Packaging of fresh fruits & vegetables
Introduction • Fruits and vegetables are consumed in fresh, minimally processed, and processed forms (canned, frozen, dried, preserves, and fermented products). • Raw material quality influences the quality of processed fruit and vegetable products. • Quality evaluation consists of measurement of appearance, texture, flavor, nutritive value, and safety of the produce. • Safety aspects need to be considered first before all other quality attributes. • Being live, quality of fruits and vegetables is directly related to the physiological status and a host of other factors such as diseases and pests, mechanical injuries, and exposure during postharvest handling
Preharvest factors Genetic, climatic, and cultural Diseases, insects, and pests Physiological Status Respiration, water loss ripening, and senscence, disorders Harvesting factors Harvesting method, stress, maturity Quality Color, flavor, texture, appearance Postharvest factors Storage temperature, humidity, atmosphere composition, light, stress Mechanical injuries
Postharvest Handling Operations 1-Sorting and Grading • Have a role in protecting and enhancing product quality. • These are generally an important part of field or packinghouse operations(storage, transport, distribution, marketing, and processing). • The produce is sorted according to size, shape, color, and appearance. Grading determines whether the product meets a specific quality standard prescribed by local or international market. • Traditionally, sorting and grading are done by hand • Color is a key sorting parameter
2- Packaging Packaging contributes greatly to efficient marketing of fruits and vegetables as it: 1-serves as an efficient handling unit 2-provides convenient 3-protects quality and reduces waste 4- provides service and sales motivation 5-reduces cost of transport and marketing 6-facilitates use of new modes of transportation Two types of packaging are common in fresh produce trade : 1-Large-sized containers are used for transport and wholesale. 2- small-sized packagers for retail trade.
Proper packaging can protect fresh produce from the environment, such as sunshine, moisture, and light. • The main purpose of packaging is to provide protection from mechanical damage. • The container must be strong enough to withstand stacking and impact of loading and unloading, without bruising or scarring the produce. • The choice of packaging material is based on the requirements of stacking height, duration of storage, pretreatments, cooling, and cost.
Modified atmosphere packaging of fresh produce
MAP technology is largely used for minimally processed fruits and vegetables including fresh, ‘‘ready-to-use’’ vegetables. • MAP is a technique used for prolonging the shelf-life period of fresh or minimally processed foods. • In this preservation technique the air surrounding the food in the package is changed to another composition. • MAP is used with various types of products, where the mixture of gases in the package depends on the type of product ,packaging materialsand storage temperature. • But fruits and vegetables are respiring products where the interaction of the packaging material with the product is important.
One of the primary effects of MAP is a lower rate of respiration, which reduces the rate of substrate depletion. • Ethylene (C2H4) is a natural plant hormone and plays a central role in the in intiation of ripening, and is physiologically active in trace amounts (0.1 ppm). • C2H4 production is reduced by about half at O2 levels of around 2.5%. • This low O2 retards produce ripening by inhibiting both the production and action of C2H4. • metabolic processes such as respiration and ripening rates are sensitive to temperature. • Biological reactions generally increase two to three-fold for every 10 C rise in temperature.
Temperature control is vitally important in order for a MAP system • to work effectively. • Film permeability also increases as temperature increases, with CO2 permeability responding more than O2 permeability. • Low RH can increase transpiration damage and lead to desiccation, increased respiration, and ultimately an unmarketable product . • One serious problem associated with high in-package humidity is condensation on the film that is driven by temperature fluctuations. • For most commodities light is not an important influence in their post-harvest handling. • However green vegetables, in the presence of sufficient light, could consume substantial amounts of CO2 and produce O2 through photosynthesis.
Gases used in modified atmosphere packaging • The three main gases used in modified atmosphere packaging • are CO2, O2 and N2. • The choice of gas is very dependent upon the food product being packed. • Used singly or in combination, these gases are commonly used to balance safe shelf-life extension with optimal organoleptice properties of the food.
