Course Content:
- Introduction: Definition of food contamination, primary sources of food contamination,
- Cross contamination and its preventive measures.
- Causes of food spoilage, growth and activity of microorganisms, chemical reactions, natural enzymes, damage by animal, insects, and rodents.
- Introduction: Methods of food preservation, pasteurization, canning, refrigeration, freezing, increasing the acidity, drying, using chemical preservatives.
Introduction
Food contamination refers to the inadvertent (i.e. unintentional) introduction or presence of contaminants in food, which can include biological or chemical agents, foreign matter, or other substances. These contaminants have the potential to compromise the safety or suitability of food, leading to adverse health effects upon consumption.
In simpler terms, food contamination involves the presence of harmful elements in food, such as chemicals or microbes like bacteria, which not only reduce the quality of food but also includes the health risks to consumers.
Primary sources of Food Contamination
In simple concept, following are the common sources of food contamination:
- Soil: Contamination can occur due to the presence of harmful microbes or chemicals in soil, which can be absorbed by plants.
- Water: Water sources used for irrigation, cleaning, or processing can introduce pathogens or chemical contaminants to food.
- Air: Airborne contaminants such as dust, pollutants, or microorganisms can settle on food surfaces during production or processing.
- Plants and Animal products: Both plants and animal-derived products can harbor contaminants from environmental sources or improper handling.
- Handling and process:
- Improper handling practices during harvesting, transportation, storage, and processing can lead to contamination.
- Inadequate sanitation of equipment, surfaces, and utensils can introduce harmful microbes or chemicals to food.
There are three ways cross- contamination occurs:
- Food to food: This type of cross-contamination happens when harmful microorganisms or contaminants from one food item are transferred to another food item, typically through direct contact.
For example, if raw meat and fresh vegetables are stored together in the same container or vessel without proper separation or wrapping, juices from the raw meat can drip i.e. fall onto the vegetables, transferring any bacteria or microbes present on the meat to the vegetables. - People to food: People can unintentionally transfer harmful microorganisms to food through poor hygiene practices. This can occur when food handlers fail to wash their hands thoroughly after using the restroom, handling raw meat, or touching contaminated surfaces.
For example, if a chef in the kitchen touches his face, hair, or other parts of his body and then handles food without washing his hands, it can transfer bacteria or viruses to the food, leading to contamination. - Equipment to food: Cross-contamination can also get occurred when equipment, utensils, or surfaces that come into contact with food are not properly cleaned and sanitized between it’s uses.
For example, if cutting boards, knives, or food preparation surfaces are not properly cleaned after handling raw meat, any bacteria present on these surfaces can transfer to other foods that come into contact with them during one after another use.
Types of Contamination Sources:
In broad concept, following are the common sources of food contamination:
- Biological Contamination: This type of contamination arises from microorganisms such as bacteria, viruses, fungi, and parasites. These microbes can enter food at any stage, including during cultivation, harvesting, processing, transportation, storage, or preparation. Common examples include Salmonella, Escherichia coli (E. coli), Listeria, and Norovirus.
- Physical Contamination: Physical contaminants are foreign objects that are unintentionally added into food during production, processing, or packaging. These can include pieces of glass, metal, stone, plastic, wood, or other materials. Physical contamination can also occur due to equipment failure, packaging defects, or poor hygiene practices.
- Chemical Contamination: Chemicals can contaminate food through various sources, including pesticides, heavy metals, industrial pollutants, food additives, and natural toxins. Pesticide residues from agricultural practices, heavy metals like lead or mercury from environmental pollution, and additives such as preservatives or colorants are common examples of chemical contaminants.
- Cross contamination: Cross-contamination occurs when harmful substances are transferred from one food to another, typically through contact with contaminated surfaces, equipment, or hands. For instance, using the same cutting board or utensils for raw meat and fresh produce without proper cleaning can lead to cross-contamination.
- Environmental Contamination: Environmental factors, such as air, water, soil, and surrounding conditions, can also contribute to food contamination. For example, polluted water sources used for irrigation or washing produce can introduce pathogens or chemicals into the food supply. Similarly, air pollution or contaminated soil may affect crops and livestock.
