Available water (water activity)
Available water (Aw) is a measure of unbound, free water in a system available to support microbial growth and chemical reactions. Decagon Aqualab is used to determined Aw of a sample using the chilled-mirror dewpoint sensor. A product sample is placed in a cup and inserted into the Decagon AquaLab chamber. A stainless steel mirror within the sample chamber is repeatedly cooled and heated until the product dew point has equilibrated, resulting in a final Aw result. The dew point sensor readings are accurate to +/- 0.003 Aw. If a sample contains a volatile compound like alcohol or propylene glycol the Decagon AquaLab volatile sensor is required. The volatile sensor measures the change in electrical capacitance of polymer thin films. The volatile sensor reading is accurate to +/- 0.01 Aw. The Decagon AquaLab cannot read samples with an Aw less than 0.03.
Benzoic acid and benzoic acid salts are extracted using dilute potassium hydroxide. The extract is acidified with acetic acid, and injected on a liquid chromatograph equipped with an ultraviolet detector. Bemzoic acid concentration is calculated from a set of standards of known concentration that are injected on the LC.
BHA and BHT
Butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are extracted from cardboard, feeds, cereals, and concentrates, by shaking with a 20 percent ethyl ether/petroleum ether solution. BHT is extracted from wax coated and plastic box liners by refluxing with hexane. Interferences are removed by first partioning into acetonitrile and then back into petroleum ether.
Ethoxyquin is extracted from the samples with methanol, separated by HPLC, and quantitated with a fluorescence detector.
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Nitrate is extracted from solid samples with water. Water samples are pH adjusted. Using an automated system, a portion of each sample extract and standard solution is split, half passing through a metallic cadmium column, where nitrate is reduced to nitrite; and half passing directly to the color reaction. In both aliquots, nitrite is reacted with sulfanilamide, under acidic conditions, to form a diazo compound, which is reacted with N-(1-naphthyl)-ethylenediamine dihydrochloride, forming a reddish-purple complex that is measured spectrophotometrically. Nitrate, corrected for nitrite concentration in the original sample, and rate of reduction through the cadmium column, is calculated from nitrate and nitrite standards of known concentration that are taken through the procedure.
Nitrite is extracted from solid samples with water. Water samples are pH adjusted. Using an automated system, nitrite is reacted with sulfanilimide, under acidic conditions, to form a diazo compound which is reacted with N-(1-naphthyl)-ethylenediamine dihydrochloride, forming a reddish-purple color complex that is measured spectrophotometrically. Nitrite concentration is calculated by comparing the absorbances of the sample solutions to the absorbances of standard solutions.
Water samples are measured directly on a pH meter. For dry samples, a portion of ground sample is mixed with a volume of water and shaken for one hour. The pH of the supernatant is measured on a pH meter.
Propionic acid is extracted from the sample with a mixture of phosphoric acid, water, and alcohol. The extract is filtered and a portion of filtrate is injected onto a gas chromatograph (GC) equipped with a flame ionization detector. Propionic acid concentration is quantitated from a set of standards of known concentration that are injected into the GC under identical conditions
Propylene glycol is extracted from the sample with methanol, and the extract is filtered. A portion of filtrate is injected into a gas chromatograph (GC) equipped with a flame ionization detector. Propylene glycol concentration is quantitated from a set of standards of known concentration that are injected into the GC. An internal standard, 1,3 butanediol, is used in the samples and the standards to increase the accuracy of the method.
Chlorideis extracted from the sample with dilute nitric acid solution. Using an automated analyzer system, sample extracts and standard chloride solutions are treated with mercuric thiocyanate. Chloride ions displace the thiocyanate, which is reacted with ferric ion, forming a red colored complex, which is measured spectrophotometrically. Chloride content in the sample is quantitated as sodium chloride from the set of standards of known concentration that are taken through the procedure.
Sorbic acid and sorbate salts are extracted using dilute potassium hydroxide. The extract is diluted with acetic acid, converting all sorbates to sorbic acid. The acidified solution is analyzed by liquid chromatography using ultraviolet detection. Sorbic acid concentration is calculated from a set of standards of known concentration.
The sample is refluxed with hydrochloric acid. Free sulfite and a consistent portion of reversibly bound sulfite is released as sulfur dioxide. The sulfur dioxide is transferred with nitrogen carrier gas to a collection flask containing hydrogen peroxide solution. The sulfur dioxide is oxidized to sulfuric acid which is measured titrimetrically using standardized sodium hydroxide solution. Results are calculated as parts per million sulfur dioxide.
Tocopherols (free alcohols)
Measures free alpha-, delta-, and gamma- tocopherol. Unlike tocopherol acetate, which is generally used as a vitamin supplement, free or mixed tocopherols are typically added for their antioxidant properties. The free tocopherols are extracted directly and analyzed by liquid chromatography with fluorescece detection.
Total titratable acidity of foods
The sample is water extracted and filtered. An aliquot of the filtrate is titrated to a phenolphthalein endpoint with sodium hydroxide solution. The volume of titer used is reported as ml 0.1N NaOH/gram sample?.