Typical technologies, processes, and operations
The mechanical operations, processes, and technologies typically used to achieve these benefits in preparing and using raw materials in manufacturing foods and beverages (Potter and Hotchkiss 1995) are briefly described below:
• Mechanical Operations. There are many mechanical operations used throughout the food system, including simple conveying of raw materials from one location to another, as well as more intense operations to change the physical structure of the material. All or most of these operations are larger scale versions of operations that have been used to prepare foods for centuries. The cracking and grinding of cereal grains to manufacture the flour used in bakery products is a very visible example. Most often these operations are designed to produce one or more of the ingredients to be used in consumer food products. The extraction of oil from soybeans and other oilseeds requires a mechanical operation before efficient separation of the oil can be accomplished. In most cases, these operations are a component of series of steps needed to ensure the most efficient use of the raw material, often including the manufacturing of an array of by-products for consumers to utilize. Another typical mechanical operation is dry mixing, involving the blending of various ingredients to ensure homogeneous and uniform distribution of the various ingredients before a final stage of manufacturing.
• Heating. The use of thermal energy to increase the temperature of a raw food or ingredient is the most recognized and widely used approach to preservation of food. By increasing the temperature to appropriate levels and holding for an appropriate time that is dependent on both the nature of the food and the objective of the process, pathogenic or spoilage microorganisms are significantly decreased in number or eliminated.
Thermal processes applied to foods in food manufacturing are based on the same principles as those governing traditional cooking of foods during preparation. The impact of heating—thermal processing—on components of the food is the same as that during cooking and often results in the enhancement of flavors and texture, as well as some modest losses of heat-sensitive nutrients. Many shelf-stable foods are available to consumers as a result of thermal processing. Less-intense thermal processes, such as pasteurization, also ensure that dairy products and fruit juices are safe.
Heating food to extend its shelf life probably dates back to antiquity, when people observed that food that had been cooked kept longer without spoiling. However, it was not until Appert and others investigated heating foods in containers that it was discovered that immediate recontamination of heated food from the environment did not occur. Since those meager beginnings, advances in mathematics, chemistry, biology, and engineering, coupled with their application to food science and technology, have resulted in development of equipment and procedures to optimize the application of heat to foods for the purpose of extending their shelf life and enhancing their edibility (texture, flavor, and visual appearance).
There are basically 3 types of heat processes that are applied to food, other than cooking: blanching, pasteurization, and canning. The latter 2 are tightly regulated by federal—and in some cases, state—agencies to ensure proper application of the technology and prevention of food-borne illness.
Blanching is a mild heat treatment (usually accomplished at temperatures below 212°F for less than 2 to 3 min) applied to foods that are to be subsequently canned, frozen, or dried. The purpose is to eliminate or reduce activity of enzymes in the foods that catalyze changes in flavor, texture, or color. Other benefits include removal of air from the food tissue to reduce oxidation, softening of the plant tissue to facilitate packing into packages, and inactivation of antinutritional properties (such as trypsin inhibitor in soybeans, a naturally occurring chemical that reduces dietary protein breakdown in the human gastrointestinal tract).
The process is usually carried out in hot water or steam, although there are processes based on hot air or microwave heating. Since the process is relatively mild, there is relatively little effect on nutrients, although when hot water is used as the heating medium some nutrients, especially water-soluble nutrients, are leached into the water.
“Pasteurization” is named after Pasteur, who demonstrated that wine spoiled because of the presence of microorganisms and that a mild heat treatment could be used to inactivate the microorganisms and thereby extend the shelf life. Pasteurization is most well known for its application to milk, which is strictly regulated through the U.S. Public Health Service/FDA's Pasteurized Milk Ordinance.
Pasteurization is most generally applied to liquids, although it is also applied to semisolid and solid foods. As applied to liquids, the temperature is elevated to 140 to 212°F for a short period of time (usually less than 1 min) to inactivate microorganisms that can cause illness (pathogens). As originally applied, the liquid was heated after it was put into the container; but by applying advances in food engineering, such as the understanding of flow dynamics and heat transfer to flowing liquids, continuous processes were developed using heat exchangers, machines used to transfer heat from a hot fluid to a colder one. Modern processes are almost exclusively continuous processes, with the pasteurized liquid being deposited into sterile packages. Most pasteurized foods are subsequently kept in refrigerated storage to extend the shelf life because not all spoilage organisms present have been inactivated.