Types of Spoilage
- Microbial spoilage: Occurs due to the growth of bacteria, yeast, and mold, leading to changes in flavor, odor, and appearance.
a. Bacterial Spoilage – Results in off-flavors, odors, and visible alterations in food. For instance, souring of milk due to the production of lactic acid.
b. Yeast – Causes staleness in products like bread.
c. Mold Spoilage – Common in bread, cheese, and fruits, leading to visible mold growth - Enzymatic spoilage: Caused by the activities of food enzymes.
a. Enzymatic browning: Occurs in fruits and vegetables when enzymes like polyphenol oxidase react with oxygen, causing browning.
b. Texture changes: Enzymes can lead to changes in the texture of foods over time. - Chemical Spoilage:
a. Oxidation: Exposure to oxygen can cause fats and oils to become rancid, resulting in off-flavors and odors in products such as oils, nuts, and processed foods.
b. Hydrolysis: Reactions like the breakdown of fats into fatty acids can result in the development of unpleasant flavors and odors in products like mayonnaise or salad dressing. - Physical Spoilage:
a. Freezer burn: Improperly sealed freezer foods can suffer from freezer burn, leading to dehydration, changes in texture, and the development of off-flavors.
b. Crystallization: The formation of sugar crystals, as seen in syrups or honey, can lead to textural changes and spoilage. - Contamination and Cross contamination: Environmental factors such as temperature abuse and moisture can contribute to contamination and cross-contamination, leading to microbial growth and spoilage.
- Environmental factors: Environmental factors are outside forces that might affect the quality and safety of food products. These factors include temperature, humidity, air quality, light exposure, and storage conditions.
a. Temperature: Temperature plays a critical role in food preservation and spoilage. Improper temperature control during storage, transportation, or processing can accelerate microbial growth and enzymatic reactions, leading to food spoilage. High temperatures can promote bacterial and fungal growth, while low temperatures can slow down deterioration but may not completely halt it.
b. Humidity: Humidity levels in the environment can affect the moisture content of food products. High humidity can create favorable conditions for mold and yeast growth, leading to spoilage. Conversely, low humidity levels can cause dehydration and texture changes in certain products, affecting their quality.
c. Air Quality: Poor air quality, including the presence of contaminants such as airborne microorganisms, pollutants, or gases, can contribute to food spoilage. Airborne microbes can settle on food surfaces and initiate microbial growth, while pollutants can react with food components, leading to chemical changes and off-flavors.
d. Light Exposure: Exposure to light, especially ultraviolet (UV) radiation, can accelerate oxidation reactions in fats and oils, leading to rancidity and off-flavors in food products. Light-sensitive compounds in foods, such as vitamins and pigments, can degrade when exposed to light, resulting in nutrient loss and changes in color, flavor, and texture.
e. Storage Conditions: Deterioration of food can also be influenced by storage conditions such as containers, packaging, and storage facilities. Proper packaging materials, such as oxygen barrier films or moisture-resistant coatings, can preserve food from external causes while also extending its shelf life. - Time and Shelf life: Extended storage times beyond the shelf life of products can also contribute to spoilage, as the quality of the food deteriorates over time.
Principles of Food Preservation
- Prevention or Delay of Microbes (Asepsis): This principle focuses on preventing or delaying the growth of microorganisms in food. Aseptic techniques involve maintaining cleanliness and sanitation during food handling, processing, and storage to minimize microbial contamination.
- Prevention or Delay of self-decomposition of food: Food naturally decomposes due to enzyme activity and other causes. Preservation methods try to slow or block this process, therefore extending the shelf life of food goods.
- Reduction of enzyme activity control of moisture content: Enzymes in food can cause spoiling by activating chemical processes that reduce food quality. Blanching, freezing, and the use of chemical agents are examples of preservation methods which try to reduce enzyme activity.
- Control of moisture content: Moisture control is necessary for minimizing microbial growth and reducing enzymatic processes. Drying, dehydration, and the addition of absorbents all help to reduce moisture levels in food products.
- Reduction of oxygen exposure: Oxygen exposure can lead to oxidation reactions, causing off-flavors, nutrient degradation, and rancidity in food. Therefore, preservation techniques such as vacuum packaging or modified atmosphere packaging reduce oxygen exposure, extending the shelf life of foods.
