The document discusses various aspects of water activity and quality attributes of foods, including how water is involved in many food preparation processes as a solvent, for heat transfer, freezing, and chemical reactions. It also examines how water hardness can impact food preparation and quality. Furthermore, the document explores browning reactions, gel formation, organoleptic qualities like flavor, and methods for measuring flavor in sensory evaluation.

1. Water Activity
• More bound water, then less water activity
• Water activity
• Ratio of the vapour pressure of water in a food at a specified
temperature to the vapour pressure of pure water at same
temperature
• Foods more perishable if higher water activity
• Microorganisms need water
• To reduce water activity
• Dry
• Freeze
• Add sugar or salt

2. Uses of Water in Food Prep
• Universal solvent
• Heat transfer
• Freezing
• Cleansing agent
• Promotion of chemical changes
• Ionization of salt
• Baking powder
• Water and pH
• Hydrolysis reactions

3. • H2O
• Two hydrogen atoms
bonded with covalent
bonds to one oxygen atom
• Is dipolar
• Negative on oxygen side
• Positive on hydrogen sides
• Hydrogen bonds

4. Water Hardness
• Types of hard water
• Temporary
• Permanent
• Hard water and food preparation
• Rehydration and softening of dried beans slowed
• Alkalinity may affect color of vegetables
• Promote cloudiness in tea
• Water may be softened

8. Quality of Attributes of Foods
BROWNING REACTION:
• Complex reactions that occur on processing imparts a brown colour. This
brown is desirable in high grade products like coffee, maple syrup, bead
crust, baked goods, roasted nuts etc. But undesirable in juices and
processed vegetables like potato.
• Three general types of browning reactions are due to
1) Reaction of aldehydes and ketones with amino compounds. This does not
require oxygen.
2) Caramelization- monosaccharides like glucose, fructose and sugar acids on
heating becomes brown. Oxygen is not required for this reaction also.
3) Enzymatic browning (oxidative changes): browning of apples or potatoes.
Oxidation of ascorbic acid
• Main pigment generated in this type of reaction is Melanin.

9. Gel formation:
Proteins also forms rigid gels even in low concentrations.
Cooling a colloidal dispersion of large protein moecules, the viscosity
increases to a point at which some rigidity is attained.
• E,g., Gelatin – a partially degraded protein from collagen of skin and
bone from animal source.
• Milk protein ; Casein. Precipitated at pH 4.7.
• Cow milk – 3 to 4 % Protein Buffalo milk – 4 – 4.7% Protein
Human milk – 0.3 - 0.6%
• Casein is precipitated by an enzyme called Rennin to prepare Cheese.
• Egg proteins : Egg white called ovalbumin. Egg yolk – lipo proteins
(Proteins associated with lipids).

10. • Pectic Substances (Ploysaccharide carohydrates)
• Gel Formation by Starch: (Pectic substances- amylose)
• Take up water and swell on mild heating. It is a reversible
process.
• On moderate heating to 70oC nearly 1000-2500 times the
weight of starch will be absorbed and swell. On further
heating, they form an enmesh retaining water inside and form
a gel.
• Thixotropic gel is formed. That is shearing reduces gel to
liquid. On leaving undisturbed, Gel is formed again.

11. • Formation depends on % of pectin, molecular weight of pectins,
sugar and acid (pH).
• Sugar is normally in the range of 65%.
• Depending on the time required for setting, pectins are available as
‘Slow settiing’(for Jams) and ‘Rapid setting’.
• Rapid setting starts at 88oC and Slow setting starts at 54oC.
• Gums and mucilages: These are tree or plant extracts. These again
plant polysaccharides. Used as thickeners.
e.g., Gum Arabic, Gum Karaya, Gum Tragacanth

12. Organoleptic qualities (Qualities as perceived by sensory
organs)
e.g., Flavour – is a combination of taste, smell and feel
Mouth – sweet, sour, salty, bitter (taste buds in tongue)
Nose – odours (olfactory nerves)
Mouthfeel – How the food is felt while chewing.
Smoot, or rough, tender or tough, sticky on tongue or roof of
mouth, chewy or watery. After taste – Lingering sensation
after swallowing the food.
Mostly a blend of sensation occurs while eating foods,
so it is difficult to sort each and every taste.

13. TASTE :
Detected through solution of soluble compounds in saliva or in food juices
and contact with taste buds. Detection overlaps but general criteria are
• Sour – on the sides of tongue
• Salt – sides and tip
• Sweet – top
• Bitter – back and near throat. Taste is also influenced by
temperature, texture etc.
ODOUR AND AROMA:
Recognized as a prelude to eating. When a rich aroma emanates while
cooking one feels juices secreting in the mouth.
• Detection is possible for some compounds even if they are present in
parts per million or billion.
• Other factors that contribute to overall sensation of flavour are hot,
burning effect of peppers, coolness of menthol.

14. TEXTURE of FOODS : (as felt when chewing) Foods may be
considered as smooth, creamy, crispy, sticky.
• Control of flavour and aroma is important since too much flavour
or aroma will set in fatigue of the nerves and failure to detect them
starts.
• Eg., Roasting of coffee or cocoa beans under proper temperature
and time otherwise burning will occur off-setting the flavour.
MEASUREMENT of FLAVOUR for QUALITY CONTROL:
• Expert Tasters: Specific to a particular industry ans were able to
detect the mild changes in taste due to any change in process
parameter.
• Panel of Tasters : Persons working in the food industry and people
from other walks of life can be trained to taste foods. A numerical
scale is used to analyse using statistical tools to judge the
acceptance of the food. Prevalent I meat, bakery and milk
processing industry.

15. • A specific vocabulary is also used to describe the comparative scores of the
product like ‘rubbery’. ‘eggy’, etc. Presence of butyric acid is defined as
‘Buttery’. Sometimes as ‘throat burn’ or ‘cooling’ depending on the effects
on mouth is used.
TERMS in food quality testing :
• Order of appearance, After taste, amplitude,.
• Amplitude : Total effects of flavour – may be low, medium or high
depending on experience of a paryicular flavour on processing.
• Method used is called as 9-point Hedonic Scale. Statistical analysis is done
for the score card and acceptability is tested.
Hedonic Scale Score
9 – Like Extremely 5 – Neither Like nor Dislike
8 – Like very much 4 – Dislike Slightly
7 – Like moderately 3 – Dislike moderately
6 – Like Slightly 2 - Dislike very much
1 – Dislike Extremely

16. SENSORY EVALUATION
Scorecard Hedonic Scale
Judge Name : Date:
Product Name :
Attributes Control Sample 1 Sample 2 Sample 3 Sample 4 Average
Score
Appearance
Flavour
Mouthfeel
Texture
AfterTaste
Overall
Acceptability
Average Score