Food - Analytical Chemistry (ACS Publications)

Food - Analytical Chemistry (ACS Publications) SKC Chang - ‎1995 - ‎...

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Anal. Chem. 1995, 67, 127R-153R

Food Sam K. C. Chang,*stl* Edna Holm,t Jurgen Schwarz,**fand Patricia Rayas-Duarte* North Dakota State University, Fargo, North Dakota 58105 Review Contents

Nitrogen and Proteins Protein Contents Infrared OR), Near-IR, and Fourier Transform IR

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Electrophoresis and Isoelectric Focusing High-Performance Liquid Chromatography (HPLC) Enzyme-Linked ImmunoadsorbentAssay (ELISA) Protein Digestibility Carbohydrates Mono- and Disaccharides Lactose and Sucrose in Milk Products Reducing Sugars Use of Capillary Electrophoresis Oligosaccharides Dietary Fiber Starch Inorganics (Minerals) Sample Preparation for Atomic Absorption Applications

Enzymes Enzyme Biosensors Flow Injection Analysis Immunosorbent Assays Flavor and Odor Chirality Wine

Beer Meat

Fish Dairy Lipids Coffee Vegetables Fruit Herbs and Spices

Flavor Enhancers Vanillin

Adulteration Irradiation Packaging

Color Anthocyanins Carotenoids Meat Pigments

Other Pigments Lipids Fat Content/Fatty Acids Food Lipid Oxidation

Vitamins Vitamin C (AscorbicAcid) Carotenes and Vitamin A

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This review was written based on the literature searches using Chemical Abstracts covering the date between October 1992 and 0003-2700/95/0367-0127$15.50/0 0 1995 American Chemical Society

October 1994. The developmentsof new methods for measuring eight major food compositions/properties were selected. New applications of developed methodologiesalso were included. The selected abstracts were primarily those published in English. Electrophoresis, HPLC, and enzyme-linked immunoassays continued to be the major methods for identification and quantifications of proteins in food materials. Microwave heating has been used on several occasions to prepare samples for mineral analysis. HPLC methods have continued to be used for analyzing amino acids, vitamins, sugars and carbohydrates. NITROQENAND PROTEINS Protein Contents. Bullock and Moore (AI) reviewed Kjeldahl, Dumas, and near-IR reflectance spectroscopy for determination of corn proteins. Feinberg (A2) developed an openvessel microwave digestion system for Kjeldahl nitrogen determination to shorten digestion times. Microwave digestion steps included decomposition of the organic matrix with sulfuric acid without catalyst, followed by oxidation with hydrogen peroxide. Digestion by microwave can reduce the time of sample preparation compared with official methods. Chan (A3) determined cereal protein using a m o d ~ e drapid bicinchoconinic acid. Solid samples were directly suspended in the BCA reagent. The reaction was carried out under sonication. The solid-phase assay showed that the method was a rapid alternative comparison with the Kjeldahl assay if numerous insoluble proteinaceous materials require screening. Reichardt (A4 reviewed the methods for W determination of protein content in foods, body fluids, or aqueous solutions by absorbance measurements in the region between 185 and 260 nm or by employment of double-wavelength spectroscopy. The differences in absorbance at 205-233, 210-233, 215-233, and 235-280 nm as well as measurements at a wavelength between 205 and 215 nm are suitable for biological samples. A simple and reliable W method for rapid determination of total tryptophan in intact proteins was developed (As). The method is based on the solubilization of proteins in sodium hydroxide and transformation of the W (285.5 nm) absorption spectrum data. The method is particularly recommended for everyday analysis of a large number of samples (As). Mapping protein foulants, including peptides, which were stained with Coomassie blue and viewed on the active surface of ultrafiltration membranes with a reflectance microspectrophotometer at 580 nm, was easy and quick compared to other methods such as SDS-polyacrylamide gel electrophoresis and scanning electron microscopy (A@, The protein concentrationin milk was determined fluorometrically by diluting samples into an aqueous solution of 0.01%bromophenol blue and illuminating with a laser light at 337.1 nm and an output of 2-3 mW. Fluorescence was

' Department of Food and Nutrition. f

Department of Cereal Science. Department of Agricultural Engineering. Analytical Chemistry, Vol. 67, No. 72,June 75, 7995 127R

measured at 540 nm (A7). A direct colorimetric method based on the reduction of Ellman’s reagent by thiol groups was used on thiol groups and disulfide bonds in corn meal-based materials. This method is rapid and convenient for screening thiol and disulfide contents in insoluble proteinaceous materials (AS). Mared (IR), Near-IR,and Fourier Transform IR (FT-IR). De La Roza and Martinez (AS) used near-IR reflectance spectroscopy to determine crude protein, dry matter, and cellulose organic matter digestibility. Bacheiner ( A l O ) measured total protein, nonprotein N, protein N, urea N, and fat contents of milk samples by IR spectrometry (Milko-Scan; MSC) . The various compositions of casein, urea, and nonprotein nitrogen caused different deviations in results when compared with that obtained from Kjeldhal methods. Liu (All)used a rapid milk analyzer (Milkoscan), which was based on IR spectroscopy, to measure grain legume protein. The Milkoscan was a rapid method for determining grain protein and was compared with the Kjeldahl procedure. There were differences between the two methods if pH