Food processing method

Extrusion in food processing involves pushing soft mixed ingredients through an opening in a perforated plate or die to create specific shapes. The extruded food is then cut to size by blades. The machine doing this is an extruder, and the mix is known as the extrudate. Typically, the extruder includes a large, rotating screw within a stationary barrel, ending at the die.

Extrusion allows for mass production of food through a continuous, efficient system ensuring uniformity. This includes pasta, breads (such as croutons, bread sticks, and flat breads), many breakfast cereals, ready-to-eat snacks, confectionery, pre-made cookie dough, some baby foods, full-fat soy, textured vegetable protein, certain beverages, and dry or semi-moist pet foods. Extruded products usually have high starch content.

Process

In food extrusion, raw materials are first ground to a coarse flour consistency. The dry mix goes through a pre-conditioner where additional ingredients are added depending on the desired product. These can include liquid sugar, fats, dyes, meats, or water. Steam is injected to initiate the cooking process. The preconditioned mix (extrudate) is then processed through an extruder, where a rotating screw forces it through the die.

During extrusion, many products puff and change texture due to reduced forces and released moisture and heat. This is known as the expansion ratio. The extrudate is cut by blades at the extruder's output, rotating at a specific speed. The product is then cooled and dried, making it rigid while retaining porosity. Cooking within the extruder generates friction and heat due to pressure (10–20 bar), causing protein denaturation and starch gelatinization under some conditions.

Many food extrusion processes apply high temperature for a short period. Essential factors in extrusion include the extrudate composition, screw length and speed, barrel temperature and moisture, die shape, and blade speed. These factors ensure uniform output based on the final product's requirements. Moisture is notably crucial, affecting the mix's viscosity and acting to plasticize the extrudate. Increasing moisture decreases viscosity, torque, product temperature, and die pressure while increasing bulk density.

Most food extrusion is done at low to intermediate moisture (below 40%). High-moisture extrusion is called wet extrusion, utilized more after the advent of twin-screw extruders (TSE) for better conveying capability. In wet extrusion of high-starch extrudate, temperature is the key rheological factor.

Salt content in the extrudate can affect the color and texture of some extruded products. The expansion ratio and airiness depend on salt concentration, possibly due to a chemical reaction between salt and starches. Color changes may result from salt altering the water activity of the extrudate, influencing browning rates. Salt is also used to evenly distribute minor ingredients like food colors and flavors post-extrusion.

History

The first extruder was designed to make sausages in the 1870s. Dry pasta and breakfast cereals have been extruded since the 1930s, with pet food following in the 1950s (first extruded dog food: Purina Dog Chow in 1957, and cat food: Purina Friskies in 1963). Some kitchen appliances, such as meat grinders and pasta makers, also use extrusion. Pastry bags operate by extrusion when squeezed by hand.

Effects

Extrusion facilitates mass food production with uniform final products by controlling various extrusion aspects. This method also allows for new processed food products," revolutionizing many conventional snack manufacturing processes." The extrusion process induces "chemical reactions within the extruder barrel and at the die."

The material of an extrusion die affects the final product. Rough bronze dies for pasta extruders yield rough surfaces favorable for liquid pasta sauces, indicated as "bronze die" pasta, marking a premium product. The effects of extrusion cooking on nutritional quality are ambiguous, changing carbohydrates, dietary fiber, proteins, amino acids, vitamins, and minerals both beneficially or harmfully.

High-temperature, short-duration extrusion minimizes vitamin and amino acid losses. Extrusion can denature antinutritional factors, destroy toxins, or kill microorganisms. It may also improve protein quality and digestibility and significantly affect a product's shape, texture, color, and flavor. The process may fragment proteins, starches, and non-starch polysaccharides to form new linkages, including Maillard reactions reducing protein nutritional value. Heat-labile vitamins may be destroyed, and the stability or bioavailability of extruded phytochemicals is still under research.

Nutritional quality improves with moderate conditions (short duration, high moisture, low temperature) but negatively impacted by high temperature (at least 200°C), low moisture (below 15%), or improper mix components. Using non-traditional cereal flours like amaranth, buckwheat, or millet can reduce the glycemic index of extruded breakfast cereals, featuring higher bulk and product density, similar expansion ratio, and significant reduction in digestible carbohydrates.

