Factors affecting microbial growth in food can be intrinsic, related to characteristics of the food itself, or extrinsic, related to external environmental conditions. Intrinsic factors include pH, water activity, nutrients, and antimicrobial contents. pH and water activity are especially important as most bacteria grow between pH 6.8-7.5 and require a minimum water activity of 0.91. Controlling the pH and water activity of foods through methods like fermentation, addition of acids or salts, and moisture reduction can inhibit microbial growth and improve food stability.
Lecture 3 intrinsic and extrinsic factorsDavid mbwiga
1) Microbial growth in food is dependent on intrinsic factors like the food's physical and chemical properties as well as extrinsic factors like storage conditions.
2) Key intrinsic factors include pH, water activity, redox potential, nutrient content, and antimicrobial constituents. The pH, water activity, and available nutrients significantly impact which microorganisms can grow.
3) Important extrinsic factors are temperature, relative humidity, and gases in the storage environment. Temperature particularly influences what microbes can grow and their growth rates, with psychrotrophs growing at refrigeration temperatures posing challenges.
Dehydration is a method of food preservation that involves removing water from food to prevent spoilage. It works by lowering the water activity level of foods, which inhibits the growth of microorganisms. There are several types of drying methods that work through evaporation of water, including direct convective drying, indirect drying, and radiation drying. The drying process can impact the physical, chemical, and sensory properties of foods through effects like protein denaturation, loss of structure, and browning reactions. By removing moisture, dehydration allows foods to be stored longer while retaining important qualities like flavor and nutrition.
Everyone knows water activity is related to microbial growth. But how can you use that knowledge to your advantage in formulation, specification, production, and packaging? In this 30 minute webinar, learn:
-what you need to know about how water activity predicts microbial growth
-how to use specific organism aw limits relevant to your industry in setting your specs
-how to use different formulation techniques (including humectants, films, coatings) to hit the water activity you need
-why you should consider hurdle technology to address certain challenges
The document discusses hurdle technology, which uses a combination of preservation methods like heating, chilling, drying, and addition of preservatives to inhibit microbial growth and improve food quality and safety. Some key hurdles mentioned are temperature, water activity, pH, redox potential, and preservatives. Hurdle technology is useful for foods that can be stored without refrigeration. It allows for milder processing conditions that maintain quality attributes like freshness. Examples discussed include hurdle-stabilized products like paneer, fruit snacks, and sauces.
What is hurdle technology,
Introduction to hurdle technology
Need of hurdle technology
Hurdle effects
How it work in food industry
Types of hurdle used in food preservation.
This document discusses microorganisms commonly found in various sugar products and how they can cause spoilage. It covers microbes found in maple syrup, honey, candies, chocolate and various sugars. Key points are:
- Maple syrup is initially sterile but becomes contaminated via tapholes with psychrotrophic bacteria like Pseudomonas.
- Honey commonly contains acidophilic and glycolytic yeasts from nectar and bee intestines. Some bacteria also come from bees.
- Candies can contain up to 2 million bacteria mainly from ingredients, air and handling. Spoilage is reduced by proper processing and storage conditions.
This document provides information on sausage making equipment, processes, safety considerations and sanitation. Key points:
1) Thermometers and scales are critical for ensuring meat and finished product temperatures and ingredient ratios are safe. Sausage is fully cooked at 160°F internally.
2) Grinders, choppers, stuffers and casings are used to grind, mix, fill and link sausages. Proper grinding plates and sharp blades are important for quality.
3) Processing involves grinding, mixing spices, stuffing into casings, potential fermentation, drying, smoking and cooking sausages to 160°F. Temperature control and sanitation are essential for safety.
Lecture 3 intrinsic and extrinsic factorsDavid mbwiga
1) Microbial growth in food is dependent on intrinsic factors like the food's physical and chemical properties as well as extrinsic factors like storage conditions.
2) Key intrinsic factors include pH, water activity, redox potential, nutrient content, and antimicrobial constituents. The pH, water activity, and available nutrients significantly impact which microorganisms can grow.
3) Important extrinsic factors are temperature, relative humidity, and gases in the storage environment. Temperature particularly influences what microbes can grow and their growth rates, with psychrotrophs growing at refrigeration temperatures posing challenges.
Dehydration is a method of food preservation that involves removing water from food to prevent spoilage. It works by lowering the water activity level of foods, which inhibits the growth of microorganisms. There are several types of drying methods that work through evaporation of water, including direct convective drying, indirect drying, and radiation drying. The drying process can impact the physical, chemical, and sensory properties of foods through effects like protein denaturation, loss of structure, and browning reactions. By removing moisture, dehydration allows foods to be stored longer while retaining important qualities like flavor and nutrition.
