LEMON PACKING PROCESS
WASH
After receiving fruit from the fields, our lemons are washed and scrubbed thoroughly using a gentle soap and chlorinated water. Then, food-grade storage wax is then applied to prevent shrinkage and preserve quality. Next, the lemons are sorted. We use Sunsort® grading technology developed by the Sunkist, a leader in optical lemon-grading equipment. After stringent inspection, the lemons are then grouped by size and grade and sent to storage.
STORAGE
While in storage, the fruit is kept at 50-52 degrees F with 90-95% relative humidity. High volumes of air fill the lemon storage rooms, where they develop their flavorful, bright yellow color before being packed.
PACK
Once the fruit is market ready, it is delivered from storage to be washed and rinsed a second time and receives an application of food-grade pack wax designed to safeguard the lemon during transit. The fruit is passed through a second set of optical lemon-grading equipment and is examined by skilled employees for quality. The fruit is then sized and placed into packaging tailored to our customers’ orders.
SHIP
Once placed into the proper packaging, the lemons are palletized and placed into pre-coolers set between 40-45 degrees before being loaded into trucks arranged by Sunkist. From there, our fruit is transported to the various domestic and international markets.
FOOD SAFETY
SETTING THE STANDARDS IN THE CITRUS INDUSTRY
Our top priority at Saticoy Lemon is the health and safety of our consumers. The Food Safety Program we have in place ensures the safest and highest quality fruit leaves our facilities. Saticoy Lemon employees receive training in food safety and safe handling procedures.
We are strong advocates within the citrus industry for improving food safety initiatives. Our commitment promises to use every resource possible to ensure the highest quality, cleanest, safest and most wholesome fruit in the world.
OUR PRACTICES
Food safety is taken very seriously at Saticoy Lemon, and accordingly we have invested the time and resources to make it a reality. We pride ourselves in growing, harvesting and packing the freshest and highest quality fruit. This is why we comply with Global Food Safety Initiative (GFSI) which sets forth standards in food safety requirements along the entire food supply chain to cover scopes such as growing, packaging, and distribution.
We follow Good Manufacturing Practices (GMPs), guidelines established by the federal government, daily in our state of the art processing plants. Our packing houses undergo and pass annual audits by a certified third party auditor.
Our fruit arrives at our processing plants and is cleaned and disinfected eliminating field contaminants. Our traceability program allows us to trace our fruit from the grower to receiver in case of a recall event. This assures that only safe fruit leaves our facilities.
LEMON PACKING AND STORAGE SYSTEMS
Lemons belong to the rue family (Rutaceae) and come originally from Asia.
In addition to lemons, the group of citrus fruits, which are mainly cultivated in subtropical regions, also includes oranges, grapefruits, mandarins, limes and easypeelers.
Lemons are berry fruit consisting of three layers:
the outer yellow peel (exocarp, flavedo), the glands of which exude the essential oil of lemon, which produces the typical citrus odor
the whitish mesocarp (albedo)
the endocarp consisting of 8 – 10 segments filled with juice sacs (vesicles)
Lemons are usually of an elongated shape with a peel of variable thickness and pointed tip. The juicy pulp of a medium-sized lemon contains 30 – 35 g of lemon juice, which has a high vitamin C content (60 – 100 mg per 100 g of fruit). Lemons are divided into winter and summer fruits.
The degree of ripeness of citrus fruit is determined on the basis of three criteria:
by the ripeness index: this is determined by the Brix value, which is a measure of the sugar/acid ratio of the fruit. According to [7], citrus fruit with a Brix value of between 10 and 16 have good flavor.
by cutting at purchase: freshness is determined by cutting the fruit in half from the stem-end to the opposite end. If the fruit is withered at the stem-end, it must not be shipped.
by peel color: the color of the peel is not necessarily a reliable indicator of ripeness, but its surface gloss is. Glossy lemons are ripe, even if they are still green or have green spots.
Fungicides are diphenyl, orthophenylphenol (OPP) and thiabendazole (TBZ). Diphenyl can be recognized from its naphthalene-like odor. The fungicides primarily prevent blue and green molds, but they do impair flavor and indication of their use is mandatory.
