食品分析(英文课件)：Determinationofashcontent

1、Determination of ash content,The significance of determination of ash content The general determination process of ash content,Teaching Aims,Classification,Major: Ca,Mg,P,K,Na,Cl,etal. Essential trace: Fe,Cu,Zn,I,et al. Harmful: Pb,Cd,Hg,etal,Determination of the ash and mineral content of foods is

2、important for a number of reasons: Nutritional labeling: Some minerals are essential to a healthy diet (e.g., calcium, phosphorous, potassium and sodium) whereas others can be toxic (e.g., lead Pb, mercury Hg, cadmium Cd, and aluminum Al). Quality: The quality of many foods depends on the concentrat

3、ion and type of minerals they contain, including their taste, appearance, texture and stability. Processing: It is often important to know the mineral content of foods during processing because this affects the physicochemical properties of foods(e.g. different grade of flour). Sanitary condition: A

4、sh contents of fresh foods rarely exceed 5,Definition: Ash: Total amount of minerals present within a food Mineral content: The amount of specific inorganic components present within a food, such as Ca, Na, K and Cl. (crude ash) Crude ash: Is the inorganic residue remaining after the water and organ

5、ic matter have been removed by heating in the presence of oxidizing agents, which provides a measure of the total amount of minerals within a food,Determination of ash content,Acid /water soluble ash content is more significant than total ash content,Water soluble ash contentrefer to the oxide and t

6、he salt of K, Na, Ca, Mg, etc Acid soluble ash contentrefer to the oxide of Fe、Al and subphosphate of alkaline-earth metals Acid insoluble ash contentrefer to the contaminants and the content of SiO2,Application example,The Classification of Flour: Ash is an important index of flour quality。The ash

7、content in wheat bran is much Higher than that in endosperm. First grade: 0.3 0.5 %, for dumpling Standard grade: 0.6 0.9 ,Natural Elements and Nutrients in Japanese Green Tea,The influence factor on ash of tea,The variety and age of tea tree/ tea leaf normal condition: Total ash content tea:4%7.5 %

8、, Water soluble ash50 % in total ash The total ash content: black teaoolong tea The sanitary condition of process adulteration,Total ash: High content-older tea, contaminants Water soluble ash: higher proportion in total ash-good quality of tea Acid-insoluble ash: high content-bad quality of tea, mo

9、re contaminants Basicity of Water soluble ash: the acid consumption neutralize the water soluble ash, can be used to identify the adulteration of tea,The significance of ash content in tea,6 chemical limit standard-4 ash indexes Total ash: maximum 8%(m/m) ,minimum 4%(m/m) Water soluble ash: (%total

10、ash), minimum 45% Basicity of water-soluble ash(KOH) Maximun3.0%(m/m), minimum1. 0%(m/m) acid-insoluble ash maximum 1. 0%(m/m),ISO 3720-standard of black tea,Determination of Ash Content,Principle: Minerals are not destroyed by heating, and that they have a low volatility compared to other food comp

11、onents,Sample Preparation,Typically, samples of 1-10g are used in the analysis of ash content. Solid foods are finely ground and then carefully mixed to facilitate the choice of a representative sample. Samples that are high in moisture are often dried to prevent spattering during ashing. High fat s

12、amples are usually defatted by solvent extraction, as this facilitates the release of the moisture and prevents spattering. Carbonization,Method,Sample amount: the ash amount should be 10-100 mg after ashing. e.g. Milk powder, seasoning, aquatic product 12g Grain and grain product, cake, etc 35g Veg

13、etable and vegetable product, etc510g 。 Fruit and fruit product 20g Ashing condition (temperature and time) Constant weight process Cooling down time in desiccator,Practical consideration in analysis of ash content,GB: export tea Total ash: 700 / 20min (fast analysis), 52525 arbitration and verify m

14、ethod,Analysis of Mineral in food,E.g,Ashing condition (temperature and time,system error Crucible Sample + crucible Ash + crucible Operating error,system error and operating error on ash analysis,scale,water-soluble ash=total ash - water-insoluble ash,The analysis of Water-soluble ash and water-ins

15、oluble ash,ashless filter paper （ quantitative filter paper ） Three grade according to the ash content：I0.01 II0.03 III0.06,Food analysis of acidity and pH,Key points： The signifiance of acidity analysis in food product The determination method and it practical application,Total Acidity Effective Ac

16、idity Volatile Acidity Total Acidity(TA) Hydrogen ions (H+) of both fixed and volatile acids present in food Active Acidity (pH) pH is the Hydrogen ion concentration H+ of a solution. Volatile Acidity (VA) Refers to the organic acids found in wine, grape juice etc that are more volatile or more easi

17、ly vaporized than the non-volatile or fixed acids (malic acid) acetic acid , butyric acid,Concept of Acidity,Concept of Acidity,Acidity in milk apparent acidity-Natural acidity derived from the alkali binding properties of casein , phosphates, citrates and CO2. Usually it is between 0.15%-0.18%. (%

18、lactic acid) True acidity/developed acidity -result from the fermentation of milk by lactic acid bacteria. When it is above 0.2%, lactic acid exists. 0T: the volume of 0.1mol/l NaOH depleted by 100ml milk sample. The apparent acidity of fresh milk is 16-18 0T,Organic acids in foods Natural component

19、s Additive Fermentation products,Purpose: Color Taste and flavor Preservation,Juice, beverage：taste-sugar/acid ratio, clarification effect Soybean sauce：suitable amount of organic acid Wine：acidity-important quality index Yellow rice wine: precursor substance of fragrance Fermentation food product：T

20、he amount of volatile acid Can：related with sterilizing time Clarification effect of juice Others ：restrain the production of unwanted browning through the control of pH,Color, taste, flavor and stability of food,E.G,Fresh milk: 1618 。T Fresh meat （pH）-（color, water holding capacity-WHC）-shelf life,Food preservation,E.G,Sample preparation: Solid sample: grinding samplemix evenlydistilled water without CO2heat at 70-80 or 100 for 0.5 or