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1 INTRODUCTION TO FOOD ANALYSIS 1126 Steven C Seideman Extension Food Processing Specialist Cooperative Extension Service University of Arkansas.

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Presentation on theme: "1 INTRODUCTION TO FOOD ANALYSIS 1126 Steven C Seideman Extension Food Processing Specialist Cooperative Extension Service University of Arkansas."— Presentation transcript:

1 1 INTRODUCTION TO FOOD ANALYSIS 1126 Steven C Seideman Extension Food Processing Specialist Cooperative Extension Service University of Arkansas

2 2 INTRODUCTION This module is a very brief overview of common methods of food analysis used in food processing organizations.

3 3 WHY ANALYZE FOOD? Government regulations require it for certain products with standards of identity (e.g.% fat and moisture in meat products). Nutritional Labeling regulations require it. Quality Control- monitor product quality for consistency. Research and Development- for the development of new products and improving existing products.

4 4 What Properties are Typically Analyzed? Chemical Composition – water, fat, carbohydrate, protein etc Physical Properties- Rheological or stability Sensory Properties- Flavor, mouth-feel, color, texture etc.

5 5 References on Analytical Techniques Official Methods; - Association of the Official Analytical Chemists (AOAC) - American Oil Chemists Society (AOCS) - American Association of Cereal Chemists (AACC)

6 6 Criteria for Selecting an Analytical Technique There are many techniques to analyze foods but each has drawbacks or compromises. You must select the technique that is required or fits into your system. For example, the most accurate techniques generally take longer to perform and you may not have the time if the food product you are making requires real time results such as in the formulation of processed meats.

7 7 Criteria for Selecting an Analytical Technique Precision Accuracy Reproducibility Simplicity Cost Speed Sensitivity Specificity Safety Destructive/ Non- destructive On-line/off-line Official Approval


9 9 What is the Purpose of the Analysis Official Samples Raw Materials Process Control Samples Finished Products

10 10 Sampling Plan A sampling plan is a predetermined procedure for the selection, withdrawal, preservation, transportation and preparation of the portion to be removed from a lot as samples. The sampling plan should be a clearly written document containing details such as; - Number of samples selected - Sample location (s). - Method of collecting samples

11 11 Factors Affecting a Sampling Plan Purpose of inspection -acceptance/rejection, variability/average Nature of the product -homogenous, unit, cost Nature of the test method -Critical/minor, destructive, cost, time Nature of the population - uniformity, sublot

12 12 Developing a Sampling Plan Number of samples selected -Variation in properties, cost, type of analytical techniques Sample location -random sampling vs systematic sampling vs judgment sampling Manner in which the samples are collected -manual vs mechanical device

13 13 The Bottom Line in Sampling Depending upon the nature of the material to be analyzed, you must determine a method of taking small subsamples from a large lot ( 5,000 lb blender, 20 combos on a truck etc) that accurately reflect the overall composition of the whole lot. An inaccurate sample of a large lot may actually be worse than no sample at all.

14 14 Preparation of Laboratory Samples You may have taken as much as 10 lbs of sub- samples from a lot that now needs to be further reduced in size; -Make the sample homogeneous by mixing and grinding and then more sub-sampling. -Be aware of any changes that might occur between sampling and analysis and take proper action ( e.g. enzymatic action, microbial growth etc). -Properly label the final sample with name, date/time, location, person and other pertinent data.

15 15 FOOD COMPONENTS Food consists primarily of water( moisture), fat (or oil), carbohydrate, protein and ash (minerals). Since food consists of these 5 components, it is important that we understand how these components are measured.

16 16 COMPOSITION OF FOODS COMPONENT Milk Beef Chicken Fish Cheese Cereal grains Potatoes Carrots Lettuce Apple Melon % Water %Carbohydrates %Protein % Fat % Min/Vit


18 18 pH Determination pH refers to the relative amounts of acid and base in a product. It is scientifically defined as the negative log of the hydrogen ion concentration. pH ranges from 0 to 14 with pH of 7 being neutral. pH values below 7 are considered acids and pH values above 7 are basic or alkaline. pH is generally determined with a pH meter although litmus paper can also be used.


20 20 Moisture Determination Moisture or water is by far the most common component in foods ranging in content from 60 – 95%. The two most common moisture considerations in foods is that of total moisture content and water activity.

