**4. Food processing and preservation**

Food processing by chemical or physical means converts the harvested food ingredients into food or other intermediate products [1]. It is the process of producing raw food ingredients into marketable products that consumers can easily prepare and use. In addition, it is easy to keep processed foods stored for a long time—examples include canned and frozen fruits and vegetables and fortified foods (micro or micronutrient-rich foods).

Food processing must be balanced with food preservation also. Food preservation is to stop or slow down the spoilage of food, and loss of quality, and improve the edibility of food for a longer time. Some technologies that increase food products' shelf life are heating, drying, canning, freezing, and others [10]. These technologies inactivate the microorganisms responsible for food spoilage and foodborne diseases or inhibit their growth. The major advantage of food processing is that it makes it more edible, palatable, and safe to consume and increases the shelf life after harvesting. New technologies were developed to meet the food requirements regarding quality, flavor, taste, and shelf life. Some commonly used food processing methods are chopping or slicing, mincing, liquefaction, fermentation, emulsification, cooking, mixing, and gasification, such as adding gas to bread or soft drinks [11]. In addition, some novel processing technologies were also developed to produce durable products available all year round regardless of their seasonality which, in turn, leads to reduced post-harvest loss.

Most food processes utilize six-unit operations: heat transfer, fluid flow, mass transfer, mixing, size adjustment, and separation [12]. The scope of food processing describes unit operations occurring after the harvest of raw materials until they are processed into food products, packaged, and shipped for retailing. The food preservation methods eliminate harmful pathogens present in the food and minimize or eliminate spoilage microorganisms and enzymes for the shelf-life extension. Food's physical, chemical, and thermal properties help identify the extent of process uniformity during physical, chemical, and thermal processes such as grinding, mixing, chemical modification, pasteurization, and sterilization. Therefore, food scientists and process engineers must adequately characterize the food's thermophysical and chemical properties.

### **4.1 Food preservation**

The goal of food preservation is to prevent the growth of bacteria, fungi, or other microorganisms and retarding the oxidation of fats that cause rancidity, thus promoting longer shelf life and reducing hazards from eating the food [1]. The main goal of preservation is to increase the safety of food products. If the safety of the foods is compromised, it can result in contamination and cause widespread illness. Several food preservation methods are designed specifically to preserve food. Traditional methods are currently used to preserve food and extend its shelf life. Some traditional food preservation methods, such as heating, cooling, pickling, boiling, sugars, and others, are discussed below [3].

#### *4.1.1 Freezing*

Freezing is a process used to preserve a wide range of foods. The challenge of frozen foods is the change in texture and structure. For example, rapid freezing can adversely affect the texture of the foods [3].

### *4.1.2 Pickling*

Pickling is a process where the foods are preserved in an edible and antimicrobial liquid, vinegar or vegetable oil, or anaerobic fermentation to increase the shelf life of foods [13]. There are two types of pickling: a) fermentation and b) chemical pickling. In the fermentation process, the bacteria in the liquid produces agents acting as preservatives, and in chemical pickling, the food is preserved in edible liquids that kill the microorganism and bacteria. The pickling method changes the food's texture, flavor, and taste. In Asia, pickling is widely used for many vegetables, including carrots, cauliflower, lemon, and raw mangoes [3]. In North America and other European countries, eggs, fish, and meat are also pickled [3]. During pickling, organic acids such as lactic acid and acetic acid are produced, which act as preservative agents. In addition to acids, brine is also used for food preservation. Both the acids and brine result in inhibiting the bacteria from growing.

#### *4.1.3 Curing*

The curing is used for vegetables, meat, and fish, where the moisture content is reduced using the osmosis dehydration process [14]. The osmotic dehydration process helps to reduce the moisture content of the foods such as fruits and vegetables, which helps to reduce microbial damage [14]. Curing also helps to improve the flavoring of the foods. Curing is done by adding salt, nitrates, sugars, and nitrites. Adding salt to the food products slows the oxidation process, which helps reduce the rancidity in the food products.

#### *4.1.4 Fermentation*

Food fermentation utilizes microorganisms' growth and metabolic activity to stabilize and transform food materials [15]. Fermentation is used for foods such as beer, wine, and cheese produced using microbes. During fermentation, the storage conditions, such as temperature, salt, oxygen level, and others, should be maintained to produce the microbes to preserve the food products.

#### *4.1.5 Drying*

This is one of the oldest technologies used for food preservation. This process exposes the food to sunlight to dry naturally. In addition, various types of commercial dryers are developed for drying foods—drying results in the evaporation of moisture content from food, further reducing the water activity and preventing the microorganisms from deteriorating the foods [1].

#### **4.2 Modern methods for food preservation**

#### *4.2.1 Refrigeration*

The cooling technique preserves the foods by reducing the growth of microorganisms and enzyme activity [16]. Some food products commonly stored using cooling methods

*Introductory Chapter: Food Processing, Preservation, and Packaging – A Brief Overview DOI: http://dx.doi.org/10.5772/intechopen.110229*

are meat, dairy, and fish, thus increasing the shelf-life of the products. Refrigeration is cooling the environment artificially to bring the temperature below ambient temperature. The refrigerator's temperature ranges from 4 to 10°C. Typically, bacterial growth is slowed at these temperatures, and most bacteria enter a dormant phase. For example, the enzymes which result in the degradation of food products at room temperature, under refrigeration slow the catalytic rate of enzymes and prevent the degradation. Refrigeration is used in many homes today to preserve fresh fruits, vegetables, meat, and milk products.

## *4.2.2 Sugaring*

During the sugar preservation of the food products, the sugar makes the foods hypertonic, and microbes do not survey in hypertonic solutions. The hypertonic solutions suck the water from the microbes and dehydrate them. The foods such as fruits and vegetables are stored in sugar or honey; examples are hams and jellies. Also, many soft drinks and concentrates are prepared based on this principle.

### **4.3 Modern methods of food preservation**

### *4.3.1 Pasteurization*

Most microorganisms and spores could be destroyed by applying sufficient heat to food items. Therefore, high-temperature short time (HTST) and low-temperature short time (LTST) are commonly used to preserve foods [17].

## *4.3.2 Freeze drying*

Freeze drying is also known as lyophilization. During this process, the moisture in the foods is removed under frozen and vacuum conditions at lower temperatures. The principle of this process is that the food's water is evaporated by sublimation at low pressure [3]. The low pressure and temperature during processing help the foods retain most of their quality attributes and shape. The process is used for heat-sensitive foods. The other technology widely used to preserve heat-sensitive foods is vacuum drying.

### *4.3.3 Vacuum packing*

During vacuum packing, the foods are placed in a plastic bag, and a vacuum is created inside the bag, by sucking the air inside the bag [3]. Under no air storage conditions, the microbes do not grow and survive. This method is used for preserving nuts as it avoids oxidation reactions, such as rancidity, and preserves the flavor.
