Yeast Leavening in Bread Making

Leavening Property of Yeast in Bread Making

• CO₂ production, sugar metabolism, and CO₂ incorporation all contribute to this process
• Sugars in the dough are fermented by yeast
• This process releases carbon dioxide which forms bubbles
• These bubbles cause the dough to rise
• Yeast breaks down fermentable sugars, focusing on maltose which aids in leavening
• This process produces CO₂
• Hexose sugars, especially maltose, are fermented by yeast
• CO₂, ethanol, and secondary metabolites are produced
• These byproducts contribute to flavor and aroma
• Gas incorporation increases dough volume creating leavening
• The flavor and texture is enhanced
• Vitamins and amino acids are fermentation products that provide health benefits

Bread Making Process

• Yeast is mixed with flour, salt, and warm water/milk
• Dough is kneaded until smooth and left to rise
• Some doughs undergo a second rising after kneading
• Longer rising improves flavor but can cause final stage failure if excessive
• Dough is then shaped, allowed to rise again, and baked

Yeast in Baking

• Most yeasts in baking are similar to those in alcoholic fermentation
• Saccharomyces exiguus is a wild yeast sometimes used in baking which is found on plants, fruits, and grains

Yeast Respiration

• Yeast produces CO₂ and water during the aerobic stage
• During the anaerobic stage, when oxygen is depleted, yeast produces ethanol, which evaporates during baking

Amylolytic Activity

• Fermentable sugars in wheat flour dough are sourced from naturally present saccharides
• Glucose, fructose, and maltose are naturally present saccharides (~0.05%)
• Sucrose and raffinose are also saccharides (0.2%-0.3%)
• Wheat bran has higher sucrose concentrations (1.75%-3.0%)
• Whole meal dough contains more free saccharides than refined flour

Role of Damaged Starch

• Fermentable sugars come from damaged starch degradation due to the low content of free saccharides
• Milling causes damaged starch (5%-8% in hard wheat flours)
• Amylase enzymes acting on starch linkages degrade starch into maltose

Types of Amylases in Wheat Flour

• Alpha-amylase (endo-amylase) randomly hydrolyzes starch into oligosaccharides and α-limit dextrins
• Beta-amylase (exo-amylase) cleaves maltose from the non-reducing end of starch chains

Amylolytic Activity in Dough

• It defines the ability of flour-water suspension to produce maltose
• Unyeasted dough experiences rapid maltose increase
• Maltose increases from 0.1% in flour, to 1% after mixing, to 2% after 180 minutes
• Higher damaged starch content and α-amylase activity leads to increased maltose levels

Enhancing Amylolytic Activity

• Fungal α-amylase or malt-derived α-amylase is often added to flour
• This addition is essential for efficient yeast strains to support dough leavening

Other Names for Saccharomyces cerevisiae

• Also known as baker's or brewer's yeast, depending on application

Kneading

• Kneading is the process of working and manipulating dough to improve elasticity and create a uniform texture
• It helps in trapping air, which contributes to the dough’s structure and rise

Panning

• Panning is the process of placing shaped dough into baking pans or molds before proofing
• Proper panning ensures a well-formed final product

Amylase

• Amylase is an enzyme that breaks down starch into simpler sugars, such as maltose and dextrin
• It plays a key role in digestion and food processing
• Alpha-amylase is in saliva and the pancreas to help break down large starch molecules
• Beta-amylase is common in plants & bacteria and breaks starch down into maltose
• Amylase enhances texture and flavor in baking, brewing, and the food industry

Microorganisms That Produce Amylase

• Bacillus subtilis is widely used in industrial amylase production
• Aspergillus niger is used for producing fungal amylase in food and fermentation
• Bacillus amyloliquefaciens produces thermostable amylase
• Saccharomyces cerevisiae produces amylase during fermentation
• Thermomyces lanuginosus produces heat-stable amylase