- Use of Preservatives: Preservatives are substances that are added to food to prevent the growth of bacteria and spoilage. Common preservatives include salt, sugar, vinegar, and chemical additives such antioxidants and antimicrobials.
- Refrigeration and Freezing: Cold temperatures slow down microbial growth and enzymatic activity, preserving the quality and safety of perishable foods. Refrigeration and freezing are effective methods for extending the shelf life of fresh produce, meat, dairy, and other perishable food items.
- Acidification: Acidification is the process of decreasing the pH of food to create an acidic environment that prevents microbial growth. Acidic conditions can be created by pickling, fermenting, or using acidic materials such as vinegar or citrus juice.
Methods of food preservation
Food preservation techniques or methods helps to extend the shelf life and safety of various food products. There are various food preservation techniques which are listed below:
- Drying:
Drying is a method or technique of food preservation that involves removing moisture from food products to prevent microbial growth and extend shelf life of food products. This process can be achieved through various techniques like:
a. Solar Drying: It is a traditional method of preserving food products. It utilizes natural sunlight to evaporate moisture from food products laid out generally in the open air. However, this technique can be risky in so many conditions as many foreign particle like stone, wood, plastic, etc. can get mixed into the food products.
Solar drying is a low-cost method that requires minimal equipment and energy input which is mostly suitable for use in areas with excessive or high amount of sunlight. This technique can be used to preserve a wide range of foods, including fruits, vegetables, herbs, and meats.
Weather factors including the amount of clouds, humidity, and fluctuations in temperature can all have an effect on solar drying effectiveness. As food products are exposed to the outside air, they are also at risk of contamination by foreign particles and pests.
b. Mechanical Drying: It is the modern method of drying which involves the use of machinery or equipment’s, such as dehydrators or air dryers, to circulate warm air and remove moisture from food products.
Mechanical drying provides better control over drying conditions, providing more consistent and efficient drying than solar drying. It is appropriate for both small-scale and industrial operations and can be used to dry a variety of food goods.
Mechanical drying requires energy or fuel to power the drying equipment, which may not be available in all locations. The cost of energy can also be a problem, particularly for large-scale operations.
c. Freeze Smoking: Freeze drying, also known as lyophilization, is a method of removing moisture from food products by freezing them and then subjecting them to vacuum conditions to remove ice crystals through sublimation.
Process: Food items are frozen and placed in a vacuum chamber, where the surrounding pressure is reduced. This causes the frozen water in the food to vaporize directly into a gas, bypassing the liquid phase, and leaving behind freeze-dried food with minimal moisture content.
Merits: Freeze drying preserves the texture, flavor, and nutritional quality of foods better than other drying methods. It results in lightweight, shelf-stable products that can be rehydrated quickly.
Challenges or Demerits: Freeze drying is a more complex and costly method than other methods of drying. It requires specialized equipment and expertise, making it more appropriate for high-value or delicate food items. In addition, freeze-dried products may cost more than traditionally dried products. - By use of high temperature:
a. Pasteurization: Pasteurization is a heat treatment process used to kill pathogens and extend the shelf life of foods, particularly liquids like milk, fruit juices, and certain beverages.
Process: The food is heated to a specific temperature (usually between 63-72°C) for a predetermined period, then rapidly cooled to prevent further bacterial growth. This process eliminates harmful bacteria while preserving the sensory qualities and nutritional content of the food.
Advantages: Pasteurization effectively reduces the microbial load in food products without significantly altering their taste, texture, or nutritional value. It helps ensure food safety and extends shelf life, allowing for longer storage and distribution.
Challenges: Although pasteurization kills the most harmful pathogens, it may not totally sterilize the food. As a result, refrigeration or other preservation techniques may be required to prevent spoiling over long periods of time.
b. Boiling:
Boiling is a cooking method in which food particles are completely immersed in boiling water or other liquids and heating it to its boiling point (100°C). It is commonly used to cook vegetables, pasta, grains, and proteins such as eggs or meats.
c. Roasting and Baking:
Roasting and baking are dry-heat cooking methods that involve cooking food in an oven or over an open flame without the use of added liquids.
