PEYNİR TOZU VE PEYNİR ALTI SUYU TOZU ÜRETİMİ
Prof. Dr. Erdoğan KÜÇÜKÖNER
Süleyman Demirel Üniversitesi, Mühendislik-Mimarlık Fakültesi, Gıda Mühendisliği Bölümü, Isparta
erdogankucukoner@sdu.edu.tr

Özet
İnsan hayatındaki öneminden dolayı, sütün ürünlere işlenmesi gıda endüstrisinde önemli bir yere sahiptir. Bu süt ürünlerinden biri olan peynir; sütün ısıtılması, starter kültür ilave edilmesi, proteolitik enzimlerle pıhtılaştırılması, pıhtının süzülerek peyniraltı suyundan ayrılması, telemenin tuzlanarak ve baskılanarak şekillendirilmesi ile elde edilen, taze veya olgunlaşmış halde tüketilen besleyici bir süt ürünüdür. Peynir tozları gıda endüstrisinde çok farklı alanlarda kullanılmakla birlikte, en yaygın olarak gıdalara lezzet verme amaçlı kullanılmaktadır. Peynir tozunun bu özelliğinden çerez kaplamaları başta olmak üzere preslenmiş çerezlerde, peynir esaslı soslarda, çorbalarda, patates cipslerinde, tuzlu çeşnilerde ve tuzlu bisküvilerde yaralanılmaktadır. Sütünün peynir yapımından sonra katı kısımdan ayrılan geride kalan sıvı kısmına ise peynir altı suyu denir. Peynir altı suyu tozu gıda sanayinde; şekerlemeler, unlu mamuller, et ürünleri, çorbalar, soslar, içecekler gibi birçok üründe kullanılmaktadır. Ayrıca, hayvan beslenmesinde ucuz ve yüksek kaliteli protein kaynağı olmasıyla beraber karbonhidrat kaynağı olarak da tercih edilmektedir.

Anahtar kelimeler: Maya, peynir, süt, peynir altı suyu.

Abstract
Processing of milk has an important place in food industry due to its importance on human-life. One of the dairy product, cheese, produced by heating of milk, addition of starter culture, coagulation (curdling) by proteolytic enzymes, draining of whey, salting and giving shape by press is a nutritious product consuming as a fresh or a ripened. Cheese powder utilized in so many different areas of food industry is widely used as a flavor enhancer
for foodstuffs. This feature of cheese powder is utilized in firstly coating of snack foods, additionally cheese-based sauces, soups, potato chips, salty dressings and in salty biscuits. Remaining aqueous phase, separated from solid part in the cheese production, is named “whey”. In food industry, whey powder is used in different food products like candies, bakery products, meat products, soups, sauces, drinks etc. Furthermore it is preferred for animal-
feeding due to its high carbohydrate content besides to being a cheap and high quality protein source.

Keywords: Yeast, cheese, milk, whey.

…

OUTLINE

• What is yeast nutrition?

• Why is it important?

• Current understanding of the needs and challenges

• Utilization of nutrients to rectifyidentified challenges

WHAT IS YEAST NUTRITION?

• Yeast cell physiology

– Refers to how yeast cells feed, metabolize, grow, reproduce, survive and ultimately die

• Yeast nutrition

– Mechanisms of how yeast cells translocate water and essential organic and inorganic nutrients from the surrounding environment, through the cell wall, across the cellular membrane and into the intracellular milieu

…

Yeasts are eukaryotic microorganisms classified in the kingdom Fungi, with about 1,500 species currently described.

• What are differences between yeasts and molds?

• What are differences between yeasts and bacteria?

• Pseudomycellium or pseudohyphae?

• “Pseudohyphae” are distinguished from true hyphae by their method of growth, relative frailty and lack of cytoplasmic connection between the cells.

• Yeast can form pseudohyphae. They are the result of a sort of incomplete budding where the cells remain attached after division.

• True yeast?

• Wild yeast?

Brettanomyces

• The cellular morphology of the yeast can vary from ovoid to long “sausage” shaped cells.

• The yeast produces large amounts of acetic acid when grown on glucose rich media (Asidogenic).

• They multiply by budding.

• They can use sugars as oxidative or fermentative.

• The most important species is B. intermedius.

– It can grow at as low as 1,8 pH.

– It can cause spoilage of beer, wine, non-alcoholic beverages and pickles.

Candida

• Candida genus was first described in 1923.

• Cells do not contain carotenoid pigment.

• Candida means “clear and bright white”

• Some species of this genus play role in fermentation of kefir, cacao, beer, ale and fruit juices.

• Some Candida spp. are commonly found in ground meat and poultry meats.

• While usually living as commensals, some Candida species have the potential to cause disease (aphthae).

• Many of them form films and can spoil foods high in acid and salt.

• Lypolytic Candida lypolytica can spoil butter and oleomargarine.

…

PURPOSE

To produce yeast in a stirred batch fermentor, obtain wet and dry yeast.

THEORY

Producing microorganisms in fermentor is a biotechnological practice. Microorganisms or their products can be obtained to use in field of medical, food etc. Adjusting working conditions like temperature, air volume (O2), pH, stirring speed of the fermentor, a desirable growth of microorganism and production of a metabolite in any scale can be obtained. Yield of fermentor, microorganism and metabolite can be calculated due to stoichiometric equations can be calculated.

Saccaharomyces cerevisiae is an important microorganism in bakery, brewing etc. Its wet and dry forms can be used in different areas. So, there is a developed industry of yeast production.

After production of S. cerevisiae in a medium that is suitable for growth of microorganism in fermentor, biomass should be separated from the medium. Separation can be done different ways like filtration, centrifugation. After separation, to get the biomass as pure, the biomass is washed with distilled water at least 2 times. So ‘cream yeast’ form has been obtained. It is pressed and extruded to increase ratio of dry matter to 30 %. This form of biomass is called ‘wet yeast’. ‘Dry yeast’ form can be obtained by drying up of wet yeast. Its dry matter ratio is 92-94 %. ….