“Canning” is primarily used to inactivate microorganisms that cause food-borne disease such as botulism, but it also inactivates microorganisms that cause food spoilage. This thermal process is commonly accomplished by holding the product at temperatures well above 230°F for several minutes. Canned food is not absolutely sterile (devoid of all viable microorganisms) but rather is commercially sterile (devoid of all viable microorganisms that could grow under normal storage conditions).
There are 2 major methods: heating the food after it has been sealed in a container (referred to as canning) and sterilizing the food, then depositing it in a sterile container within a sterile environment and sealing the container (referred to as aseptic processing). These processes can also be optimized for retention of nutrients and quality factors such as taste, flavor, and color. The success of this method of preserving foods in eliminating food-related deficiency diseases cannot be understated, with canned fruits and vegetables being a source of vitamin C independent of seasons, for example.
| Prescott and Proctor (1937), of the Massachusetts Inst. of Technology, described the importance of canning as follows: “No technologic advance has exerted greater influence on the food habits of the civilized world than the development of heat treatment and the use of hermetically sealed (air-tight closure) containers for the preservation of foods.”|
• Refrigeration and Freezing. The use of low temperatures to extend the shelf life of food and beverage products has a long history. The use of ice to reduce the temperature of foods and prevent spoilage has been recognized for centuries. Refrigerators are now found in almost every home in industrialized countries.
Although the reduction of temperature does not eliminate microbial populations, it reduces the rate of microbial growth enough to prevent product spoilage and extend the shelf life of most food products. Most fruits and vegetables are refrigerated to extend their freshness. In addition, refrigeration also reduces the reaction rates of enzymes that cause deterioration of most quality attributes of a food or beverage, making high-quality products available to the consumer for extended periods of time (Heldman and Hartel 1997).
Some foods and beverages receive a mild heat treatment to inactivate enzymes and eliminate microorganisms that can cause disease but still require refrigeration to control the growth of surviving microorganisms that can cause spoilage. Pasteurized milk is probably the best example, but many other foods and beverages are also pasteurized and then refrigerated. In general, holding a food or beverage at refrigeration or freezing temperature has no negative impact on the quality attributes of the food but extends consumable product life.
“Freezing” is a more intense use of refrigeration to reduce the temperature of a product to levels below the freezing temperature of water in the product. Lower temperatures cause the liquid water to change phase to ice. At these reduced temperatures (−0.4 to −14°F), the deterioration rates for product quality attributes are reduced to below those at refrigeration temperature, and microbial growth is reduced to negligible levels.
It is not unusual for frozen fruits, vegetables, and some meat products to maintain high quality for as much as 1 y while frozen. Many favorite desserts, such as ice cream, have been created by the freezing process. Most nutrients are not affected by freezing; however, it is difficult to freeze a food product without impact on the some of its more evident quality attributes. The formation of ice crystals within the structure of a plant or animal food results in a series of reactions with potential impact on texture and flavor. Thus, careful control of the time to freeze the product and the temperature of the frozen product during distribution and storage is important to minimize such reactions and ensure the best possible quality attributes over time (Erickson and Hung 1997).
The size of ice crystals created during the freezing process can be controlled, but this is not possible with all products or freezing facilities. For example, small pieces of fruits or vegetables can be frozen very rapidly, and the product structure is preserved with uniform distribution of small ice crystals. In contrast, a large portion of beef or any product in a large package will require a longer time to freeze and will result in a less-uniform distribution of larger ice crystals. The extent of the impact on product quality depends on an array of factors occurring after freezing, including control of temperature during storage and distribution and final preparation of the food. For many foods, the quality attributes of refrigerated and frozen foods compare favorably to those of the fresh counterparts (Mallet 1993).
