Understanding Fresh Produce Spoilage: Five Causes and Prevention

• Various reasons are behind the fresh produce spoilage of the vast diversity of fruits and vegetables.
• Respiration, transpiration, microbial growth, damage and injury, and internal degradation are common causes.
• Product-specific temperature thresholds, relative humidity, ethylene, oxygen, and carbon dioxide are the five ambient conditions that determine the spoilage rate.
• Controlling ambient conditions helps to reduce spoilage and its effects on maintaining quality and extending shelf life.

Around 40–50% of the fruits and vegetables are lost or wasted from farm to plate. Fresh produce spoilage is alive, has a high water content, and is susceptible to spoilage that can be biological, physical, and chemical in nature. The highly perishable nature of fresh fruit and vegetables can affect and reduce postharvest quality and shelf life. Therefore, it is crucial to know the factors that cause spoilage and how postharvest management can reduce losses in the supply chain.

Fresh Produce Diversity

Fresh produce can be vegetables and fruits from several plant parts, such as leaves, stems, roots, and reproductive organs (flowers and fruits).

The difference in tissue type presents a diversity of freshness, quality attributes, and spoilage possibilities. Some are more prone to spoilage, like water-rich berries and lettuce, which are highly perishable and have a shelf life of only a few days. On the other hand, apples, onions, and potatoes can be stored for months. Therefore, spoilage characteristics are product-specific, and different ambient factors in the postharvest stage must be monitored for postharvest quality retention and shelf life extension.

Despite the differences, common spoilage mechanisms and atmospheric factors have been found across fresh produce. Identifying common mechanisms allows us to group similarly affected fresh produce for transportation and storage in shared environments without creating individual conditions for shelf life extension.

The five common mechanisms that cause spoilage in fruits and vegetables are respiration, transpiration, microbial growth, degradation of internal bio compounds, and damage and injury.

1. Respiration

Even after harvest, fresh produce tissue remains alive and continues to respire. During respiration, the tissue takes oxygen from the air to metabolize or break down the complex sugars for energy and produce carbon dioxide and water. The tissue uses energy to ripen, which eventually leads to senescence.

The metabolic process controlling sugar content, firmness, and aroma development depends on respiration. Higher respiration rates can deteriorate the quality parameters, which, beyond certain threshold limits, spoil the tissue. Therefore, higher respiration rates are linked with shorter shelf life and lower quality.

Fruits, vegetables, and nuts have different respiration rates. For example, berries have a high rate, bananas and tomatoes have a moderate rate, and dry nuts have the lowest respiration rate. Nonclimacteric food experiences similar respiration rates through fruit development. However, climacteric fruits’ respiration rapidly increases to reach a climacteric peak that triggers ethylene production and ripening.

Factors like high temperature that increase respiration rate must be monitored and controlled. Controlled atmosphere (CA) storage and transport and modified atmosphere packaging (MAP) maintain oxygen levels low to limit aerobic respiration but high enough to prevent the start of anaerobic decay. Without oxygen, anaerobic respiration will lead to fermentation and decay. Ethylene must be monitored as it can also indicate increased respiration.

2. Transpiration

Transpiration is the water vapor loss from fresh produce into the air through fruit skin or surface. Water loss after harvest, which is not replenished, results in product wilting, turgor loss, shriveling, and shrinking.

Transpiration reduces quality parameters like firmness, texture, glossiness, and taste until the product is unmarketable to consumers. The next effect is a reduction in nutritional quality and an increase in senescence. The extent of acceptable water loss is product-specific and varies from 3% to 10%. Transpiration also leads to weight loss and reduced profits for the supply chain without visible spoilage.

Transpiration impacts on quality are severe in leafy vegetables, those with a high surface area-to-weight ratio like bell peppers, and in more mature fruits. Also, nonclimacteric fruits are more susceptible to transpiration than climacteric fruits.

The transpiration rate is influenced by respiration, which produces intrinsic heat, ambient temperature, and relative humidity. Practically all fresh produce requires a high relative humidity of 95–100% for optimum storage, packaging, transport, and shelf life extension. Few vegetables, like onions and garlic, are managed in low relative humidity.

Figure 1: Moldy citrus, Pixabay. (Image credits: https://pixabay.com/photos/mould-mold-fruit-mould-rotten-6887246/)

3. Microbial Growth

Nutrient-rich fruits and vegetables with high water content provide ideal habitats for microbes, especially bacteria and fungi. The principal spoilage microorganisms are saprophytic and originate from fields, orchards, irrigation water, handling, and contamination.

All fruits and vegetables are susceptible to microbial spoilage, but to specific groups:

• Acidic fruits like citrus attract Penicillium spp.
• Berries are more likely to be affected by fungi like Botrytis cinerea and Rhizopus stolonifer.
• Vegetables like crucifers, peas, beans, onions, potatoes, carrots, lettuce, asparagus, and celery are spoilt by Pseudomonas spp and Erwinia carotovora

Microbial infection spoils flavor, appearance, firmness, texture, color, and safety. Spoilage caused by pathogenic bacteria can result in severe health consequences. Fungi produce poisonous substances like mycotoxins, especially aflatoxins, that harm people, livestock, and domestic animals. Aflatoxins are even carcinogenic.

