FOOD CHARACTERISTICSHandout MK. Pengawasan Mutu 2011/2012

Food CharacteristicsChemical SensoryBiological &MicrobiologicalPhysical

Food CharacteristicsPhysicalShapeColorTextureSizeFreshnessDefects AppearanceTotal solids, etcSurface condition

Food CharacteristicsChemical Nutritional valueMoisture contentFunctional valuepHFood additivesChem contaminantsEtc

Food CharacteristicsBiological &MicrobiologicalTotal bacteriaTotal coliform bacteriaTotal moldFree from pathogenic mosEtc

Food CharacteristicsSensoryFlavorAromaTasteTextureEtc

Physical AttributesPhysical attributes of food are related with the appearance of food products, including:ColorShapeSizeTextureEtc.

AppearanceThe first impression

COLORColor 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.

COLORColor 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.

COLORLight 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 colorChemical compositionThe 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 colorEffect of lightingThe 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 colorIn 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 colorLighting 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 sensesColor 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 scalesThere 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 SystemThe basic colors however are only three: red, green and blue, and other colors are derived by mixing these three.The Commission Internationale de lEclairage (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 SystemSometimes, 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 SystemThere 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

SizeSize 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.

SizeSome other measurements of size:Ferets 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 longestMinor axis, which the longest line that can be drawn through the object perpendicular to the major axis.

SizeArea 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.

SizeIn 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.

SizeSize features can also be used for sorting of fish, and many other products such as pizza, wheat grains.

ShapeShape 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.

ShapeSome shape measurements applied to food industries:Compactness: the ratio of area over the square perimeter --- effective for perfect circle food productsElongation: the ratio of major axis over the minor axisConvexity: the ratio of convex perimeter over the perimeterRoughness: the ratio of area over the square major axis

ShapeHowever, 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 momentBoundary encodingFourier descriptor

TextureTexture 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:

TextureCritical: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.

TextureCrispDryJuicyCreamyCrunchyChewySmoothHardTenderSoft

FattyWateryStickyToughGreasySlipperyFirmCoarseSpringyetc

Some of common texture vocabs:

TextureThe 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.

TextureRelation between textural parameters and popular nomenclature:Mechanical characteristics

Primary parametersSecondary parametersPopular termsHardnessSoft firm hard CohesivenessBrittleness

Chewiness

GumminessCrumbly crunchy brittleTender chewy toughShort mealy pasty gummy

Texture

Primary parametersSecondary parametersPopular termsViscosityThin - viscousElasticityPlastic elastic AdhesivenessSticky tacky - gooey

TextureGeometrical characteristics

Primary parametersSecondary parametersPopular termsParticle size and shapeGritty, grainy, coarse, etc

Particle shape and orientationFibrous, cellular, crystalline, etc.

TextureOther characteristics

Source: Bourne (2002)

Primary parametersSecondary parametersPopular termsMoisture content Dry moist wet - wateryFat contentOilinessGreasinessOilyGreasy

ReferencesBourne, 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.

*Structure is the spatial arrangement of structural elements (water and oil droplets, gascells, fat crystals, strands, granules, micelles, and interface) and assemblies (fibers,proteins, cell walls, cells, and tissue), and their interaction governs values for porosityand density.