**2. Starch**

The different kinds of starch with commercial importance are corn, wheat, potato and cassava starch:



\* Corn Production Source (2011).

Table 1. Kinds of corn\*

These four types of starches are industrially produced and present great applicability in the food industry. Other starch sources, such as other cereals, tubers and fruits are produced at smaller amounts, limiting their wide utilization, and some are produced with research purposes for viability of new starch sources (Govindasamy, 1996, 1997; Alves et al., 1999).

The different kinds of starch with commercial importance are corn, wheat, potato and

 Corn, *Zea Mays*, is grown in most countries throughout the world. It requires, however, warmer climates than those found in the temperate zones to grow to maturity. It is classified into several kinds, with different uses (Table 1), and it has the largest

 Wheat starch granules are divided in two groups by size, B-starch (15 - 20 % and 2 - 15µ) and the larger A-starch (80 - 85 %, 20 - 35µ in diameter) granules. B-starch is contaminated with pentosans, fibers, lipids and protein to an extent requiring special

 Cassava is the term usually applied to the roots, and tapioca is the name given to starch and other processed products. There are many varieties of cassava, but they fall into two main categories, namely bitter and sweet cassava (*Manihot palmata* and *Manihot aipi*), depending on their content of cyanohydrins. For industrial purposes bitter varieties are most frequently used because of their higher starch content. Sweet cassava

 Potato starch: 75% of the potato crop is grown for industrial processing and Danes produce per capita more starch than any other nation (Corn Production Source, 2011).

> Hard and soft starch Become indented at maturity

Hard, horny, rounded, or short and flat kernels soft and starchy endosperm completely enclosed by a hard outer layer

A waxy appearance (only branchedchain starch)

heat

multicoloured kernels

is preferred for food because of its taste and dough forming ability.

Corn Scientific name Use Characteristics

Food, animal feed, and industrial products

Food, animal feed, and cornstarch manufacturing

Special starches for cornstarch manufacturing

Green corn is eaten

Tortillas, chips, and

Popcorn *Zea mays everta* Popcorn They are popped on exposure to dry

These four types of starches are industrially produced and present great applicability in the food industry. Other starch sources, such as other cereals, tubers and fruits are produced at smaller amounts, limiting their wide utilization, and some are produced with research purposes for viability of new starch sources (Govindasamy, 1996, 1997; Alves et al., 1999).

Indian *Zea mays* Food and animal feed White, red, purple, brown, or

fresh, canned, or frozen High percentage of sugar

baked goods Soft corn

**2. Starch** 

cassava starch:

production.

treatment in the factory.

Dent *Zea mays* 

Flint *Zea mays* 

Waxy *Zea mays* 

Sweet *Zea saccharata* 

Flour *Zea mays* 

Table 1. Kinds of corn\*

\* Corn Production Source (2011).

*Indentata* 

*indurata* 

or *Zea rugosa* 

*amylacea* 

Starch must be gelatinized in the human diet in order to be digested by the amylolytic enzymes of the human digestive system. The classic model of obtaining gelatinized starches, where starch granules are slowly heated in a medium with little agitation and much water, which promotes imbibition, swelling and polymer release (Leach, 1965) for a prolonged time, such as in the obtaining of cooked rice, corn flour porridges, was replaced by other methods, such as extrusion, spray-drier and drum dryer, which promote fast starch gelatinization and followed by drying may obtain flours and/or pregelatinized starches of long-term stability and quick preparation.

Pregelatinized starches or flours are paste-forming products in the presence of cold water or (partially or totally) soluble products in cold water (Colonna et al.,1984) and present the following characteristics: they disperse more easily and absorb more water than their untreated matches, they form gel at room temperature and are less prone to deposit (Powell, 1965).

The use of gelatinized starch in food products affects their characteristics and qualities, such as bread volume and crumb (Williams & Lesselleur, 1970); elasticity and softness of pastas (pasta), digestibility and palatability, tolerance in the properties of beating and cake mixtures, ice creams, doughnuts, growth of sugar crystals in food products (Powell, 1965); texture, volume, shelf-live and stability during thawing of cakes and breads (Michael & Brown, 1968).