• BREAD MAKING
•Bread is one of the most consumed food products known to humans, and for some people, it is the principal source of nutrition.
different from most other food fermentations:
•-the purpose is not to extend the shelf-life of the raw materials (starting material is much more perishable than the finished product)
•-none of the primary fermentation end products actually remain in the food product
•contains carbohydrates, lipids, and proteins, essential vitamins of the B complex and of vitamin E, minerals and trace elements.
•There are numerous variations of the breadmaking process; tradition, cost, the kind of energy available, the kind of flour, the kind of bread required, and the time between baking and consumption of bread.
Principal ingredients
•Flour
•The most important characteristics of flour:
•the quantity and quality of gluten,
•the water absorption capacity,
•the diastatic activity.
•After kneading: cohesive, viscoelastic mass retains the gas formed
•YEAST
•Commercial yeast production in the world: exceeds 1.8 million tons/year.
•used by: the baking, brewing and distilling industry
•Yeast is also a commercial source of natural flavourings, flavour potentiators and the dietary supplements.
•first compressed yeasts: in England at 1792
•The large-scale commercial production of bread:
in the US at 1868, by Charles Fleischmann.
•yeast strains are developed
•- to tolerate high sugar
•- to tolerate high salt concentrations
•- to high temperatures used in fermentation
•Currently: more than 500 species of yeasts, belonging to around 50 genera
Saccharomyces: ‘sugar fungus’
•S. cerevisiae have been isolated from : breweries, wine, berries, cheese, pear juice, honey, eucalyptus leaves, kefir.
•Reproduction
•Asexual reproduction usually occurs by budding.
•Sexual reproduction
Bakers’ yeast ( S. cerevisiae.)
•Based on moisture content: compressed (most common), granular, dried in the form of a pellet, instantaneous, encapsulated, frozen, or in the form of a ‘cream.’
•Based on maltose adaptation: standard and rapid
•Tolerance to high osmotic pressure : important in frozen dough.
Hybrid Strains
•rapidly fermenting strains: produce high volumes of CO2 for automated bakeries
•strains with intermediate activity, for traditional bakeries;
•and strains which ferment more slowly, for in-store bakeries.
Growth Requirements
•S. cerevisiae is
a heterotroph, i.e. requires organic compounds for growth.
a mesophile, growing best in the temperature range 25–40°C.
Glucose and fructose are readily utilized,
•sucrose and maltose are preferred.
•Other malto oligosaccharides can also be utilized,
•S. cerevisiae cannot utilize pentoses, other hexoses, the disaccharides lactose or cellobiose or the polysaccharides.
•In industry, the preferred carbon sources are cane or sugar-beet molasses( fermentable sugar conc. of 50–55% and around 80% total soluble solids. )

Nitrogen
•can utilize – inorganic nitrogen (ammonium sulphate, ammonium chloride, ammonia. -Urea

