Heat Treatment in Food Preservation: Historical Development and Microbial Inactivation

The destruction of microorganisms by heat is fundamentally due to the inactivation of enzymes necessary for their metabolism. Enzymes, being proteins, are sensitive to temperature changes; high heat denatures these proteins, rendering them non-functional. This process effectively kills or deactivates the microorganisms, ensuring food safety and preservation.

The choice of heat treatment in food preservation depends on various factors, including the type of microorganism, additional preservatives used, and the impact on the food's quality. Different microorganisms have varying heat resistances; for instance, spores of certain bacteria require higher temperatures for inactivation. The presence of other preservatives, such as acids or salts, can enhance the effectiveness of heat treatment, potentially allowing for lower temperatures or shorter processing times. However, these treatments must balance microbial destruction with maintaining the food's nutritional and sensory qualities.

The modern food preservation process has its roots in early 19th-century France. Nicolas Appert, known as the "father of canning," pioneered the technique of preserving foods by sealing them in glass jars and boiling them. This innovation earned him a prize of 12,000 French francs from the French government in recognition of his method's potential to preserve food safely for extended periods.

In 1819, William Underwood established the first canning factory in Baltimore, USA, marking the beginning of the commercial canning industry. However, the initial method of boiling water required approximately six hours to preserve foods, which was inefficient. The addition of salt to the water bath raised the boiling temperature, reducing the processing time but causing corrosion to the cans. This challenge led to the development of heating in steam under pressure, a method that significantly shortened processing times and enhanced efficiency. These early pressure chambers have since evolved into modern retort systems, which are standard in the industry today.

In 1945, researchers investigated the effects of heating the germ at various moisture levels and durations in a hot air oven on enzyme activities and storage stability at 37°C in laminated metal foil. Their studies revealed that all heat treatments completely destroyed lipoxidase activity, while proteolytic activities were significantly reduced, contingent on moisture levels. Surprisingly, raw germ samples exhibited a smaller increase in peroxides compared to heat-treated samples, highlighting the nuanced effects of heat treatment on food preservation. This research contributed to the optimization of heat treatment processes, ensuring both food safety and quality.
Heat Treatment in Food Preservation: Historical Development and Microbial Inactivation

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Infrared Heating for Food

Infrared is a type of energy source that’s commonly found in nature. Infrared heating utilizes radiative and conductive heat transfer mechanisms to generate and transfer heat. The IR radiation does not penetrate deeply and heats only a few millimeters below the surface of foods. The absorbed energy can then be conducted to other areas within the food.

Infrared is part of the electromagnetic spectrum that is located between the visible region and microwaves, and its wavelength ranges from 0.5 to 100 µm.

Infrared heating provides significant advantages over conventional heating, including reduced heating time, uniform heating, reduced quality losses, absence of solute migration in food material, versatile, simple, and compact equipment, and significant energy saving.

Infrared heating was first used industrially in the 1930s for automotive curing applications and rapidly became utilized in the manufacturing and the electronics industry.

Infrared heating can be applied to various food processing operations, namely, drying, baking, roasting, blanching, pasteurization, browning meats and other foods, and sterilization.

Infrared heaters can be powered by electricity, natural gas, or propane. Different heaters will have different maximum output levels, different controls, and different designs. The efficiency of an infrared equipment mainly depends on the type of heat source used. The emitter determines the color of light, process emission wavelength, process temperature, and power density.
Infrared Heating for Food

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Food extrusion technology

Food extrusion can be defined as a process of mixing, homogenizing, and shaping low moisture food materials and more recently high moisture food materials are forced through an opening or die with a design specific to the food, and is then cut to a specified size by blades.

Extrusion cooking is a versatile and very efficient technology in food processing. The process is a high-temperature short-time (HTST) process which inactivates enzymes and reduces microbial contamination. Extrusion cooking is mostly preferred, as it has high productivity and significant nutrient retention as compared to conventional cooking.

While food is being forced through the extruder, the food mix is thermomechanical cooked to a high temperature (usually in the range 100°C–180°C), pressure and shear stress that are generated in the screw-barrel assembly.

The laminar flow within the channels on the extrusion screw and extruder die aligns the molecules in the direction of flow to create the crunchy or chewy texture in fabricated food.

Extrusion cooked melts transit from high pressure to low (atmospheric) pressure when they exit the die. The extrudates generally require no further processing except for some minimal drying.

The entire process is continuous and capable of happening in less than a minute. The most common used extruders in the food industry include single-screw and twin-screw systems, with twin-screw systems more widely used because of their flexibility.

Extrusion brings gelatinization of starch, denaturation of proteins, reduces lipid oxidation and anti-nutritional factors. In addition, it is considered a versatile, low cost and very efficient technology in the food processing.
Food extrusion technology

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Radio frequency heating in food process

Radio frequency (RF) and microwave (MW) are electromagnetic (EM) waves. In RF and MW heating, which are also called dielectric heating or dielectric loss heating, heat is generated within the products by molecular friction in high-frequency alternating electric fields.

In very simple terms, radio frequency heating of foods arises from the direct conversion of electrical energy to heat within the volume of the food itself. With an electric field alternating at the 27.12 MHz radio frequency, the electric field alternates 27, 120, 000 cycles per second. The energy release resulting from the movement of the molecules and the space charge is displacement causes the material to rapidly heat throughout.

The rapid heating method of RF offers considerable advantages over conventional slow heating processes, rendering significant applications in different food products. The physical factors such as shape, geometry and product position, as well as dielectric properties, are the fundamental factors that affect the RF heating systems.
Radio frequency heating in food process

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Chicken barbecue

Cooking meat or chicken slowly over hot coals, known as barbecuing, has been done in America since colonial days. It is characterized by a high-spirited competitiveness based on distinct regional preferences.

For example, in Oklahoma, barbecue refers to meat that has been slowly cooked over wood smoke at a low temperature.

The name ‘barbecue’ assigned to slow roasting over an outdoor fire, can likely be traced back to the West Indian term barbacoa, which is the word natives of Haiti used to describe the grill over which they roasted meat.

Chicken (Gallus gallus) is a very popular food, as it can be prepared a multitude of ways. Barbecued chicken is a perennial favorite, which is not surprising as it is easy to prepare and delicious.

Barbecue chicken needs to be seasoned early (giving the chicken time to absorb the spices) and cooked over a low flame for even browning.

When cooking chicken on a barbecue rack, always grease the rack well first. The collagen on the skin will turn into a sticky gelatin, which causes it to stick to the rack.

To really solve the problem, try baking the chicken for 15 to 20 minutes in a preheated oven, breast side up, allowing the gelatin time to infuse into the fat and meat or to be released into the pan.
Chicken barbecue

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