chapter 3 protein

8/18/2019 Chapter 3 Protein

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CHAPTER 4

PROTEIN


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∗ Protein contain amino acid- "!ildin( "loc)s ofprotein

∗ Protein needed to "!ild and repair "ody tiss!e and

for the meta"olic f!nction of o!r "ody∗ Total of #$ amino acids and * are essential

n!trients

∗ +!st "e o"tained daily from diet

INTRODUCTION


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STRUCTURE ANDCLASSIFICATION

∗ ,-amino acids are the "asic !nits of proteins.

∗ These amino acids consist of an ,-car"on atomcoalently attached to a hydro(en atom an amino

(ro!p and side-chain R (ro!p.


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A+INO ACI'(monomer)

PEPTI'E

(several amino acids)

PROTEIN

(many peptides)


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Essential Nonessential

Isoleucine Alanine

Leucine Asparagine

Lysine Aspartate

Methionine Cysteine*

Phenylalanine Glutamate

Threonine Glutamine*

Tryptophan Glycine*

aline Proline*

!erine*

Tyrosine*

Arginine*

"istidine*

http://en.wikipedia.org/wiki/Isoleucinehttp://en.wikipedia.org/wiki/Alaninehttp://en.wikipedia.org/wiki/Leucinehttp://en.wikipedia.org/wiki/Asparaginehttp://en.wikipedia.org/wiki/Lysinehttp://en.wikipedia.org/wiki/Aspartatehttp://en.wikipedia.org/wiki/Methioninehttp://en.wikipedia.org/wiki/Methioninehttp://en.wikipedia.org/wiki/Aspartatehttp://en.wikipedia.org/wiki/Lysinehttp://en.wikipedia.org/wiki/Asparaginehttp://en.wikipedia.org/wiki/Leucinehttp://en.wikipedia.org/wiki/Alaninehttp://en.wikipedia.org/wiki/Isoleucine


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Classi#ication o# $ased on Composition%

imple proteins

composed o# entirely amino acids only&'g& Alumin Gloulin&

Comple& or Con/!(ated proteins

Made up o# amino acids and other organic compounds&The nonamino acid group is termed as the prosthetic

group&

'g& +ucleoproteins lipoprotein


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GENERALCHARACTERISTICS

Amphoteric properties&

Amino acids are amphoteric molecule (dipolar ions) that is

they have oth asic and acidic groups&

Monoaminomonocao,ylic aminoacids e,ist in a-ueous solution as

dipolar molecules .hich means they

have oth positive and negative

charges and the overall molecules is

electrically neutral&

At lo. p" the caro,yl

group accepts a proton and

ecome uncharged so that

the overall charge on the

molecule is positive&

At high p" the amino group

loses its proton and ecomes

uncharged (neutral) thus the

overall charge on the

molecule is negative&


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Protein str!ct!re

PRI+AR0 TR1CT1RE

the se-uence o# residues in the polypedptide chain&

ECON'AR0 TR1CT1RE

a local regulary occuring structure in proteins and is mainly

#ormed through hydrogen onds et.een ac/one atoms&!ocalled random coils loops or turns don0t have a stale

secondary structure& There are t.o types o# stale

secondary structures% Alpha helices and "eta-sheets


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TERTIAR0 TR1CT1RE the pac/ing o# alphahelices etasheets and random

coils .ith respect to each other on the level o# one .hole

polypeptide chain&

--gloular protein % tightly coiled and #olded into agloular protein % tightly coiled and #olded into asome.hat spherical shapesome.hat spherical shape

#irous proteins % long polypeptide chains .hich #irous proteins % long polypeptide chains .hich

are inter molecularly lin/edare inter molecularly lin/ed

21ARTENAR0 TR1CT1RE

only e,ists i# there is more than one polypeptide chain

present in a comple, protein&


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∗ A protein from animal source, that contain all theessential amino acid in sucient amounts for the

body’s maintenance and growth∗ Meat, poultry, sh, shellsh, egg and milk (cheese

& yogurt

∗ !elatin is one of animal protein that is incomplete

protein

Complete protein


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∗ "rotein from plant sources, that does not pro#ide allthe essential amino acid

∗

Most of the plant proteins e$cept soybeans andcertain grains

∗ %upport maintenance but not growth

∗ est protein source from plants are legumes, beans,

peas and lentils

Incomplete protein


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∗ "rotein contains ',,) and *

∗ +he * gi#es the name of amino to the amino acidsthat make up protein

∗ +he amino acids of protein molecule are oined bypeptide bonds

∗ "eptide bond is formed by the condensation of aminegroup (-*)- of one amino acid with the acid group(') of another amino acid resulting in theformation of water molecule

