PINEAPPLE POST HARVEST

1.0 Introduction

This training module will be used for training Field Staff (TOT), who will then train the farmers. Both levels of the training will be interactive and live specimens will be used for demonstration. To enable practical demonstrations, the training will therefore be carried out near a farm. If not, the trainees will visit a farm with the produce at the period when harvesting and post-harvest handling are being carried out.

1.1 Broad Aim

The broad aim of this manual is to provide a technical understanding on pineapple post-harvest handling for trainers to train smallholders and small and medium scale enterprises (SMEs) in the post-harvest management of pineapples. This module therefore intends to help the horticulture smallholder farmers to gain knowledge on the following:

1. Maturity at harvest and the correct method of harvesting pineapples.
2. Harvesting and be able to practice harvesting of pineapples.
3. Causes of post-harvest losses of pineapple and their control.
4. Post-harvest handling of pineapples including sorting, trimming and grading, transportation and storage.
5. Post-harvest diseases of pineapples.
6. Preparation of pineapples for the local and international market to increase the farmers’ profitability

In agriculture, postharvest handling of fruit is the stage of fruit production immediately following harvest, including cooling, cleaning, sorting and packing. After the fruit is ready for harvest from the instance it is separated from its parent plant, the fruit begins to deteriorate. Postharvest treatment largely determines final quality, whether a fruit or fruit product is sold for fresh consumption. It also covers storage, transportation, and the intermediate processing of fruits into a different form for increased storage.

Both quantitative and qualitative losses occur in horticultural commodities between harvest and consumption. Qualitative losses, such as those in edibility, nutritional quality, caloric value, and consumer acceptability of fresh produce, are much more difficult to assess than quantitative losses. Quality standards, consumer preferences and purchasing power vary greatly across countries and cultures and these differences influence marketability and the magnitude of post-harvest losses.

1.2 Training Methodology

I.Set inductions

The trainer will set induction to place learners in a receptive frame of mind that will facilitate learning before explaining why learners need the course. This will involve welcoming of participants as well as giving a summary of the main themes to be covered in the module. The participants will be asked to give their expectations for the course as the facilitator writes them down. The trainer will then guide the participants in matching their expectations against the course objectives and discussing them.

II.Mini-lectures

The lecture method will be used to effectively introduce the pineapple sub-sector and its industrial potential. There will also be mini-lectures on the role of quality standards/specifications for enhanced market access, role of SPS and healthy food safety standards and the importance of using appropriate processing technologies. The trainees will be allowed to ask questions and give comments during each subtopic presentation.  The trainers will use practical examples that are relatable to trainees to build on their existing knowledge. Questions will also be asked by the trainers to spur up discussions and check on the trainees’ understanding of the principles. The lectures will be brief and delivered using power point presentations, flip charts, a copy of the training module and face to face discussions.

III.Small group discussions

The group discussions will be used to stimulate the critical analytical faculties of the trainees and generate interest on the topics. The learners will be divided into smaller groups and each group assigned a specific task to collectively discuss and derive possible solutions. Each trainee will be provided with a book to note down the discussions. One representative from the group will then present the main points to the plenary. The facilitators will give advice on the group presentations where necessary.

IV.Experiential sharing

The trainers will ask the trainees to share their experiences in pineapple growing, harvesting and processing.

V.Practicum

This will involve group discussions and practical sessions technology application to help the trainees understand and identify the various quality standards and give some of the remedies to the challenges faced in different countries.

2.0 Post-Harvest considerations

The pineapple fruit (Ananas comosus) should be harvested when it is firm and mature. Pineapples do not improve in eating quality after harvest. The sugar content does not increase after harvest. Therefore, the fruit must be picked at the optimum maturity and ripeness stage to suit the intended market. Pineapples are judged mature when they have reached full size and attained a nice yellow color, depending on variety. There is no single full proof indicator of the pineapple fruit maturity. However, several external and internal fruit characteristics can be used in combination as indices to determine harvest maturity.

The external indices include fruit surface color (in most cultivars), the extent of fruitlet (eye) flatness, and fruit size. The internal indices include percentage of soluble solids (sugar content) and appearance. The amount of fruit surface yellowing may be used as a guide for determining when to harvest in certain cultivars. Generally, the more yellow the surface area (less chlorophyll), the more mature and riper the fruit. The natural progression of surface color change during pineapple fruit maturation is from green to yellow to reddish brown.