1- Carbon dioxide • Carbon dioxide is a colourless gas, asphyxiant and slightly corrosive • in the presence of moisture, dissolves readily in water. • The high solubility of CO2 can result in pack collapse due to the reduction of headspace volume. • In some MAP applications, pack collapse is favoured, for example in flow wrapped cheese for retail sale.
2- Oxygen • Oxygen is a colourless , odourless gas that is highly reactive and • supports combustion. • Oxygen promotes several types of deteriorative reactions in foods including fat oxidation, browning reactions and pigment oxidation. • to increase shelf life of foods the pack atmosphere should contain a low concentration of residual oxygen.
3- Nitrogen • Nitrogen is a relatively un-reactive gas with no odour , taste, or color. • Nitrogen does not support the growth of aerobic microbes and therefore inhibits the growth aerobic spoilage but does not prevent the growth of anaerobic bacteria. • The low solubility of nitrogen in foods can be used to prevent pack collapse by including sufficient N2 in the gas mix to balance the volume • decrease due to CO2 going into solution.
4- Carbon monoxide • Carbon monoxide is a colourless, tasteless and odourless gas that is highly reactive and very flammable. • It has a low solubility in water but is relatively soluble in some organic solvents. • Commercial application has been limited because of its toxicity and the formation of potentially explosive mixtures with air.
5- Noble gases • The noble gases are a family of elements characterized by their • lack of reactivity and include (He), ( Ar ) , ( Xe ) and ( Ne ). • These gases are being used in a number of food applications now e.g. potato-based snack products. • It is difficult to see how the use of noble gases would offer any preservation advantages compared with N2 they are being used.
1- Vegetables • An important fact when dealing with vegetables is that they are still ‘‘living’’ structures and continue to respire as long as there are nutrients and gases available. • Water loss is loss of saleable weight and thus a direct loss to the grower or processor. • A loss in weight of only 5% will cause many vegetables to appear wilted or shriveled, and under warm, dry conditions without the correct packaging this can happen in a few hours.
Packaging films can achieve significant increase in shelf life by reducing the loss of the vegetables’ stored energy reserves through lowering the respiration rate. • LDPE was found as good alternative to PVC for wrapping vegetables.
2- Fruit • One of the major benefits of MAP is the prevention or retardation of fruit ripening and associated biochemical and physiological changes. • Temperature is the most effective environmental factor in the • prevention of fruit ripening. • Both ripening and C2H4 production rates increase with an increase in temperature.
To delay fruit ripening, fruits should be held as close to 0 C as possible, without suffering chilling injury. • The use of MAP as a supplement to proper temperature maintenance in the effort to delay ripening is consequentially more effective for chilling sensitive fruits, but is generally beneficial for all fruits. • Reducing O2 concentration below 8% or elevating • CO2 concentration above 1% retards fruit ripening.
It has been established that 2% O2 level anaerobic respiration may • result in the development of off-flavours and off-odours. • Fruits exposed to such low O2 levels may also loose their ability to attain uniform ripeness upon removal from MAP. • Successful applications of MAP on fruits include Royal Gala apples, Granny Smith apples, lemons (whole peeled/ sliced), and oranges (whole, peeled, and sliced). • The effectiveness of modified atmospheres and packaging materials on the growth of Penicilliumexpansumand patulin production. • PE is an excellent packaging material for the storage of apples since it inhibited the growth of P. expansum , thereby allowing patulin to be produced.
3- Fresh-cut fruits and vegetables • Demand for fresh-cut fruit and vegetables has been increasing in • recent years, mainly because consumers look for freshness and • convenience when they purchase these commodities. Packaged fresh-cut vegetables are becoming more and more popular because they offer several advantages. These products are perceived by consumers to be more nutritious, convenient, and efficient in terms of meal preparation (ready-to-eat)
In general, fresh-cut products have a short shelf life, which is • mainly due to mechanical stresses. • At the cut surface, cells and membranes are damaged leading to alterations in tissue metabolism . • Although these alterations are different, many authors • have observed an increase in carbon dioxide and ethylene evolution, water loss, alterations in flavor and aroma, in volatile profiles, and • increase in the activity of enzymes related to enzymatic browning .
