MicroBiology

FOOD FERMENTATIONS ASSIGNMENT – Microbiology

Introduction

History:

The early cradle of civilisation for cheese appears to be that fertile agricultural country “Fertile crescent” situated between the river Euphrates and Tigris in Iraq ( 6000-7000 BC ) . Sir Leonardo Woolley in1924 concluded that cheese had been made from the milk of caprine animals. He came to this decision from the archeological study he carried on around Ur.

A scene on the walls of Ramesid grave ( 100BC ) shows caprine animals being lead to crop and their tegument suspended from poles as bags. As the animate being tegument was convenient for storage of liquid for mobile folks. This lead to storage of milk in the tegument bags and agitation of milk sugars in the warm clime would take to the clotting of milk in bags. These curds which are acidic would hold been broken by the swaying animate beings during the journey to bring forth curd and whey.They used whey as reviewing drinks during hot journeys a curd was preserved by acerb agitation and by adding salt to it which became a high beginning of protein addendum.These activities lead to the premise that the cheese was evolved from fermented milks, by petroleum agitation through the draining whey by a fabric or perforated bowl to go forth solid curds which on salting became cheese. The pierced bowls were found in several locations of Europe and Asia which were made of discharged earthen ware.

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The baskets woven from reed and other root were besides found which were used for run outing whey from curd.

Cheese:

Cheese consists of proteins and fat from milk. It is produced by curdling of milk protein casein which is coagulated by add-on of enzyme rennet.

Comparison between initial substrate and concluding merchandise:

Cow ‘s milk typical cheeseWater- 87 % water- 36 % -39 %Lactose-5 % fat- 30 % -32 %Fat- 3.5 % -4 % proteins- 26 % 28 %Protein- 3.2-3.4 % salt- 2 % -2.

5 %Minerals- & lt ; 1 % minerals- 1 %Lactose- & lt ; 1 %

Difference:

Cheese contains less H2O and more milk solids, signifier of fat and protein than the milk from which it was made. Therefore cheese devising can be concluded as concentration procedure in which the whey is removed and solids are concentrated. Removing H2O non merely concentrates or solidifies the solid affair, but besides decreases microbic affair and enzymatic activity such that cheese is much better preserved than milk.

This procedure occurs via a combination of biochemical, biological and physical-chemical activities.The transition of liquid milk into solid mass of cheese is done via curdling of milk protein. Milk, as noted above contains about 3.

3 % of protein fraction, 80 % of it is casein ( 2.5 % of milk ) and the staying 20 % is jointly known as whey proteins. When milk coagulates, and the curdled stuff is separated the soluble whey proteins are released into H2O or whey fraction. The casein matrix non merely contains some H2O, but besides a big part of lipid fraction that was originally present in the milk.

Cheese readying involves two major rules.

They are

1. curdling of milk2. squashing out H2OThree ways of initial curdling of milk -1. By acids produced by lactic acid bacteriums.2. By add-on of enzyme rennet.3.

By combination of moderate acid add-on ( pH-6.0 ) plus high heat ( & gt ; 85 grades ) .The first manner of cloting milk is based on same rule which is used for yogurt. When milk reaches a pH of 4.6, casein is at its isoelectric point and its minimal solubility, therefore it starts precipitating.

It is of import to gain that casein coagulates at pH 4.6 whether acidification occurs via agitation generated acids or merely by add-on of nutrient class acids into the milk. In fact the ulterior procedure is preferred by some of the manufacturers of bungalow, pick, due in portion to ease of industry and the riddance of starter civilization as an ingredient.The 2nd manner of cloting milk is simple and most normally used method.

This is done by adding enzyme rennet into milk. This enzyme hydrolyzes a specific enzyme peptide bond located between methionine and phenylalanine in K casein. This hydrolysis of this bond is sufficient to clot milk. The hydrolysis of the peptide bond consequences in dissociation of parts of K casein from casein micelle.

Due to this activity the anionic phosphates of beta casein gets exposed. Thus the staying casein micelle becomes sensitive to calcium mediated precipitation.The 3rd manner of cloting milk is a combination of two events.

It is a combination of modern acerb add-on ( pH6.0 ) , plus high heat ( & lt ; 85 grades ) . Whey proteins are denatured under these conditions. Thus the precipitate that formed consists non merely casein, but besides whey proteins.

Even in solutions where casein is absent this procedure can ensue in adequate precipitated whey protein to organize a cheese.E.g. : Ricotta cheese, Latino – manner cheese a queso fresco, queso blanco.Gjetost. ( A whey derived cheese popular in Norway ) .