If the fruit is allowed to remain on the plant until the full yellow stage it will have a flatter, less desirable flavor due to excess sugar content coupled with decreased acidity. The fruit will also be more susceptible to bruise damage at the full yellow stage. At very advanced stages of over-maturity, the surface color of the fruit changes to reddish-brown. Once the fruit has been harvested, the change in surface color and amount of yellowing should not be used as an indicator of fruit ripeness, since postharvest color changes are not correlated with eating quality.

The pineapple is a compound fruit comprised of numerous individual fruitlets. The fruitlets mature progressively from the bottom part of the fruit to the top. As the fruitlets mature, they become flatter. The extent of fruitlet flatness is usually a good indicator of overall fruit maturity. The bottom fruitlets are much flatter (and riper) than the top ones. Fruit which is ready for harvest should reach the appropriate size indicative of the cultivar. This is largely based on previous growing experience.

However, individual fruit size by itself is not a reliable index of harvest maturity. It should be used in addition to surface color and fruitlet flatness. Fruit maturity is highly correlated with soluble solids content. Pineapple fruit should have a minimum of 12% soluble solids near the base and 10% near the top. This is determined by taking two cross sections of the fruit; one at the point of its largest diameter near the base and another in the upper third portion of the fruit, and squeezing a few drops of juice from each cross section onto the prism of a hand-held refractometer.

The following are the quality indices for pineapple grading:

Ripeness (green to yellow) should be at least 75%. The sugar to acid ratio should be between 18 – 20. Sugar should be measured using a refractometer and acid measured as citric acid. The acidity of pineapple increases with ripening.

Uniformity of size and shape.

Freedom from blemishes caused by decay and injury.

Uniformity of the ripe skin color.

Tops (crown leaves) - green color, medium length, and straightness.

3.0 Harvesting

 Pineapple fruits are non-climacteric. They do not ripen or improve in eating quality after harvest. Their sugar content also does not increase after harvest. Therefore, the fruit must be picked at the optimum maturity and ripeness stage to suit the intended market. They should be harvested when at least 75% ripe (change of skin color from green to yellow) and firm.

Figure 1 Pineapple harvesting guidelines

Pineapples are judged mature when they have reached full size and attained a nice yellow color, depending on variety.  Pineapples are ripe and ready to harvest when the entire outer skin develops a yellowish color and a pineapple scent with the flesh having an orange-yellow color. It's best to allow the fruit to fully ripen on the plant because once picked, it won't get any sweeter, although the outer skin will continue to ripen.

 

It is difficult to tell when pineapple is ready to be harvested. A good, ripe fruit has a dull, solid sound. For fresh consumption, fruits are harvested at ‘one- or two-eyes ripe’ meaning that the bottom one or two eyes have turned color. However, the use of this harvest index depends on cultivar as well as the destination of the market. At 127 days after flower induction, the fruits normally reach the stage of 25% shell color which means a quarter of the fruit shows an attractive yellow-orange color. Harvesting is usually done between 7 and 14 days after the fruit has yellowed.

Figure 2 Pineapple harvesting techniques

 When harvesting ripe pineapple, use a clean knife or pruning snips and cut the pineapple from the stalk at the fruit’s base. Before cutting, wipe your blades off with rubbing alcohol so that you don’t transfer any diseases to the mother plant and the developing suckers or pups. If you harvest the pineapple before it totally changes color, you can allow the outer skin to finish ripening indoors at room temperature. Don’t refrigerate fruits that aren’t fully ripe because the cold interferes with the ripening process and chill damage can occur. You can store ripe pineapples in the refrigerator for about a week before using them.

 

The internal indices include percentage of soluble solids (sugar content) and appearance. The amount of fruit surface yellowing may be used as a guide for determining when to harvest in certain cultivars. Generally, the more yellow the surface area (less chlorophyll), the more mature and riper the fruit. The natural progression of surface color change during pineapple fruit maturation is from green to yellow to reddish- brown.

