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Lecture notes study book Food Science of A. K. Haghi - ISBN: 9781926895017 (FOOD SCIENCE)
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SAUCES AND STARCH CHAPTER 18INTRODUCTION TO STARCH
1. Starch is a component of cereal grains, vegetables and legumes.
STARCH
Polysaccharide
Long chains of repeating glucose molecules
Linked together in form of either amylase or amylopectin.
TYPES OF STARCH MOLECULES/FRACTIONS
Amylose:
Cooked starch paste contributes thickening (hot) and for the cooked and cooled starch
paste contributes gelling (cold) characteristics.
Amylopectin:
*Cooked starch paste: contributes cohesive and thickening properties.
Structure of a starch granule
Size and shape
In plants starch is deposited in the form of granules in the leucoplasts.
Starch granules from different plants have characteristics sizes and shapes.
Diameters vary form 2-150 microns
E.g. Rice very small and round
Maize – small and round or polygonal
Potato – large and oyster shell shape
Internal organisation
Each granule consists of concentric layers
Within each layer the molecules are arranged in a radial fashion and set more or less parallel
to each other
Due to linear chain segments of amylopectin
, Micelles linked by amorphous areas: Composed of amylose and the remaining branches
amylopectin. This is a less ordered arrangement.
ORDERLY ARRANGEMENT OF AMYLOSE AND AMULOPECTIN IN A STARCH GRANULE
THE STARCH GRANULE
polysaccharide
consists of hundred thousand glucose units linked together.
contains two fractions namely amylose and amylopectin.
amylose is linked together to form a long chain.
amylopectin are linked to form branches.
amylose contributes to the forming of gels in a cooked, cooled liquid.
amylopectin causes the liquid to thicken, but cannot form a gel.
Starch from corn, wheat and rice is higher in amylose than potatoes and tapioca.
Waxy starches that contain only amylopectin have been developed from rice, corn, sorghum and
barley.
THE EFFECT OF MOIST HEAT ON STARCH
STAGE 1 THE REVERSIBLE SWELLING OF STARCH
Starch granules living plant cells and contain water.
Starch is commercially dried for the consumer and for shelf life. Starch shrinks. i.e.
Mazeina. (corn flour) when the product looses water.
When the dry powder is mixed with water, a small amount of water may be absorbed the
granule, but stronger intermolecular bonds remain intact and prevent any noticeable swelling.
This process is limited and reversible, which means the water can evaporate and the starch
will stay behind.
When starch and water is mixed and left to stand a suspension forms that settles to the
bottom of the container when left standing.
STAGE 2 SWELLING AND THICKENING: GELATINISATION
When starch is heated in water, a number of changes gradually occur over a temperature range
that is characteristic of a particular starch.
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