A review on the improvement of extruded food processing equipment: extrusion cooking in food processing

The extrusion technique, which combines mixing, shaping, texturing, and heating to create a unique food product, is gaining popularity in the worldwide agro-food processing sector. Extrusion cooking is a high-temperature, short-time (HTST) method that kills bacteria and inactivates enzymes. Compared to conventional cooking, extrusion cooking is favored because of its high productivity and substantial nutrient retention. Extrusion technology has become an essential tool in the food processing industry with its various benefits over other processing methods. It is a low-cost approach that provides a platform for processing a variety of items from several food categories by altering major or minor components and processing conditions. Extrusion technique is used in the food sector to create a wide range of supplemental foods, pet foods, morning cereals, pasta, snacks, and other textured foods. It’s a low-cost method of reintroducing food processing waste and by-products into the food supply. Extrusion technology’s flexibility allows for the production of value-added products and nutritionally dense fortified goods using various low-cost raw ingredients. Extruded goods are microbiologically safe, have a longer shelf life, and have less moisture content. This technology’s advantages include product diversity and excellent quality and new food productivity and low processing time.


Introduction
Extrusion processing is the technique of plasticizing proteinaceous, starchy, and wet food ingredients using a mixture of mechanical shear, heat, pressure, and moisture in a die (Shelar & Gaikwad, 2019).The late 1950s saw the introduction of extrusion cooking in food and feed production.The technologies employed have gained the reputation, efficiency, and adaptability since then (Cheftel, 1986;Y. Liu et al., 2019;Moscicki, 2011;Moscicki & van Zuilichem, 2011;Tiwari & Jha, 2017;Zhang et al., 2021).The extrusion cooking technique is generally employed in the food business for cereal and protein processing and in the pet food and feed industries (Ganjyal, 2020;Moreno et al., 2018;Mosibo et al., 2020).Extruder technology has advanced in the previous decade, allowing for more complex goods, novel flavor creation, encapsulation, and sterilizing (Ajita, 2018;Offiah et al., 2019;Zhang et al., 2017).
In the food sector, thermoplastic extrusion is referred to as High-Temperature, Short-Time (HTST) process because it allows for the manufacture of a wide range of food and feed products with little or no change of basic equipment and proper process management (Adeleye et al., 2020;Shelar & Gaikwad, 2019).Rice, wheat, corn, and more recently, soy have all been subjected to this method.Extruders can work at low, medium, or high shear based on the raw materials being used and required qualities for the finished product; typically, thermoplastic extruders are utilized at high shear (Xu et al., 2015).Low shear (cold extrusion) is used in the production of pasta and processed meat products, medium shear is used in the production of meat analogs and some pet foods, and high shear (thermoplastic extrusion) is used in the production of expanded snack foods, morning cereals, and textured vegetable proteins (Guy, 1994).
Raw material qualities and extruder operational circumstances, according to Fellows (2009), are the two most important elements that determine extruded product attributes.The following might be highlighted as key features of the raw material: pH, chemical composition, physical condition, moisture content, and kind of material.Die diameter, pressure, temperature, and shear force, the latter of which is controlled by the extruder's internal design and length, as well as screw geometry and rotation speed, are the operating factors that might be highlighted as essential.The thermoplastic extrusion method has the following benefits, according to Harper (2019) and Steel et al. (2012): high production yields, low prices, flexibility, excellent product quality,

A review on the improvement of extruded food processing equipment: extrusion cooking in food processing
Yermek ABILMAZHINOV 1 * , Galiya ABDILOVA 1 , Anton NESTERENKO 2 , Zhanna DIBROVA 3 , Vladimir ERMOLAEV 4 , Irina MIRONOVA 5,6 , Viacheslav ZHENZHEBIR 4 , Evgeny PONOMAREV 3 , Valentina VLASOVA 3 and no effluents.Food extrusion is a type of extrusion used in food processing in which a mixture of raw materials is pushed through an aperture or die with a food-specific pattern and then trimmed to size by blades.The extruder is the machine that pushes the mixture through the die, and the mixture is known as the extrudate (Reque et al., 2014;Riaz, 2000).
The extruder is made out of a big, spinning screw that is snugly fitted into a stationary barrel and has a die at the end that forms the desired enlarged result.Food preparation at high temperatures poses a difficulty in the food processing industry, as high temperatures cause food to lose its nutritional content.As opposed to traditional cooking, Extrusion cooking is recommended to prevent this since it has a short processing time, considerable nutrient retention, and great productivity.Extrusion cooking is an HTST technique for reducing microbial contamination and inactivating enzymes in food (Mościcki et al., 2012).Extrusion causes the starch to gelatinize, proteins to denaturize, lipid oxidation to be reduced, and antinutritive factors to be reduced.Furthermore, it is regarded as a flexible, low-cost, and highly efficient food processing technology capable of delivering a wide variety of nutritionally rich value-added products (Bordoloi & Ganguly, 2014).It is a modern food processing technology used to create a wide range of supplemental, textured, and snack foods.Extruded foods contain less moisture, are nutritionally dense, are microbiologically safe, and have a longer shelf life (Pathak & Kochhar, 2018).