Food is placed in a hot oven or exposed to direct heat, which causes browning and caramelization on the outermost layer. Roasting is commonly used to cook larger portions of meat, whereas baking is used to prepare bread, pastries, casseroles, and other baked products.
d. Blanching:
Blanching is a brief cooking method that involves immersing food in boiling water or steam for a short period, followed by rapid cooling in ice water.
Blanching is commonly used to partially cook vegetables, fruits, and nuts before freezing or further processing. It helps preserve color, flavor, and texture, while also killing surface bacteria and enzymes that can cause spoilageBlanching is a rapid cooking technique which involves immersing food in boiling water for a short time before quickly chilling in cold water.
Blanching is a common method for partially cooking vegetables, fruits, and nuts before freezing or getting them ready for processing. It helps preserve color, flavor, and texture while eliminating surface bacteria and enzymes that can cause spoilage. Blanching protects the freshness and nutritional content of food by inactivating enzymes that can cause color and flavor changes when stored. It also loosens skins, making fruits and vegetables easier to peel and process. However, over-blanching can cause nutrient loss and textural degradation in food.
e. Other Techniques of high temperature: Frying, Cooking
f. Sterilization: Sterilization is a food preservation technique that involves heating food above 100 degrees Celsius to kill all types of microbes, including bacteria, molds, yeasts, and their spores. Unlike pasteurization, which uses lower temperatures to eliminate harmful pathogens while maintaining food quality, sterilization is intended to completely destroy all germs present in the food product.
Sterilization techniques can be achieved using steam sterilization (autoclaving), hot water bath sterilization, and dry heat sterilization. Steam sterilization is one of the most common methods, and it involves exposing food to steam that is saturated under pressure, which rapidly raises the food’s temperature to achieve sterilization. - By use of low temperature:
a. Cellar storage: Cellar storage is a traditional and cost-effective method of preserving food without the need for electricity or specialized equipment. It is the process of storing food in cold, dark, and often underground areas like root cellars or basements. These environments often maintain low and consistent temperatures, making them suitable for storing certain kinds of foods.
Hence, the cool, dark, and humid conditions of cellar storage helps to slow down microbial growth and enzymatic activity in perishable foods to some extend.
b. Chilling: Chilling involves storing food products at temperatures above freezing but below room temperature, typically between 0 to 5 degrees Celsius (32 to 41 degrees Fahrenheit). Chilling slows down microbial growth and enzymatic activity, extending the shelf life of perishable foods.
In this technique, food is stored in refrigerators or walk-in coolers at temperatures that prevent spoilage. Chilling helps to maintain the freshness, texture, and nutritional content of foods such fruits, vegetables, dairy products, and cooked meats.
c. Refrigeration: Refrigeration is the process of storing food at temperatures lower than room temperature using refrigerator, usually between 2 and 8 degrees Celsius (36 to 46 degrees Fahrenheit).
d. Freezing: Freezing involves storing food products at temperatures below freezing, typically between -18 to -20 degrees Celsius (-0.4 to -4 degrees Fahrenheit). Freezing rapidly reduces the temperature of food, halting microbial growth and enzymatic activity, effectively preserving the food’s quality and safety.
In this technique, food items are placed in freezers or deep freezers, where they are rapidly cooled to freezing temperatures. It can store food products for long period of time, even upto month. However, thawing is required before preparing the food products. - Irradiation:
Food irradiation involves exposing food products to a controlled amount of ionizing radiation, typically gamma rays, electron beams, or X-rays. This process effectively kills harmful bacteria, parasites, insects, and other pathogens, reducing the risk of foodborne illness and spoilage.
The radiation damages the DNA of microorganisms, preventing them from reproducing and causing spoilage. Irradiation does not significantly affect the taste, texture, or nutritional value of food. - By increasing acidity or fermentation
Increasing acidity through fermentation, pickling, and the use of chemical preservatives are all techniques for preserving food by preventing the growth of microbes. Here’s a brief description of each method:
a. Pickling (अचार हाल्नु): Pickling is a food preservation technique that involves soaking food in a solution of vinegar, salt, and spices, resulting in an acidic and flavored brine (solution of salt and water) that blocks microbial growth. Pickling can be done using fermentation (fermented pickles) or vinegar (quick pickles).
b. Use of chemical preservatives: Chemical preservatives are artificial or natural substances added to food to reduce the growth of microbes, prevent spoilage, and increase shelf life. These preservatives can work by changing the pH of the food, preventing enzyme activity, or eliminating microbe membranes.
