RED CABBAGE POST

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.

Proper and timely harvest and post-harvest handling are very important in the maintenance of high quality of marketed cabbage. The red cabbage (usually purple in color) is a highly perishable product and therefore begins to deteriorate soon after harvest. The maturity of the red cabbage at harvesting is an important factor in determining good eating quality.

The deteriorative factors include water loss (transpiration), respiration, microbial damage leading to rotting, consumption by higher animals like rodents and physical injury from harvesting and transportation. These deteriorative factors cause the highest post-harvest losses in cabbage. Proper harvesting and post-harvest handling are therefore very important to obviate quality deterioration.

Post-harvest handling includes measures to prevent water loss – packaging and storage humidity, prevent respiration – packaging and temperature reduction, microbial damage – sanitation and use of antimicrobials, and prevent physical damage. Sorting, trimming and grading are also important in making red cabbage market-ready.

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.

At the end of this training the horticulture smallholder farmers are expected to achieve the following:

  1. Ability to recognize maturity of red cabbage at harvest.
  2. Demonstrate the proper harvesting technique for cabbage.
  3. Possess knowledge of the deteriorative factors for the cabbage and methods of control to reduce losses.
  4. Acquire knowledge of sorting, trimming and grading of the produce for the market.
  5. Gain knowledge and be able to package the cabbage for the market and storage.
  6. Be able to describe the storage conditions for the cabbage.

 

2.0      Pre-Harvest considerations

A mature head of cabbage (Brassicaceae Cruciferae) generally weighs between 3 to 5 pounds, depending on the variety. Cabbage should be harvested promptly when the heads are firm and mature. Delaying harvest even for a few days beyond maturity can result in split heads and increased incidence of field disease. Unharvested cabbage may develop significant infestations of Alternaria leaf spot and downy mildew, particularly during wet weather. These diseases can be spread through normal harvesting and handling. Harvesting immature heads, on the other hand, reduces yield. The immature heads are also too soft to resist handling damage and have a shorter shelf life than mature heads.

Field workers have a major influence on quality. They should be made aware of the importance of good sanitation practices, be properly instructed in selecting for maturity, and be cautioned against rough handling of cabbages. An experienced picker should be able to determine the level of maturity quickly and consistently by feel and the size of the head. The head is harvested by bending it to one side and cutting it with either a Russel knife or a common butcher knife. Harvesting knives should be sharpened frequently to reduce effort and lessen picker fatigue. The head should not be removed by snapping or twisting it since this practice damages it and results in inconsistent stalk length and trim. Broken stalks are also more susceptible to decay.

3.0      Harvesting

Harvesting should be done when heads reach the desired size and firmness. Overly mature heads will split. For most cabbage varieties, maturity is achieved in around 70 days from planting. Most early varieties will produce heads weighing between 1- to 3-pounds. To harvest, cut each cabbage head at its base with a sharp knife. Remove any yellow leaves (retain loose green leaves; they provide protection in storage) and immediately bring the head indoors or place it in shade. Alternatively, pull up the plant (roots and all) and hang it in a moist cellar that reaches near-freezing temperatures.

To get two crops, cut the cabbage head out of the plant, leaving the outer leaves and root in the garden. The plant will send up new heads. Pinch off those until only four or so smaller heads remain. Harvest when tennis ball-size (perfect for salads!). After harvesting, remove the entire stem and root system from the soil to prevent disease. Only compost healthy plants; destroy any with maggot infestation. 

The following harvesting indices should be observed:

  • Maturity Period: 2.5 – 4 months after transplanting depending on variety and location.
  • Maturity: when the head becomes compact and firm.
  • Harvest the heads before they pass the prime stage to avoid cracking or splitting.
  • Cut heads at the base and leave the outer leaves to protect the head and keeping it fresh.
  • Avoid bruising the head as it encourages rotting.
  • Yields: 15 – 68 tons per acre (depending on the variety and crop husbandry).
  • Varieties with firm solid heads have good storability.
  • Harvest early in the morning to take advantage of the low temperatures and transfer to a cool place for temporary storage to avoid accumulation of field heat.

4.0 Post harvest handling

4.1 Sorting, trimming and grading

Sorting is done to separate poor produce from good produce. It helps to further classify the good produce based on other quality parameters, such as size. Trimming is done on red cabbage, unlike the white cabbage to remove the lower leaves and excess stem to leave a compact head.  Systematic grading coupled with appropriate packaging and storage will extend postharvest shelf life, wholesomeness, freshness, and quality, and will substantially reduce losses and marketing costs. Cabbages are usually graded mainly based on:

  • Size
  • Freedom from defects such as insect, disease, and mechanical damage

Grading can however also be based on:

  • Shape
  • Color
  • Weight (and maturity) related to size
  • Maturity

4.2 Packing

Packaging of cabbage may vary from wholesale to retail. It can be done in one layer wooden or plastic crates, ventilated cardboard boxes, or perforated polythene bags. As much as possible heavy compacting should be avoided by limiting the size of the package. Heads of cabbage can also be packaged as unit wraps using cling films which helps to minimize water loss. They are then packed in a secondary package like a fiberboard carton or a crate.

