Dr. Zaffar Mehmood. Definitions: Food: means a raw, cooked, or processed edible substance, ice,...
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FOOD BIOTECHNOLOGY BIT 313 3(3-0) Dr. Zaffar Mehmood
Dr. Zaffar Mehmood. Definitions: Food: means a raw, cooked, or processed edible substance, ice, beverage, or ingredient used or intended for use or for
Definitions: Food: means a raw, cooked, or processed edible
substance, ice, beverage, or ingredient used or intended for use or
for sale in whole or in part for human consumption, or chewing gum.
Food Technology: is the application of food science &
engineering principles to the selection, preservation, processing,
packaging, distribution, and use of safe, nutritious, and wholesome
food Food Security: Food security is achieved when all people, at
all times, have physical, social and economic access to sufficient,
safe and nutritious food to meet their dietary needs and food
preferences for an active and healthy life. (800 million people
suffer from hunger) Food Safety: A suitable product which when
consumed orally either by a human or an animal does not cause
health risk to consumer Food Biotechnology: Application of
technology to modify genes of animals, plants, and microorganisms
to create new species which have desired production, marketing, or
nutrition related properties. Called genetically engineered (GE)
foods, they are a source of an unresolved controversy over the
uncertainty of their long-term effects on humans and food
chains
Slide 3
Principles of Biochemistry Biochemical Building blocks Proteins
Carbohydrates Lipids Nucleic acids Protein synthesis Enzymes
Slide 4
Proteins 1. The 20 amino acids that cells use to make proteins
have a common core structure. a. Most amino acids have a central
carbon atom to which is attached a hydrogen atom, an amino group,
NH3 +, and a carboxyl group, COO. b. The side chain or R group
distinguishes each amino acid chemically. 2. Assembly of the amino
acids to form peptides and proteins occurs by stepwise fusion of
the carboxyl group of one amino acid with the amino group of
another, with loss of a molecule of water during the reaction to
form a peptide bond. 3. Proteins can have a broad diversity of
structures depending on their amino acid sequences and composition.
4. The central carbon and the atoms involved in end-to-end linkage
of the amino acids form the polypeptide backbone, with the side
chains protruding outwardly to interact with other parts of the
protein or with other molecules.
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Proteins continued The 20 common amino acids can be classified
into groups with similar side chain chemistry. 1. The nonpolar or
hydrophobic amino acidsglycine, alanine, valine, leucine, and
isoleucinehave alkyl side chains (or simply a hydrogen atom in the
case of glycine). 2. Serine and threonine are small, polar amino
acids that have hydroxyl groups. 3. The sulfur-containing amino
acids are cysteine and methionine. 4. The aromatic amino acids,
phenylalanine, tyrosine, and tryptophan, have ring structures and
are nonpolar with the exception of the hydroxyl group of tyrosine.
5. The acidic amino acids, aspartic acid and glutamic acid, have
carboxyl groups. 6. The amides of the carboxylic amino acids,
asparagine and glutamine, are uncharged and polar. 7. Members of
the basic group, histidine, lysine, and arginine, have weak-base
side chains. 8. Proline is unique; it is an amino acid because its
side chain loops back to form a five-membered ring with its amino
group, which causes proline to produce kinks in the polypeptide
backbone. Essential amino acids: Histidien, Isolucine, lucine,
lysin, methionine, phenylalanine, threonine, tryptophan,
valine.
Slide 8
Protein structure: A. Primary structure refers to the linear
sequence of amino acids linked by peptide bonds to make up a
protein. B. Secondary structure describes the twisting of the
polypeptide backbone into regular structures that are stabilized by
hydrogen bonding. 1. The -helix is a coiled structure stabilized by
intrastrand hydrogen bonds a. The structure is both extensible and
springy, which contributes to the function of proteins that are
primarily -helix, such as keratins of fingernails,hair, and wool.
b. Amino acid side chains project outward, away from the axis of
the -helix and decorate its exterior surface. 2. _-Sheet structures
are made from highly extended polypeptide chains that link together
by hydrogen bonds between the neighboring strands and can be
oriented in parallel or antiparallel arrays. a. Due to the very
extended conformation of the polypeptide backbone, -sheets resist
stretching. b. The amino acid side chains project on either side of
the plane of a -sheet. c. Silk is composed of the protein fibroin,
which is entirely -sheet. C. Tertiary structure is formed by
combinations of secondary structural elements into a
three-dimensional organization that is mainly stabilized by
noncovalent interactions, such as hydrogen bonds. 1. Protein
folding is the complex process by which tertiary structures form
within the cell. 2. Regions of proteins that are capable of folding
independently and that often have distinct functions are called
domains. 3. The side chains of highly polar amino acids tend to
reside on the exterior of proteins, where they can form hydrogen
bonds with water. 4. The side chains of nonpolar amino acids are
normally clustered in the interior of proteins to shield them from
water. D. Quaternary structure occurs in proteins that have
multiple polypeptide chains, called subunits.