• Dehydration. Drying is intended to halt or slow the growth of microorganisms and rate of chemical reactions. The removal of water provides food processors excellent opportunities to reduce volume and weight, extend shelf life, and convert liquids to powdery products, such as instant coffee or a vegetable soup base mix. This process is one of the oldest techniques used to preserve foods, one of the most utilized, and the most energy intensive (von Loesecke 1943; Saravacos 1965; King 1968; Thijssen 1979).
Water removal is usually performed via evaporation, vaporization, or sublimation (drying while frozen) by means of a simultaneous heat, mass, and momentum transfer mechanism (Whitaker 1977). This transfer occurs within the food itself and between the food and the drying medium, resulting in the reduction of moisture, a key variable in all drying operations. In addition to water removal, chemical reactions occur, such as Maillard browning (nonenzymatic browning) of amino acids/reducing sugars such as glucose, caramelization of sugar, denaturation/degradation of cross-linking proteins, and pyrolysis (decomposition or transformation of a compound caused by heat) of the various organic constituents. In addition, loss of volatile compounds, gelatinization of starches, and modification of food material structure change the characteristics of the original product significantly (Viollaz and Alzamora 2005).
Many types of dryers, dehydration methods, and associated equipment are applied to a very wide range of foods. Sun drying on trays, mats, or platforms is the traditional method and is still used today. Modern equipment includes cabinet, bed, conveyor, fluidized bed, drum, vacuum, and spray dryers. Freeze drying (lyophilization), osmotic dehydration, microwave, and innovative light-driven refractance-window dryers are also in use. With continuous technological advances in different fields, drying is constantly evolving to offer better quality and novel products.
Mathematical modeling and process simulation have significantly contributed to the understanding of the intricacies of this very complex process and the design of new dryers and drying systems. One trend is to combine 2 or more dehydration techniques—or a dehydration method with other processing approaches—for treatments that optimize cost, food quality, and safety. Examples of these combinations include microwave–vacuum drying, ultrasound-assisted air drying, and encapsulation and flavor impregnation to add value.
• Acidification. Raw foods and beverages vary significantly in levels of acid they contain. Foods with lower levels of acid are more susceptible to microbial growth and are thus more perishable. The intentional adjustment in the level of acid in a food has been a preservation method for centuries, in making pickles, for example. This approach to preservation is based on the inability of many spoilage microorganisms and pathogens to grow at high levels of acid. Increasing the acidity prevents growth of many microorganisms and extends the shelf life of the product, while maintaining many of its attributes. This preservation method can be accomplished by addition of acid to adjust the overall acidity level of the product, or biologically through fermentation. Since acid alone may not be sufficient to fully protect the product, adjustments in acidity are frequently used in combination with other techniques such as heat, additives, or refrigeration to accomplish preservation and safety.
• Fermentation. The use of microorganisms to change a perishable food into a less-perishable product is another very old way of preservation that has been used around the world by societies without access to refrigeration to extend the edible life of a fresh food. Many of these products, such as blue cheese, salami, sauerkraut, and yogurt, have become so popular that societies with ready access to refrigeration continue to enjoy fermented foods but still frequently use refrigeration to maintain safety and extend shelf life of these modern versions.
Although some microorganisms lead to food spoilage and others cause food poisoning, specific microorganisms that can induce desirable changes in foods are used to overpower those that can lead to unappealing or unsafe foods. Fermentation microorganisms primarily work to change the chemical makeup of a product, making it less likely that undesirable microorganisms will reproduce and compromise product safety or quality. Beneficial microorganisms synthesize natural preservatives, such as lactic acid and other acids (increasing the acidity of the food), carbon dioxide (lowering the oxygen content), and ethanol (discouraging growth of undesirable microorganisms). Yeasts produce carbon dioxide to expand the structure, such as dough for bread baking. They are also responsible for the production of ethanol to produce beer, wine, and other alcoholic beverages.
