Etiket Arşivleri: Introduction

Introduction the Food Processing Industry

INTRODUCTION

THE FOOD PROCESSING INDUSTRY
HISTORY OF FOOD PROCESSING
PROCESSING CONCEPTS
GENERAL PROCESSING CONCEPTS
KINETICS OF QUALITY CHANGE
SUMMARY
Vocabulary
food processing preservation raw materials ingredients marine materials intermediate foodstuffs value added kindred manufacture or process animals fowl dairy products, canned and preserved fruits and vegetables, grain mill products, bakery products, sugar and confectionery products beverages sophistication shelf life thermal energy
Vocabulary2
commercial refrigeration, orange juice concentrate, storage, blend retort sterilization pasteurization, inhibit microbial growth potato flakes elevated temperatures pathogens Blanching spoilage organisms inactivate selected enzymes quality deterioration pathogenic spores heat sensitive thaw vulnerability storage and distribution
THE FOOD PROCESSING INDUSTRY
Definition of food processing
The status of food processing industry

major categories of food products
The major categories under food and kindred products include meat products, dairy products, canned and preserved fruits and vegetables, grain mill products, bakery products, sugar and confectionery products, fats and oils, beverages, and miscellaneous food preparations and kindred products.
The status of food processing industry
The food processing industries are among the largest of 20 industry groups within the manufacturing sector of the U.S. economy. in 1985, the value of shipments from the food processing industry was close to $302 billion. over $400 billion by 1995. nearly double the size of petroleum refining and 3 times the magnitude of the paper industry.
The value of production from the food processing industry is $ 100 billion in 2003 in China .
Definition of food processing
A simple definition of food processing is the conversion of raw materials or ingredients into a consumer food product.
“Commercial food processing” is defined as that branch of manufacturing that starts with raw animal, vegetable, or marine materials and transforms them into intermediate foodstuffs or edible products through the application of labor, machinery, energy, and scientific knowledge.
HISTORY OF FOOD PROCESSING
Some of the earliest forms of food processing resulted in dry food products. These references to various types of commodities date to very early times and the use of thermal energy from the sun to evaporate water from the product and establish a stable and safe dry product

The history of chilled and/or refrigerated foods dates to very early times as well. The first references are to the use of natural ice used to preserve food products for extended periods of time. A patent for use of a commercial refrigeration process for fish was registered in l842.

The use of high temperature to produce safe food products dates to the 1790s in France. Napoleon Bonaparte offered a prize to scientists to develop preserved foods for the armies of France. This offer lead to the research of Nicholas Appert and the commercial sterilization of foods. In the 1860s, Louis Pasteur, working with beer and wine, developed the process of pasteurization.
Purpose of processing
One purpose of processing is to achieve and maintain microbial safety in the product. It was quite evident that foods without some form of preservation could create illness after consumption. The second common factor is the interest in extending the shelf life of the product. In most situations, there is a desire on the part of the consumer to have an opportunity to acquire many of the seasonal commodities on a year–round basis.
PROCESSING CONCEPTS
Concentration, freezing,canning, drying,
manufacturing of orange juice concentrate
Manufacturing of frozen peas
Pasteurization of Milk
Manufacture of a canned soup
Manufacture of dry potato flakes

manufacturing of orange juice concentrate
Beginning with several preliminary steps such as washing and grading, the first key step is juice extraction. In commercial operations, removal of the juice from the orange occurs in a highly efficient and high-volume process. Following extraction, the juice is concentrated by reducing the water content while retaining the desirable components of the product before the product is placed in the final package for delivery to the consumer.

The shelf-life is extended further by reducing the temperature to well below the freezing point of water. The partially frozen product has a highly desirable storage stability for extended periods of time. The frozen juice concentrate is placed in storage and is maintained in the frozen state until the consumer is prepared to use the product.
Manufacturing of frozen peas
The processing steps begin with the harvesting of the vegetable, followed by a series of cleaning and sorting steps. After cleaning and sorting, the first processing step is blanching. This mild thermal treatment is critical in establishing extended shelf life. Following the blanching step, the product is packaged and the temperature is reduced to well below the freezing point of water.

The combination of blanching and freezing provides a significant shelf life for a product. The product is held in a frozen state throughout storage and distribution to the consumer. The product is maintained in a frozen state until the consumer is ready for final preparation and consumption
Manufacture of a canned soup
the raw materials are ingredients that have received some degree of preliminary processing. These ingredients are blended and concentrated to reduce the water content to some predetermined level. After the concentration step, the product is filled into the can and sealed. Following the filling operation, the most critical step in the manufacture is the retort sterilization of the can and contents.

The retort sterilization step accomplishes the desired long-term shelf-stability of a product. Following the commercial sterilization step, the product is placed in storage for distribution to the consumer. These types of products are shelf stable, with nearly unlimited shelf life at room temperatures.

Pasteurization of Milk
The steps involved begin with raw milk at the point of production followed immediately by refrigerated storage to inhibit microbial growth. The key step in the manufacturing of the final product is pasteurization, during which the product temperature is elevated to an established value as required to ensure microbial safety Following pasteurization, the product is filled into containers and placed in refrigeration storage.
Manufacture of dry potato flakes
After cleaning and sorting, the first key step is peeling of the raw potato. At this point the raw potatoes are converted into a slurry, followed immediately by drum drying to remove water. The combination of producing the potato slurry along with the type of drying creates the appearance of a potato flake. This dry product has significant storage stability at room temperature placed in a container.

