INTRODUCTION TO FOOD ANALYSIS 1126. Steven C Seideman Extension Food Processing Specialist Cooperative Extension Service University of Arkansas. INTRODUCTION. This module is a very brief overview of common methods of food analysis used in food processing organizations. WHY ANALYZE FOOD?.
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INTRODUCTION TO FOOD ANALYSIS1126 Steven C Seideman Extension Food Processing Specialist Cooperative Extension Service University of Arkansas
INTRODUCTION • This module is a very brief overview of common methods of food analysis used in food processing organizations.
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.
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.
References on Analytical Techniques • Official Methods; - Association of the Official Analytical Chemists (AOAC) - American Oil Chemists Society (AOCS) - American Association of Cereal Chemists (AACC)
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.
Precision Accuracy Reproducibility Simplicity Cost Speed Sensitivity Specificity Safety Destructive/ Non-destructive On-line/off-line Official Approval Criteria for Selecting an Analytical Technique
What is the Purpose of the Analysis • Official Samples • Raw Materials • Process Control Samples • Finished Products
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
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
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
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.
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.
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.
COMPONENT Milk Beef Chicken Fish Cheese Cereal grains Potatoes Carrots Lettuce Apple Melon % Water %Carbohydrates %Protein % Fat % Min/Vit 87.3 5.0 3.5 3.5 0.7 60.0 0 17..5 22.0 0.9 66.0 0 20.2 12.6 1.0 81.8 0 16.4 0.5 1..3 37.0 2.0 25.0 31.0 5.0 10-14 58-72 8-13 2-5 0.5-3.0 78.0 18.9 2.0 0.1 1.0 88.6 9.1 1.1 0.2 1.0 94.8 2.8 1.3 0.2 0.9 84.0 15.0 0.3 0.4 0.3 92.8 6.0 0.6 0.2 0.4 COMPOSITION OF FOODS
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.
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.
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
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
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.
Aw Microorganism 1.0-0.95 Bacteria 0.95-0.91 Bacteria 0.91-0.87 Yeasts 0.87-0.80 Molds 0.30-0.20 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 WATER ACTIVITY
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 : 13.4 - 19.1% • Non-protein nitrogen: free amino acids, nucleic acids, amino sugars, some vitamins, etc. • Total organic nitrogen = protein + non-protein nitrogen
Types of Protein Analysis • Kjeldahl – measures the amount of nitrogen in a sample. • Lowry- measures the tyrosine/tryptophan residues of proteins.
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
Sulfuric acid Heat, catalyst Total organic nitrogen - Kjeldahl method Digestion Protein (NH4)2SO4 (ammonium sulfate) Protein N NH4+ + H2SO4 (NH4)2SO4
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
(mL acid sample-mL acid blank) 14g N g sample mole 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) 100 1000 (mL acid sample-mL acid blank) 1.4 g sample
Total organic nitrogen - Kjeldahl method • Calculation %Protein = %N conversion factor Conversion factor: generally 6.25 • most protein: 16% N Conversion factor egg or meat 6.25 milk 6.38 wheat 5.33 soybean 5.52 rice 5.17
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
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 50C 10 min 650 nm (20-100 g)
Lowry Method • Advantages • most sensitive (20-200g) • more specific, relatively rapid • Disadvantages • color development not proportional to protein concentration • color varying with different proteins • interference (sugars, lipids, phosphate buffers, etc)
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
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.
Solvent Extraction Methods • Sample preparation: Best under nitrogen & low temperature • Particle size reduction increases extraction efficiency • Predrying sample to remove water is common.
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
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
Types of Fat Analysis • Extraction Methods Continuous – Goldfinch Semi-Continuous- Soxhlet Discontinuous- Mojonnier • Instrumental Methods Dielectric Infrared Ultrasound
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.
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
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
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
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