What is Fresh Produce Postharvest Physiological Disorder?

• Physiological disorders are stress responses in fresh produce that cause cellular necrosis and can be expressed in many ways.
• Fresh produce susceptibility to physiological disorders varies by genotype and can result from one or more environmental factors.
• The causal factors of postharvest physiological disorder can be preharvest and/or postharvest conditions.

Physiological disorders and pathological causes account for quality deterioration in one-third of fresh produce that is lost or wasted.  Therefore, recognizing physiological disorders in postharvest fresh produce and understanding their causes is crucial to prevent rejection and food loss in the supply chain. This article covers the basics of physiological disorders so stakeholders can understand the storage needs of their fresh produce.

Postharvest Physiological Disorder

Postharvest physiological disorders are abnormal changes in fresh produce caused by cellular necrosis due to altered metabolism in response to stress. Physiological disorders are non-pathological changes resulting from interactions between genotype and environment.

Wild plants lack physiological disorders because natural selection excludes genotypes not adapted to their environment. Crop cultivars, by contrast, show many physiological disorders because breeders select genotypes for specific traits (better quality and higher yield) and grow them under cultivated conditions.

As a result, fresh produce can lose color, texture, flavor, appearance, and nutritional value. Physiological disorders also make fresh produce more susceptible to microbial attack, decay, and enzymatic deterioration.

Disorders vary by intrinsic plant type, species, cultivar, and strain, and type of stress. For example, ‘Honeycrisp’ is more prone to bitter pit than other apple cultivars. Late-ripening apple varieties like Fuji are more susceptible to Watercore.

External environmental conditions that act as stress and produce postharvest physiological disorders can occur in preharvest and postharvest stages.

Physiological Disorders Caused by Pre-harvest Conditions

Preharvest disorders are also considered predetermined disorders linked to later stages of fruit development on the tree and can occur in storage without disruptions in postharvest environmental conditions. These can occur during growth and fruiting and are influenced by climate, agricultural practices, and harvest maturity. Nutrient availability and nutritional imbalances can also cause physiological disorders.

Harvest maturity

Fruit maturity at harvest is crucial not only for quality and shelf life, but also for susceptibility to specific physiological disorders. Apples harvested too early can develop bitter pit, but fruits harvested late and when overripe are more likely to develop chilling injury. Harvesting apples late in the season can also produce lenticel breakdown on the peel, appearing as circular dark spots that enlarge during storage.

Seasonal variations

Seasonal variations produce year-to-year differences in growing conditions. Hot summers can produce lenticel blotch pit if temperatures exceed 90°F (32.22 °C). This problem occurs in apple varieties such as Fuji, Gala, Honeycrisp, Golden Delicious, and Red Delicious. Symptoms include dry, brown, sponge-like patches near the calyx and lenticels on the flesh, which develop before harvest and become visible during packaging and storage.

Similarly, increased rainfall and sunlight also cause physiological disorders.

Orchard and farm management

Rootstock choice, nutrient and water supply, and crop load can cause physiological disorders.

• Lenticel breakdown in apples like Ambrosia, Fuji, Gala, and Honeycrisp can also occur due to irregular water supply, accompanied by high humidity and low wind.
• Tomatoes get cracks due to heavy rainfall or irrigation after a long dry period.
• Sun scald occurs due to exposure to extreme heat; see Table 1.
• Vigorous plant growth and late-maturity harvesting cause watercore, which affects the flesh as sorbitol-rich liquid accumulates in intercellular spaces. The condition starts developing preharvest, but symptoms appear after harvest. Slight Watercore can disappear in storage.
• Low crop load can also contribute to bitter pit in apples.

Correcting management practices, such as choosing the right rootstocks or applying timely foliar sprays, can improve growing conditions; for example, changing overall nutrition can prevent bitter pit in apples.

Mineral deficiencies

Providing adequate nutrition at the correct times is essential for proper development to maintain yield and quality. Nutrient uptake and transport, plant water relations, and fruit development can influence susceptibility to disorders.