Quality / Duration of storage of Lemons
The fruits should have thin peel, be nearly seedless and very juicy, i.e. have a minimum juice content of 20 – 25%, be undamaged and unmarked (dry and hard peel and spots indicate over-aging and off-flavors) and have a firm, glossy peel.
Experience has shown that it is the care taken with preparation of the fruit for shipping which very largely determines whether individual batches withstand the rigors of transport. Such preparation for shipping is carried out in packing houses. These include:
Post-ripening of green or unsatisfactorily colored fruit to achieve a salable peel color in ripening rooms.
Removal of dirt, sooty mold, spraying residues and scale insects in washers.
Coating with a layer of wax and treatment with preservatives and marking accordingly.
Grading of the fruits by size (gaging), color and other external features.
Counting, weighing and packing. Marking each package with details of number of fruit, quality class, variety and origin.
Storage until shipment in cold stores.
Waxing to prevent loss of aroma and weight is required because the washing process removes the natural wax layer. The film of wax sprayed onto the peel only partially seals the pores so that the fruits are still able to respire.
Maximum duration of storage and transport is as follows:
Designation Temperature Rel. humidity Max. duration of storage Source
10 – 11°C 80 – 90% 12 weeks [1]
12 – 14°C 85 – 90% 16 – 24 weeks [5]
Green lemons 12 – 14°C 85 – 90% 4 – 20 weeks [39]
Yellow lemons 10 – 11°C 85 – 90% 4 – 6 weeks [39]
Where controlled atmosphere transport is used, transport and storage duration may be extended. The following parameters apply in such a case [16]:
Temperature Rel. humidity O2 CO2 Suitability for controlled atmosphere
10.0 – 12.8°C 85 – 90% 5% 5 – 10% good
Intended use
Since lemons are citrus fruit having a juicy/aromatic flesh with a high acid content, they are primarily used for their juice and for seasoning. The flesh and juice are used to make lemonade, soft drinks, jams and the like, while the highly fragrant lemon oil is extracted from the peel in the countries of cultivation.
Figure
(Click on the Figure to enlarge it.)
Photo, lemons
Figure 1
Countries of origin
This Table shows only a selection of the most important countries of origin and should not be thought of as exhaustive.
Europe Spain, Italy, Turkey, Cyprus
Africa South Africa, North Africa, Egypt
Asia Israel, India
America Chile, Uruguay, Argentina, USA, Brazil, Mexico
Australia
Container transport
Refrigerated container with fresh air supply or controlled atmosphere.
Cargo handling
Because of its impact- and pressure-sensitivity, the fruit has to be handled with appropriate care.
The required refrigeration temperature must always be maintained, even during cargo handling.
In damp weather (rain, snow), the cargo must be protected from moisture, as there is otherwise a risk of premature spoilage.
Stowage factor
1.71 m3/t (cartons on disposable pallet) [1]
2.55 – 2.80 m3/t (boxes and cartons) [14]
Stowage space requirements
Cool, dry, good ventilation
Segregation
Fiber rope, thin fiber nets, wooden dunnage
Cargo securing
Because of its considerable impact- and pressure-sensitivity, packages of this cargo must be secured in such a way that they are prevented from damaging each other. Spaces between packages or pallets must be filled, to prevent slippage or tipping. By selecting the correct packaging size or cargo unit (area module or area module multiple), holds can be tightly loaded (without spaces).
Back to beginning
Risk factors and loss prevention
RF Temperature
Lemons require particular temperature, humidity/moisture and ventilation conditions (SC VII) (storage climate conditions).
A written cooling order must be obtained from the consignor before loading is begun. This order must always be complied with during the entire transport chain.
The following Tables merely constitute an estimate of appropriate temperature ranges. Temperatures may deviate from these values, depending on the particular transport conditions.
Designation Temperature range Source
Travel temperature 10 – 11°C [1]
10 – 13°C [2]
12 – 14°C [5]
10 – 12°C [6]
The cargo and holds/containers should be precooled prior to loading.
