Food Composition and Quality Analysis

• Course provides comprehensive understanding and practical skills for analyzing food composition and quality.
• Analyzing nutrients, additives, contaminants, and sensory attributes will contribute to informed decision-making.

Why Analyze Food?

• Government regulations mandate standards of identity for certain products such as fat and moisture levels in meat.
• Nutritional labeling regulations require analysis.
• Quality control monitors product quality for consistency.
• Research and development uses analysis for new product development and improvement of existing products.

Properties Typically Analyzed

• Chemical composition analysis includes moisture, ash, fat, protein, and carbohydrate content.
• Physical properties analysis includes rheological properties or stability.
• Sensory properties analysis includes flavor, mouth-feel, color, and texture.

References on Analytical Techniques

• Association of the Official Analytical Chemists (AOAC) provides official methods.
• American Oil Chemists Society (AOCS) is a reference.
• American Association of Cereal Chemists (AACC) is a reference.

Criteria for Selecting an Analytical Technique

• Techniques for analyzing foods often involve trade-offs.
• Select the technique required or fits your system's needs.
• Accurate techniques require more time but may not suit "real time" needs.
• Critical criteria are precision, accuracy, reproducibility, simplicity, cost, and speed
• Equally important are sensitivity, specificity, safety, destructiveness, online capability and official approval

Sampling and Sample Preparation

• Sampling and sample preparation is critical.

Purpose of Analysis

• Analysis can occur on official samples, raw materials, process control samples, and finished products.

Sampling Plan

• Sampling plan should be predetermined for selection, withdrawal, preservation, transportation, and preparation.
• A clearly written document containing the number of samples, location, and method of collecting samples is required.

Factors Affecting a Sampling Plan

• The purpose of inspection is acceptance or rejection, variability/average
• The nature of the product as homogenous, unit, cost
• The nature of the test method includes Critical, minor, destructive, cost, and time
• The nature of the population is uniformity, sublot

Developing a Sampling Plan

• The number of samples should consider variation in properties, cost, and type of analytical techniques
• Sample location can be random, systematic, or judgmental.
• The manner in which samples are collected can be manual vs mechanical device.

Bottom Line in Sampling

• Determine a method of taking small subsamples from a large lot that accurately reflect the overall composition.
• An inaccurate sample of a large lot is worse than no sample at all.

Preparation of Laboratory Samples

• Reduce the subsamples from a lot into appropriate sizes
• Make the sample homogeneous by mixing, grinding, and sub-sampling.
• Changes that can occur between sampling and analysis must be avoided.
• Proper labeling with sample name, date/time, location, and pertinent data is essential.

Food Components

• Food primarily consists of water (moisture), fat (or oil), carbohydrate, protein, and ash (minerals).
• Importance of understanding how these 5 components are measured.

Composition of Food

• Milk 87.3% water, 5.0% carbohydrates, 3.5% protein, 3.5% fat
• Beef 60.0% water, 17.5% protein, 22.0% fat
• Chicken 66.0% water, 20.2% protein, 12.6% fat
• Fish 81.8% water, 16.4% protein, 0.5% fat
• Cheese 37.0% water, 2.0% carbohydrates, 25.0% protein, 31.0% fat
• Cereal grains 10-14% water, 58-72% carbohydrates, 8-13% protein, 2-5% fat
• Potatoes 78.0% water, 18.9% carbohydrates, 2.0% protein, 0.1% fat
• Carrots 88.6% water, 9.1% carbohydrates, 1.1% protein, 0.2% fat
• Lettuce 94.8% water, 2.8% carbohydrates, 1.3% protein, 0.2% fat
• Apple 84.0% water, 15.0% carbohydrates, 0.3% protein, 0.4% fat
• Melon 92.8% water, 6.0% carbohydrates, 0.6% protein, 0.2% fat

pH Determination

• pH refers to the relative amounts of acid and base.
• It is scientifically defined as the negative log of the hydrogen ion concentration.
• pH ranges from 0 to 14, with pH 7 being neutral.
• Values under 7 are acids, above 7 are basic or alkaline.
• Measured with a pH meter or litmus paper.

Moisture Determination

• Moisture or water is the most common component in foods, ranging from 60-95%.
• Considerations are total moisture content and water acidity.

Moisture Content

• Total moisture content is generally determined using a drying method.
• Moisture is removed by heat, and determined as weight loss.
• % water = (wet weight of sample - dry weight of sample)/wet weight of sample

Methods of Moisture Loss Measurement

• Convection or forced draft ovens (AOAC) are very simple and common.
• Vacuum Oven - Sample is placed in oven under reduced pressure, reducing the boiling point of water.
• Microwave Oven - Uses microwaves as a heat source; the method is very fast.
• Infrared Drying - Uses an infrared lamp as a heat source; method is very fast.

Water Activity

• Water activity (Aw) is the amount of free, unbound water available for microbial growth and enzyme activity.
• Water activity affects vitamin decomposition and can reduce color, taste and flavor stability.
• Two general types of sensors are capacitance sensors and chilled-mirror dew point methods.

