ITP330 PEMBEKUAN PANGAN (Freezing of Foods) · •Menurunkan laju reaksi kimia/biokimia ......

32
1 Purwiyatno Hariyadi Email: [email protected] Web: phariyadi.staff.ipb.ac.id ITP330/Fateta/IPB/Freezing of Foods 11/25/2016 ITP330 -- Freezing of Food - 2016 phariyadi.staff.ipb.ac.id ITP330 PEMBEKUAN PANGAN (Freezing of Foods) Purwiyatno Hariyadi, PhD Department of Food Science & Technology, Bogor Agricultural University, BOGOR, Indonesia ITP330 -- Freezing of Food - 2016 phariyadi.staff.ipb.ac.id Outline Freezing systems Frozen food properties (density, thermal conductivity, enthalpy, apparent specific heat, and apparent thermal diffusivity) Freezing time (freezing curve, Plank’s equation, prediction of freezing time, freezing rate)

Transcript of ITP330 PEMBEKUAN PANGAN (Freezing of Foods) · •Menurunkan laju reaksi kimia/biokimia ......

Page 1: ITP330 PEMBEKUAN PANGAN (Freezing of Foods) · •Menurunkan laju reaksi kimia/biokimia ... eutectic point. EF: Freezing continuous to freezer temperature Titik Beku air Super cooling

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ITP330 PEMBEKUAN PANGAN(Freezing of Foods)

Purwiyatno Hariyadi, PhD• Department of Food Science & Technology, Bogor Agricultural

University, BOGOR, Indonesia

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

Outline

Freezing systems

Frozen food properties (density, thermal conductivity, enthalpy, apparent specific heat, and apparent thermal diffusivity)

Freezing time (freezing curve, Plank’s equation, prediction of freezing time, freezing rate)

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Aspek engineering

Design (keperluan refrigerasi, T) Laju pembekuan (the rate at which freezing

progress)

Mutu produkProduktivitas

PEMBEKUAN PANGAN

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

• Penyimpanan produk pada T < suhu beku

• Umumnya pada T < 28 °F (-2 °C), atau khususnya pada < 0 °F (-18 °C)

• Sebagian besar air (~95%) beku

• daya awet produk beku ` bbrp bulan --- tahun• Laju pembekuan dipengaruhi oleh bbrp faktor :

perlu dikendalikan

• Pertumbuhan mikroorganisme dihambat, bbrp bahkan inaktif

PurwiyatnoHariyadi/IPN/ITP/Fateta/IPB

PEMBEKUAN PANGAN

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Things to notice:

• Pressure and temperature both affect the phase of matter.

• All three phases of matter exist at the triple point

Melting/Freezing

Boiling/Condensating

pembekuan

PEMBEKUAN PANGAN

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

PENGARUH POSITIF

• Menurunkan/menghambat pertumbuhan m.o.• Menurunkan laju reaksi kimia/biokimia• Meningkatkan daya simpan produk (3-40 lipat untuk setiap penurunan suhu 10°C)

PEMBEKUAN PANGAN

Pengaruhnya pada Produk Pangan :

+

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PENGARUH NEGATIF

• Kerusakan kimia• Kerusakan fisik (textural)

PEMBEKUAN PANGAN

Pengaruhnya pada Produk Pangan :

+

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

PENGARUH NEGATIF

• Freezer burn ?• Package properly • Control temperature fluctuations in storage.

• Oxidation? • Off-flavors • Vitamin loss • Browning

• Recrystallization?

PEMBEKUAN PANGAN

Pengaruhnya pada Produk Pangan :

+

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- Penurunan titik beku = f (konsentrasi, BM)

m.KT

m.BMTRT

f

A2

0Agf

kg

kJ335air

kg

kJ,pembekuanlatenpanas

K.mol

J314.8gastatankonsR

K273,Kair)A(murnipelarutbekutitikT

.pelarutmg1000

solutmolmolalitasm

g

0A

dimana:

BMA = Berat Molekul pelarutK = konstanta molal titik beku

Lar. X dlm air Tf = (1.86 m)oC

A

A0Ag

1

XlnT

1

T

1

R

XA = fraksi mol air1 = panas laten pembekuan

SIFAT PRODUK PANGAN BEKU

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

Ice cream mix dengan komposisi sbb:10% butterfat12% solid-not-fat (54.5%: laktosa)15% sukrosa0.22% stabilizer

37.22% Air = 62.78%

Ditanya Tf = ?

m.BMTRT

A2

0Ag

f

m = ?

solvenkg

solutmolm

Solut? sukrosa BM = 342laktosa BM = 342solut lain diabaikan !!