Everyone knows water activity is related to microbial growth. But how can you use that knowledge to your advantage in formulation, specification, production, and packaging? In this 30 minute webinar, learn:
-what you need to know about how water activity predicts microbial growth
-how to use specific organism aw limits relevant to your industry in setting your specs
-how to use different formulation techniques (including humectants, films, coatings) to hit the water activity you need
-why you should consider hurdle technology to address certain challenges
The document discusses hurdle technology, which uses a combination of preservation methods like heating, chilling, drying, and addition of preservatives to inhibit microbial growth and improve food quality and safety. Some key hurdles mentioned are temperature, water activity, pH, redox potential, and preservatives. Hurdle technology is useful for foods that can be stored without refrigeration. It allows for milder processing conditions that maintain quality attributes like freshness. Examples discussed include hurdle-stabilized products like paneer, fruit snacks, and sauces.
What is hurdle technology,
Introduction to hurdle technology
Need of hurdle technology
Hurdle effects
How it work in food industry
Types of hurdle used in food preservation.
This document discusses microorganisms commonly found in various sugar products and how they can cause spoilage. It covers microbes found in maple syrup, honey, candies, chocolate and various sugars. Key points are:
- Maple syrup is initially sterile but becomes contaminated via tapholes with psychrotrophic bacteria like Pseudomonas.
- Honey commonly contains acidophilic and glycolytic yeasts from nectar and bee intestines. Some bacteria also come from bees.
- Candies can contain up to 2 million bacteria mainly from ingredients, air and handling. Spoilage is reduced by proper processing and storage conditions.
This document provides information on sausage making equipment, processes, safety considerations and sanitation. Key points:
1) Thermometers and scales are critical for ensuring meat and finished product temperatures and ingredient ratios are safe. Sausage is fully cooked at 160°F internally.
2) Grinders, choppers, stuffers and casings are used to grind, mix, fill and link sausages. Proper grinding plates and sharp blades are important for quality.
3) Processing involves grinding, mixing spices, stuffing into casings, potential fermentation, drying, smoking and cooking sausages to 160°F. Temperature control and sanitation are essential for safety.
INTRODUCTION:
BREAD is a dietary product obtained from the fermentation and the subsequent baking of a dough mainly made of cereal flour and water, made in many different ways and sometimes enriched with typical regional ingredients.
Ingredients of bread:
Flour is the bulking ingredient of bread, it forms the structure of the product,contains gluten which helps to form an elastic stretchy dough.
Yeast is a raising agent. Yeast produces gases to make the bread rise.
Salt is required to bring out flavour in the bread, it is used in small quantities.Too much of this ingredient will stop the yeast from growing.
Yeast needs energy to grow. Sugar provides the food for the yeast; it is needed to help the yeast grow.
Water is used to bind the flour together and helps to form the structure of the bread.
Fats or oils improve the texture of the bread, preventing it from going stale quickly.
Starter culture:
Baker's yeast is the common name for the strains of yeast commonly used as a leavening agent in baking bread and bakery products, where it converts the fermentable sugars present in the dough into carbon dioxide and ethanol. Baker's yeast is of the species Saccharomyces cerevisiae, which is the same species (but a different strain) commonly used in alcoholic fermentation which is called brewer's yeast.
Bread Making Process
Mixing has two functions: to evenly distribute the various ingredients and allow the development of a protein (gluten) network to give the best bread possible.
Once the bread is mixed it is then left to rise (ferment).
Any large gas holes that may have formed during rising are released by kneading.
Moulding the dough into desired loaf shape.
During the final rising the loaf fills with more bubbles of gas, and once this has proceeded far enough they are transferred to the oven for baking.
The loaf is then placed in a preheated oven to bake. Such a high heat will kill the yeast, thus stopping its process of rising and growth.
The whole loaf is cooled to about 35°C before slicing and wrapping can occur without damaging the loaf.
Types of Bread
1. White Bread
2. Brown Bread
3. Wholemeal bread
4. Rye bread
Apart from above there are several types like Crisp bread, Flatbread is often simple, made with flour, water, and salt.
Microbial spoilage
Molds are the primary spoilage organisms in baked goods, with Aspergillus, Penicillium, and Eurotium being the most commonly isolated genera.
Quality control
As a foodstuff, bread is subject to stringent government food processing regulations, including, but not limited to the percent of additives allowed, sterilization of plant equipment, and cleanliness of plant workers. In addition to adhering to these regulations, processors control the quality of their products to meet consumer expectations by installing checkpoints are various stages of the processing.
Hurdle technology for food preservationDeepak Verma
This document discusses hurdle technology, which uses a combination of preservation methods at optimal levels to inhibit microorganisms without compromising food quality. It explains that hurdle technology combines physical hurdles like heat treatment, freezing or modified atmosphere with physic-chemical hurdles like low pH, salt or preservatives. Some examples given are pickles which use acid and salt, and sausages which employ smoke, salt and preservatives. The advantages of hurdle technology are maintaining food safety, quality and nutrition while allowing for minimally processed foods.