Composition of proteins


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∗ Condensation. remo#al of water molecule ()-

and formation of a bond∗ Hydrolysis . in#ol#es the addition of water by

breaking down the bond/

∗ "eptide bond are not easily broken

∗ )eat treatment re0uired to break down the peptidebond to yield amino acid from protein

Composition of proteins


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∗ +he fourth attachment the side chain (1di2erent for each amino acids that gi#es the

amino acid its uni0ue identity and chemicalnature

∗ +he simplest amino acid is glycine with onlyone )ydrogen for the 1 group

∗ Amino acid that are acidic contain more acidgroups than amine group

∗ Alkaline amino acid contain more amine group

than acid groups

Amino acid


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PROTEIN IN 5OO'


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rotein in foods allo!se"eral important

reactions to occ#r d#rin$food preparation

F#nctions of protein infood

"ydration

6enaturation7

coagulation'n4ymatic

reaction

$u##ering

$ro.ning


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∗ )ydration is ability of protein to dissol#e and attractwater

∗

ne of the capability is to form gel∗ "rotein strands trapping water that results in rm

structure called gel∗ !elling ability of proteins allow them to be used as

binders, stabili3ers and thickeners in food such as- confectioneries (gums, marshmallows

- desserts (ice-cream, puddings, pie llings,custards

Hydration


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read making

∗

4ater or milk is combined with yeast and two maorproteins of wheat (gliadin and glutenin

∗ 5neading process helps to attract the water or milk(hydration and yield protein gluten

∗

6lastic 0uality of a dough to stretch with the '- produced by the yeast during fermentation

E%ample of &ydration'(


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Denat#ration)coa$#lation

Denat#ration of proteins in#ol#es the disruption andpossible destruction of both the secondary and tertiary

structures/

%ince denaturation reactions are not strong enough tobreak the peptide bonds, the primary structure(se0uence of amino acids remains the same after adenaturation process/

8enaturation disrupts the normal alpha-heli$ and betasheets in a protein and uncoils it into a random shape/


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∗ 9arge protein molecules are broken down into

smaller form with the application of heat, p)e$tremes, alcohol, physical or chemicaldisturbances

∗ 8enaturation results in coagulation- curdling of the

proteins

Denat#ration)coa$#lation


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6$amples∗ )ardening of egg white with heating

∗ %ti2ening of egg white during the whipping process

Denat#ration


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∗ 6n3ymes are proteins formed within the li#ing cells

∗ Act as biocatalyst to speed up chemical reaction

∗ Loc* and *ey concept describes en3yme action∗ An en3yme combine with a substrate, speeding up

the reaction than later produce a product

∗ After the reaction the en3yme is freed unchanged

∗ 1eact with another substrate

En+ymatic reaction


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∗ :sed widely in the processing of wines, cheeses,corn syrup, yogurt, baked goods, sausages and

uices/∗ 6$amples of en3ymes;- Rennin aids in cheese processing by con#erting

milk to curd- apain to tenderi3e meats

- ectinase, cell#lase, amylase used during fruit uice processing to enhance clarity, impro#eltration, reduce bitterness

En+ymes #se -y t&e foodind#stry


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∗ "rotein is a good bu2er∗ 'ompounds that resist e$treme shifts in p)

∗ +he bu2ering capacity of protein is due to theiramphoteric nature

∗ Amphoteric . capable of acting chemically as eitheracid or base

.#/erin$


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∗

'ontributes to the golden crust of baked goods,browning of meats, dark colour of roasted co2ee

∗ +he temperature conduci#e to the M/1 is


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∗ A reaction in which an en3yme acts on aphenolic compound in the presence of o$ygen

to produce brown-coloured product∗ >t re0uires three compounds

i/ $ygen

ii/ "olyphenolase en3yme

iii/ "henolic compound

En+ymatic -ro!nin$


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? Methods for

? %oluble & >nsoluble "rotein - 5eldahl (organicnitrogen & 8umas (combustion - measures totalnitrogen (*

rotein Analysis


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The 59eldahl method may e ro/en do.n into three main

steps%

'i(estion the decomposition o# nitrogen in organic samplesutili4ing a concentrated acid solution& This is accomplished y

