Water plays an important role in many foods, affecting texture, enabling chemical reactions, and supporting microbial growth. Many fresh foods are composed of 75% or more water. There are three forms of water in foods: free water, which can be squeezed out; absorbed water, which is attached to molecules like proteins and carbohydrates; and bound water, which is trapped within crystals or other substances and cannot promote microbial growth. Determining the moisture content of foods is important for factors like shelf life and susceptibility to contamination.

1. FORMS OF WATER
BY
ASSIST. PROF. Dr. BERCIYAL GOLDA. P

2. CONTENTS
Introduction
Water
Watercontentof someselectedfoods
Formsof waterinfoods
Freewater
Absorbedwater
Boundwater
Determinationof moisturecontent
 ovendryingmethod
 vaccum oven
 distillationmethod

3. Water plays many very important roles in food. It affects
texture (dry and brittle versus moist and soft), enables the
activity of enzymes and chemical reactions to occur (acts as a
solvent), supports the growth of microorganisms, makes it possible
for large molecules like polysaccharides and proteins to move
about and interact, and conducts heat within food.
Many foods such as meat, poultry, seafood, fruits and
vegetables are composed of 75% and more water, so water is the
most abundant component in many fresh foods. Other foods such
as dairy products, and fresh baked goods also contain high levels
of water (about 35% or more). Foods that are high in moisture
are at
risk of contamination from the growth of microorganisms such as
bacteria, yeast and mold, while dry foods like pasta generally
have long shelf lives.
INTRODUCTION

9. All foods contain at least some water.
Most natural foods contain water up to 70% of their weight. Water in
foods is classified in to three types:
Forms of water
Free water Absorbed water Bound water
Water are lightly
entrapped
Water are held
tightly
Less than 6%
unfreezable
water

11. Free water is the water that can literally be squeezed
out of a food, like the juice in an orange, or the water that
sometimes separates in sour cream or yogurt.
Free water can promote the growth of microorganisms.
Most water in foods is called free water
 Free water is lightly entrapped & therefore easily
pressed from food
 It acts as a dispersing agent & solvent & can be removed
by drying foods

13. oAdsorbed water (spelled with a “d”) is water that is
attached to the surface of molecules like
polysaccharides and proteins.
o It is not readily squeezed out of the food. When
food scientists refer to the hydration of proteins, such
as gluten, and carbohydrates, such as starch, they are
referring to adsorbed water.
oAdsorbed water can promote the growth of
Microorganisms.

15.  Bound water is water that is physically trapped
within crystals, such as crystalline starch, or other
substances in food (some food scientists prefer to
define just the free and bound forms of water).
 Bound water cannot promote the growth of
microorganisms.
 Bound water is the equilibrium water content of a
sample at some temperature and low relative humidity.
It does not freeze at low temperature (-40Cº or lower).
 It is unavailable as a solvent for additional solutes.
 It moves with a macromolecule in experiments
involving sedimentation rates, viscosity or diffusion.
 It exixts in the vicinity of solutes and other
nonaqueous substances and has properties differing
significantly from those of bulkwater in the same
system.

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