color - share story & experience · 10/20/2010 4 color evaluation objek harus teriluminasi...
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10/20/2010
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WBS
COLOR (WARNA)
COLOR Salah satu atribut kualitas yang penting untuk produk
pangan
Karakteristik fisik yang menentukan daya terima konsumen
kerusakan fisik juga dapat ditunjukkan dengan perubahan
warna
Absorpsi jumlah panjang gelombang tertentu dalam area
visible menentukan warna bahan pangan
Fenomena yang melibatkan komponen fisik dan fisiologis
400 to 500 nm (blue), 500 to 600 nm (green and yellow),
and 600 to 800 nm (red), biasanya diekspresikan dalam
istilah hue, value, and chroma pada Munsell color system.
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Electromagnetic spectrum
Cahaya didefinisikan sebagai energi radiasi yang dapat
dievaluasi secara visual dalam frekuensi 3.9×1014 Hz sampai
7.9 × 1014 Hz
Visible spectrum and its relation to the
electromagnetic spectrum.
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Warna yang dikenal oleh mata manusia berhubungan dengan
radiasi cahaya dalam nilai kisaran berikut
violet-blue (380 < λ < 480 nm)
green (480 < λ < 560 nm)
yellow (560 < λ < 590 nm)
orange (590 < λ < 630 nm)
red (630 < λ < 750 nm)
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Color Evaluation
Objek harus teriluminasi
Fenomena fisik (interaksi cahaya dengan objek)
- transmission
- refraction
- absorption
- scattering
- and others.
Wavelengths not absorbed but reflected by or transmitted
through an object are visible to observers.
For example:
- a blue object reflects the blue light spectrum but absorbs
red, orange, yellow, green, and violet.
- if all radiant energy in the visible region is reflected from an
opaque surface, the object appears white.
- if it is almost completely absorbed, the object is black.
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Transmission
light goes through the object and essentially does not change
the object is transparent
A colorless object transmits all light with the exception of a
small amount that is reflected.
if none of the light is transmitted the object is black and is
said to be opaque.
Refraction
light goes through two media that have different densities
As example, light travels through medium 1 (such as air) and
then goes through medium 2 (such as water). For any two
media, the refractive index (Ri) is defined as:
Ri depends on light wavelength, and this is clearly observed
when white light goes through a prism
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Refraction and color
Absorption
light may also be absorbed or lost as visible light when it
interacts with matter
if the object only absorbs only part of the light, it appears
colored
if all light wavelengths are absorbed, the object appears black
if none of the wavelengths is absorbed, the object appears
white.
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Scattering
light is scattered when it interacts with matter travels in
many different directions
The deviation of light direction (scattering) is associated with
the interaction between light and the particles in the
diffusion medium.
Scattering is only observed when the particles and the
diffusion medium have different Ri
In the light–material interaction, if part of the light is
scattered and another part transmitted, then the material is
translucent.
On the other hand, if light scattering is so intense that no
light is transmitted, then the object is opaque.
Scattering is very common; the colors of the sky (blue), of
the clouds (white), and most white colors are due to this
phenomenon.
White materials do not show absorption and each light
component is scattered the same amount.
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Color Measurement
total carotenoid content vs color for squash
desirable to follow the changes in color of a product during
storage, maturation, processing
often used to determine the ripeness of fruits.
color of potato chips is largely controlled by the reducing
sugar content, storage conditions of the potatoes, and
subsequent processing
color of flour reflects the amount of bran. Freshly milled
flour is yellow because of the presence of xanthophylls
Colour Measurement System
Color is a characteristic of light, which is measurable in
terms of intensity and wavelength
Color of a material becomes visible only when light from a
luminous object or source illuminates strikes the surface
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Color order system
Susunan three-dimensional
Lima color order systems yang digunakan untuk pangan:
1. Munsell
2. CIE : The Commission Internationale de l’Eclairage (CIE)
(The International Commission on Illumination)
3. CIE L∗a∗b∗ (CIELAB)
4. Hunter Lab
5. Lovibond.
CIE L∗a∗b∗ (CIELAB) Color Spaces
Lokasi warna pada sistem ini ditentukan dengan koordinat L∗, a∗, danb∗.
L∗ menunjukkan perbedaan antara cerah atau terang (light) (L∗ = 100) dan gelap (dark) (L∗ = 0).
a∗ menunjukkan perbedaan antara hijau (green) (−a∗) dan merah(red )(+a∗)
b∗ menunjukkan perbedaan antara biru (blue) (−b∗) dan kuning(yellow) (+b∗)
Jika L, a, b diketahui maka warna tidak hanya dideskripsikan tapidapat ditunjukkan lokasinya
CIELAB L∗, a∗, and b∗ dikalkulasikan berdasarkan the tristimulus values (Marcus,1998)
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Hunter Lab Color Space
Berdasarkan L, a, b
L menunjukkan kecerahan 0 (black) hingga 100 (white).
a menunjukkan −a (greenness) to +a (redness)
B menunjukkan −b (blueness) to +b (yellowness).
Hunter scale juga berasal dari nilai X, Y , Z
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Color Differences (Perbedaan warna)
Total perbedaan warna (E∗) pada CIE L∗a∗b∗ (CIELAB) total color adalah jarak antar warna dalam CIE
∆L∗ adalah perbedaan kecerahan:
L∗sample − L∗standard
∆ a∗ adalah perbedaan merah/hijau:
a∗sample − a∗standard,
∆ b∗ adalah perbedaan kuning/biru :
b∗sample − b∗standard.
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Irisan kentang yang digoreng dengan minyak biji bunga
matahari dalam microwave dengan waktu penggorengan yang
berbeda dievaluasi dengan skala CIE.
Sebagai standar digunakan a BaSO4 dengan nilai L∗, a∗, and b∗96.9, 0.0, dan 7.2.
Tentukan E* dan evaluasi hasilnya!
Peningkatan nilai E∗ menunjukkan warna keripik kentang semakin gelap
Solusi:
Nilai L, a, b hasil analisa disajikan dalam tabel berikut hasil
perhitungan ∆E*
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References
Sahin, S. & Sumnu, S.G. 2006, Physical Properties of Foods, Springer, USA.
MacDougall, D.B (ed). 2002, Colour in food: Improving quality, Woodhead Publishing Limited & CRC Press LLC, Boca Raton.
Delgado-Vargas,F. & Paredes-López, O. 2003, Natural Colorants for Food and Nutraceutical Uses, CRC Press LLC, Boca Raton.
Meilgaard, M., Civille, G. V., & Carr, B.T. 1999, Sensory Evaluation Techniques Third Edition, CRC Press LLC, Boca Raton.
Nielsen, S.Z. (ed). 2003, Food Analysis, third edition, Kluwer Academic/Plenum Publishers, New York.