Fermented dairy products include yogurt and a host of ripened cheeses. Fermented cucumbers are called pickles in Western countries, but pickling is another word for fermenting and is used to produce pickled eggs, pig's feet, and even snakes in certain countries. Many countries and cultures have their own favorite types of fermented products, such as injera from Ethiopia, kimchi (fermented cabbage) from Korea, salami and other fermented sausages from Italy and Germany, and sauerkraut from northern Europe. Harvested cacao beans are fermented before cleaning and roasting, making all chocolate products the result of at least one fermentation step.
• Water Activity. A very important and useful tool in the control of food quality attributes and food safety is water activity (aW). Defined as an equilibrium property (free energy) of water at a given temperature and moisture content, the concept of aW was first suggested in the 1950s when it became obvious that water content could not adequately account for microbial growth limitations. During the 1960s, researchers demonstrated that aW is also important in controlling the rates of chemical deterioration in foods, and then in the 1980s it was also found to relate to the texture of crisp dry foods and caking of powders such as instant coffee. aW is not the same as water content, or the quantitative amount of water in a sample, nor is it a measure of free compared with bound water in a food, an early misconception that is now abandoned.
Through the research of hundreds of food scientists, a number of aW paradigms have been established and used by food manufacturers to create safe, tasty, and nutritious dry and semimoist foods such as crispy snacks and breakfast cereals, semimoist cookies, and creamy confections. For example, it is known that at aW values between about 0.3 and 0.65, changes in product texture occur (for example, loss of crispness and onset of stickiness, caking, or hardening), and that at aW values around 0.85 and greater, significant growth of microorganisms, including illness-causing bacteria, occurs. In fact, the concept of aW is used in regulation of food processing to ensure food safety. The Code of Federal Regulations (21 CFR 110.80 [b]) requires that “Foods such as but not limited to dry mixes, nuts, intermediate moisture foods, and dehydrated foods that rely on the control of aW for preventing the growth of microorganisms shall be processed to and maintained at a safe moisture level. Compliance … may be accomplished by any effective means including (i) monitoring the aW of ingredients and finished product, (ii) controlling the soluble solids-water ratio, (iii) protecting finished foods from moisture pickup … so that the aW does not increase to an unsafe level … .” In addition, aW is the key to control of enzyme activity, lipid oxidation, and many other reactions that have an impact on food quality, such as degradation of vitamins and changes in color, flavor, and aroma (Labuza and others 1970). Figure 2 depicts the water content and aW of a few common foods.
Specific knowledge of the relationship of aW to moisture content, such as that shown in Figure 2, is useful to food manufacturers for choosing specific ingredients, such as in making a high- or intermediate-moisture food that will maintain a safe aW level (generally below 0.85). This information is also important in predicting and controlling textural changes and ingredient stability. Foods such as dry mixes, nuts, and dehydrated foods rely on control of aW for preventing the growth of microorganisms. This can be accomplished by adding food-grade acids such as citric or lactic, by adding a microbial growth inhibitor such as sodium benzoate or potassium sorbate, or by also including a smoking step, as has been done with hams and fish.
The systematic control of aW through product formulation ensures the maximum quality and shelf life for dry and intermediate-moisture foods (Labuza and others 1970), such as beef jerky, gummies, dried raisins and cranberries, or chewy granola bars. Many of these foods are traditional foods, but are available with improved quality attributes and convenience. Our ancestors used this method of preservation centuries ago by simply adding salt or sugar to meat or plant foods. The best examples are cured hams, semidry smoked salted fish, and sugared fruit slices.
• Smoking. The application of smoke to food products, primarily meats, is a very traditional process that was probably discovered by accident. It has been speculated that when ancient cave dwellers learned to cook food over open fires, it quickly became obvious to them that the smoke from the fire helped reduce the spoilage of perishable food products such as meat and also imparted a very distinctive, desirable flavor. Over time, the smoke process was expanded to include not only meat, fish, and poultry but also, more recently, sausage products, ham, bacon, cheeses, and many other foods for which a unique smoked flavor and increased shelf life are desired. Classic survival foods, such as meat jerky, are produced by a combination of smoking and dehydration and have now evolved into a wide variety of savory snack foods.