The document discusses hurdle technology, which combines multiple preservation methods or "hurdles" like reduced temperature, low pH, and use of preservatives to inhibit microbial growth in foods. It provides examples of hurdle combinations used to preserve cauliflower for 180 days through a study testing different treatments of salt, acids, and preservatives stored at ambient and refrigerated temperatures. The best treatment was found to be 8% salt, 0.3% citric acid, and certain levels of potassium metabisulphite and sodium benzoate stored at ambient temperatures, as it was the lowest cost method while still preventing microbial growth for 180 days.
Microbial spoilage of Fish & sea products9404577899
1. The document discusses contamination, preservation, and spoilage of fish and seafood.
2. It describes the various bacteria that can be found on fish from different environments and how boats and equipment can become contaminated.
3. The preservation methods discussed include heat, low temperatures, irradiation, drying, and use of preservatives. Spoilage is said to be caused by enzymatic, mechanical, bacterial, and chemical processes.
Cereals and cereal products are susceptible to contamination and spoilage by microorganisms if not properly stored. Moisture content above 13% allows mold and bacterial growth. Common spoilage microorganisms include various bacteria and mold species. Proper preservation methods include low storage temperatures below 7°C, use of preservatives like propionates, and irradiation to reduce microbes. Mold growth is a major cause of bread spoilage and can be prevented through proper cooling, low humidity storage, and surface treatments. Ropiness of bread is caused by Bacillus species surviving baking and growing if conditions are favorable.
This document provides an introduction to food microbiology presented by Dr. Greeshma P.V. of St. Mary's College. It discusses the scope of food microbiology including microorganisms' role in food spoilage, preservation, safety, and fermentation. It also describes various microorganisms important in food microbiology such as molds, yeasts, and bacteria. Additionally, it examines factors affecting microbial growth in food and various methods for preserving food, as well as the microbiology of food commodities and foodborne illness.
This document discusses various food borne pathogens that can contaminate food and cause disease. It defines pathogens as anything that can produce disease, and food borne pathogens as microorganisms present in food that cause food contamination. Food borne diseases result from consuming contaminated food or food containing pathogenic bacteria, viruses, toxins, or chemicals. The main causes of food borne illness are cross-contamination, improper food temperature control, and poor personal hygiene among food handlers. The document goes on to describe examples of biological, chemical, and physical contaminants and specific food borne diseases caused by bacteria, viruses, fungi, parasites, and toxins.
Food spoilage is caused by the growth of microorganisms like bacteria, yeasts, and molds. Several factors influence microbial growth in food, including temperature, pH, moisture content, and nutrient levels. Food preservation techniques aim to inhibit microbial growth through methods like reducing water activity by drying and salting foods or lowering the pH. Proper control of factors like temperature, gases, and humidity during food storage is important for limiting spoilage.
The document discusses food microbiology and methods for detecting microbes in food. It describes how microorganisms are introduced to foods and both their beneficial roles in fermentation and spoilage when conditions allow undesirable growth. Detection methods discussed include plate counts, membrane filtration, and microscopic analysis. Intrinsic food factors like pH, water activity, and natural antimicrobials and extrinsic storage conditions like temperature and atmosphere that influence microbial growth are also summarized.
Water activity (aw) is defined as the ratio of the vapor pressure of water in a food to the vapor pressure of pure water at the same temperature. It indicates how available the water is in a food for microbial growth and chemical reactions. Most bacteria do not grow below an aw of 0.91 and molds below 0.80, while S. aureus can grow down to 0.86. Measuring aw can predict spoilage and determine enzyme and vitamin activity in foods. Stability depends on both aw and pH. Common methods to control aw include drying, adding salt or sugar, and freezing.
Thermal Death Time# TDT# Thermal Processing# Food Pocessing Technology# Thermal Death Time Concept # TDT Curve # Unit operations in Food Processing # Food Technology in Industry# Food
This document discusses the use of chemicals to preserve foods. It explains that chemical preservatives interfere with microbial cell functions to prevent spoilage. Common chemical preservatives are categorized into two classes. Class I includes salt, sugar, spices, vinegar and alcohol, which preserve foods through osmosis or acidity. Class II includes benzoic acid, sulfur dioxide, nitrates and nitrites, which are considered generally safe within regulatory limits. Specific preservatives discussed are sulfur dioxide, benzoic acid, and sorbic acid, which inhibit microbial growth through various mechanisms.
The document discusses factors that affect microbial growth in foods. It describes the microbial growth curve and identifies four main factors that influence growth: intrinsic properties of the food itself, extrinsic environmental conditions, implicit properties of microorganisms, and processing factors. Specific intrinsic factors discussed include nutrients, pH, water activity, and antimicrobial constituents. Extrinsic factors include temperature, relative humidity, and atmospheric gases. Implicit factors include microbial interactions like mutualism and antagonism.