Minerals The major minerals required:
phosphorus, potassium, calcium, sodium, magnesium,s ulphur.
Vitamins S. cerevisiae requires :
biotin, pantothenic acid, inositol and thiamin
These (except for thiamin)are available from molasses. Sugar-beet molasses, however, is deficient in biotin
Oxygen
•S. cerevisiae possesses a remarkable ability to adapt to varying levels of available O2.
•very low levels of O2: : shuts off the respiratory enzymes. ( ‘waste’ product is ethanol.)
•When adequate O2 is available; sugar is converted by the respiratory enzymes to CO2 and H2O
•The max. theoretical yields of yeast solids:
•microaerophilic (anaerobic) :7.5 kg/100 kg of sugar utilized.
aerobic conditions : 54.0 kg/100 kg of sugar utilized
If > 5% glucose: TCA (tricarboxylic acid) cycle is almost completely blocked.
Even if the culture is aerated, glucose can only be fermented, this phenomenon being known as the ‘glucose effect’ or the ‘Crabtree effect’.
• For aerobic growth: sugar has to be supplied incrementally μ does not exceed 0.2
•and the respiratory quotient (RQ) is maintained at 1.
•S. cerevisiae grows optimally at pH 4.5–5.0, can tolerate a pH range of 3.6–6.0.
Temperature
•S. cerevisiae has one of the shortest generation times amongst yeasts, 2.0–2.2 h at 30°C.
•Bakers’ yeast production is optimal: at 28–30°C.
Preparation of Medium
•The molasses (containing 50% fermentable sugars and 80% soluble solids) is usually diluted with an equal weight of water, and the pH is adjusted to 4.5–5.0 with sulphuric acid.
•Then clarified using a centrifuge or filter.
•The clarified molasses is then sterilized by the high temperature short time (HTST) process.
defoamer (silicone, edible oil), 0.01 g l−1.
•The molasses is then transferred to the fermenter, pitching yeast.
•More clarified molasses: the fed-batch cultivation.
Cultivation
•In industry, stainless steel fermentors with a capacity of 200 m3 or more are used.
•bubbling compressed air
•eight stages, from 0.2 kg of yeast to 100 000 kg of yeast. (the entire process is known to involve 24 generations of the yeast)
• a typical cultivation tank : airlift fermenter.
•Metabolic heat generation: 14 650 J/ g yeast solids, to keep temp at 28–30°C, cooling is necessary.
If the depth of the broth> 3 m,
use of compressed air
Maturation : At the end of the final stage of yeast cultivation, the feed rate is greatly reduced results in a low proportion of budding cells, which confers higher stability on compressed yeast in storage.
Finishing Stages
•Yeast Cream (20% yeast solids)
continuous centrifuge at 4000–5000 g.
•Yeast cream can be stored at 4°C for few days
•Compressed Yeast
•from yeast cream by Rotary vacuum filters .
•mixed with 0.1–0.2% of emulsifiers( monoglycerides, diglycerides, sorbitan esters and lecithin,)
•then extruded through nozzles.
•cut and packaged ( 500 g) in wax paper or polythene sheet.
• must be rapidly cooled, and stored at 5–8°C.
•Active Dry Yeast (moisture content of 4.0–8.5%. )
•Active dry yeast is stored at room temp.
•produce thin strands or small particles, then dried in a tunnel drier, ( 2–4 h the air inlet temp. 28–42°C. )
•continuous drying, fluidized-bed drying, airlift drying
•Emulsifiers ( sucrose esters or sorbitan esters, 0.5–2.0%) are mixed to facilitate rehydration.
•Antioxidants ( butyl hydroxyanisole(BHA) at 0.1%), added to prevent undesirable oxidative changes.
•1 g compressed yeast ≡ 0.4-0.45 g dry yeast
•Rehydration:
•X g yeast + 4X g water at 37.8-44.5 C
•T < 32 C …..or T>46 C
–The glutothione leaches out of yeast and causes to dough become soft and sticky
–Cell contents ( a acids, vitamins, nucleic acids,
coenzymes,glutothione and inorganic salts) leaches out and fermentative power of yeast decreases.
• heat resistant strains are used: heat resistant strains generally carries low gassing power.
Temperature
• at 4 °C, no activity, no fermentation
• at 10–15 °C, yeast activity, fermentation; slow
• at 20–40 °C, fermentation ; very active
• at 45 °C yeast activity slows down
• at 55 °C, the yeast dies.
•pH
•very tolerant to fluctuations in pH (2–8),
•but the optimum pH :4 and 6.
•the pH of dough is 5
Presence of Dough Inhibitors
The Cu and Cl in water, inhibits fermentation
•acetic and propionic acid, fermentation inhibitors
Sources of Sugar used by Yeast
•Yeast uses
•(1) trehalose (Trehalose is a non-reducing sugar, two glucose ( 1-1 alpha bond) very resistant to acid hydrolysis)
•(2) free sugar from flour
•(3) sugars obtained by the action of enzymes
•(4) added sugars such as sucrose.
•Order: 1- trehalose 2-free sugars and sugars added 3- maltose.
Production and Retention of Gas
•Kneading ; air is incorporated into the dough.
•These bubbles contain mainly nitrogen; low solubility in water
•Yeast cannot create new bubbles
•The more bubbles: finer the grain.
•CO2 is produced in the aqueous phase, as pH decreases this phase becomes saturated with CO2 .
•the newly formed CO2 is retained in preexisting bubbles.
•the quality of gluten is important to retain the gas
•At the pH of dough, most of the carbon dioxide is present as CO2 and a small amount of this as CO32− HCO3−, or H2CO3.
•Half of the total CO2 produced is lost in initial fermentation, punching, rounding, molding, and final fermentation.
Salt -to provide flavor, influence the rheological properties of dough.
• Higher concentrations of salt inhibit enzymatic reactions and also inhibit the fermentation.
•salt used: 1–2% (based on flour weight).
Optional Ingredients
•Fat
•increases the shelf-life,
•produces a finer grain,
• yields a greater volume of baked foods
•The crust is more elastic and softer.
•The shortening effect ( film between the starch and protein)
•The shortening effect is greater for fat with a lower melting point than for harder fats. ( hydrogenated vegetable fats)
•the use of fat requires less water in the formulation
Sugar
•promotes fermentation, browning of the crust,
•sweeter taste, dough more stable, more elastic, and shorter, and the baked goods more tender.
Milk and Dairy Products ( skim-milk powder, whey)
•promotes browning, a softer crust, a longer shelf-life
Oxidants ( the oxidation of -SH groups of protein )
•improved gas retention, firmer gluten, dough maturation is shorter, the oven spring is greater, the volume is larger,
The oxidant commonly used is ascorbic acid
Enzyme Active Preparations
•Flours with a low enzyme activity: yields
breads that do not brown well, stale rapidly.
-Add fermentable sugars or enzyme active preparations((malted flour, malt extract, and bacterial or fungal α-amylases).
•Emulsifying Agents(monoglycerides, lecithin)
to make bread softer during storage,
•staling is delayed.
steps in breadmaking
• Ingredients:flour, water, salt, yeast
Mixing:
Rules for mixers
•-use 90 % of maximum capacity designated
•-if producing sponge use 60% of max capacity
•-don’t go below half of the maximum capacity designated
•hydration of protein to form gluten and the spreading of the gluten over the surface of the free starch granules to form a continuous matrix.
• otherwise a clay-like dough will result that will lack gas retention.(if Protein < 7% )
if excessive amounts of the starch granules are damaged in milling ; sticky dough results
•Mixing time(↑) = f of
• T(↑),
• absorption level(↑),
•flour strength(↑),
•salt addition,use of oxidizing agent, reducing agent(↓),
•enzyme supplementation (↓),
•mixer design ( mixing bar area↓ )and speed
•Stages of mixing
•1 – uniform blending
•2- pick up stage , gluten begins to form
•3- clean up stage , most important reference point, drier and more elastic dough, this stage is completed when the dough clears away from the mixer bowl
•4-development stage , critical
•5-overmixing ( let down stage)
Heat production during mixing:
•Due to dehydration 6.5 btu / lb flour
•Frictional heat 42.5 btu/hp/min
•keep temp of the dough: ( 25.5-27 C) by
•adding ice
•use chilled water
•refrigeration
Dough divider :
•Divide dough volumetrically 9600 dough pieces /h
•lubricated with mineral oil to prevent sticking of dough while dividing
Rounding:
• Dough with a rotary motion produces a ball-shaped piece with smooth skin.
improves the retention of gas.
•Dough is less viscous.
•After rounding, dough needs a floortime (2 to 20 min) Conical rounder
•Moulder The function of moulders is to sheet, curl and seal the rounded dough pieces
• O curling pressure
•Dough ball → thin sheet → cylindrical shape → sealing
• O of dough rolls board
•Rollers ( 2 to 3 in series)
•To prevent moisture accumulation on one end of the sheet after two rolling direction of rolling reversed
•The molded dough is placed either in tins or on a baking tray and kept in a proofing cabinet continue fermentation (final proof).
Fermentation, Final Proof, or Proving:
-starch is converted into sugars by enzyme action.
-sugars CO2 and ethanol
-as CO2 produced, the dough expands and retains it, the skin should remains flexible.
-retained gas =f (quality of the gluten )
– The more retained gas, the more bread volume.
The temperature =f(the kind of bread and the breadmaking process (28–30 °C)
– The RH :60 and 90%, =f( formulations and ferm. temp.)
•If the relative humidity is < 75%, the skin of the dough will be very dry and will lose its elasticity. •Initially, dough has a pH of about 6.2, and during fermentation, the values are about 5.76 or 5.67. •acidic environment improves the formation of gluten •The capacity of dough to withstand excessive mechanical work is called dough tolerance.( doughs that ferment slowly are more tolerant.) •Tray type proofer •Straight Dough Method •• Advantage: •less processing time, labor, power, and equipment. •Fermentation losses are smaller •• Disadvantage: •small variations in processing lead to noticeable variations in the final quality of breads. •less flexible than the sponge dough, •requires limited fermentation time, does not permit correction of overfermentation. •do not have a soft texture, •the bread volume is lower, •Sponge and Dough Process permits the use of strong and soft (weak) flour, using the strong flour to make the sponge and the soft in the final dough. (50% / 50%.) • Advantage: • permits greater variations in the operations of the process improves the volume, texture, and shelf-life of the bread. •the longer fermentation time….more aroma. •Disadvantage: •more fermentation time and labor than the straight dough method, • more difficult to control. •difficult to divide, laminate, and mold. •How to manipulate fermentation time? •By amount of yeast: y*t/n=x •y: percent yeast used normally •t: normal fermentation time •n: new fermentation time •x: percent yeast for new fermentation time •2% yeast 4 h fermentation •To reduce 3 h we need 2*4/3=2.66 % yeast needed ( one can vary fermentation time by 30% in both direction but not more than that) •If greater changes required, changes in other parameters should be considered such as fermentation temperature and fermentation substrate. •0.5 C ferment time by 15 minutes •At most 45 minutes of change is allowed by temp. change •BAKING •Temperature of Baking •the baking temp. 200–275 °C is a function of the type of baking oven, the duration of baking, and the size and type of bread desired (formulation used). •small items :a higher temperature and a shorter time •large items :a lower temperature and a longer time. •soft dough (low consistency): a higher temperature than hard dough •hard dough (less water to evaporate) Duration of Baking •duration of baking depends on the temperature used. •During baking, the following changes take place: gelatinization of the starch, •denaturation of the protein, •the formation of aromatic substances. Relative Humidity •injection of satd steam into the oven RH •dough is covered with a fine surface layer of water, which keeps it moist and elastic for some time. •advantages: delayed formation of crust, increases the volume (with a satisfactory oven spring), improves the color and shine, and produces a fine crust. • low pressure steam, 2-5 psia saturated, is added during first minute of baking) •if steam is not added → • surface dries out quickly because of inadequacy of moisture, •surface layer starch undergoes pyrolysis rather than partial gelatinization •crust will not acquire the desired gloss •the evaporative process absorbs considerable heat from the surface thereby slowing the rate of heat penetration into the loaf interior. •Type of Oven •Heat tr. by conduction, convection, and radiation. •Coal, oil, or electricity may be used to heat the oven the most common: •the hot air oven, rotary hearth oven, the reel oven, the pan rack oven, a continuous belt, tunnel oven •Transfer of heat •Convection, radiation and conduction on the surface (> 100 °C)