The 2nd major rule in fabricating cheese is Squashing Out Water from coagulated milk. The first measure involves increasing the surface country of individual big hasty mass by cutting it into literally 1000000s of smaller regular hexahedron of curd. This is because to vaporize H2O from interior matrix of precipitant to outside environment. Smaller the size of the regular hexahedron, the easier for H2O to acquire evaporated from the precipitant. This measure favours an increased rate of synaeresis. Then, when these curds are stirred and so heated, the curds psychiatrist and synaeresis is farther enhanced.

Acidification is another procedure that enhances the rate of synaeresis. As discussed earlier, at pH 4.6 casein reaches its isoelectric point where the H2O keeping capacity lessenings and synaeresis additions.

Stairss involved in cheese devising:

1. Standardization of milk2. Homogenization of milk3. Heat intervention4. Starter cultures add-on5.

Coloring material and additives6. Rennet add-on7. Curdling8. Cuting the clot9. salting10. maturation of cheese

1. Standardization of milk:

Milk varies in composing from season O season, because of strain influences, so the cheese produced at different times of twelvemonth vary in fat to protein ratio. As fat and protein constitute chief organic structure of the cheese it is of import to standardise the milk at the ratio of fat to protein ( casein ) which is fundamentally of 0.

68:1 or 0.70:1 and for petroleum protein as it can be easy estimated the ratio of 0.9:1 can be used.The methods of standardising milk for cheese:If milk is with excessively high fat content it is adjusted by adding skimmed milk, low fat milks or planing the portion of the milk and adding the skim milk to the balance of the high fat milk. Standardizing milk utilizing standard extractor by taking sufficient pick and milk together are of right criterion.

When milk is lacking in fat: so it is adjusted by adding pick, adding milk richer in fat, by adding pick which is produced by planing portion of the milk to the balance of low fat milk.Standardizing of milk to take down fat per centum through usage of standardizing extractor which skims of extra fat pick is less complicated when big capacity silo armored combat vehicles are used. As these armored combat vehicles are preset mathematically i.e.

the fat to protein ratio is preset which extracts the known measure of pick. Standardizing to a higher fat per centum involves adding pick to milk or taking away some of the skim milk, this add-on of pick to raw milk is a complicated procedure as it gives troubles in guaranting equal commixture unless milk and pick are warmed together.Standardization of milk is carried as a portion of entire cheese procedure, affecting heat intervention to destruct unwanted bacteriums before the milk is passed over to cheese devising.

2 ) Homogenization of milk:

Homogenization of skim milk disturbs the Ca casein phosphate composite in milk and salt balance ; it besides breaks the fat globules into smaller size.

As than fat globules are broken into smaller size the original fat globule membrane which cover the globule is non equal. To milk it is supplemented from serum by other protein and lipid constituents. Since the fat globule membranes are disturbed, lipolytic membranes penetrate to the fatty nucleus more quickly. Normally the milk is separated into skim and pick and merely pick is homogenised and later they are combined before concluding heat intervention in instance of some assortments of blue veined cheese. Homogenisation force per unit area used for this intervention varies by all the old experience with the milk supply. By and large two phase homogenises are used. First phase homogeniser runing at low force per unit areas from 6895 to 10342 kN/m2 ( 1000-1500 pounds per square inch ) is used.

The 2nd phase homogenizing operating at 3447 to 5516 kN/m2 ( 500-800 pounds per square inch ) is used. The optimal temperature for homogenization is about sixty-eight grades or 156 F.

3. Heat intervention of cheese milks:

The heat intervention of milk for cheese devising is standardization of biological quality of milk by destructing unwanted or harmful bacteriums and some enzymes which are harmful for cheese doing. In this procedure of heat intervention some bacteriums utile in the cheese devising procedure ( lactic bacteriums ) are destroyed along with some of the milk enzymes lipases.

Therefore cheese shapers use low temperatures in order to continue utile enzymes and bacteriums. Heat intervention of milk comprised of two separate parts. They are temperature to which the milk is heated and the clip during which milk is held at that temperature called as retention temperature.