Criteria for ideal indicators for pathogenic microorganisms in foodNada Sami
The document discusses criteria for ideal indicators of pathogenic microorganisms in food. It outlines that indicators should be of enteric origin and present in higher numbers than pathogens. It then examines various bacterial groups as potential indicators, including coliforms, fecal coliforms, E. coli, and enterococci. While no single indicator meets all criteria, these groups satisfy many as they are nonpathogenic and share habitats with foodborne pathogens. The document evaluates their ability to indicate fecal contamination and potential presence of pathogens in different foods.
The document discusses various food preservation methods including heat processing techniques like pasteurization and appertization which involve applying heat to destroy microorganisms. Other methods discussed are irradiation, high pressure processing, low temperature storage through chilling and freezing, use of chemical preservatives, and modification of atmosphere around foods. Heat processing requires controlling factors like heat sensitivity of microbes, describing heat processes accurately. Spoilage can result from underprocessing or post-contamination. Proper preservation prevents growth of spoilage-causing microorganisms.
This document discusses hurdle technology, which uses a combination of preservation methods to inhibit microbial growth in foods. It describes over 60 potential hurdles including physical methods like heat/cold treatment, chemical hurdles like pH levels and preservatives, and microbially derived hurdles. The hurdles work to disturb the homeostasis of microorganisms and cause metabolic exhaustion. Case studies demonstrate using hurdle technology with blanched cauliflower preserved for 180 days and mangoes preserved with aloe vera gel and calcium chloride.
This document discusses microbial spoilage of milk and milk products. It notes that dairy products are susceptible to spoilage due to their high nutritional content, water activity, and moderate pH. Common spoilage microorganisms include psychrotrophs during refrigerated storage, thermoduric microorganisms after pasteurization, and molds/yeasts after heat treatment. Sources of contamination include milking animals, equipment, and the surrounding environment. Spoilage can result in off flavors, rancidity, gas production, souring, texture changes, and discoloration. Specific microorganisms are associated with defects in products like pasteurized milk, cream, butter, cheese, and yogurt.
All information regarding which factors involve in food for growth of microorganisms.
Introduction, Food as a substrate for microorganism
a. pH, aw, O-R potential
b. Nutrient Content
c. Accessory food substances
d. Inhibitory substances & biological structure
e. Combined effects of factors affecting growth
Interactions between microorganisms and our foods are sometimes beneficial.
The interactions between microorganisms, plants, and animals are natural and constant.
The ecological role of microorganisms and their importance in all the geochemical cycles in nature.
In most cases microorganisms use our food supply as a source of nutrients for their own growth. This, of course, can result in deterioration of the food. By increasing their numbers, utilizing nutrients, producing enzymatic changes, and contributing off-flavors by means of breakdown of a product or synthesis of new compounds they can “spoil” a food.
This is a normal consequence of the action of microorganisms, since one of their functions in nature is to convert reduced forms of carbon, nitrogen, and sulfur in dead plants and animals to the oxidized form required by plants, which in turn are consumed by animals.
So by simply “doing their thing” in nature they frequently can render our food supply unfit for consumption. To prevent this we minimize the contact between microorganisms and our foods (prevent contamination) and also eliminate microorganisms from our foods, or at least adjust conditions of storage to prevent their growth (preservation).
Bsc food technology
Second semester
Food microbiology
Notes
Third unit
Contamination and spoilage of food
Factors influencing the growth of micro organisms in food
INTRODUCTION:
BREAD is a dietary product obtained from the fermentation and the subsequent baking of a dough mainly made of cereal flour and water, made in many different ways and sometimes enriched with typical regional ingredients.
Ingredients of bread:
Flour is the bulking ingredient of bread, it forms the structure of the product,contains gluten which helps to form an elastic stretchy dough.
Yeast is a raising agent. Yeast produces gases to make the bread rise.
Salt is required to bring out flavour in the bread, it is used in small quantities.Too much of this ingredient will stop the yeast from growing.
Yeast needs energy to grow. Sugar provides the food for the yeast; it is needed to help the yeast grow.
Water is used to bind the flour together and helps to form the structure of the bread.
Fats or oils improve the texture of the bread, preventing it from going stale quickly.
Starter culture:
Baker's yeast is the common name for the strains of yeast commonly used as a leavening agent in baking bread and bakery products, where it converts the fermentable sugars present in the dough into carbon dioxide and ethanol. Baker's yeast is of the species Saccharomyces cerevisiae, which is the same species (but a different strain) commonly used in alcoholic fermentation which is called brewer's yeast.
Bread Making Process
Mixing has two functions: to evenly distribute the various ingredients and allow the development of a protein (gluten) network to give the best bread possible.
Once the bread is mixed it is then left to rise (ferment).
