CS代考 Food Microbiology and Safety

Food Microbiology and Safety
AProf Helen Billman-Jacobe

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Intended learning outcome
Explain how and why microbial enzymes are used in food production

Microbial products for food production: Enzymes
Enzymes are the large biomolecules that are required for the numerous chemical interconversions that sustain life.
They accelerate all the metabolic processes in the body and carry out specific tasks.
Enzymes are highly efficient, which can increase reaction rates by 100 million to 10 billion times faster than any normal chemical reaction.
Microbial enzymes are currently acquiring much attention with rapid development of enzyme technology.

Microbial enzymes are often preferred over live microorganisms due to :
• their economic feasibility
• high yields
• consistency
• ease of product modification and optimization
• stability
• high catalytic activity
• rapid growth of microbes on inexpensive media
• regular supply due to absence of seasonal fluctuations •

Some uses of microbial enzymes in food processing
pectinase for treatment of fruit juice (fresh juice or wine industry) pectinase in chocolate fermentation
lactase to make low lactose foods
amylases for the conversion of starch into dextrins or glucose proteases in cheese manufacture
proteases in soybean products (miso, soy sauce or tempeh) glucose isomerase for the production of fructose-rich corn syrup.

Major uses
• treatment of fruit juices to reduce the cloudiness, viscosity and bitterness of fresh fruit juices
• break down grape pulp for winemaking extraction of tomato pulp
• to remove the mucilaginous coat from coffee beans in coffee fermentation

is a general term for enzymes commonly referred to as pectic enzymes.
Pectic enzymes is a collective term that includes • pectin lyase
• pectin methylesterase
• polygalacturonase
These break down pectin, a polysaccharide substrate that is found in the cell walls of plants

Pectins are high molecular weight acid polysaccharides, primarily made up of α-(1→4) linked D-galacturonic acid residues with a small number of rhamnose residues in the main chain and arabinose, galactose and xylose in the side chain. Different pectinases cleave different bonds in pectin

Pectin in fruit juice processing
During the early stages of fruit juice production, the fruit pulp has a lot of associated pectin giving the juice a gelatinous and viscous texture
Pectin impacts on the sensory properties of the juice and its colour, but also importantly impacts on the juice extraction process.
Pectin, a major component of juice cloud, is thought to play an important role in juice destabilization.
Pectin forms calcium pectate complexes and causes the precipitation of cloud particles

Pectinase in fruit juice processing
Pectinase is used commercially to aid in extracting juice from fruit.
By enzymatically breaking down the cell wall, pectinase releases the juice from within the cells.
Pectinases can be used to clarify cloudy juices such as apple juice
Cloudy juices are processed with some pectinases, particularly polygalacturonases, but with the purpose of stabilising the cloud of the juice

Apple juicing process

Product Description
Fructozym® P is a liquid, highly concentrated pectolytic enzyme preparation for a fast and complete pectin degradation in fruit mash and fruit juice.
rapid breakdown of pectic substances in fruit mash for enhanced pressability and liberation of valuable fruit ingredients.
complete pectin degradation in juice, precondition for good clarification and filtrability.
rapid degradation of pectin results in a drastic reduction of mash viscosity, thus good pressability, high juice yield a
In the juice, Fructozym® P breaks down the pectin skeletal structure which has a stabilizing effect on sediments, thus creates the prerequisite for good clarification and filtrability.
http://www.vigoltd.com/files//b647b152-f5db-4a0c-9938- a182009548fe/94371%20Fructozym_P.pdf

Microbial pectinase
Bacillus, Erwinia, ,
Aspergillus, Rhizopus, Penicillium and Fusarium are good producers of pectinases
Filamentous fungi, such as Aspergillus niger and Aspergillus carbonarius and Lentinus edodes, are preferred in industries since approximately 90% of produced enzymes may be secreted into the culture medium

Aspergillus niger
Aspergillus is particularly useful industrially
The fungal metabolites produced by Aspergillus are penicillin, citric acid, koji acid, L_malic acid, amylase, catalase, cellulase, galactosidase, glucanase, glucosidase, hemicellulase, lipase, pectinase and protease
It is ‘Generally Recognised as Safe’
Aspergillus niger produces more than one different type of pectinase Grown in solid state or submerged fermentation systems (more later)

is used in the manufacture of low lactose dairy products
Lactase (β-D-galactosidase) hydrolyzes milk lactose into its constituent monosaccharides, glucose and galactose.
Chemical and physical changes that occur as a result of lactose hydrolysis
The principal changes are • reducedlactosecontent
increased carbohydrate solubility increasedsweetness
higher osmotic pressure
reduced viscosities morereadilyfermentablesugar.
Enzymatic hydrolysis of lactose in dairy foods improves product quality and provide low-lactose products for the lactose intolerant people

Beta-galactosidase is highly important in the dairy industry, in the hydrolysis of lactose into glucose and galactose with an improvement in the solubility and digestibility of milk and dairy products.

Natural sources include
• animal organs such as the intestine, the brain and skin • peaches, almonds and certain species of wild roses
Bacteria: Escherichia coli, Lactobacillus bulgaricus, Streptococcus lactis and Bacillus sp
Yeasts: Kluyveromyces lactis, K. fragilis and Candida pseudotropicalis Filamentous fungi: Aspergillus foetidus, A. niger, A. oryzae and A. phoenecia.

Lactase from different LAB fount in dairy fermentations
In this research paper, scientists compared different Lactobacillus bacteria to see which produced the most lactase and the highest activity lactase
J. Sci. Res. 4 (1), 239-249 (2012)

Harvesting microbial products
from cultures: Batch culture
Cell density and medium composition change constantly throughout the growth cycle so it is impossible to choose and maintain a particular environment
Increasing:
cell numbers Concentration of metabolic waste products
Decreasing: Oxygen Nutrients pH
Constant: Volume Temperature Mixing speed

Continuous culture
Continuous systems can achieve steady state conditions for a prolonged period Continuous culture systems can take a number of forms
• Stirred reactors-mixing is assumed to be instantaneous and perfect and the growth rate of the population is constant

Harvesting microbial products from cultures: Continuous culture,
In ports supply fresh medium containing the substrate
The impeller mixes the liquid culture
Out port is where the culture products are collected. Cells may be recycled
Gas supply constant O2.
The culture volume remains constant and the flow rate is set to match the growth rate so the cell density remain constant
F = flow rate S = substrate X = cells
P = product

Harvesting microbial products from cultures: Solid state
Base Acid sensors
Temp sensor

Harvesting microbial products from cultures: Solid state

Summary: Microbial enzymes
Enzymes can be produced from cultures for use in food processing
Methods of culture include batch culture, continuous culture, submerged fermentation and solid state fermentation
Examples: Pectinases, Lactase

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