Extrusion process principles
Raw ingredients are put into the extruder barrel, and the food is conveyed along with it by the screws.Smaller flights further down the barrel limit the amount of the meal and make it more resistant to movement.As a consequence, it compresses the barrel as well as the gaps between the screw flights.The screw kneads the material into a semi-solid, plasticized mass as it advances deeper down the barrel.Extrusion cooking (or hot extrusion) occurs when food is cooked to a temperature above 100 °C (Senanayake & Clarke, 1999).The temperature rises quickly as a result of frictional heat and any extra heating.The food is subsequently transferred to a portion of the barrel where pressure and shearing are enhanced even more because of the smaller flight.Eventually, when the food emerges under pressure from the die, it expands to its finished state and cools quickly as moisture is blasted out as steam via one or more limited dies at the discharge end of the barrel (Mulye et al., 2014) (Figures 1 and 2).Shells, squirls, doughnuts, strips, spheres, rods, and Tubes are just a few examples of the forms that may be made.Enlarged, low-density snack foods and ready-to-eat (RTE) puffed cereals are typical items (Cho et al., 1995).Foods like pasta and meat products are mixed and shaped using cold extrusion, where the item's temperature remains constant (Menis-Henrique et al., 2020).Pet meals, liquorice, surimi, and fish pastes are all made with low-pressure extrusion at temperatures below 100 °C (Navale et al., 2015).

The categorization of an extruder
Extruders are machines that are used to process extrusions.Homogenization or mixing, size reduction, shaping, dehydration, pasteurization, heat cooking, enzyme inactivation, texturization, protein denaturation, starch gelatinization, and shearing are some of the unit activities that food extruders may execute simultaneously (Singh et al., 2020).Extruders are made up of five basic components (Mount 3rd, 2017) (Figure 1).
• The system of pre-conditioning: Steam or water is used for pre-conditioning, and the mixture is done by hand.This is utilized when the moisture level of the substance is approximately 20-30%, and the material has a long residence period.Preconditioning promotes consistent particle hydration, lowers retention periods inside the extruder, and boosts throughput, all while extending the equipment's life and lowering energy costs.
• The system of feeding: For an effective and consistent extrusion process, raw material feeding into the extruder should be continuous and uninterrupted.
• The worm or screw: Material is conveyed into the extruder barrel by a screw, which shears the material and ensures the quality of the finished product.The screw of the extruder influences the protein denaturation, dextrinization and gelatinization of starch, and cooking degree, but it also ensures the quality of the end product.Mono-piece or multi-piece screws are available.The quantity and form of screw components might differ, and each segment serves a unique role.Certain components simply transport raw or pre-conditioned content into the extruder barrel, whereas others compact and degas the feedstock.Shear, backflow, and kneading must all be promoted.To promote mechanical energy dissipation, backflow, and dispersive mixing into the extruder, certain kneading screws feature interrupted flights.The following are the main aspects of screw design (Kowalski et al., 2018;Liu et al., 2010) (Figure 3).It is separated into three sections (Figure 1): sleeves, kneading, and feeding, which are frequently jacketed to allow for the circulation of superheated oil or steam for heating and air or water for chilling, allowing for exact control of temperature in the different parts of the extruder.• The cutting mechanism and the die: The die has two purposes; it shapes the finished product and promotes material flow resistance within the extruder, increasing inside pressure.The die can come in a variety of shapes and sizes, as well as a variety of orifice counts.The cutting mechanism should be able to produce uniformly sized end items.The rotation speed of the cutting blades determines the size of the product.This system can be vertical or horizontal (Tiwari & Jha, 2017).Screw, barrel, and die configurations can all affect them.The raw material utilized and the intended final result will determine which of these things is chosen.Extruders are classified according to (Muthukumarappan & Swamy, 2020): • Operational strategy o Hot extruders: HTST settings under pressure are often used to thermomechanically change raw materials.It's mostly utilized to make textured food and feed items like ready-to-eat breakfast cereals and snacks, among other things.
o Cold extruders It's used to gently combine and mold dough within the extruder without using direct heat or cooking.It's mostly used to make pasta in the food industry.

• Construction method o Single-screw extruder
A single revolving screw is contained in a metal barrel in a single screw extruder.Single scews with a consistent pitch and a variety of patterns are the most often used single scews.The raw materials are supplied into the feed section by a hopper, and the material is conveyed to the transition section via a revolving screw.The screw channel gets shallower at the transition region, and the material is compressed, resulting in a rise in the material's temperature.The substance gets more cohesive when the starch becomes gelatinized.The metering portion transports it farther and pushes it through the die hole (Rokey, 2000).
o Twin-screw extruder It's made up of two equal-length parallel screws that spin inside the housing for greater control.Twin-screw extruders are used for huge numbers of twin-screw extruders in the same barrel, generally the interior face of the barrel of moisture extrusion.It's much more intricate than constituents like fibers, lipids, etc., and other complex ingredients, as well as more advanced goods.The location of the screws and their non-intermeshing screws will vary depending on the situation (Huber, 2000) (Figure 4).