Deficiency or too much of a nutrient can cause physiological disorders. For example, bitter pit in apples is dark, dry, sunken spots that are water-filled. It develops due to low calcium and boron, and excessive nitrogen, potassium, and magnesium in cells. Low calcium causes fruit softening in papaya and blossom-end rotting in tomatoes.

Table 1: “Physiological Disorders of Selected Fruits and Vegetables,” Mishra, V. K., & Gamage, T. V. (2007). Mishra and Gamage (2007). (Credits: Handbook of food preservation pp. 37-66)

Physiological Disorders Caused by Postharvest Factors

Postharvest conditions that cause physiological disorders include harvest and handling practices, temperature, and gas composition.

Low-Temperature Physiological Disorders: Chilling Injury

Table 2: “Chilling Injury of Fruits and Vegetables Stored above Freezing Temperatures,” Mishra, V. K., & Gamage, T. V. (2007). (Credits: Handbook of food preservation pp. 37-66)

Cool storage is often the most important and effective technology for maintaining fresh produce quality and extending shelf life. However, the low temperatures involved can cause chilling and freezing injuries in fresh produce, making it susceptible to microbial attacks and mechanical damage.

Chilling injury occurs in crops of tropical and subtropical origin that cannot tolerate cold. Table 2 shows the lowest temperatures that fresh produce can tolerate. Temperate apples and asparagus can be stored at 2°C, whereas tropical mangoes, bananas, and tomatoes should be stored at 13°C to prevent chilling injury. Hence, tropical and sub-tropical fresh produce should not be kept below 10°C.

Chilling injury can manifest as browning, pitting, scalding, darkening of the peel, flavor and texture changes, internal discoloration, a water-soaked appearance, and an inability to ripen. Symptom severity depends on the species, duration, and storage temperature.

In postharvest stages, precooling for adaptation, intermittent warming, controlled-atmosphere storage, and high relative humidity can reduce chilling injury in fresh produce.

Low-Temperature Physiological Disorders: Freezing injury

Table 3: “Relative susceptibility of fruits and vegetables to freezing injury,”Mishra, V. K., & Gamage, T. V. (2007). (Credits: Handbook of food preservation pp. 37-66)

Freezing injury occurs in fresh produce due to accidental exposure or storage at freezing temperatures (0°C), leading to ice crystal formation in cells and often irreversible damage. Freezing injury also causes osmotic stress and damages the cell membrane, leading to water loss and cell death.

Freezing injury depends on the produce type, variety, field temperature, and solute composition. Not all fresh produce is equally susceptible to freezing injury; some can tolerate a little freezing and recover after one or two spells. Susceptibility doesn’t depend on the freezing point between –0.1 and –1.8°C but on the season in which the crop is grown. Fresh produce grown in warm seasons is more susceptible to freezing injury than that from cold seasons. So, summer crops like berries, tomatoes, and lettuce are more prone to freezing injury than apples and cabbages; see Table 3 for susceptibility of common fresh produce.

Symptoms of freezing injury range from peel and internal tissue discoloration to pitting, blistering, and a water-soaked appearance. Fruits on the sides or openings of crates are more prone to freezing. The damage is most severe on the exposed surface.

Fresh produce with freezing injury decays faster, has a shorter shelf life, and deteriorates in quality. Freezing injury damage occurs during cooling, storage, transportation, and distribution.

High Temperature Physiological Disorders

Exposing fresh produce to high temperatures during postharvest can cause disorders and injuries that lead to burnt peel, pulp darkening, and an inability to ripen normally. Scalds in tomatoes and apples are examples of high-temperature damage.

Fresh produce can also develop disorders if exposed to room temperatures during ripening after a period of cool storage. As a result, consumers experience these problems more than packers or growers. These common physiological disorders include mealiness, wooliness, internal browning, black pit cavity, and low flavor. Stone fruit such as peaches, plums, apricots, prunes, and nectarines are most susceptible to these problems. Early-season peaches and nectarines are most susceptible to these disorders, with no seasonal variation in susceptibility seen in plums.

Ideal management techniques to prevent these disorders include cool storage, controlled-atmosphere storage above freezing temperatures, and picking at the correct maturity.

