Main Causes of Food Deterioration: Biological and Chemical Factors

Food doesn’t stay fresh forever. From the moment it is harvested, slaughtered, or processed, a countdown begins. A range of biological, chemical, and physical factors start working – sometimes individually, often together – to break down the colour, flavour, texture, nutritional value, and safety of food. According to the FAO, meat, fish, and poultry can become unfit for consumption within just 1-2 days at room temperature if no preservation measures are taken. Understanding these deteriorative factors is the first step toward controlling them – and reducing the massive food losses that affect economies and food security worldwide.

What is food deterioration? 🔗

Food deterioration refers to any undesirable change in the physical, chemical, or nutritional properties of food. When these changes make the food unsafe or unacceptable to the consumer, it crosses the line into food spoilage. Changes can range from subtle – a mild loss of vitamin content – to obvious – visible mould growth, foul odour, or slimy texture. A 2025 review published in the International Journal of Food Science and Nutrition notes that the principal factors causing food deterioration can be broadly grouped into intrinsic factors (internal characteristics of the food), extrinsic factors (external conditions), and miscellaneous factors. Let’s look at each major cause in detail.

Biological factors of food deterioration 🔗

Biological agents are among the most significant contributors to food spoilage. These include microorganisms, natural food enzymes, and insects or pests. They work by breaking down food components to extract nutrients for their own growth, or by accelerating natural decay processes.

Microorganisms: bacteria, yeast, and moulds 🔗

Microorganisms are the primary agents of food spoilage. Three main groups are responsible: bacteria, yeasts, and moulds. Each operates differently, but all feed on the organic compounds present in food.

Bacteria are the most common spoilage organisms, especially in high-moisture, low-acid foods like meat, fish, milk, and fresh vegetables. Some bacteria cause not just spoilage but also serious food poisoning. Certain species form heat-resistant spores that survive inadequate processing and can resume growth later. At an optimal temperature of around 37°C, bacterial populations can multiply from 1,000 to 10,000,000 organisms in just seven hours, as documented by the FAO’s food technology resource.

Yeasts are single-celled fungi that typically spoil foods high in sugar or acid, such as fruit juices, jams, and fermented products. They produce alcohol and carbon dioxide during fermentation, which can cause swelling in sealed packages and off-flavours in drinks.

Moulds are filamentous fungi that grow on the surface of food, producing visible fuzzy or coloured patches. They thrive even at relatively low moisture and acidic pH levels. Beyond visual spoilage, some moulds produce mycotoxins – toxic secondary metabolites that pose serious health risks when consumed.

Several factors determine which microorganisms will dominate and how fast spoilage will occur. These include the food’s water activity (a_w), pH level, nutrient composition, oxygen availability, and storage temperature. For instance, most bacteria require a water activity above 0.9 to grow, while moulds can survive at much lower levels. Foods with a pH below 4.5 are generally resistant to bacterial spoilage but remain susceptible to yeasts and moulds.

Enzymes: the internal catalysts of decay 🔗

Enzymes are naturally present in all living tissues – fruits, vegetables, meat, and fish. After harvest or slaughter, these enzymes continue to function, catalysing chemical reactions that lead to softening, browning, flavour loss, and nutritional degradation.

A well-known example is enzymatic browning. When you cut an apple or a potato, the enzyme polyphenol oxidase (PPO) reacts with oxygen to convert phenolic compounds into brown pigments called melanins. This doesn’t immediately make the food unsafe, but it signals the beginning of quality loss. Enzymes like pectinesterase and polygalacturonase break down pectin in fruits, causing tissue softening and over-ripening. In dairy products, bacterial proteinases and lipases – especially those produced by psychrotrophic bacteria like Pseudomonas – can cause flavour and texture defects even under refrigeration.

Incomplete inactivation of enzymes is a common reason for shortened shelf life in processed foods. That’s why blanching (brief heat treatment) is a standard step before freezing vegetables – it deactivates enzymes that would otherwise continue to degrade the product during frozen storage.

Insects, parasites, and rodents 🔗

Larger biological agents also cause significant food deterioration. Insects such as weevils, grain beetles, and moths are particularly damaging to stored grains, cereals, and dried foods. They cause direct physical damage by feeding on food, and they also introduce microorganisms through their excrement and body parts, accelerating microbial spoilage.

