Lecture 4- Moisture Analysis1.pdf

Food Analysis: Moisture Analysis Saji George Associate Professor, Department of Food Science and Agricultural Chemistry, Macdonald-Stewart Building, Room-1039 (MS1-039) Tel: 514-398-7920, Fax: 514-398-7990 Email: saji.georg...

Food Analysis: Moisture Analysis Saji George Associate Professor, Department of Food Science and Agricultural Chemistry, Macdonald-Stewart Building, Room-1039 (MS1-039) Tel: 514-398-7920, Fax: 514-398-7990 Email: [email protected] Web: http://safe-nano.lab.mcgill.ca/ SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 1 Scope of this lecture To provide a basis for, Principles Procedures, Applications, and Pre-cautions of moisture analysis. SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 2 Major Components of Foods The Components included in a “Proximate Analysis” approach are: (1) Moisture (2) Ash (3) Protein (4) Fibre (5) Fat The carbohydrate is generally not included, because it exists in different forms. %Carbohydrates are measured by difference of the measured other components: %CHO= 100- (%H2O+ %Ash+ %Protein+ %Fibre+ %Fat). SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 3  Major Components of Foods Food Dry Matter H2O Organic Inorganic Ash Non-nitrogenous N-containing Crude protein components Non-fatty components Fatty components Fat CHO Fiber SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 4  Moisture Analysis SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 5 Relevance of moisture analysis Food produce= Water + Dry matter ▪ Provides structure Often the expensive (Quality factor) part ▪ Standard of identity Define the (define the product) nutritional part ▪ Cheap filler (economic Convenient for relevance) transport ▪ Undesired in dry prdts SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 6  Moisture Determination ✓ Moisture determination is one of the most important and most widely used analytical measurements in processing and testing of food products. ✓ Why is it important to measure moisture in food materials? - Food safety (mold growth produces aflatoxins) - Shelf-life/stability - Food quality - Economic considerations (control economic fraud) - Government regulations (i.e. standardized foods) SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 7  Moisture Determination Common level of moisture in the food materials: - High moisture foods - Intermediate moisture foods - Low moisture foods Examples: Fresh fruits 65-95% Meat and Fish 50-70% Dry beans 8-12% bread 34-36% Nuts 3-8% SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 8  Forms of water in food 1. Free water/Bulk water: Water in food that is free from any other constituents Each water molecule is surrounded only by other water molecules Physicochemical properties that are the same as those of pure water such as melting point, boiling point, density, compressibility, heat of vaporization, electromagnetic absorption spectra 2. Capillary or trapped water. Water that is held in narrow channels formed by physical barriers by capillary forces. It has physicochemical properties similar to that of bulk water SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 9  Forms of water in food 3. Physically bound water: Water that is physically bound with other molecules such as protein, polysaccharides Has different physicochemical properties than bulk water 4. Chemically bound water: Water that is bound chemically, for example, lactose monohydrate; salts such as Na2SO4 · 10H2O. Different physicochemical properties to bulk water, e.g., lower melting point, higher boiling point, higher density, lower compressibility, higher heat of vaporization, different electromagnetic absorption spectra SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 10  Moisture Determination Methods for measurement of moisture in foods: 1. Drying methods: removal of water in the form of water vapour 2. Distillation methods: removal of water by a distillation process. 3. Chemical methods use a chemical reaction in which water is involved. 4. Physical methods take advantage of physical properties of water, e.g. electrical or dielectric properties. SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 11  Drying Methods Drying methods deal with the removal of water in the form of vapour, and the lost of weight is taken as a measure of the moisture content. Heat Water (Liquid) Water (Vapor) Indirect Method Less specific to water Simple skills SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 12  Drying Methods Different drying methods Solute and boiling point 1. Oven drying According to Raoult’s law, the BP of water increases 0.512 oC for every 1 molecular weight (1 mol) of a ▪ Convection Oven, solute dissolved in 1.0 L of water. ▪ Forced air oven ▪ Microwave oven The boiling point elevation continues throughout the ▪ Vacuum oven drying process as solute concentrations increase. 