Which temperatures and keeping times are used depends on the desire of cheese shaper to accomplish certain aims. Therefore low temperatures of 65 grades, for devastation of some coli signifiers are used to maintain the lipase enzymes integral, but at that place purpose should be to destruct infective bacteriums at all times at temperature around ( 71.6 grades ) for 5 seconds. In UK due to job with STAPHYLOCOCCUS AUREUS toxins in cheese, milk is heat treated to 69 grades with 15 seconds of keeping clip and normal HTST intervention. In other many states three systems are in usage concerned with cheese doing. They are-1. Flash heating to temperatures from 75 to 95 grades without keeping clip.2.

High temperature, short-holding systems utilizing temperature from 71-75 grades and keeping clip from 15 to 40 seconds.3. Low temperature long keeping systems utilizing temperatures from 61 to 65 grades and keeping clip of 20 to 40 proceedingss.

After efficient heat intervention so figure of micro beings should hold been reduced by 92-99 % .

If the original Numberss high so the Numberss of subsisters after the heat intervention will be high. A entire putting to death of 99 % is possible in ideal conditions. The subsisters will be capable of proliferation if incubated near to optimum growing temperatures, so the cheese milks should non be held warm for appreciable periods before farther usage.

Equipment for heat intervention:

The equipment used for cheese milk heat intervention is variable. The little volume cheese dairy is equipped with simple VATs or armored combat vehicles which may or may non be jacketed to transport hot H2O or steam.

The big graduated table mill operations require heat money changers for most signifiers of heat transportation into or out of liquid milk or whey, so they are provided with most economical use of heat. The heat money changers are of cannular type or multi-plate type. A composite works made from unstained steel is besides required.

The units including heat money changers, pumps, centrifuges armored combat vehicles etc. Are connected so that air is excluded from the milk being processed. In such a system cleansing and autoclave is automated.Starter civilization add-on: the milk already heat treated is cooled to a temperature of 21-29 grades which is necessary to bring on the growing of inoculated starting motor bacterium. Three most of import activities of starter civilization are:1. Glycolysis – transition of milk sugar to lactic acid.2. Proteolysis – debasement of protein ironss into simpler substances such as peptones peptides, aminic acids, etc.

3. Lipolysis – hydrolysis of fatty acids from milk fat into keto acids, ketones, esters, etc. Which are responsible for spirit and olfactory property.The starting motor can be composed of one civilization strain of a bacteria or a civilization of two, three or more separate types of bacteriums.

Organisms used in cheese as starting motors:

Streptococcus lactic, S. Cremoris, Leuconostic cremoris, and S. Lactis subsp.

diacetylactis are used for low scald cheese. S. lactis produces lactis acerb rapidly and reduces the fabrication clip but some strains produce the antibiotic nisin and some cause acrimonious spirits in cheese. S. cremoris grows more easy and produces good flavoured cheese. So a starting motor can hold appropriately paired strains of S. lactis and S.

cremoris. When more spirit is required in softer cheese assortments S. lactis subsp. diacetylatis is included in the starter civilization.The starter civilization is added harmonizing to formula in measures from 0.05-4 % or5 % the measure of starting motor added is frequently controlled by the penchant of the cheese shaper to let the bacteriums to turn in cheese milk easy in order to bring forth lactic acid required for the following phase.

This maturation of milk by starting motor may be rather prolonged, up to 2hrs, whereas vaccination of larger measures of starting motor ( 2-4 % ) shortens the maturation clip to 5-20 proceedingss. During this ripening period the micro organisms other than starting motor may besides turn. Thus coli signifier beings proliferate in less acerb conditions, but subsequently they are held in cheque by more rapid lactic acid production. The direct-to-the VAT frozen civilization methods of starter civilization are used for vat milk and majority starting motors. Some cheese shapers add starter into the VAT while the filling returns which saves clip. Starter which is farinaceous does non let go of its bacteriums into the milk such granules are hardened by blistering procedure and hence persist in cheese as white batchs.

Colour and Additives:

Colour and any chemicals such as Na nitrate or Ca chloride are added to the milk before it is ripened or while the temperature is raised to renneting temperature of 28.

9-30 grades. Colour need non be diluted before adding to the VAT but must be equally distributed and stirred into the milk. Chemicals must be added in solution and measures which is usually specified by the formula.

Rennet add-on:

Testing of milk for suitableness to have rennet differs from cheese shaper to cheese shaper. The sourness or pH at which rennet is added governs the type of clot and the velocity at clot signifiers. There are two methods of rennet add-on:* The trial cup ( Marshall ) – the cup is a vessel keeping 500ml with an accurately sized hole in the base.

