COMPARATIVE STUDY ON THE PRODUCTION OF OXIDIZED STARCH FROM SORGHUM USING SODIUM HYPOCHLORITE AND POTASSIUM PERMANGANATE

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COMPARATIVE STUDY ON THE PRODUCTION OF OXIDIZED STARCH FROM SORGHUM USING SODIUM HYPOCHLORITE AND POTASSIUM PERMANGANATE

ABSTRACT

This project is the production of oxidized starch from sorghum starch using sodium hypochlorite and potassium permanganate. After the analysis  Table 1 shows that; the starch oxidized with NaOCl has the lowest percentage yield of (88%) as compare with KMn04 (91 %). And Table  2 shows the effect  of sodium  hypochlorite  concentration   on starch viscosity. Increase  in concentration  lead to the decrease in starch viscosity.  The sample produced by treatment with chlorine at 5.0% this effect was more pronounced (at 67.2.2^oC the torque 4% was at 29.7), for a high concentration starch slurry (20%). This starch also presented cold swelling, with detectable viscosity (around 20% of torque) at the beginning of the analysis (50^oC), these results are in agreement with those of that found lower pasting temperature for different corn starches when oxidized, mainly at the concentration 5.0% of  NaOCl related with structural weakening of the starch granules.

CHAPTER ONE

1.0       INTRODUCTION 

Oxidized starch is widely used in food and non-food industries where film formation and adhesion properties are desired. The major application of oxidized starch is as a surface sizing agent and as a coating binder in paper industry. Native starch paste is often not used in  such  applications  because  of  the  low  solubility  and  high  viscosity  of  the  pastes. Aqueous solutions of native  starch are more prone to retrogradation than those of oxidized starch.

Based on the behavioral  diversities of native starches such as being  biodegradable, the presence of functional  groups and its macroscopic  granular structure,  the starch chemist by selection of raw material followed by application of selected modification techniques can devise products with  a broad range of functional characteristics.

Oxidized starch is produced  by reaction of starch with oxidizing agent. During the course of the reaction  several  reactions occur which  leads to the  introduction  of carbonyl and carboxyl groups and degradation  of starch molecules.  Hence oxidized starch exhibits  low viscosity  due to depolymerisation  and  improved stability of starch dispersion  from the presence of functional  groups.  (Maurer, 1999).

Starch can be oxidized with oxidizing agent namely periodate, dichromate, permanganate, persulphate,   hypochlorite and hydrogen peroxide. Depending on the starch source,  it has been  established  that  the  property  of  oxidized  starch  produced  is  influenced  by the concentration of the oxidizing   agent and the rate of addition, time, temperature and pH.in the commercial practice,  alkaline  hypochlorite is the common used oxidizing agent. The other known oxidizing agents are rarely  used.  The reason for this preference is  not clear and seems to be based on mere convention. (Miller,   1995).

Also  compared  to other cereals  sorghum starch  is not commonly  utilized  m industrial applications  though its  grain composition  is very much similar to the most popularly used cereal corn.  (Watson, 1984).  Sorghum is also readily available and cheap.

1.1       SORGHUM

Sorghum is a genus of plants and grass family.  Most species  are native to Australia with  some extending  to Africa, Asia, Mesoamerica and certain islands in Indian and pacific oceans. (FAO, 1995).

One of the specie is grown for grain while many others are used as fodder plants either intentionally   cultivated or allowed to grow naturally in pasture lands. The plants are cultivated   in warm  climates   world-wide   and naturalized   in many  places.   (FAO, 1995). Other   names   include   durra,    Egyptian    millet,    guinea   corn;    milo   etc.   sorghum    for centuries    has  been  one  of  the  most  important   staple  foods  for  millions   of poor  rural people   in the  semiarid   tropics   of  Asia  and  Africa.   For some impoverished    region of the   world,   sorghum    remains    a  principal    source   of  energy,    proteins,   vitamins    and minerals.   Sorghum   grows  in harsh  environments    where  other  crops  do not grow  well such  as cassava.

Grain  sorghum   is the third  most  important   cereal  crop  grown  in the  United  States  and the  fifth  most  important   cereal   crop  grown   in the  world.   In 2010, Nigeria  was the world’s  largest producer of grain sorghum followed by the US and India.

1.2       ORIGIN

Rich  finds  of  sorghum  bicolor  have  been  recovered  from  Qasribrim  in Egyptian Nubia,  the  wild  example  have  been  dated  back  to  circa  800-600BCE  and  the domesticated one no earlier than CE 100. Most cultivated varieties of sorghum can be traced  back to  Africa  where  they  grow  on savannah  lands.  Sorghum  was  planted extensively  in parts of the Middle East, No11h Africa and Europe (Wayne and Richard, 2005). the   name  sorghum  comes  from  Italian  sorgo  in   turn  from  latinsyricum(granum) meaning grain of Syria.