If the fruit is allowed to remain on the plant until the full yellow stage it will have a flatter, less desirable flavor due to excess sugar content coupled with decreased acidity. The fruit will also be more susceptible to bruise damage at the full yellow stage. At very advanced stages of over-maturity, the surface color of the fruit changes to reddish-brown. Once the fruit has been harvested, the change in surface color and amount of yellowing should not be used as an indicator of fruit ripeness, since postharvest color changes are not correlated with eating quality. Color stages are categorized as follows.

• CS1: all eyes green, no traces of yellow
• CS2: 5 to 20% of the eyes yellow
• CS3: 20 to 40% of the eyes yellow
• CS4: 40 to 80% of the eyes yellow
• CS5: 90% of eyes yellow, 5 to 20% reddish brown
• CS6: 20 to 100% of eyes reddish brown

Figure 3 Maturity indices or ripening stages of pineapple followed in different countries

Figure 4 Maturity indices or visual ripening stages of pineapple followed in different countries

4.0 Post-harvest handling

4.1 Cleaning

Pineapple fruits are quite perishable and should ideally be packed for the market within a day of harvest. The initial step in preparation for market involves cleaning and disinfection of the outside of the fruit. For the domestic market, this generally involves trimming of the stem at the base of the fruit to a length of 1-2 cm, removing any damaged or unsightly leaves in the crown, and a gentle dry brushing of the fruit surface to remove dirt and dust.

A similar protocol should be followed for the export market, with more emphasis placed on fruit uniformity and quality. Depending on the export market requirements, all fruits which are undersized, oversized, over ripe, under-ripe, damaged, bruised, or show fungal or insect damage should be discarded. The stem must be trimmed very close to the base and the crown has to be cut back to a length of 10 cm. The fruit then has to be washed in a soap solution and thoroughly scrubbed on the outside with a brush to remove all live insects.

The wash water should be properly chlorinated (150 ppm free chlorine) and maintained at a pH of between 6.5 to 7.0. In addition, an approved postharvest fungicide should be added to the wash solution to reduce decay. Bayleton and Benomyl are two postharvest fungicides commonly used. After washing, the fruit must be dried and inspected by a trained and certified inspector. Fruit approved for export by the inspector can then be packed. The wash water can also be chlorinated (500 – 600ppm) or sulphated (300 – 500ppm sodium/potassium metabisulphite) to increase the degree of disinfection against fungal spoilage.

4.2 Sorting and grading

Regardless of the market destination, the fruit should be sorted according to size, shape, firmness, external color, insect damage, and decay. Visibly damaged fruit should be rejected. Different markets have different quality requirements and the fruit should be graded to conform to the individual market standards. However, there are certain minimal requirements for pineapple fruit intended for any market. The fruit should:  

• Be clean and free of dirt or stains.
• Be ripe and firm be well shaped and have fully developed eyes (fruitlets).
• Be free of punctures, wounds, and cuts.
• Be free of sunburn, insect damage and decay.
• Have a well cured butt.
• Have a crown (crown can be single or multiple).

4.3 Waxing

For maximum potential shelf life, pineapple fruit are sometimes waxed after cleaning and drip drying. The wax is applied by dipping, fogging or spraying and serves to reduce water loss, gaseous exchange (absorption of oxygen and expulsion of carbon dioxide in respiration) and form an attractive sheen.  Several types of food-grade waxes are appropriate for pineapples, and they can be applied by dipping or spraying. The most commonly used waxes for pineapples are mixtures of carnauba and paraffin or polyethylene and paraffin. The type of wax chosen must be approved as food grade. The wax should be applied only to the fruit surface and not the crown, as many waxes cause injury to the crown. Beneficial effects of waxing include a reduction in fruit internal browning, less moisture loss and a shinier external appearance. The wax layer should not be too thick to limit gaseous exchange and induce anaerobic respiration.

4.4 Packing

All fruits packed in the same carton or container should be uniform in size, shape, and external color. Immature or over mature fruit should not be packed for export. It is important that the carton be properly ventilated and be of sufficient strength to withstand the rigors of distribution without collapsing. Weak cartons do not have sufficient physical strength to be stacked and result in major losses of the fruit upon arrival in the destination market. A carton with enough bursting strength should be used to avoid damage to the product during transport and handling.