Depending upon the species and variety, all citrus fruits are highly cold-sensitive. Grapefruit, lemons and limes are more susceptible to chilling damage than are oranges and mandarins, and late-ripening varieties are more temperature-sensitive than early varieties. While oranges can withstand temperatures of 5°C, more temperature-sensitive types should never be shipped below 10°C. Green citrus fruits require higher transport temperatures than do yellow; the higher is the acid content of the fruit, the greater is its cold-sensitivity.
Chilling damage is manifested in citrus fruits in particular by spots on the peel (brown dots on the peel), accompanied by a bitter taste and unpleasant odor, rot and cell wall collapse. The glossiness of the peel is lost and the albedo layer (inner layer of the peel), which is normally white, turns a dark color. When the fruit is divided up, the segments, which have a low juice content, break up and the whole fruit is glassy and soft. The severity of the chilling damage is determined not only by the extent to which the temperature has fallen beneath the limit, but also by the length of exposure to this temperature. Chilling damage does not generally occur in cold stores, but instead prior to cooling or after leaving the cold stores.
Excessively rapid warming of refrigerated fruit results in condensation and spoilage.
During loading, pulp temperature measurements must be performed continually. The pulp temperature must never be < 4°C or > 25 – 30°C as storage life and appearance are impaired outside this range. Fruits punctured for pulp temperature measurement must be discarded as they would rapidly spoil and infect the other fruit. The measurements must be recorded.
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RF Humidity/Moisture
Lemons require particular temperature, humidity/moisture and ventilation conditions (SC VII) (storage climate conditions).
Designation Humidity/water content Source
Relative humidity 80 – 90% [1]
85 – 90% [2]
85 – 90% [5]
85 – 90% [39]
Water content approx. 90% [1]
Maximum equilibrium moisture content 85% [1]
It is essential to protect lemons from moisture (seawater, rain, condensation, snow) as moisture in particular promotes green and blue mold and black rot.
In general, due to the high water content of lemons of approx. 90%, a relative humidity of 85 – 90% is required. Only lemons, oranges and mandarins with a dark green peel color are able to withstand a relative humidity of 82 – 85%.
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RF Ventilation
Lemons require particular temperature, humidity/moisture and ventilation conditions (SC VII) (storage climate conditions).
Recommended ventilation conditions: circulating air, 40 – 60 circulations/hour with continuous supply of fresh air
The addition of fresh air is extremely important as citrus fruit can start to ferment within a few hours due to anaerobic respiration (resulting in total loss of the fruit). If ventilation is inadequate, storage damage may occur, taking the form of a bitter flavor and peel scab.
Back to beginning
RF Biotic activity
Lemons display 2nd order biotic activity.
They are living organs in which respiration processes predominate, because their supply of new nutrients has been cut off by separation from the parent plant.
Care of the cargo during the voyage must be aimed at controlling respiration processes (release of CO2, water vapor, ethylene and heat) in such a way that the cargo is at the desired stage of ripeness on reaching its destination. Inadequate ventilation may result in fermentation and rotting of the cargo as a result of increased CO2 levels and inadequate supply of atmospheric oxygen (see Ventilation).
Back to beginning
RF Gases
CO2 evolution at 10°C: 12.5 mg/kg*h [1]
Upper limit of permissible CO2 content 0.1 vol.% [1]
< 0.5 vol.% [39]
Ethylene evolution
Active behavior The rate of ethylene production is very low, being below 0.1 µl/kg*h [16].
Passive behavior Lemons are moderately sensitive to ethylene [16] and should thus not be stored with goods having an elevated ethylene production rate (allelopathy).
In fresh fruit, metabolic processes continue even after harvesting. The fruit absorbs oxygen (O2) and excretes varying amounts of carbon dioxide (CO2) and ethylene (C2H4) as well as aromatic compounds during the conversion of starch into sugar (ripening process).
Levels of respiratory gases which promote ripening, such as ethylene as well as carbon dioxide, should be kept as low as possible. If ventilation is inadequate, storage damage, such as a bitter flavor and peel scab, may occur. The supply of fresh air must thus be constant in order to dissipate these gases.
LEMON PACKING SYSTEMS
There has been much discussion in the Florida Fresh Citrus Industry about the possibility of handling lemons in a conventional packing house. The advantages of keeping idle machinery and key people productive in the summer months are obvious if the special problems of handling this variety can be overcome.
