Transcript FOOD CHARACTERISTICS - Soegijapranata Catholic University

Handout MK. Pengawasan Mutu
2011/2012
FOOD CHARACTERISTICS
Physical
Chemical
Food
Characteristics
Biological &
Microbiological
Sensory
Physical
Shape
Color
Food
Characteristics
Size
Surface condition
Texture
Freshness
Defects
Total solids, etc
Appearance
Chemical
Nutritional value
Food
Characteristics
Moisture content
Functional value
pH
Food additives
Chem contaminants
Etc
Biological &
Microbiological
Total bacteria
Food
Characteristics
Total coliform bacteria
Total mold
Free from pathogenic mos
Etc
Sensory
Flavor
Food
Characteristics
Aroma
Taste
Texture
Etc
Physical Attributes
• Physical attributes of food are related with the
appearance of food products, including:
– Color
Appearance
– Shape
The first
– Size
impressio
– Texture
n
– Etc.
COLOR
 Color is the one of the most important image
features because it contains the basic human
vision.
 Color significantly affects the consumer
perception of quality.
 If the color is unacceptable, the other two
major quality factors,
flavor and texture, are not
likely to be judged at all.
COLOR
 Color may be defined as the impact of the
wavelengths of light in the visual spectrum
from 390-760 nm on the human retina.
 The retinal cells may be sensitive to black and
white only or to red, green and blue (RGB)
wavelengths of light.
 The correct interpretation by the brain in terms
of color depends on the adequacy of signals.
COLOR
• Light is the basic stimulus of colors, it is important to
consider the electromagnetic spectrum.
• Visible light forms only a small part of the
electromagnetic spectrum, with a spectral range from
approximately 390 nm (violet) to 750 nm (red).
• The sensitivity of the eye varies even within this narrow
visible range. Under conditions of moderate-to-strong
illumination, the eye is most sensitive to yellow-green
light of about 550 nm.
Factors affecting color
 Chemical composition
 The appearance of a product as judged by its
color often be used to determine the pigment
content of a product, which in turn is often an
index of quality.
 Color measurement can be used to evaluate
pigment content (carotenoid, anthocyanin,
chlorophyl, etc.)
 Colorimetry and chromatography can be used to
measure the pigment content of food product.
Factors affecting color
 Effect of lighting
 The type of light falling on a object will affect the
perception of color.
 For example, when green light is directed onto a
white sheet of paper, the paper will appear to be
green.
 But within fairly narrow ranges, the human brain
will compensate for small shifts in the color of the
lighting because the brain anticipates what the
color should be.
Factors affecting color
 In food products, it is possible to make products
look better or worse depending on the lighting.
 Lighting in supermarkets is designed for the ability
to make product more favorable. But no single
lighting arrangement is optimum for every food
product. Example :
Cranberry juice under normal fluorescent tube light
with a high blue component will appear almost
black, while under warm fluorescent lighting with a
higher yellow-red component will appear much
redder.
Factors affecting color
 Lighting to improve color appearance had been
studied in detail in the red meat industry.
 It is possible to make cuts of red meat look much
redder by illuminating them with a pink light or by
placing a reflector painted red near the display
case.
 However, sometimes this method is considered
as a fraud because the consumer sees the actual
color when product is unpacked at home.
Interaction of color with other senses
 Color seems to have significant effect on the
perception of sweetness, but only have little effect
on the perception of saltiness.
 Many studies have shown that solutions colored
dark red will perceived to be sweeter than others of
the same sucrose concentration in lighter colors or
distilled water.
Color scales
• There are three characteristics of light by which a color
may be specified: hue, saturation, and brightness.
• Hue is an attribute associated with the dominant
wavelength in a mixture of light waves, i.e., it represents
the dominant color as perceived by an observer.
• Saturation refers to relative purity or the amount of
white light mixed with a hue.
• Brightness is a subjective term, which embodies the
chromatic notion of intensity.
• Hue and saturation taken together are called
chromaticity.
• Therefore, a color may be characterized by brightness
and chromaticity.
Color scales-CIE System
• The basic colors however are only three: red, green
and blue, and other colors are derived by mixing these
three.
• The Commission Internationale de l’Eclairage (CIE)
defined a system of describing the color of an object
based on three primary stimuli: red (700 nm), green
(546.1 nm), and blue (435.8 nm).
• The amounts of red, green, and blue needed to form
any given color are called the’ ‘tristimulus” values, X,
Y, and Z, respectively.
• A plot that represents all colours in x (red)-y (green)
coordinates is known as a chromaticity diagram
Color scales-CIE System
Color scales-CIE System
• Sometimes, tristimulus systems of representation of
colors are not easily understood by the users in
terms of object color. Other color scales therefore
were developed to relate better to how we perceive
color, simplify understanding.
• A 3-dimensional rectangular L, a, b, color space was
evolved, in which at L (lightness) axis – 0 is black
and 100 is white, a (red-green) axis – positive
values are red; negative values are green and zero
is neutral, and b (blue-yellow) – positive values are
yellow; negative values are blue and zero is neutral.
Color scales-CIE System
• There are two popular L, a, b color scales in use
today – Hunter L, a, b, and CIE L∗, a∗, b∗.
