PRODUCTION OF GLUCOSE SYRUP FROM CASSAVA STARCH USING RICE (Oryza sativa) MALT AS SOURCE OF HYDROLYSING ENZYMES

PRODUCTION OF GLUCOSE SYRUP FROM CASSAVA STARCH USING RICE (Oryza sativa) MALT AS SOURCE OF HYDROLYSING ENZYMES

   CHAPTER ONE

INTRODUCTION

1.1 Background of Study

Starch, the raw material required for the production of low molecular weight products such as glucose/dextrose, maltose, maltotriose and dextrin is widely applied in sugar, spirits, textile as well as brewing (Selmi et al., 2000). Starch is found in the endosperm of cereal grains (Stare and McWilliam, 1977), roots and tubers of crops (Omemu et al., 2004). The conversion of starch to various sweeteners is achieved through a chemical (acid) or an enzymatic process. The use of enzymes however has more advantages to the former (Yankov et al., 1986) due to the formation of undesirably coloured and flavoured breakdown products, and the process appears to be totally random which is not influenced by the presence of α-1, 6-glycosodic linkages and its difficulty to control (Chaplin, 2004). Conditions for enzyme hydrolysis are milder therefore refining stages to remove ash and colour is minimized. The enzymatic hydrolysis of starchy crops has been practiced on an industrial scale for many years and is gradually replacing the traditional acid hydrolysis process (Underkofler et al., 1965; Barfoed, 1976).

The industrial processing of starch to glucose, maltose and dextrin involves gelatinization, liquefaction and saccharification processes (Hall, 2001) using amylolytic enzymes from microbial or plant sources (Robyt and Ackerman, 1955). Carbohydrate based agricultural products like starch tubers and cereal occur abundantly in most developing countries of the tropics (Okolo et al., 1995).

 Cereal grains such as maize, millet and sorghum are important staple foods found in the diet of the people within the North-eastern Nigeria. These cereals are widely cultivated within the sub-region, and to a larger extent, the country with an aggregate annual production of 23.9 million tonnes in year 2003 (FAO Reviews, 2006). However, despite their importance, a large proportion of these cereals are lost yearly due to non-availability of appropriate technology and industry to harness these into various useful products such as glucose syrup, maltose syrup, high fructose corn syrup and maltodextrins.

Enzymes involved in the starch hydrolysis include α-, β-amylases and glucoamylase (also called γ-amylase). α-Amylase (EC 3.3.1.1) is an extracellular enzyme which is widespread among higher plants, animals and microorganisms. It catalyses the hydrolysis of the α-D-(α-1,4) glycosidic linkage in starch components and related carbohydrates (Demirkan et al., 2005). Glucoamylase (E C 3.2.1.3), an industrial enzyme, hydrolyses            α – (1,4) and (1,6) glycosidic bonds of starch from the non-reducing ends successively to produce glucose and is used for the production of glucose from starch (Hiromi et al., 1966). By using β-amylase or fungal α-amylase, glucose syrups containing over 50% maltose, or even over 70% maltose (extra-high-maltose syrup) can be produced (Dziedzic and Kearsley, 1995). This is possible because these enzymes remove two glucose units (one maltose molecule) at a time from the end of the starch molecule. High-maltose glucose syrup has a great advantage in the production of hard candy: at a given moisture level and temperature, a maltose solution has a lower viscosity than a glucose solution, but will still set to a hard product. Maltose is also less humectant than glucose, so candy produced with high-maltose syrup will not become sticky as easily as candy produced with a standard glucose syrup.

Glucose syrup produced from enzymatic or acidic hydrolysis of starch is a concentrated aqueous solution of glucose, maltose and other nutritive saccharides. Glucose or dextrose sugar is found in nature in sweet fruits such as grapes or honey. It is less sweet than sucrose (cane sugar). Glucose syrup is made from the enzymatic or acid hydrolysis of starch which could be from potatoes, wheat, barley, rice and cassava (Hull, 2010).

Glucose syrup exists in many different versions depending on the degree of starch hydrolysis. There are also some variants with different levels of fructose due to isomerisation of the glucose molecule. Glucose syrups without fructose are less sweet than sucrose. Glucose syrups are given a dextrose equivalent (DE) number based on the degree of breakdown. The higher the number, the more starch has been hydrolysed (van der Poel et al., 1998).

Glucose syrups are essentially industrial sugars used in the manufacture of food products, pharmaceuticals but are mainly consumed in the confectionery industry (Bello-Pérez et al., 2002; Akinola and Ayanlele, 2004) containing 10 – 40 % glucose. Glucose syrup containing over 90 % glucose is used in industrial fermentation.  Glucose syrups and invert sugar are typically used to avoid crystallisation of sucrose, but also ingredients like proteins, texturisers and stabilisers influence crystallisation. Glucose syrup is an important industrial product of starch hydrolysis that has been applied as bulk sweetener in the food, (Rothwell, 1981) pharmaceutical, (Aboje, 2007) and confectionary industry (Fox and Cameron, 1982). The production of glucose, maltose and dextrins from starch of maize (Sutherland et al., 1986), banana (Bello-Perez et al., 2002) cassava (Aboje, 2007) and sweet potato (Omemu et al., 2004) has been well documented in many parts of the world.

• Justification of Study

Nigeria grows more cassava than any other country in the world. The production of cassava is concentrated in the hands of numerous small holder farmers located primarily in the south and central regions of Nigeria. A significant population of cassava growers in Nigeria have made the transition from traditional production systems to the use of high-yielding varieties and mechanization of processing activities. Thus, the need to diversify the use of cassava in our growing economy is important. Glucose syrup production from cassava starch is easy and the raw materials used for its production is one that is readily available in Nigeria and to Nigerians, and it is cheap to produce with processes that do not require the use of expensive chemicals or machine. Importantly too, it does not produce any toxic materials.

1.3 Aim of Study

This study aimed at the production of glucose syrup by the enzymatic hydrolysis of cassava starch using rice malt as the source of hydrolysing enzymes.

1.4 Objectives of Study

• Use the syrup produced to determine the concentration of reducing sugar and total carbohydrate present.
• To know the level of dextrose equivalent (DE) present in the glucose syrup.
• To know the effect of varying the time of incubation for the saccharification step of glucose syrup production.

 CHAPTER TWO

LITERATURE REVIEW

2.1 Cassava

Cassava (Manihot esculenta), also called yuca, mogo, manioc, mandioca, and tapioca, is a woody shrub of the Euphorbiaceae (spurge family) native to South America, is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy, tuberous root, a major source of carbohydrates. It differs from the similarly-spelled yucca, an unrelated fruit-bearing shrub in the Asparagaceae family. Cassava, when dried to a starchy, powdery (or pearly) extract is called tapioca, while its fermented, flaky version is named garri, especially in Nigeria (FAO, 1995).

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