Presentation on theme: "INTRODUCTION TO FOOD ANALYSIS 1126"— Presentation transcript:
1 INTRODUCTION TO FOOD ANALYSIS 1126 Steven C SeidemanExtension Food Processing SpecialistCooperative Extension ServiceUniversity of Arkansas
2 INTRODUCTIONThis 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 etcPhysical Properties- Rheological or stabilitySensory 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 PrecisionAccuracyReproducibilitySimplicityCostSpeedSensitivitySpecificitySafetyDestructive/ Non-destructiveOn-line/off-lineOfficial Approval
9 What is the Purpose of the Analysis Official SamplesRaw MaterialsProcess Control SamplesFinished Products
10 Sampling PlanA 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/averageNature of the product-homogenous, unit, costNature of the test method-Critical/minor, destructive, cost, timeNature of the population-uniformity, sublot
12 Developing a Sampling Plan Number of samples selected-Variation in properties, cost, type of analytical techniquesSample location-random sampling vs systematic sampling vs judgment samplingManner 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 grindingand then more sub-sampling.-Be aware of any changes that might occur between sampling andanalysis and take proper action ( e.g. enzymatic action, microbialgrowth etc).-Properly label the final sample with name, date/time, location, personand other pertinent data.
15 FOOD COMPONENTSFood 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.
18 pH DeterminationpH 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 ContentThe 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 samplewet weight of sample
22 Methods of Moisture Loss Measurement Convection or forced draft ovens (AOAC)- Very simple; Most commonVacuum 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 methodInfrared 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 signalChilled-mirror dew point method (AquaLab): dew point temperature change due to ERH change.
24 WATER ACTIVITY Foods Aw Microorganism Meat, fish, sausage, milk BacteriaBacteriaYeastsMoldsNo microorganismproliferationFoodsMeat, fish, sausage, milkCheese, cured meat (ham), fruit juice concFermented sausages (salami), dry cheeses, margarineJuice conc, syrups, flour, fruit cakes, honey, jellies, preservesCookies, crackers, bread crustsRead 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 contentJohan Kjeldahl (1883) developed the basic processPrinciple: total organic N released from sample and absorbed by acidDigestion: sulfuric acid + catalystNeutralization and distillation; Sodium hydroxideTitration; Hydrochloric acid
29 Total organic nitrogen - Kjeldahl method DigestionProtein (NH4)2SO4(ammonium sulfate)Protein N NH4+ + H2SO4 (NH4)2SO4Sulfuric acidHeat, catalyst
34 Total organic nitrogen - Kjeldahl method Advantages:applicable to any foodssimple, inexpensiveaccurate, official method for crude protein contentDisadvantages:measuring total N not just protein Ntime consumingcorrosive reagents
35 Lowry MethodPrinciple: Color formation between tyrosine and tryptophan residues in protein and Biuret reagent and Folin-Ciocalteau phenol reagent (750 nm or 500 nm).Procedureprotein solution + biuret reagentroom temp10 min+ Folin reagent50C 10 min650 nm( g)
36 Lowry Method Advantages Disadvantages most sensitive (20-200g) more specific, relatively rapidDisadvantagescolor development not proportional to protein concentrationcolor varying with different proteinsinterference (sugars, lipids, phosphate buffers, etc)
37 Infrared Spectroscopy Principle: absorption of radiation of peptide bond at mid-infrared (MIR) and near-infrared (NIR) bandsAdvantagesNIR applicable to a wide range of foodsrapid, nondestructivelittle sample preparationDisadvantagesexpensive instrumentscalibration for different samples
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 temperatureParticle size reduction increases extraction efficiencyPredrying sample to remove water is common.
41 Solvent Extraction Methods Solvent selectionIdeal solventhigh solvent power for lipidslow solvent for other componentseasy to evaporatelow boiling pointnonflammablenontoxicgood penetration into samplesingle componentinexpensivenon-hygroscopic
42 Solvent Extraction Methods Common SolventsEthyl ether - best solvent for fat extraction, more expensive, explosion, fire hazard, hygroscopicPetroleum ether - cheaper, more hydrophobic, less hygroscopicHexane - soybean oil extraction
44 Solvent Extraction Methods Continuous extraction: Goldfish methodPrinciple: Solvent continuously flowing over the sample with no build-upAdvantages: fast, efficient.Disadvantages: channeling – not complete extraction.
45 Solvent Extraction Methods Semicontinuous extraction: Soxhlet methodPrinciple: Solvent building up in extraction chamber for 5-10 min before siphoning back to boiling flask.Advantages: no channelingDisadvantages: 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 flaskAdvantages: no prior removal of moistureDisadvantages: constant attention
47 Instrumental Methods Dielectric method Infrared method Principle: low electric current from fatInfrared methodPrinciple: Fat absorbs infrared energy at a wavelength of 5.73 mUltrasound methodPrinciple: sound velocity increases with increasing fat content
51 DefinitionsAsh: total mineral content; inorganic residue remaining after ignition or complete oxidation of organic matterMinerals:Macro minerals (>100 mg/day)Ca, P, Na ,K, Mg, Cl, STrace minerals (mg/day)Fe, I, Zn, Cu, Cr, Mn, Mo, F, Se, SiUltra trace mineralsVa, Tn, Ni, Sn, BToxic minerallead, 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 ashinghigh temperatureWet ashingoxidizing agent and/or acidLow-temperature plasma ashingdry ashing in partial vacuum at low temperature
54 Dry Ashing Principles Instrumentation High temperature (>525C) overnight (12-18 hr)total mineral contentInstrumentationMuffle furnaceCruciblequartzporcelainsteelnickelplatinum
55 General Procedure for Dry Ashing g pretreated sample into a crucible2. Ignite crucible to constant weight at ~550C for hr3. Cool in desiccator4. Weigh cooled crucible% ash (db) = 100wt after ashing - crucible wtSample wt solid%/100
56 Dry Ashing Advantages Disadvantages safe and easy no chemical many samples handled at one timeresultant ash for further mineral analysisDisadvantagesloss of volatilesinteractionlong 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 electrodereference electrodereadout deviceTypes: glass membrane, polymer-body, solid-state
58 Ion-Selective Electrodes Activity (A) vs. Concentration (C)A=C =activity coefficientA: chemical activityC: a measure of ions in solution is a function of ionic strength; ionic strength is a function of concentration and charge on all ionsA C
59 Ion-Selective Electrodes Advantagesmore precise, rapid, practicaldirect measurement of a wide range of ionsinexpensive and simpleDisadvantagesinability to measure below 2-3 ppmunreliable at low concentration (10-4M)Applications:processed meats: salt, nitratebutter and cheese: saltmilk: Calow-sodium products: sodiumsoft drink: CO2wine: Na, Kcan vegetable: nitrate
61 PHYSICAL PROPERTIESWhile 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.
63 COLOR Color can be described in terms of hue, value and chroma; Hue is the aspect of color which wedescribe by words like green, blue,yellow and redValue or lightness describes the relationship betweenreflected and absorbed light, without regard to specificwavelength.Chroma describes reflection at a given wavelength andshows how much a color differs from gray.
64 HUNTER L,a,bThe 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 TEXTUREThe 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 ViscosityViscosity: 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 RegimeThe 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 RegimeThe "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 RegimeThe 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 printerTorsion deviceSpindleBrabender Cup(rotates)Heat-at 1.5oC per Minute
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 weightThe 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.
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.
77 Sensory PropertiesTrained 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 SUMMARYThis 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).