Water Activity and Microorganism

• Bacteria grow with Aw of 1.0-0.95
• Bacteria grow with Aw 0.95-0.91
• Yeasts grow with Aw 0.91-0.87
• Molds grow with Aw 0.87-0.80
• No microorganism proliferation occurs with Aw 0.30-0.20

Water Activity and Foods

• Meat, fish, sausage, and milk has bacterium
• Fermented sausages had yeast
• Cookies, crackers, bread crust has no microorganisms

Protein Analysis

• Proteins are made of amino acids.
• Amino acids are the building blocks of protein.
• Nitrogen is the most distinguishing element, ranging from 13.4 - 19.1%.
• Non-protein nitrogen includes free amino acids, nucleic acids, amino sugars, and some vitamins.
• Total organic nitrogen = protein + non-protein nitrogen.

Types of Protein Analysis

• Kjeldahl measures the amount of nitrogen in a sample.
• Lowry measures tyrosine/tryptophan residues.

Total Organic Nitrogen - Kjeldahl Method

• Used for crude protein content.
• Johan Kjeldahl (1883) developed the basic process.
• Principle: Total organic N is released from the sample and absorbed by acid.
• The method involves digestion with sulfuric acid + catalyst.
• Then neutralization and distillation with sodium hydroxide.
• Followed by titration with hydrochloric acid.

Total Organic Nitrogen - Kjeldahl Method

• Calculation: moles HCl = moles NH3 = moles N in the sample
• %N = N*(HCI)× (mL acid sample-mL acid blank) / 1000 og sample x mole × 100
• %N = N*(HCI) × (mL acid sample-mL acid blank) / g sample × 1.4
• N*=Normality of HCI

Total Organic Nitrogen - Kjeldahl Method

• Calculation: %Protein = %N × conversion factor
• Conversion factor: generally 6.25, most protein: 16% N
• Egg or meat conversion factor is 6.25
• Milk conversion factor is 6.38
• Wheat conversion factor is 5.33
• Soybean conversion factor is 5.52
• Rice conversion factor is 5.17

Total Organic Nitrogen - Kjeldahl Method: Advantages

• Applicable to any foods.
• Simple and inexpensive.
• Accurate, official method for crude protein content.

Total Organic Nitrogen - Kjeldahl Method: Disadvantages

• Measures total N, not just protein N.
• Time-consuming.
• Uses corrosive reagents.

Lowry Method

• A color formation between tyrosine and tryptophan residues occurs with Biuret and Folin-Ciocalteau reagents
• Color forms at 750 nm or 500 nm.

Lowry Method: Advantages

• Most sensitive (20-200µg).
• More specific and relatively rapid.

Lowry Method: Disadvantages

• Color development not proportional to protein concentration.
• Color varies with different proteins.
• Interference from sugars; lipids and phosphate buffers.

Infrared Spectroscopy

• Absorption of radiation of peptide bond at mid-infrared (MIR) and near-infrared (NIR) bands occurs.

Infrared Spectroscopy: Advantages

• NIR applicable to a wide range of foods.
• Rapid, nondestructive.
• Little sample preparation needed.

Infrared Spectroscopy: Disadvantages

• Expensive instruments.
• Calibration is different for each sample.

Crude Fat Analysis

• Fats refers to lipids, fats and oils.
• The most distinguishing feature of fats is their solubility.
• Fats are soluble in organic solvents but insoluble in water.

Solvent Extraction Methods

• Sample preparation requires nitrogen and low temperatures.
• Particle size reduction increases extraction efficiency.
• Predrying sample is common.

Solvent Selection

• An ideal solvent should have high solvent power for lipids.
• An ideal solvent includes low solvent power for other components.
• An ideal solvent should be easy to evaporate and have a low boiling point.
• Also, it should be be nonflammable, nontoxic, and allow good penetration.
• An ideal solvent consist of a single component, be inexpensive, and non-hygroscopic.

Common Solvents

• Ethyl ether is the best solvent for fat extraction but is expensive, explosion, fire hazard, hygroscopic
• Petroleum ether is cheaper, hydrophobic, and less hygroscopic
• Hexane for soybean oil extraction

Types of Fat Analysis

• Extraction Methods are continuous, semi-continuous, and discontinuous
• Continuous uses Goldfinch, Semi-Continuous uses Soxhlet, Discontinuous uses Mojonnier
• Instrumental Methods include Dielectric, Infrared, and Ultrasound

Continuous Extraction

• The Goldfish method involves solvent continuously flowing over the sample without build-up.
• It is fast and efficient but causes channeling and incomplete extraction.

Semicontinuous Extraction

• The Soxhlet method builds up solvent in the extraction chamber for 5-10 min before siphoning back to boiling flask.
• Semicontinuous Extraction has no channeling but is time consuming.

Discontinuous Extraction

• The Mojonnier method is a wet method because it has a mixture of ethyl ether and petroleum ether in a Mojonnier flask.
• Discontinuous Extraction requires no prior removal of moisture but constant attention.