Rodents contaminate food supplies with droppings, urine, and hair, while also gnawing through packaging and storage containers. Effective pest management – through proper storage, fumigation, and hygienic practices – is essential to prevent these losses, especially in tropical and developing regions where storage infrastructure may be limited.

Chemical factors of food deterioration 🔗

Chemical reactions play a major role in food spoilage. They can occur naturally within the food, or be triggered by external conditions such as exposure to oxygen, light, heat, or moisture. The two most important chemical spoilage reactions are lipid oxidation and non-enzymatic browning (the Maillard reaction).

Lipid oxidation 🔗

Lipid oxidation is one of the leading causes of quality deterioration in foods containing fats and oils. It occurs when unsaturated fatty acids in the food react with oxygen, producing a cascade of undesirable compounds. Research published in Frontiers in Nutrition describes this as a process where fats slowly degrade when exposed to oxygen, light, and metal ions like iron and copper.

The process follows a well-known three-stage chain reaction:

Initiation – a hydrogen atom is removed from an unsaturated fatty acid, forming a free radical. This step is triggered by heat, light, or trace metals. Propagation – the free radical reacts with oxygen to form peroxyl radicals and hydroperoxides, which in turn attack more fatty acid molecules, creating a self-sustaining chain. Termination – hydroperoxides decompose into secondary products like aldehydes, ketones, and alcohols, which are responsible for the off-flavours and stale odours associated with rancid food.

Foods particularly vulnerable to lipid oxidation include nuts, fried snacks, vegetable oils, oily fish, meat products, and milk powder. The reaction not only degrades taste and smell but also destroys essential fatty acids and fat-soluble vitamins, reducing the nutritional value of food. According to the IUFoST shelf-life module, oxidative rancidity in foods like spray-dried milk fats and infant formula is a particularly serious concern.

To control lipid oxidation, food manufacturers use antioxidants (both synthetic, such as BHA and BHT, and natural, such as tocopherols and plant polyphenols), oxygen-barrier packaging, and cool, dark storage conditions.

Non-enzymatic browning (Maillard reaction) 🔗

The Maillard reaction is a chemical reaction between amino acids and reducing sugars that occurs when food is heated. It was first described by French chemist Louis Camille Maillard in 1912, and it produces brown pigments called melanoidins along with a wide range of flavour and aroma compounds.

This reaction is responsible for the desirable golden-brown crust on bread, the roasted flavour of coffee, and the caramelised surface of grilled meat. However, when it occurs uncontrolled during storage or processing, it becomes a cause of deterioration. In dried fruits, the Maillard reaction causes unwanted darkening. In milk powder and dehydrated foods, it produces off-flavours and reduces nutritional quality by destroying amino acids – particularly lysine, an essential amino acid.

The rate of the Maillard reaction is influenced by temperature, pH, water activity, and the type of sugar and amino acid involved. It proceeds most rapidly at water activity levels around 0.6-0.7 and is accelerated by higher temperatures and alkaline conditions. Excessive Maillard reactions during food processing can also generate potentially harmful compounds, including acrylamide and advanced glycation end-products (AGEs), which have been linked to health concerns in several studies.

Other chemical reactions 🔗

Hydrolytic rancidity is another important chemical deterioration pathway. It occurs when lipase enzymes or moisture break down triglycerides into free fatty acids. These short-chain fatty acids produce the rancid smell and taste found in degraded butter, coconut, and cocoa products.

Vitamin degradation is an often-overlooked form of chemical deterioration. Vitamins C and A are particularly sensitive to oxidation, light, and heat, losing their potency during prolonged or improper storage.

Physical and environmental factors 🔗

Physical and environmental conditions don’t just cause direct spoilage – they also accelerate biological and chemical deterioration.

Temperature 🔗

Temperature is arguably the single most critical factor in food spoilage. Higher temperatures accelerate microbial growth, enzymatic activity, and chemical reactions. Most spoilage bacteria grow in the range of 7°C to 70°C. Refrigeration slows microbial growth significantly, and freezing halts it almost entirely, though it doesn’t kill all microorganisms.

However, temperature extremes can also cause problems. Freezing damages cell structures through ice crystal formation, leading to texture changes and moisture loss upon thawing. Chilling injury affects sensitive fruits and vegetables like bananas, bell peppers, and tomatoes when stored below their optimal temperature range (typically 5-15°C), causing pitting, discoloration, and off-flavours. In climacteric fruits, higher temperatures after harvest also increase ethylene production, which accelerates ripening and senescence.