Asumsi bahwa hanya gula (laktosa + fruktosa) yang memp. Efek menurunkan titik beku) !!

Contoh :

SIFAT PRODUK PANGAN BEKU

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Fraksi gula = 0.15 + 0.12 (0.545) = 0.2154 g/gFraksi air = 0.6278 Konsentrasi gula dlm air =

airg1000

gulag1,343

airg

gulag3431.0

6278.0

2154.0

m003.1airg1000

gulamol342

1.343

m

kg

J335.1000

kg

mol003.1

mol

g18K273

g18

mol1

K.mol

J314.8

T

2

f

Tf = 1,86 K

Contoh (lanjutan):

SIFAT PRODUK PANGAN BEKU

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

Air murni = 335

Larutan solid x dlm air = (335 mw)

kg

kJ

kgkJ

mw = Fraksi massa airContoh:

Kadar air

Selada 94.8 316.3 Strawberi 90.8 289.6 Kacang panjang 88.9 297.0 Kentang 77.8 258.0 Daging kambing 58.0 194.0 Kacang merah, biji kering 12.5 41.9 Kurma kering 24.0 79.0

kg

kJ

Perhitungan berdasarkan pd rumus

= 335 mwkg

kJ

Air:mol

J6030

mol1

1018

kg

J10335

kg

kJ335

33

PANAS LATEN PEMBEKUAN

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T-t Diagram :

A schematic freezing curve for water, displayingsensible heat loss (Regions I and III) and latent heat loss (Region II).

KURVA PEMBEKUAN … untuk air murni

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

Removal of heat (Q) from Region I (sensible heat), II (latent heat), and III (sensible heat) :

(1) Q1 = mCp1T1

m = weight of food Cp1 =specific heat of food above freezing T = temperature difference

(2) Q2 = mw ........> mw = weight of water ........> = latent heat

(3) Q3 = mCp2T3........> m = weight of food ........> Cp2 = specific heat of frozen food ........> T3 = temperature difference

KURVA PEMBEKUAN … untuk air murni & energi

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Titik Beku air

Super cooling

Titik eutektikAir

Larutan

Suhu

Waktu

Titik beku = f(waktu)

Driving force for nucleation/crystallization(i.e. T = T – Tf)

Removal of latent heat

Removal of sensible heat

KURVA PEMBEKUAN … untuk produk pangan

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

Freezing process

AB: Food is cooled below its freezing point (Tf), below 0oC

B: water remains liquid although temp below Tf supercooling

BC: Temp rises rapidly to Tf as ice crystals begin to form and latent heat of crystallization is released.

CD: heat is continued to be removed from foods freezing point is depressed

DE: solute becomes supersaturated and crystallize eutectic point.

EF: Freezing continuous to freezer temperature

Titik Beku air

Super cooling

Titik eutektikAir

Larutan

Suhu

Waktu

Titik beku = f(waktu)

A

B

C

DE

F

Tf

Tm

Freezing Process

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T

Tf

Ice

Sugar-Ice solid

LiquidSolubility line

Sugarcrystal

glass

eutectic

PHASE DIAGRAMPhase Diagram

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

3-21

KURVA PEMBEKUAN … untuk produk pangan

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Ti

Tf

T

t

Setelah terjadi pembekuan, konsentrasi solute pada sisa larutan menjadi lebih tinggi .....> penurunan titik beku lebih besar .....> Tf

()

You can’t freeze all of the water(Still have unfrozen (unfreezable) water : 5-10%)

KURVA PEMBEKUAN … untuk produk pangan

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

You can’t freeze all of the water(Still have unfrozen (unfreezable) water : 5-10%)

KURVA PEMBEKUAN … untuk produk pangan

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KURVA PEMBEKUAN … untuk produk IKAN

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KURVA PEMBEKUAN … untuk produk IKAN

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Buah anggur (grape) ........> kadar air 84.7%........> Tf = -1.8oC (271.2oK)

A

A0Ag

1

XlnT

1

T

1

R

1 = 6003

Rg = 8.314 K.mol

JmolJ

XA=?

