3. Analisa Proksimat

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INTRODUCTION TO FOOD ANALYSIS

1126

Steven C Seideman

Extension Food Processing Specialist

Cooperative Extension Service

University of Arkansas

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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.

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COMPOSITION OF FOODS

COMPONENT

MilkBeefChickenFishCheeseCereal grains

PotatoesCarrotsLettuceAppleMelon

% 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

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MOISTURE DETERMINATION

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Moisture Determination

• Moisture or water is by far the most common component in foods ranging in content from 4 – 95%.

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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

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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

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PROTEIN ANALYSIS

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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

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Types of Protein Analysis

• Kjeldahl – measures the amount of nitrogen in a sample.

• Lowry- measures the tyrosine/tryptophan residues of proteins.

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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

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Total organic nitrogen - Kjeldahl method

Digestion

Protein (NH4)2SO4

(ammonium sulfate)

Protein N NH4+ + H2SO4 (NH4)2SO4

Sulfuric acid

Heat, catalyst

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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

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Total organic nitrogen - Kjeldahl method

– Titration (direct titration)

H2BO3

- + H+ H3BO3

– Calculationmoles 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) 14g N

g sample mole1000 100

(mL acid sample-mL acid blank)

g sample 1.4

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Total organic nitrogen - Kjeldahl method• Calculation

%Protein = %N conversion factorConversion factor: generally 6.25 – most protein: 16% N

Conversion factoregg or meat 6.25milk 6.38wheat 5.33soybean 5.52rice 5.17

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Kjeldahl Apparatus

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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

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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).

• Procedureprotein solution + biuret reagent

room temp10 min

+ Folin reagent 50C 10 min

650 nm

(20-100 g)

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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)

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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

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Crude Fat Analysis

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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.

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Solvent Extraction Methods• Sample preparation: Best under nitrogen &

low temperature– Particle size reduction increases extraction

efficiency– Predrying sample to remove water is common.

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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

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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

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Types of Fat Analysis

• Extraction Methods

Continuous – Goldfinch

Semi-Continuous- Soxhlet

Discontinuous- Mojonnier • Instrumental Methods

Dielectric

Infrared

Ultrasound

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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.

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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

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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

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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

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CARBOHYDRATE ANALYSIS

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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

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Ash and Mineral Analysis

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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

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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%

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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

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Dry Ashing• Principles

– High temperature (>525C) overnight (12-18 hr)– total mineral content

• Instrumentation– Muffle furnace– Crucible

• quartz• porcelain• steel• nickel• platinum

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General Procedure for Dry Ashing

1. 5-10g pretreated sample into a crucible

2. Ignite crucible to constant weight at ~550C for 12-18 hr

3. Cool in desiccator

4. Weigh cooled crucible

% ash (db) = 100

wt after ashing - crucible wt

Sample wt solid%/100

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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

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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.

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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).

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COLOR

• More subjective color determination systems include;

- Paint color match pages

-The Pantone Matching System.

- Actual photos of finished food products

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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”

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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).