The secret to low post-harvest losses while growing vegetables

Mr Peter Kariuki, a tomato farmer in Githabai area in Kingop sorts out his tomatoes after harvest.The farm produce is starting to rot due to lack of market despite the fact that other parts of the country are experiencing drought. PHOTO BY JAMES MUNYEKI

Fresh vegetables are extremely perishable and have relatively short shelf lives. Being able to maintain a level of freshness from the field to the dinner table presents many challenges.

A grower who can meet these challenges, will be able to expand his or her marketing opportunities. Special skills are required for proper harvesting, handling, grading and packaging of vegetables to insure optimum produce quality at the marketplace.

Every producer should have products reach the end consumer as quickly as possible. Unfortunately, they have no control once the produce leaves their farm or packing sheds. However, maximum speed and efficiency in handling produce on the farm or at the shed will help maintain quality.

Consequently, a grower must be prepared to operate in advance of the actual harvest operation. Pre-harvest preparation should include lining up sufficient labour, supplies (containers and packaging items), cleaning the grading/packing shed, and determining if all equipment is operable.

Careful harvesting

Once the produce reaches harvest maturity, delays for any reason can result in major quality and crop losses. In addition, the nutritive content of produce is not static either. Biosynthetic and degradation reactions will even continue to occur during handling and storage.

Most post-harvest problems are management problems, and therefore, are people problems. With all vegetables, care should be taken to prevent injury due to harvesting and handling errors. A crucial time to be aware of this is during the harvesting operation. The hands of the harvest worker are the most important hands that ever touch the product. The truly skilled worker should not inflict injury to the product.

Broken skin and bruises reduce eye appeal and provide a ready access to decay organisms and enhance physiological breakdown. Although speed is an important consideration, excessive, unsupervised speed may result in a greater incidence of injury and quality losses. Therefore, time should be spent to properly train and monitor the performance of all personnel to insure maximum efficiency without sacrificing quality. Equally important is the need for periodic inspection and repair of all harvest containers, bulk bins and grading equipment to insure that these items are not causing injury to the produce.

Reduce injuries

Bruise damage will cause respiration rates and ethylene production to increase dramatically. This shortens the shelf life. There are several management practices that can reduce or eliminate harvest injury. Remove protruding nails or staples and smooth the rough edges on field containers. Harvest workers should not have long, sharp fingernails. Don’t overfill containers! Severe damage can result when stacked. Consider the time of day of harvest. Many products are more turgid in the early morning and bruise more easily.

Transporting

Transport from field to packinghouse can be another source of injury. Roads should be maintained in good condition. Drivers should exercise care and remember that they are transporting living material. The springs and shock absorbers on trucks and trailers must be properly maintained.

Dumping or unloading at the packing shed is also a trouble spot. Dry dumping is an option for certain produce items. If a wet dump is necessary, appropriate flow control out of the dumping area is needed to minimise bruising. The packing line itself should have as few drops and shears as possible. Shears that are essential should be designed properly.

Rapid cooling as soon as possible after harvest is essential to the maintenance of optimum quality. The first consideration at harvest is removal of the produce from direct sunlight, and secondly, to pre-cool as quickly as possible. Produce stored at less than optimum relative humidity will suffer excessive water loss and begin to shrivel. Many vegetables are unacceptable for marketing if weight loss reaches 5 per cent because of their undesirable appearance and textural changes that may accompany water loss.

Appearance plays a major role in vegetable sales success. Therefore, a grower should pay special attention to maturity, size, colour, shape, and freedom from blemishes and dirt when grading and sorting produce. Each package or display bin should contain produce having similar qualities. If vegetables are to be shipped, container size is an important consideration. A good rule of thumb is, the further a grower is from the market, the greater the marketing cost, and the greater the requirement for careful grading and packaging.

A good package should protect the product during storage and transit, facilitate temperature management, protect from water loss, be compatible with any special treatments required by the product, and be compatible to existing handling systems. One of the newest developments in packaging has been the use of materials that allow for modification of the atmosphere within the package, thus the term modified-atmosphere (MA) packaging. This involves the use of plastic films that allow depletion of oxygen and accumulation of carbon dioxide within the container, which will increase the shelf life of some commodities. The high cost of MA may be wasted if other aspects of post-harvest management are ignored.

To sum it up, quality cannot be improved after harvest, only maintained; therefore it is important to harvest the produce at the proper stage and size and at peak quality.

The writer is an expert and Consultant on Sustainable Agriculture and Agricultural Innovations.

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