ENDRIKA WIDYASTUTI FOOD SCIENCE AND TECHNOLOGY AGRICULTURAL TECHNOLOGY BRAWIJAYA UNIVERSITY 2012 1
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Starch Ingredients Must be cooked Gel slowly Show syneresis Break down under shear Break down under acid conditions Forms complexes
Amaranth starch (Bar: 1 µm)
Arrowroot starch (Bar: 20 µm)
Buckwheat starch (Bar: 5 µm)
Cassava starch (Bar: 10 µm)
Corn starch (Bar: 10 µm)
Oat starch (Bar: 5 µm)
Potato starch (Bar: 50 µm)
Rice starch (Bar: 2 µm)
Kidney bean starch (Bar: 20 µm)
Unheated starch granule
Heated starch granule
What is STARCH ? Complex carbohydrate made up of two components Components:
Amylose (linier chain) Amylopectin (branched chain)
Properties(viscosity) depend on amounts of the components
Amylose
Linear component of starch Contains 1,4-alphaglucosidic bonds Molecular weight: less than 0.5 million Can form coils which will trap iodine and turn blue
Amylopectin
Branched component of starch Contains 1,4-alphaglucosidic as well as 1,6-alpha-glucosidic bonds Molecular weight: 50500 million Limited coiling causes purplish-red color when iodine added
Amylopectin in Granules
Amylopectin structure (Chaplin, 2004)
Amylopectin General Structure
Amylose vs. Amylopectin Starches usually contain more amylopectin than amylose Generally roots/tubers contain more amylopectin than cereals Roots/Tubers: 80% amylopectin Cereals: 75% amylopectin Waxy corn and rice contain virtually all amylopectin
Characteristics of Amylose and Amylopectin CHARACTERISTIC
AMYLOSE
AMYLOSPECTIN
FORM
Essentially linear
Branched
LINKAGE
-1,4 (some -1,6)
-1,4; -1,6
POLYMER UNITS
200-2,000
Up to 2,000,000
MOLECULAR WEIGHT
Generally <0.5 million
50-500 million
GEL FORMATION
Firm
Non-gelling to soft
Starch Composition Starch Tapioca Potato Wheat Corn Waxy corn Hi amylose Rice
% amylose % amylopectin 17% 83% ~20% ~80% 25-26% ~75% 24-28% ~75 ~0% ~100% ~ 75% ~ 25% 22% 78%
Starch Granule Made in the cytoplasm of plant cells Amylopectin forms in concentric circles with amylose dispersed in between Held together by hydrogen bonds The granule swells when heated in water
Starch Granule
Granule Structure
Functions
Gelatinization Structure in baked products Thickener in sauces, soups, and dressings
Dextrinization Gelation
Pie filling
Gelation As a starch paste cools, a gel is formed Free amylose molecules lose energy as the temperature decreases and form hydrogen bonds The bonds create a network that holds the swelled granules in place
Gelatinization
When starch is heated in water Hydrogen bonds break, allowing water to enter the granule and the granule swells Amylose migrates out of the granule H-bonding between water and amylopectin increases Reduced free water changes the viscosity of the starch mixture, thickening it
Gelatinization and Temperature Gradually thicken with temperature Can be heated to 100oC without much granule rupture If held at 95oC will implode and lose viscosity
Gelatinization and Type of Starch Best thickening ability: potato starch Worst thickening ability: wheat starch More amylopectin=more translucent=more stringy
Gelation and Starch Source The more amylopectin (less amylose), the softer the gel Potato starch=high amylopectin=good thickening agent=soft gel Corn starch=less amylopectin=less effective thickening agent=strong gel
Viscosity and Type of Starch
Gelatinization and Sugar
Used together in pie fillings and puddings Sugar competes with the starch for water so less water available for gelatinization Delays gelatinization and decreases viscosity Increases gelatinization temperature The more sugar added, the longer the delay Disaccharides have a stronger effect than monosaccharides
Gelatinization and Acid Used together in fruit pie fillings, specifically lemon fillings Acid breaks down starch molecules so the paste is thinner Decreases viscosity Acid effect can be minimized by adding after gelatinization or heating rapidly
Gelation and Other Effects
Heating Moderate temperature and rate of heating Enough amylose needs to be released from the
granule without the granule bursting
Agitation Agitation during cooling disrupts amylose
network Should mix flavorings immediately after removing from heat
Gelation and Other Effects
Sugar Decreases gelatinization and amylose
release Softer gel
Acid Decreases gelatinization by hydrolysis of
granules Softer gel
Aging Gels
Syneresis Loss of water from a gel Amylose molecules pull together, squeezing
water out
Retrogradation Realignment of amylose molecules Hydrogen bonds break and reform into more
orderly crystals Can by reversed by gently heating Examples: refrigerated pudding, stale bread
Dextrinization When starch is heated without water A higher temperature is reached than with water Bonds break throughout the starch forming dextrins
How to compare starches?