Sorghum  is  well  adapted  to  growth  m  hot,  arid  or  semi-arid  areas.  The  many subspecies   are  divided   into  four   groups  grain   Sorghums   such    as  milo,   grass sorghum(for  paste  and  hay),sweet  sorghums  formerly  called  guinea  corn  used  to produce sorghum syrups and broom corn for brooms and brushes.

The FAO reports that 440000 square kilometres were devoted worldwide to the production in 2004.In the US sorghum is used primarily as a maize com substitute for livestock   feed  because  their  nutritional  values   are  very  similar.  Some  hybrids commonly grown for feed have been developed to deter birds and therefore contain a high concentration  of tannins  and  phenolic  compounds  which  causes  the need  for additional processing to allow the grain to be digested.  (FAO, 2010).

1.3       CULTIVATION

Sorghum requires  an average  temperature   of at least  25°C  to produce  maximum   grain yields  in a given  year.  Maximum   photosynthesis    is achieved   at daytime   temperatures of at  least  30°C.   Night  time   temperature    below    13°C   for  more  than  a few  days  can severely  reduce  the plants  potential   grain  production.     Sorghum  cannot  be planted   until soil  temperatures    have  reaches   l 7°C.   the  Jong   growing   season  usually   90-120 days, causes   yields    to  be  severely    decreased   if plants  are  not  in  the  ground   early  enough sorghum   in  general    is   a  very  competitive    crop  and  does  well   in   competition    with weeds   in  narrow   rows.    Sorghum   produces   a  chemical    compound   called   sorgoleone, which  the  plant  uses  to  combat  weeds.  The  chemical    is  so effective   in preventing   the growth   of  weeds   it  sometime    prohibits      the  growth   of  other  crops   harvested   on  the same  field  (F AO,   1995).

Sorghum’s    growth  habit  is similar    to that  of  maize  but  with  more  side  shouts  and  a more  extensively   branched   root  system.   The  root  system  is  fibrous  and can extend  to a depth  of  up  to  l .2m.   The  plant  finds  75%  of  its water   in the  top  metre  of  soil  and because   of  this,   in  dry  areas;   the  plan’s   production    can  be  severely   affected   by  the water   holding    capacity   of  the  soil.  The  plant  require   up  to  70- 100mm of  moisture every   10  days  in early  stages  of growth,   and  as  sorghum   progresses   through   growth stages   and  the  roots  penetrate    more   deeply   in  to  the  soil  to  tap   into   hidden   water reserves,    the  plants   need  progressively    less   water.   By  the  time  the  seeds  heads  are filling  optimum  water  conditions   are down  to about  50mm  every  10 days.  (Wayne  and Smith,   2005).

1.4       SCIENTIFIC   CLASSIFICATION

Kingdom:        Plantae

Order:              Poales

Family:            Poaceae

Subfamily:       Panicoideae

Tribe:               Andropogoneae

Genus:             Sorghum

1.5       COMPOSITION

The structure and composition of the sorghum kernel is  quite similar  to that of corn. The  kernels  are  flattened  spheres  measuring  about  4.0mm   long,  3.5mm  wide  and 2.5mm  thick. The weight of individual  kernels ranges from 8 to 50mg with  an average of 28mg.  colors of the prehybrid varieties range from white  through pale orange, tan and  red to dark red- brown.  Most grain in commercial  channels is a brownish  red colour  because  one  or both  parents  of the  best hybrids  have  that  colour.  (Martin,2007).

The structure of the sorghum germ is identical to that of corn germ.  The endosperm differs  from  that  of  the  corn  only  in  the  relative  proportions  floury  and  horny endosperm entirely surrounds the floury region. The dense peripheral endosperm layer comprises  a  larger portion  of the  kernel  than  in  corn  and  results  in much  greater problems in much greater problems during starch purification.  (Watson et al, 2005).

The pericarp of grain sorghums show the most differences from corn.it  is covered with a thick   layer  of wax.  (Seckinger  et al,  1996) most varieties  have a thick mesocarp layer in the pericarp layer containing very small unrecoverable starch granules; some varieties  have a thick orange pigmented  testa  layer (Sanders,  1995) which  shatters during wet milling and adds coloured particles to the starch. The epidermis  layer of pericarp  of some varieties contains water- soluble, flavone-type  pigments ranging in colour  from  red to orange.  In some  varieties,  a purple  flavonoid  contained  in the glume  which  surrounds  each  seed  leaches  into  the  seed  and  gives  a  gray  cast  to isolated starch.