the crumb inside (< 100 °C)
•Energy requirement
•Approximately 235 btu ( 150-250 ) is needed to bake 1 lb of bread ( = f ( oven temp and initial dough temp)
•Cp of dough 0.65-0.88 btu/ lb-C
•Modern oven heat input 325-400 btu / lb bread
•Coal-fired brick peel ovens 1780 btu / lb bread
•Relative heat utilization :
•Heating medium calorific value heat needed to bake fuel needed per 100 lb
• ( btu / lb of bread baked) bread baking
•1- natural gas 1000 btu / ft3 800 80 ft3
•2- manufactured gas 546 btu / ft3 610 112 ft3
•3- fuel oil 140000 btu/gal 950 0.76 gallons
•4- electricity 3412 btu / kwh 475 13.9 kwh
•*natural gas is cheapest and electricity is most expensive one
•*sp.gr. of propone = 1.5 times sp gr of air, sp gr of natural gas = 0.5 times sp gr of air
•*baking time and temp =f( product formulation)
•lean formulas call for higher temp and shorter baking time than richer ( containing sugar and dairy ingredients enter readily into thermal browning reactions formulas)
•Cooling
•reduce temp quickly to 35-40 C, final bread moisture •in slicer not to obtain crippled
•undesirable moisture condensation in the package
Wash cooling chamber with
detergent and use microbiological
filter for air to prevent
mold infection. →→
•Physical–Chemical Changes During Baking
•There are three phases depending on the temperature the dough reaches:
•1. oven spring (enzyme active zone) (from 30 to 60 or 70 °C); ( due to 57 % gas expansion, 39 % decrease in gas solubility and 4 % increased yeast activity)
•2. gelatinization of starch (55–60 °C) to no higher than 90 °C;
•3. browning and aroma formation above 100 °C
•Pan Breads
•breads that are baked in pans, either open or closed.
•in North America, Eastern and Western Europe, Australasia,
•automated or semi-automated equipment.
•always sold presliced in polyethylene bread bags
•Hearth Breads (artisan breads, rustic breads), french, italian bread
•stiff and dry doughs; baked directly on the hearth, or floor, of the oven, without pan
•Buns and Rolls ( for Hamburger and hot dog )
•richer in formulation
•while rolls tend to be made from leaner formulas
•(baked with steam, light, slightly crispy crust)
•Flat Breads
•These are the most widely consumed of all bread types.
•Single-layered flat breads
•North and Central Americans: tortilla.
•Tanoor bread : Middle East, India, and Pakistan.
•( wheat flour, soda (sodium bicarbonate), yeast, and water) Sourdough can be used in place of the yeast.
•Ciabatta : lean formula sponge dough, usually consisting of wheat flour, water, yeast, and salt.
•double-layered flat bread : Arabic bread (pita bread)
•pocket is formed largely by a second proofing step that is not given to single-layered flat breads.
•Baking :at high temperatures, normally 400 °C, for short periods of time, 90–100 s. (enhance pocket formation)
•KEEPING OF BREAD
•Crust staling :
•crust 12 % m, crumb 44-45 % m
•storage in a closed chamber…. crust moisture increase to 28 % ( this moisture is taken from crumb, also from air air if conditions are suitable )
•( this is staling ) crust staling is irreversible
•crumb staling :
• moisture loss of crumb, starch retrogradation, modification of protein structure
•surface active agents -keeping crumb softness longer -improvement in mixing and fermentation tolerance -better moisture retention –opt loaf volume
Retardation of staling
•-surfactant
•-bread from high protein flour stale less than low protein flour ( higher specific volume of bread slower firming rate)
•-adding milk products
•-small amount of glycerol ( 0.5 %)
•- use of lecithin
•- adding malt extract ( due to amylolitic activity )
•- soy flour and soy isolate addition
•-shortenings
•-short time dough process staling < long time dough process staling
•-low temp freezing is the most effective way of retarding staling
•store at -9 C for 3 days and then thaw → like fresh bread
•store at -34.4 for 30 days and than taw → like fresh bread
•to stabilize bread its temp has to be lowered below its freezing point which is about -6.7 C
•at -23,-29 C with air speed of 200-500 ft / min reaches freezing point in 2 hrs then keep at -18 C
•one can prevent staling by keeping bread below -18 C and above 55C but keeping above 55 C will accelerate rope formation.
•Ropiness:
•bacterial spoilage of bread: initially unpleasant fruity odor, followed by enzymatic degradation of the crumb that becomes soft and sticky because of the production of extracellular slimy polysaccharides
•primarily Bacillus subtilis
•and occasionally Bacillus
• licheniformis, Bacillus pumilus,
• and Bacillus cereus
Trabzon Vakfıkebir Bread ( around 3000 g. )
•late staling due to high internal moisture ( approx 48 %) and lower cooling loss ( 9%, normally 15-20 %).
Baked at 170-180 C for 115 min ( total processing time ≈20 hours)
•Properties: -indirect dough method , -thick and tough crust -long processing time and high tolerance → yields highly aromatic bread
•-long shelf life -late staling- one week:due to sour dough→ delays enzymatic breakdown of starch so water holding capacity is high as a result unfermented sugars are responsible for delayed staling. if 36.8 % •production flow sheet:
•10 kg sour dough from previous production ( first sour dough)
• ↓ 15-18 hours of rest
•second sour dough preparation ( 20 min ) …first sour dough +25 kg flour + water 20 min
• ↓ kneading → tough dough (25 C, 75 % RH, rest 3 h)
• main dough mixing ( 25 C , 22 min) 100 kg flour+ second sour dough 20 kg
• ↓ 22 min kneading +30 min resting+20 sec kneading
•main fermentation (25 C , 135 min, 75% m)
• ↓
• dividing dough by hand ( 3400 g)
• ↓
• rounding by hand ( by hand)
• ↓
• final fermentation ( 25 C, 100 min, in cloth covered plastic pans )
• ↓
• shaping ( add some flour to original dough to proper tougher dough,
• prepare cylinder of 1 cm diameter and 20 cm length for lining)
• ↓
• baking ( 170-180 C , 115 min)
Sourdough Fermentation
•Most yeast breads have a slightly acidic pH, due to acids produced by the yeast and, dissolved CO2 in the dough. acids also are produced by lactic acid bacteria (present in the flour, in the yeast preparations, or in )the dough.
•The perception of sourness occur when the pH is near 4.0( yeast breads pH 5.0 to 6.0 )
•If lactic acid bacteria added : the pH <4.0, sour but appealing flavor , better preservation.
•the very first breads made: sourdough breads.
Commercially available.:in addition to L. sanfranciscensis, available strains include L. brevis, L. delbrueckii, and L. plantarum.
•authentic sourdough breads are almost always made via a sponge and dough process.
•RYE BREAD
rye : second most common cereal ( to make bread.)
rye : high conc. of pentosans ( xylose, arabinose, 4 to 5 times more than that found in wheat.)
•may have both positive and negative effects.
•1-high water-binding capacity, decrease retrogradation and delay staling
•2-interfere with gluten formation, giving an inelastic dough that retains gas poorly.
•rye proteins do not form a viscoelastic dough.
( a small loaf volume and a dense crumb texture. )
• rye flour contains more α amylase (excessive starch hydrolysis, poor texture and reduced loaf volume.)
•The addition of sourdough cultures compensate for these complications.
• -1-as the pH decreases the pentosans become more soluble, begin to swell and form a gluten-like network that enhances dough elasticity and gas retention( act like gluten.)
•2-at low PH α amylase lose activity so excessive hydrolysis is avoided.
•3-Some sourdough bacteria also have the ability to ferment pentosans
• 4-acidic conditions enhance the water-binding capacity of the starch granules, decreases staling
•Another potential problem of rye bread and other whole grain breads:
•the presence of phytic acid that is capable of binding zinc, iron, calcium, and other divalent metal cations, preventing their absorption in turn reducing the bioavailability of essential minerals
•Cereal grains:as much as 4% phytic acid
•whole grain bread: less than 0.2%, this is still enough to be a nutritional concern.
•Solution to phytic acid problem: Degradation of phytic acid via the enzyme phytase, which is present in flour and is also produced by yeasts.
•Lactobacillus sanfranciscensis, Lactobacillus plantarum, and other sourdough bacteria also produce this enzyme
•Thus, the sourdough fermentation also enhances the nutritional quality of rye and other whole grain breads.
•FROZEN DOUGH
•One of the hottest trends in the baking industry
•small retail bakery operations: eliminate the need for dough production equipment and labor,
•The frozen dough, produced somewhere else and brought to small bakeriesw where they are thawed overnight in the refrigerator, given a final proof, and baked.
•the quality of bread varies: due to the loss of yeast viability during storage.
•Doughs made using cold-sensitive yeasts require longer proof times
•the normal bakers’ yeast: cryosensitive that they may fail to provide any leavening at all after the dough-thawing step.
•for frozen dough: yeast strain must be cryotolerant.
•What makes some yeast strains resistant to the effects of freezing? And what can be done to improve cryotolerance
•cryotolerance in S. cerevisiae is due the ability of the organism either to transport extracellular cryoprotectant solutes from the environment or to synthesize them within the cytoplasm.
•these agents prevent dehydration, by re-structuring the bound water in the cytoplasm.
•Microbial cryoprotectants are typically small, polar molecules: amines (e.g., betaine, carnitine, proline, and arginine), and sugars.
•In S.cerevisiae, the disaccharide trehalose is the most important cryoprotectant (although some amino acids like arginine also have cryoprotective activity).
when environmental stresses ( like low temp) are applied the cell responds by increasing synthesis of trehalose. ( and transporting extracellular trehalose, if available).
•under non-stress conditions, the enzymes used to synthesize trehalose are turned off and the hydrolytic enzymes turned on .
•Trehalose can also serve as a storage carbohydrate .
• If, the trehalose degradation pathway is blocked, then higher levels of trehalose can be maintained, making the yeast more cryotolerant.
•Arginine hydrolyzing enzyme arginase was inactivated. This led to increased intracellular concentrations of arginine and an increase in freeze tolerance and gassing power compared to the parent strain.