Any large gas holes that may have formed during rising are released by kneading.
Moulding the dough into desired loaf shape.
During the final rising the loaf fills with more bubbles of gas, and once this has proceeded far enough they are transferred to the oven for baking.
The loaf is then placed in a preheated oven to bake. Such a high heat will kill the yeast, thus stopping its process of rising and growth.
The whole loaf is cooled to about 35°C before slicing and wrapping can occur without damaging the loaf.
Types of Bread
1. White Bread
2. Brown Bread
3. Wholemeal bread
4. Rye bread
Apart from above there are several types like Crisp bread, Flatbread is often simple, made with flour, water, and salt.
Microbial spoilage
Molds are the primary spoilage organisms in baked goods, with Aspergillus, Penicillium, and Eurotium being the most commonly isolated genera.
Quality control
As a foodstuff, bread is subject to stringent government food processing regulations, including, but not limited to the percent of additives allowed, sterilization of plant equipment, and cleanliness of plant workers. In addition to adhering to these regulations, processors control the quality of their products to meet consumer expectations by installing checkpoints are various stages of the processing.
Hurdle technology for food preservationDeepak Verma
This document discusses hurdle technology, which uses a combination of preservation methods at optimal levels to inhibit microorganisms without compromising food quality. It explains that hurdle technology combines physical hurdles like heat treatment, freezing or modified atmosphere with physic-chemical hurdles like low pH, salt or preservatives. Some examples given are pickles which use acid and salt, and sausages which employ smoke, salt and preservatives. The advantages of hurdle technology are maintaining food safety, quality and nutrition while allowing for minimally processed foods.
The document discusses hurdle technology, which combines multiple preservation methods or "hurdles" like reduced temperature, low pH, and use of preservatives to inhibit microbial growth in foods. It provides examples of hurdle combinations used to preserve cauliflower for 180 days through a study testing different treatments of salt, acids, and preservatives stored at ambient and refrigerated temperatures. The best treatment was found to be 8% salt, 0.3% citric acid, and certain levels of potassium metabisulphite and sodium benzoate stored at ambient temperatures, as it was the lowest cost method while still preventing microbial growth for 180 days.
Microbial spoilage of Fish & sea products9404577899
1. The document discusses contamination, preservation, and spoilage of fish and seafood.
2. It describes the various bacteria that can be found on fish from different environments and how boats and equipment can become contaminated.
3. The preservation methods discussed include heat, low temperatures, irradiation, drying, and use of preservatives. Spoilage is said to be caused by enzymatic, mechanical, bacterial, and chemical processes.
Cereals and cereal products are susceptible to contamination and spoilage by microorganisms if not properly stored. Moisture content above 13% allows mold and bacterial growth. Common spoilage microorganisms include various bacteria and mold species. Proper preservation methods include low storage temperatures below 7°C, use of preservatives like propionates, and irradiation to reduce microbes. Mold growth is a major cause of bread spoilage and can be prevented through proper cooling, low humidity storage, and surface treatments. Ropiness of bread is caused by Bacillus species surviving baking and growing if conditions are favorable.
This document provides an introduction to food microbiology presented by Dr. Greeshma P.V. of St. Mary's College. It discusses the scope of food microbiology including microorganisms' role in food spoilage, preservation, safety, and fermentation. It also describes various microorganisms important in food microbiology such as molds, yeasts, and bacteria. Additionally, it examines factors affecting microbial growth in food and various methods for preserving food, as well as the microbiology of food commodities and foodborne illness.
This document discusses various food borne pathogens that can contaminate food and cause disease. It defines pathogens as anything that can produce disease, and food borne pathogens as microorganisms present in food that cause food contamination. Food borne diseases result from consuming contaminated food or food containing pathogenic bacteria, viruses, toxins, or chemicals. The main causes of food borne illness are cross-contamination, improper food temperature control, and poor personal hygiene among food handlers. The document goes on to describe examples of biological, chemical, and physical contaminants and specific food borne diseases caused by bacteria, viruses, fungi, parasites, and toxins.
Food spoilage is caused by the growth of microorganisms like bacteria, yeasts, and molds. Several factors influence microbial growth in food, including temperature, pH, moisture content, and nutrient levels. Food preservation techniques aim to inhibit microbial growth through methods like reducing water activity by drying and salting foods or lowering the pH. Proper control of factors like temperature, gases, and humidity during food storage is important for limiting spoilage.
The document discusses food microbiology and methods for detecting microbes in food. It describes how microorganisms are introduced to foods and both their beneficial roles in fermentation and spoilage when conditions allow undesirable growth. Detection methods discussed include plate counts, membrane filtration, and microscopic analysis. Intrinsic food factors like pH, water activity, and natural antimicrobials and extrinsic storage conditions like temperature and atmosphere that influence microbial growth are also summarized.
