A new twist on grain processing
November 01, 2004
by World Grain Staff
by Joseph P. Kearns and Suzi Fraser Dominy
Extrusion cooking has its roots in the petfood and aquatic feed industries. In recent years the technology has come into its own in human food product development, particularly as a means to add value to cereals and oilseeds for the convenience and specialty food sectors.
TEXTURIZED SOY PROTEINS
Texturized soy proteins (TSP) for use as meat substitutes were among the first food products developed through extrusion. Recent advances have provided new opportunities to add value to this long established product.
Newly developed soy flours or combinations of soy products used for today’s TSPs have increased potential water uptake from around 2.5:1 to 3.5:1and in some cases better than 4:1 — i.e. 4 parts water added to 1 part of TSP by weight. And as all millers well understand, there are considerable financial implications in buying and selling water.
There is also a benefit in terms of product quality: at this moisture level TSP becomes more meat-like in texture and appearance and therefore performs better as a finished product.
As an example, the effect of using texturized soy from concentrate in ground beef patties at 8% inclusion will reduce weight loss during cooking from 34% to 23%. Sold weight in a restaurant is higher, the consumer likes the juicier burger and the cost of the item is less with an improved amino acid profile. A value-added success all along the food chain by making a product that has a better water holding capacity via extrusion cooking.
TSPs have also been used for many years as structured meat analogs or meat replacers in vegetarian diced-meat dishes or as vegetarian "stew-meat." These products are typically dried after extrusion resulting in a very shelf-stable product. The product is re-hydrated either by a food processor making prepared foods or directly by the end-user. Typically the products are flavored in the rehydration step.
However, this product has not fulfilled its potential over the years as it takes about 30 minutes in boiling water to re-hydrate. Recently, commercialization of high moisture meat analog — layered, fibrous whole muscle-like structures suitable as whole muscle vegetarian meat analogs — and fibrous soy protein — a muscle fiber-like structure ideally suited for restructured vegetarian meats or restructured vegetarian meat jerky — are giving this category new opportunities.
Textured soy protein and extruded cereal processing technologies are also the basis of protein-based and proteinfortified snack foods and nutritional bars that are currently finding a ready market.
Products based on texturized protein technology result in products that expand more than texturized proteins, have a softer texture and normally include savory flavors. Those based on expanded cereal technology produce products that are less expanded than expanded cereals, have a harder texture but normally have a sweet flavor.
Typical protein raw materials for these products would include soy flour, soy concentrate and soy isolate. Starch sources would normally include rice or corn flour, other cereal grains and purified starches.
QUICK COOKING RICE
One of the best examples of value addition to cereals is quick cooking rice. Extrusion technology can elevate low value broken rice into a premium product with an even higher market value than whole rice.
Quick cooking rice (QCR) is produced by moderate temperature extrusion as a fully cooked and gelatinized product. The consumer just needs to boil QCR for three minutes then allow it to stand, making preparation time just 10-12 minutes, compared with the 25-30 minutes it takes to cook whole rice.
QCR is made from rice flour from long, medium or short grain varieties and extrusion additives such as monoglycerides and spray dried fats or oils. Other micro-ingredients can be added to produce a variety of value-added rice products and might include colors, flavors, vitamins, protein enrichment and minerals.
The total cost of producing QCR, based on a system for 2,500 kg/hr on a per tonne basis is shown in Table 1. This is an estimate only as the cost of rice differs from country to country.
Taking as an example the "minute rice" available in stores in the Kansas City, Missouri, U.S. area, the retail price is U.S.$2-U.S.$3 per kilo, while the manufacturing costs are about U.S.$0.51 per kilo: a clear indication of the value added benefit to the producer.
QCR is made on an extruder barrel that is relatively short in length. This is done to keep the energy input at the optimum level. The same technique is used to produce instant foods for babies and beverage drink powders for children of all ages. QUICK COOKING PASTA
Quick cooking pasta is another example of a cereal-based product that has added value. Traditional pasta is produced by low temperature extrusion and it is not cooked or gelatinized. It must be boiled for preparation and neither hot water nor cold water re-hydration is acceptable. Microwave cooking is possible in limited situations.
