Food Ingredient Analysis Manual

Author: Chief Editor: Ning Zhengxiang
Publisher:
Publish Date: 1998-03-01
Features: This book is a specialized monograph on various analytical and determination methods for food components. It covers three aspects: 1) Analytical and determination methods for various organic components in food. This section primarily discusses the determination of natural organic components in food and biological materials—such as carbohydrates, proteins, and amino acids, lipids and fatty acids, organic acids, nucleic acids and nucleotides, vitamins, hormones, food toxins, as well as artificially added food colorings, flavor enhancers, antimicrobial agents, aroma compounds, and other food additives during food processing. 2) Analytical and determination methods for inorganic components and elements in food. This section primarily discusses the determination of moisture state and content, CO2 content, as well as the measurement of major, minor, and trace elements in food. 3) Analytical methods for enzymes in food. This section primarily discusses the separation and purification methods for enzymes in biological materials, the determination of enzyme activity and enzyme kinetic constants, as well as the activity determination of glycosidases, proteases, lipases, oxidoreductases, transferases, isomerases, and food flavor enzymes in food and biological materials. This book extensively collects various analytical and determination methods for food components. The methods for each specific component are arranged in the order of qualitative identification methods, titration methods, photometric methods, potentiometric methods, chromatographic methods, and spectroscopic methods to meet the needs of various samples, conditions, and accuracy requirements. For each determination method, in addition to emphasizing practical operations, the book also provides brief explanations on the objectives and principles of food inspection and analysis, applicable ranges, precautions during operation, and the advantages and disadvantages compared to similar methods. This book serves as a reference tool for food science and technology professionals, particularly for analytical workers and inspectors in enterprises and research institutions. It can also be used as an experimental guide and teaching reference for students and teachers in related disciplines such as science, engineering, agriculture, medicine, and commerce. Excerpt: This method is also known as the rapid method and is suitable for the determination of reducing sugars in various types of food. It is a national standard analytical method. 2. Reagents (1) Alkaline tartrate copper solution A: Weigh 15 g of copper sulfate and 0.05 g of methylene blue, dissolve them in water, and dilute to 1000 mL. (2) Alkaline tartrate copper solution B: Weigh 50 g of potassium sodium tartrate and 75 g of sodium hydroxide, dissolve them in water, add 4 g of potassium ferricyanide, and completely dissolve. Dilute with water to 1000 mL and store in a glass bottle with a rubber stopper. (3) Zinc acetate solution: Weigh 21.9 g of zinc acetate, add 3 mL of glacial acetic acid, dissolve in water, and dilute to 100 mL. (4) Glucose standard solution: Accurately weigh 1.000 g of pure glucose dried to constant weight at 98–100°C, dissolve it in water, add 5 mL of hydrochloric acid, dilute with water to 1000 mL. This solution is equivalent to 1 mg of glucose per mL. 3. Determination (1) Sample preparation ① Dairy products, dairy products, and protein-containing cold foods: Weigh about 2.5–5 g of solid samples (or 25–50 mL of liquid samples) into a 250 mL volumetric flask, add 50 mL of water, mix well, add 5 mL of zinc acetate solution and 5 mL of 10.6% potassium ferricyanide solution, dilute to the mark with water, mix well, and let stand for 30 min. Filter with dry filter paper, discard the initial filtrate, and reserve the filtrate. ② Alcoholic beverages: Pipette 10 mL of sample into an evaporating dish, neutralize with 1 mol/L NaOH solution, and evaporate to one-quarter of the original volume on a water bath. Transfer to a 250 mL volumetric flask, add 50 mL of water, mix well, and proceed with the following steps starting from "add 50 mL of zinc acetate solution" as per the method. ③ Foods containing a large amount of starch: Weigh 10–20 g of samples into a 250 mL volumetric flask, add 200 mL of water, heat in a 45°C water bath for 1 h while stirring occasionally, cool, dilute to the mark with water, mix well, and let stand. Pipette 200 mL of the supernatant into another 250 mL volumetric flask, and proceed with the following steps starting from "add 50 mL of zinc acetate solution" as per the method. ④ Carbonated beverages: Pipette 100 mL of sample into an evaporating dish, remove the carbon dioxide on a water bath, transfer to a 250 mL volumetric flask, wash the evaporating dish with water, and add the wash water to the volumetric flask. Dilute to the mark, mix well, and reserve. (2) Standardization of alkaline tartrate copper solution: Pipette 5.0 mL of alkaline tartrate copper solution A and 5.0 mL of solution B into a 150 mL conical flask, add 10 mL of water, add 2 glass beads, and slowly add about 9 mL of glucose standard solution from a burette. Heat to boiling within 2 min and continue adding the glucose standard solution at a rate of 1 drop every 2 s until the blue color just disappears. Record the total volume of glucose standard solution consumed. Perform the parallel operation in triplicate and take the average value. Calculate the mass of glucose equivalent to 10 mL (5 mL each of A and B solutions) of alkaline tartrate copper solution.