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7 Food Preservation and Preservation Technology
Food microorganisms include food preservation, high-temperature sterilization of food and the characteristics of thermophilic microorganisms, low-temperature preservation of food and the characteristics of psychrophilic bacteria.
Edited at 2024-01-20 17:23:57
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Food Preservation and Preservation Technology
food preservation
Core: Prevent pollution, kill and inhibit microbial reproduction and delay the decomposition of tissue enzymes
Methods: using physicochemical biology
Purpose: Maintain nutritional value and sensory properties for a long time
High temperature sterilization of food and characteristics of thermophilic microorganisms
Principles and methods of high temperature sterilization
Principle: High temperature causes irreversible deformation of microbial proteins and nucleic acids or destruction of other components causing death (such as cell membranes being dissolved by heat)
Sterilization effect: Disinfection, sterilization
Temperature range: pasteurization, high temperature sterilization
dry heat sterilization
At high temperatures, the proteins in microbial cells coagulate and deform to achieve sterilization.
Flame sterilization: vaccination tools and contaminated items
Dry heat sterilization/hot air: 160 to 170 degrees Celsius, one to two hours
moist heat sterilization
Pasteurization
Applied to foods that are not suitable for high temperature processing
A sterilization method that is usually heated at less than 100°C to kill pathogenic bacteria and reduce the number of microorganisms.
Temperature and time combination: low temperature for a long time, high temperature for a short time
The effect varies depending on the type of food
Low-acid food pH greater than 4.6: no spore-forming pathogens, such as Mycobacterium tuberculosis in milk
Acidic food: pathogenic bacteria ➕ spoilage bacteria ➕ enzymes
Ultra-high temperature instant sterilization method
UHT: greater than 130 degrees Celsius, maintained for 3 to 5 seconds, kills vegetative cells and heat-resistant spore bacteria, suitable for liquid food
Preheat for 4 to 6 minutes at 75 to 85 degrees Celsius; 2 to 3 seconds at 135 to 150 degrees Celsius.
High pressure steam sterilization
Principle: Place the sterilized items in a closed pressure sterilization pot, and heat the water in the sterilization pot compartment to boil to generate steam.
Good sterilization effect
intermittent sterilization
High temperature resistant microorganisms
Thermotolerant bacteria: growth itself does not require high temperatures and survives at higher temperatures
After pasteurization, the remaining microorganisms include Streptococcus and Lactobacillus
Thermophiles: High temperature is necessary for growth and metabolic activities. They do not grow when ≤40°C. The optimal temperature exceeds 50°C and the maximum temperature exceeds 70°C.
Commonly used in the food industry are Bacillus, Clostridium and thermophilic anaerobic bacteria
Thermal lethality of microorganisms
Thermal lethal temperature
TDP: Indicates the minimum temperature required to kill all a certain number of certain microorganisms in a specific environment. It is also related to time and is no longer used in quantitative processing.
Usually refers to the heating treatment of a certain microorganism within a certain period of time, starting from the lowest heat treatment temperature at which the microorganism dies.
Thermal lethality rate curve
At a certain temperature, the relationship curve between heating time and the number of remaining microorganisms
Thermal death time TDT curve
TDT: The shortest heat treatment time required to kill all microorganisms or spores under specific conditions and thermal lethal temperature
The thermal death time curve is related to the environment, the type and quantity of microorganisms
D value, Z value, F value
D: Exponential decrement time, the time min required to kill 90% of microorganisms by heating at a constant temperature
test methods
Z: The temperature value required to change D by 10 times
To reduce D by one logarithmic period, the temperature needs to be increased
The temperature increases by 1Z, and D becomes one-tenth of the original value.
Reflects the tolerance of microorganisms to different temperatures
F: Thermal sterilization effect is equivalent to the equivalent sterilization time under 121℃
Using the thermal death time curve, the sterilization temperature and time combination can be converted into the sterilization time at 121 degrees Celsius for easy comparison.
12D: Minimum heat treatment intensity required to reduce the probability of survival of the most heat-resistant Clostridium botulinum spores to 10 to the power of 12, for use in low-acidic foods
Factors affecting microbial heat resistance
Water-peptide bonds are easily broken
High water activity and poor heat resistance, dry cells are more heat resistant than wet cells
Fat – affects water activity
Fat will enhance heat resistance, long-chain fatty acids are stronger than short-chain fatty acids
Protein and Colloidal Protection
Under the same pH value and the same bacterial count, the higher the protein and colloid content, the stronger the heat resistance. For example, nutritious broth has better heat resistance than pea soup.
carbohydrate
Enhance heat resistance and affect water activity
Salt
Reduce water activity and increase heat resistance; increase water activity and increase heat sensitivity.
