Preparation, physicochemical and texture properties of texturized rice produce by Improved Extrusion Cooking Technology

Abstract

Using broken rice and rice bran as raw material, texturized rice (TR) was prepared by Improved Extrusion Cooking Technology (IECT) in which gelatinization is formed by means of low temperature and high pressure. The expansion of extrudate was hardly changed so that TR showed similar texture properties and shape with polished rices. The effect of rice bran addition (0% and 4%) and IECT conditions, including feed moisture content (26.6–33.4%), screw speed (20.1–32.6 rpm) and shearing compression metering zone temperature (SCMT, 69.8–120.2 °C) on the physicochemical, texture and nutritional characteristics of TR, were investigated by response surface methodology using Central Composite Design. When the bran addition was 4%, feed moisture content was 30%, screw speed was 26.6 rpm, SCMT was 95 °C, prepared TR contained 16.61 ± 0.02% of total dietary fiber, 9.40 ± 0.04% of protein, 3.68 ± 0.03% of fat, 2.42 ± 0.02 μg/g of thiamin, 0.52 ± 0.01 μg/g of riboflavin and 16.07 ± 0.12 mg/100 g of γ-oryzanol (dry matter content). The content increase of TDF for TR was 15.81% and the content increases of nutrients for thiamin, riboflavin, and γ-oryzanol were 1.39 μg/g, 0.24 μg/g, and 8.99 mg/g dry matter content, respectively, compared with those of polished rice.

Introduction

The milling process is widely applied in rice production in order to meet the consumer specifications for polished rice over brown rice, such as soft textured properties and whiteness, better eating properties correlating with higher water binding capacity, swelling ratio, and peak viscosity, less cooking time, digestibility and shorter cooking time (Mohapatra and Bal, 2006). However, it would unavoidably produce broken kernels (10–15%) and bran (Courtois et al., 2010), which would cause losses of all kinds of nutrients (Chen et al., 1998). In particular, the losses of thiamin and riboflavin would be as much as 68–82% and 57% (Kyritsi et al., 2011), respectively. γ-oryzanol of bran was 6.42 g/kg when bran came from the first milling break (Lloyd et al., 2000). The initial gamma-oryzanol content of the brown rice was 48.2 mg/100 g (Ohtsubo et al., 2005).

Therefore, nutrient fortification of polished rice has been widely studied in recent years. Three categories of nutrient fortification methods are: (a) soaking method: the nutrients are added at the desirable concentration forming soaking water solutions, soaking of brown or milled rice to certain moisture level, steaming under pressure and drying to a moisture-safe limit (Bello et al., 2006); (b) Spraying method: the nutrient solution is applied directly on the kernel using a rotary cylinder. The fortified kernel is air-dried and a water insoluble component is added. Usually, protective coatings are used to prevent the loss of vitamins during washing and cooking (Shrestha et al., 2003); (c) Powder type fortification: the nutrients are added in rice flour followed by extrusion cooking to result in fortified rice-based grains (Shrestha et al., 2003). Fortification is usually applied to a limited amount of kernels, which afterward are mixed with normal rice. In particular, extrusion cooking has been widely investigated to improve nutritional quality of extruded products. Hagenimana et al. (2006) evaluated some functional, physical, pasting, and digestibility characteristics of the extrudates made from long-grain, high-amylose, milled rice flours by extrusion cooking. Ding et al. (2005) studied extrusion cooking conditions on the physicochemical properties and sensory characteristics of rice-based expanded snacks.

Conventional extrusion cooking is a continuous high-temperature and short-time process, which physically modifies moistened expansible starchy and proteinaceous material, and makes starchy and proteinaceous material swell through the unique combination of high temperature, pressure and shear forces. The Improved Extrusion Cooking Technology (IECT) which is reconstituted from traditional single-screw extruders is a new gelatinization technology. Compared to the traditional extrusion cooking machines, our transformed single-screw extruder shows the characters with longer screw (1950 cm), longer residence time (40–68 s), higher die pressure (13.356–19.102 MPa), lower temperature (69.8–120.2 °C) and lower screw speed (20.1–32.6 rpm) than traditional extrusion cooking extruders. Furthermore, the new forming mold and rotary cutting knife which are not included in traditional extruders are added. The conventional extruders include BCTG-62/BCTC-22 (Buhler AG, Switzerland) with temperature 200 °C, screw speed 1200 rpm (Ceacilia and Peter, 2009), Brabender 20 DN bench top extruder (South Hackensack, NJ) with temperature 140–180 °C, screw speed 49–133 rpm (Martín-Cabrejas et al., 1999), Werner & Pflederer Continua 37 co-rotating twin-screw extruder (Stuttgart, Germany) with temperature 86.4–153.6 °C and screw speed 132.3–367.7 rpm (Ding et al., 2005) and Werner & Pfleiderer Ramsey ZSK-57 co-rotating twin-screw extruder (NJ, USA) with temperature 143–177 °C and screw speed 226–344 rpm (Meng et al., 2010). In those extruders, high temperature and high pressure make the material (such as starch) expand to change the extrudate structure so as to improve extrudate properties (edible quality, taste, etc). The extrudate shows 2–5 times and even larger expansion in the process of extrusion cooking. However, Improved Extrusion Cooking Technology in which gelatinization is formed by means of low temperature and high pressure makes the expansion of extrudate be hardly changed by forming complexes between starch and fat as well as protein. Material components (rice flour) gelatinize and form non-Newtonian fluid which encapsulates nutrients in the condition of high temperature and high pressure. At the same time, it is also a process of mixing, cooking, kneading, and shearing the mixed gels. Texturized rice (TR) is formed after cutting and aging effect, which is rich in nutrients and shows similar texture properties and shape to polished rice.

Rice bran, a by-product obtained from outer rice layers, is a good source of B complex vitamins, dietary fiber, ferulic acid and its esterified derivative (γ-oryzanol as inhibitory neurotransmitter) (Qureshi et al., 2002). The aim of the present study was to prepare TR by IECT, in which flour from broken rice was used as raw material and carrier, and rice bran rich in various nutrients was added. Furthermore, the physicochemical, texture and nutritional characteristics of TR were investigated.