oiling a homogeneous sample in concentrated sul#uric acid&

The end result is an ammonium sul#ate solution&

'istillation adding e,cess ase to the acid digestion

mi,ture to convert +": 8 to +"; #ollo.ed y oiling and

condensation o# the +"; gas in a receiving solution&

Titration to -uanti#y the amount o# ammonia in the receiving

solution& The amount o# nitrogen in a sample can e

calculated #rom the -uanti#ied amount o# ammonia ions in the

receiving solution&


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The #ood sample to e analy4ed is .eighed into a digestion

flask and then digested y heating it in the presence o#%

•s!lf!ric acid (an o,idi4ing agent .hich digests the #ood)•anhydro!s sodi!m s!lfate (to speed up the reaction y

raising the oiling point)•a catalyst s!ch as copper seleni!m titani!m or

merc!ry (to speed up the reaction)&

'i(estion


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6igestion converts any nitrogen in the #ood (other than that

.hich is in the #orm o# nitrates or nitrites) into ammonia and

other organic matter to C:=) and thus remains in solution%

+(#ood) (+":)=!>: (?)

'i(estion


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Ne!trali6ation

A#ter the digestion has een completed the digestion #las/ is

connected to a receiving flask y a tue& The solution in the

digestion #las/ is then made al/aline y addition o# sodium

hydro,ide .hich converts the ammonium sul#ate into

ammonia gas%

(+":)=!>: 8 = +a>" =+"; 8 ="=> 8 +a=!>: (=)


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Ne!trali6ation

The ammonia gas that is #ormed is lierated #rom the solution

and moves out o# the digestion #las/ and into the receiving

#las/ .hich contains an e,cess o# oric acid& The lo. p" o#

the solution in the receiving #las/ converts the ammonia gas

into the ammonium ion and simultaneously converts the oric

acid to the orate ion%

+"; 8 ";$>; (oric acid) +":8 8 "=$>;

(orate ion) (;)


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Titration

The nitrogen content is then estimated y titration o# the

ammonium orate #ormed .ith standard sul#uric or hydrochloricacid using a suitale indicator to determine the endpoint o# the

reaction&

"=$>; 8 "8 ";$>; (:)


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The concentration o# hydrogen ions (in moles) re-uired to reach

the endpoint is e-uivalent to the concentration o# nitrogen that

.as in the original #ood ('-uation ;)& The #ollo.ing e-uation

can e used to determine the nitrogen concentration o# a

sample that .eighs m grams using a x M "Cl acid solution #orthe titration%

Titration

@here v s and v are the titration volumes o# the sample and lan/ and ?:g

is the molecular .eight o# nitrogen +&


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A lan/ sample is usually ran at the same time as the material

eing analy4ed to ta/e into account any residual nitrogen.hich may e in the reagents used to carry out the analysis&

>nce the nitrogen content has een determined it is converted

to a protein content using the appropriate conversion #actor%Protein B 2 +&@

Titration


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The 59eldahl method is .idely used internationally and is still

the standard method #or comparison against all othermethods&

Its universality high precision and good reproduciility have

made it the ma9or method #or the estimation o# protein in#oods&

A'7ANTA3E


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It does not give a measure o# the true protein since all

nitrogen in #oods is not in the #orm o# protein&

6i##erent proteins need di##erent correction #actors ecausethey have di##erent amino acid se-uences&

The use o# concentrated sul#uric acid at high temperatures

poses a considerale ha4ard as does the use o# some o# thepossile catalysts&

The techni-ue is time consuming to carryout&

'IA'7ANTA3E


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T&e Com-#stion 0et&od

Nitrogen is released after combustion at high

temperature in pure oxygen.

Nitrogen is measured by thermal conductivity

detection.

This procedure is relatively expensive because of

instrument costs and pure gases.

http://www.uwex.edu/ces/forage/nfta/comb.htm


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∗ +he method consists of combusting a sample of

known mass in a high temperature (about


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!


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T&e Com-#stion 0et&od

The gasses are then passed over special columns that asor

the caron dio,ide and .ater&

A column containing a thermal conductivity detector at the end

is then used to separate the nitrogen #rom any residual caron

dio,ide and .ater and the remaining nitrogen content is

measured&


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∗ +he 8umas method has the ad#antages of beingeasy to use and automate/

∗ >t is also considerably faster than the 5eldahlmethod, taking a few minutes per measurement, ascompared to the hour or more for 5eldahl/

∗ >t also does not make use of to$ic chemicals or

catalysts

Ad"anta$es


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∗ ne maor disad#antage is its high initial cost/

∗

Also, as with 5eldahl, it does not gi#e a measure oftrue protein, as it registers non-protein nitrogen inaddition

Disad"anta$es


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chapter 3 protein

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