This can be done and is being done successfully by two Florida Packing Houses, Golden Gem Growers, Inc. in Umatilla and Gracewood Fruit Company in Vero Beach.
This concept requires a few specific facilities which are not found in all Florida packing houses but are present in many. This paper will discuss these facilities plus others which are desirable if available.
The Fresh Lemon Industry in Florida is a young and growing industry. It is rather unique in that the fruit matures during a time of year when no other Florida Citrus is in season. Since the major problem facing most Florida fresh fruit operations is the lack of full utilization of packing equipment, there has been some interest in utilizing this idle capacity during the summer for packing lemons. There has been much debate over the wisdom of this approach since the handling of lemons in a conventional packing house presents many difficulties which must be solved to have a successful operation.
The basic technology for packing fresh Florida Lemons has been worked out for several years. The ideal situation of course is to have a packing plant designed specifically for lemons which would run lemons only. It would have all the machinery, equipment, and cold rooms necessary to do a good job. However, the only way this approach can be justified is to control enough lemons that this plant could be operated for several months each year. It would require approximately one-half the present bearing acreage of Florida Lemons to support such a plant.
Therefore the ideal situation for a company with a conventional packing house with nothing to pack in August and usually September would be to pack lemons in this plant if the obstacles can be overcome. The advantages of such an operation are fairly obvious. The units packed during this period could do much to lower the unit overhead cost for the entire year. In addition the Supervisory and other Key people would become much more productive during this period of time. The same is true for the sales organization. This is the line of reasoning that led us into the fresh lemon packing business.
In 1970 one of our members, Callery-Judge Groves requested we consider packing fresh lemons since they grew lemons and were very interested in having them packed fresh if at all possible. They furnished the fruit to experiment with so that we could find out how our machinery would do with lemons. Our first experiment was with twelve pallet bins of lemons which we handled in many different ways. After this experiment they furnished us with two trailer loads of lemons which we packed and sold on the fresh fruit market with good results. From that cautious beginning this operation has grown to the point where we stay extremely busy on lemons during the months of August and September, sometimes beginning in July and ending in October.
To further discuss this subject I would like to break it down into several points which I consider important in the handling of fresh lemons in a conventional packing house. The first four points are absolutely essential. The remaining points are certainly desirable, but not as important as the first four.
LEMON PROCESSING AND PACKING
After harvest, fruits and vegetables need to be prepared for sale. This can be undertaken on the farm or at the level of retail, wholesale or supermarket chain. Regardless of the destination, preparation for the fresh market comprises four basic key operations:
1. Removal of unmarketable material,
2. Sorting by maturity and/or size,
3. Grading,
4. Packaging.
Any working arrangement that reduces handling will lead to lower costs and will assist in reducing quality losses. Market preparation is therefore preferably carried out in the field. However, this is only really possible with tender or perishable products or small volumes for nearby markets. Products need to be transported to a packinghouse or packing shed in the following cases: for large operations, distant or demanding markets or products requiring special operations like washing, brushing, waxing, controlled ripening, refrigeration, storage or any specific type of treatment or packaging.
These two systems (field vs. packinghouse preparation) are not mutually exclusive. In many cases part field preparation is completed later in the packing shed. Because it is a waste of time and money to handle unmarketable units, primary selection of fruits and vegetables is always carried out in the field. In this way products with severe defects, injuries or diseases are removed.
Lettuce is an example of field preparation where a team of three workers cut, prepare and pack (Figure 22). For distant markets, boxes prepared in the field are delivered to packhouses for palletizing, precooling, and sometimes cold storage before shipping. Mobile packing sheds provide an alternative for handling large volumes in limited time. Harvest crews feed a mobile grading and packing line (Figure 23). On completion of loading, the consignment is shipped to the destination market and replaced by an empty truck. In mechanized harvesting, the product is transported to the packhouse (Figure 24) where it is prepared for the market. In many cases, harvest crews make use of an inspection line for primary selection on the field.
Figure 22: Lettuce field preparation for the fresh market.
Figura 23: Mobile packing shed for market preparation of celery.
Figure 24: Mechanized harvest of tomato.
