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physics > Optical properties > Flashcards

Optical properties Flashcards

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1
Q

Application

A

= physical properties of the food
= Food composition: moisture, sugar, salt
= consumer judgment on food appearance and produce some kind of visual effect.

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2
Q

determined by the way they interact with electromagnetic radiation

A

Visible

infrared

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3
Q

Different

A

Transmittion Reflection
Refraction Diffraction
Absorption Scattering

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4
Q

Colorimetry

A
  • Colour measurement
  • Organoleptic perception of properties
    - Perception
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5
Q

Gloss

A

light specularly reflected from a plain smooth surface.

represents intensity of light reflected at the surface at different angles of incidence and viewing.

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6
Q

Translucency

A

an opaque-to-transparent scale.

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7
Q

In liquid foods, light is ____ when interacting with

suspended particles. Most foods are neither fully opaque nor fully transparent, but are _______.

A

scattered

translucent

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8
Q

Color

A

a beam of light composed of irregularly distributed energy emitted at different wavelengths

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9
Q

Objects modify light colorants in the food selectivity ___________________

A

absorb some wavelengths of incident light while reflecting or transmitting others

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10
Q

Rayleigh’s theory

A

describes scatter by particles which are much smaller than the wavelength of light

Diffuse reflectance occurs where light is reflected from a
particles surface which is greater than the wavelength of light impinging on it

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11
Q

The particles primarily responsible for scattering in milk are

A

fat globules and casein micelles.

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12
Q

Syneresis

A

Cheese Manufacture

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13
Q

Colour wavelength

A

~ 400- 750

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14
Q

~ 400 - 435

A

Purple - comple yellowish green

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15
Q

Blue

A

435- 480 comple yellow

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16
Q

Green

A

500-560 comple red

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17
Q

580 - 595

A

Yellow comple blue

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18
Q

610 - 750

A

Red comple green

19
Q

Infrared wavelength

A

> 750

20
Q

color perceived when the eye views a food is related to the factors

A

= the spectral composition of the light source
= the chemical and physical characteristics of the food
= and the spectral sensitivity properties of the eye

21
Q

To evaluate the colorimetric properties of a food, which factors need to be standardise

A

= instrumental sensor

= Visual colorimeters facilitate visual comparisons and eliminate differences in interpretation between operators

22
Q

Colour: 3 measures

A

Hue, Lightness and Saturation

23
Q

Hue

A

- Used for the classification of colour
- Mix hues
- continuum of these hues results in the color wheel

24
Q

Lightness

A

Separate bright and dark colours

25
Q

Saturation

A

Vivid vs dull

color saturation or vividness

26
Q

Numerical Expression of Colour

A

description of color for purchase specifications of food
commodities or packaging materials involves color
tolerances, which are defined in one, two, or three
dimensions in color space to avoid variability of the human eye

27
Q

color analysis systems

A

Munsell CIE Hunter

28
Q

Munsell

A

Colours described by: Hue/ Value (Lightness) / Chroma (purity)

hue scale based on ten hues distributed on a circumference (scaled 1 to 10)

lightness ranges from black to white (0 to 10) and is
distributed on a perpendicular line

Chroma is of irregular length beginning with 0 for the
central gray to the limit of purity obtainable by available
pigments in the Munsell book of color.

29
Q

Munsell Renotation System

A

Any given color is expressed as a letter/number combination

H V/C) in terms of its hue (H), value (V), and chroma (C

30
Q

CIE

A

Commission Internationale de l’Eclairage (CIE)

Yxy system - tristimulus values XYZ defined by CIE (1931)

Lab* system - provide more uniform color differences in relation to visual differences (1976)

31
Q

XYZ tristimulus \ Yxy

A
  • XYZ tristimulus values
  • Yxy color space form
  • foundation of present CIE color spaces
  • based on the three-component theory of color vision
    eye possesses receptors for three primary colors (red, green, and blue) and that all colors are seen as mixtures of these three primary colors.
  • graphing colour into two dimensions independent of lightness [ Y is the lightness]

- x and y are the chromaticity coordinates calculated from the tristimulus value XYZ

32
Q

Lab* color space or CIELAB

A
  • one of the most popular colour spaces

- Overcome original Yxy space problems

  • L* indicates lightness
  • a* and b* are chromaticity coordinates
33
Q

Lab*: Colour Difference

A

Delta values associated with this color scale

ΔL, Δa, and Δb* indicate how much a standard and sample differ from one another or individual samples differ from eachother in L, a, and b*.

34
Q

The total color difference, ΔE*

A

a single value which takes into account the differences
between the L, a, and b* of the sample and standard.

Will not indicate if L, a, and/or b* are out of tolerances

May be misleading

35
Q

Hunter Lab

A

- Overcome original Yxy space problems

-Similar to Lab* color space but calculated differently

36
Q

Colour measurement

A

Tristimulus colorimeters - measure only some parameters related to sensory colors

Spectrophotometers .- measures intensity of light through the completely visible spectrum

37
Q

Colorimeters are very useful in

A

the quality control of foods, and give results normally correlated with visual measurements.

38
Q

Colorimeter mainly used in

A

production and inspection applications for color difference measurements and color chart measurement

39
Q

Spectrometer required for

A

more complex/precise applications - e.g. Research

40
Q

Colorimeter features

A
  • Built in light source
  • Data memory
  • Data communication
  • Data display
  • Constant illumination/ viewing angles
  • Constant ‘observer’
  • Elimination of area effect and contrast effect
  • Colour- difference measurment
41
Q

Colour measurement - application

A
  • Perform quality control and continuous inspection during processing operations
  • Fruit ripeness
  • Milk or cream discoloration during sterilization

- Degree of roasting of coffee grains

- Browning of apples slices during storage

42
Q

Continuous color measurements are used in

A

in tasks involving color sorting (or “electronic sorting”) by using in-line systems

43
Q

Color sorting is used for

A

for a very wide range of food materials in screening defects.

physics (6 decks)

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