Moisture and water activity 🔗

Moisture content and water activity (a_w) directly influence the rate and type of spoilage. High-moisture foods like fresh fruits (which may contain 90-95% water) and fresh fish (about 70-80% water) are highly perishable. On the other hand, dried foods with low water activity resist microbial growth but may still undergo chemical deterioration like lipid oxidation and non-enzymatic browning.

Moisture exchange between food and its environment is equally damaging. Dry crackers become soggy in humid conditions, while soft baked goods lose moisture and become hard and stale. In multi-component foods, moisture migration between different parts – such as from the moist crumb to the dry crust in bread – accelerates staling.

Oxygen and light 🔗

Oxygen is essential for aerobic microbial growth, lipid oxidation, and enzymatic browning. Removing or reducing oxygen through vacuum packaging or modified atmosphere packaging (MAP) is one of the most effective ways to slow spoilage.

Light, especially ultraviolet radiation, accelerates fat oxidation, causes vitamin loss (particularly vitamins C and B2), and triggers colour changes. A review in the International Journal of Food Science and Nutrition notes that light exposure can cause the loss of pigments like anthocyanins and lycopene, which are naturally unstable under light. This is why many light-sensitive products like milk, beer, and cooking oils are packaged in opaque or dark-coloured containers.

Physical stress and mechanical damage 🔗

Physical damage during harvesting, transportation, and handling creates entry points for microorganisms and triggers enzymatic browning at wound sites. Bruised fruits deteriorate much faster than intact ones because the ruptured cells release enzymes and substrates that accelerate decay. For brittle processed foods like biscuits, chips, and cereals, vibration and compression during transport can cause breakage, leading to consumer rejection.

How multiple factors work together 🔗

In reality, these deteriorative factors rarely act in isolation. A study published in the International Journal of Food Microbiology highlights that the primary spoilage factors are associated with both intrinsic food properties and cross-contamination during harvesting and processing, combined with temperature abuse. High temperatures accelerate both microbial multiplication and chemical oxidation. Insect damage creates physical wounds that invite bacterial infection. Excess moisture promotes mould growth while also speeding up the Maillard reaction in dried products.

This interconnected nature of spoilage is precisely why effective food preservation relies on a multi-hurdle approach – combining several barriers (low temperature, reduced water activity, acidification, modified atmosphere, and antioxidants) to create conditions where spoilage organisms and reactions cannot overcome all obstacles simultaneously.

Controlling food deterioration 🔗

Managing food deterioration is essential for food safety, nutrition, and economic sustainability. Key strategies include:

Temperature control – refrigeration (0-5°C) for perishable items and freezing (below −18°C) for long-term storage. Proper cold chain management throughout distribution is critical.

Moisture control – drying, dehydration, and the use of desiccants reduce water activity below the threshold needed for microbial growth. Adding salt or sugar also binds available water.

Atmosphere modification – vacuum packing and modified atmosphere packaging reduce oxygen availability, slowing oxidation and aerobic microbial growth.

pH adjustment – fermentation, pickling, and acidification lower the pH to levels that inhibit bacterial growth (below 4.5).

Antioxidants and preservatives – natural and synthetic antioxidants slow lipid oxidation, while preservatives like sodium benzoate and sulfur dioxide inhibit microbial growth.

Thermal processing – blanching inactivates enzymes; pasteurisation and sterilisation destroy microorganisms. The intensity of the treatment depends on the food’s pH and composition.

Proper handling and hygiene – minimising physical damage during harvest and transport, maintaining clean processing environments, and ensuring personal hygiene all reduce contamination and subsequent spoilage.

What do you think? Given that biological, chemical, and physical factors all interact to cause food deterioration, which preservation strategy do you think offers the most practical impact for reducing food waste in everyday households? And how might a better understanding of these spoilage mechanisms change the way you store food at home?

References

1. https://www.fao.org/4/ad379e/ad379e02.htm
2. https://www.foodsciencejournal.com/assets/archives/2025/vol10issue5/10093.pdf
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC10307983/
4. https://iufost.org/iufostftp/Module1_Chapter2_Modes_of_Food_Deterioration.pdf
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC12154226/
6. https://pubmed.ncbi.nlm.nih.gov/8913806/