A commonly used package in the international trade of pineapples is a full telescopic two-piece corrugated fiber board carton.  Top and bottom ventilation, in addition to side vents are required, particularly where sea shipments are used. A typical carton’s inside dimensions is 30.5 cm wide x 45 cm long x 31 cm deep. The preferred method of packing is to place the fruit vertically on the base, and then to place dividers between the fruits to prevent rubbing and movement.

With some cartons, this is not possible and fruits are laid horizontally in alternating directions. Where two layers of fruits are packed, a divider is required between the layers. Another commonly used export carton for pineapples is a single-layer corrugated fiber board carton.

4.5 Storage Conditions

1. Temperature

For maximum postharvest life, pineapple fruit should be cooled to 8°C as soon as possible after harvest and maintained at this temperature during transport to market. At this temperature, pineapples harvested at the quarter-yellow stage have a shelf life of approximately 3 weeks. Storage at higher temperatures will result in reduced shelf life, to as short as only a few days at ambient temperature (30-32°C). Fruits that are quarter yellow at harvest, gain about four additional days of shelf life for every 6°C decrease in storage temperature from 32° to 8°C.

On the other hand, pineapple fruits are subject to low temperature breakdown, also known as chilling injury, and should not be stored below 8°C. Sensitivity to chilling injury is related to the ripeness stage of the fruit, with mature green fruit being more susceptible. Internal tissue darkening and postharvest decay are typical symptoms of chilling injury. Pineapples harvested at more advanced stages of ripeness will have short market life. For example, fruit harvested at the half-yellow color stage will have about 10 days of storage life at 8°C followed by an additional week of market life.

1. Relative Humidity

Pineapple fruits are susceptible to wilting, shrinking and shriveling in low relative humidity (RH) storage environments. Most of the weight loss occurs through the leaves of the crown. The rate of transpiration and water loss from the fruit becomes increasingly greater with decreasing RH. Ideally, pineapples should be held at 90 to 95% RH.

4.6 Transport

Fruit should be transported carefully to market in order to minimize bruise damage and subsequent postharvest decay. Use of strong protective packaging will help to minimize bruise damage. Proper loading and stacking of the cartons in the bed of the transport vehicle is essential to protect the product. Sufficient air circulation through the sides of the cartons is necessary to avoid product re-warming during transport.

The pineapple cartons should be covered and never exposed to direct sunlight during transport. This will accelerate the rate of ripening and softening of the fruit, in addition to possible sunburn damage. In the absence of refrigeration, the fruit should be transported during the cooler part of the day.

4.7 Market handling

Today, pineapple consumers not only consider the physical appearance of the fruit to make a purchasing decision but also color, sweetness, aroma, fruit uniformity, size and country of origin or brand name. The proper time for harvest depends on its end use. Fruits for export should be cut when the fruit is completely developed but green. Pineapples for domestic market are cut mature but not fully ripened. Harvest is made manually; the fruit is torn to tear it from the peduncle. For transport, fruits are placed on leaves or a sawdust bed alternated with crowns, to decrease mechanical damage.

It is not advised to pile up too many layers of fruit. Harvested fruits are placed in trucks or wagons crown side down and up to 3 layers high. It is important to avoid fruit overheating either in the field as well as during transport and handling. Fruits are taken to the packing plant and then washed and coated with a mixture of a fungicide and a liquid wax.

For international markets pineapple is classified as: US Select (10 fruits of 1.4 to 1.8 kg), No. 1 (8 fruits of 1.81 to 2.0 kg) and No. 2 (6 fruits of 2.01 to 2.5 kg). Packing for export markets is done in a one-piece box made of telescopic fiber capable of holding 9 kg or 18 kg. In order to get better fruit strength during transport and prevent damages, pineapples with 1/4 ripening (yellow color at the base of the fruit covering 25% of the surface) are selected.

5.0 Causes and remedies to post-harvest deterioration in pineapple

Physical injury due to rough harvesting and handling – careful harvesting and handling.

Water loss leading to shriveling – humidity more than 80% in the store.

Respiration leading to loss of sugar and sweetness – control oxygen availability and increase CO₂ and control temperature.