21 21 Moisture Content The total moisture content of foods is generally determined by some form of drying method whereby all the moisture is removed by heat and moisture is determined as the weight lost. % water = wet weight of sample-dry weight of sample wet weight of sample

22 22 Methods of Moisture Loss Measurement Convection or forced draft ovens (AOAC) - Very simple; Most common Vacuum Oven -Sample is placed in oven under reduced pressure thereby reducing the boiling point of water. Microwave Oven - Uses microwave as a heat source; Very fast method Infrared Drying - Uses infrared lamp as a heat source; Very fast

23 23 Water Activity ( a w ) Water Activity (Aw) is the amount of free water in a sample that is not bond and therefore free for microbial growth, enzyme and vitamin decomposition and can reduce color, taste and flavor stability. Two general types of sensors: –Capacitance sensor: electrical signal –Chilled-mirror dew point method (AquaLab): dew point temperature change due to ERH change.

24 24 WATER ACTIVITY Aw Microorganism Bacteria Bacteria Yeasts Molds No microorganism proliferation Foods Meat, fish, sausage, milk Cheese, cured meat (ham), fruit juice conc Fermented sausages (salami), dry cheeses, margarine Juice conc, syrups, flour, fruit cakes, honey, jellies, preserves Cookies, crackers, bread crusts


26 26 PROTEINS Proteins are made up of amino acids. Amino acids are the building blocks of protein. Nitrogen the most distinguishing element versus other food components (carbohydrates, fats etc) Nitrogen ranges in proteins : % Non-protein nitrogen: free amino acids, nucleic acids, amino sugars, some vitamins, etc. Total organic nitrogen = protein + non-protein nitrogen

27 27 Types of Protein Analysis Kjeldahl – measures the amount of nitrogen in a sample. Lowry- measures the tyrosine/tryptophan residues of proteins.

28 28 Total organic nitrogen - Kjeldahl method Crude protein content Johan Kjeldahl (1883) developed the basic process Principle: total organic N released from sample and absorbed by acid –Digestion: sulfuric acid + catalyst –Neutralization and distillation; Sodium hydroxide –Titration; Hydrochloric acid

29 29 Total organic nitrogen - Kjeldahl method Digestion Protein (NH 4 ) 2 SO 4 (ammonium sulfate) Protein N NH H 2 SO 4 (NH 4 ) 2 SO 4 Sulfuric acid Heat, catalyst

30 30 Total organic nitrogen - Kjeldahl method Neutralization and distillation ( NH 4 ) 2 SO 4 + 2NaOH 2NH 3 + Na 2 SO 4 + 2H 2 O NH 3 + H 3 BO 3 NH 4 + : H 2 BO H 3 BO 3 (boric acid) (ammonium-borate complex) excess Color change

31 31 Total organic nitrogen - Kjeldahl method –Titration (direct titration) H 2 BO H + H 3 BO 3 –Calculation moles HCl = moles NH 3 = moles N in the sample %N = N*(HCl) N*=Normality of HCl (HCl) (mL acid sample-mL acid blank) 14g N g sample mole (mL acid sample-mL acid blank) g sample 1.4

32 32 Total organic nitrogen - Kjeldahl method Calculation %Protein = %N conversion factor Conversion factor: generally 6.25 –most protein: 16% N Conversion factor egg or meat6.25 milk6.38 wheat 5.33 soybean 5.52 rice 5.17

33 33 Kjeldahl Apparatus

34 34 Total organic nitrogen - Kjeldahl method Advantages: –applicable to any foods –simple, inexpensive –accurate, official method for crude protein content Disadvantages: –measuring total N not just protein N –time consuming –corrosive reagents

35 35 Lowry Method Principle: Color formation between tyrosine and tryptophan residues in protein and Biuret reagent and Folin-Ciocalteau phenol reagent (750 nm or 500 nm). Procedure protein solution + biuret reagent room temp10 min + Folin reagent 50 C 10 min 650 nm ( g)

36 36 Lowry Method Advantages –most sensitive ( g) –more specific, relatively rapid Disadvantages –color development not proportional to protein concentration –color varying with different proteins –interference (sugars, lipids, phosphate buffers, etc)

37 37 Infrared Spectroscopy Principle: absorption of radiation of peptide bond at mid-infrared (MIR) and near-infrared (NIR) bands Advantages –NIR applicable to a wide range of foods –rapid, nondestructive –little sample preparation Disadvantages –expensive instruments –calibration for different samples

38 38 Crude Fat Analysis

39 39 Fats Fats refers to lipids, fats and oils. The most distinguishing feature of fats versus other components ( carbohydrates, protein etc) is their solubilty. Fats are soluble in organic solvents but insoluble in water.

