August 22, 2023 at 6:41 pm | Updated August 28, 2023 at 3:58 pm | 7 min read
- Bruising occurs during harvest and postharvest operations like sorting, grading, and packing. As demand for fresh fruits rises and operations get mechanized, the bruising impact on fruit quality increases.
- Bruising damage is initially not visible but can spoil the appearance and several physiochemical parameters to downgrade quality and weight, leading to considerable economic losses.
- Environmental factors like temperature and relative humidity during handling, storage, transportation, and ripening can influence bruise susceptibility.
Bruising is the most common mechanical damage which fruits suffer. Bruising is a significant purchase barrier, more important than pricing in influencing consumer choice. Bruising also has other severe consequences on fresh fruit quality. The economic impact of fruit bruising on the fruit industry is substantial. Understanding bruising susceptibility can help stakeholders develop strategies to reduce the problem.
What is Fruit Bruising?
Bruising is the damage to subcutaneous fruit tissue caused by external force without any skin rupture. The external pressure and stress cause cell breakage and distortion of cells. Further cell membrane breakage leads to the release of enzymes into intercellular spaces. The discoloration of the injured tissue can identify bruising.
Fruits get bruised when impact and compression forces are applied to a small part of fruits. It could be due to fruit drop, compaction of fruit against rigid container walls, or with another fruit.
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Soft-skinned fruits like strawberries, blueberries, cherries, grapes, peaches, prunes, apples, and pears are more prone to bruising. Bruising is usually an issue for the fresh fruit market and doesn’t usually matter for processing. However, like olives, bruising can also affect the processed product quality in some cases.
Downgrading of bruised fruits’ quality leads to rejection and economic losses along the supply chain. Around 30–40% of produce is affected by bruising and other mechanical damage like cuts, splits, punctures, or abrasions.
Bruise damage is not immediately visible, see Figure 1; the internal effects that produce severe external defects and quality deterioration develop over time and are discussed below.
Figure 1: “RGB images of bruised ‘Golden Delicious’ apples; bruises are mostly invisible to an eye and digital camera,” Nturambirwe et al. (2021). (Image credits: https://doi.org/10.3390/s21154990)
Bruising Impact on Internal Fruit Quality
Bruising damage affects several physiological processes and changes physiochemical quality parameters and nutritional value.
When cell content is released into intercellular spaces due to cell damage, some cell constituents, like phenolic compounds, can undergo oxidization and turn brown. Internal browning is one of the classic symptoms of bruising that develops even with slight tissue damage.
Alterations in Physiological Processes
Bruise damage significantly affects physiological processes like fruit respiration, ethylene production, and transpiration.
- The respiration rate is increased, for example, in sweet potatoes by 72%.
- This rise in respiration and the bruising stress increase production of ethylene, a phytohormone responsible for ripening and senescence. Ethylene is also released in response to pathogenic infection.
- Faster ripening in the bruised spots can follow increased respiration and ethylene production rates, reducing the shelf life of fruits.
- Bruising leads to significant moisture loss, reducing fruit freshness and shriveling and weight loss. For example, a single bruise on an apple increased the moisture loss rate by up to 400%.
- Senescence is more in bruised fruits due to postharvest rots and decay than in un-bruised fruits. It can result from microbial spoilage or get accelerated due to high ethylene production.
Fruit bruise damage can also lead to microbial spoilage of the bruised tissue and quality losses. Pathogens that cause decay enter more easily through damaged tissue and spread to the whole fruit. Depending on the pathogen, fungal or bacterial, it can cause fermentation, mildews, or rot. The quality of the injected fruit is downgraded, and it can infect neighboring healthy, undamaged fruits. Moreover, infected fruits will be rejected.
All bruised fruits are not unsafe, especially those with fresh and minor bruises, but over time bruises can be infected and contaminated.