The smoke application process has evolved dramatically from open campfires to a highly controlled, scientific process, but the benefits have remained the same. Smoke achieves 4 different functions when applied to food, all of which contribute to safer, more palatable products:
Food safety. Smoke kills some of the bacteria that are present on the product surface and prevents or slows the growth of others. While this has been one of the most important roles of smoke for food preservation in the past, this effect is less critical today because several other antimicrobial processes are available. Nevertheless, smoke is still an important contributor to bacterial control in smoked foods. The antibacterial effect of smoke is due to several components of wood smoke, specifically acids and alcohol, which are formed during combustion of wood and deposited on the product surface. Furthermore, most smoke processes are done with application of heat at the same time, and the combination of smoke with mild heating increases the control of both spoilage and pathogenic bacteria. Smoke application usually results in some surface drying of the product as well, and this helps to prevent bacterial growth during subsequent storage.
Quality—flavor and aroma. Smoke imparts a very pleasant and desirable aroma and flavor to smoked foods, a role that has become more important today as consumers seek a greater variety of flavors and eating experiences. Wood smoke can be derived from a variety of wood sources, including hickory, apple, mesquite, and others, to add to the variety of flavors that can be achieved.
Quality—visual appeal. Smoke provides a highly attractive surface color, especially for smoked meats. The deep, rich mahogany color of a smoked ham is easily recognized by consumers and communicates assurance that the associated aroma and flavor expected of a smoked ham will be delivered.
Preservation. Smoke functions as an antioxidant or flavor protector. Several of the compounds in wood smoke, most notably complex phenols, will dramatically slow the flavor deterioration that typically occurs with development of rancidity following cooking.
Despite the advantages, 3 criticisms have occasionally been leveled at the use of smoke for food preservation. First is that atmospheric emissions result from combustion of wood to generate smoke. Second is that it degrades some food nutrients; this has been demonstrated to be of very minor importance—smoke has been shown to not significantly alter the nutrient value of food under normal circumstances. Third is that combustion of wood can generate undesirable compounds (polycyclic hydrocarbons) shown to be toxic and/or carcinogenic.
Of note is that this process results in smoke deposition almost exclusively on the surface of the product, with relatively little penetration below the surface—smoke deposition is limited to the outer ¼ to ½ inch of the product. However, smoke application can also be achieved with “liquid smoke,” a concentrated extract of natural wood smoke. Liquid smoke contains all of the important functional components of natural smoke and results in the same effects on color, flavor, and bacterial control, but it is much more consistent in composition than natural smoke and therefore more reproducible in effect.
Other significant advantages to liquid smoke are that no atmospheric emissions are generated during smoke application, the undesirable toxic/carcinogenic components of natural smoke are not included in the extract, and the liquid smoke can be mixed into a product during manufacturing for a more uniform smoked flavor. Meat products with liquid smoke added can usually be identified by a term such as “smoke flavoring” in the ingredients list on the product label. Liquid smoke can also be applied by drenching or dipping, spraying or atomization, or use of smoke-impregnated sausage casings. These application methods result in surface deposition of smoke components with product effects that are very similar to those produced by the surface application of natural smoke.
• Irradiation. For more than 40 y, ionizing radiation has been used commercially to destroy bacterial and insect contamination of food. Common sources of ionizing radiation today are electron beams, X-rays, and, more often, gamma rays (with the radioactive isotope cobalt-60, the same source used for radiation therapy in hospitals). Elaborate physical safeguards assure worker safety.
Irradiation is particularly effective in reducing microbial contamination of hamburger meat and poultry, which can be contaminated by pathogens such as Escherichia coli O157:H7, Salmonella, and Campylobacter and result in food-borne illness. Irradiation also may be applied to eliminate insects in a wide variety of foods, for example, flour, spices, fruits, vegetables, and grains (IFT 2004), to prevent seeds from sprouting, and to control pathogens in fresh shell eggs, seeds for sprouting, fresh or frozen molluscan shellfish (for example, oysters, clams, mussels, and scallops), and fresh iceberg lettuce and fresh spinach (Morehouse and Komolprasert 2004, FDA 2008). Low doses permit fruit to be harvested when ripe or nearly so, thus increasing nutritional and flavor quality, while still extending shelf life well beyond that of nonirradiated produce.
