there is a strong trend towards reducing the use of chemicals in horticulture, including post-harvest fungicides, sprout suppressants and antioxi-dants for scald control. Increasingly, consumers are prepared to pay for organic products and the retail sector is encouraging the trend (Geier, 1999). Another and perhaps more significant factor in the trend to reduce usage of post-harvest chemicals is the escalating costs to the agrochemicals industry of the registration of new pesticides or reregistration of currently used pesticides (Crossley and Mascall, 1997). Post-harvest use of pesticides on fruits and vegetables is an extremely small market compared with pre-harvest applications on major world crops such as cereals and oilseed crops. Many chemicals are now being voluntarily deregistered by their producers for post-harvest use. Others have been deregistered by regulatory bodies on the basis of new health and safety data. In 1994 the EU began the process of harmonising maximum residue levels (MRLs) for each crop/pesticide active ingredient combination in use across EU countries. Where the chemicals have been found to be out of patent and where no chemical company is willing to pay the cost of the new data requirements, the active ingredient is being or has been banned. The implications of this pesticide 'harmony' in Europe are potentially serious for the European horticulture industry as well as international growers exporting to Europe (Aked and Henderson, 1999).
It is clear that the fresh produce sector urgently needs alternatives to post-harvest chemicals and developments of these technologies will grow in the future. Among the technologies already in use or in development are controlled and modified atmosphere storage, for example, to manage scald in apples (Dover, 1997) and physical treatments such as heat (Barkai-Golan and Phillips, 1991), the use of biocontrol agents (Koomen, 1997), 'natural' chemicals such as plant extracts and methods to stimulate natural disease resistance in crops such as UV applications (Joyce and Johnson, 1999).
One new chemical which may gain future approval for use on fresh produce is the gaseous inhibitor of ethylene action, 1-methylcyclopropene (1-MCP). 1-MCP inhibits ripening in climacteric fruit and ethylene-stimulated senescence and is active at very low (ppb) concentrations (Serek et al., 1995).
7.13.4 Increased emphasis on the health aspects of fresh produce consumption
Consumers have long been encouraged by government health advisors to increase their consumption of fresh produce on the basis that these food products are vital dietary sources of certain minerals and vitamins. However, it is now widely believed that high levels of fresh produce consumption may ward off many fatal diseases such as cancer and heart disease (Joshipura et al., 2001; Wallstrom et al., 2000). As further advances are made in understanding the links between diet and disease, it is likely that the nutritional value of fruits and vegetables will become an important quality factor. Thus the maintenance throughout storage of key chemical components that are found to have specific health benefits will pose additional challenges to the post-harvest technologist.
7.13.5 Genetically modified (GM) fruits and vegetables
Despite consumer concerns about the desirability of genetically engineered crops, it is likely that new GM products (for example, with altered colour, flavour or nutritional properties) will become available on the market in the future. Novel properties in a product may change its responses to storage and require new approaches to maintaining product quality. Genetic alterations have already been directed to reducing unwanted quality changes. The first GM fresh product to be marketed was the FlavrSavr tomato which was engineered using antisense RNA technology to have reduced levels of polygalacturonase (Fuchs and Perlak, 1992). This increased the shelf-life of the tomato by preventing the excessive softening which accompanies over-ripening. Other fruits such as tomatoes and melons have been manipulated to reduce ethylene synthesis. Such fruits can have extremely extended shelf-lives. Susceptibility to post-harvest damage and disorders has been manipulated in a number of crops, for example, polyphenol oxidase activity has been reduced in potatoes (Bachem et al., 1994) removing sensitivity to bruising. Other research around the world seeks to do the same thing in a diverse range of crops, including pineapples, apples, lettuces and grapes to prevent a range of browning reactions which accompany physical and physiological injury (Thwaites, 1995). There are other ways in which the shelf-life of fresh produce could be extended genetically, for example, by enhancing the synthesis of antimicrobial compounds.
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