• They are similar in organization, but will have
different numerical values.
• Hunter L, a, b and CIE L∗, a∗, b∗ scales are both
mathematically derived from X, Y, Z values.
• Hunter scale is over expanded in blue region of
color space, while CIE scale is over expanded in
yellow region. The current recommendation of
CIE is to use L∗, a∗, b∗.
Color scales-CIE System
Size
 Size is very important feature since it can
determine the loss of products during processing
and the final product yields.
 Size can be measured in three dimensions such
as volume in the real world. However, it is usually
reduced to one or two dimensional measurements.
 Size features include weight, volume, diameter,
area, surface area, perimeter, length, skeleton
length and width.
Size
• Some other measurements of size:
– Feret’s diameter: determined by the distance of
2 pixels with the smallest and the largest
coordinates
– Major axis: the longest line that can be drawn
across food products, calculated by measuring
the distance between two boundary pixels and
by taking the longest
– Minor axis, which the longest line that can be
drawn through the object perpendicular to the
major axis.
Size
 Area has become a very popular measurement for
the quality evaluation of fruit and vegetables such as
the determination of tomato ripeness.
 Length measurements might also be used especially
for those long shape food products such as
cucumber, banana, which usually measured by
skeleton length, mid-line of the products.
Skeleton length
Size
• In meat industry, the calculation of surface area
and volume of ellipsoid meat joints can be used to
determine shrinkage during processing.
• The measurement of area is also important in
meat --- the area of marbling/intramuscular fat and
the overall area to determine the marbling score.
Size
• Size features can also be used for sorting of fish,
and many other products such as pizza, wheat
grains.
Shape
• Shape is generally referred to the profile or
physical structure of objects geometrically.
• Conventional measurements of shape called
size dependents --- try to combine different
size parameters together to form
dimensionless expressions for shape
description.
Shape
• Some shape measurements applied to food
industries:
– Compactness: the ratio of area over the square
perimeter --- effective for perfect circle food
products
– Elongation: the ratio of major axis over the minor
axis
– Convexity: the ratio of convex perimeter over the
perimeter
– Roughness: the ratio of area over the square
major axis
Shape
• However, those measurement are doubted. Are they
sufficient enough for describing the shape of food
products, especially those with the irregular shape,
such as broccoli, the whole body of fish, etc.
• Some size independent measurements are
developed:
– Spatial moment
– Boundary encoding
– Fourier descriptor
Texture
• Texture can be generally correlated to the sensory
properties of food products.
• Texture can also be used to determine chemical or
physical properties of food products --- contain more
information about chemical or physical properties
than color and size.
• Textural properties of food product will be change
during storage.
• The importance of texture in the overall acceptability
of foods varies widely, depending upon the type of
food:
Texture
• Critical:
Food in which texture is the dominant quality
characteristic, such as meat, potato chips,
cornflakes, etc.
• Important:
Food in which texture makes a significant but not a
dominant contribution to the overall quality, for
example most fruits, vegetables, cheeses, bread,
cereal based foods, candy, etc.
• Minor:
Food in which texture makes a negligible
contribution to the overall quality, for example most
beverages, thin soups, etc.
Texture
Some of common texture vocabs:
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Crisp
Dry
Juicy
Creamy
Crunchy
Chewy
Smooth
Hard
Tender
Soft
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Fatty
Watery
Sticky
Tough
Greasy
Slippery
Firm
Coarse
Springy
etc
Texture
• The textural properties of food are group of physical
characteristics that arise from the structural
elements of food, are sensed primarily by the feeling
of touch, are related to the deformation,
disintegration, and flow of the food under a force
and are measured objectively by function of mass,
time and distance.
Texture
• Relation between textural parameters and popular
nomenclature:
– Mechanical characteristics
Primary parameters
Secondary parameters
Soft – firm – hard
Hardness
Cohesiveness
Popular terms
Brittleness
Chewiness
Gumminess
Crumbly – crunchy –
brittle
Tender – chewy – tough
Short – mealy – pasty –
gummy
Texture
Primary parameters
Secondary parameters
Popular terms
Viscosity
Thin - viscous
Elasticity
Plastic – elastic
Adhesiveness
Sticky – tacky - gooey
Texture
– Geometrical characteristics
Primary parameters
Secondary parameters
Popular terms
Particle size and shape
Gritty, grainy, coarse, etc
Particle shape and
orientation
Fibrous, cellular,
crystalline, etc.
Texture
– Other characteristics
Primary parameters
Secondary parameters
Dry – moist – wet watery
Moisture content
Fat content
Popular terms
Oiliness
Greasiness
Oily
Greasy
Source: Bourne (2002)
References
• Bourne, M.C. (2002). Food Texture and Viscosity:
Concept and Measurement 2nd Ed. Academic Press.
New York.
• Francis, F,J. (1995). Quality as influenced by color.
Food Quality and Preference 6 : 149-155.
• Zheng, C., Sun DW., and Zheng L. (2006). Recent
developments and applications of image features for
food quality evaluation and inspection – a review.
Food Science and Technology 17: 642-655.