Instrumental Methods

• Dielectric method employs low electric current from fat.
• Infrared method uses fat absorbing infrared energy at a wavelength of 5.73 µm.
• Ultrasound method uses that sound velocity increases with increasing fat content.

Carbohydrate Analysis

• Carbohydrates are the most abundant food component next to water.
• %carbohydrate=100% - (H2O + ash + fat + protein)
• Types include monosaccharides, disaccharides, oligosaccharides, and polysaccharides
• Monosaccharides are glucose, fructose, galactose
• Disaccharides are sucrose, lactose, maltose
• Oligosaccharides are raffinose
• Polysaccharides are starch, cellulose

Ash and Mineral Analysis

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

Ash Contents in Foods

• Wheat flour, whole grain 1.6%
• Macaroni, dry, enriched 0.7%
• Milk, whole, fluid 0.7%
• Butter, with salt 2.1%
• Apple, raw with skin 0.3%
• Banana, raw 0.8%
• Egg, whole, raw 0.9%
• Hamburger, regular, plain 1.7%

Methods for Determining Ash

• Dry ashing involves high temperature.
• Wet ashing uses an oxidizing agent and/or acid.
• Low-temperature plasma ashing is dry ashing in partial vacuum at low temperature.

Dry Ashing Principles

• Involves high temperature at >525°C overnight (12-18 hr)
• Measures the total mineral content.

Dry Ashing Instrumentation

• A Muffle furnace is used.
• A crucible must be employed that consists of quartz, porcelain, steel, nickel, or platinum.

General Procedure for Dry Ashing

• Place 5-10g of pretreated sample into a crucible.
• Ignite crucible until constant weight at ~550°C for 12-18 hr.
• Cool in desiccator.
• Weigh cooled crucible.
• Ash (%) = (Weight of Residue /Weight of sample) x 100

Dry Ashing Advantages

• Safe and easy.
• No chemical needed.
• Many samples can be handled at one time.
• The resulting ash is used for further mineral analysis.

Dry Ashing Disadvantages

• Loss of volatiles.
• Interaction.
• Long time and expensive equipment.

Ion-Selective Electrodes

• Used for direct measurement via chemical potential of cations
• Cations may include (Ca, Na, K), anions (Br, Cl, F), or dissolved gases (O2, CO2).
• The primary components are sensing electrode, reference electrode, and readout device.
• Types: glass membrane, polymer-body, solid-state.

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

Ion-Selective Electrodes

• More precise, rapid, and practical measurement of a wide range of ions.
• It is generally inexpensive and simple.
• Inability to measure below 2-3 ppm and unreliable at low concentration (10-4M) are limits

Ion-Selective Electrodes applications include

• Processed meats for salt, nitrate.
• Butter and cheese, for sale
• milk for Ca
• low-sodium products for sodium content
• soft drink for CO2 content
• wine for Na, K content
• can vegetables for nitrate

Physical Properties of Foods

• Chemical properties measure components like water and fat, carbohydrates, and protein.
• Physical properties determine how processing affects the color and texture of foods.

Physical Properties

Include:

• Color
• Texture
• Viscosity
• Texture analysis
• Sensory properties

Color

• Described in terms of hue, value and chroma.
• Hue is the aspect described by words like green, blue, yellow and red.
• Value or lightness describes the relationship between reflected and absorbed light.
• Chroma describes reflection at a given wavelength.

HUNTER L, a, b

• In the Hunter system, L measures white to black, a measures green to red, and b measures blue to yellow.

Color

• Subjective systems include paint color match pages, The Pantone Matching System and photos.

Texture

• Measurements of texture can be divided into those for liquids (viscosity) versus solid foods.

Fluid Viscosity

• Key property of liquids which describes resistance to flow.
• The viscosity of a solution increases non-linearly with polymer concentration.

Fluid Viscosity cont.

• The polymers act as isolated "particles" too dilute to interact with each other
• can be approximated as spheres of rg radius (Stokes radius)
• viscosity increases as polymer coils start to overlap
• as concentration increase, the individual polymer molecules are shown with solid-like behavior

Brookfield (Rotational) Viscometer

• Viscosity measurement by sensing the torque required to rotate a spindle at constant speed while immersed in the sample fluid.

Brabender Viscoamylograph and Rapid Visco Analyzer

• Used for measurements during the pasting process

Brabender RVA applications

• Brabender and RVA Applications can be used to measure starchs, doughs, baking products, noodle quality etc.

Bostwick Consistometer

• Measures consistency by measuring the distance material flows under its own weight.
• Unit constructed from stainless steel with leveling screws and level
• the trough is graduated.
• Mainly used for measuring highly vicious foods

Instron Universal Testing Machine

• An accurate and versatile machine used for precise measurement of properties and behavior in compression, flexure etc,
• Weighing system employs strain gauge load cells for measuring the load

Sensory Properties

• Trained sensory panels of people that characterize texture like/dislike
• Consumer panels usually determine like/dislike, desirability etc.