NOTES
FOOD SCIENCE AND TECHNOLOGY
COURSE: FOOD CHEMISTRY
TOPIC: WATER
INTRODUCTION:
Water is an important basic element in all foods. Water is called the
universal solvent, and it is a necessity for the growth & metabolism of
microbes and various chemical reactions that occur in food products.
Water occurs in food systems as free water and bound water. Water is
found as an intracellular and extracellular component in foods. The
importance of water as a crucial component necessitates the
understanding of the properties and behavior in food systems. The way
water behaves in foods can provide information on the stability of a
product as well as its shelf life. The following topics will be dealt.
1.Definition of water in food
2. Structure of water and ice
3. Types of water
4. Water activity and sorption phenomena
5. Water activity and shelf life
6. Water activity and packaging
1. Definition of water in food:
Water is a chemical compound composed of two hydrogen atoms and
one oxygen atom. The liquid stage of this compound is termed water,
the solid state as ice and gaseous state as steam. Water is also the most
, substantial component of foods and acts as a medium by supporting
chemical reactions. Water has an important role in the stability of most
food products. The quantity and characteristic of water present in
foods has an impact on the chemical processes of value in terms of
food safety. The physical & chemical stability as well as growth of
microbes in a food can be controlled by optimizing the water within
foods by various methods. The water content of a food product alone
cannot provide a view of the potential microbial response and chemical
reactions even though it is the most widely discussed concept in terms
of water content of foods. Water content is measured by drying,
infrared or nuclear magnetic resonance techniques but the measure of
‘water activity’ along with the total water is essential to describe its
water status. The measurement of water activity is more relevant in
understanding the quality and safety aspects of water.
2. Structure of water and ice:
The function of water can be understood better when there is clear
knowledge about its structure and the state it occurs in a food system.
Physical properties of water exhibit various physical properties which
can be understood on comparison to the properties of molecules like
water. Water appears to have a high melting point of 00 C and boiling
point temperature of 1000 C. There is also a considerable difference in
the density, vapor pressure, thermal conductivity of water at 00 C &
1000 C and ice which further changes on freezing. The thermal
diffusivity, which is indicative of the rate at which a material can
undergo a change in temperature or the rate at which heat moves
inside a compound, is 9 times higher in ice than water. This change
causes water to freeze at a rate nine times faster than thawing. The
reason for the unusual behavior of water and ice can be further
understood by their chemical structure.
FOOD SCIENCE AND TECHNOLOGY
COURSE: FOOD CHEMISTRY
TOPIC: WATER
INTRODUCTION:
Water is an important basic element in all foods. Water is called the
universal solvent, and it is a necessity for the growth & metabolism of
microbes and various chemical reactions that occur in food products.
Water occurs in food systems as free water and bound water. Water is
found as an intracellular and extracellular component in foods. The
importance of water as a crucial component necessitates the
understanding of the properties and behavior in food systems. The way
water behaves in foods can provide information on the stability of a
product as well as its shelf life. The following topics will be dealt.
1.Definition of water in food
2. Structure of water and ice
3. Types of water
4. Water activity and sorption phenomena
5. Water activity and shelf life
6. Water activity and packaging
1. Definition of water in food:
Water is a chemical compound composed of two hydrogen atoms and
one oxygen atom. The liquid stage of this compound is termed water,
the solid state as ice and gaseous state as steam. Water is also the most
, substantial component of foods and acts as a medium by supporting
chemical reactions. Water has an important role in the stability of most
food products. The quantity and characteristic of water present in
foods has an impact on the chemical processes of value in terms of
food safety. The physical & chemical stability as well as growth of
microbes in a food can be controlled by optimizing the water within
foods by various methods. The water content of a food product alone
cannot provide a view of the potential microbial response and chemical
reactions even though it is the most widely discussed concept in terms
of water content of foods. Water content is measured by drying,
infrared or nuclear magnetic resonance techniques but the measure of
‘water activity’ along with the total water is essential to describe its
water status. The measurement of water activity is more relevant in
understanding the quality and safety aspects of water.
2. Structure of water and ice:
The function of water can be understood better when there is clear
knowledge about its structure and the state it occurs in a food system.
Physical properties of water exhibit various physical properties which
can be understood on comparison to the properties of molecules like
water. Water appears to have a high melting point of 00 C and boiling
point temperature of 1000 C. There is also a considerable difference in
the density, vapor pressure, thermal conductivity of water at 00 C &
1000 C and ice which further changes on freezing. The thermal
diffusivity, which is indicative of the rate at which a material can
undergo a change in temperature or the rate at which heat moves
inside a compound, is 9 times higher in ice than water. This change
causes water to freeze at a rate nine times faster than thawing. The
reason for the unusual behavior of water and ice can be further
understood by their chemical structure.