Extrusion's raw materials and ingredients
Extrusion cooking techniques may be used with various foods, such as proteins, meat, cereals, legumes, oilseeds, tubers, starches, and grains.The kind of material, its physical condition, chemical composition, pH, and moisture content are the most important aspects of raw materials for extrusion cooking (Twombly, 2020).Solid raw materials make up most of the raw materials used in food extrusion (Zhu & Yu, 2020).Starch is used to make numerous goods, such as biscuits, morning cereals, and snacks, whereas protein is utilized to make meat-like products used as partial or full meat substitutes in several pet food products, dry foods, and ready meals (Offiah et al., 2019).

Extrusion technology's advantages
• By varying the ingredients, extruder working conditions, and dies, you may create a wide range of products.• Extruders may alter starches, proteins, and other food components to create a wide range of novel meals (Singh et al., 2007a); • Extrusion cooking does not create substantial process effluents because it is a low-moisture process; • Extrusion cooking uses HTST, which keeps many heatsensitive components of a dish intact while reducing nutritional and taste losses (Rao & Kiranmai, 2020); • Extrusion is a continuous process that produces a large amount of material; • Extrusion processing is energy-efficient since it cooks food items at low moisture levels.Lower moisture decreases the amount of heat needed to cook and redry the food afterward (Offiah et al., 2019); • Compared to other heating and shaping processes, extrusion has reduced processing costs and better output (Moreno et al., 2018).

Extrusion technology's disadvantages
• The nutritional characteristics of proteins generally deteriorate when food item containing proteins and reducing sugars is heated (Singh et al., 2007b); • Excessive heat causes the color of the product to fade; • Different chemical processes, such as non-enzymatic browning and caramelization, might occur due to the high temperatures and low moisture conditions utilized (Camire, 2000).

Application of extrusion technology
Extrusion technology is used in the food production market to ensure extruded foods for pets and humans and add value to food residues and waste (Rizvi et al., 1995;Zhengrong, 2000).Extrusion is a cost-effective way to incorporate by-products and residues from food processing back into the food supply (Leonard et al., 2020).

Meat analogues
A meat analog, also known as a meat replacement, fake meat, faux meat, or imitation meat, is a substance that mimics the visual and chemical properties of many forms of meat.Meat analogs are commonly manufactured from soy protein or gluten (Chiang et al., 2019;Dekkers et al., 2018) (Tables 1 and 2).
Textured vegetable proteins (TVP) are made-up plant products that can entirely substitute meat in a meal.Defatted soya proteins make TVP heated extrusion, which results in enlarged high protein chunks, grains, strips, nuggets, and other forms with meat-like textures (Caporgno et al., 2020).TVP is a porous, insoluble, and fibrous material that can absorb many water or other liquids.When hydrated, textured soy proteins are processed to mimic poultry, fish, or meat in structure and appearance.Soy protein products have grown more popular because of their diverse functional characteristics, good nutritional quality, and low prices (Boukid, 2021).

Conclusions
Extruder technology has progressed significantly during the previous three decades.On the other hand, technical innovations will be required in the development of new generation extruders and complementary equipment aimed at enhancing effectiveness and efficiency, improving throughput, simplifying process control, facilitating the production of a wide range of complex snacks, and boosting the quality of the end product.In addition, it's always been critical to cater to customer needs that are currently strongly linked to healthy and nutritious foods that encourage well-being and a pleasant way of life.Extruders make it possible to make a wide range of nutritious meals.In creating functional meals, extruders' capacity to mix various components in new foods may be used.Conventional snacks or morning cereals can be improved by adding additional fibers or whole-grain flour as components during extrusion, resulting in appealing cereal-based products with physiological benefits.
Extrusion processing allows for creating high-nutritive, lowcost, and convenient food items with a lot of flexibility.Extruded snacks have the potential to replace low-nutrient traditional snacks.The extrusion method increased the nutritional content of the goods while lowering antinutrients such as phytic acid and tannic acid.It also enhanced antioxidant activity and protein digestibility.This technique plays a key role in manufacturing a wide variety of meals and components due to its positive benefits, such as eliminating antinutritional factors, contaminated microbes, reduced lipid oxidation, and enhanced soluble dietary fibers.

Figure 2 .
Figure 2. Dough expansion as it exits the die.

Figure 3 .
Figure 3.The most important aspects of screw design.

Table 1 .
Meat analogs in their most common forms.

Table 2 .
Nonmeat protein sources that can be used as meat substitutes.