The difficulties encountered with fresh-cut fruit, while not insurmountable, require a new and higher level of technical and operational sophistication. • Post-harvest quality loss is primarily a function of respiration, onset or progression of ripening water loss (transpiration), enzymatic discoloration of cut surfaces, decay (microbial), senescence and mechanical damage suffer during preparation, shipping, handling and processing . • Extended shelf life was observed in fresh-cut mangoes, pineapples, and mixes packaged in PET due to reduced O2 and elevated CO2 atmosphere. • The results suggest that shelf life of fresh-cut fruit could be extended using appropriate semi-rigid containers.
Increased water activity and mixing of intracellular and intercellular enzymes and substrates may also contribute to flavor and texture changes . • Successful applications of MAP on the quality of some fresh-cut food include :mushroom, tomato , pineapple , lettuce , potato , ….. • Degradation of cut vegetables in terms of appearance was delayed by N2 gas packaging.
Fresh-cut products often have significantly different packaging • requirements than the whole product. • The MA packaging technique consists of the enclosure of • Respiring produce in polymeric films in which the gaseous environment is actively or passively altered to slow respiration, reduce • moisture loss and decay and/or extend the shelf life of the products.
Conclusions 1. The greatest extension of shelf life occurs at the lowest possible oxygen concentration before anaerobic respiration is initiated. 2. The recommended percentage of O2 in a modified atmosphere for fruits and vegetables for both safety and quality falls between 1 and 5%, although the oxygen level will realistically reach levels below 1% in MAP produce. 3- These physiological changes may be accompanied by flavor loss, cut surface discoloration, color loss, decay, increased rate of vitamin loss, rapid softening, shrinkage and a shorter storage life. 4- proper temperature management during product preparation and refrigeration throughout distribution and marketing is essential for maintenance of quality.
5-To provide packaging films with a wide range of physical properties, many of these individual films are combined through processes like lamination and co-extrusion. 6-Polyethylene is most commonly used to provide a hermetic seal and also as a medium of control for characteristics like anti-fogging Abilities . 7- The degree to which atmospheric modification takes place in packages is dependent upon several variables such as film permeability to O2 and CO2, product respiration and the influence of temperature on both of these processes . 8-Temperature and headspace atmosphere are two important factors to prolong shelf life. Modified atmosphere packaging (MAP) can be interpreted as a dynamic system with two gas fluxes, the respiration rate of the fresh product and the gas exchange through the barrier
9. Successful control of both product respiration and ethylene production and perception by MAP can result in a fruit or vegetable product of high organoleptic quality Maintaining proper storage temperatures is often most difficult at retail level. 10. Oxygen, CO2, and N2, are most often used in MAP/CAS. Among them, CO2 is the only one with a direct antimicrobial effect . 11-It was clear that temperature fluctuation, even if it should occur only once, can seriously compromise the benefits of modified atmosphere packaging and safety of the packaged produce.
References 1-M ShafiurRahman - Handbook of Food Preservation 2- Sandhya ,KrishiVigyan Kendra, Punjab Agricultural University, Samrala, Ludhiana, India.(2010). Modified atmosphere packaging of fresh produce: Current status and future needs. LWT - Food Science and Technology 3- Nitaigour P. Mahalik and Arun N. Nambiar .(2010). Trend in food packaging and manufacturing systems and technology. Trends in Food Science & Technology 4- Kata Galic , Mario Scetar and Mia Kurek.(2011). The benefits of processing and packaging. Trends in Food Science & Technology 5- A. Lucera a, C. Costa a, M. Mastromatteo c, A. Conte a,b, M.A. Del Nobile. (2010). Influence of different packaging systems on fresh-cut zucchini (Cucurbitapepo). Innovative Food Science and Emerging Technologies 6- KablanTano, Mathias K. Oul´e, Gilles Doyon, Robert W. Lencki, Joseph Arul . (2007). Comparative evaluation of the effect of storage temperature fluctuation on modified atmosphere packages of selected fruit and vegetables. Postharvest Biology and Technology