40 40 Solvent Extraction Methods Sample preparation: Best under nitrogen & low temperature –Particle size reduction increases extraction efficiency –Predrying sample to remove water is common.

41 41 Solvent Extraction Methods Solvent selection –Ideal solvent high solvent power for lipids low solvent for other components easy to evaporate low boiling point nonflammable nontoxic good penetration into sample single component inexpensive non-hygroscopic

42 42 Solvent Extraction Methods Common Solvents –Ethyl ether - best solvent for fat extraction, more expensive, explosion, fire hazard, hygroscopic –Petroleum ether - cheaper, more hydrophobic, less hygroscopic –Hexane - soybean oil extraction

43 43 Types of Fat Analysis Extraction Methods Continuous – Goldfinch Semi-Continuous- Soxhlet Discontinuous- Mojonnier Instrumental Methods Dielectric Infrared Ultrasound

44 44 Solvent Extraction Methods Continuous extraction: Goldfish method –Principle: Solvent continuously flowing over the sample with no build-up –Advantages: fast, efficient. –Disadvantages: channeling – not complete extraction.

45 45 Solvent Extraction Methods Semicontinuous extraction: Soxhlet method –Principle: Solvent building up in extraction chamber for 5-10 min before siphoning back to boiling flask. –Advantages: no channeling –Disadvantages: time consuming

46 46 Solvent Extraction Methods Discontinuous extraction: Mojonnier method (wet method extraction) –Principle: a mixture of ethyl ether and petroleum ether in a Mojonnier flask –Advantages: no prior removal of moisture –Disadvantages: constant attention

47 47 Instrumental Methods Dielectric method –Principle: low electric current from fat Infrared method –Principle: Fat absorbs infrared energy at a wavelength of 5.73 m Ultrasound method –Principle: sound velocity increases with increasing fat content


49 49 Introduction Next to water, carbohydrates are the most abundant food component %carbohydrate=100% - (H 2 O + ash + fat + protein) Types of carbohydrates include; –monosaccharide: glucose, fructose, galactose –disaccharide: sucrose, lactose, maltose –oligosaccharids: raffinose –polysaccharide: starch, cellulose

50 50 Ash and Mineral Analysis

51 51 Definitions Ash: total mineral content; inorganic residue remaining after ignition or complete oxidation of organic matter Minerals: –Macro minerals (>100 mg/day) Ca, P, Na,K, Mg, Cl, S –Trace minerals (mg/day) Fe, I, Zn, Cu, Cr, Mn, Mo, F, Se, Si –Ultra trace minerals Va, Tn, Ni, Sn, B –Toxic mineral lead, mercury, cadmium, aluminum

52 52 Ash Contents in Foods Wheat flour, whole grain1.6% Macaroni, dry, enriched0.7% Milk, whole, fluid0.7% Butter, with salt2.1% Apple, raw with skin0.3% Banana, raw0.8% Egg, whole, raw0.9% Hamburger, regular, plain1.7%

53 53 Methods for Determining Ash –Dry ashing high temperature –Wet ashing oxidizing agent and/or acid –Low-temperature plasma ashing dry ashing in partial vacuum at low temperature

54 54 Dry Ashing Principles –High temperature (>525 C) overnight (12-18 hr) –total mineral content Instrumentation –Muffle furnace –Crucible quartz porcelain steel nickel platinum

55 55 General Procedure for Dry Ashing g pretreated sample into a crucible 2. Ignite crucible to constant weight at ~550 C for hr 3. Cool in desiccator 4. Weigh cooled crucible % ash (db) = 100 wt after ashing - crucible wt Sample wt solid%/100

56 56 Dry Ashing Advantages –safe and easy –no chemical –many samples handled at one time –resultant ash for further mineral analysis Disadvantages –loss of volatiles –interaction –long time and expensive equipment

57 57 Ion-Selective Electrodes Direct measurement via chemical potential of cations (Ca, Na, K), anions (Br, Cl, F), or even dissolved gases (O 2, CO 2 ) Components: –sensing electrode –reference electrode –readout device Types: glass membrane, polymer-body, solid-state

58 58 Ion-Selective Electrodes Activity (A) vs. Concentration (C) A= C =activity coefficient A: chemical activity C: a measure of ions in solution is a function of ionic strength; ionic strength is a function of concentration and charge on all ions A C

59 59 Ion-Selective Electrodes Advantages –more precise, rapid, practical –direct measurement of a wide range of ions –inexpensive and simple Disadvantages –inability to measure below 2-3 ppm –unreliable at low concentration (10 -4 M) Applications: –processed meats: salt, nitrate –butter and cheese: salt –milk: Ca –low-sodium products: sodium –soft drink: CO 2 –wine: Na, K –can vegetable: nitrate

60 60 Physical Properties of Foods

61 61 PHYSICAL PROPERTIES While chemical properties measures the chemical components of food such as water, protein, fat, carbohydrates, the physical properties determine how the chemical properties and processing ultimately effect the color and texture of foods.