2.2 The packhouse
A packinghouse allows special operations to be performed. Another advantage (over field preparation) is that products can be prepared continuously for 24 hours regardless of the weather. With its capacity to process large volumes, farmers associations, cooperatives, or even community organizations can take advantage of these opportunities.
The size and degree of complexity of a packing shed depends on the following factors: crop(s) and volume to be processed, capital to be invested, its objectives such as handling of owner's production or to provide service to others. Packing sheds range from a straw shelter to highly automated facilities. In some cases storage rooms as well as offices for commercial sales are annexed to packing sheds.
A packhouse can be defined as a place protected from weather for both, product and personnel. It is organized in such a way that product is prepared in a centralized handling operation. To some extent, this is similar to a factory assembly line, where raw material from the field undergoes a sequence of activities resulting in the final packaged product.
2.2.1 General considerations about design
A packinghouse needs to be located close to the production area and within easy access to main roads or highways. It also needs to have one entrance to facilitate and control supply and delivery. Moreover, it needs to be large enough for future expansion or additional new facilities. Sufficient space outside is also required to avoid congestion of vehicles entering and leaving. Buildings should be designed to ensure sufficient shade during most of the day in the loading and unloading areas. They also need good ventilation in summer and protection in winter.
Packinghouses are usually built with cheap materials. However, it is important to create a comfortable environment both for produce and workers. This is because product exposed to unfavorable conditions can lead to rapid deterioration in quality. Also, uncomfortable working conditions for staff can lead to unnecessary rough handling.
A packinghouse should have adequate room for easy circulation with ramps to facilitate loading and unloading. Doors and spaces should be sufficiently large to allow the use of forklifts.The reception area should be large enough to hold product equivalent to one working day. The main reason for this is to keep the packinghouse in operation in the event of an interruption in the flow of product from the field (rain, machine breakdown, etc).
Electricity is critical for equipment, refrigeration and particularly lighting. Because packhouses usually work extended hours or even continuously during harvest time, lighting (both, intensity and quality) is critical in identifying defects on inspection tables. Lights should be below eye level to prevent glare and eyestrain (Figure 25). Light intensity should be around 2 000-2 500 lx for light coloured products but 4 000-5 000 for darker ones. The working area together with the whole building should have lighting. This is in order to avoid the contrasts caused by shaded areas, resulting in temporary blindness when the eyes are raised. Dull colours and non-glossy surfaces are a requirement for equipment, conveyor belts and outfits. In this way, defects are not masked because of the reflection of light. It also helps to reduce eye fatigue.
A good supply of water is important for washing product, trucks, bins and equipment, as well as for dumping. In some cases it may also be necessary for hydro cooling. Provision of an adequate waste water disposal system is as important as a good source.
Administration offices should be located on clean and quiet areas and if possible elevated. This is so that the entire operation is visible. (Figure 26). Packinghouses should have facilities or laboratories for quality analysis.
After working out the details of the building layout, it is important to prepare a diagram for the movement of product throughout the packinghouse and activities to be undertaken for the entire operations. Handling must be minimized and movement of product should always be in one direction without crossovers. It may be possible to undertake operations concurrently, such as working simultaneously on different sizes or maturity stages.
2.2.2 General considerations about lemon packing operations
2.2.2.1 Reception
Preparation and packing operations should be designed to minimize the time between harvest and delivery of the packaged product. Reception is one area where delays frequently occur (Figure 27) and the product should be protected from the sun as much as possible. Product is normally weighed or counted before entering the plant and in some cases samples for quality analysis are taken (Figure 28). Records should be kept, particularly when providing a service to other producers.
Preparation for the fresh market starts with dumping onto packinghouse feeding lines. Dumping may be dry (Figure 29) or in water (Figure 30). In both cases it is important to have drop decelerators to minimize injury as well as control the flow of product. Water dipping produces less bruising and can be used to move free-floating fruits. However, not all products tolerate wetting. A product with a specific density lower than water will float, but with other products salts (sodium sulfate, for example) are diluted in the water to improve floatation.
Figure 25: Lighting at eye level causes blinding and eye fatigue. Lighting fixtures should also be covered to prevent glass shattering over produce if broken.