Chemical preservatives such as sodium benzoate, potassium sorbate, sulfites, and nitrites are commonly used in processed foods, beverages, condiments, and baked goods.
c. Fermentation: Fermentation is a technique which involves the conversion of sugars and carbohydrates in food into organic acids and alcohol by microorganisms such as bacteria, yeast, or molds. This process increases the acidity of the food, which prevents the growth of harmful bacteria and preserves the food for long time.
Growth and activity of
microorganisms
Intrinsic Factors
Microorganism growth and activity in food are influenced by a variety of factors, including components that are included in the food itself. Here’s a brief description for each intrinsic factor:
- pH value
- Water activity
- Oxidation-reduction potential
- Nutrient content
- Antimicrobial constituents
- Biological Structure
- pH Value:
Every organism has minimum and maximum. Some organisms survive and grow in low or acidic pH environments. Some survive or grow in alkaline pH, whereas others grow in neutral pH.
For example: Yeast and molds are more acid tolerant than bacteria.
pH range for various micro-organism:
a. Mold – 1.5 to 9.00, allowing them to grow and survive in both acidic and alkaline conditions.
b. Yeast – They are found in pH value range of 2.0 to 8.5. They are commonly found in acidic foods like fermented beverages and in neutral environments such as bread dough.
c. Gram positive bacteria – Gram-positive bacteria typically found in a pH range of 4.0 to 8.5.
d. Gram negative bacteria – Gram-negative bacteria have a pH range of 4.5 to 9.0 and are generally more sensitive to acidic conditions compared to gram-positive bacteria.
Based on pH ranges, microorganisms can be grouped as:
a. Neutrophiles – Neutrophiles are microorganisms that survive and grow in environments with neutral pH, typically ranging from 6 to 8. Example: Escherichia coli and Staphylococcus aureus
b. Acidophiles – Acidophiles are microorganisms that prefer acidic environments and grow best at pH levels below 5.5. Example: Lactobacillus acidophilus.
c. Alkaliphiles – Alkaliphiles are microorganisms that survive and grow in alkaline environments, preferring pH levels above 8.5. Examples: Bacillus alcalophilus, Alkalibacillus spp, Bacillus pseudofirmus, Natronobacterium spp. - Water Activity (aw) or Moisture Content
Water activity (aw), often known as moisture content, is an important factor in determining food stability and safety. It refers to the amount of water available for biological activity inside a food matrix, which can be influenced by osmotic pressure and environmental conditions.
The formula for calculating water activity (aw) is the ratio of the vapor pressure of water present in a food substrate (solution) to the vapor pressure of pure water at the same temperature. This ratio ranges from less than zero to more than 1, although no food can have a water activity of either 0 or 1.
Formula: Water Activity (aw) = P / P0
Where,
P= Vapor pressure of water in food
P0= Vapor pressure of pure water at same temperature
Microorganisms have varying requirements for water activity levels to support their growth and activity. Bacteria typically require higher water activity levels compared to fungi, with bacteria generally unable to grow below a water activity level of 0.91, while molds can grow in environments with water activity levels as low as 0.80.
Also, Gram-negative bacteria are particularly sensitive to low water activity levels compared to gram-positive bacteria.
Based on water activity range microorganisms can be grouped as:
- Halotolerant – Halotolerant microorganisms have the ability to grow and survive in environments with high concentrations of salt. Example: Staphylococcus aureus, a bacterium commonly found on human skin and mucous membranes.
- Osmotolerant – Osmotolerant microorganisms are capable of thriving in environments with high concentrations of osmotically active solutes, such as sugars or salts. Example: Saccharomyces cerevisiae, commonly known as baker’s yeast, is an osmotolerant fungus used in baking and fermentation processes.