GENERAL PROCESSING CONCEPTS
Most food processing operations are designed to extend the shelf life of the product by reducing or eliminating microbial activity. This general objective implies that the processing operation meets the minimum requirement of ensuring any human health safety concerns associated with microbial activity.
(a) The addition of thermal energy and elevated temperatures
(b) The removal of thermal energy or reduced temperatures
(c) The removal of water or reduced moisture content
(d) The use of packaging to maintain the desirable product characteristics established by the processing operations.

The addition of thermal energy and elevated temperatures
Numerous food processing operations use thermal energy to elevate product temperatures and achieve extended shelf life. Pasteurization is an excellent example of a processing operation utilizing an established time/temperature relationship to eliminate vegetative pathogens from a food product,it also reduces the population of spoilage organisms resulting in extended shelf life of the product at refrigeration temperatures.
Blanching
Blanching is a process similar to pasteurization but with specific application to fruits and vegetables. Again the process involves the use of an established time/temperature relationship as required to inactivate selected enzymes within the food product. In the final analysis, the result of the process is product stability and the reduction of product quality deterioration during storage.
Commercial sterilization
Commercial sterilization is the use of an established temperature/time relationship to eliminate selected pathogenic spores from a food product The same process also causes a significant reduction in spoilage microorganisms in the product and the absence of oxygen within the container prevents growth even at room temperatures.

Disadvantages of Thermal Processes
One of the most recognized disadvantages is the reduction in nutrient content of the product due to the thermal process. Most nutrients in food are heat sensitive and are reduced by processing at even minimum time/temperature relationships. In similar manner, most quality attributes in food products are heat sensitive, and the use of typical thermal processes results in a reduction in desirable quality attributes
The removal of thermal energy processes
There are two categories of processes based on this concept. The chilling followed by storage at refrigeration temperatures is used to control growth of spoilage microorganisms and achieve the desired extended shelf life. This approach to extended shelf life is used for many perishable products, including fresh fruits and vegetables, as well as fresh meats and seafoods.
The process of food freezing
The removal of additional thermal energy leads to frozen foods. The process involves sufficient removal of thermal energy from the product to cause phase change of water within the product inhibit microbial growth, and achieve extended shelf life. The formation of ice within the food product can result in significant changes in physical characteristics of the product both as a result of the process and subsequent thawing.
Disadvantages of frozen foods
These include the vulnerability of the product to thermal abuse during storage and distribution. This particular disadvantage would apply to both refrigerated foods and frozen foods. In addition, frozen foods have the additional disadvantage of the undesirable quality changes resulting from formation of ice crystals within the product structure. In most situations, these undesirable changes are associated with the size of the ice crystals formed during the process.
Removal of water
To reduce product moisture content and achieve extended shelf- life. The process objective is limit or eliminate growth of microorganisms.
One of the primary categories of water-removal processes is referred to as product concentration. These processes remove sufficient water from a liquid food to inhibit microbial growth. higher concentration limit the availability of water to microbial populations and inhibit microbial growth.
Dehydration
These processes provide removal of water from a food to a level where microbial activity is limited or eliminated. Most often, dehydrated foods have moisture contents that are well below 10%. Again, the inhibiting effect on microbial activity is associated with limiting the availability of water for microbial growth.
The disadvantages with the removal of water
The dehydrated foods is very different in physical appearance as compared to the original product. The disadvantages include (1) the significant changes in the product including visible reductions in product quality attributes, (2) those associated with the amount of energy required to remove water from the food products.
Packaging
Packaging is required to maintain the product characteristics. Packaging materials and containers vary significantly from one product to another and are influenced by the type of processing operations used prior to packaging. The packaging material is selected to maintain the desirable product characteristics.
KINETICS OF QUALITY CHANGE
During processing,the product quality attributes changes. These changes include positive impacts such as the reduction of microbial populations, along with loss of nutrients or more visible attributes like color. the impact of processing is a function of time. many of the changes may be described by the following first–order equation:
First order reaction

Influence of time & temp.
The impact of a process on quality will vary with the processing time and the rate constants (k) which is influenced by temperature. According to the Arrhenius equation .
The Influence of Temperature on the Rate Constant

The Arrhenius equation and similar expressions are very useful in describing the impact of temperature on the rate of change in product quality during processing and storage. In addition, the combined influence of temperature and time for a process is estimated by expressions like Eq.(1.2) and (1.4).

Q=Q0-kt

SUMMARY
Food processing is the process to ensure food product safety and extend shelf life. These processes and the associated steps make up one of the larger manufacturing industries. Most of food processing history is based on preservation of the food product, either to control human health concerns or to extend the product shelf life.
In general, food processing operations are associated with the use of thermal energy to elevate product temperatures, remove thermal energy from a product and reduce temperature, remove water, and use packaging to maintain the product attributes.

Problems
How many concepts associated with processing of foods are there? What are they?
What are the principles of these processing concepts to achieve extended foods shelf-life
What is Arrhenius equation, how to make use of it in food processing and storage.
How to understand the relationship between food processing and storage.