Industrial Applications of Amylase

• It is used in baking to improve dough handling and bread texture
• It is used in brewing to breakdown starch into fermentable sugars for alcohol
• It is used in dairy processing to modify starch-based thickeners in yogurts and puddings
• It is used in the textile industry to remove starch-based sizing agents
• It is used in the paper and pulp industry to improve paper coating and quality
• It is added to laundry and dishwashing detergents to break down starch-based stains
• It is used in biofuel production to convert starch into fermentable sugars for biofuel
• It helps in digestive enzyme supplements and the formulation of glucose syrups
• It is applied in the biodegradation of food waste and wastewater

Amylase Reaction With Starch

• Amylase binds to starch (α polysaccharide composed of amylose and amylopectin) in substrate binding
• Amylase cleaves the α-1,4 glycosidic bonds in starch through hydrolysis, producing smaller carbohydrate molecules

Formation of Products

• Substrate binding and the hydrolysis of glycosidic bonds causes this by the amylase reaction
• Alpha-amylase breaks starch into maltose, maltotriose, and dextrins
• Beta-amylase produces maltose units
• Glucoamylase further breaks down maltose into glucose

Gram's Iodine in Starch Hydrolysis Test

• Used to determine whether bacteria can break down starch using amylase
• Iodine reacts with starch to form a blue-black complex if starch is present
• If bacteria produce amylase, they break down starch into smaller sugars
• Hydrolysis will be evident by a clear zone around bacterial growth, confirming amylase activity
• If no starch hydrolysis occurs, the iodine stains medium blue-black, indicating starch is still present

Results of Starch Hydrolysis

• Positive test results in a clear zone
• Negative test results in a blue-black color
• It is commonly used to differentiate amylase-producing bacteria like Bacillus species

Fermenter

• It's also called a bioreactor
• It converts organic substrates into desirable products using microorganisms such as bacteria, molds, and yeasts
• A contamination-free environment is ensured during the process
• Specific conditions like temperature, agitation, aeration, and pH are maintained
• Optimized monitoring of oxygen levels occurs
• Nutrients and reagents are provided, with inoculation and sampling available
• Optimized for scale-up
• It involves minimal liquid loss and usage for diverse types of microorganisms

Stages of Fermentation

• Upstream processing happens in the preparatory stages
• This involves the preparation of liquid medium and the removal of particulates and inhibitory chemicals
• Sterilization of medium and air purification also takes place
• Fermentation processing converts substrates into the desired product using biological agents
• This includes bacteria, molds and yeasts
• Downstream processing happens after fermentation
• This involves the separation of microbial cells from fermentation broth, purification and concentration
• The final step is waste disposal or recycling

Fermenter Shape

• It is mostly made in cylindrical shapes
• The shape facilitates uniform mixing, aeration, and temperature control for microbial growth
• It minimizes zones where microorganisms don't receive nutrients/oxygen
• The cylindrical design withstands internal pressure
• This makes it ideal for steam sterilization and maintaining aseptic conditions
• Volume-to-surface area ratio is optimized, ensuring efficient heat transfer and gas exchange

Sauerkraut

• "Sauerkraut" means sour cabbage
• It is made from cabbage with ascorbic acid, vitamins, and minerals
• It is used for salads and culinary use
• Post-harvest losses can be as high as 60%

Fermentation and Preservation of Sauerkraut

• Fermentation has been used for preservation and product development since ancient times, making sauerkraut an acid-fermented product
• Natural fermentation happens with 2-3% salt
• Lactic acid is the major product, giving it a unique flavor & texture

Microflora of Sauerkraut

• Wild fermentation happens since there is no starter culture
• This process relies on natural bacteria from cabbage leaves
• The process is governed by pH changes

Floral Succession of Sauerkraut

• Coliform bacteria start fermentation
• Leuconostoc (Heterofermentative lactic acid bacteria) produces CO₂ & acid
• Lactobacillus or sometimes Pediococcus succeeds Leuconostoc
• Final fermentation involves a stepwise succession of three bacterial groups
• Lactobacillus (or sometimes Pediococcus) succeeds Leuconostoc as the pH continues to decrease

Salt in Sauerkraut Fermentation

• Salt creates osmotic imbalance, drawing out water and nutrients from cabbage leaves
• The fluid forms a rich growth medium for fermentation microbes
• Spoilage organisms and pathogens are inhibited, but desired thrived
• Cabbage contains about 90% water, and salt dissolves completely in it
• The actual salt concentration in brine is around 2.8%
• If salt isn't evenly distributed, it can lead to spoilage (low salt pockets) or failed fermentation (high salt pockets)

