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Extraction of Starches From Wheat and Corn

CHAPTER 1

Introduction

1.1. Starch 

Starch (Amylum: Latin) is the most abundant carbohydrate found in nature. It is the major source of nutrition for humans. It consists of two types of polysaccharides; amylose contains linear chains of α-(1 → 4) D- glucopyranosyl units and amylopectin which additionally contain a number of short chains linked to the linear chains by α-(1 → 6) linkage (Visakh, 2015).

1.2 Sources of Starch

Starch is abundantly found in the form of tiny white granules various parts of different plants. Most significant starchy parts include seeds such as cereal grains (corn, rice, wheat, barley, oat, and sorghum), roots (sweet potato, cassava, arrowroots, and yam), tubers (potatoes) and stems (sago palm). The most important commercial sources of starch are corn, wheat ,potato and cassava (Swinkels, 1985) which accounted for 77%, 7%, 4% and 12% (Figure 1.2) of total starch production (Waterschoot, Gomand, Fierens, & Delcour, 2015).

Figure 1.1: Commercial sources of starch

Corn and wheat kernals contain abundant amount of starch in them. The corn kernal contain 72% starch (Ranum, Peña‐Rosas, & Garcia‐Casal, 2014) and the wheat endosperm consists of 80-85% starch (Onipe, Jideani, & Beswa, 2015). While the tubers  cassava and potato contains 35% and 18-22% starch respectively (de Bragança & Fowler, 2004).

Corn and wheat starch have many advantages over other starhes as they can be easily interchanged in industrial application because the contain almost the same amount of amylose and amylopectin in them (de Bragança & Fowler, 2004).

  • 1.2.1. Wheat

Wheat (Tritium aestivum) is the leading cereal crop and ranks third in production after corn and rice around the globe. The annual global wheat production has reached 720 million metric tonnes during the year 2015-2016 (Bashir, Swer, Prakash, & Aggarwal, 2017).

It is widely used for human consumption and comprised of three fractions – bran, germ, and endosperm. The wheat grains contain as high as 80-85% starch (Onipe, Jideani, & Beswa, 2015). Amylopectin content in wheat starch ranges from 70-80% and is readily digested by humans and amylose content represents 20-30% of the wheat starch which is difficult to digest by humans. (Hazard et al., 2012).

Wheat starch has wide applications in baking, confectionary and canning as well as in the production of adhesives (Guzmán‐Maldonado, Paredes‐López, & Biliaderis, 1995).

Figure 1.2: Wheat grain structure (Onipe, Jideani, & Beswa, 2015).

  • 1.2.2. Corn

Corn (Zea mays L.) is the economically important crop used worldwide for food. Corn comprises 72% starch, 10% protein, 4% fat and is grown throughout the world (Ranum, Peña‐Rosas, & Garcia‐Casal, 2014). About eighty percent of the world’s starch production is from corn (Waterschoot, Gomand, Fierens, & Delcour, 2015).

In Pakistan after wheat and rice the third most important cereal crop is corn (Tariq & Iqbal, 2010). Corn is used as staple food, feed for poultry and livestock and is also used for starch extraction (Memon, Zakria, Mari, Nawaz, & Khan, 2011). Besides its use as human food and animal feed, it also has a large number of industrial applications i.e. corn starch is used to produce corn syrup, anhydrous sugar, maltodextrin, dextrose, glucose syrup and its starch also acts as a binding and thickening agent (K. D. Kaur, Jha, Sabikhi, & Singh, 2014). Corn starch is the most important feedstock for ethanol production (Cook et al., 2012).

Figure 1.3: Corn grain structure (Shukla & Cheryan, 2001).

 

1.3. Starch Extraction methods

Corn and wheat contain a significant amount of starch. Below are the descriptions of starch extraction methods.

1.3.1. Starch Extraction From corn

Starches are extracted by different methods. I.e. corn starch is extracted by water, acid and alkaline steeping. The most widely used methods are acid and alkaline steeping (Dimler, Davis, Rist, & Hilbert, 1944)

  • 1.3.1.1. Traditional method for extraction of Starch

The reported method described the water steeping of flour for starch extraction. Corn flour was soaked in distilled water for 24 hours and slurry was blended. Then the slurry was passed through sieve and the filtered product was centrifuged at 2000 × g for 20 minutes. The precipitates containing starch were washed and dried (Palacios-Fonseca et al., 2013).

  • 1.3.1.2. Alkaline Steeping Method for Starch Extraction

The alkaline steeping method was reported by Wand and Wang (2001). The corn flour was soaked in dilute NaOH for 18 hours. The flour is blended, filtered, centrifuged and the slurry was neutralized with HCl and pH was maintained at 6.5. The slurry was washed with distilled water and dried in oven to obtain starch (Palacios-Fonseca et al., 2013).

  • 1.3.1.3. Acid Steeping Method for Starch Extraction

Adkin and Greenwood (1966) reported the acid steeping method for corn starch extraction. The corn kernels were steeped in sodium acetate with the addition of mercuric chloride. The softened kernels then washed, blended, filtered and centrifuged. The supernatant was discarded and starch was followed shaking with toluene and NaCl and then centrifuged and dried (Adkins & Greenwood, 1966). This method is also reported by (Banks & Greenwood, 1975) and named as toluene method (X.-Z. Han, Campanella, Guan, Keeling, & Hamaker, 2002).

Madson described the method for extracting starch from corn by ammonium hydroxide to increase yield. The method comprises steeping corn in ammonium hydroxide and water mixture for 45 minutes and 20 hours with pH 11.3 and 11.4. This method provides high yield of starch in short time (Madson, 2012).

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1 comment

Ormeman September 19, 2021 - 9:03 pm

Extraction and characterization of polysaccharides from tamarind seeds, rice mill residue, okra waste and sugarcane bagasse for its Bio-thermoplastic properties

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