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CARBOHYDRATES Monosacharides: Carbohydrates have a carbon
backbone bearing hydroxyl groups with either an aldehyde or ketone
at one carbon. B. Simple sugars may take on several types of
structures in solution. 1. Simple sugars or monosaccharides are
classified according to the number of carbons in the backbone. a.
Pentoses have five carbons; examples include ribose and ribulose.
b. Hexoses have six carbons: examples include glucose, galactose,
fructose, and mannose. Hexoses have six carbons: examples include
glucose, galactose, fructose, and mannose. 2. Most sugars are
asymmetric and designated either D- or L- in stereochemistry. 3.
Simple sugars in aqueous solution usually form cyclic structures,
either hemiacetals or hemiketals a. The rings may have five or six
members. b. Depending on how the cyclic structure was formed, the
substituents at the connecting carbon may be anomershaving either
or configuration. 4. The hexoses are structurally distinguished by
different configurations at one or more carbons. a. Diastereomers
are molecules differing in configuration at one or more carbons. b.
Epimers are molecules that differ in their configurations at only
one carbon, thus glucose and galactose are both epimers and
diastereomers. Modifications of one or more groups convert simple
sugars into a variety of sugar derivatives. a. Replacement of OH by
H converts the sugar into a deoxymonosaccharide, such as
deoxyribose. b. Replacement of OH by NH2 converts the sugar into an
amino sugar designated as -osamine, eg, glucosamine.
Slide 11
LIPIDS Lipids are formed from structural units with a
pronounced hydrophobicity. This solubility characteristic, rather
than a common structural feature, is unique for this class of
compounds. Lipids are soluble in organic solvents but not in water.
Water insolubility is the analytical property used as the basis for
their facile separation from proteins and carbohydrates. Some
lipids are surface-active since they are amphiphilic molecules
(contain both hydrophilic and hydrophobic moieties). Hence, they
are polar and thus distinctly different from neutral lipids. The
majority of lipids are derivatives of fatty acids. In these
so-called acyl lipids the fatty acids are present as esters and in
some minor lipid groups in amide form (Table 3.1). The acyl residue
influences strongly the hydrophobicity and the reactivity of the
acyl lipids. Some lipids act as building blocks in the formation of
biological membranes which surround cells and subcellular
particles. Such lipids occur in all foods, but their content is
often less than 2%. Nevertheless, even as minor food constituents
they deserve particular attention, since their high reactivity may
strongly influence the organoleptic quality of the food. Primarily
triacylglycerols (also called triglycerides) are deposited in some
animal tissues and organs of some plants. Lipid content in such
storage tissues can rise to 1520% or higher and so serve as a
commercial source for isolation of triacylglycerols. When this
lipid is refined, it is available to the consumer as an edible oil
or fat. The nutritive/physiological importance of lipids is based
on their role as fuel molecules (37 kJ/g or 9 kcal/g
triacylglycerols) and as a source of essential fatty acids and
vitamins. Apart from these roles, some other lipid properties are
indispensable in food handling or processing.
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c. Oxidation of the terminal CH2OH to COOH converts the sugar
into a -uronic acid, such as glucuronic acid. C. Sugars can be
polymerized or interconnected to create chains termed
oligosaccharides ( 8 sugars) or polysaccharides (> 8 sugars) 1.
The linkage between sugars is formed by condensation of the
hemiacetal or hemiketal of one sugar with a hydroxyl of another
sugar with loss of water in the reaction. 2. The linkage is called
a glycosidic bond and can either be classified as or depending on
the stereochemistry of the anomeric carbons at the bridge points.