Introduction

DEFINITION OF FOOD FERMENATION:

Microbial(1) activities(2), usually anaerobic(3), on suitable substrate under controlled(4) or uncontrolled (5) conditions resulting(6) in the production of desirable (7) foods or beverages which are characteristically more stable(8), palatable(9) and nutritious(10) than the raw substrate.

What do fermentation scientist do:

1-Fermentation industry beer, wine, dairy fermentation,  pickling, oriental fermented foods

2- Industrial fermentations organic acids, antibiotics, medicine

3-New product development genetic engineering

4-Teaching, Research, Extension University, Government,  Industry

History of Fermentation

1-Pre-scientific ERA– before 17th century

n  a-traditional microbiological process( beer, wine, bread, vinegar, cheese, pickling

n  b-traditional food preservation   sun drying, salting, freezing

n  c-food borne diseases and spoilage    accepted as fate or act of God

2-ScientificEra

n  a- Elucidation of biological processes through scientific developments in microbiology ,

n  -improvement of traditional processes

n  -development of new industries based on m.o. not previously exploited

n  -antibiotics, enzyme biotechnology

n  b-new preservation procedures   freeze drying, microwave, radiation

n  c-control of food spoilage and food borne  diseases by understanding mechanism better

3-Future

n  a- continue to improve traditional methods

n  b-biotechnology

n  c-new technologies

Some cornerstones of fermentation

n  Discovery of microorganism by Antonie von Leewenhoek

n  1810 Canning by Appert

n  1854 Pasteur showed that microbes are responsible for fermentation.

n   Fermentation is the conversion of sugar to alcohol to make beer and wine.

n   Microbial growth is also responsible for spoilage of food. Bacteria that  use alcohol and produce acetic acid spoil wine by turning it to vinegar (acetic acid).

General classification of microorganisms

Microbial activity

n  Microorganisms that carry out their metabolism using oxygen are referred to as aerobic microorganisms.

n  Some microorganisms can  substitute nitrate, others sulfate or ferric ion, for oxygen and thus grow in the absence of oxygen. These microorganisms are referred to as anaerobic.

n  Obligate (or strictaerobes: the presence of oxygen is required

n  Obligate (or strictanaerobes: the absence of oxygen is required, oxygen is toxic to the cells

n  Facultative anaerobes: can survive with or without oxygen

n  Microaerophiles: require low concentrations of oxygen and don’t do well either at atmospheric oxygen concentrations or without oxygen

n  Biotechnology: Biotechnology is the scientific activity concerning the integrated application of biochemistry, microbiology and process technology on biological systems on the behalf of industrial  processes and environmental management..

n  Biochemical engineering The application of engineering principles to biologically based processes (in fermentation processes: manipulating living cells so as to promote their growth and production in a desired way); Maximize productivity Minimize costs

n  Fermentation , the act or process of fermenting; a slow decomposition process of organic substances  induced by microorganisms, or by complex nitrogenous organic substances (enzymes) of vegetable or animal origin, usually accompanied by evolution of heat and gas, e.g. alcoholic fermentation of sugar and starch, and lactic fermentation.

    Nutrient requirements

n  All microorganisms need for their microbial activity the presence of several nutrients.

n  Water: Major component of all fermentation process is consistent, clean water. PH, dissolved salts and microbial contamination are important factors. Long before plants are set up near by good water sources.  Now water treatment is applied. There might be different  characteristic water requirement for different type of food production.

n  Hard water for English Burton beer, high carbonate water for darker beers.

n  In SCP production large amount of water is used so recycling should be applied.

Carbon source:

n  -Carbohydrates Carbohydrates are capable of being used by all microorganisms,.

n   Glucose is the most readily metabolized sugar.

n   Most fungi can use disaccharide’s.

n   Most common carbohydrate is starch( from maise, cereals and potatoes)

   Sugar cane, sugar beet.

n   Corn steep liquor which is by product of starch production from corn.

n  -Hydrocarbons : petroleum products

n  -Lipids

          Energy source:

n  either from light(photosynthesis)or oxidation of medium components

n  Most industrial organisms are chemoorganotrophs( common

   energy source organic materials.

n  Purines and pyrimidines :

n  It is generally only in bacteria that cases of purine and  pyrimidine metabolism have been reported.

    Vitamins and growth factors

n  There is considerable species variation in the requirements of vitamins and related factors by other microorganisms. 

n  Many of the natural carbon and nitrogen sources contain all or  some of the required vitamins. Generally, vitamins A, C, D, and K are not necessary for growth. In glutamic acid production biotin is required.

Nitrogen sources

n  Inorganic nitrogen sources: ammonia gas and ammonium nitrates( cause alkaline drift),  ammonium salts ( cause acidic drift)

n  Organic nitrogen amino acids, proteins, urea

Chemical elements and inorganic ions

n  Mineral nutrients required by microorganisms are species dependent but consists generally of Fe, K, Mg, Mn.

n  Sometimes S, N, Ca, Co, Cu, P, Zn are required.

   AEROBIC CATABOLISM

    Microbial cells consist of a wide variety of chemical substances which have to be synthesized or taken up from outside the cell.

n  These processes require a lot of energy.

n  Each cell has to provide the necessary energy and different possibilities  for its supply are developed: a number of organisms can use light energy; most microorganisms, of course, obtain it from the oxidation of chemical compounds.

n  Chemicals used as sources for energy are metabolized and energy is conserved either by substrate-level phosphorylation or by building up an electrochemical gradient across the cytoplasmic membrane.

