Postharvest Technology for Non-Climacteric Fruits: Best Practices and Benefits

• Non-climacteric fruits have a short storage life as they must be harvested ripe.
• Several steps, like precooling and treatments, prepare the non-climacteric fruits for quality retention.
• Modified atmospheric packaging, controlled atmospheric storage, and different packaging systems maintain suitable environmental conditions during storing, transportation, and marketing to extend shelf life.

Ripening is the last stage of fruit development, where biochemical changes make them colorful, softer, sweeter, aromatic, and tastier. Senescence is the next stage after ripening, where the quality deteriorates. Postharvest technology is focused on retaining quality, prolonging shelf-life, and delaying decay based on ripening processes. Find out what postharvest technology is helpful in the case of non-climacteric fruits.

Non-climacteric Fruits and Vegetables

Fruits and vegetables ripen in two broad ways: non-climacteric and climacteric. The two types have significant differences in biochemical and physiological changes during ripening.

Figure 1.: “Schematic model of strawberry (A) and grape berry (B) developmental and ripening stages and the changes in hormone content from green to ripe fruit. Dotted areas represent hormone levels at strawberry achenes (A) and grape berry seeds (B). Filled areas represent receptacle/pulp or entire fruits” Perotti et al., 2023. (Image credits: https://doi.org/10.1093/jxb/erad271).

To plan for postharvest management of non-climacteric fruits, here are the salient features of its ripening processes that you must keep in mind:

• The fruit’s respiratory rate keeps decreasing from the beginning to the end of ripening.
• Autocatalytic ethylene production is not central to ripening. However, many hormones, such as ethylene, abscisic acid, auxins, and others, play a minor role by either promoting or inhibiting ripening. See Figure 1.
• Fruits must be allowed to fully ripen on the mother tree, as little or no postharvest ripening is possible.
• Fruit growth can continue even after ripening starts.
• Ethylene produces over-ripeness, senescence, and decay, just as in climacteric fruits.

Examples of non-climacteric fruits are strawberries, lychee, cherries, grapes, citrus, etc.

Postharvest technology aims to restrict the quality deterioration of fresh produce between harvest and consumption due to spoilage. The measures start immediately after harvest and cover environmental changes, packaging, storage, and transport. Postharvest technology for non-climacteric fruits is particularly crucial because they are harvested ripe and are highly perishable.

The farms of non-climacteric fruits meant for fresh consumption or processing are close to large markets or factories to sell before quality falls. The harvest slated for far away markets enters the cold chain.

1. Precooling

The first step for both local and long-distance markets involves precooling. The process removes field heat, preferably within an hour of harvest, to reduce temperatures to 4°C. Precooling slows respiration, ripening, water loss/transpiration, senescence, and decay, all of which adversely affect quality. Delays in precooling can reduce shelf-life, sugars and vitamins, freshness, and firmness.

Commercial precooling methods include room cooling, hydro cooling, forced-air cooling, vacuum cooling, and contact ice cooling.

2. Treatments

Following precooling, various physical and chemical treatments are used to prepare fruits for more extended storage by reducing microbial infections and pest attacks.

Physical Methods

Among the physical methods used are low and high temperature and UV irradiation.

• High-temperature treatments reduce insect pests, pathogen infection, and fruit ripening and increase resistance to chilling injury to increase shelf-life.
• Low-temperature treatments involve cold storage of fruits and vegetables to preserve texture, flavor, and color. The treatment can extend shelf-life by months. For example, strawberries stored between 18-20°C can last 6-7 months without quality loss.
• Irradiation with UV-C prevents fungal decay and improves phytochemical content, sugar levels, and stress resistance to enhance quality.

Physical methods, which are non-toxic, are preferable to chemical treatments.

Figure 2.: “Fruits treated with coatings have prolonged shelf life: (a) untreated fruits have 10 days of shelf life with improper color development; and (b) shelf life of fruits treated with coatings on 16th day and (c) with coatings on 21st day,” Kuchi and Sharavani 2019. https://www.intechopen.com/chapters/65574

Chemical Treatments

Fumigation with gases, liquid dips, and solid coatings are common treatments for fresh produce. The benefit will depend on the chemical and the species.

