Properties of Starch after Extrusion: A Review

Abstract

Food extrusion has evolved over the past decades and is now a unique research area. Starch is a primary ingredient of raw materials that are widely used in food extrusion. Extrusion is a thermomechanical process that can break the bonds of starch, leading to starch gelatinization, melting, and degradation. This article reviews the effects of extrusion on structure (crystallinity, morphology, molecular weight) and physico-chemical properties (expansion ratio, water absorption index, water soluble index, texture, pasting property, and digestion) of starch. In addition, some applications of extruded starches are described. This review is of significance as it provides an overview of the effects of extrusion on starch properties and indicates the potential of extrusion applications in the food industry.

Phenolics, Antioxidant Activity, and In Vitro Starch Digestibility of Extruded Brown Rice Influenced by Choerospondias axillaris Fruit Peels Addition

“…Extrusion processing has been applied in the food industry for decades to manufacture cereal‐based products with distinct textural attributes, such as snacks, breakfast cereals, and instant foods . However, many extruded cereal products are perceived to have an undesirable nutritional profile because they are high in calories and fat, but low in micronutrients and nutraceuticals .…”

“…Extrusion processing has been applied in the food industry for decades to manufacture cereal-based products with distinct textural attributes, such as snacks, breakfast cereals, and instant foods. [1] However, many extruded cereal products are perceived to have an undesirable nutritional profile because they are high in calories and fat, but low in micronutrients and nutraceuticals. [2] Therefore, a growing number of researches have investigated the potential of improving the nutritional profile of extruded cereal products by incorporating functional ingredients, such as fruits, [2] vegetables, [3] or edible byproducts.…”

Role of starch gelatinization and fragmentation in extruded flour functionality

“…The molecular weight of the starch polymers significantly affects the physical properties of starch, such as solubility and viscosity. Therefore, determining the degree of degradation of starch during extrusion is essential for establishing processingstructure-property relationships (Ye et al, 2018). From SEC studies it has been concluded that amylopectin, not amylose, is the component most affected by extrusion processing .…”

“…When starch is gelatinized by extrusion, its crystalline structure is disrupted due to the breaking of inter-and intra-molecular hydrogen bonds. This results in more exposed hydroxyl groups for forming hydrogen bonds with water and the presence of starch in an amorphous state (water molecules can diffuse easier) (Ye et al, 2018). Thus, WAI of extruded starch is normally higher than that of native starch, albeit it can be lower if extensive dextrinization or melting takes place (Altan, McCarthy, & Maskan, 2009;Ding, Ainsworth, Plunkett, Tucker, & Marson, 2006;Kadan, Bryant, Pepperman, 2003;Sarawong, Schoenlechner, Sekiguchi, Berghofer, & Ng, 2014).…”

“…Extrusion is known to generally result in higher water solubility and water absorption of the extruded starchy material. In this sense, a higher water solubility is useful in products cooked at lower temperatures, such as soups, sauces, puddings, and desserts (Ye et al, 2018). Meanwhile, a high water absorption and cold-viscosity allows the addition of more water to the dough/batter system, improving its handling characteristics (increasing dough consistency) and reducing the typical dryness of products during storage (Ye at al., 2018), something that can be desirable for bakery products or instant food applications.…”