The major carbohydrate-metabolizing pathways are:

n  Embden–Meyerhof–Parnas (EMP) pathway, also called glycolysis

n  Entner–Doudoroff (ED) pathway

n  pentose phosphate (PP) pathway.

n  The three pathways differ in many ways, but two generalizations can be made:

n  1. All three pathways convert glucose to glyceraldehyde 3-phosphate (GAP) by different routes.

n  2. The GAP is converted to pyruvate via reactions that are the same in all three pathways.

      Transport into the Cell

n  1. Passive transport: facilitated diffusion (e.g. Zymomonas mobilis and erythrocytes). As facilitated diffusion is only found in a few organisms or cell types, it will not be discussed further here.

n  2. Active transport: symport with a proton, protons or sodium ions. In this process of active transport the substrate can accumulate to a high concentration in the cytoplasm in a chemically unaltered form. Active transport requires energy and is linked to energy available from ion gradients or ATP hydrolysis.

n  3. Group translocation: phosphotransferase system (PTS). Group translocation is the process whereby a substance is transported while simultaneously being chemically modified, generally by phosphorylation.

Embden–Meyerhof–Parnas Pathway

n  The process of sugar breakdown is called glycolysis.

n  The enzymatic reactions of a glycolytic pathway will form pyruvate  coupled to ATP synthesis by substrate-level phosphorylation.

n  The overall reaction is:

n  Glucose+2 ADP3−+2 Pi2−+2 NAD+2 Pyruvate−+2 ATP4−+2 NADH+2 H++2 H2O

Entner–Doudoroff Pathway

n  There is a second important pathway for the breakdown of carbohydrates which is only found in prokaryotes.

n   It was first discovered in 1952 by Entner and Doudoroff in Pseudomonas saccharophila.

n  The ED pathway viewed as an alternative to the EMP pathway

n  Prokaryotes, which carry out the ED pathway, lack the key enzyme phosphofructokinase of the EMP pathway.

n  Because of the net production of only 1 mole ATP per mole glucose fermented, this pathway is usually found in aerobic bacteria

n  The overall reaction is:

n  Glucose+NADP++NAD++ADP3−+Pi2−2 Pyruvate−+NADPH+NADH+3H++ATP4−

      Pentose Phosphate Pathway

In bacteria, about 80% of the glucose is degraded aerobically via the EMP and ED pathway,about 20% enters the PP pathway for generation of ATP, regeneration of NADPH and the synthesis of precursors for nucleotide
and aromatic amino acid biosynthesis. So many variations of the PP pathway are possible, depending on the need of the growing cell.
 

The overall reaction is:

Glucose+ATP4−+2 NADP++H2OPentose 5-P2−+CO2+ADP3−+2 NADPH+3 H+

Distribution of Embden–Meyerhof–Parnas (EMP),

Entner–Doudoroff (ED), and pentose phosphate (PP) pathway in bacteria and some eukarya

n  Oxidation of Pyruvate to Acetyl Coenzyme A

n  In all the major carbohydrate catabolic pathways, pyruvate is a common product,

n  oxidized during aerobic growth by the pyruvate–dehydrogenase complex:

n  Pyruvate−+NAD++CoASHAcetylCoA +CO2+NADH

The Tricarboxylic Citric Acid Cycle

To finish the respiratory metabolism of glucose, acetyl coenzyme A enters the tricarboxylic acid (TCA) cycle to produce carbon dioxide, water, reduced coenzymes and ATP

The overall reaction is:

Acetyl CoA+ADP3−+Pi2−+Q+2 H2O+NADP++2 NAD+   2 CO2+ATP4−+QH2+NADPH+2 NADH++H++3 H++CoASH

n  Other Substrates as Sources for Metabolic Activity

Living organisms can use a variety of substrates for growth:

almost every naturally occurring organic compound can serve as a source for cell carbon or energy.

These can be low-molecular-mass compounds or polymers,  such as glycogen, starch, cellulose, polysaccharides, lipids, fatty acids and proteins.

Polymers cannot enter the cell; they must be cleaved outside into monomers and dimers which are small enough to be transported into the cell and then enter the metabolic pathways.

Carbohydrates  Glucose is not the only carbohydrate that can be converted to pyruvate by glycolysis

          Anaerobic Breakdown of Carbohydrates

The terms glycolysis and fermentation have been applied to the anerobic decomposition of carbohydrate to the level of lactic acid.

n  The final product in some organisms is lactic acid; in others, the lactic acid is further metabolized anaerobically to butyric acid, butyl alcohol, acetone and propionic acid.

The two most common forms of fermentation are lactic and alcoholic.

          Fermentation

In glycolysis, the same reactions occur whether oxygen is present or not.

The products are primarily pyruvic acid, NADH and ATP.

The essential difference between aerobic and anaerobic processes occurs with pyruvic acid and NADH.

In the case of fermentation reactions, pyruvic acid is converted to a variety of organic compounds.

These reactions involve the transfer of electrons and hydrogen from NADH to organic compounds.

Fermentation is a major source of energy for those organisms that can only survive in the absence of air (obligate anaerobes).

n  Other fermentative organisms that can grow in the presence or absence of air (facultative anerobes) use fermentation as a source of energy only when oxygen is absent.

In fermentation, energy gain is very low and occurs as a result of substrate-level phosphorylation.

