Classification and characterization of foodstuffs

Bambang SAJur. ITP FP UNS

Konduksi

)( 21 TTL

kAq

Persamaan Umum :

dimana T = suhu di beberapa titik x = tebal permukaan

A= luas permukaan k= thermal conductivity (Btu/hr.ft.ºF)

-dT/dx = perbedaan suhu

dx

dTkAq

3

Convection heat transfer untuk bidang datar

Flow

qTw

T∞

wall

Transfer panas pada dinding mendekati nol.

)( TThAq w

Classification according to source and state

Raw materials : originating from animal and vegetable sources

Semi-Raw materials Processed food

Classification according to source and state

Solids : (a) homogeneous (gels, protein terlarut) (b) heterogeneous : (1) capillary porous rigid materials : wheat kernels, (2) capillary porous colloidal materials : meat and vegetables

Classification according to source and state

Powders Liquids : (a) Low-viscosity (b) High-

viscosity Slurries or dispersions : milk or peas

in water Emulsions : milk Foams : whipped cream

Foods Contains

Water : 60 – 70 % Proteins Lipids Carbohydrates Vitamins and minerals

Food Properties : Physical properties

Density : density dan bulk density Energy : specific enthalpy Specific heat (cp) or specific heat

capacity Latent heat Thermal conductivity

Density (kg/m3)

drymeter

bulkPorositas

Specific enthalpy

Sum of internal energy and the kinetic energy (unit : J/kg or N m/kg or W s/kg

Specific heat (cp) or specific heat capacity

The amount of heat necessary to raise the temperature of 1 kg of the material by 1o C or 1 K (unit : J/kg. K)

T

pdTch0

Tch pJika Cp konstan)

Cp composition

piip CCC

Dimana :Ci = mass consentration

Termal properties of food constituents

Component Mass cons(kg/kg)

Density(kg/m3)

Spec. Heat(kJ/kg)

Thermal conduc. (W/m K)

Water Cw 1000 4.182 0.60

Carbohydrate Cc 1550 1.42 0.58

Protein Cp 1380 1.55 0.20

Fat Cf 930 1.67 0.18

Air Ca 1.24 1.00 0.025

Ice Ci 917 2.11

Inorganic minerals

Cm 2400 0.84

Foodstuffs containing mainly water

Cp = 4.18 Cw + 2 Cd for fish and meat Cw < 0.25

Cp = 1.67 + 2.5 Cw for fruit and vegetables Cw > 0.5

While Cd = spesific heat dry matter

(Cw = 1 – Cd)

Foodstuffs containing mainly water

Cp = 1.40 + 3.2 Cw for cereals low water content

Latent Heat

The amount of heat removed to frozen the water at 0oC is 334 kJ/kg at

The amount of heat necessary to vaporized the water at 100 oC and 101,3 kPa is 2256 kJ/kg

Depending on composition, the freezing point of most foodstuffs is between -0,5 oC and -4 oC.

Boiling point

Boiling point of foodstuffs is higher than 100 oC, depending on the concentration of solids.

XTBPR 52.0

Where X = the mole fraction of solute

Thermal conductivity

If thermal conductivities in a two-component material are k1 and k2, the total effective conductivity depends on the heat flow derection

Thermal Cond. Effective

ckckkeff 21 )1(

(a) (b)

21

21

)1( kcck

kkkeff

Where c = the volume fraction of material 2

If random material

1

2

21

2121 )1(

)1())1((kcck

kkbckckbkeff

21

11

kb

kb

keff

(2)

(1)

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