62 62 Physical Properties Physical properties include; Color Texture Viscosity (liquids) Texture analysis machines Sensory panels Trained Consumer

63 63 COLOR Color can be described in terms of hue, value and chroma; Hue is the aspect of color which we describe by words like green, blue, yellow and red Value or lightness describes the relationship between reflected and absorbed light, without regard to specific wavelength. Chroma describes reflection at a given wavelength and shows how much a color differs from gray.

64 64 HUNTER L,a,b The Hunter L,a,b system describes the color of a food in terms of L (100=white; 0= black), a (green- red) and b (blue to yellow).

65 65 COLOR More subjective color determination systems include; - Paint color match pages -The Pantone Matching System. - Actual photos of finished food products

66 66 TEXTURE The methods of measuring the texture of foods can be roughing divided into those used for liquids (viscosity) versus those used for more solid foods.

67 67 Fluid Viscosity Viscosity: a key property of liquids and a measure of the resistance to flow. More energy required to make a viscous fluid flow than a non-viscous fluid. The viscosity of a solution increases non-linearly with polymer concentration. The properties of the solution are conventionally split into three regions:

68 68 Dilute Regime The polymers act as isolated "particles" too dilute to interact with each other. They can be approximated as spheres of radius r g (the Stokes radius - the smallest sphere that can contain the polymer). Semi-Dilute Regime The "particles" start to interact significantly because their total excluded volume approaches close packing. Further increase in concentration leads to much greater overlap of polymer coils and rapid increase in viscosity. Concentrated Regime The individual polymer molecules overlap in a tangled mass. The viscosity of concentrated polymer solutions is very high and as the concentration increases further starts to show some solid-like behavior.

69 69 Brookfield (Rotational) Viscometer Viscosity measurement by sensing the torque required to rotate a spindle at constant speed while immersed in the sample fluid.

70 70 Brabender Viscoamylograph and Rapid Visco Analyzer llllllll ^ ^ Scale - linked to printer Torsion device Spindle Brabender Cup (rotates) Heat-at 1.5 o C per Minute

71 71 Brabender Profile

72 72 Brabender and RVA Applications Starch, flours, baking products, noodle quality, extrusion, sprouting and enzyme activity, malting and brewing, storage, Effect of amount of water added during extrusion on RVA pasting curves of corn based extrudates. Lower water addition causes a higher degree of cook in the extrudate and this is reflected in a progressive change in the RVA pasting curve.

73 73 Bostwick Consistometer A simple, dependable instrument which determines sample consistency by measuring the distance which a sample of material flows under its own weight The unit is constructed of stainless steel and is equipped with two leveling screws and a level. The gate is spring operated and held by a positive release mechanism, permitting instantaneous flow of sample. The trough is graduated in 0.5cm divisions. Used extensively in the food industry for jams, jellies, tomato paste, ketchup, condensed soup and other highly viscous products.

74 74 Bostwick Consistometer 30 sec reading

75 75 Instron Universal Testing Machine A highly accurate and versatile material testing instrument for the precise measurement of the properties and behavior of materials in tension, compression, flexure and torsion. The instrument weighing system employs strain gauge load cells for measuring the load applied to the specimen under test. The output from the load cell is applied to a solid state load cell signal conditioning amplifier which provides a wide range of full scale load ranges for each type of load cell used. The controls provide for adjustment and calibration of the load weighing system to obtain accurate and reliable test data. The load cell amplifier output is in a signal form suitable for controlling the pen servo system of the chart recorder.

76 76 Texture Analyzer

77 77 Sensory Properties Trained Sensory Panels – a few well trained people that characterize flavor, texture and odor versus like/dislike, Consumer Panels- usually consist of 200 plus people who determine like/dislike, desirability etc. Additional detailed information on sensory panels can be found in the module Sensory Evaluation of Foods; 1213

78 78 SUMMARY This module has presented the topic of Food Analysis by discussing why we analyze food, sampling and preparation, the components of food generally analyzed for (water, protein, fat, carbohydrates) and some general methods of analyzing the physical properties of food (color, viscosity and texture).

79 79

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