Microbial growth is affected by ambient temperature, relative humidity, and gas atmosphere. Therefore, these environmental factors must be monitored and controlled to prevent pathogens and limit their effects on fresh produce quality. In CA facilities and MAP, elevated carbon dioxide levels are used for its antimicrobial qualities.

4. Degradation of Internal Components

Figure 2: “Change in total chlorophyll of lettuce (α) and broccoli (b) at 4 different temperatures (Ν=6) ( Ι=  LSD),” Manolopoulou & Varzakas, 2016. (Image credits: http://www.foodandnutritionjournal.org/?p=2916)

Chemical changes occurring for various reasons can lead to spoilage and quality deterioration in fruits and vegetables.

One primary reason for this is environmental factors such as temperature and relative humidity. These two ambient factors can degrade nutrients like ascorbic acid, phenols, flavonoids, and phytosterols.

High temperatures also degrade pigments like chlorophyll and anthocyanins, affecting sensory and nutritional quality. Chlorophyll breakdown due to high temperatures is well known and can even affect photosynthesis. Among vegetables, broccoli heads, and lettuce can lose their green colors. In Figure 2, it is apparent that higher temperatures cause faster and more chlorophyll degradation. However, tissue type and surface area matter; lettuce has more chlorophyll reduction and color change as it is exposed to more incident light.

Similarly, the molecular structure of anthocyanins will change due to heat, leading to browning in the presence of oxygen. For example, juices kept at room temperature will lose their color faster than juices in cold conditions.

Another factor changing internal chemical composition is the higher postharvest respiration rate.

Higher temperatures cause most changes, and refrigeration is used to control and limit internal degradation.

5. Damage and Injury

Fruit and vegetables are delicate and easily injured or damaged during harvest, handling, storage, transport, and packing due to falls, vibration, or pressure. Soft-skinned fresh produce like berries and tomatoes are more susceptible to damage.

The skin can remain intact during bruising or crack and break during severe injury. Bruising and mechanical injuries can deteriorate quality. Although the effects of bruising may not be immediately apparent, internal tissue undergoes physiochemical changes that spoil quality.

The stress of damage and injury increases the rate of respiration, transpiration, and ethylene production, speeding up the senescence of damaged tissue. Breaks and cracks in the skin also result in cellular leakage and increased microbial growth inside the tissue.

Another type of injury arises from chilling when storage temperatures are too low. Internal browning occurs in apples, pineapples, and pomegranates, while pitting occurs in papaya, oranges, watermelons, and cucumbers. The temperatures that cause chilling injury are product-specific, and it is necessary to know them, as chilling injury is entirely preventable with proper monitoring.

Monitoring Atmosphere with Sensor Technology

Since ambient temperature, relative humidity, ethylene, oxygen, and carbon dioxide thresholds are crucial for limiting postharvest spoilage effects, precision instruments should be used to monitor their levels for better control. The F-901 AccuRipe & AccuStore from Felix Instruments Applied Food Science can remotely monitor and control all the relevant ambient conditions. It is ideal for transport, storage, ripening, and degreening facilities.

Felix Instruments also produces portable gas analyzers for use anywhere in the supply chain to monitor various ranges of the gases ethylene, carbon dioxide, and oxygen:

F-940 Store It! Gas Analyzer

F-950 Three Gas Analyzer

F-960 Ripen It! Gas Analyzer

F-920 Check It! Gas Analyzer

While it is impossible to eliminate the causes behind fresh produce spoilage, controlling the five ambient conditions can reduce the process and its effects. Reducing spoilage will help increase food security, avoid carbon emissions, save natural resources used for agriculture, and make fresh produce supply chains more sustainable.

Sources

Enaru, B., Drețcanu, G., Pop, T. D., Stǎnilǎ, A., & Diaconeasa, Z. (2021). Anthocyanins: Factors Affecting Their Stability and Degradation. Antioxidants, 10(12), 1967. https://doi.org/10.3390/antiox10121967

 

Lamberty, A., & Kreyenschmidt, J. (2022). Ambient Parameter Monitoring in Fresh Fruit and Vegetable Supply Chains Using Internet of Things-Enabled Sensor and Communication Technology. Foods,11, 1777. https://doi.org/10.3390/foods11121777

 

Magoulas, A. (2016, Mar 25). Protecting Your Family from Food Spoilage. Retrieved from https://www.usda.gov/media/blog/2016/03/25/protecting-your-family-food-spoilage

 

Manolopoulou, E., & Varzakas, T. (2016). Effect of Temperature in Color Changes of Green Vegetables. Curr Res Nutr Food Sci ,4 (Special Issue Confernce October 2016). doi : http://dx.doi.org/10.12944/CRNFSJ.4.Special-Issue-October.02

 

Sonwani, E., Bansal, U., Alroobaea, R., Baqasah, A. M., & Hedabou, M. (2022). An Artificial Intelligence Approach Toward Food Spoilage Detection and Analysis. Front. Public Health 9:816226.doi: 10.3389/fpubh.2021.816226

 

USDA. (2013). Molds on Food: Are They Dangerous? Retrieved from https://www.fsis.usda.gov/sites/default/files/media_file/2021-02/Molds_on_Food.pdf