AXlnK2.271

1K273

1

K.molJ

314,8

molJ

6003

Ln XA = - 0.01755XA = 0.9826 (effective mol fraction of water )

ml

grapem

SUHU AWAL PEMBEKUAN PROD PANGAN

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

XA = fraksi mol air = 0.9826

XA = 0.9826 =

EBM

3.15

18

7.8418

7.84

BME = 183.61

Juice anggur dapat dianggap bertingkah laku mirip/sama dgn- lar. x dlm air- BMx = 183.61

- XA = 09826- Xx = ........ dst

mol

g

SUHU AWAL PEMBEKUAN PROD PANGAN

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SUHU AWAL PEMBEKUAN PROD PANGAN

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Hubungan antara % air beku vs. suhu

PROD PANGAN BEKU

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• EQUIPMENT RELATED • rate of heat transfer• size of refrigeration unit

• FOOD/PRODUCT QUALITY• slow freezing

• result in formation of few, large ice crystals•damaging to cell structure/quality

• rapid freezing• results in many small ice crystals•gives best product quality

• water ice: ~ 9% increase in volume

LAJU PEMBEKUAN

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LAJU PEMBEKUAN

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Slow Freezing

LAJU PEMBEKUAN

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Rapid Freezing

LAJU PEMBEKUAN

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LAJU PEMBEKUAN

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LAJU PEMBEKUAN

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LAJU PEMBEKUAN

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• Slow Freezers 0.2 cm/h

- Still air and cold stores

• Quick Freezers 0.5-3 cm/h

- Air blast and plate freezers

• Rapid Freezers 5-10 cm/h

- Fluidized bed freezers

• Ultra rapid Freezers 10-100 cm/h

- Cryogenic freezers

-- Klasifikasi berdasarkan pada laju pergerakan “ice front”

LAJU PEMBEKUAN

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Freezing time

Freezing time: time required to lower the temperature of a food from an initial value to a predetermined final temperature at the thermal center.

Freezing time depends on: Size and shape of the product Thermal conductivity of the food material Area of the food available for heat transfer Surface heat transfer coefficient of the medium Temperature difference between the food and freezing

medium Type of packaging film in the case of packaged foods

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- Pendugaan keperluan pembekuan ukuran sistem “mechanical

compression” evaluasi beban refrigerasi/pembekuan

- Disain peralatan + proses, untuk : memperoleh pembekuan yg diinginkan

- koef pindah panas- laju pembekuan

WAKTU/LAMA PEMBEKUAN

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• Time-temperature method• Time required to freeze between two temperatures

(usually T = -5oC or –10oC)• Velocity of ice front

- rate of freezing- must be able to see ice front

• Appearance of specimen- internal conditions

• Thermal methods- calorimetric techniques- not real-world condition

+Time-temp. methods most common+many people use time to freeze to

–10oC as standard.

WAKTU/LAMA PEMBEKUAN

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• panas laten adalah energi utama yang hrs diperhitungkan pada proses pembekuan • ~ 75% total energi pd proses pembekuan

333.3 kJ/kg air144 BTU/lb air

• Terjadi perubahan sifat fisik bahan selama proses pembekuan ~ f (T,m)

WAKTU/LAMA PEMBEKUAN

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Plank’s Method (for infinite slab)

Plank’s equation is an approximate analytical solution for a simplified phase-change model.

• Plank assumed that the freezing process:

(a) commences with all of the food unfrozen but at its freezing temperature.

(b) occurs sufficiently slowly for heat transfer in the frozen layer to take place under steady-state conditions.

WAKTU/LAMA PEMBEKUAN

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Tf

T1

Plank’s Method (for infinite slab)

WAKTU/LAMA PEMBEKUAN

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xfrozen frozen

Tf Tf

Ts

T1

Ts

T1

qq

unfrozen

a

Plank’s Method (for infinite slab)

WAKTU/LAMA PEMBEKUAN

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

Convection:

q

hr

BTU= Qt = h (Ts – T1) ...... Pers. 1

h = convective heat transfer coeff. at the product surface.Conduction:

sff TTx

A.kq .......... Pers. 2

Tf = initial freezing pointx = x (t)

Combine 1&2:

h

1

k

xTT

q

f

1f

........... Pers. 3

Plank’s Method (for infinite slab)

WAKTU/LAMA PEMBEKUAN

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Ingat Pers 3 :

h

1

k

xTT

q

f

1f

Plank’s Method (for infinite slab)