Oxygen Supply During Sauerkraut Fermentation

• Oxygen exclusion is critical during fermentation
• Spoilage organism grow if oxygen is present, and it increases acid-loving molds and yeasts

Temperature and Time of Sauerkraut Fermentation

• Optimal temperature is 70°F (21°C)
• Fermentation occurs for 3-6 weeks if conditions are favorable

Key Changes at the End of Sauerkraut Fermentation

• Typical aroma develops
• All fermentable carbohydrates are consumed
• Acid content increases to 1.85 - 2.2%
• pH drops to 3.5 – 3.7

Increased Keeping Quality of Fermented Cabbage

• Fermented cabbage (sauerkraut) has increased keeping quality due to the production of lactic acid by naturally occurring lactic acid bacteria (LAB)
• Lactic acid lowers pH, creating an acidic environment that prevents spoilage and inhibits the growth of harmful bacteria
• Natural preservation is enhanced by producing antimicrobial compounds, consuming oxygen, which reduces oxidation and microbial spoilage
• The fermentation process is regulated as it slows down, ensuring gradual and controlled acidification

Inoculum of Sauerkraut

• Inoculum is not needed because naturally-occurring lactic acid bacteria are already present
• These bacteria initiate spontaneous fermentation under anaerobic conditions
• Salt promotes selective growth of beneficial microbes without the need for an external starter culture

Salt Addition During Sauerkraut Fermentation

• Salt draws out water from cabbage cells, creating a brine that prevents spoilage
• It selectively inhibits undesirable microorganisms while allowing beneficial lactic acid bacteria to thrive
• Adding salt enhances flavor, texture, and firmness, preventing excessive softening of cabbage tissues

Wine

• The product of alcoholic fermentation of fruit juices for fermentable sugars
• Classified as a primary metabolite, produced during the primary growth phase of microorganisms
• Ethanol is formed as part of energy metabolism in yeast and certain bacteria under anoxic conditions

Microbial Fermentation

• Saccharomyces ellipsoides is the primary yeast
• Wild yeasts on fruit ferment sugars naturally
• Selected yeasts are used for controlled production
• Alcoholic beverage production is a major global industry

Types of Alcoholic Beverages

• Produced by the fermentation of fruit juice makes wine
• Produced by the fermentation of malted grains makes beer
• Produced by concentrating alcohol through distillation makes distilled beverages

Types of Wine

• All sugars are fermented in dry wine
• Some sugars remain unfermented or extra sugar is added in sweet wine
• Brandy or alcoholic spirits are added in fortified wine
• Significant CO₂ comes from final fermentation in sparkling wine

Alcohol Content

• Most wines have 11-12% alcohol content
• Dessert wines have a higher alcohol content of 19-21%

Organoleptic Tests in Wine

• Oxidation in white turning brown indicates oxidation and over-aging of Appearance
• Bacterial spoilage comes as a silky, wavy sheen in cloudy wine with a distinct odor of Appearance
• High content of acidic red wines appear bright in color regarding Appearance
• Color changes depends on if it is White Wine or Red Wine

Bouquet vs. Aroma

• The bouquet comes from odors developed through aging (esterification, oxidation)
• Aroma comes from the odor derived from fresh grapes

4 Aspects of Taste

• Sour (acidity) is important for all wines
• Sweetness is essential for sweet table and dessert wines and critical for sparkling wines
• Saltiness is not a primary characteristic in wine
• Bitterness is present in red wines and is caused by acidity balance, low acidity results in flat or insipid taste

Flavor Combinations

• The combination of bouquet (aging-related odors), aroma (grape-derived odor) and taste perception on the tongue

Red vs. White Wine

• Red wine is made from red/black grapes, fermented with grape skins that gives it a dark color and tannins
• White wine is made from white/green/red grapes without skins, resulting in a lighter color and milder taste

Examples of Metabolites in Wine

• Ethanol is the primary metabolite produces during yeast fermentation
• Penicillin is the secondary metabolites produced