- Aerotolerant- tAerotolerant microorganisms are capable of growing in the presence of low water activity levels, such as those found in dry or dehydrated foods. They do not require oxygen for growth and can survive in anaerobic or microaerophilic conditions.
Example: Bacillus species, such as Bacillus subtilis, are aerotolerant bacteria commonly found in soil and dust.
We can control the water activity in food products, using various methods such as drying, salting, or adding preservatives, which can reduce the growth and proliferation of harmful microbes, lowering the risk of foodborne illness and spoilage.
- Oxidation – Reduction Potential (Eh) or Redox Potential
The oxidation-reduction also known as redox potential of a substance is defined as a measurement of a transfer of electrons between atoms or molecules and is closely related to presence of oxygen.
It is typically measured in terms of millivolts (mV).
The redox potential depends on following factors:
a. pH of food: The acidity or alkalinity of the food can affect the redox potential, with certain pH ranges favoring oxidation or reduction reactions.
b. Availability of oxygen: Oxygen availability is important in determining redox potential because aerobic environments enhance oxidation reactions and anaerobic conditions favor reduction reactions.
c. Poising capability or buffering capacity: The ability of the food to resist changes in redox potential due to external factors such as oxygen exposure or microbial activity.
d. Food composition: Components such as proteins, ascorbic acid, and reducing sugars can influence the redox potential by acting as electron donors or acceptors in oxidation-reduction reactions.
Based on it, microorganisms can be classified as:
a. Aerobes: These microorganisms thrive in environments with high redox potential (+500 to +300 mV), where oxygen is readily available for aerobic respiration. Examples include molds, yeasts, Bacillus species, and Moraxella. They require oxygen for growth and metabolism.
b. Anaerobes: Anaerobic microorganisms grow best in environments with lower redox potential (+100 to -250 mV or lower), where oxygen is absent or limited. Examples include Clostridium species, which are capable of fermentation and can tolerate low-oxygen or oxygen-free conditions.
c. Facultative anaerobes: These microbes are able to survive in a wide range of redox potentials (+300 to +100 mV) and adapt to both aerobic and anaerobic environments. Lactic acid bacteria, such as Escherichia coli and Salmonella species, have the ability to switch between aerobic and anaerobic metabolism based on oxygen availability. - Nutrient Content:
Nutrient content is a major factor influencing microbial growth and its metabolic activities. Microorganisms require a variety of nutrients including proteins, carbohydrates, lipids, vitamins, minerals (such as sulfur, phosphorus, and nitrogen), and water, to support their growth and metabolic activities.
Food serves as the primary source of nutrition for microbial growth. These nutrients serve as building blocks for cellular structures, energy sources for metabolism, and cofactors for enzymatic reactions essential for microbial growth and reproduction.
Microorganisms typically feed on simple carbohydrates and amino acids as these nutrients are easily digested, producing energy and supporting cellular functions. As microbial populations increase and consume readily available nutrients, they may begin to use more complex forms of nutrients found in the food substrate to sustain their growth and metabolic activity.
Differences in Nutritional Requirements:
Microorganisms’ nutritional needs vary based on their species and metabolic characteristics. Gram-positive bacteria often have higher nutritional requirements than yeast and gram-negative bacteria. Molds have lower nutritional requirements than bacteria because they can survive in numerous environments and metabolize a wide variety of surfaces. - Biological Structures
Biological structures, such as natural coverings on certain foods, serve an important role in preventing microbial contamination and spoilage. These protective barriers protect the food from microbes and aid to maintain its quality and integrity.
Examples include the shell of eggs, the husk or testa of seeds, and the peel of fruits and vegetables. These natural coverings function as physical barriers, preventing bacteria from accessing the food’s internal components. They help to maintain the freshness and quality of the food by reducing the possibility of contamination and spoilage.
The effectiveness of these protective barriers can be influenced by factors such as the maturity of the plant foods. As fruits and vegetables ripen, their natural coverings may undergo changes in composition and structure, affecting their ability to resist microbial penetration. Also, physical damage due to handling in the process of harvest, transportation or storage can allow penetration of microorganism inside of the food products. - Antimicrobial Constituents
Antimicrobial components are naturally occurring chemicals present in both plants and animals that have the ability to prevent the growth or activity of harmful microbes.