4.3 Storage

To maximize the storage potential of cabbage, it should be kept as cool as possible including without freezing. Heads should be trimmed to remove loose wrapper leaves prior to storage. Defective cabbage showing signs of insect damage, sunscald and bruising should be discarded or marketed prior to storage. Harvesting cabbage as soon as mature will prevent cracking of heads.

Cabbage cultivars vary in their ability to store for extended periods of time. Dense-headed cultivars which mature slowly store for longer periods. Cabbage intended for long-term storage (5-6 months) should be stored at 0°C and 98-100% relative humidity.

A number of physiological disorders occur in stored cabbage. Oedema, is characterized by rough, brown dots on the undersurface of leaves caused by erratic watering during the growing season. Black speck and pepper spot occur as numerous dark spots on leaves which develop a few weeks into storage. Freezing damage results in water-soaked leaves which usually lead to decay. Vein streaking also occurs during storage of cabbage, and is characterized by brown marks on the midrib of outer leaves.

These physiological disorders can cause significant economic losses. Their incidence varies with growing conditions and cultivar. Some of these disorders can be prevented by putting up controls.  Cabbage to be stored should be mature and disease-free and should not have been exposed to prolonged frost or cold. Further trimming may be necessary, mainly to remove the discolored butt upon removal from storage.

4.4 Transport

Care must be taken that trucks are not overloaded as the bottom layers of produce would be crushed. Generally, the produce should be covered with a sheet to prevent frosting or desiccation, but on warmer days, when sweating and heating might occur, the sheet should be left off. Compacting when loading onto a truck should be avoided. Gunny or plastic bags are inappropriate unless the loading is a monolayer of bags.

5.0 Causes and remedies to post-harvest deterioration of red cabbage

  • Consumption by higher animals like insect and rodents - protective packaging.
  • Loss of water leading to weight loss, wilting and shriveling – water barrier packaging and control of RH to more than 85%.
  • Growth of microorganisms leading to rotting - cleaning and sanitation.
  • Physical injury during harvesting, handling and transportation – care in handling along the chain.
  • Respiration leading to loss of sweetness in the sweet varieties – limit gaseous exchange.
  • Physiological damage in refrigerated storage due to chilling injury (takes time to manifest with symptoms similar to bacterial damage – no use of very low temperatures in refrigerated storage.

6.0      Post-Harvest diseases & Pests

I. Botrytis cinerea (Botrytis),

This is the causal agent of grey mould, which is a prevalent fungus found on stored  cabbage. It is the main reason for loss of cabbage intended for long-term storage. Botrytis is an opportunistic pathogen that easily invades weak, damaged, or senescent tissues; therefore, mature healthy leaf tissues of plants are more resistant to Botrytis attack. In the field, the use of fungicides is a common practice to kill pathogens. During post harvest handling, storage under the controlled atmosphere is favorable to reduce its occurrence.

Figure 1 Botrytis cinerea on red cabbage

 

II.Sclerotinia

 This is caused by the fungus Sclerotinia sclerotiorum which can cause serious losses in the field, in storage, and under transit and market conditions. S. sclerotiorum is widely distributed in relatively cool and moist areas throughout the world. Although cabbage can be infected during any growth stage, most plants are infected in the field after midseason.


Infections may occur on the stem at the soil line, on the leaves at their bases, or where the foliage comes in contact with the soil; but most infections originate at the top or on the sides of midseason to mature cabbage heads in New York State. The infections begin as tan, water-soaked, circular areas, which soon become covered by white, cottony fungal growth. The host tissue becomes soft and watery as the disease progresses.

The fungus eventually colonizes the entire cabbage head and produces large, black, seedlike structures called sclerotia on the diseased tissue.  Implementation of a single control measure will not be effective against white mold because the fungus that causes the disease (S. sclerotiorum) is an aggressive pathogen with a wide host range. White mold on cabbage can be managed most successfully by combining cultural practices that discourage disease development. For example, growers should avoid planting cabbage in fields that are surrounded by dense woods that will restrict air circulation and subsequently delay drying. Rows should be planted in the direction of the prevailing winds to promote air drainage and drying of plant and soil surfaces.

Figure 2 Sclerotinia on red cabbage

 

 

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 index for harvesting red cabbage.
  2. Describe the harvesting methods for red cabbage.
  3. Explain why the vegetables are preferably harvested early in the morning.
  4. Describe the sorting, trimming and grading of red cabbage.
  5. Describe the precooling and disinfection of the vegetable and give its importance.
  6. Briefly discuss the packaging of red cabbage for the market, transportation and storage.
  7. Enumerate the causes of post-harvest spoilage and loss of red cabbage and methods of control.
  8. Describe the storage of red cabbage to maintain quality.