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Presentation on theme: "INTRODUCTION TO FOOD ANALYSIS 1126"— Presentation transcript:

Steven C Seideman Extension Food Processing Specialist Cooperative Extension Service University of Arkansas

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

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

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 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 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 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 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 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 COMPOSITION OF FOODS COMPONENT Milk Beef 60.0 0 17..5 22.0 0.9 Chicken
Fish Cheese Cereal grains Potatoes Carrots Lettuce Apple Melon % Water %Carbohydrates %Protein % Fat % Min/Vit


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 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 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 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 Water Activity (aw) 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 WATER ACTIVITY Foods Aw Microorganism Meat, fish, sausage, milk
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 Read the slide


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

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 Total organic nitrogen - Kjeldahl method
Digestion Protein (NH4)2SO4 (ammonium sulfate) Protein N  NH4+ + H2SO4  (NH4)2SO4 Sulfuric acid Heat, catalyst

30 Total organic nitrogen - Kjeldahl method
Neutralization and distillation (NH4)2SO4 + 2NaOH  2NH3 + Na2SO4 + 2H2O NH3 + H3BO3  NH4+ : H2BO3- + H3BO3 (boric acid) (ammonium-borate complex) excess Color change

31 Total organic nitrogen - Kjeldahl method
Titration (direct titration) H2BO3- + H+  H3BO3 Calculation moles HCl = moles NH3 = moles N in the sample %N = N*(HCl)   %N = N*(HCl)  N*=Normality of HCl (HCl) (mL acid sample-mL acid blank) g N g sample mole 100 1000  (mL acid sample-mL acid blank)  1.4 g sample

32 Total organic nitrogen - Kjeldahl method
Calculation %Protein = %N  conversion factor Conversion factor: generally 6.25 most protein: 16% N Conversion factor egg or meat milk wheat soybean rice

33 Kjeldahl Apparatus

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 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 Lowry Method Advantages Disadvantages most sensitive (20-200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 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 Crude Fat Analysis

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

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

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 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 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 Instrumental Methods Dielectric method Infrared 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 Introduction Next to water, carbohydrates are the most abundant food component %carbohydrate=100% - (H2O + ash + fat + protein) Types of carbohydrates include; monosaccharide: glucose, fructose, galactose disaccharide: sucrose, lactose, maltose oligosaccharids: raffinose polysaccharide: starch, cellulose

50 Ash and Mineral Analysis

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 Ash Contents in Foods Wheat flour, whole grain 1.6%
Macaroni, dry, enriched 0.7% Milk, whole, fluid % Butter, with salt % Apple, raw with skin 0.3% Banana, raw % Egg, whole, raw % Hamburger, regular, plain 1.7%

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

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 Dry Ashing Advantages Disadvantages 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 Ion-Selective Electrodes
Direct measurement via chemical potential of cations (Ca, Na, K), anions (Br, Cl, F), or even dissolved gases (O2, CO2) Components: sensing electrode reference electrode readout device Types: glass membrane, polymer-body, solid-state

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 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 (10-4M) Applications: processed meats: salt, nitrate butter and cheese: salt milk: Ca low-sodium products: sodium soft drink: CO2 wine: Na, K can vegetable: nitrate

60 Physical Properties of Foods

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

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

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 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 Dilute Regime The polymers act as isolated "particles" too dilute to interact with each other. They can be approximated as spheres of radius rg (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 Brookfield (Rotational) Viscometer
Viscosity measurement by sensing the torque required to rotate a spindle at constant speed while immersed in the sample fluid.

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

71 Brabender Profile

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 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 cm divisions. Used extensively in the food industry for jams, jellies, tomato paste, ketchup, condensed soup and other highly viscous products.

74 Bostwick Consistometer
30 sec reading

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 Texture Analyzer

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 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).



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