Ph
antibacterial ingredients
Number of microorganisms: secrete protective substances
Age: low activity
The heat resistance in the stable phase is better than that in the logarithmic phase Old spores are more heat-resistant than new spores
growth temperature
Thermophiles are better than psychrophiles
Time and temperature: high temperature has good sterilization effect
The heat resistance of microorganisms themselves
Thermophiles are the most heat-resistant
Bacteria are better than non-spore bacteria
Positive is better than negative
Cocci are better than non-spore bacteria
Yeast and mold are sensitive, their spores are better than vegetative bodies, and sclerotia are heat-resistant
Spores as sterilization indicator bacteria
Canned production, non-acidic killing of Clostridium botulinum spores is the standard
In the fermentation industry, killing spores of Bacillus stearothermophilus is the standard
Heat resistance mechanism
Bacterial enzymes and proteins have the best high-temperature activity
Cell membrane: rich in long-chain saturated fatty acids, covalently cross-linked lipid bilayer, with a complete hydrophobic inner layer
Nucleic acids have high G and C content and more hydrogen bonds
Thermal stability of enzymes
Primary structure, increased hydrogen bonds, ionic bonds or hydrophobic bonds
Heat-promoting stabilizing factors: heat-resistant enzyme stabilizers such as calcium zinc, heat protectants
Application of thermophilic bacteria
Fermentation industry, high temperature resistance, fast growth, reducing pollution
Construction of genetically engineered bacteria
High temperature resistant enzyme: DNA polymerase, degrades starch, cellulose, protein, high temperature resistance, PH, salt tolerance
Low-temperature preservation of food and characteristics of psychrotrophic bacteria
Principles and methods of cryopreservation
principle
Enzyme activity and chemical reaction delay
The growth and reproduction rate of microorganisms is reduced or completely inhibited
Low temperatures prevent or slow spoilage
hibernate
method
Normal storage, cold temperatures
10～15, short term, vegetables and fruits
Refrigeration, refrigerator temperature
-1 to 8 days or weeks
frozen storage, freezing temperature
Less than -18, the growth arrest enzyme is inactivated
-5°C for Vibrio and -34°C for Rhodotorula foliaceus
Generally used for concentrated juice, bacon, ice cream, fruits
Microorganisms that tolerate low temperatures
Psychrophilic bacteria
Low temperature is necessary for growth
Microorganisms that grow between 0 and 20 degrees Celsius and have an optimal temperature between zero and 15 degrees Celsius
Generally located in seawater or extremely cold areas
Psychrotolerant bacteria
Mesophilic bacteria cause refrigerated food to deteriorate
0 to 7 degrees Celsius, such as Alcaligenes, Pseudomonas, Streptococcus
Effects of low temperature on physiological functions of microorganisms
low metabolic rate
Temperature drops, growth rate is low, lag period and generation time are extended
Higher enzyme activity at low temperature: Pseudomonas fragariae produces lipase at -29 degrees Celsius
Growth rate changes little with temperature
Temperature coefficient Q10
When the temperature increases by 10 degrees Celsius, the rate of biochemical reaction increases by a factor of 1.5 to 2.5.
The larger Q 10, the more significant the effect of temperature on growth.
Cell membranes transport solutes more efficiently—membrane function
mesophilic bacteria
Low temperature affects solute uptake
Protein conformational changes, leading to inactivation of permeable membrane proteins
Changes in the structure of the cytoplasmic membrane and decreased activity of permembrane enzymes
Lack of active transport energy
Psychrotolerant bacteria
Cold resistant sugar delivery system
Contains higher levels of unsaturated fatty acids
At low temperature, the transport permembrane enzyme activity is high
cold shock protein
Psychrotolerant bacteria have larger cells
Flagellar synthesis is more efficient
High nutritional requirements
Oxygenation is beneficial: aerobic or facultative anaerobic
Effects of freezing on microorganisms
Effects of freezing on microorganisms
Sudden death during freezing followed by gradual death
Death is fastest at temperatures slightly below freezing, especially at -2 degrees Celsius. It slows down at lower temperatures, and very slowly at -20 degrees Celsius.
Surviving microorganisms gradually die during storage
Cold shock: The temperature drops suddenly and live bacteria die in large numbers
Cold shock is related to culture temperature
Pseudomonas is sensitive to freezing when cultured at 30°C, but not sensitive when cultured at 10°C.
Resistance of microorganisms to freezing
Cocci are better than negative bacilli
Staphylococcus aureus and Clostridium are far superior to Salmonella
Endospores and toxins have no effect
Characteristics of some psychrotolerant and psychrotrophic bacteria
Increased unsaturated fatty acids
Increased low temperature
The conditional pathogenic bacteria of Pseudomonas are as high as 59-72% and have strong viability.