The synthesis of ATP in fermentation is restricted to the amount formed during glycolysis.

During glycolysis, glucose is oxidized to pyruvic acid, which is the physiologically important first intermediate product in the aerobic or anaerobic dissimilation of glucose.

Pyruvate may also be reached via the metabolism of sugars other than glucose or the metabolism of fatty acids and amino acids.

Pyruvate is a sort of Grand Central Station, in that it is the point of arrival and departure of a wide variety of metabolic substrates and products.

Pyruvate is reduced to lactic acid.

It may also be decarboxylated and reduced to ethyl alcohol.

Conversely, it may serve as the  source of amino acids, fatty acids and aldehydes.

The anaerobic system of biological oxidations that does not use oxygen as the final acceptor of electrons is called anaerobic respiration.

In anaerobic respiration, compounds such as carbonates, nitrates and sulphates are ultimately reduced.

Many facultative anaerobic bacteria can reduce nitrate to nitrite under anaerobic conditions.

This type of reaction permits continued growth when free oxygen is absent, but the accumulation of nitrite which is produced by the reduction of nitrate is eventually toxic to the organisms.

Certain species of Bacillus and Pseudomonas are able to reduce nitrite to gaseous nitrogen. This process occurs when aerobic organisms are grown under anaerobic conditions.

The organisms which reduce sulphate and carbonate are strictly anaerobic

n  Desulfovibrio desulfuricans reduces sulphate to hydrogen sulphide as it oxidizes carbohydrate to acetic acid.

Methanobacterium bryanti is able to couple the reduction of CO2 to methane with the oxidation of carbohydrate to acetic acid.

Some organisms (strict aerobes) are enzymically equipped to use only free oxygen as the final hydrogen (e−) acceptor, but others (facultative aerobes) are equipped to use as the final hydrogen (e−) acceptor either free oxygen or some reducible inorganic substrate, commonly a nitrate.

n  In fermentations, usually only NAD or NADP functions as the hydrogen (e−) carrier. Flavine adenine dinucleotide (FAD) and cytochrome systems are not required since the final hydrogen (e−) acceptor is not oxygen but an organic substance – commonly pyruvic acid.

Fermentation may be caused by facultative organisms under anaerobic conditions, e.g. Saccharomyces cerevisiae, by strictly anaerobic organisms, e.g. Clostridium or by organisms that do not utilize free oxygen, e.g. species of Lactobacillus.

Depending on the conditions of growth, the substrate and the organisms involved, the end products of fermentation vary greatly.

          Lactic Fermentation

  The products of glucose fermentation by all species of Streptococcusmany species of Lactobacillus and several other species of bacteria are mainly lactic acid with minor amounts of acetic acid, formic acid
and ethanol
.

Several species of Streptococcus produce more than 90% of lactic acid based on the sugar used, and hence this type of fermentation is referred to as homolactic fermentation.

The homolactic fermentation which forms only lactate is the characteristic of many of the lactic acid bacteria, e.g. Lactobacillus casei, Streptococcus cremoris and pathogenic streptococci, a heterolactic fermentation converts only half of each glucose molecule to lactate.

Both these fermentations are responsible for the souring of milk and pickles.

n  The heterofermentative metabolic sequence found in Leuconostoc and some species of Lactobacillus ferments glucose according to the equation: GlucoseLactate+Ethanol+CO2

The heterofermentative metabolic sequence in Leuconostoc and some species of
Lactobacillus
.

          Alcoholic Fermentation

The major substrates yielding ethanol are the sugars which in yeasts are degraded to pyruvate by the EMP or glycolytic pathway.

There is a net yield of one ATP for each pyruvate formed from glucose.

The identical metabolic route for ethanol formation is found in the bacterial species Sarcina ventriculi, Erwinia amylovora and Zymomonas mobilis, which also possess the enzymes pyruvate decarboxylase and alcohol dehydrogenase.

       Butyric Fermentation

The butyric fermentation is initiated by a conversion of sugars to pyruvate through the EMP pathway.. The ATP yield per mole of glucose fermented is 2.5 moll

Fermentation of glucose to butyrate by Clostridium butyricum, C. kluyveri and C. pasteurianum. FdF, Ferredoxin F

      Mixed Acid (Formic) Fermentation

This is a characteristic of most Enterobacteriaceae.

These organisms dispose of their substrate in part by lactic fermentation

  but mostly through pyruvate breaking down into formate  and acetyl-CoA, which in turn generates an ATP.

The formic fermentation yields three ATP per mole of glucose fermented (compared with two in lactic fermentation.

           Propionic Fermentation

This pathway extracts additional energy from the substrate.

Pyruvate is carboxylated to yield oxaloacetate, which is reduced to yield succinate and is then decarboxylated to yield propionate.

The lactate is first oxidized to pyruvate; part is then reduced to propionate and the rest is oxidized to acetate and CO2:

This process of extracting energy from lactate yields only one ATP per nine carbon atoms fermented.

n  Hence, propionic acid bacteria grow slowly

General pathways for the formation of fermentation products from glucose by various organism

Overview of fermentation products formed from pyruvic acid by different bacteria.