WAKTU/LAMA PEMBEKUAN

Jumlah energi yang dibebaskan selama proses pembekuan

qdt = mi f = f dV f

qdt = f f A dx

so, q = f f A dx/dt .............. Pers. 4

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

dtTTdxh

1

k

x1f

fff

fT

01f

2

a

0 fff dtTTdx

h

1

k

x

h2

a

k8

a

TTt

2

if

fff

Pembekuan selesai lempeng jika x = a/2

Ti = Suhu PembekuanSuhu ruang pembeku

h1

kx

ATT

dt

dxA

f

1fff

Kombinasi Pers. 3 dan 4 ………………….>

Plank’s Method (for infinite slab)

WAKTU/LAMA PEMBEKUAN

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h

Pa

k

Ra

TTt

f

2

if

fff

Where:Infinite slab Sphere Infinite sylinder Cube

P 1/2 1/6 1/4 1/8R 1/8 1/24 1/6 1/24a Thickness Diameter Diameter Edge

f= latent heat of fusion [=] kJkg

kg

kJ water = 333.22 = 144

lbBTU

General Plank’s Equation :

WAKTU/LAMA PEMBEKUAN

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

a

b c

P dan R untuk bentuk bata

a : dimensi terpendekc : dimensi terpanjang

2 = c/a1 = b/a

Lihat chart/diagram :dengan diketahui nilai 2 dan 1 maka dapat dibaca nilai P dan R

General Plank’s Equation :

WAKTU/LAMA PEMBEKUAN

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ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

Chart providing P and R constants for Plank’s equation when applied to a brick or block geometry.

In this figure,

β1 and β2 are the ratios of the two longest sides to the shortest.

It does not matter in what order they are taken.

General Plank’s Equation :

WAKTU/LAMA PEMBEKUAN

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

Limitation of Plank’s method:

• no superheating or supercooling• thermal properties are constant• can’t incorporate a variable heat transfer

coeff.• can’t handle varying freezing point

General Plank’s Equation :

WAKTU/LAMA PEMBEKUAN

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ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

1. AIR FREEZING - Products frozen by either "still" or "blast" forced air.

• cheapest (investment) • "still" slowest, more changes in product • "blast" faster, more commonly used

2. INDIRECT CONTACT - Food placed in direct contact with cooled metal surface.

• relatively faster • more expensive

3. DIRECT CONTACT - Food placed in direct contact with refrigerant (liquid nitrogen, "green" freon, carbon dioxide snow)

• faster • expensive • freeze individual food particles

METODE PEMBEKUAN

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

• Blast freezing – a very cold air blasted on the food cools food very quickly.

• Close indirect contact – food is placed in a multi-plate freezer and is rapidly frozen.

• Immersion – food is placed into a very cold liquid (usually salt water – brine) or liquid nitrogen, this is known as cryonic freezing.

METODE PEMBEKUAN …commercial freezing

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ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

• Mechanical Freezers- Evaporate and compress the refrigerant in a continuous cycle

• Cryogenic Systems- Use solid and liquid CO2, N2 directly in contact with the food

METODE PEMBEKUAN …freezing equipments

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

METODE PEMBEKUAN …freezing equipments

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ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

A typical fluidized bed freezer

METODE PEMBEKUAN …freezing equipments

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

METODE PEMBEKUAN …freezing equipments

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ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

Batch Freezer

Source: Unit operations for food the food industries by: W.A. Gould

Blast Type

METODE PEMBEKUAN …freezing equipments

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

Source: Unit operations for food the food industries by: W.A. Gould

Hydraulic Pump

Top Pressure plate

Connecting Linkage

Corner Headers

Refrigerant hoses

Trays

Contact plates

Polyurethane and polystyrene insulated doors

METODE PEMBEKUAN …freezing equipments

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ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

METODE PEMBEKUAN …freezing equipments

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

METODE PEMBEKUAN …freezing equipments

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ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

METODE PEMBEKUAN …freezing equipments

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

METODE PEMBEKUAN …freezing equipments

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Selamat belajar …

ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

1. Water evaporation from the surface of the product can result in considerable weight loss in blast air freezers.

2. Individually quick frozen (IQF) products can be produced in belt freezers and fluidized bed freezers.

3. Cryogenic freezing results in frozen products with large ice crystals.

4. The rate of freezing in plate freezers is high.5. Water activity of a frozen product is only a function of

temperature.

Quiz

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ITP330 -- Freezing of Food - 2016phariyadi.staff.ipb.ac.id

6. Bound water does not freeze.7. Bound water affects water activity of a frozen product.8. As water in a solution changes to ice, solute

concentration increases and freezing point decreases.9. Heat capacity and thermal conductivity below the

freezing point change significantly with temperature.10.Thawing is slower than freezing because the thermal

conductivity of ice is lower than that of water.

Quiz