1.6       CHEMICAL     COMPOSITION

Proximate Analysis of Grain Sorghum.

 (Miller, 1995}   ..

The chemical composition of commercial grain sorghum based on proximate analysis is  shown above.  The grain sorghum differs from corn in minor ways. Moisture content is generally lower  because the grain  dries  more in the field before harvest compared with corn; starch and protein contents are 1-2%  higher,  while total fat is always lower because the germ constitutes  a smaller proportion of the kernel than it does in corn. Furthermore  the  pericarp  wax  amounts  to  about  8% of  the total  fat  and  must  be removed  in  refining crude oil. (Hubbard et al, 2005).   Analysis   of the wax indicates that it is comprised of saturated fattyacids, aldehydes and alcohols of 27-30 carbons atoms. (Bianchi  et al,  1997).  All sorghum varieties  contains tannins but dark- brown, bird resistant varieties  contain  tannin  levels so high as so reduce digestibility   when fed. (Maxon and Rooney, 2002).

1.7       STARCH

Starch or amylum  is a carbohydrate  consisting   of a large number  of glucose  units joined  by glycosidic   bonds  (a  covalent  bond that joins  a carbohydrate  molecule to another group which may or may not be another carbohydrate).  This polysaccharide   is produced by most green plants as an energy store.  It is the most common carbohydratein  human   diets  and  is  contained    in  large  amounts   in  such  staple   foods   as  potatoes, wheat,  maize,   rice and cassava.

Pure starch  is  a white,  tasteless   and  odourless   powder  that  is  insoluble     in  cold   water and alcohol.  It consist of two types of molecules the linear and helical  amylase and the branched amylopectin.  Depending  on the plant, starch generally contains 20 to 25% amylase and 75 to 85%  amylopectin by weight. (Brown and Poon, 2005).

Structure  of Amylose molecule

Structure  of Amylopectin molecule

1.  7.1 AMYLOSE   CONTENT  OF VARIOUS   STARCHES

(FAO,    1995).

1.  7.2 AMYLOPECTIN  CONTENT  OF VARIOUS STARCHES

(FAO,  1995)

 Starch-possess properties such as high viscosity,   insolubility,   low dispersion rate and stability which makes its application  unsuitable for use in food products as thickening agent,  stabilizer or emulsifier;  in pharmaceuticals as a disintegrant; in construction; oil exploration;  textile and as a binder  in paper industry.  It is as a result of this, that starch is  modified  to  allow  it function  properly  under conditions  frequently  encountered during processing or storage so as to increase their stability  against excessive  heat, acid, shear, time, cooling  or freezing; to change their texture;  to decrease or increase their viscosity;   to lengthen  or shorten gelatinization  time;  or to increase their visco-stability.  (Smith et. al,  2005).

1.8       STARCH MODIFICATION

Starch has various applications  in industry. And to obtain or effect its use in any of this industry its modification is required. In general the susceptibility of starch modification is determined primarily by the fact that the material is biodegradable, its macroscopic granular structure and by the presence of certain functional groups. Moreover  depending on the location of the hydroxyl group and the bond type (alpha (l-4)   glycosidic  versus  alpha  (1-6)-glycosidic),   starch  reveals  different  properties when chemical modification is concerned.

Hydroxyl group at carbon C-6 is  primarily alcohol while at C-2 and C-3 carbons it is secondary alcohols. (Bemiller  et al 2009).

It is the presence of the three (3) hydroxyl groups in glucose  that makes it susceptible to substitution reactions and enables the number of possible modification of starch.

The grain size of the starch also affects the reactivity. The larger the grains are, the

higher the modification  susceptibility  is as external factors have easier access to the larger  grains. (Lewandowicz and Maczynski, 2000).

1.8.1    GRANULE SIZE DISTRIBUTION OF VARIOUS STARCHES

Starch is modified according to the modification  process utilized  and is divided into three (3) main groups;

1.9       PHYSICAL PROPERTIES OF OXIDIZED  STARCH

• Oxidized  starch is  whiter  than the native starch and the degree of whiteness increases  with the extent of treatment. (Hall et al, 2011).
• They are sensitive  to heat, tending  to yellow or brown when exposed to high temperature.  This yellowing  tendency  during drying  has  been related to the aldehyde   content.  With  increasing  aldehyde  content,  the  oxidized  starch becomes increasingly yellow on storage., (Walton, 2010).
• Oxidized starches gelatinize at a lower temperature than native starches.
• They produce aqueous dispersions of greater clarity and lower viscosity.  These dispersions   have fewer tendencies to set back or gel, (Anne,   2004).