Water activity (aw) is defined as the ratio of the vapor pressure of water in a food to the vapor pressure of pure water at the same temperature. It indicates how available the water is in a food for microbial growth and chemical reactions. Most bacteria do not grow below an aw of 0.91 and molds below 0.80, while S. aureus can grow down to 0.86. Measuring aw can predict spoilage and determine enzyme and vitamin activity in foods. Stability depends on both aw and pH. Common methods to control aw include drying, adding salt or sugar, and freezing.
Thermal Death Time# TDT# Thermal Processing# Food Pocessing Technology# Thermal Death Time Concept # TDT Curve # Unit operations in Food Processing # Food Technology in Industry# Food
This document discusses the use of chemicals to preserve foods. It explains that chemical preservatives interfere with microbial cell functions to prevent spoilage. Common chemical preservatives are categorized into two classes. Class I includes salt, sugar, spices, vinegar and alcohol, which preserve foods through osmosis or acidity. Class II includes benzoic acid, sulfur dioxide, nitrates and nitrites, which are considered generally safe within regulatory limits. Specific preservatives discussed are sulfur dioxide, benzoic acid, and sorbic acid, which inhibit microbial growth through various mechanisms.
The document discusses factors that affect microbial growth in foods. It describes the microbial growth curve and identifies four main factors that influence growth: intrinsic properties of the food itself, extrinsic environmental conditions, implicit properties of microorganisms, and processing factors. Specific intrinsic factors discussed include nutrients, pH, water activity, and antimicrobial constituents. Extrinsic factors include temperature, relative humidity, and atmospheric gases. Implicit factors include microbial interactions like mutualism and antagonism.
Criteria for ideal indicators for pathogenic microorganisms in foodNada Sami
The document discusses criteria for ideal indicators of pathogenic microorganisms in food. It outlines that indicators should be of enteric origin and present in higher numbers than pathogens. It then examines various bacterial groups as potential indicators, including coliforms, fecal coliforms, E. coli, and enterococci. While no single indicator meets all criteria, these groups satisfy many as they are nonpathogenic and share habitats with foodborne pathogens. The document evaluates their ability to indicate fecal contamination and potential presence of pathogens in different foods.
The document discusses various food preservation methods including heat processing techniques like pasteurization and appertization which involve applying heat to destroy microorganisms. Other methods discussed are irradiation, high pressure processing, low temperature storage through chilling and freezing, use of chemical preservatives, and modification of atmosphere around foods. Heat processing requires controlling factors like heat sensitivity of microbes, describing heat processes accurately. Spoilage can result from underprocessing or post-contamination. Proper preservation prevents growth of spoilage-causing microorganisms.
This document discusses hurdle technology, which uses a combination of preservation methods to inhibit microbial growth in foods. It describes over 60 potential hurdles including physical methods like heat/cold treatment, chemical hurdles like pH levels and preservatives, and microbially derived hurdles. The hurdles work to disturb the homeostasis of microorganisms and cause metabolic exhaustion. Case studies demonstrate using hurdle technology with blanched cauliflower preserved for 180 days and mangoes preserved with aloe vera gel and calcium chloride.
This document discusses microbial spoilage of milk and milk products. It notes that dairy products are susceptible to spoilage due to their high nutritional content, water activity, and moderate pH. Common spoilage microorganisms include psychrotrophs during refrigerated storage, thermoduric microorganisms after pasteurization, and molds/yeasts after heat treatment. Sources of contamination include milking animals, equipment, and the surrounding environment. Spoilage can result in off flavors, rancidity, gas production, souring, texture changes, and discoloration. Specific microorganisms are associated with defects in products like pasteurized milk, cream, butter, cheese, and yogurt.
All information regarding which factors involve in food for growth of microorganisms.
Introduction, Food as a substrate for microorganism
a. pH, aw, O-R potential
b. Nutrient Content
c. Accessory food substances
d. Inhibitory substances & biological structure
e. Combined effects of factors affecting growth
Interactions between microorganisms and our foods are sometimes beneficial.
The interactions between microorganisms, plants, and animals are natural and constant.
The ecological role of microorganisms and their importance in all the geochemical cycles in nature.
In most cases microorganisms use our food supply as a source of nutrients for their own growth. This, of course, can result in deterioration of the food. By increasing their numbers, utilizing nutrients, producing enzymatic changes, and contributing off-flavors by means of breakdown of a product or synthesis of new compounds they can “spoil” a food.
This is a normal consequence of the action of microorganisms, since one of their functions in nature is to convert reduced forms of carbon, nitrogen, and sulfur in dead plants and animals to the oxidized form required by plants, which in turn are consumed by animals.
So by simply “doing their thing” in nature they frequently can render our food supply unfit for consumption. To prevent this we minimize the contact between microorganisms and our foods (prevent contamination) and also eliminate microorganisms from our foods, or at least adjust conditions of storage to prevent their growth (preservation).