The sides of the cup are straight, white and marked into five divisions. The cup is filled with vat milk and 1ml of rennet is stirred into the milk. The milk runs from the base until it sets. The degree of clot on the side divisions indicates the coagulability of the milk.* The 2nd method uses a vessel keeping 112ml of VAT milk into which is moved 3.5ml of rennet. A straw or a piece of wood coal is made to revolve by the stirring action.

The from adding the rennet until the rotary motion ceases is measured in seconds, where 22s indicate normal curdling and equates with in an sourness of 0.21 % . Milk taking more than 22s is judged as non ready for rennet.Curdling: 10 factors which influence the complete curdling are-* The curd tenseness rises when the measure of rennet per 450litres addition from 28 to 140ml, but it does non increase with more rennet.* The curd tenseness additions with temperature up to 40 grades and so diminutions. Therefore curd formed at 40 grades is rubberlike and will non cut flawlessly if left for excessively long.* Low curd tenseness and longer coagulating times occur if the milk has been cold stored before renneting. Curd tenseness additions with add-on of Ca chloride up to a upper limit.

* The ratio of fat to plane milk can act upon the curd soundness. High fat milk gives softer curds.* Decreased pH additions curd tenseness up to pH 5.8 when the tenseness begins to diminish.

Most milks are rennetted between pH 6.5 and 6.35.* Coating of the K casein by denaturized protein or free fatty acids released by proteolysis and lipolysis affects the completeness of curdling.* Proteolysis or interaction with the amino acids on the either sides of the phenylalanine and methionine in the K casein may ensue in such harm that the cleavage is uncomplete and soft curd consequences.* The sum of whey proteins in the curd affects the soundness of the curds.* Dilution with affects the curd tenseness.

* Some coagulators produce softer curds ab initio.

Cuting the clot:

The clot is ready to cut after a period of from 25min to 2hours. But some cheese shapers calculate the clip for cutting by multiplying the clip taken to put by three.The chief method employed is to immerse the manus, rod or thermometer root, below the surface bed and to raise the clot doing it to interrupt in a cleavage line.

A clear cleavage with green whey at the base of the cleft indicated that the curd id ready cut. A soft irregular cleavage with white whey indicates the curd is excessively soft. The sides of the cleft show the quality of curd. These farinaceous curds indicate the curd Idaho excessively steadfast.

If the clot becomes excessively steadfast, knives or curd surfs crush the curd instead than cutting it flawlessly. During the film editing of clot, and in blistering procedure the cuts surface environing each curd atom assumes some importance in the cheese curd ripening during which it becomes about an osmotic membrane. Fat globules are held in the matrix of casein web partially by physical enclosure and partially by loose bonding of the globule membrane and protein.

Stiring and scalding:

Blistering or cooking the curd causes the protein matrix to shrivel and throw out more manner. The addition in temperature besides speeds up the metamorphosis of bacteriums enclosed within the curd.

Lactic acerb production additions, the pH diminutions and this sourness aid in shriveling the atoms to throw out more manner. Lactose is the chief metabolite of the lactic bacteriums in curd for the production of lactic acid. The strength of the lactose solution is the commanding factor in the metamorphosis of bacteriums.

So, lessening in lactose concentration effects the growing of bacteriums and production of lactic acid.The maximal scald temperature used is beyond 40 degree centigrade.

Salting of cheese:

Untextured cheese is salted chiefly by submergence in seawater at a temperature of 8-16 grade for 15 min. Up to 5 yearss depending on size of cheese and type of curd. The purpose is produce the salt content of 1.5-2.

4 % . The salting phase halts the acerb production so the ph of the curd does n’t diminish after salting. The rate and pH at which salt is added to the curd are the commanding factors in farther maturation of the cheese.Cheese maturation: newly made cheese has basically none of the spirit, olfactory property, and visual aspect belongingss of aged or ripened cheese. Cheese maturation is a consecutive procedure with each measure trusting on the preceding measure.

Many factors contribute to maturing procedure, including the micro beings, enzymes and chemical & A ; physical reactions. Manipulating and commanding these activities and reactions depend on features intrinsic to the cheese such as wet present inside cheese, pH of cheese, salt content, Eh. The extrinsic factors that influence the procedure of maturing include managing of milk, temperature and humidness of the maturation room.

Bibliography:

1 ) cheese doing pattern by R.scott, 2nd edition, P 1, 120-124, 133-149, 186-190, 1952 ) Microbiology and engineering of fermented nutrients by R. W. hutkins, p 145-205.