In objective evaluations, laboratory instruments instead of humans are used to measure the characteristics of foods quantitatively. The two major types of objective evaluation tests, physical and chemical, attempt to mimic the five senses, and serve as the basis of most objective food testing.
Physical tests measure certain observable aspects of food such as size, shape, weight, volume, density, moisture, texture, and viscosity. Using instruments to evaluate foods provides more objective data than sensory testing, and is less costly and time consuming. Despite the benefits of objective tests, however, they cannot substitute for sensory testing by real human beings to determine overall acceptability.
Selected Physical Tests for Food Evaluation
Microscope used to observe microorganisms as well as starch granules, the grain in meats, the crystals of sugar and salt, the fiber in fruits and vegetables, and for any texture changes in processed foods.
Spectrophotometer measures color by detecting the amount and wavelength of light transmitted through a solution. Spectroscopy is based on the principle that the molecules in foods and beverages will absorb light at different wavelengths on the spectrum. The amount of absorption parallels the amount of substance found in the sample. Spectroscopy can be used to determine the amount of caffeine in coffee or the concentration of riboflavin (vitamin B2) in milk.
Weight is measured in pounds/ounces or milligrams/grams/kilograms.
Volume quantifies the area occupied by a mass, while density is the measure of mass (weight) in a given volume. Specific density relates a substance’s density to an equal amount of water.
Penetrometer simulates teeth biting into a food to measure its tenderness.
Warner-Bratzler Shear evaluates meat and baked product tenderness by measuring the force required to cut through a cylindrical sample. Short meter Measures tenderness by determining the resistance of baked goods, such as cookies, pastries, and crackers, to breakage. Puncture testing evaluates the firmness of fruit or vegetable tissue.
Line-spread test measures the consistency of batters and other viscous foods. Food is placed in a hollow cylinder in the middle of the spread sheet; the cylinder is then lifted, allowing the food to spread, and the spreading distance is measured in centimeters.
Viscometer measures the viscosity of food such as pudding, sour cream, salad dressing, sauces, cream fillings, cake batters, (or viscosimeter) and catsup.
Polarimeter or refractometer measures the concentration of various organic compounds, especially sugars, in solution by determining the angle (refractive index) of polarized light passed through the solution.