Irradiation works by damaging the DNA of living organisms; the targets are typically bacteria and insects, but the DNA of the plant or animal food is of course also affected. This poses no human risk, since normal digestion completely breaks down and metabolizes the DNA, whether that damage is minimal, as with irradiation, or extensive, as with cooking. Low doses of irradiation can achieve sprout inhibition and insect de-infestation; medium doses are required for reduction of spoilage and pathogenic bacteria; and high doses are required for sterilization. Irradiated foods must be labeled as such (21 CFR 179.26[c]). Irradiation is also used at high doses and in far higher volume to sterilize joint implants, bandages, sutures, drugs, cosmetics, and wine and bottle corks (Crawford and Ruff 1996; UW Food Irradiation Education Group 2010).
The effects of irradiation on nutritional quality vary depending on nutrient, food, and irradiation conditions (for example, dosage, temperature, and atmospheric conditions). Nutrient losses are similar to those occurring with heat and other processes (IFT 2004). Thiamin (vitamin B1) is sensitive to irradiation, but loss can be minimized with packaging techniques (Thayer 1990; Fox and others 1995, 1997).
Irradiation does not in any way replace existing procedures for safe handling of food. Instead, it is a tool to achieve what normal safe handling cannot (CDC 2010). Irradiation cannot make food safe that is already spoiled (UW Food Irradiation Education Group 2010).
Because of the usefulness of irradiation in dealing with microbial risks, the Centers for Disease Control and Prevention and other public health authorities have endorsed its use (CDC 2010). The same conclusions on safety and effectiveness have been reached by international agencies (WHO 1997; Morehouse and Komolprasert 2004). Codex Alimentarius, the international food standard-setting agency, has published a General Standard for Irradiated Foods (CAC 2003a) and a Recommended International Code of Practice (CAC 2003b). Although regulations of irradiation of food vary from country to country, regulations in several countries have been or are being harmonized through compliance with the Codex General Standard (Morehouse and Komolprasert 2004). In the United States, food irradiation is regulated as a food additive, because in the Food Additives Amendment of the Federal Food, Drug, and Cosmetic Act of 1958 Congress defined radiation sources as food additives.
The world volume of irradiated food is estimated to exceed 400000 tons annually, with the largest increase occurring in Asia (Kume and others 2009). The food industry has been slow to adopt food irradiation in the more developed nations because of the large capital investment required; there is little incentive to invest in irradiation equipment because of funds already allocated for refrigeration, canning, and other major processes. The situation is very different in developing areas, where existing processes are much less extensive and postharvest losses and the risks of food-borne illness are far greater. Some argue that this is where the need for irradiation is greatest and the ability to afford it is the lowest. In the United States, irradiation could reduce E. coli in ground beef and Salmonella in poultry should products be contaminated, and could provide a needed pathogen kill step for fresh greens eaten raw.
• Extrusion. This process pushes a material through a specially engineered opening to give a desired shape and texture through increases in temperature, pressure, and shear forces. The pushing force is applied by using either a piston or a screw. In food applications, screw extrusion is predominant. Examples of traditional extruded foods are pasta, noodles, vermicelli, and breakfast cereals. Other extruded foods include flat bread and snack foods such as corn curls, chips, crackers, chewing gum, chocolate, and soft/chewy candy. Extrusion is also used to create flavors and encapsulate them for heat stability in processing. Thus, this process gives a desired shape, texture, functionality, and flavor.
Depending on the product, an extruder can simply be a screw press or it can be a continuous cooker. In the case of a screw press, the product is usually further processed extensively, such as by frying, baking, flaking, coating, or drying, as in the extrusion process to produce cornflakes. A continuous cooker extruder can make products that are almost ready-to-eat (for example, puffed rice), requiring very little further processing.