Butanol and acetone fermentation in Clostridium acetobutylicum.(strict anaerobe)

Metabolic  regulators added
to media 
Precursors

Some intermediary chemicals, when added to fermentation medium directly incorporated to product Example : phenylethylamine, phenylacetic acid in penicillin fermentation

Inducers
:  
Compounds that increase production of final products during fermentation.( Common in enzyme fermentations)Example: To induce alphaamylase production via fermentation add starch( an inducer and substrate for the enzyme )

Inhibitors:   When certan inhibitors are added to fermentations more of a specific product may be produced or a metabolic intermediate which is normally metabolised is acumulated. Example : Ethanol fermentation may be modified to produce glycerol by adding sodiumbisulphite (acetaldehyde is electron acceptor  in forming NAD+ from  NADH2 , if sodiumbisulphite is added it  forms complex with acetaldhyde and it is no longer electron acceptor, instead dihydroxyacetonephosphate act as electron acceptor then when it is reduced glycerol is formed)

Typical Inoculum Preparation

CLASSIFICATION OF FERMENTATION  PROCESSES

BASED ON DEPENDENCE OF PRODUCT FORMATION ON ENERGY METABOLISM

Type I: The product is derived directly from primary energy metabolism. ( growth, carbohydrate metabolism and product formation runs parallel.

Examples: Single cell production, ethanol, gluconic acid production

                                                                                                                                                             time

________________     specific growth rate

————————-              specific carbohydrate consumption rate

……………………………              specific product formation rate

Type II: The product is also derived from the  substrate used for the primary energy metabolism, but production takes place in a secondery pathway which imary meatabolism

Examples : citric, itaconic and some amino acids productions

Type III:

Primarymetabolism functions first,accomponied by substrate consumption and growth. Afterwards the product is formed by the rections of intermediary metabolites.

Example: antibiotics and some vitamin productions

        SUBMERGED FERMENTATIONS               

n  Industrial fermentations may be carried out either batchwise, as fed-batch operations, or as continuous cultures.

Batch and fed-batch operations are quite common, continuous fermentations being relatively rare.

For example, continuous brewing is used commercially, but most beer breweries use batch processes.

Fermentation methodologies.

(A) Batch fermentation.

(B) Fed-batch culture.

(C) Continuous-flow well-mixed fermentation.

      (Feed: F, Xf, Sf  ,Harvest : F, X, S, P,  Volume: V time: t)

(D) Continuous plug flow fermentation, with and without recycling of inoculum.

Typical growth profile of microorganisms in a batch submerged culture

A batch fermentation can be considered to be a closed system.

At time t=0 the sterilized nutrient solution in the fermentor is  inoculated with microorganisms and incubation is allowed to proceed.

n  In the course of the entire fermentation, nothing is added,  except oxygen (in case of aerobic microorganisms), an antifoam agent,  and acid or base to control the pH.

The composition of the culture medium, the biomass concentration, and the metabolite concentration generally change constantly as a result of the metabolism of the cells.

Lag phase

Physicochemical equilibration between microorganism and the environment following inoculation with very little growth.

Log phase

By the end of the lag phase cells have adapted to the new conditions of growth. Growth of the cell mass can now be described quantitatively as a doubling of cell number per unit time for bacteria and yeast’s, or a doub­ling of biomass per unit time for filamentous organisms as fungi.

By plotting the number of cells or biomass against time on a semilogarithmic graph, a straight line results, hence the term log phase.

Although the cells alter the medium through uptake of substrates and excretion of metabolic products, the growth rate remains constant during the log phase.  Growth rate is independent of substrate
concentration as long as excess substrate is present.

Stationary phase

As soon as the substrate is metabolized or toxic substances have been formed, growth slows down or is completely stopped.

The biomass increases only gradually or remains constant during this stationary phase, although the composition of the cells may change.

Due to lysis, new substrates are released which then may serve as energy sources for the slow growth of survivors.

The various metabolites formed in the stationary phase are often of great biotechnological interest.

Death phase

In this phase the energy reserves of the cells are exhausted. A straight line may be obtained when a semilogarithmic plot is made of survivors versus time, indicating that the cells are dying at an exponential rate.  

The length of time between the stationary phase and the death phase is dependent on the microorganism and the process used.

The fermentation is usually interrupted at the end of the log phase or before the death phase begins

 Cell growth modeling in a batch reactor

The simplest way to model cell growth will be to consider an unstructuredunsegregated model for cell growth. For this kind of model,

rx = dX/dt = µX
(1)

where,

rx = rate of cell generation (g/l-hr)

X = cell concentration (g/l)

µ = specific growth rate (hr-1)

Monod’s equation

µ = µmaxS/(Ks +
S)                  
(2)

where,

µ= specific growth rate (hr-1)

µmax = maximum specific growth
(hr-1)

S = substrate concentration (g/l)

KS = saturation constant for
substrate (g/l) ( substrate concentration at ½ of µmax)

 

Figure depicts the dependence of µ on S according to Monod’s equation.

One should note that Monod’s equation is empirical and does not have any mechanistic basis. The equation is only valid for an exponentially growing culture  under condition of balanced growth.

The equation   does   not work   well   in   transient conditions. Despite   its   simplicity  and no fundamental basis, it works

Diauxic growth :

When two fermentable substrates are available readily fermentable  one will be used first and  when it is exhausted second one will be used.