Candida is 50% more active at 10 degrees Celsius than at 25 degrees Celsius
Lipid solidification theory: With the increase in the synthesis of unsaturated fatty acids, lipids remain liquid and fluid at low temperatures to ensure cell membrane function.
Synthesizes high levels of polysaccharides, making them sticky
Low temperature production: dextran, viscous milk, viscous dough
Spoilage: bread becomes sticky, milk becomes sticky, meat becomes sticky
Leuconostoc and Pediococcus glucan synthase is inactivated when the temperature is higher than 30 degrees Celsius. Lactobacillus: thermosensitive glucan synthase
pigment formation
Serratia marcescens, its heat-sensitive enzyme, Prolosporium sweet potato
A large number of marine psychrophilic/psychrotolerant bacteria secrete pigments
Some molds and yeasts
Thermophiles do not secrete pigments
Different utilization of substrates
Fermentation of glucose, fermentation of sucrose
Hydrogenase synthesis system, sensitive to temperature
Applications of psychrophilic bacteria
Fermented foods to reduce contamination by mesophilic bacteria
Lipases and proteases are used in food and detergents Beer processing, cheese maturation
Used in medicine and food
Chemical preservation of food
Measures to use additives to improve the storage stability of food and maintain the original quality as much as possible, such as preservatives, antioxidants, anti-aging agents, anti-browning, etc.
Overview of preservatives
Principle: Acts on the cell membrane, increasing the permeability of the cell membrane, overflowing the contents, and breaking the respiratory chain; interfering with the enzyme system, destroying normal metabolism; coagulating and denaturing proteins, interfering with survival and reproduction
Conditions for functioning
Antibacterial spectrum: types of microorganisms inhibited
envirnmental factor
antibiotic
It is a secondary metabolite of microorganisms. It is highly efficient, non-toxic and has wide applicability. It is used to inhibit or kill microorganisms.
Nisin
A hydrophobic, positively charged small peptide composed of 34 amino acids
Non-toxic natural preservatives, no adverse effects on food
Principle: Destroy the cell wall, increase permeability, and leak content; inhibit cell wall peptidoglycan synthesis, blocking cell membrane and phospholipid synthesis
Antibacterial effect
Fungi, negative and invalid, negative after chelation with EDTA
Inhibit positive, strongly inhibit spore germination
factors that play a role
Low PH, high solubility, strong stability; Ph less than 4.5 anti-corrosion; combined use
application
Such as, canned fish products and alcoholic beverages
Natamycin
Streptomyces, fermentation method
Inhibit mold, yeast
Used in bakery, sausages, beverages and jams
subtilisin
32 aa make up a short peptide, which is stable to acid, has strong heat resistance and inhibits positive reactions.
Antibacterial properties: Sorbate is better than benzoate and propionate
Benzoic acid/salts and parabens
Mechanism: Undissociated state
Penetrates the cell membrane and enters the cell, interfering with the permeability of the membrane and inhibiting the absorption of amino acids by the membrane.
Interfere with the function of enzymes, such as the respiratory enzyme system
stunted growth
Benzoic acid-benzoic acid
White needle-like crystal, stable compound, slightly soluble in water and easily soluble in ethanol
Antibacterial activity is closely related to pH
Low Ph and strong antibacterial effect, suitable pH is 2.5~4 Ph neutral effect is weak
Mainly acts on yeast and mold, yeast is the best, bacteria is weak
toxicity
9 to 15 hours liver damage
Benzoic acid reacts with glycine in the human body to produce hippuric acid The remaining reacts with gluconic acid to form glucoglycic acid. These substances do not accumulate in the body and are safe preservatives.
Sodium benzoate
White granules or powder, easily soluble in water
Mainly acts on molds and yeasts
Used in juices, soft drinks, ketchup
Paraben-paraben
Low pH sensitivity: acidic and neutral, with a certain effect at 8.0
Broad antibacterial spectrum: completely inhibit negative and positive
It is better at inhibiting mold than yeast, but weakly against negative bacteria and lactic acid bacteria.
Sorbic acid and salt
Colorless needle-like crystals or powder, easily soluble in alcohol, Its salt is easily soluble in water, stable to light and heat, and easy to oxidize and color.
Functional characteristics
Generally used in the form of calcium salt, sodium salt, potassium salt
Acid type preservative: Ph affects the preservative effect
Antibacterial effect
mechanism
Combines with benzoic acid and sulfhydryl group to destroy enzyme action
Fungus inhibitors: mold, yeast
Ineffective against aerobic spoilage bacteria: Staphylococcus aureus, Salmonella, Pseudomonas Lactic acid bacteria are ineffective
propionate
mold inhibitor
Used in bread, cakes, cheese
lipophilic acid
Low-acid foods work better
Mechanism: Undissociated molecules have antibacterial activity
Nitrates and Nitrite
Sodium nitrite and sodium nitrate effects
Keep the meat red
According to national standards, only sodium (sub)nitrate and potassium nitrate can be used as color-protecting agents, and they can only be used in some meat products.
