Modern methods apply these biochemical principles using advanced technology:

Controlled fermentation: Uses precise temperature and pH control to guide fermentation by beneficial microorganisms. Yeast converts glucose to ethanol and carbon dioxide:

$C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + energy$

The alcohol and organic acids produced create conditions that inhibit spoilage microorganisms.

Pasteurization: Applies heat to destroy pathogens while preserving food quality. Low-Temperature Long-Time (LTLT) uses 63°C for 30–60 minutes, while High-Temperature Short-Time (HTST) uses 72°C for 15 seconds. Ultra-High Temperature (UHT) uses 135°C–150°C for 2–5 seconds.

Pressure canning: Heats food under high pressure (about 240°F or 116°C) to destroy heat-resistant bacterial spores, particularly Clostridium botulinum that causes botulism. This is essential for low-acid foods.

Sterilization: Exposes food to temperatures of 110°C–121°C for 15–30 minutes under pressure to destroy all microorganisms, including spores. Foods can be stored at room temperature for months or years.

Dehydration: Removes water using solar drying, hot air drying, freeze-drying, or vacuum drying. Reduced moisture limits microbial growth and enzyme activity.

Refrigeration and freezing: Uses low temperatures to slow or stop microbial growth and enzymatic reactions. Freezing turns water to ice, making it unavailable for microorganisms.

Vacuum packaging: Removes air from packages before sealing, limiting oxygen available for microbial growth and chemical reactions that cause spoilage.

Irradiation: Exposes food to controlled ionizing radiation (beta particles or gamma rays) that damages microbial DNA, killing bacteria, moulds, and insects while delaying ripening in fruits.

Chemical preservation: Uses preservatives such as salt, sugar, benzoic acid, sorbic acid, and propionic acid that interfere with microbial cell division, membrane permeability, and enzyme activity.

Pascalization (High Pressure Processing): Uses high pressure (300–600 MPa) to destroy microorganisms and inactivate enzymes without heat. This preserves nutritional value and sensory qualities.

Hurdle technology: Combines multiple preservation techniques—mild heat, low temperature, reduced water activity, and acidity control—to create multiple barriers against microorganisms. Each hurdle adds pressure on microbial survival, making the food environment too difficult for spoilage organisms.

Ultraviolet (UV) light treatment: Uses UV radiation to inactivate microorganisms on food surfaces without heat or chemicals.

Heat Effects

• Carbohydrates: Starch undergoes gelatinization (swelling and thickening) during moist heat. Dextrinization occurs during dry heat, breaking starch into smaller, soluble dextrins.
• Proteins: Heat causes denaturation (unfolding) and coagulation. This changes texture but does not destroy protein content.
• Fats: Moderate heat melts fats. High heat causes breakdown into glycerol and fatty acids, producing potentially harmful compounds.
• Vitamins: Heat-sensitive vitamins (especially vitamin C and B vitamins) are reduced during processing. Fat-soluble vitamins (A, D, E, K) are more stable but can still degrade with prolonged high heat.

Chemical Changes

When fats are heated, they react with oxygen to form peroxides and aldehydes, which cause rancid flavours:

$Unsaturated\ Fat + O_2 \xrightarrow{heat} Peroxides \xrightarrow{further\ heat} Aldehydes + Ketones$

In Tanzania, a small-scale food vendor in Dar es Salaam selling mchele (rice) and nyama (meat) can apply these principles daily to reduce losses. For example, using refrigeration to store prepared food overnight prevents microbial growth and spoilage, or drying mbuna (small fish) using solar drying preserves them for sale at the market days later. Understanding that salt draws moisture from microbial cells helps the vendor use appropriate amounts of salt when preserving dagaa (Lake Victoria sardines) to extend their shelf life without making them too salty for customers.