Microbial growth (pineapples are acidic, bacteria cannot grow – only fungi that spoil by fermentation) - sanitation and treatment with chlorine and Sulphur dioxide as water dips or fumigation.

Consumption by higher animals (insects and rodents) – sanitation and fumigation.

Inadequate humidity - humidity to more than 80%.

Inadequate temperature regulation – low temperature including refrigeration.

6.0 Post-Harvest diseases & Pests

Pineapples are susceptible to a number of postharvest diseases. Decay is significantly higher in mechanically injured fruit, when poor sanitation practices are followed, or if postharvest cooling is not provided. The fused nature of the fruitlets means that the flesh of the fruit is not sterile and contains yeasts and bacteria. The most common diseases are black rot, fruitlet core rot, and yeasty fermentation.

I. Black Rot

 

Caused by the fungus Thielaviopsis paradoxa, black rot is typically the most common and severe postharvest disease of pineapple. It is also referred to as stem end rot, water blister, or soft rot and is characterized by a soft watery rot of the flesh. The severity of this disease depends on the amount of fruit bruising or wounding incurred during harvest and packing, the level of inoculum on the fruit, and the postharvest temperature. There is also a strong correlation between rainfall duration prior to harvest and postharvest incidence of this disease. Black rot does not occur in the field unless the fruit is overripe or injured.

Black rot usually starts at the point of detachment of the fruit (stem end), although it can readily infect bruised or other damaged areas of the fruit. Infection occurs 8 to 12 hours after wounding and symptoms begin as a soft, watery rot which later darkens due to growth of the dark-colored fungal mycelium and spores. Fungal growth is rapid at temperatures between 21-32°C.

Control of black rot is achieved by minimizing mechanical injury to the fruit coupled with appropriate postharvest sanitation (150 ppm chlorine wash plus fungicide treatment). The most effective postharvest fungicides for controlling black rot are thiabendazole, benomyl, and captan. For effective control, the fruit must be dipped in the fungicide within 6 hours after harvest. Storage of the fruit at 7°C is also necessary to inhibit growth of the fungus.

Figure 5 Black rot on pineapple fruit

 

 

II. Fruitlet Core Rot

This is a postharvest fungal disease-yeast-mite complex of pineapples caused by the fungi Penicillium funiculosum, Fusarium moniliforme var. subglutinas, the round yeast Candida Guilliermondi, the fruit mite Steneotarsonemus, and the red mite Dolichotetranychus floridanus. This disease complex is also called black spot or fruitlet brown rot. Symptoms appear as brown to black colored areas in the center part of individual fruitlets. The principal means of reducing the incidence of fruitlet core rot is by spraying the crop with an acaricide to control the mites which spread the disease.

Figure 6 Fruitlet core rot on pineapple

III.Yeasty Fermentation

Pineapple fruits are not sterile inside and contain many non-growing, but viable yeasts and bacteria. In damaged, overripe, and inter-fruitlet cracked fruit, existing yeasts may start to grow or new yeasts may invade. The yeast Saccharomyces is most often responsible for fermentation. Symptoms include fermentation, with bubbles of gas and juice escaping through cracks in the skin. The skin eventually turns brown and leathery and the internal flesh becomes spongy with a bright yellow flesh. Control strategies include careful handling to minimize mechanical injuries, prompt cooling and maintenance of optimum temperature and relative humidity throughout post-harvest handling, and treatments through application of fungicides, such as thiabendazole (TBZ).

7.0 Evaluation of training

This evaluation can be done as a quick written test during training of field staff. For farmer training, it can be done as a guided discussion of the answers to the questions by the trainer, in a plenary session. It is meant to assess the extent of learning:

1. Describe the maturity for harvesting of pineapples.
2. Explain why pineapples should not be harvested before ripening.
3. Describe the method of harvesting pineapples.
4. Describe sorting, trimming and grading of pineapples.
5. Describe cleaning and disinfection of pineapples.
6. Explain the reasons for waxing pineapples.
7. Describe the packaging of pineapples for the market and for storage.
8. Enumerate the causes of spoilage and post-harvest loss in pineapples.
9. Briefly discuss the storage of pineapples to maintain quality.