Food Spoilage: Types and Causes

Food Spoilage: Types and Aetiology

• Food spoilage is a process that makes a product undesirable or unsuitable for consumption.
• It's a complex ecological phenomenon resulting from microbial activity determined by prevailing conditions.
• This involves biochemical reactions within food constituents.

Types of Undesirable Changes in Food

• Change in colour: Example, bananas turning brown over time.
• Change in smell: Often rancid smells in spoiled oils.
• Change in consistency: Milk splitting is an example.
• Change in texture: Spoilage often leads to rotting, like rotting carrots.
• Mechanical damage: Damage from impacts like eggs with a broken shell.

Major Causes of Food Spoilage

• Biological spoilage: Growth of microorganisms (bacteria, yeasts, molds), and activity of food enzymes. Damage from pests, insects, and rodents also contribute.

• Physical spoilage: Reactions with oxygen, light, or chemical reactions within the food itself.

• Chemical spoilage: Temperature abuse or physical damage can lead to spoilage.

• Specific Spoilage Factors:

  • Microbial growth and activity (bacteria, yeast, molds)
  • Food enzyme activity
  • Loss/gain of moisture
  • Reactions with oxygen and light (rancidity, color changes)
  • Damage from pests, insects, and rodents
  • Non-enzymatic reactions (oxidation, mechanical damage)
  • Inappropriate storage temperature (hot or cold)

Spoilage due to Enzymatic Activity

• Enzymes in foods contribute to deterioration.
• Endogenous enzymes:
  • Post-harvest senescence and spoilage of fruits and vegetables
  • Oxidation of phenols to orthoquinones by phenolases and polyphenol oxidases (PPO) which lead to browning
  • Sugar-starch conversion in plant tissues by amylases

Spoilage due to Insects, Pests, and Rodents

• Insects and pests attack fruits, vegetables, grains, and processed products.
• Warmer and humid environments promote insect and pest growth.
• Presence of pests causes loss of nutritional quality, creates off-flavors, and accelerates decay.
• Rats and mice carry disease-producing microorganisms which contaminate food.

Spoilage due to Chemical Reactions

• Chemical reactions occur in the presence of atmospheric oxygen and sunlight
• Lipid oxidation and non-enzymatic browning affect food quality, colour, and flavour.
• Lipid oxidation is influenced by light, oxygen, high temperature, iron, and copper.
• Maillard reaction (reducing sugars and amino acids reacting to form brown pigments in the presence of heat) and caramelization (sugars reacting in the presence of high heat and low moisture).

Spoilage due to Physical Factors

• Temperature, moisture, and pressure can cause spoilage.
• Physico-chemical reactions from freezing, burning, drying, and bruising of fruits and vegetables during storage and handling.
• Food processing or storage leads to colour deterioration due to chlorophyll degradation (leading to dull olive-brown colour).
• Anthocyanins (food pigments) react with metals which can cause unwanted colour changes (e.g., purple discoloration from tin reaction with cherries).

Most Common Manifestations of Spoilage

• Visible microbial growth (molds, slime).
• Degradation of food structure causing texture loss.
• Chemical products of microbial metabolism in the form of odors and off-flavors.
• Gas production

Factors Affecting Microbial Growth

• Intrinsic factors: Water activity, pH, redox state, nutrient content, antimicrobial presence, and biological structures.
• Extrinsic factors: Storage temperature, storage relative humidity, atmospheric gases, and microbial activities.
• Other factors: Photo reactivity, presence of oxygen, invader pests, mishandling.

Nutrients and Other Constituents in Food

• Proteins are degraded by proteolytic enzymes, leading to putrefaction.
• Carbohydrates are affected primarily by yeasts and molds, with subsequent production of various acids and alcohol.
• Microbes degrade fats to produce fatty acids and glycerol.

Acidity & Water Content

• Foods with pH below 4.5 are generally acidic and susceptible to molds and yeasts, while non-acidic foods are more vulnerable to bacteria.
• Microbes require at least 13% free water. Available water (water activity, a_w) is crucial.
• Salt/sugar preservation inhibits most microbial growth.

Physical and Environmental Factors

• Temperature (20-50°C) is ideal for microbial growth, with pathogens growing between 6 and 35°C.
• Some fungi can survive and grow at lower temperatures (e.g., Botrytis cinerea).
• Anaerobic microorganisms spoil airtight canned foods. Oxygen is necessary for mold growth.

Presence of Inhibitory Substances

• Food contains natural or added inhibitory substances that prevent microorganisms growth.

Biological Structure Inhibits Spoilage

• Healthy tissues in plants and animals are usually sterile or have minimal microbial content.
• Natural coverings (seed testa, nut shells, fruit coverings) protect against microbial entry.

Types of Foods Based on Spoilage Rate

• Perishable: Spoil quickly and need specific storage. Examples include milk, fruits, vegetables, fish.
• Semi-perishable: Can be stored for longer periods with proper care, like potatoes.
• Non-perishable: Remain good for a long time without specific handling (unless mishandled), examples include sugar, flour.

Explore the intricate world of food spoilage, including its types and major causes. Understand how microbial activity and environmental factors contribute to undesirable changes in food products. This quiz provides insights into how spoilage affects color, texture, and overall quality of food.