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Objective Methodsof Food Analysis

Brookfield Viscometer

Measures the thickness, or viscosity, of liquid dispersions such as salad dressings.

A measure of liquid texture.

Brookfield viscometer

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Compensating Polar Planimeter Measures the area of irregularly shaped

areas, for example the cross-sectional area of a loaf of bread, which may be related to loaf volume.

An indirect measure of texture.

Compressometer/ penetrometer

Measures compression of, or penetration into, a food sample.

Direct texture measurement.

Largely replaced by the texture analyzer in 45300 lab

Compressometer/penetrometer

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Hydrometer

Measures solution density (specific gravity).

Indirect texture measurement.

Hydrometer

Instron Materials Tester

A very versatile machine that measurestexture in many different ways.

Can measure compression, withdrawal, extrusion, energy required to do a process, etc.

Not as user friendly as the TextureAnalyzer.

4

Jelmeter

Measures the rate of flow of pectin dispersions through a pipette.

As pectin concentration increases, rate of flow decreases.

An indirect measure of texture.

Linespread Apparatus

Measures the amount of spread of a flowable liquid under the influence of gravity.

A direct texture measurement.

Linespread Apparatus

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pH Meter

Measures concentration of hydrogen ion in solution.

A measure of sourness

Also important to many chemical reactions that occur in food preparation, processing, or preservation.

pH Meter

Reflectance Meter

Measures color, hue, and the like.

A measure of appearance

Replaced in the 45300 lab by the Hunter colorimeter

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Reflectance Meter

Refractometer

Measures the bending of light as it passes from air into another medium.

Can be used to measure the concentration of dissolved solids, for example the sugar concentration in a syrup. This would berelated to texture.

May also be used to measure the degree of hydrogenation in fats.

Refractometer

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Seed Volume Apparatus

Measures volume, typically for baked goods such as bread, muffins, and cakes.

Related to texture.

Seed Volume Apparatus

Shear Press

Measures the force needed to cut through a particular food, such as meat or vegetables.

A direct texture measurement.

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Shear Press

Shortometer

Measures the breaking strength of crisp baked goods such as cookies, pie crust, and crackers.

A direct texture measure.

Largely replaced by the texture analyzer in 45300 lab

Shortometer

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Spectrophotometer

Measures the absorption of light by chemical compounds as a function of wavelength.

Related to appearance and color.

Spectrophotometer

Vernier Caliper

Provides an accurate measure of length.

An example of it’s use would be in measuring the percent sag of gels.

In this case, the measurement providesan indirect measure of texture.

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RapidViscoAnalyzer

Measures the viscosity (thickness) as a function of time and temperature for dispersions of starch.

Provides very useful information about starch cooking characteristics.

A direct measure of texture.

RapidViscoAnalyzer

Texture Analyzer

Essentially, a very user friendly Instron-type machine.

Measures forces to cut, compress, puncture, etc.

A direct texture measurement.

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Texture Analyzer

Hunter Colorimeter

Measures the color of food samples

Can report L, a, b values or other color parameters

A direct measure of appearance/color

Hunter Colorimeter

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Brookfield texture analyzer

Essentially, a very user friendly Instron-type machine.

Measures forces to cut, compress, puncture, etc.

A direct texture measurement.

Brookfield texture analyzer

Brookfield computerized viscometer Measures the thickness, or viscosity, of

liquid dispersions such as salad dressings.

A measure of liquid texture.

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Brookfield computerized viscometer

Liquid chromatograph A form of column chromatography used in food

chemistry to separate, identify, and quantify compounds.

HPLC utilizes a column that holds chromatographic packing material

(stationary phase),

a pump that moves the mobile phase(s) through the column, and

a detector that shows the retention times of the molecules. Retention time varies depending on the interactions between the stationary phase, molecules being analyzed, and the solvent(s) used.

Liquid chromatograph

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Gas chromatograph A gas chromatograph is an instrument for separating

chemicals in a complex sample.

A gas chromatograph uses a flow-through narrow tube known as the column, through which different chemical constituents of a sample pass in a gas stream (carrier gas, mobile phase) at different rates depending on their various chemical and physical properties and their interaction with a specific column material, called the stationary phase.

As the chemicals exit the end of the column, they are detected and identified. The function of the stationary phase in the column is to separate different components, causing each one to exit the column at a different time (it'sretention time).

Gas chromatograph

Chromatography simulation

Differential scanning calorimeter (DSC ) This instrument

measures heat flow during heating processes such as starch gelatinization, protein denaturation or fat crystal melting. Very useful for determining the thermal properties of various foods.

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Food Rheology

Rheology -- the science of the deformation and flow of matter.

Rheos (Greek) -- to flow

Viscosity

Viscosity may be thought of as the internal friction of a fluid.

Shear stress = force applied over an area/area = F/A.

When stress is applied, this produces a shearing strain (movement).

Viscosity

Viscosity () is defined as the ratio of shear stress to the rate of change of strain.

If we let the rate of change of strain be represented by D, then

= (F/A)/D, or, solving for F

F = AD

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Viscosity

Graphical representations of flow behavior typically plot F vs. D (or D vs. F, more properly shearing stress vs rate of shearing strain) and vs. D.

In experiments using the older model Brookfield viscometer, plot the spindle speed for D, plot the scale reading for F, and plot for .

Newtonian Flow

Sca

le r

ead

ing

Spindle speed

D

Viscosity isindependent ofshear rate

Bingham Plastic

Sca

le r

ead

ing

Spindle speed (related to shear rate)

Spindle speed

Yield Value

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A ketchup poem

You shake and shake the ketchup bottle.

First, none will come; and then, a lot 'll.

Some messy guy

Pseudoplastic

These are called shear thinning fluids.

Sca

le r

ead

ing

Spindle speedSpindle speed

Dilatant

These are known as shear thickening fluids.

Sca

le r

ead

ing

Spindle speed Spindle speed

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Thixotropic

time

Sca

le r

ead

ing

Spindle speedNote the hysteresis loop -- a characteristic of thixotropicflow

Rheopectic

These are characterized by an increase in viscosity at constant shear rate.

Examples: beaten egg white or whipping cream

Food Rheology -- Examples

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The electromagnetic spectrum

RED ORANGE YELLOW GREEN BLUE VIOLET

700 nm 400 nmLower energy Higher energy

The electromagnetic spectrum

700 nm 400 nmLower energy Higher energy

Munsell Color NotationHue -- what the color is

Value -- lightness/darkness

Chroma -- saturation of the color

Color wheel

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C. I. E. System

X = amber filter measurement from the reflectance meter

Y = green filter measurement from the reflectance meter

Z = blue filter measurement from the reflectance meter

Then these values are transformed.

C. I. E. System

x = X/(X + Y + Z) y = Y/(X + Y + Z) z = Z/(X + Y + Z)

x is the dominant wavelength of the color (like Munsell hue)

y is the purity of the color (degree of saturation)

Y is used as the third parameter and represents lightness/darkness (value)

C. I. E. System

As an example, Blue lake green beans might have the following designations for x, y, and Y 0.376x0.428y0.1445Y

By reference to the C. I. E. color chart it is possible to see what this color is.

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CIE Color Chart

Green bean values:0.376x0.428y

Green bean color

Hunter Notation

White

Black

+a-aREDGREEN

-b

BLUE

+bYELLOW

a = red to green

b = yellow to blue

L= lightness

L

Hunter Notation (another view)

Image courtesy of Medallion Laboratories (www.medlabs.com/bernie.htm)