Scribd
Upload
137 views21 pages

Food Water Activity Insights

Water activity (aw) is a measure of the availability of water in a food. It determines the rate of deterioration in foods from microorganisms, chemical reactions, and physical injuries. The aw of a food depends on its moisture content, composition, temperature, and humidity. A lower aw retards the growth of microorganisms and slows enzymatic and non-enzymatic reactions. An aw of 0.3 provides optimal stability for foods. Decreasing aw through the use of humectants like salt, glycerol, and sucrose can improve a food's shelf life.

Uploaded by

Madupa Ovitigala
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
137 views21 pages

Food Water Activity Insights

Water activity (aw) is a measure of the availability of water in a food. It determines the rate of deterioration in foods from microorganisms, chemical reactions, and physical injuries. The aw of a food depends on its moisture content, composition, temperature, and humidity. A lower aw retards the growth of microorganisms and slows enzymatic and non-enzymatic reactions. An aw of 0.3 provides optimal stability for foods. Decreasing aw through the use of humectants like salt, glycerol, and sucrose can improve a food's shelf life.

Uploaded by

Madupa Ovitigala
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 21

Water activity and Sorption

properties of Food
Water in Food
Water in Food

Intracellular or Dispersing Medium or Dispersed Phase


Extracellular Solvent (Emulsions)
Component • Butter
• Vegetable & Animal • Margarine
Products
Water in Food

Free Water

Bound Water
Water in Food

❑Water molecules that form hydrogen


Free Water bonds only between other water
molecules
❑Is lightly entrapped & therefore easily
Bound Water
pressed from food
❑Acts as a dispersing agent & solvent
❑Can be easily removed by drying and
evaporation
Water in Food

❑Water molecules that are


electrostatically bound to the
dissolved substances
❑Remains unfrozen at temperature
Free Water below 0⁰C
❑Is unavailable as a solvent
Bound Water ❑Amount of unfreezable water vary
from one food to another (is based on
the protein content)
❑Severe conditions are needed to
remove bound water (vacuum oven,
distillation)
Water in
Food

Free Water

Bound Water
Food Deterioration & Water
Activity

Microorganisms Chemical Reactions Physical Injuries

Rate of Deterioration Water Content


Moisture Content

Wet-Weight Basis Dry-Weight Basis


𝑚𝑎𝑠𝑠 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟
𝑚= × 100
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟
𝑚= × 100
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑𝑠
𝑚= × 100
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 + 𝑠𝑜𝑙𝑖𝑑𝑠
Moisture Content vs. Food
Deterioration

Food
Stability
Prediction
Moisture
Content
?
Moisture Content vs. Food
Deterioration
Potato Starch is stable at a relatively high
moisture content (20%)

Food
Moisture
Stability
Content
Prediction

Peanut oil deteriorates if moisture


content exceeds 0.6%
Water Activity (aw)

➢ Measure of the availability of water molecule to


enter into microbial, enzymatic or chemical reactions

➢ Determines the shelf life of food

➢ Bound water is inversely related to water activity


(As the % of bound water in a food increases the aw
decreases)
Moisture Content and aw of Different Foods
Importance of Water Activity in Foods
Water Activity (aw)

➢ Water in foods exerts a vapour pressure

➢ Amount of vapour pressure depends on,


▪ Moisture content
▪ Composition of food
▪ Temperature and humidity of air
▪ Concentration of dissolved solutes
Water Activity (aw)

➢ Ratio of the vapour pressure of water (P) in a food to the


saturated vapour pressure of water (P0) at the same temperature

𝑃
𝑎𝑤 =
𝑃0
Water Activity (aw) & Relative Humidity
(RH)

➢ aw is a measure of relative humidity (RH)

➢ Hence, the relative humidity (RH ) of the atmosphere in


equilibrium with the food is,

𝑅𝐻% = 𝑎𝑤 × 100%
Effect of Water Activity (aw)

➢ Decreased aw,
▪ Retards the growth of microorganisms
▪ Slows enzyme catalyzed reactions
▪ Retards non enzymatic browning
➢ With aw at 0.3, the product is most stable with respect to,
▪ Lipid oxidation
▪ Non enzymatic browning
▪ Enzymatic activity
▪ Various microbial parameters
Effect of aw on microbiological and in biochemical reactions
Interaction of aw , pH, and temperature in some foods
Effect of Water Activity (aw)

➢ To decrease aw thus improving the shelf life of food is by the


use of additives with high water binding capacity (humectants)
▪ Common salt
▪ Glycerol
▪ Sucrose

You might also like