2. Freeze-drying 3. Infrared drying SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 13  Temperature-%moisture relationship Moister loss is a function of time and temperature Rise in temperature shows the % mass loss (percentage moisture) Beyond 185oC decomposition of protein occur Carbohydrates breaks down at higher temperature and release water Oxidation of fatty acid could increase the weight of sample SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 14  Drying Methods Convection Oven: As heating takes place, water is lost from a sample, and moisture remains in the chamber (105-1100C for 22-24h). Liquid samples are normally dried initially on a steam bath at 100 °C to minimize spattering Disadvantages: ▪ Longer analysis time ▪ Loss of volatile components other than water ▪ Larger temperature gradient SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 15 Forced Air Oven: Air is circulated by a fan T0 can be higher and time will be shorter (1350C for 4h) Temperature differential not >1oC. Process is faster, efficient and the water vapour will not condense due to the fan Possibility of lipid oxidation leading to weight gain can occur at high temperatures SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 16  -Microwave Analyzer: Microwave drying is a rapid technique that allows in-process analysis There is an in-built micro balance that monitors the loss of weight The microwave energy (Power) and time have to be defined to ensure an accurate measurement. May not be good for heterogenous food sample The pan used should not absorb micro- wave energy (fiberglass and quartz fiber) SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 17  -Vacuum Oven: The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid Drying under reduced pressure (25– 100 mm Hg) Faster rate of evaporation Removal of water without decomposition…temperature 95- 1020C or (60–70 0C) for high-sugar products SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 18  Vacuum Oven Method Vacuum oven is based on the fact that water boils at lower T0 under vacuum For example: 760 mmHg --- Tbp is 100°C 234 mmHg --- Tbp is 70°C 92.5 mmHg --- Tbp is 50°C Purpose of vacuum pump is to reduce the oven’s pressure to between 25-50 mmHg. SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 19  Components of Vacuum Oven Drying agents Vacuum pump To dry the air Vacuum oven for the vacuum pump to operate normally SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 20  Vacuum Oven Method A lab pan Wt of the empty pan=20 grams a laboratory desiccator SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 21  Vacuum Oven Method 5 grams After 6h Reweight the sample + 24 grams the pan SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 22 Wt of the empty pan= 20g Wt of wheat sample = 5g Wt of the wheat and the pan after drying = 24g Loss of weight= 25-24 = 1g 1g Moistuer% = x 100 = 20% 5g SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 23 Common drying agents for vacuum oven: 1- Anhydrous CaCl2 (most safe) 2- Anhydrous SO3 3- Phosphorus Pentoxide P2O5 4- Concentrated H2SO4 (most effective) SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 24 Vacuum oven has some practical advantages: 1- Reduced T0 in drying chamber has some positive points: 1.1- Reduction in loss of volatiles, non water components (700C). 1.2- Less effect on degradation of some components (e.g. sugars especially fructose). 2- Shorten analysis time (3-8h). SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 25  Oven Drying Methods Factors that affect oven drying methods are : - Temperature - Time - Particle size (uniform, small particles for analysis through grinding); because surface area will be larger so some loss of water will be effective In small particles the distance that water molecules will migrate are smaller (less) to the surface where they will be loss SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 26  Infra Red drying - Penetrating infrared rays that dry the sample - It can significantly shorten the drying time to 10-25min. - The heat of infrared lamp is 1730- 2230 0C. - Infrared drying ovens can be equipped with an analytical balance to read moisture content directly. - Infrared drying techniques are not approved by AOAC International. SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 27 Rapid Moisture Analyzer Technologies: ❑ For quicker decision making ❑ Rapid drying using halogen or ceramic heaters ❑ Detect moisture levels from 50ppm to 99% using sample weights of 150mg – 40g. ❑ The sample is placed on an aluminum pan. ❑ Usual temperature is 250C- 2750C. ❑ The instrument is equipped with a digital balance, and automatically weights and calculates %Moisture. SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 28 Thermogravimetric Analysis: ❑ mass of a sample is continuously measured as it is heated at a controlled rate in a controlled atmosphere ❑ An inert gas (e.g., nitrogen) is used to avoid oxidation and gain mass ❑ Can acquire higher temperature hence it can be used for measuring decomposition, and weight % ash SAJI GEORGE @ S.A.F.E NANO, MCGILL UNIVERSITY 29