…

BREAD MAKING

Bread is one of the most consumed food products known to humans, and for some people, it is the principal source of nutrition.Bread is an inexpensive source of energy: it contains carbohydrates, lipids, and proteins, and it is important as a source of essential vitamins of the B complex and of vitamin E, minerals and trace elements. There are numerous variations of the breadmaking process; tradition, cost, the kind of energy available, the kind of flour, the kind of bread required, and the time between baking and consumption of bread. Principal ingredientsFlourThe breadmaking quality of flour: f (the variety of the grain, all agricultural and climatic conditions, including the harvest, and the milling process.) The most important characteristics of flour:1. the protein content, 2. the quantity and quality of gluten, 3. the water absorption capacity, 4. the diastatic activity. The kneading of the flour and water gives the dough a cohesive, viscoelastic mass that retains the gas formed during fermentation. YEASTCommercial yeast production worldwide exceeds 1.8 million t per year.The yeasts are used mostly by the baking industry, but also by the brewing and distilling industries. Yeast is also a commercial source of natural flavourings, flavour potentiators and the dietary supplements. The first yeasts used for baking were obtained from the mashes produced in the manufacture of beer. The first compressed yeasts used for baking and brewing were made in England in about 1792, and by 1800 they were available throughout northern Europe. The large-scale commercial production of bread in the US was facilitated by the introduction of an improved strain of compressed yeast in 1868, by Charles Fleischmann. The vigorous research and development effort that ensued yielded yeast strains suited to each type of fermentation and leavening. For example, some of these strains were able to tolerate high sugar or salt concentrations The vigorous research and development effort that ensued yielded yeast strains suited to each type of fermentation and leavening. For example, some of these strains were able to tolerate high sugar or salt concentrations, or the high temperatures used in fermentation and the proving of dough. Anton van Leeuwenhoek (1632–1723) of Holland was possibly the first human to set eyes on a yeast, when he observed a droplet of fermenting beer with the aid of one of the first microscopes, capable of 250–270-fold magnification. Louis Pasteur (1822–1895) carried out extensive systematic studies which revealed the nature of yeasts and their extraordinary biochemical capabilities. Currently more than 500 species of yeasts, belonging to around 50 genera, are known. Bakers’ yeast and the yeasts used in brewing, wine-making and distilling are strains of Saccharomyces cerevisiae, belonging to the family Saccharomycetaceae in Ascomycotina. The genus Saccharomyces (translation ‘sugar fungus’) derives its name from its common occurrence in sugary substrates such as nectar and fruits. Strains of S. cerevisiae have been isolated from diverse sources, including breweries, wine, berries, cheese, pear juice and must, honey, eucalyptus leaves, kefir. ReproductionAsexual reproduction usually occurs by budding.The vegetative cells are diploid or polyploid, and this phase predominates in the life cycle of the yeast. Sexual reproduction involves the production of asci, within which ascospores develop directly following meiosis of the diploid nucleus. The sporulation of S. cerevisiae is encouraged by media containing acetate, such as acetate agar. Sporulation also occurs on potato–dextrose agar.