Bsc food technology
Second semester
Food microbiology
Notes
Third unit
Contamination and spoilage of food
Factors influencing the growth of micro organisms in food
final factors affecting food microbiologyRenuPathak11
This document discusses factors that affect microbial growth in food, including intrinsic and extrinsic factors. Intrinsic factors are inherent to the food and include pH, water activity, nutrients, and antimicrobial substances. The pH and water activity levels influence which microorganisms can grow, with different microorganisms having varying minimum requirements for pH and water activity. Foods also vary in their nutrient content and natural antimicrobial properties, affecting their susceptibility to microbial spoilage.
1) Many factors influence the growth and heat resistance of microorganisms in food, including temperature, pH, water activity, redox potential, nutrient levels, and number of microorganisms present.
2) The optimal temperature, pH, and water activity levels vary between bacterial species, with psychrotrophs growing at refrigeration temperatures and thermophiles growing at higher temperatures.
3) Higher numbers of microorganisms, pH levels closer to optimal, and more water or fat content can increase heat resistance by providing a protective environment.
This document discusses intrinsic factors that affect microbial growth in foods, including nutrient content, pH, redox potential, water activity, and antimicrobial barriers. It explains that microbes require nutrients like water, energy sources, nitrogen, vitamins and minerals. The pH and water activity of foods can determine which microbes can grow. Redox potential influences whether microbes are aerobic or anaerobic. Certain food constituents like essential oils and lysozyme in eggs have natural antimicrobial properties. Overall, the document provides an overview of how the inherent properties of foods can promote or inhibit microbial growth.
Food spoilage is caused by the growth of microorganisms like bacteria, yeasts, and molds. Several factors influence microbial growth in food, including pH, moisture content, temperature, gas concentration, and relative humidity. Food preservation techniques aim to inhibit microbial growth through methods like reducing water activity by drying and salting foods or lowering the pH through fermentation. This prevents food from being damaged or contaminated, rendering it unsuitable for human consumption.
This document discusses the intrinsic and extrinsic factors that affect the growth and survival of microorganisms in food. Intrinsic factors include nutrients, growth factors/inhibitors, water activity, pH, and redox potential. Extrinsic factors are environmental conditions like temperature, gaseous composition, salt concentration, and water quality. Different types of microbes have varying optimal ranges for these factors, such as psychrophilic, mesophilic, and thermophilic bacteria for temperature, and halophilic, halophobic, and halotolerant bacteria for salt concentration. The interplay between these intrinsic and extrinsic parameters determines whether conditions are suitable for microbial growth.
Heat kills microorganisms by changing the physical and chemical properties of their proteins. When heat is used to preserve foods, the number of microorganisms present, the microbial load , is an important consideration. Various types of microorganisms must also be considered because different levels of resistance exist. For example, bacterial spores are much more difficult to kill than vegetative bacilli. In addition, increasing acidity enhances the killing process in food preservation.
Thermal processing using heat is one of the most widely used food preservation techniques. It works by destroying microorganisms through changing their protein structures. There are two main types of foods for heat processing - acid foods which can be preserved at boiling temperatures due to their natural acidity, and low-acid foods which require pressure canning to reach higher temperatures in order to destroy the toxin-producing Clostridium botulinum bacteria. Blanching is a heat treatment used to inactivate enzymes in foods and is tested for effectiveness using the peroxidase test, which detects residual enzyme activity that could impact food quality during storage.
This document discusses food microbiology and food spoilage. It begins by introducing food storage and factors that contribute to food deterioration like microorganism growth. The major causes of food spoilage are microbial growth, enzymatic reactions, chemical reactions, vermin, and physical changes. Specific microorganisms like bacteria, yeasts and molds are responsible for food spoilage. Factors like temperature, pH, moisture content and nutrients influence microbial growth in food. Food preservation techniques aim to prolong food storage life by preventing microbial spoilage.
Water activity is the moisture content of the food which is available for microbial growth.By controlling water activity the food can be preserved for longer duration
Factors Influencing Growth of Microorganisms in FoodNeeraj Chauhan
The growth of microorganisms in food is influenced by both intrinsic and extrinsic factors. Intrinsic factors include the nutrient content, pH, water activity (aw), and biological structures of the food. Extrinsic factors are relative humidity, temperature, and gaseous environment where the food is stored. Microbial growth is supported by foods that are nutrient-rich, have neutral pH, high aw, and are damaged or processed in ways that allow microbes to penetrate tissues. Relative humidity, temperature that is optimal for the specific microbe, and ambient oxygen levels also impact growth. Understanding these various factors is important for food microbiologists to control spoilage and pathogen growth.