Raw Materials in Winemaking

• Grapes are rich in sugars
• Saccharomyces cerevisiae or Saccharomyces ellipsoideus are the yeast products

Inoculation in Winemaking

• Inoculation ensures a controlled and efficient fermentation
• It prevents contamination and helps in consistent flavor and alcohol production

Centrifugation

• It uses centrifugal force to separate particles based on size, shape, density, viscosity, rotor speed
• Denser particles move outward, and less dense particles stay closer to the center

Types of Filtration

• Filtration is a physical separation method that removes solids from a liquid using a filter medium
• Solid particles are retained on the filter, and liquid passes through

Filtrate

• Filtrate is the liquid that passes through the filter, and oversize is the solid material retained by the filter
• Filtration is used in various industries for purification and product recovery

Centrifugation Techniques

• Filtration separates membranes with specific pore sizes
• Sedimentation allows cells to settle based on gravity
• Flocculation uses chemicals to aggregate cells for easier separation
• Chromatography separates cells or components based on interactions with a stationary phase

Centrifugation

• Separates particles based on size, shape, and density by applying centrifugal force
• Heavier particles move outward (form a pellet), while lighter ones stay in the supernatant

Svedberg

• Measuring the units and the sedimentation during centrifugation
• Higher values indicate larger, denser particles
• It provides maximum production of desired molecules before reaching the stationary phase

Late Log Phase Cultures

• They are preferred for higher biomass yield due to active growth
• Metabolically active cells with intact cell walls
• It prevents the release of unwanted intracellular components

Milk as a Nutritional Source

• Complete and nutritious food, rich in protein, vitamins, minerals, carbohydrates and lipids
• It serves as the primary protein source for humans

Milk/Types of Proteins

• The primary protein in cow's milk, existing as calcium caseinate in a colloidal suspension known as casein
• A phosphoprotein containing phosphate groups, forming micelles that remain dispersed at normal milk pH (~6.6)

Types of Casein

• α-Casein (Alpha)
• β-Casein (Beta)
• κ-Casein (Kappa)
• γ-Casein (Gamma)

Casein Solubility

• It is insoluble in water and precipitates when acids or enzymes are added, insoluble in water and precipitates when acids or enzymes are added

Isoelectric point of Casein

• pH 4.6 (casein precipitates at this pH)
• Unlike whey proteins, casein does not denature at high temperatures

Separation of Casein From Milk

• Acid precipitation is done by lowering the pH to 4.6 to neutralize negative charges
• Organic acids used for this are acetic acid, citric acid
• Enzymatic precipitation does rennet to cleave κ-casein to allow micelles aggregate and form curds (used in cheese production)

Uses of Casein

• It has a high nutritional value of essential amino acids
• It is slowly digested and forms a gel in the stomach and slowly releases protein
• Used as the basis of curd formation for cheese production
• Has industrial applications in adhesives, paints and coatings
• It is also a dietary supplement, used in protein powders

Lactalbumins

• Refined as water-soluble whey proteins that remain when casein is precipitated

Lactalbumins Function

• Essential for lactose synthesis is mammary glands
• It is easily digestible and highly bioavailable, rich in tryptophan, the sports supplement protein/whey
• Used in sports supplements and infant formulas

Lactoglobulins

• Major whey proteins, particularly β-lactoglobulin, that bind and transport fat-soluble molecules
• It is a carrier of fat-soluble vitamins (A, D, E, K).
• Also rich in branched-chain amino acids (BCAAs) for muscle growth. Has antioxidant properties and used for emulsification

Acid Precipitation of Casein

• Casein micelles have been neutralized and caused to precipitate
• This is achieved through the leaves of the calcium ions solution

Common acids used

• The typical Hydrocholirc (HCl), Sulfuric (H2SO2), Acetic Acid (vinegar) and Citric Acid

Whey - Serum Proteins

• 18% of milk proteins, Do no contain phosphorus or remain pH 4.6

Natural Casein Separation-Curd Formation

• Lactobacillus ferments lactose and lowers the production causing the to coagulates

Curd Formations

• Curd is process of lactose, proteins essential

Whey Proteins vs Casein

• 80% Whey including the the production
• Includes lactalbumins proteins, Lactobacillus