Water dipping through washing helps to remove most dirt from the field. For thorough cleaning, more washings and brushing are required. Water rinsing allows produce to maintain cleanliness and be free of soil, pesticides, plant debris and rotting parts. However, in some cases this is not possible. This is because of insufficient water. If recirculated water is used, this needs to be filtered and settled dirt removed.
Figure 26: Elevated administration offices allow process supervision.
Chlorination of dumping and washing waters with a concentration 50-200 ppm of active chlorine, eliminates fungi spores and bacteria on the surface of diseased fruits. This prevents the contamination of healthy fruit. In addition to this, bruising should be avoided since this is the entry for infection by decay organisms. At depths greater than 30 cm and for periods of time longer than 3 minutes, water tends to penetrate inside fruits, particularly those that are hollow such as peppers. Water temperature also contributes to infiltration. It is recommended that fruit temperature is at least 5 °C lower than liquid.
Figure 27: Delays should be avoided either at reception or delivery, particularly when produce is exposed to the sun.
2.2.2.2 Removal of lemon rejects in the lemon packing process
After dumping, the first operation that usually follows is the removal of unmarketable material. This is because handling of plant material that cannot be sold is costly. This is performed prior to sizing and grading. Primary selection is one of the four basic operations for market preparation carried out in the field. This step involves the removal of over mature, too small, severely damaged, deformed or rotting units.
Very small produce is usually mechanically removed by mesh screens, pre-sizing belts or chains. Bruised, rotted, off-shaped units, wilted or yellow leaves are usually removed by hand. Garlic and onions are topped to remove the dry foliage attached to the bulbs by specific equipment (Figure 31) and in many crops soil and loose parts are removed by brushing (Figure 32). In crops where water dipping is possible, differential floatation could be used to separate rejects. In addition to this, detergents and brushes can be used to remove soil, latex, insects, pesticides etc. Clean fruits should be dried with sponges or hot air.
Culls as well as other plant parts from cutting, peeling, trimming, bruised and spoiled fruits can be used for animal feeding. Although they provide a good source of energy and are extremely tasty, their high water content makes them bulky and expensive to transport. In addition to this, their nutritional value is less than other food sources. This is because of their low protein and dry matter contents (in terms of volume). Their inclusion in the diet must be in the right proportions to avoid digestive problems. Another disadvantage is that in many cases they are highly perishable and cannot be stored. This means that they cannot be gradually introduced into the animal's diet. When not used for animal feeding, they can be disposed as sanitary fillings or organic soil amendments.
Figure 28: Sampling for quality before grading.
2.2.2.3 Sizing
Sizing is another basic operation undertaken in a packhouse and can be carried out before or after sorting by colour. Both operations should always be carried out before grading. This is because it is easier to identify units with defects on a uniform product, either in terms of size or colour.
There are two basic systems - according to weight or dimensions (diameter, length or both). Spherical or almost spherical products like grapefruits, oranges, onions, and others, are probably the easiest to sort by size. Several mechanisms are available from mesh screens to diverging belts (Figure 33) or rollers with increased spaces between them (Figure 34). Sizing can also be performed manually using rings of known diameter (Figure 35). Sorting by weight is carried out in many crops with weight sensitive trays. These automatically move fruit onto another belt aggregating all units of the same mass (Figure 36).
Figure 29: Dry dumping of lemons (Photograph: P. A. Gómez, INTA E.E.A. Balcarce).
2.2.2.4 Grading
Amongst the four basic operations, this is probably the most important. It consists of sorting product in grades or categories of quality. Two main systems exist: static and dynamic. Static systems are common in tender and/or high value crops. Here the product is placed on an inspection table where sorters remove units which do not meet the requirements for the grade or quality category (Figure 37). The dynamic system is probably much more common. Here product moves along a belt in front of the sorters who remove units with defects (Figure 38). Main flow is the highest quality grade. Often second and third grade quality units are removed and placed onto other belts. It is much more efficient in terms of volume sorted per unit of time. However, personnel should be well trained. This is because every unit remains only a few seconds in the worker's area of vision. There are two types of common mistakes: removing good quality units from the main flow and more frequently, not removing produce of doubtful quality.