The color development mechanism is that under acidic conditions, nitroso groups combine with myoglobin to form nitrosated myoglobin.
flavor development
acting microorganisms
Inhibit some putrefactive toxin-producing bacteria
Perigo factor (nitrite reacts with the medium to generate antibacterial effects): When nitrite is heated in a specific medium, anti-botulinum factors or inhibitors are produced, which increases the antibacterial effect by about ten times. This anti-botulinum factor Botulinum toxin factors or inhibitors are called ~
Clostridium: Clostridium botulinum, Clostridium perfringens
High concentrations of Staphylococcus aureus, lactic acid bacteria, and intestinal bacteria have no obvious inhibitory effect
Antibacterial effect is better under acidic conditions
Scope of use
Meat products, canned meat
Nitrite toxicity
nitrite
Moderately toxic, 0.2 may cause poisoning, 3g can cause death
Change normal hemoglobin into methemoglobin, causing it to lose its oxygen-carrying function and causing tissue hypoxia
When sodium nitrite is converted into nitrite, it combines with amines to form nitrosamines, which can cause cancer.
Salt and sugar and microbial properties
principle
Increase osmotic pressure, separate microbial plasmoids, decrease water activity, reduce dissolved oxygen, and inhibit aerobic microorganisms.
Salt tolerance of various microorganisms
Bacteria can grow if less than 5%, and mold will grow if it exceeds 5%.
Greater than 20% is mainly yeast growth
Halobacteria: A certain concentration of salt is necessary for the growth of bacteria, such as Vibrio parahaemolyticus
Halotolerant bacteria: Tolerant, but grow better without salt, Lactobacilli and some molds
sugar
Six times more sugar produces the same effect as salt
Bacteria are sensitive, yeast and mold are resistant to hypertonicity
Other antibacterial agents
Antioxidants: prevent or delay food oxidation
Flavor
Spices: allicin, cloves
Fatty acids and esters
Food radiation preservation and radiation resistance properties of microorganisms
cold sterilization cold sterilization
Kills microorganisms without causing an increase in material temperature
Radiation sterilization: technology of irradiation with radiation to extend shelf life
Purpose: Insecticide, sterilization, bud inhibition and disinfection
The maintenance of normal physiological signs and various activities of living bodies depends on the stability at the atomic level. The ultra-high energy of ionizing radiation can destroy the chemical bonds of biomolecules, change the properties of molecules, and cause damage to living organisms.
High energy ray types
Ultraviolet: 200-275 nanometers, short-wave sterilizing ultraviolet, absorbed by proteins and nucleic acids, with weak penetrating power, suitable for killing surface organisms and causing DNA damage
Acts on nucleic acids and causes lethal mutations
Transmits through the air and can sterilize surfaces and air
B-ray
Strong penetrating power, launch treatment
Y-ray
Strong penetrating power and wide application
x-ray
High energy
principle
Use high-energy rays to destroy living functions, denature proteins, and undergo chemical changes
Dissociation of water molecules and passivation of biologically active substances
disulfide hydrogen bond cleavage
Protein deamination and decarboxylation, fat oxidation, carbohydrates are more stable
Influencing factors
Microbial radiation resistance
Viruses are most resistant to radiation
Spores are better than yeast and better than mold and bacteria
Positive is better than negative, Pseudomonas, Flavobacterium are sensitive
Toxin is ineffective
D value: the radiation dose required to kill 90% of microorganisms in food
Represents radiation resistance
Low temperature, large D value High temperature, small D value
Bacteria count
More is stronger
medium
Protein protected, buffer sensitive
oxygen
Vacuum effect is better
physical state
Stem cells are better than wet cells, frozen cells are better
Radiation sterilization type
Radiation corrosion protection
To eliminate spoilage bacteria and regulate physiological functions
Radiation sterilization
Pasteurized, extended shelf life, medium dose
irradiation sterilization
Can achieve commercial sterility, long-term storage at room temperature, high dosage, complete sterilization
Effects of irradiation on food quality
unfavorable
change color, change taste
High amino acid loss rate
Causes softening of fruits and vegetables
advantage
The sterilization effect is obvious and penetrates deep into the internal harmful organisms.
No preservatives required and no non-food substance residues
Energy saving, continuous operation, accurate control
Generates less heat and maintains the original flavor of food to the greatest extent
Little impact on quality, low-dose irradiation will not cause obvious sensory changes
Irradiated Food Safety
Other cold sterilization methods
ultrasound
high pressure
high voltage discharge
Dry preservation and controlled atmosphere preservation p327, p320
Comprehensive antiseptic and preservation theory and technology p330