Change in Physiochemical Parameters
Bruising can change the concentrations of crucial quality attributes like soluble solid content (SSC), titrable acidity, and color. SSC can increase (as in bananas), decrease (in tangerines), or remain unaffected (as in pomegranates) due to bruising depending on species. SSC can increase due to faster ripening, where starch is converted to sugars.
The sugar-to-acidity ratio can also alter, affecting fruit taste. Moreover, there can also be a reduction in the production of nutraceuticals such as vitamin C than in unbruised tissue, so the nutritional quality of fruits and vegetables like tomatoes can fall.
External Sensory Changes
Bruising changes sensory qualities like firmness, external color, and weight loss.
Loss in Firmness: Bruising damage accelerates the loss of firmness. The extent of firmness loss is also influenced by storage temperature, duration, and drop height increase.
Weight Loss: Increased respiration rate increases the fruits’ temperature and accelerates moisture content loss. As a result, weight loss is a common effect of bruising damage, especially in long storage duration, even under low temperatures. Weight loss cause shriveling, affecting customer preference and reducing economic returns for fruits sold by weight.
Color: Outer skin color changes due to more production of pigments like lycopene and carotenoids, depending on the species, turning bruised areas red to brown. Color changes are due to a reduction in greenness because the injured areas produce more ethylene, which leads to faster ripening of these areas to brown.
The effects of bruising can be controlled or worsened by environmental conditions and maturity stages of the fruits at bruising. Knowing how bruising occurs at several stages, from farms to retailers (See Figure 2), and how they develop can help to control bruising damage.
How Do Fruits Get Bruised?
While some causes are obvious, a complete understanding of harvest, postharvest handling, and environmental storage conditions influencing bruise damage susceptibility is still lacking. Below, some of the main factors leading to and compounding bruising are discussed.
Figure 2.: Bruising can occur at all stages of the fresh fruit supply chain from orchard to retail stores” Hussein et al. 2020. (Image credits: https://doi.org/10.1016/j.hpj.2019.07.006)
Fruits are more prone to bruising during harvest. For example, 35% of apples suffer bruising during harvest and transport.
Harvest time, method, and season affect bruising damage susceptibility.
- Time of day: Fruits harvested in the morning suffer more bruising damage than when harvested in the late afternoon. During warmer parts of the day, fruits have less turgor. They are likely to suffer wilting and shriveling, so the same impact energy has less effect than on more hydrated morning fruits, for example, bananas.
- Season: Fruits harvested later in the season suffer more bruise damage than at the beginning.
- Harvest method: Mechanical harvesting produces more bruises than handpicked fruits, such as plums and prunes. For instance, handpicking bruised 9-50% of olives while straddling a mechanical harvester could bruise 91-100% of the olives.
Using proper harvesting equipment and correct techniques by trained personnel can reduce the incidence and severity of bruising.
Post Harvest Handling
As demand for fresh fruits increases, mechanization is used in postharvest handling operations for sorting, grading, packing, and transporting. As in harvesting, mechanization increases bruising susceptibility. Fruits get bruised due to fruits dropping on other fruits in bins and on hard surfaces in sorting and grading machines. Improper equipment, packaging, and supervision are other factors that increase bruising.
The bruising during harvest and postharvest stages also depend on the fruit maturity, ripeness, and duration after harvest. In addition, environmental conditions during storage and transport are also crucial in influencing changes to physiological and biochemical quality parameters.
Environmental Factors Contributing to Bruising Susceptibility
The environmental conditions influencing bruising susceptibility are temperature and humidity.
Temperature: Temperature is one of the significant factors affecting bruising susceptibility during handling, as it influences fruit tissue flexibility. Higher temperatures cause loss of cell moisture content and lower fruit turgor, so there is less bruising damage. Hydrated fruits have more turgor, making them stiffer, less elastic, and susceptible to even slight pressure. For example, sweet cherries should be handled between 10- 20°C in the postharvest stages to minimize bruising.
However, the lower temperature during storage and ripening is better for reducing bruising susceptibility by sinking the rate of metabolic activities, like respiration and ethylene production, that change fruit texture and physiological processes. Therefore, cherries should be cooled to 0°C within a few hours after harvest.