 (when  glucose and galactose are exist in lactic fermentation glucose will be used first and then galactose)

Fed-batch fermentation

An enhancement of the closed batch process is the fed batch fermentation. In the fed-batch method the critical elements of the nutrient solution are added in small concentrations at the beginning of the
fermen­tation
 and these substances continue to be added in small doses during the production phase.

n  d(VX)/dt= VµX

n  X* dV/dt+ V*dX/dt=  VµX

n  Since F= dV/dt

n  µ= F/V+ 1/X*(dX/dt)

n  D=F/V ( dilution rate)

µ=
D+ 1/X*(dX/dt)
 

Continuous fermentation

nIn continuous fermentation, an open system is set up.

 Sterile nutrient solution is added to the bioreactor continuously and an equivalent amount of converted nutrient solution with microorganisms is simultaneously taken out of the system.

n  In the chemostat in the steady state, cell growth is

controlled by adjusting the concentration of one substrate.

In the turbidostat, cell growth is kept constant by using  turbidity to monitor the biomass concentration and the rate of feed of nutrient solution is appropriately adjusted.

Continuous bioreactor dynamics

For a continuously fed bioreactor, the cells are continuously supplied substrate at growth limiting level,  and hence they remain in the exponential phase.

nSince the cells remain in the exponential phase, Monod’s equation can be applied.

 A cell balance on the reactor can be written
as

 

                               FX – FXf +
V(dX/dt) = rx     
 (3)

where,

F = volumetric flow rate (l/hr)

X = cell concentration inside the reactor and in the outlet stream
(g/l)

Xf = cell concentration in the feed (g/l)

V = reactor volume (l)

rx = rate of cell generation (g/l-hr)

 

nFor a sterile feed (Xf = 0), and noting that the reaction rate can be written in terms of the specific growth rate (rx = µX),  equation (3) can be reduced to

 

dX/dt = (µ-
D)X
(4)

where,

D = dilution rate = F/V (hr-1)

 

nA balance on the substrate yields the following equation

 

FS – FSf + V(dS/dt) =
rsV       
(5)

where,

F = volumetric flow rate (l/hr)

S = cell concentration inside the bioreactor and in the outlet stream (g/l)

Sf = substrate concentration in the feed (g/l)

V = reactor volume (l)

rs = rate of substrate consumption (g/l-hr)

 

A yield
parameter (Yx/s) is defined that relates the amount of cell mass produced per
amount of substrate consumed, and is mathematically represented as

 

Yx/s = mass
of cells produced/mass of substrate consumed = rx/-rs

Combining
equations (1), (5), and (6) yields

 

dS/dt = D(Sf – S) –
µX/Yx/s       
(7)

 

The CSTBR
(continuous stirred tank bioreactor) is now completely described by equations
(4) and (7)

At SS (with fixed Sf and D),                              µ
= D   
(8)

S = DKS/(µmax –
D)                
(9)

X = Yx/s (Sf – S)
(
10)

D  must be less than µmax for a realistic value of S to be achieved.

 

Relationship between dilution rate and specific growth rate for a steady
state CSTBR

 

n  X = 0   (11) and S = Sf  (12)

n  Equation (11) and (12) define a situation called washout.

nThis situation is encountered whenever the value of dilution rate equals or exceeds µmax.

nA rigorous discussion of washout would point to the fact that whenever µ (Sf), i.e., µ evaluated at Sf , is less than µmax, then the critical dilution rate for washout will occur at D = µ (Sf), and not at D = µmax.

nStart up is an important consideration as well. The general procedure in the start up avoiding washout would be to initiate cell growth in a batch mode until the exponential phase is reached.

nAt this point, the sterile feed would be started with a dilution rate such that D < µ (Sf).

n A non washout steady state would be reached after a transient phase.

Introduction

FE 222 FLUID MECHANICS
Transport Processes and Separation Process Principles (Includes Unit Operations) (4th Edition) by Christie John Geankoplis, published by Pearson Education,Inc
(Used to be Transport Processes and Unit Operations, 3rd ed…..)
Unit Operations of Chemical Engineering (7th edition)(McGraw Hill Chemical Engineering Series) by Warren McCabe, Julian Smith, and Peter Harriott
2 exams 30 % each
final 40 %