Hybrid Strains

Cells of opposite mating types can be fused to produce hybrid yeast strains.( or new techniques like  protoplast fusion and the construction of recombinant DNA),

This technique can be used to combine industrially desirable traits such as high growth rates, high yields, resistance to drying and CO2 production. rapidly fermenting strains: produce high volumes of CO2 for automated bakeries strains with intermediate activity, for traditional bakeries; and strains which ferment more slowly, for in-store bakeries. Bakers’ yeast is Saccharomyces cerevisiae.

• Based on moisture content: compressed (most common), granular, dried in the form of a pellet, instantaneous, encapsulated, frozen, or in the form of a ‘cream.’

• Based on maltose adaptation: standard and rapid

• Rapid yeast is more active than standard yeast, and is adapted for use in accelerated bread making systems.

• Tolerance to high osmotic pressure : important in frozen dough.

Commercial Production of Bakers’ Yeast Sources

• Industries requiring yeast cultures can either obtain them from culture collection centres or isolate and develop their own cultures.

• Saccharomyces can be isolated from natural sources, and maintained in pure culture by conventional microbiological techniques.

• The source material (fermenting sugary materials, fruit juices or
soil) is usually serially diluted and plated onto potato–dextrose agar (PDA) or yeast extract–peptone–dextrose agar (YEPDA).

• The growth of yeasts in preference to bacteria is achieved by the pH of the medium being below neutral (usually 4–6) and the incorporation of antibacterial antibiotics.

• Enrichment culture is a technique by which strains with characteristics required by industry (e.g. tolerance to high temperatures) can be isolated from natural habitats.

• The required strains are selected either by gradually increasing exposure to the factors to which tolerance is required, or by cultivation with very high levels

• Maintenance of Cultures

• If yeasts are used regularly( for batch process): the simplest method is to use agar slopes or broth.

• Normally, slope and broth cultures are subcultured once every 2 months.

• After allowing for adequate growth at ambient temperature, they are kept at 4–8°C until use.

• The drawback of this simple technique is the risk of contamination and the development of genetic variants .

• These undesirable effects can be prevented by the incorporation of a ‘selection pressure’:  the incorporation of a high sugar or salt concentration in the maintenance medium, to retain yeasts which will be tolerant to high concentrations in the fermentation.

Preservation of Cultures

• Yeasts that are sensitive to dehydration in slope or stab cultures may be maintained by overlaying with mineral oil.

• All microorganisms except non-sporulating bacteria sporulate in soil, and in this form remain viable and functional for up to 2 years.

• The inclusion of glycerol (5–20%) in the suspension medium and storage at −20°C are recommended.

• Well-equipped culture collection centres have facilities for the extended storage of cultures in liquid N2 at −196°C or by lyophilization.

Growth Requirements

• S. cerevisiae is a heterotroph, i.e. requires organic compounds for growth. a mesophile, growing best in the temperature range 25–40°C. bakers’ yeast has basic nutritional requirements for carbon and nitrogen sources, minerals and vitamins.

• Carbon

• A limited range of sugars is utilized as a carbon source by S. cerevisiae.

• Glucose and fructose are readily utilized, and of the disaccharides, sucrose and maltose are preferred.

• Other malto oligosaccharides can also be utilized, but less readily.

• S. cerevisiae cannot utilize pentoses, other hexoses, the disaccharides lactose or cellobiose or the polysaccharides.

• In industry, the preferred carbon sources are cane or sugar-beet molasses, which have a fermentable sugar concentration of 50–55% and around 80% total soluble solids.

Nitrogen

• S. cerevisiae can utilize

• inorganic nitrogenous compounds ( ammonium sulphate, ammonium chloride , ammonia. Urea can be used to provide N2
in the commercial production of yeasts. )

Minerals

• The major minerals required: phosphorus (an important component of nucleic acids) potassium calcium sodium magnesium sulphur. Iron, zinc, copper, manganese and cobalt are required as trace elements. These requirements are largely met by the molasses, with the exceptions of phosphorus and magnesium.

• Phosphorus is supplied in the commercial production of yeasts as phosphoric acid or as phosphate of sodium, potassium or ammonium.

• Magnesium is supplied as magnesium sulphate in the growth medium.

Vitamins

• S. cerevisiae requires : biotin, pantothenic acid, inositol and thiamin These (except for thiamin)are available from molasses.. Sugar-beet molasses, however, is deficient in biotin A mixture of
-aspartate and oleic acid was found to completely eliminate the requirement for biotin.

• Molasses must be supplemented with thiamin to enable maximum growth of the yeast.

Oxygen

• S. cerevisiae possesses a remarkable ability to adapt to thrive in varying levels of available O2.

• In very low levels of O2: shuts off the respiratory enzymes. The yeast then leads a fermentative life, in which sugar is partially and non-oxidatively utilized for energy and the ‘waste’ product is ethanol.

• adequate O2 is available; sugar is converted by the respiratory enzymes to CO2 and H2O, as well as to intermediates needed for the cell biomass.

• in microaerophilic conditions (often erroneously termed ‘anaerobic’ conditions), the yeast grows significantly more slowly than in aerobic conditions.

• The maximum theoretical yields of yeast solids:

• microaerophilic (anaerobic) :7.5 kg/100 kg of sugar utilized. aerobic conditions : 54.0 kg/100 kg of sugar utilized In the case of S. cerevisiae: the conc. of the sugar influences the availability of O2. If the medium contains > 5% glucose: glucose utilization via the TCA (tricarboxylic acid) cycle is almost completely blocked.