Precooked pastas are produced by moderate temperature extrusion. They are fully cooked or gelatinized, and it is not necessary to boil for preparation. Hydration occurs in 5 to 10 minutes in hot water and 20-60 minutes in cold water. These products can also be microwaved.
Quick cooking pasta is produced by moderate extrusion temperatures as well and is also fully cooked. The preparation time is in the 2-5 minute range with hotwater hydration and 15-30 minutes in cold water. Microwave cooking works well since the water needs to reach boiling then simply set for the re-hydration time.
Quick cooking pasta also has an advantage in that the raw materials do not need to be expensive durum flours. Flours from durum, semolina, hard wheat, soft wheat and other cereal grains can be used including corn and rice. This gives the product great versatility due to the range of product textures and utilization of flour blends.
A further advantage is the drying time. Due to the porosity, such products dry in 40-80 minutes with a temperature in the 80° C range with humidity levels in the dryer of 3%-40%. (Figure 1).
BABY FOODS AND DRINK POWDERS
Infant cereals that are hydrated in water or milk are often produced on a drum drying system. Similar products with corresponding characteristics can be produced by extrusion with reduced utility costs as the value-added benefit.
Products made on the drum drying process have the appearance of small flakes, while the product made on the extrusion process looks more granular. While the appearance is different, the performance is very similar. The major value-added advantage gained by extrusion in this application is elimination of the requirement for drying: a significant cost saving compared with drum-dried products, which start at or near 80% moisture. The energy to remove this moisture is greater then the energy consumed on an extrusion cooker.
There is a great deal of recipe flexibil- ity for producing infant cereal products. The recipes are usually based on flours of a single cereal grain or a blend of flours. Rice flour is a commonly used base because of its high digestibility and low incidence of allergic reaction. However, other grain sources can be used such as maize, wheat and oats.
The recipes often have a dietary calcium source added, such as dicalcium phosphate, at a level of about 1% -1.5%. Other nutritional supplements, such as iron or potassium could also be added.
Enhanced protein levels and flavor can be obtained by adding dry milk or nonfat dry milk to the extruded cereal base at a level of about 30%. Some clients may choose to use dry milk rather than non-fat dry milk in order to increase the energy content of the final product. Due to the sugars and the proteins in dry milk, products tend to brown very readily in the extrusion process. Added dry milk also dramatically reduces expansion and lengthens hydration time. Therefore, it is recommended that milk products be added after grinding. Soy or other proteins can also be added to infant foods to further enhance the protein content.
It is important to remember that as the extruder makes the starchy portion more soluble, the protein portion becomes less soluble and does not suspend well – especially in a drink product. Protein fortification is best accomplished by adding either soy concentrate (from a variety with a high Nitrogen Solubility Index) or isolate to the extruded cereal base post extrusion at levels up to 50%. Adding protein to the cereal base prior to extrusion may be appropriate if it is to be used as porridge only. If the product is to be used as a drink mix, the proteins will settle out very quickly.
PREMIUM BREAKFAST CEREAL FLAKES
Premium breakfast cereal flakes are produced by extrusion where the established extrusion process has been adjusted but not changed drastically. The acceptable finished product is mostly related to the look of the product and the resultant mouth feel and what is referred to as "bowl life" or crispness in milk.
Extrusion is already well established as a means of producing breakfast cereal flakes. However, "standard" extruded cereal flakes have a "cardboard," smooth surface and all look stamped from the same mold. Today an understanding of how to control shear damage in the extrusion process is making the production of better breakfast cereal flakes a reality. (See figures 2 and 3 on page 34).
Added value can be achieved with the production of extruded premium flakes not just with the improved quality compared with other extruded flakes but in lower production cost compared to batch cooking. Relatively simple modifications can be made to existing lines to achieve these results. Further development is in progress. WG
Joe Kearns is corporate sales manager, Wenger Manufacturing, Inc. He may be contacted at firstname.lastname@example.org