Fluids essential to life
Human body 65% water
Earth’s surface is 2/3 water
Atmosphere extends 17km above the earth’s surface
History shaped by fluid mechanics
Geomorphology
Human migration and civilization
Modern scientific and mathematical theories and methods
Warfare
Affects every part of our lives
History
Weather & Climate
Vehicles
Environment
Physiology and Medicine
Sports & Recreation
SPORTS
The main unit operations usually present in a typical food-processing line, including:
1. Flow of fluid – when a fluid is moved from one point to another by pumping, gravity, etc.
2. Heat transfer – in which heat is either removed or added (heating; cooling; refrigeration and freezing).
3. Mass transfer – whether or not this requires a change in state. Processes that use mass transfer include drying, distillation, evaporation, crystallization, and membrane processes.
4. Other operations requiring energy, such as mechanical separation (filtration, centrifugation, sedimentation, and sieving); size adjustment by size reductions (slicing, dicing, cutting, grinding) or size increase (aggregation, agglomeration, gelation); and mixing, which may include solubilizing solids, preparing emulsions or foams, and dry blending of dry powders (flour, sugar, etc.).
All theoretical equations in mechanics (and in other physical sciences) are dimensionally homogeneous; i.e., each additive term in the equation has the same dimensions.
Example is the equation from physics for a body falling with negligible air resistance:
S =S0+ V0t + ½ gt2
where S0 is initial position, V0 is initial velocity, and g is the acceleration of gravity.
Each term in this relation has dimensions of length {L}.
However, many empirical formulas in the engineering literature, arising primarily from correlations of data, are dimensionally inconsistent. Referred as dimensional equations. Defined units for each term must be used with it.
Fluids: Statics vs Dynamics
Continium mechanics : Branch of engineering science that studies behavior of solids and fluids
Fluid mechanics: Branch of engineering science that studies behavior of fluids
Fluid statics: Deals with fluids in the equilibrium state of no shear stress (study of fluids at rest)
Fluid dynamics: Deals with the fluids when portions of the fluid are in motion relative to other parts. (study of fluids in motion)
Density
Pressure
Pressure field
Pressure is a scalar field:
p = p(x; y; z; t)
The value of p varies in space, but p is not associated with a direction.
The pressure at any point in a stationary fluid is independent of direction.
A pressure sensor will not detect different values of pressure when the orientation of the sensor is changed at a fixed measurement point.
Atmospheric Pressure
Equality of pressure at the same level in a static fluid
Variation of pressure with elevation
General variation of pressure in a static fluid due to gravity
Variation of pressure in an incompressible fluid (liquid)
Variation of pressure in an compressible fluid (gas)
Pressure distribution for a fluid at rest
Incompressible fluid
Liquids are incompressible (density is constant):
Some Pressure Levels
10 Pa – The pressure at a depth of 1 mm of water
10 kPa – The pressure at a depth of 1 m of water, or the drop in air pressure when going from sea level to 1000 m elevation
10 MPa – A “high pressure” washer forces the water out of the nozzles at this pressure
10 GPa – This pressure forms diamonds
Some Alternative Units of Pressure
1 bar – 100,000 Pa
1 millibar – 100 Pa
1 atmosphere – 101,325 Pa
1 mm Hg – 133 Pa
1 inch Hg – 3,386 Pa
The bar is common in the industry. One bar is 100,000 Pa, and for most practical purposes can be approximated to one atmosphere even if 1 Bar = 0.9869 atm
Bourdon Gauge:
Pressure scales
Absolute pressure: pabs is measured relative to an absolute vacuum; it is always positive. (The pressure of a fluid is expressed relative to that of vacuum (=0)
Gauge pressure: pgauge is measured relative to the current pressure of the atmosphere; it can be negative or positive. (Pressure expressed as the difference between the pressure of the fluid and that of the surrounding atmosphere.)
Usual pressure gauges record gauge pressure.
Measuring Pressure
Barometers
Piezometer
Rough edges or burrs on or near the edges of the
piezometer holes deflect the water into or away from the piezometer , causing erroneous indications. The case as in W shows the tube pushed into the flow,
causing the flow to curve under the tip which pulls the water level down.
Errors caused by faulty piezometer tap installation increase with velocity.
By determining the height to which liquid rises and using the relation P = ρgh, gauge pressure of the liquid can be determined.
To avoid capillary effects, a piezometer’s tube should be about 1/2 inch or greater.
Measuring Pressure with Manometers
Manometers
A somewhat more complicated device for measuring fluid pressure consists of a bent tube containing one or more liquid of different specific gravities. Such a device is known as manometer.
In using a manometer, generally a known pressure (which may be atmospheric) is applied to one end of the manometer tube and the unknown pressure to be determined is applied to the other end.
In some cases, however, the difference between pressure at ends of the manometer tube is desired rather than the actual pressure at the either end. A manometer to determine this differential pressure is known as differential pressure manometer.
The manometer in its various forms is an extremely useful type of pressure measuring instrument, but suffers from a number of limitations.
While it can be adapted to measure very small pressure differences, it can not be used conveniently for large pressure differences – although it is possible to connect a number of manometers in series and to use mercury as the manometric fluid to improve the range. (limitation)
A manometer does not have to be calibrated against any standard; the pressure difference can be calculated from first principles. ( Advantage)
Some liquids are unsuitable for use because they do not form well-defined menisci. Surface tension can also cause errors due to capillary rise; this can be avoided if the diameters of the tubes are sufficiently large – preferably not less than 15 mm diameter. (limitation)
A major disadvantage of the manometer is its slow response, which makes it unsuitable for measuring fluctuating pressures.(limitation)
It is essential that the pipes connecting the manometer to the pipe or vessel containing the liquid under pressure should be filled with this liquid and there should be no air bubbles in the liquid.(important point to be kept in mind)
Manometers – measure DP
Manometers – Various forms
Simple U – tube Manometer
Inverted U – tube Manometer
U – tube with one leg enlarged
Two fluid U – tube Manometer
Inclined U – tube Manometer
Simple U – tube Manometer
The maximum value of P1 – P2 is limited by
the height of the manometer.
To measure larger pressure differences
we can choose a manometer with higher density, and to measure smaller pressure differences with accuracy we can choose a manometer fluid which is having a density closer to the fluid density
Simple U – tube manometer
U – tube with one leg enlarged
Two fluid U-tube Manometer
Small differences in pressure
in gases are often measured
with a manometer of the
form shown in the figure.
Inclined Manometer
To measure small pressure differences need to magnify Rm some way.