Even if the culture is aerated, glucose can only be fermented, this phenomenon being known as the ‘glucose effect’ or the ‘Crabtree effect’.

• For aerobic growth, therefore, the sugar has to be supplied incrementally so that the rate of growth of the yeast (μ) does not exceed 0.2 and the respiratory quotient (RQ) is maintained at the value of 1.

• In aerobic conditions, as much as a third of the available sugar is metabolized via the hexose monophosphate pathway, generating NADPH, which is mainly utilized in synthetic reactions.

• aerobic growth conditions:  the yeast’s metabolism is elegantly balanced, generating chemical energy for cellular metabolism and precursor molecules for cell growth and proliferation.

• The TCA cycle is important: involved in the production of both the biomass precursor molecules and the chemical energy.

• S. cerevisiae also possesses the enzymes involved in the ‘glyoxylate shunt’. This replenishes the TCA intermediates taken up for biomass formation.

pH

• S. cerevisiae grows optimally at pH 4.5–5.0, although it can tolerate a pH range of 3.6–6.0.

• At higher pH values, the yeast’s metabolism shifts, producing glycerol instead of ethanol in microaerophilic conditions.

• In the production of bakers’ yeast an initial pH at the lower end of the range inhibits the growth of bacterial contaminants.

• As the process progresses towards harvesting, the pH is raised slightly so that any colouring matter taken up by the yeast from the molasses is desorbed.

Temperature

• S. cerevisiae has one of the shortest generation times amongst yeasts, 2.0–2.2 h at 30°C.

• Bakers’ yeast production is optimal: at 28–30°C.

Preparation of Medium

• The molasses (containing around 50% fermentable sugars and 80% soluble solids) is usually diluted with an equal weight of water, and the pH is adjusted to 4.5–5.0 with sulphuric acid.

• The diluted molasses is clarified using a desludger centrifuge.

• Clarification by filtration is recommended for beet molasses, but is not necessary for cane molasses.

• The clarified molasses is then sterilized by the high temperature short time (HTST) process.

• Other sterilization methods, which involve prolonged heating at low temperatures, cause caramelization and hence a decrease in the fermentable sugar content.

• Medium supplements are added: a nitrogen source (e.g. urea, 2.5 g l−1); potassium orthophosphate (KH2PO4), 0.96 g l−1; hydrated magnesium sulphate (epsomite,MgSO4.7H2O),                  defoamer (silicone, fatty acid derivatives or edible oil), The molasses is then transferred to the fermenter, filling it to about two-thirds of its total volume, and pitching yeast is added.

• More clarified molasses is added incrementally in the fed-batch cultivation.

• A substrate of starch (from corn, sorghum or tubers), hydrolysed by acids or enzymes, or of sugar cane juice, does not require elaborate clarification.

• Supplementation with a nitrogen source, minerals and vitamins is, however, necessary.

Cultivation

• In industry, bakers’ yeast is produced in fermentation tanks with a capacity of 200 m3 or more.

• Tanks, and all connecting tubes, should preferably be made of stainless steel.

• The design and operation of fermenters for the production of bakers’ yeast must be carefully considered given the interrelationship between aeration, the specific growth rate of yeast and the substrate concentration.

• The facility for bubbling compressed air (as a source of O2) into the medium, to ensure effective aeration, is therefore particularly important.

• In practice, O2 transfer in a fermentation system can be manipulated by adjusting the bubble size and by the dispersion of air in the cultivation medium, by using mechanical agitation close to the point of entry of air into the medium.

• The facility for bubbling compressed air (as a source of O2) into the medium, to ensure effective aeration, is therefore particularly important.

• In practice, O2 transfer in a fermentation system can be manipulated by adjusting the bubble size and by the dispersion of air in the cultivation medium, by using mechanical agitation close to the point of entry of air into the medium.

• The level of dissolved O2 during fermentation can be determined by using O2 electrodes

• a typical cultivation tank used for the production of bakers’ yeast, an airlift fermenter.

• It consists of a cylindrical vessel, provided with a sparger (aerater) at the bottom for producing air bubbles in the medium.

• Aerobic growth results in the generation of almost 14 650 J of heat per gram of yeast solids, and because cultivation has to be carried out at 28–30°C, cooling is necessary.

• This is achieved by cooling coils.

• Directional flow of the cultivation medium is achieved by pumping air in at the bottom of a ‘draft tube’. If the depth of the broth exceeds 3 m, the use of compressed air, to overcome the hydrostatic pressure of the liquid, is recommended.

• The manufacture of bakers’ yeast begins with a number of stages which build up production, and involve the inoculation of the medium with pitching yeast. This development process is usually divided into eight stages, in which the yeast solids are gradually built up from the slope or flask culture of yeast.

• Over the eight stages, 0.2 kg of yeast solids give a final yield of about 100 000 kg of yeast.

• In the first two stages, sterilized medium and pure yeast cultures are employed in pressurized tanks, but the subsequent stages are operated in open tanks.

• The entire process is known to involve 24 generations of the yeast

Maturation

At the end of the final stage of yeast cultivation, the feed rate is
greatly reduced. This allows the yeast cells to mature and results in a low proportion of budding cells, which confers higher stability on compressed yeast in storage.

Finishing Stages

• Yeast Cream

• The culture broth can be centrifuged in a continuous centrifuge (with a vertical nozzle) at 4000–5000 g, leading to almost complete recovery of the yeast cells.

• In the first run, around two-thirds of the fluid can be removed and in subsequent runs further concentration of the cells is achieved, producing a slurry called ‘yeast cream’, which contains about 20% yeast solids.

• Yeast cream can be stored at 4°C for a number of days, with good retention of viability.

• Compressed Yeast

• This is prepared from yeast cream by filtration or by pressing in a filter press.

• Rotary continuous vacuum filters can also be used.

• The pressed cake thus obtained is mixed with 0.1–0.2% of emulsifiers such as monoglycerides, diglycerides, sorbitan esters and lecithin, and then extruded through nozzles.

• The extruded material, in the form of thick strands, is cut into suitable lengths and packaged (usually in packs of about 500 g) in wax paper or polythene sheet.

• The compressed yeast must be rapidly cooled, and stored at 5–8°C.

• Active Dry Yeast (moisture content of 4.0–8.5%. )

• Active dry yeast is useful in situations (e.g. homes) where storage at low temperatures is not possible.

• It is prepared by spreading out the pressed yeast cake to produce thin strands or small particles, which are then dried.

• Generally, a tunnel drier is used, taking 2–4 h with the air inlet temperature maintained at 28–42°C.

• continuous drying or fluidized-bed drying (airlift drying), is also available.

