Water Activity More bound water, then less 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

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

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

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

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.

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).

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.

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

QUALITY ATTRIBUTES OF FOODS: 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.

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.

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.

TERMS in food quality testing : 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

Attributes Control Sample 1 Sample 2 Sample 3 Sample 4 Average Score Appearance   Flavour Mouthfeel Texture AfterTaste Overall Acceptability