Replacing 5%-15% wheat and white flour with dietary fiber in extruded breakfast cereal mix notably slows carbohydrate hydrolysis, increasing slowly digested carbohydrates and reducing quickly digested carbohydrates.

Products

Extrusion has allowed new processed food production and "revolutionized many conventional snack manufacturing processes." Extruded food products typically have high starch content. Directly expanded foods, like breakfast cereals and corn curls, are produced at high temperature, low moisture, and high shear. Unexpanded foods, like pasta, are made at intermediate moisture and low temperature. Texturized products, such as meat analogues, use plant proteins and a long die to create fibrous, meat-like structures.

Extrusion-produced processed cheeses and cheese analogues include low moisture, low-temperature varieties preferred for extrusion over higher moisture or temperature cheeses. Cheddar cheese extruded at lower moisture and 80°C was favored in studies for quality. An extrudate mean residence time of approximately 100 seconds enables various textured processed cheeses.

Confectionery extrusion includes products like chewing gum, liquorice, and toffee. Other extruded foods include various breads (croutons, bread sticks, and flatbreads), ready-to-eat snacks, pre-made cookie dough, baby foods, certain beverages, and dry or semi-moist pet foods. Examples include cheese curls, macaroni, Fig Newtons, jelly beans, sevai, and some french fries.

Extrusion also modifies starch and pelletizes animal feed.

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References

Further reading

In the ever-evolving landscape of pet care and nutrition, food extruder machines have emerged as a revolutionary tool for pet food manufacturers. These advanced pieces of equipment offer a multitude of advantages, ranging from improved product quality to increased efficiency in production processes. In this article, we delve into the various benefits of utilizing a dog food extruder machine in the pet food industry.

Enhanced Product Quality

One of the primary advantages of dog food extruder machines is their ability to produce high-quality pet food products consistently. These machines utilize precise temperature and pressure control mechanisms, ensuring that the ingredients are cooked thoroughly and evenly. As a result, the final product is not only more palatable but also nutritionally superior, meeting the dietary needs of dogs more effectively.

Versatility and Customization

Dog food extruder machines offer unparalleled versatility and customization options for pet food manufacturers. These machines can process a wide range of ingredients, including grains, meats, vegetables, and supplements, allowing manufacturers to create customized formulations tailored to the specific nutritional requirements of different dog breeds and life stages. Additionally, extrusion technology enables the incorporation of functional ingredients such as probiotics, antioxidants, and vitamins, further enhancing the health benefits of the final product.

Improved Digestibility

Another significant advantage of dog food extruder machines is their ability to improve the digestibility of pet food. The extrusion process breaks down complex carbohydrates and proteins into smaller, more digestible forms, increasing the bioavailability of nutrients and reducing the risk of digestive issues in dogs. This enhanced digestibility not only promotes better nutrient absorption but also contributes to overall digestive health and well-being in canine companions.

Cost Efficiency

Dog food extruder machines offer substantial cost savings for pet food manufacturers in the long run. While the initial investment may seem significant, the efficiency and productivity gains achieved through extrusion technology result in lower production costs per unit of pet food. Moreover, the ability to process a wide range of ingredients allows manufacturers to optimize ingredient utilization and minimize waste, further reducing operational expenses over time.

Increased Production Efficiency

In addition to cost savings, dog food extruder machines significantly enhance production efficiency in pet food manufacturing facilities. These machines operate continuously, with minimal downtime between batches, maximizing throughput and minimizing production bottlenecks. Furthermore, extrusion technology enables rapid processing and extrusion of ingredients, reducing overall production time and increasing output capacity to meet growing market demand.

Consistent Product Quality

Consistency is key in the pet food industry, and dog food extruder machines excel in delivering uniform product quality with every batch. Unlike traditional cooking methods, which may result in variations in texture, flavor, and nutrient content, extrusion technology ensures consistent product characteristics across all batches, fostering consumer trust and brand loyalty. This uniformity is essential for meeting regulatory standards and satisfying consumer expectations for premium-quality pet food products.

Conclusion

In conclusion, dog food extruder machines offer a myriad of advantages for pet food manufacturers, ranging from enhanced product quality and customization to cost efficiency and increased production efficiency. By leveraging extrusion technology, pet food manufacturers can elevate their offerings, delivering nutritionally superior and consistently high-quality products that meet the diverse needs of dogs. As the pet food industry continues to evolve, extrusion technology will undoubtedly play a pivotal role in shaping its future.

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