• Emulsifiers such as sucrose esters or sorbitan esters (0.5–2.0%) are mixed with the dried yeast to facilitate rehydration.

• Antioxidants, such as butyl hydroxyanisole(BHA) at 0.1%, are also added, to prevent undesirable oxidative changes.

• 1 g compressed yeast = 0.4-0.45 g dry yeast

• Rehydration:

• X g yeast + 4X g water  at 37.8-44.5 C

• T < 32 C …..or  T>46 C

– The glutothione leaches out of yeast and causes to dough become soft and sticky

– Cell contents ( a acids, vitamins,  nucleic acids, coenzymes,glutothione and inorganic salts) leaches out and fermentative power of yeast decreases. To produce dry yeast products heat resistant strains are used and heat resistant strains generally carries low gassing power.

Lysine-enriched Yeast

• Strains of bakers’ yeast which can convert precursor molecules such as 5-formyl-2-oxovalerate or 2-oxo-adipate to lysine, with high efficiency, have been reported.

• The use of such strains for the fortification of lysine-deficient cereals has potential.

Vitamin-enriched Yeast

• The addition of thiazole and pyrimidine to the cultivation medium has been shown to cause bakers’ yeast to synthesize high levels of thiamin (around 600 μg g−1).

• The irradiation of bakers’ yeast with ultraviolet light has been shown to convert ergosterol to calciferol (vitamin D2), with a vitamin potency reaching as much as 180 000 USP units per gram of yeast.

• Such strains will be useful for the fortification of food, feed and pharmaceuticals.

• High µ(sp g rate)..high potein..high activity..low carbohydrate..low stability Low µ.. low p..low a…high c…high stability

• Better sanitation, fewer fermentation stages, lower PH

lower contamination

• High µ(sp g rate)..high potein..high activity..low carbohydrate..low stability

• Low µ.. low p..low a…high c…high stability

• Better sanitation, fewer fermentation stages, lower PH

• Should be free of Salmonella, Listeria , E. coli and low coliform

• Normal level of bacteria and wild yeast available –no problem because  flour and other ingredients contain these ( bakers yeast outnumbers them)

• Low PH  gives higher purity but darker color

• Storage time, temp makes yeast darker, gummier and lower performance

• Tendency of yeast to grow via respiration when high level of oxygen are present is known as

Pasteur effect

• commercial bakers yeast fermentations use high aeration and incrimental feeding to maintain high oxygen and low sugar levels throughout the process.

• Maltose Adaptation

• for good production of gas: yeast requires a plentiful and continuous supply of glucose as an energy source.

• The action of α- and β-amylases of flour in damaged starch gives maltose ; transported into the cell; broken down into two molecules of glucose.

• metabolic system active ;when yeast detects  maltose ;takes some time (lag phase).

• maltose adaptation is different for rapid and standard yeast strains.

• The choice of one over another depends on the breadmaking process to be used.

Temperature

• at 4 °C, no activity,  no fermentation

• at 10–15 °C, yeast activity, fermentation; slow

• at 20–40 °C, fermentation ; very active

• at 45 °C yeast activity slows down

• at 55 °C, the yeast dies.

• the best storage temperature: 4 °C (0–10 °C).

• an increase of 1 °C gives an 8–12% increase in fermentation speed.

• at 38 °C, more gas production, also lactic and butyric fermentation (which is undesirable).

• pH

• very tolerant to fluctuations in pH (2–8),

• but the optimum pH :4 and 6.

• Usually, the pH of dough is 5

Presence of Dough Inhibitors

• The copper and chlorine in water, fermentation inhibitors.

• Organic acids, acetic and propionic acid, fermentation inhibitors.

Sources of Sugar used by Yeast

• Yeast uses

• (1) trehalose (Trehalose is a non-reducing sugar formed from two glucose units joined by a 1-1 alpha bond very resistant to acid hydrolysis) endogenous

• (2) free sugar from flour

• (3) sugars obtained by the action of enzymes in oligosaccharides and polysaccharides in the flour, or added as additives

• (4) added sugars such as sucrose.

• Order: 1- trehalose 2-free sugars and sugars added 3- maltose.

Production and Retention of Gas

• Kneading ; air is incorporated into the dough, and air bubbles are formed.

• These bubbles contain mainly nitrogen;low solubility in water, and oxygen is quickly used up

• Yeast cannot create new bubbles, as the pressure (P) in a bubble is related to the radius (r) of the bubble and the interfacial tension (γ) by the law of Laplace: P = 2γr.

• The more bubbles are formed, the finer the grain is.

• carbon dioxide is produced in the aqueous phase, the pH decreases, and this phase becomes saturated with carbon dioxide.

• the dough is leavened, because the aqueous phase is saturated by CO2 and the newly formed CO2 is retained in preexisting bubbles.

• the quality of gluten is also very important to retain the gas

• carbon dioxide is retained in the dough in two phases: contained within the gas cells and dissolved in the aqueous phase.

• At the pH of dough, most of the carbon dioxide is present as CO2 and a small amount of this as CO32− HCO3−, or H2CO3.

• Only 45% of the total gas produced is present at the end of
fermentation. (lost in  initial fermentation, punching, rounding, molding, and final fermentation.

Salt

• to provide flavor,

• influence the rheological properties of dough.

• Higher concentrations of salt inhibit enzymatic reactions and also inhibit the fermentation activity of yeast.

• In general, the proportion of salt used is 1–2% (based on flour weight).

Water

• Mineral constituents of the dough water (mainly carbonates and
sulfates)

• give a firmer, more resistant gluten;

• the doughs do not collapse during fermentation,

• the gas retention is improved, and with a normal volume,

• the grain is finer and more elastic

Optional Ingredients

• Fat

• fat increases the shelf-life,

• produces a finer grain,

• yields a greater volume of baked foods (10%).

• The crust is more elastic and softer.

• The shortening effect ( film between the starch and protein)

• mono and diglycerides or lecithin, promote the formation of this film

• The shortening effect is greater for fat with a lower melting point than for harder fats. ( hydrogenated vegetable fats)

• the use of fat requires less water in the formulation.

Sugar

• promotes fermentation,

• browning of the crust,

• sweeter taste.

• dough more stable, more elastic, and shorter, and the baked goods more tender.

Milk and Dairy ProductsMilk, skim-milk powder, whey containing lactosepromotes browning, a softer crust, and a longer shelf lifeOxidantsthe oxidation of -SH groups of protein to -SS-groups,improved gas retention. disulfide bonds: between protein chains lead to a firmer gluten The time of dough maturation is shorter, the oven spring is greater, the volume is large, the quality of the grain is better.The oxidant commonly used is ascorbic acid