Line spread test:
Measures thickening power Poor heated starch into cylinder, lift cylinder
and measure spread after specified time using concentric circles
Universal Texture Analyzer:
Percent sag:
Measures gel strength
Measures gel strength Measure molded gel height and compare to
unmolded gel height Stronger gel=small % sag, weaker gel=large % sag
Visco/Amylo/Graph
ViscoAmyloGraph heating
constant temperature
Viscosity
65oC
30oC 90oC
Time
Starch Gelation and Pasting A m y lo s e S w e llin g
C o lla p s e
A g g re g a tio n
C E
V is c o s ity
A = P a s te in itia tio n te m p e ra tu re B = P e a k P a s te T im e
D C = P e a k V is c o s ity D /C = S ta b ility ra tio E /D = S e t b a c k ra tio
B A T im e Tem p
50
65
90
95
80
Gelatinization and Pasting “Starch gelatinisation is the collapse (disruption of molecular order) within the starch granule, manifested in irreversible changes in properties such as granular swelling, native crystalline melting, loss of birefringence and starch solubilisation. The point of initial gelation and the range over which it occurs is governed by the starch type, concentration, method of observation, granular type and heterogeneities within the granule population under observation.” “Pasting is the phenomenon following gelatinisation in the dissociation of starch. It involves granular swelling, exudation of molecular components from the granule; and eventually the total disruption of the granules”
Pasting Cycle
Pasting characteristics of different native starches (from Food Additives, 2nd Ed 2002, Brane et al. Eds)
Gelatinization of starches Type Corn Waxy Corn High Amylose Potato Rice Tapioca Wheat
% Amylopectin % Amylose Gelatinization Range °C Granule Size m 73 99 20-45 78 83 82 76
27 1 55-80 22 17 18 24
62-72 63-72 67-100+ 58-67 62-78 51-65 58-64
5-25 5-25 5-25 5-100 2-5 5-35 11-41
Exogenous and Endogenous Effects on Starch Pasting Characteristics
Acid pH Sugar Lipids Proteins Shear
Effect of Acid on Starch Pasting
V is c o s ity
C o rn s ta rc h + w a te r
C o rn s ta rc h + w a te r + 1 .7 % a c e tic a c id
T im e
Effect of pH on Pasting of Corn Starch
V is c o s ity
pH 4
pH 10
p H 2 .5
T im e
Effect of Sugars on Pasting of Corn Starch
Perubahan pati pada: 1. Pra proses/pascapanen 2. Selama proses 3. Pasca proses/penyimpanan
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1.
2. 3.
Bahan hasil pertanian masih melakukan respirasi Terjadi hidrolisis: (produk mjd lebih manis) Pati -> maltodekstrin dan gula Terjadi oksidasi: Glukosa -> energi, CO2 dan air
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4. Perubahan proporsi pati -> perubahan tekstur dan rasa bahan (menjadi manis) 5. Pengendalian perubahan dapat ditekan dengan perlakuan pendinginan (paling ekonomis)
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a.
b. c.
d. e.
f. 09/03/2012
Swelling Gelatinisasi Retrogradasi Esterifikasi Hidrolisis Isomerisasi 48
Pati bila diberi air akan mengalami pengembangan ? volume 2. Kekuatan swelling sebanding dengan meningkatnya suhu larutan pati 1.
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1.
2.
Peristiwa rusaknya ikatan antarmolekul pada larutan pati dengan naiknya suhu Larutan pati mengalami gelatinisasi (kanji) dan viskositas menjadi tinggi (lebih kental).
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1.
2. 3.
Terjadi ikatan balik (set back) pada ikatan hidrogen antara gugus OH pada pati Terjadi selama pendinginan. Pati menjadi tidak terlarut.
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Amilosa
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4. Berhubungan dengan jumlah cabang pada rantai pati 5. Pati ber-amilopektin tinggi (jagung ketan) tidak mengalami retrogradasi pada pendinginan/ pembekuan. 09/03/2012
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1. Pati -> esterifikasi antara gugus OH -> panjang rantai dapat diatur
2. Sifat larutan pati hasil esterifikasi: a. lebih tahan terhadap panas b. kemampuan hidrolisis rendah c. stabil dalam pH rendah d. swelling dapat dihambat meskipun dalam air panas atau mendidih. 09/03/2012
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3. Produk pati ini banyak digunakan sebagai: a. makanan bayi b. salad dressing c. Stabiliser d. pengental
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-Dilakukan dengan: a. pH rendah b. Pemanasan suhu tertentu (mempercepat kerja enzim) c. tekanan tinggi d. Penambahan enzim (amilase) -hasil dari proses: pati --> dextrin maltosa -> glukosa 09/03/2012
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-Banyak digunakan dalam industri bahan pemanis dari tepung tapioka -> industri HFS (High fructose syrup).
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a. Proses isomerisasi merupakan perubahan glukosa -> fruktosa b. Tingkat kemanisan fruktose meningkat 3 kali lipat dibanding glukosa
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3. Menggunakan enzim isomerase 4. Teknik yang digunakan adalah imobilized enzyme -enzim diambil dari mikroba dan dijerap dalam matrik resin -larutan glukosa dilewatkan kolom yang berisi imobilized enzim
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1. Higroskopis,
Tepung yang mengandung gula reduksi cenderung mudah menyerap uap air, kemasan harus kedap air, dan ruang RH rendah 2. Perubahan aroma
Timbulnya bau (jawa=apek) yang dimulai dengan menyerap uap air atau penyimpanan yang terlalu lama 09/03/2012
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3. Perubahan warna
Timbul warna kuning kecoklatan akibat oksidasi dan penyimpanan terlalu lama 4. Serangga dan Rodentia
Akibat sanitasi gudang dan kemasan yang kurang baik 09/03/2012
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Amilosa (%)
Ukuran Granula (Um)
Rerata Ukuran (Um)
Beras ketan
0
2 – 15
6
Jagung ketan
70
4 – 20
10
Jagung
28
5 – 25
14
Ubi kayu
17
3 – 30
14
Ubi jalar
18
4 – 40
7 dan 20
Gandum
26
3 – 35
Ubi garut
21
9 – 40
19
Sagu
26
15 – 50
23
Kentang
20
10 - 100
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Sumber Pati