3. The important difference between and glycosidic bonds can be
seen in the digestibility of the major plant polysaccharides
cellulose and starch. a. Cellulose, the primary component of plant
cell walls, is made up of _1,4- linked glucose, which cannot be
broken down by digestive enzymes. So humans cannot use cellulose as
a direct dietary source of glucose. b. Starch, the main form of
stored sugar in plants, is made up of _1,4- linked glucose, which
can be hydrolyzed by enzymes of the digestive tract, eg, -amylase.
Thus, starch is an important dietary source of glucose.
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BENEFITS OF FERMENTATION: the use of mild conditions of pH and
temperature which maintain (and often improve) the nutritional
properties and sensory characteristics of the food the production
of foods which have flavours or textures that cannot be achieved by
other methods low energy consumption due to the mild operating
conditions relatively low capital and operating costs relatively
simple technologies.
Slide 26
Fermentation and enzyme technology The main advantages of
technical enzymes are: they cause highly specific and controlled
changes to foods there is minimal loss of nutritional quality at
the moderate temperatures employed lower energy consumption than
corresponding chemical reactions the production of new foods, not
achievable by other methods.
Slide 27
The main factors that control the growth and activity of
micro-organisms in food fermentations are: availability of carbon
and nitrogen sources, and any specific nutrients required by
individual micro-organisms substrate pH moisture content incubation
temperature redox potential stage of growth of micro-organisms
presence of other competing micro- organisms
Slide 28
APPLICATION OF ENZYME TECHNOLOGY: micro-encapsulation in
polymer membranes which retain the enzyme but permit the passage of
substrates and products electrostatic attachment to ion exchange
resins adsorption onto colloidal silica and/or cross linking with
glutaraldehyde covalent bonding to organic polymers entrapment in
polymer fibres (for example cellulose triactetate or starches)
co-polymerisation with maleic anhydride adsorption onto charcoal,
polyacrylamide, or glass
Slide 29
LIMITATIONS OF TECHNOLGY the higher cost of carriers, equipment
and process control changes to the pH profiles and reaction
kinetics of enzymes loss of activity (2560% loss) risk of microbial
contamination
Slide 30
ENZYME CHARACTERISTICS: short residence times for a reaction
stability to variations in temperature and other operating
conditions over a period of time (for example glucose isomerase is
used for 1000 h at 6065C) suitability for regeneration.
Slide 31
The requirements of commercial enzyme production from
micro-organisms are as follows: micro-organisms must grow well on
an inexpensive substrate substrates should be readily available in
adequate quantities, with a uniform quality micro-organisms should
produce a constant high yield of enzyme in a short time methods for
enzyme recovery should be simple and inexpensive the enzyme
preparation should be stable
Slide 32
Bread Industry Basic ingredient, flour Types of wheat and wheat
milling Composition (Germ 2.5%, Endosperm 82.5% and Bran 15%
(epidermis, epicarp, endocorp, testa and aleauron layers)). Milling
72 % extraction, 28% Bran and shorts. Cake flour and Baking flour
Ideal flour: (colour, strength, tolerance, High absorption,
Uniformity). Compressed bakers yeast. 30% solids, 2c storage./
dried yeast. Leavening: Mechanical, CO2, Chemicals, Water
vapours.
Slide 33
Baking Flour mixing stages: Pick up, drying, clean up, runny
Fermentation: 5C, 25-30C, humidity 70-75%. Punching. Proofing:
35-40C and 80-85% humidity. Types of Fermentation: Straight Dough
and Sponge Dough Method Straight dough: weighing sifting and
blending flour tempering of water, preliminary mixing of yeast
dried milk etc. Dough mixed dough placed in trough dough allowed to
rise, turned and folded rounding intermediate proof moulding
Panning pan proof baking cooling slicing.
Slide 34
Sponge Dough Process: weighing sifting and blending flour
tempering of water, preliminary mixing of yeast dried milk etc.
Dough mixed sponge mixed sponge placed in trough sponge allowed to
mature sponge placed in mixer sponge broken up and mixed with dough
ingredients final dough placed in trough allowed to rise sometimes
turned and folded dough sent to bench or divider Dividing and
scaling rounding intermediate proof Moulding panning pan proof
baking cooling slicing.