Humidity: Humidity could have an influence depending on species and cultivars. For example, ‘Golden Delicious’ and ‘Golden Supreme’ apple cultivars had 0.07% and 0.04% less bruise susceptibility in the low relative humidity (RH) of 35-49% than at high or 100% RH. However, high, low, or medium RH did not affect bruising damage in ‘Williams’ apples during storage and ripening.
Storage Duration: During postharvest operations, freshly harvested fruits are more susceptible to bruising than those cold stored longer. Extended storage duration changes the texture of fruits and increases skin resistance, which decreases the amount of energy absorbed by the fruit tissue.
Measuring Bruising Impact on Fruit Quality
Figure 3: “Bruise measurements (A) bruise diameter and (B) bruise depth,” Pathare and Al-Dairi 2021. (Image credits: https://www.frontiersin.org/articles/10.3389/fsufs.2021.658132/full)
Given the substantial losses due to quality downgrading through bruise damage and the possible gains in developing strategies to reduce the problem, detecting, measuring, and analyzing bruise damage is vital.
Bruises can be measured by:
- assessing external bruise area (BA), bruise volume (BV), and bruise susceptibility (BS), see Figure 3
- estimating internal physiochemical changes in SSC, external and internal color, firmness
There are destructive and non-destructive means of measuring bruises. Some of the non-destructive and non-invasive methods are as follows:
- External bruise measurement is possible by hyperspectral imaging, nuclear magnetic resonance imaging, and thermal imaging.
- Internal physiochemical parameters like SSC, titrable acidity, and external and internal color can be measured in real-time by small portable near-infrared (NIR) spectroscopy-based tools like the F-750 Produce Quality Meter and F-751 series manufactured by Felix Instruments Applied Food Science.
Reducing Bruising Damage
There are many critical points causing bruising and many factors determining bruising susceptibility. That makes it challenging to control bruising. But it can provide opportunities too. Careful handling of fruits and mindful maintenance of environmental conditions to minimize the impact of bruising on fruit quality can be achieved through personnel training. Careful fruit handling and environmental maintenance can minimize bruising impact on fruit quality through personnel training.
Crisosto, C. H., Garner, D., Doyle, J., & Day, K. R. (1993). Relationship between fruit respiration, bruising susceptibility, and temperature in Sweet Cherries. HortScience, 28(2), 132–135. https://doi.org/10.21273/hortsci.28.2.132
Hart, J. and Levin, R. (2018, September 25). Is bruised produce safe to eat?. MSU Extension. https://www.canr.msu.edu/news/is_bruised_produce_safe_to_eat
Hussein, Z., Fawole, O. A., & Opara, U. L. (2020). Harvest and postharvest factors affecting bruise damage of fresh fruits. Horticultural Plant Journal, 6(1), 1–13. https://doi.org/10.1016/j.hpj.2019.07.006
Opara, U. L., & Pathare, P. B. (2014). Bruise damage measurement and analysis of fresh horticultural produce—a review. Postharvest Biology and Technology, 91, 9–24. https://doi.org/10.1016/j.postharvbio.2013.12.009
Pathare, P. B., & Al-Dairi, M. (2021a). Bruise damage and quality changes in impact-bruised, stored tomatoes. Horticulturae, 7(5), 113. https://doi.org/10.3390/horticulturae7050113
Pathare, P. B., & Al-Dairi, M. (2021b). Bruise susceptibility and impact on quality parameters of pears during storage. Frontiers in Sustainable Food Systems, 5. https://doi.org/10.3389/fsufs.2021.658132
Nturambirwe, J. F. I., Perold, W. J., & Opara, U. L. (2021). Classification Learning of Latent Bruise Damage to Apples Using Shortwave Infrared Hyperspectral Imaging. Sensors (Basel, Switzerland), 21(15), 4990. https://doi.org/10.3390/s21154990
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