Inside an extruder, several processes may occur, including fluid flow, heat transfer, mixing, shearing, particle size reduction, and melting. In pasta manufacturing, for example, the main objective of the extrusion process is to partially gelatinize starch, compact the dough, and give it the desired shape. In the case of chocolate manufacturing, however, the extruder is used as a reactor to generate key flavor attributes. And, in the case of flat bread, an extruder is used to develop the desired expanded and porous structure.
Food extrusion is generally considered a high-temperature, short-time (HTST) process. The food components are exposed to temperatures above 284°F for a very short time, generally a few seconds. This gives a distinct advantage over conventional pressure cooking, in which the exposure could be several minutes at temperatures near 212 to 248°F.
Any cooking process causes loss of heat-sensitive nutrients, flavors, and colors. A combination of higher temperature and shorter time is desirable because it retains nutrients better than a combination of lower temperature and longer time. It has been found that vitamins A, C, E, B1, and folic acid are very sensitive to extrusion, whereas the B-complex vitamins B2, B6, B12, niacin, calcium pantothenate, and biotin are stable during extrusion.
Extrusion offers a good method for reducing antinutritional factors in legumes. For example, in peas, extrusion has been found to be more effective than germination for reducing tannins, polyphenols, and trypsin inhibitors. Extruders have been used as bioreactors for pretreatment of cereal grains for subsequent ethanol fermentation, enzymatic conversion of starch to glucose and maltose, and sterilization of ground spices such as black pepper, white pepper, and paprika. Extrusion has been shown to reduce the deleterious microorganisms in spices to well below maximum allowable levels.
Extrusion is an environmentally friendly process that uses heat and power efficiently and does not produce effluents. In addition, the same equipment can be used to make a variety of products. Extruded products are safe to consume, with no known harmful effects.
• Modified/Controlled Atmosphere. The shelf life of many fresh foods has been extended by controlling the composition of the gas environment in direct contact with the product. For products with shelf life limited by chemical or enzymatic reactions involving oxygen, reducing or eliminating the oxygen content of the environment provides significant extension of the product shelf life (Floros 1990).
The shelf life of fresh fruits and vegetables is extended by controlling both the oxygen and carbon dioxide composition of the atmosphere surrounding the products, which are still actively undergoing respiration and continue to convert oxygen to carbon dioxide. Large-scale controlled-atmosphere storage of fruits and vegetables has become a standard approach to maintaining the highest product quality between the time of harvest and delivery to the consumer. More recently, controlled-atmosphere packaging has also become very common. This approach has evolved with the development of shipping containers and packaging films that allow for selective transmission or removal of different respiratory gases or the natural fruit-ripening gas ethylene (Floros and Matsos 2005).
The modification of product atmosphere must be approached with caution, because of the response of certain microbial populations. The most serious concerns are with anaerobic pathogens, such as Clostridium botulinum, that have the potential to grow and produce toxins in an oxygen-free environment. Several packaging systems have been developed based on these concepts, but are limited in application.
• Additives. Food additives are adjuncts to food processing. They extend the range and flexibility of the relatively few food processes available, and they improve the economics of the processes. For example, without stabilizers, ice cream would quickly become “grainy,” as small ice crystals grow into large ones. Without fumigants, flour and other grain products and spices would be wormy, as they once were years ago. Without fortification of milk and flour and the addition of iodine (in the form of iodate) to salt, rickets and goiter would still occur. Without artificial colors, many foods, such as gelatin, would be unattractive because natural colors lack the stability and coloring power of the synthetics. Without nonnutritive sweeteners, a great many sweetened beverages, desserts, and confections would have unacceptable calorie contents or contain levels of sugar that cannot be consumed by certain individuals, such as people with diabetes and many others. Anticaking agents, enzymes, preservatives, emulsifiers (which allow immiscible liquids such as oil and water to form a stable mixture), humectants (which affect moisture retention through their affinity to water and stabilizing action on water content), and many other additives add significantly to the safety, nutritive value, attractiveness, convenience, and economy of our modern food supply.