Rejects mainly on aesthetic grounds provide a second or even third quality grade. These can be marketed in less demanding outlets or used as raw material for processing.
Figure 30: Water dumping of apples.
Small scale processing, however, needs to be able to achieve a standard of quality similar or even better than large industries. This is not always possible because industrial plants tend to use specific varieties and processes. In addition to this, surpluses for the fresh market and sub-standard products do not provide uniform raw material. The industrial yield is low and this together with the low technology in the manufacturing process can result in a product of variable quality. At this point, it is important to highlight that the quality of a processed product will depend both upon, the quality of the raw material and the manufacturing process.
2.2.3 Special operations
These operations are commodity specific. They are different from basic operations because they are carried out on every crop independent of size and sophistication of the packinghouse.
2.2.3.1 Colour sorting
These are common in fruits and fruit vegetables and can be undertaken electronically. Fruits are usually harvested within a range of maturity (Figure 39) that needs to be uniform for sale. Harvesting within a narrow range of maturity reduces colour sorting. However, this is only possible for low-volume operations.
Figure 31: Topping onions before grading.
2.2.3.2 Waxing
Some fruits such as apples, cucumbers, citrus, peaches, nectarines and others, are waxed for the following reasons: to reduce dehydration, improve their postharvest life by replacing the natural waxes removed by washing and to seal small wounds produced during handling. Waxes are also used as carriers of some fungicides or just to increase shine and improve appearance. Different types and formulae of waxes are available.
These can be applied as sprays or foams, or by immersion and dripping or in other ways. Uniform distribution is important. Soft brushes, rollers or other methods are used to ensure that application on the surface of fruit is thorough and texture is even. Heavy application can block fruit gas exchange and produce tissue asphyxia. Internal darkening and development of off-flavors and off-odors are some of the characteristics. It is very important that waxes are approved for human consumption.
2.2.3.3 Degreening
The main causes of greening are climatic conditions before harvest. For example, citrus often reaches commercial maturity with traces of green colour on the epidermis (flavedo). Although not different from fruits with colour, consumers sense that they are not ripe enough and have not reached their full flavor. Degreening consists of chlorophyll degradation to allow the expression of natural pigments masked by the green colour. In purpose built chambers, citrus fruits are exposed from 24 to 72 hours (depending on degree of greening) to an atmosphere containing ethylene (5-10 ppm) under controlled ventilation and high relative humidity (90-95%). Conditions for degreening are specific to the production area. Artés Calero (2000) recommends temperatures of 25-26 °C for oranges, 22-24 °C for grapefruit and lemon and 20-23 °C for mandarins.
Figure 32: Brushing and hand removal of damaged fruits before grading. (Photograph: S. Horvitz, INTA E.E.A. Balcarce).
Figure 33: Sizing onion bulbs by diverging belts. The different speed of belts makes bulbs rotate besides moving forward to a point where bulb diameter equals belt separation.
Figure 34: Sizing with rollers of increasing distance between them.
Figure 35: Sizing with rings of known diameters (Photograph: P. A. Gómez, INTA E.E.A. Balcarce).
Figure 36: Sizing by weight. Individual trays deposit fruit on the corresponding conveyor belt.
Figure 37: Static quality grading system. Product is dumped onto an inspection table where defective units are removed.
2.2.3.4 Controlled ripening
Maturity at harvest is the key factor for quality and postharvest life. When shipped to distant markets, fruits need to be harvested slightly immature (particularly climacteric ones) to reduce bruising and losses during transport. Prior to distribution and retail sales, however, it is necessary to speed up and achieve uniform ripening. The main reason for this is so that product reaches consumers at the right stage of maturity. As with degreening, ethylene is used but at higher concentrations. Banana provides a typical example of this type of operation. It can however, also be carried out on tomatoes, melons, avocados, mangoes and other fruits (Table 3).
Controlled ripening is performed in purpose built rooms where temperature and relative humidity can be controlled and ethylene removed when the process has been completed. The process involves initial heating to reach the desired pulp temperature. This is followed by an injection of ethylene at the desired concentration. Under these conditions, the product is maintained for a certain amount of time followed by ventilation in order to remove accumulated gases. On completion of the treatment, the temperature is reduced to the desired level for transportation and/or storage. Ethylene concentration and exposure time are a function of temperature, which accelerates the process.