1.10     WHY STARCH  IS OXIDIZED.

• Obtain low viscosity
• Obtain high-solid dispersions and resistance to viscosity increases or gelling in aqueous dispersion.
• Cause depolymerisation  which results in a lower viscosity  dispersion.
• Introduce a carbonyl  and carboxyl groups which minimize  retrogradation  of amylase thus giving viscosity stability.
• Improve whiteness and reduce microbial content, (Maurer,  1999).

1.11     APPLICATIONS OF OXIDIZED STARCH

• PAPER  INDUSTRY: About  80-85% of  Oxidized  starch  is used  primarily  in  paper  industry  as a  paper coating binder where it’s  high fluidity  and good binding and adhesive properties  make it  effective  in high  solids  pigmented  coating  colours.   (Lucas  and  Fletcher,  2012). Oxidized  starches  were  also  used  for  paper  and paperboard  surface  sizing to  seal pores, tie down loose surface fibers, improve surface strength, and provide hold out of printing inks. Viscosity stability of oxidized starch dispersions  as well as the range of viscosities   available   made  them  particularly  suitable.   (Zuderveld  and  Stoutjesdijk, 2005).
• TEXTILE  INDUSTRY: Starch has a long  history   in the  manufacture    of textiles;   it is used  primarily   as warp sizing    but  also   in  finishing   and   printing   (Radley,    1998).   The  high   fluidity,   stable viscosity,   and  flow  properties   at high  solids  of oxidized   starch  allows  for greater  add• on to the yarn  and provides  good abrasion  protection.   Such  starches  are readily  soluble and can be desized  from  the woven  cloth. Oxidized   starches   may  be  used  in back-  filling  where   a mixture   of  starch  and  filler such  as clay  is applied   to the  back  of a fabric  to fill the  interstices   of the  weave  and impart  opacity   and  stiffness.   The  lower  oxidized   starch  penetrates   fabric  to  a greater extent  than do higher  viscosity   starches.  (Moore,  2012).
• CONSTRUCTION INDUSTRY: Oxidized  starches are also used in the fabrication of construction materials such as insulation and wall boards and acoustic tiles to provide adhesive, binding and sizing properties.
• FOOD  INDUSTRY: In food industry, slightly  oxidized starches have been used in batters and beading’s for foodstuffs such as fried fish where it is claimed to give good adhesion to the food. It is used as stabilizers  in ice-cream and milk pudding production.  Oxidized  starch can  also  replace  Arabic  gum  due to  its excellent  stability  leading  to a  clear  food product.
• LAUNDRY: Oxidized starch is used in laundry finishing, sometimes in aerosol cans for home use. (Antinori and Rutenberg, 2000).

1.12     JUSTIFICATION OF THE  WORK

The application of starch in the paper, food and textile industry is very important as  it  has  numerous  advantages.  Native  starch  has  high  viscosity  and  other functional properties which makes its application unsuitable (Gollieb and Capelle, 2005).  It is as a result that starch is modified to allow it function properly.

The study is expected to provide information  on how to produce oxidized starch using the  suitable  oxidizing  agent  and to  study the  effect  of concentration  on starch. This information will serve to clear our doubt on why alkaline hypochlorite is mostly used for the oxidation of starch.

1.13     SCOPE  OF THE WORK

The study will be based on the oxidation of sorghum starch using two oxidizing agent viz; NaOCI and KMnO₄ at different concentration. Also the viscosity  and viscosity  stability will  be determined.

1.14     LIMITATION OF THE  STUDY

In any research there must be some short falls and this research is not an exception since  sodium  bisulphite  (NaHSO₃)    is the most  used reducing  agent  its  lack of availability  lead to the use of sodium thiosulpbate  (Na₂S₂O₃). Also lack of basic equipment apparatus such as temperature controlled water bath,  rheometer lead  to the use of other modified method.

1.15     AIM AND OBJECTIVES

• Oxidizing   sorghum   starch   using  two   oxidizing    agents   viz;   Sodium hypochlorite (NaOCl) and Potassium permanganate (KMnO₄).
• To establish the oxidizing agent suitable for the oxidation of starch.
• To  determine  the  effect  of  different  concentration  on  physicochemical properties  of  sorghum  starch  which  could  provide   information   used  to improve the manufacturing  process as well as the product properties  for some certain application

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