Examples of antimicrobial constituents found in plant
a. Clove- Essential oil and Eugenol
b. Garlic- Allicin
c. Mustard Oil- Allyl isothiocyanate
d. Sage – Eugenol and Thymol
e. Cabbage, Broccoli, Turnips- isothiocyanates
f. Cinnamon – Cinnamaldehyde
g. Thyme – Thymol
h. Neem – Azadirachtin
i. Cranberry – Proanthocyanidins (PACs)
j. Oregano – Carvacrol
k. Citrus fruits – Citrus essential oils
l. Ginger – Gingerol
m. Turmeric – Curcumin
Examples of antimicrobial constituents found in animals
a. Milk- lactoferrin and conglutinin
b. Honey – Hydrogen peroxide, Methylglyoxal (MGO)
c. Egg- lysozyme and ovotransferrin (conalbumin)
Extrinsic Factors
Extrinsic factors which means external factors which include temperature, relative humidity, and gas composition, all of which have an impact on enzyme activity and the growth of bacteria. Here’s a brief description for each extrinsic factor:
- Temperature
- Relative humidity
- Gases in environments
- Temperature
Enzymatic reactions and microbial growth rates are highly influenced by the environmental temperature.
Different microorganisms survive at different temperature ranges. Yeast and molds normally grow at temperatures ranging from 10 to 35 degrees Celsius.
Based on temperature, microorganism can be classified as:
- Psychrotrophs: These microorganisms prefer cold temperatures and can grow at temperatures typically between 0 to 20 degrees Celsius. Example: Pseudomonas spp., Enterococcus spp., Moritella spp., Oleispira spp., Polaromonas spp.
- Mesophiles: Mesophilic microorganisms thrive at moderate temperatures, typically ranging from 20 to 40 degrees Celsius. Example: Salmonella, Staphylococcus, Clostridium, Shigella, Bacillus
- Thermophiles: Thermophilic microorganisms prefer high temperatures and grow best above 45 degrees Celsius, with an optimum growth temperature ranging from 50 to 70 degrees Celsius. Example: Sulfolobus spp., Geobacillus spp., Pyrococcus spp.
- Extremophiles: These microorganisms thrive in extreme conditions, including extreme cold and hot temperatures. Example: Psychrotrophs, which can grow at both low and moderate temperatures, demonstrate adaptation to a wide temperature range.
- Relative Humidity
Relative humidity refers to the concentration of water vapor present in the atmosphere, with a close relationship to water activity; when low water activity foods are exposed to high humidity environments, moisture transfer from air to food occurs, increasing water activity and potentially leading to mold growth and spoilage.
For example: Storing bread at high humidity environment can make it soggy and moldy. - Presence and concentration of gases
- Presence and activity of microorganisms
- Light
Light can play important role as external factor which influence the growth and survival of microorganisms.
Based on it, microorganism can be classified as:
- Phototrophs – These microorganisms utilize light energy to carry out photosynthesis, converting light into chemical energy to fuel their metabolic processes. , and fluctuating humidity can cause dried fruit to become moldy too.
Example: Proteobacteria (also called as purple bacteria), cyanobacteria, Chloroflexi - Chemotrophs- Unlike phototrophs, chemotrophs do not require light for energy. Instead, they obtain energy from chemical substances through processes such as fermentation or respiration. Many bacteria and fungi fall into this group, growing in environments where light is limited or dark completely.
- Mixotrophs- Mixotrophs can use both light and chemical energy sources for growth and metabolism. They are able to switch between phototrophic and chemotrophic forms according on environmental conditions.
Important Questions
- What is blanching objective? Describe various preservation techniques by application of heat.
- Describe role of Ph and oxidation reduction potential in the growth of microorganisms.
- Explain principles of food preservation. Give account on preservation of food by application of low temperature and chemical preservation.
- Give account on principle, advantage and disadvantages of drying, irradiation and fermentation.
- What are various causes of food spoilage. Explain with example.
- Describe cross contamination. Explain how various intrinsic factors affect the growth of microorganisms.
- Define food contamination. Describe various causes that results food spoilage.
- What are chemical preservatives.