Slide 35
Beer Prodution:
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Beer Fermentation ICT Requirement: Continuous beer fermentation
stirred vs. unstirred tanks single vessels vs. multiple vessels in
a series open systems vs. closed systems Major issue of
contamination. Choice of Carrier material: (i) attachment to the
support surface, which can be spontaneous or induced by linking
agents; (ii) Entrapment within a porous matrix; (iii) containment
behind or within a barrier;and (iv) self-aggregation, naturally or
artificially induced
Slide 39
Immobilized Cell technology High cell mass loading capacity
Easy access to nutrient media Simple and gentle immobilization
procedure Immobilization compounds approved for food applications
High surface area-to-volume ratio Optimum mass transfer distance
from flowing media to centre of support Mechanical stability
(compression, abrasion) Chemical stability Highly flexible: rapid
start-up after shut-down Sterilizable and reusable Suitable for
conventional reactor systems Low shear experienced by cells Easy
separation of cells and carrier from media Readily up-scalable
Economically feasible (low capital and operating costs) Desired
flavor profile and consistent product Complete attenuation
Controlled oxygenation Control of contamination Controlled yeast
growth Wide choice of yea st
Slide 40
MILK FERMENTATION Cow's milk contains approximately 3.2%
protein, 4.8% lactose, 3.9% lipids, 0.9% minerals, traces of
vitamins, and 87.2% water. Among the proteins, casein in colloidal
suspension as calcium caseinate is present in higher amounts than
the other two soluble proteins, albumin and globulin. Lactose is
the main carbohydrate and is present in solution. lipids are
dispersed as globules of different sizes in emulsion (fat in
water). Minerals are present in solution and as colloid with
casein. Water-soluble vitamins are present in aqueous phase,
whereas fat-soluble vitamins are present with the lipids. The solid
components (12.8%) are designated as total solids (TS), and TS
without lipids is designated as solid-not-fat (SNF; ca. 8.9%). The
whey contains principally the water-soluble components, some fat,
and water
Slide 41
Milk compositin (Fat) Fat globules, are surrounded by a polar
milk fat globule membrane (MFGM). Triacylglycerols are the
predominant lipid fraction (98%) of the total lipids alongwith 2%
Diacylglycerols, monoacylglycerols, fatty acids, phospholipids, and
sterols. The phospholipids are integral components of the MFGM. 65%
saturated (26% palmitic acid and 15% stearic acid). Rest are short-
and middle-chain fatty acids, including 3.3% butyric acid. These
fatty acids and the breakdown products of these fatty acids are
important contributors to the flavor of many cultured dairy
products.
Slide 42
Milk Proteins Caseins 80% of the total protein and are
insoluble at a pH of 4.6, but are heat stable. The casein micelles
exist as a colloidal dispersion, with a diameter ranging from 40 to
300 nm and containing approximately 10,000 casein molecules. The
principal casein proteins, s1, s2, , and , present in the ratio
40:10:35:12, Whey proteins remain soluble at pH 4.6 and are heat
sensitive. Four major proteins, - lactoglobulin (50%), -lactalbumin
(20%), blood serum albumin (10%), and immunoglobulins (10%).
Cysteine and cysteine residues in these proteins form disulfide
linkages with other proteins following heat treatment
Slide 43
The production of lactic acid by lactic acid bacteria decreases
the pH of the milk to cause coagulation of the casein. A pH below
5.3, colloidal calcium phosphate is solubilized from the casein
micelle, causing the micelles to dissociate and the casein proteins
to aggregate and precipitate at the isoelectric point of casein (pH
4.6). The resulting gel, which is somewhat fragile in nature,
provides the structure for sour cream, yogurt, and acid-
precipitated cheeses, such as cream cheese andcottage cheese.
Slide 44
Lactic Acid Bacteria: Lactic Acid Bacteria Streptococcus,
Lactococcus, Leuconostoc, and Lactobacillus genera. These bacteria
are gram-positive bacteria and belong to either the
Streptococcaceae or Lactobacillaceae families. Optimal temperature
for growth, with 2030 C the optimal temperature for mesophilic
bacteria and 3545 C. Although the lactic acid bacteria are quite
diverse in growth requirements, morphology, and physiology, they
all have the ability to metabolize lactose to lactic acid and
reduce the pH of the milk to produce specific cultured dairy
products.
Slide 45
DVI Many commercial dairy processors now use the direct vat
inoculation (DVI) process for frozen or freeze-dried cultures (up
to 10 12 bacteria per gram of starter) in the processing of
cultured dairy products. Benefits: Direct addition of the cultures
No on-site culture preparation. Increased phage resistance, minimum
formation of mutants, enhanced the ability to characterize the
composition of the cultures, improved the consistent quality of
cultured dairy products. Limitations: Additional cost of these
cultures, the dependence of the cheese plants on the starter
suppliers for the selection and production of the starters,
increased lag phase of these cultures in comparison to on-site
culture preparation.