Table 3: Conditions for controlled ripening of some fruits.
Ethylene concentration (ppm)
Ripening temperature °C
Exposure time to these conditions (hr.)
Avocado
10-100
15-18
12-48
Banana
100-150
15-18
24
Honeydew melon
100-150
20-25
18-24
Kiwifruit
10-100
0-20
12-24
Mango
100-150
20-22
12-24
Stone fruits
10-100
13-25
12-72
Tomato
100-150
20-25
24-48
Adapted from Thompson, 1998.
Figure 38: Dynamic quality grading system. Sized onion bulbs continuously flow on inspection tables where defective products are removed. Final inspection is performed before bagging (right hand side).
Figure 39: Fruits are harvested within a range of maturity and they should be separated by colours before packing. (Photograph: S. Horvitz, INTA E.E.A. Balcarce).
2.2.3.5 Pest and disease control
Different treatments are performed to prevent and control pests and diseases at postharvest level. Fungicides belonging to different chemical groups are widely used in citrus, apples, bananas, stone fruits and other fruits. Most have a fungistatic activity. This means that they inhibit or reduce germination of spores without complete suppression of the disease. Chlorine and sulfur dioxide are amongst those most widely used.
Chlorine is probably the most widely used sanitizer. It is used in concentrations from 50 to 200 ppm in water to reduce the number of microorganisms present on the surface of the fruit. However, it does not stop the growth of a pathogen already established. Table grapes are usually fumigated with sulfur dioxide to control postharvest diseases at a concentration of 0,5% for 20 minutes followed by ventilation. During storage, periodic (every 7-10 days) fumigations are performed in concentrations of 0.25%. During transport, pads impregnated with sodium metabisulfite can be used inside packages. These slowly generate sulfur dioxide in contact with the humidity released by fruits.
Gas fumigation is the most important method for eliminating insects, either adults, eggs, larvae or pupae. Methyl bromide was probably the most widely used fumigant for many years but it is banned in most countries. It has been replaced by temperature (high and low) treatments, controlled atmospheres, other fumigants or irradiation.
It is also possible to prevent some postharvest physiological disorders with chemical treatments. For example, calcium chloride (4-6%) dips or sprays for bitter pit in apples. Other methods include dipping or drenching fruits in chemical solutions to avoid storage scalds or other disorders. Similarly, the addition of low concentrations of 2.4-D to waxes assists in keeping citrus peduncles green.
2.2.3.6 Temperature treatments
Cold can be used in low temperature tolerant fruits (apples, pears, kiwifruit, table grapes, etc.) and other potential carriers of quarantine pests and/or their ovipositions. Exposure to any of the following combinations of temperatures and time is provided in the following recommendations (Table 4).
Heat treatments like hot water dips or exposure to hot air or vapor have been known for many years for insect control (and for fungi, in some cases). When restrictions were extended to bromine based fumigants, however, heat treatments were reconsidered as quarantine treatments in fruits such as mango, papaya, citrus, bananas, carambola and vegetables like pepper, eggplant, tomato, cucumber and zucchinis. Temperature, exposure and application methods are commodity specific and must be carried out precisely in order to avoid heat injuries, particularly in highly perishable crops. On completion of treatment, it is important to reduce temperature to recommended levels for storage and/or transport.
Hot water immersion requires that fruit pulp temperature is between 43 and 46,7 °C for 35 to 90 minutes. This depends on commodity, insect to be controlled and its degree of development (U.S. E.P.A., 1996). Dipping in hot water also contributes to reduced microbial load in plums, peaches, papaya, cantaloupes, sweet potato and tomato (Kitinoja and Kader, 1996) but does not always guarantee good insect control (U.S. E.P.A., 1996). For the export of mangoes from Brazil, it is recommended that dipping is performed at 12 cm depth in water at 46,1 °C and for 70-90 minutes (Gorgatti Neto, et al., 1994).
Table 4: Combinations of temperature and exposure time for fruit fly quarantine treatments.