Freezing

Slow: 18°C to -25°C Fast: CO2 around -80°C Fast: N2 ice-crystals (damage cell/membranes)

Freezing slowly: large ice-crystals membranes seriously damaged

Freezing fast: small ice-crystals damage with membranes not significant

Frozen fast (fast-food) defrost fast Frozen slow (meat) defrost slow Large ice-crystals become large water particles Cell needs time to re-absorb and hold water particles because

membranes are damaged If thawing takes place fast no time for cells to re-absorb water

huge thawing loss

Freezing

Freezer-Burn

Materials not packed

Water sublimates from hard (ice) to gas Water Activity (Aw) of material is higher as there is relative

humidity from surrounding environment Surface area of meat gives away water concentration of salt

within these layers is enhanced water penetrates from the core towards the surface

Drying out of surface denaturing of proteins Less functional proteins less water-binding capacity

Packed materials

Microclimate between meat and packaging maintains moisture within the material

Water doesn’t sublimate out proteins are not denatured But, over a long period of time ‘freezer- burn’ is caused

Freezer-Burn

Warm – Meat – Effect

Pork: within 1 hour after slaughtering Beef: within 3-4 hours after slaughtering Carcass is deboned right after slaughtering Meat is minced or chopped with the addition of salt and water or

ice Fibers or cells swell by the presence of salt and water Once energy is consumed and muscle remains contracted

gap between actin and myosin becomes greater ‘links’ from myosin cannot lock into actin No actin-myosin complex High solubility of protein no phosphates are needed

Cold shortening

Mostly by beef and sheep (more ATP as in pork) Temperature below + 14°C during early phase of rigor mortis Sarcoplasmatic Reticulum (SPR) damaged Enhanced concentration of Ca2 + ions Ca2 + mainly responsible for muscle concentration Damaged SPR can’t absorb Ca2 + ions Concentration of Ca2 + ions always high

High number of ‘links’ between actin and myosin

Meat always ‘hard and tough’

Solubility of protein greatly reduced

Remedy 1: Moderate ‘cooling’ temperatures during first hours after slaughtering

Remedy 2: (Not used often too labor intensive)

Hanging of carcass in ‘H’-bone Gravity of large parts of the body are counter-acting the shortening of

fibres (muscles)

Cold shortening

Remedy 3: Electric stimulation Not only pork would cause PSE Only by animals with ‘slow’ glycolysis after slaughtering (beef &

sheep) 400-600 volts, max. 30 seconds Muscle is forced to ‘perform’ work ATP (energy) is used Sarcoplasmatic Reticulum is not damaged Meat can be chilled fairly quickly afterwards because no energy

is left in muscle

Cold shortening

Values

pH- value: Very important within meat

technology Concentration of hydrogen

ions Concentration of ions are re-

calculated by using the negative decadic logarithms

Example: concentration is 10 -7

pH - value is 7 7 is neutral. 1 is extremely

sour. 14 is extremely alkali

Aw - value: Is the amount of the total

water within meat/meat- product, which isn’t bound by dissolved substances like protein, sugar, salt etc.

It’s the ‘free’ water within the product

‘Free’ water is food for microorganisms

The pH Scale While it is quite valid to use an amount of H+ or OH as a

measure of acidity or alkalinity these values are somewhat cumbersome because of the wide range of possible concentrations involved

The pH scale is an attempt to quantify the measurement of acidity simply

pH means ‘potential of Hydrogen’ (pH) and is defined mathematically as: pH= - log 10 [H+]

[H+] = the concentration of hydrogen ions measured in mol per liter. Note: the determination of concentrations is beyond the scope of this course. Suffice to say that concentration expressed in mol per liter are not equal to those expressed in percent

Eg: 10% HCI [H+] = 0.274 mol per liter

1.0% HCI [H+] = 0.0274 mol per liter

10% CH3COOH [H+] = 0.01 mol per liter

Because of the logarithmic nature of pH as the amount of H+ and thus concentration of H+ increases the pH decreases

Eg : [H+] = 0.001 M pH= - log10(0.001)= - (-3.0)= 3.0

[H=]= 0.1 M pH= - log10(0.1)= - (-1.0)= 10 When basic substances are added the amount of H+ decreases

and thus the pH must increase It has been found experimentally that in substances which are

neutral the concentration of H+ is always 0.0000001 mol per liter (at 25 °C). Hence, the pH of a neutral solution will be:

pH= -log10 (0.0000001) = -(-7.0) = 7.0

Clearly then:

Acidic conditions are where pH < 7.0

Alkaline conditions are where pH > 7.0

The pH Scale

Thank you