COLOR (WARNA) COLOR WBS

Transkripsi

1 COLOR (WARNA) WBS 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. 1

2 Electromagnetic spectrum Cahaya didefinisikan sebagai energi radiasi yang dapat dievaluasi secara visual dalam frekuensi Hz sampai Hz Visible spectrum and its relation to the electromagnetic spectrum. 2

3 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) 3

4 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. 4

5 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 5

6 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. 6

7 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. 7

8 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 8

9 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, dan b. 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 tapi dapat ditunjukkan lokasinya CIELAB L, a, and b dikalkulasikan berdasarkan the tristimulus values (Marcus,1998) 9

10 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 10

11 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. 11

12 Irisan kentang yang digoreng dengan minyak biji bunga matahari dalam microwave dengan waktu penggorengan yang berbeda dievaluasi dengan skala CIE. Sebagai standar digunakan a BaSO 4 dengan nilai L, a, and b 96.9, 0.0, dan 7.2. Tentukan E* dan evaluasi hasilnya! Solusi: Nilai L, a, b hasil analisa disajikan dalam tabel berikut hasil perhitungan E* Peningkatan nilai E menunjukkan warna keripik kentang semakin gelap 12

13 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. 13