Mechanical Damage and Metal Contamination Disorders

Abrasion combined with contamination from heavy metals such as iron, copper, and aluminum can cause inking, staining, and black staining disorders in stone fruits, peaches, and nectarines. Abrasion damages peel cells, releasing anthocyanins and phenols that react with heavy metals to form dark brown and black coloration. Heavy metals can come from foliar nutrients, insecticides, and fungicides. The discoloration occurs as spots or stripes on the fruit peel.

Reducing abrasion by handling fruits gently and maintaining hygienic and clean conditions for handling and storage helps limit these disorders. In the preharvest phase, choose sprays without heavy metals.

Physiological Disorders due to Gas Composition

During long periods of storage and transport, normal gas concentrations can change because of fresh produce respiration and ripening, or because of storage in special controlled-atmosphere facilities.

Exposure to low oxygen and high carbon dioxide (CO2) can also cause some physiological disorders like internal browning. Ethylene also produces physiological disorders, for example, russet spotting in lettuce or changes in the internal appearance of kiwifruit. Ethylene can also aggravate or alleviate other physiological disorders. Ethylene increases rusty brown discoloration in lettuce, but the gas reduces hard-core severity in potatoes.

Susceptibility to these disorders depends on fresh produce variety, low crop load, and exposure to high CO2 at harvest time.

Physiological Disorders Due to Biochemical Changes

Several physiological disorders also result from enzymatic and chemical changes that can cause tissue softening, pigment loss, off-colors, off-flavors, and loss of nutritional value and taste.

Enzymes act as catalysts for many chemical processes in fresh produce, which cause these disorders; some examples are listed below:

• Tissue softening occurs when pectinases degrade pectin and cellulases and amylases break down cellulose and starch, respectively.
• Phenols undergo enzymatic oxidation, leading to browning on the cut surfaces of fruits and vegetables like apples, potatoes, bananas, and mushrooms.
• Lipase-mediated lipid degradation causes off-flavors in beans and peas.

Limiting Fresh Produce Physiological Disorders

The techniques needed to reduce or control the processes that trigger physiological disorders vary by problem. In many cases, controlled-atmosphere facilities with the correct gas composition, appropriate temperature and relative humidity (RH), and knowledge of harvest maturity are the answers. Sometimes, for freezing injury, you need to know internal chemical composition, like SSC.

Felix Instruments Applied Food Science supplies precision devices that can monitor the three gases oxygen, carbon dioxide, and ethylene, along with temperature and RH around the clock in controlled-atmosphere facilities. The company also offers fresh produce quality meters that check SSC levels in real time. The quality meters can also measure parameters such as dry matter content, internal and external color, and titratable acidity, which are used to assess harvest maturity. These technologies provide stakeholders with real-time quantitative data to apply research recommendations precisely and reduce physiological disorders.

Contact us to find out more about our gas analyzers and quality meters for your supply chain needs.

Sources

 

Fallik, E., & Ilic, Z. (2019). Positive and negative effects of heat treatment on the incidence of physiological disorders in fresh produce. Postharvest physiological disorders in fruits and vegetables, 111-126.

 

Hossain, M. I., Ferdousi, J., Saha, S. R., Rob, M. M., Afroz, T., Pramanik, S., … & Nath, D. D. (2024). Postharvest physiology of fruits and vegetables and their management technology: A review. Journal of Animal and Plant Sciences, 34(2), 291-303.

 

Kader, A. A. (1985). Ethylene-induced senescence and physiological disorders in harvested horticultural crops. HortScience, 20(1), 54-57.

 

Mahajan, P. V., Caleb, O. J., Singh, Z., Watkins, C. B., & Geyer, M. (2014). Postharvest treatments of fresh produce. Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 372(2017), 20130309.

 

Mishra, V. K., & Gamage, T. V. (2007). Postharvest physiology of fruit and vegetables. In Handbook of food preservation (pp. 37-66). CRC press. https://d1wqtxts1xzle7.cloudfront.net/62471899/Handbook_of_Food_Preservation20200325-50299-hu1jr6-libre.PDF?