Slide 46
Enzyme Coagulation: Rennet: a mixture of chymosin and pepsin,
obtained from calf stomach, is most commonly recognized as the
enzyme for coagulation of casein. Proteases: from microorganisms
and produced through recombinant DNA technologies have been
successfully adapted as alternatives to calf rennet. Chymosin: in
rennet, cleaves the peptide bond between Phe-105 and Met-106 of
-casein, releasing the hydrophilic, charged casein macropeptide,
while the para--casein remains associated with the casein micelle.
The loss of the charged macropeptide reduces the surface charge of
the casein micelle and results in the aggregation of the casein
micelles to form a gel network stabilized by hydrophobic
interactions. Temperature influences both the rate of the enzymatic
reaction and the aggregation of the casein proteins, with 4042 C,
the optimal temperature for casein coagulation. The use of rennet
to hydrolyze the peptide bond and cause aggregation of the casein
micelles is used in the manufacture of most ripened cheeses.
Slide 47
Homogenization: Milk fat globules have a tendency to coalesce
and separate upon standing. Homogenization reduces the diameter of
the fat globules from 110 m to less than 2 m and increases the
total fat globule surface area. The physical change in the fat
globule occurs through forcing the milk through a small orifice
under high pressure. The decrease in the size of the milk fat
globules reduces the tendency of the fat globules to aggregate
during the gelation period. In addition, denaturation of the whey
proteins and interactions of the whey proteins with casein or the
fat globules can alter the physical and chemical properties of the
milk proteins to result in a firmer gel with reduced syneresis.
Milk to be used to process yogurt, cultured buttermilk, and
unripened cheeses is commonly homogenized to improve the quality of
the final product.
Slide 48
Pasturization: The heat process, which must be sufficient to
inactivate alkaline phosphatase, also destroys many pathogenic and
spoilage microorganisms, and enzymes that may have a negative
impact on the quality of the finished products. The
time-temperature treatments for the fluid milk pasteurization have
been adapted for the milk to be used in the processing of cultured
dairy products (62.8 C for 30 minutes or 71.1 C for 15 seconds).
More severe heat treatments than characteristic of pasteurization
causes denaturation of whey proteins and interactions between -
lactoglobulin and -casein. In cheeses, this interaction decreases
the ability of chymosin to hydrolyze the casein molecule and
initiate curd precipitation and formation.
Slide 49
Pasteurization has a significant effect of the flavor profile
of the milk. Cultured dairy products produced from pasteurized
milks tend to have less intense flavor characteristics due to the
heat inactivation of the naturally occurring microorganisms and
enzymes in the milk that contribute to flavor formation. Lactones
and heterocycles are also formed during the heat treatment of raw
milk to contribute cooked flavors.
Slide 50
Cooling The processing of cultured dairy products relies on the
metabolic activity of the starter cultures to contribute to acid
formation and flavor and texture development. Once the desired pH
or titratable acidity is reached for these products, the products
are cooled to 510 C to slow the growth of the bacteria and limit
further acid production and other biological reactions.
Slide 51
Probiotics Probiotics are live microorganisms which, when
administered in sufficient quantity, confer a health benefit to the
host. They must have (a). Viable cells (b). Enough quantity.
Improved carbohydrate digestion in the gastrointestinal (GI) tract.
reduction of the incidence of diarrhoea. immune system enhancement,
blood cholesterol reduction. Official recognition. In light of
these potential health benefits,digestive health is considered as
one of the ten key food trends for 2010. Market predicted to reach
US$30 billion by 2015 (Starling 2010).
Slide 52
Prebiotics Prebiotics are nondigestible food ingredients that
beneficially affect the host by selectively stimulating the growth
and/or activity of one or a limited number of bacteria in the GI
system, and thereby confer health benefits to the host (Roberfroid
2007). This definition overlaps with the definition of dietary
fiber, with the exception of its selectivity for certain bacterial
species and a wider range of health effects. Peptides, proteins,
and lipids contain prebiotics characteristics, but some
carbohydrates have received the most attention, including
lactulose, inulin, and a range of oligosaccharides that supply a
source of fermentable carbohydrate for the beneficial bacteria in
the colon (Prado et al. 2008).