Processes of pasteurisation and sterilisation in foodstuffs

Pasteurization represents a foundational thermal preservation technology designed to heat food matrices below 100°C (typically between 62°C and 85°C) followed by rapid chilling. The primary microbiological objective is the complete thermal inactivation of vegetative pathogenic microorganisms (including Salmonella spp., Listeria monocytogenes, Campylobacter jejuni, Escherichia coli, and Coxiella burnetii), alongside the denaturing of indigenous spoilage enzymes, thereby extending product stability and consumer safety.

Industrial food processing employs distinct kinetic parameters: low-temperature long-time batch pasteurization (LTLT: 62–65°C for 30 minutes), continuous high-temperature short-time plate heat exchange (HTST: 71–75°C for 15–20 seconds), and flash pasteurization (85–90°C for 1–4 seconds). Because pasteurization does not destroy heat-resistant bacterial endospores (spores), low-acid foods (such as fresh market milk) mandate continuous cold-chain refrigeration (2–6°C). Conversely, for high-acid matrices featuring pH values below 4.5 (such as citrus juices, fruit preserves, and tomato passata), pasteurization achieves commercial shelf stability because acidic conditions completely inhibit endospore germination and outgrowth.

Sterilization is an intensive thermal process conducted at temperatures exceeding 100°C (typically 115°C to 140°C) aimed at achieving commercial sterility. This standard mandates the total inactivation of all vegetative microbial forms alongside exceptionally heat-resistant bacterial endospores, most critically the neurotoxigenic spores of Clostridium botulinum (utilizing the validated 12D thermal death concept) and spoilage thermophiles of the Bacillus genus. Traditional retorting within pressurized autoclaves (115–121°C for 15 to 30 minutes) represents the industrial benchmark for canned meats, fish, legumes, and shelf-stable ready meals.

A technological revolution in fluid dairy and beverage processing was realized with Ultra-High Temperature (UHT) continuous-flow systems. UHT technology subjects the liquid stream to 135–150°C for an ultra-short interval of 2 to 5 seconds via direct steam infusion or indirect tubular heat exchangers, followed by immediate flash cooling and aseptic filling into multilayer barrier packaging. By drastically curtailing thermal holding time, UHT successfully inactivates bacterial endospores while circumvents excessive Maillard browning, caramelization, and severe vitamin degradation, granting unopened products a shelf life of 6 to 9 months at ambient room temperature without chemical additives.

Thermal preservation techniques inevitably exert distinct biochemical and sensory impacts on food matrices. Mild HTST pasteurization (72°C for 15 seconds) induces minimal micronutrient degradation, causing less than 10% loss of heat-labile vitamins (folate, ascorbic acid, thiamine, and cobalamin). Concurrently, native whey proteins retain their folded tertiary conformations, ensuring that the fresh flavor profile and organoleptic mouthfeel of milk remain virtually indistinguishable from raw products.

Conversely, conventional in-container retort sterilization (115–121°C for prolonged durations) precipitates 30% to 50% losses of heat-sensitive vitamins and accelerates non-enzymatic Maillard browning reactions between lactose and protein-bound lysine, generating cooked flavor volatiles and mild color darkening. Modern continuous UHT processing (135–150°C for 2–4 seconds) successfully circumvents this by drastically curtailing thermal residence time: vitamin retention approximates 85–90%, native mineral bioavailability is preserved, and sensory degradation is minimized while achieving commercial microbiological sterility.

Navigating commercial dairy choices requires matching shelf-life requirements with organoleptic preferences and storage conditions. Traditionally pasteurized milk (5–7 days shelf life) and ESL (Extended Shelf Life) microfiltered milk (shelf life up to 21 days, combining ceramic membrane bacterial filtration with gentle thermal treatment) deliver maximum flavor freshness and native mouthfeel. However, they strictly mandate unbroken cold-chain refrigeration at 2–6°C throughout storage and domestic transit.

Conversely, aseptic UHT milk packaged in multilayer barrier cartons guarantees commercial microbiological sterility at ambient room temperature for up to 6 months unopened, offering unmatched logistics convenience for pantry storage. Nevertheless, consumers must adhere to a crucial food safety rule: once the aseptic carton seal is breached, the product is exposed to ambient airborne microflora, requiring immediate refrigeration at 2–6°C and consumption within 48 to 72 hours, exactly like fresh pasteurized milk.