The practical definition of a food additive—not the far longer, involved legal definition—is “Any substance added to food in small amounts to achieve a particular technical effect.” The Code of Federal Regulations (21.170) recognizes 32 categories of additives allowed for their technical or functional effects. Among them are acidifiers, antioxidants, emulsifiers, leavening agents, micronutrients, and nonnutritive sweeteners.
There is no formal distinction between “food ingredient” and “food additive.” Common usage would suggest that an ingredient used at less than perhaps 1% of a food would be an “additive.” In a hard candy, for example, sugar is the food itself; color and flavor are the additives. In a lightly sweetened beverage, however, sugar could be an “additive.” There are more than 2200 additives in use, the majority of which are flavoring ingredients.
Figure 3 displays the distribution of additives in use during the recent decade, ranked by per capita annual consumption in the United States food supply. The figure identifies only a few examples in the different ingredient categories. The graph shows use, the amount that disappears into the food supply. Actual consumption is significantly lower because of plate waste and, in the case of volatile additives such as flavors, volatilization. Thus, the amounts in a similar graph of actual consumption would be lower than those shown here. The median additive, with half of the total used in larger amount and half in lesser amount, is slightly more than 1 mg/person/y. The per capita consumption of a heavily used substance, such as a nutritive sweetener, frequently exceeds the per capita consumption of an ingredient in a much less used category. For example, a flavoring ingredient that because of its potency is used at very low levels will have a per capita consumption much lower than almost all other ingredients added to food.
• Packaging. Many different types of food packages are used for several different reasons. Food is packaged primarily to contain the product, protect the product from contamination, enable convenience, and provide information (Paine 1991; Robertson 1993; Yam and others 2005; IFT 2008).
Most food products are delivered to the consumer in some type of package. Foods that have received some type of preservation process are placed in a package to ensure that the product attributes enhanced by the process are maintained. Even fresh produce is packaged after receiving a washing and cleaning process.
Packaging offers a critical component of food safety by preventing contamination from pathogens. In addition, packaging extends the shelf life of the product by providing a physical barrier to or protection from atmospheric oxygen and moisture, light, and other agents that would accelerate deterioration of the product. Finally, packaging is the vehicle by which legally required information is presented to the consumer in the form of the label bearing information about the product identity, quantity, ingredients, nutrient content, expiration date, and commercial source.
Packaging has advanced from glass bottles, paperboard cartons, tin-plated soldered side-seam steel cans, and aluminum foil to 2-piece aluminum cans with “pop tops;” plastic, flexible, rigid, semirigid, and multilayer containers; microwave safe packages; and active and intelligent packaging (Floros and others 1997, 1998; Suppakul and others 2003; Ozdemir and Floros 2004; Yam and others 2005; Han and Floros 2007; IFT 2008). Innovations were driven by a number of forces, including convenience, consumer desire for minimally processed foods, changes in retail and distribution practices; foodservice needs; trend toward more sustainable packaging; and demands for global and fast transport of food (Suppakul and others 2003; IFT 2008).
Aseptic packaging is a major area of food packaging that has significantly increased the safety, quality, availability, and convenience of certain foods around the world, while reducing the amount of energy needed to preserve and store such foods. The major difference between aseptic packaging and traditional methods of food packaging is that in aseptic packaging the product and the packaging material are continuously sterilized separately. Then, under aseptic conditions that prevent recontamination of the product, the sterile package is filled with the cooled sterile product and hermetically sealed to produce a shelf-stable final product with extended shelf life and no need for refrigerated storage. This technique has allowed for substantial improvements in the quality of the final product, mainly due to the much milder heat treatment that the product undergoes compared to the traditional thermal process (Floros 1993). Large-scale aseptic bulk processing and packaging, combined with aseptic storage and transportation, contributes significantly to reduction of postharvest fruit and vegetable losses and greater availability of these food products around the world.
Many advances in the packaging of food took place in the past 20 to 30 y, producing a wide variety of new materials and processing technologies. The steady accumulation of research developments indicates that food packaging will continue to evolve and respond to the changing needs of the food system and the increased demands of consumers.