In the food industry, pregelatinized starches are used to achieve thickening or water retention without employing heat, for example, puddings, instant lactic mixtures and breakfast foods; to prepare ready-to-use bread mixtures, where the increased absorption and retention of water improves the quality of the product, to work as an agglutinant in the meat industry; and, as a filling for fruit pies, as they make the use of heat dispensable and increase flavor retention. They also have a non-food use, such as in the industries of textiles and in drugs, paper, metallurgy, etc (Powell, 1965).

Pregelatinized flours may be obtained on an industrial basis through extrusion or drumdrying and through the use of atomizers (spray-drier).

The use of atomizers is economically limited as starch pastes are highly viscous and require drying at a low content of solids (Chiang & Johnson, 1977).

Drum-dryers are simple and commonly used, but they present the disadvantage of highcost products due to low efficiency, low production, difficult operation, constant need for drum maintenance and adjustment (Greenwood, 1976).

The extrusion process presents the advantages of versatility, high productivity and low cost (Smith, quoted by Harper, 1979) and more strict control of the desired gelatinization degree, where small modifications in the equipment and/or in the raw material may lead to different final results (El-Dash, 1982). According to Lorenz & Jansen (1980), the low cost of gelatinization through extrusion is due to the fact that it efficiently converts electrical energy into thermal energy and also the manpower and space per kilogram of cooked product required are lower than any other cooking method.

The market of fast preparation products has grown and many varieties of pregelatinized flours are available in the market nowadays. The main trends in the use of thermoplastic extrusion process applied to starchy ingredients will be approached in this chapter.

Physical and/or Chemical Modifications of Starch by Thermoplastic Extrusion 43

variables act with opposite end values and when both values are high or low, low degrees of gelatinization occur. Other works showed that the extrusion process destroys the organized crystalline structure of the starch granule, with different degrees of intensity which depend on the ratio of amylose to amylopectin and on the independent variables used such as humidity and shear (Charbonnieri et al., 1973). Thus, starch may be gelatinized, which is what occurs at the extruder with humidity lower than 20% (Linko et al.,1981), dextrinized, which happens in more severe conditions and with low humidity content (Gomez & Aguillera, 1983, 1984). The process may also lead to starch liquefaction and partial

The production of snacks through extrusion represents a great achievement for the Food Technology area as it efficiently converts crude cereal flours into products with different

At first, snacks were obtained from whole grains combined with moisture content, cooking

The second generation snacks presented more expansion ability, and were obtained with flours refined from cereals and cereal and tuber starches. These snacks have a large volume and require appropriate packagings to avoid humidity, light and heat, and they must protect the product against mechanical shocks, in order to avoid breaking during transport and storage. These facts boosted the development of third generation snacks (Huber &

Third generation snacks are not expanded through the extrusion process, for this reason they are known as pellets or half-products, for they will be expanded through a process of deep-frying or hot air, or with the use of microwaves, during consumption. Although they have an additional process for expansion, these products present great advantages in

With the worldwide tendency of weight gain by the population, studies showed that gelatinized starch, if excessively consumed, contributes to an increased number of diseases, such as obesity, diabetes and increased blood triglycerides, which may lead to serious heart

Slowly digestible starch (SDS): amount of glucose released between 20 and 120 min of

Resistant starch (RS): total starch minus amount of glucose released within 120 min of *in* 

Studies evaluating the digestibility of starches in snacks showed that they presented RDS type starch (Singh et al., 2007; Goni et al., 1997). Thus, the tendency is to promote the return of the use of the whole grain, addition of fibers and ingredients leading to increased SDS and RS in snacks, in addition to ingredients beneficial to health, such as antioxidants, and omega oils. That is, the new generation of snacks must include benefits to the consumer's

Rapidly digestible starch (RDS): amount of glucose release after 20 min.

temperature and drying, considered the first generation (Huber & Rokey, 1990).

hydrolysis of starch molecules (Faubion et al., 1982).

transport and storage (Huber & Rokey, 1990).

diseases (Jenkins et al., 1980).

*in vitro* digestion.

A ranking for starch has been made:

*vitro* digestion (Singh et al., 2010).

health, in addition to being nutritious.

shapes, flavors and long shelf-life.

Rokey, 1990).