• Fumigation uses several gases like methyl bromide, nitrous oxide, hydrogen sulfide, etc. For example, in strawberries, methyl bromide is effective against pests, nitrous oxide minimizes ethylene concentration to retard senescence, hydrogen sulfide acts as an antioxidant to reduce stress effects, etc.
• Dips or additives to external application solutions of growth regulators like salicylic acid or nutrient calcium can be beneficial. Salicylic acid can improve nutritional value by increasing ascorbic acid, antioxidants, and total soluble solids and preventing fungal infections. While calcium improves firmness and reduces physiological disorders in strawberries.
• Coatings can protect highly perishable and tropical fruits by blocking water loss, gas exchange, and microbes. Standard coatings are chitosan, starch-based, and botanicals. See Figure 2. Fruits remain fresher, retain color and texture, and have better shelf and storage life through coating use.

Figure 3.: “(a) Strawberries packed in corrugated fiberboard boxes (side view) and (b) strawberries packed in corrugated fiberboard boxes with laminated polyethylene (top view),”

Storage

In addition to treatments, the storage conditions can help prolong the postharvest lifespan when done correctly. Two methods are used. One by altering the environment and the other through packing.

Packaging

The fresh produce must be packaged immediately after precooling. Non-climacteric fruits are highly perishable and soft since they are harvested ripe. Therefore, special care is needed to prevent bruising and damage through physical impact or vibrations during transport or storage.

The first packaging can be films to protect fruits and prevent damage and water loss. The films can be perforated cellophane sheets, low-density polyethylene bags, polyvinyl chloride, or hydrophilic starch films.

These packs are then kept in outer cardboard boxes of appropriate size and should be perforated for cold air circulation to maintain low temperatures. See Figure 3. Packaging boxes should be sturdy enough not to lose shape when moist or due to stacking.

Storage Environmental Conditions

Modified-atmosphere packaging (MAP) and controlled-atmosphere (CA) storage rooms achieve altered conditions. The usual proportions of oxygen and carbon dioxide are changed. Ethylene levels are also monitored to prevent overripening and senescence of non-climacteric fresh produce.

• Carbon dioxide content is increased to reduce respiration rate, which can trigger ethylene even in non-climacteric fruits. Higher CO2 levels will also improve firmness and prevent fungi and bacteria infection. The exact concentrations of CO2 and O2 will differ with species.
• Ethylene management is essential to keep concentrations low. Even though ethylene is unnecessary for ripening, some non-climacteric fruits respond to ethylene production. Moreover, ethylene is the hormone responsible for senescence and decay in all fruits. Maintaining levels below 0.005 µL/L can extend shelf-life by 60% in 23 fruits and vegetables. Most commercial storage and transportation conditions have ethylene above 0.005 µL/L so ethylene scrubbers will be necessary.

CA and MAP are well-established for storing and transporting cherries, berries, strawberries, etc. Unlike climacteric fruits, ethylene is not used for artificial ripening, but the phytohormone can degreen citrus.

Precision Tools

Gas analyzers monitoring the levels of the three gases in MAP and CA can be a great asset during storage and transport. Felix Instruments Applied Food Science produces several gas analyzers with varying gas ranges and resolutions for real-time measurement and analysis of CO2, O2, and ethylene that are suitable for changing needs in the cold chain. The firm also produces a Near Infra-red spectroscopy-based  F-750 Produce Quality Meter that can be used for non-destructive estimation of various quality parameters like ripeness, total soluble sugars, titrable acidity, and external and internal color.

The two kinds of precision tools can help stakeholders maintain proper storage, packaging, and transport conditions to improve quality and extend shelf-life to reduce food loss. Postharvest technology for non-climacteric fruits is essential in this context, as it can significantly enhance the preservation of these fruits from farm to table.

Sources

Ku, V. V. V. , Shohet, D. , Wills, R. B. H., & Kim, G. H. (1999). Importance of low ethylene levels to delay senescence of non-climacteric fruit and vegetables. Australian Journal of Experimental Agriculture 39, 221-224.

Kuchi, V. S., & Sharavani, C. S.R. (2019). Fruit Physiology and Postharvest Management of Strawberry. IntechOpen. doi: 10.5772/intechopen.84205

Perotti, M. F., Posé, D., Martín-Pizarro, C. (2023). Non-climacteric fruit development and ripening regulation: ‘the phytohormones show,’ Journal of Experimental Botany, 74 (20), 6237–6253, https://doi.org/10.1093/jxb/erad271