Microbial growth in food depends on intrinsic, extrinsic, and implicit factors. Intrinsic factors include the food's pH, moisture content, and nutrients. Most bacteria grow in foods with pH above 4.5 while fungi can grow in all foods. Foods also contain antimicrobial constituents that inhibit microbes. Extrinsic factors are the storage environment's temperature, humidity, and gases. Temperature and humidity control can prevent microbial spoilage. Carbon dioxide inhibits fungi and ethylene to preserve foods longer. Both intrinsic food properties and extrinsic storage conditions impact the microbes that can grow and spoil foods.
The document discusses various factors that influence the growth and activity of microorganisms in food. Internally, key factors include nutrient contents, water activity, pH, redox potential, and osmotic pressure. Externally, temperature is a major influence on microbial growth rates, with psychrophiles, mesophiles, and thermophiles having different optimal temperature ranges. The heat resistance of microorganisms is also affected by time, temperature, microbial type, number, pH, water content, and food composition. Controlling these internal and external factors is important for preventing microbial spoilage of foods.
The document discusses various factors that influence the growth and activity of microorganisms in food. Internally, key factors include nutrient contents, water activity, pH, redox potential, and osmotic pressure. Externally, temperature is a major influence on microbial growth rates, with psychrophiles, mesophiles, and thermophiles having different optimal temperature ranges. The document also discusses how these various factors affect the heat resistance of microorganisms.
1. The document provides an introduction to food microbiology, discussing factors that influence food spoilage such as microorganism growth, pH, moisture content, and temperature.
2. It describes various food preservation methods including inhibiting microorganism growth through reducing water activity via drying or salting, or lowering pH with fermentation or acids.
3. The document also discusses killing microorganisms using heat treatments like pasteurization or sterilization, irradiation, or gases. Combining inhibition and killing principles is often used in food preservation depending on the food.
- The human body contains about 65% water, with some tissues containing over 90% water. Plants and animals generally contain 60-90% water.
- Different food products contain varying amounts of water, from around 3-4% in dry cookies to over 90% in foods like watermelon and milk. Meat contains around 50% water while vegetables can contain as much as 96% water.
- Water plays an important role in many chemical reactions in foods and is essential for enzyme and bacterial activity. It has properties like crystallization and boiling points that impact food consistency, structure and other physical characteristics.
This document discusses intermediate moisture foods (IMF), which are foods with a water activity between 0.6-0.9 that prevents microbial growth. Examples include jams, jellies, candies, baked goods, honey, and dried meats. IMF have 10-50% moisture. Water activity measures the availability of water for microbial growth. IMF provide food preservation by controlling water activity and may include additional preservatives. While IMF don't require refrigeration, they can contain high sugar or salt and their texture may deteriorate if not properly handled.
1. Factors affecting microbial growth in food
(a) Intrinsic factors:
oThey include:
pH, water activity, oxidation reduction potential, nutrient
content, antimicrobial contents, biological structure.
(b) Extrinsic factors:
oAre factors external to the food that affect microbial
growth.
Temperature,Concentration of gases in the environmentand
RH
2. Intrinsic factors:
o These are inherent in the food.
-They include:
Hydrogen ion concentration (pH) will see this
Moisture content Wa two factors
Nutrient content of the food
Antimicrobial substances
Biological structures
3. Hydrogen ion concentration (pH)
• Most bacteria grow best at neutral or weakly
alkaline pH usually between 6.8 and 7.5.
• Some bacteria can grow within a narrow pH
range of 4.5 and 9.0, e.g. Salmonella
4. cont
• Other microorganisms especially yeasts and
molds and some bacteria grow within a wide
pH range, e.g. molds grow between 1.5 to
11.0, while yeasts grow between 1.5 and 8.5.
5. Introduction
What is PH?
o It is measure of the acidity or alkalinity of a
solution in water.
o The acidity or alkalinity of a water solution is
determined by the relative number of hydrogen
ions (H+) or hydroxyl ions (OH-) present.
6. Cont
• Acidic solutions have a higher relative number
of hydrogen ions, while alkaline (also called
basic) solutions have a higher relative number
of hydroxyl ions.
• Acids are substances which either dissociate
(split apart) to release hydrogen ions or react
with water to form hydrogen ions.
7. cont
o Bases are substances that dissociate to release
hydroxyl ions or react with water to form
hydroxyl (OH)ions.
10. cont
o Increasing the acidity of foods, either through
fermentation or the addition of weak acids, has
been used as a preservation method since
ancient times.
o In their natural state, most foods such as meat,
fish, and vegetables are slightly acidic while
most fruits are moderately acidic.
11. cont
o The pH is a function of the hydrogen ion
concentration in the food:
i.e. pH = -log10 [H+]
12. pH values of some food products
Food type Range of pH values
Beef 5.1 - 6.2
Chicken 6.2 – 6.4
Milk 6.3 – 6.8
Cheese 4.9 - 5.9
Fish 6.6 - 6.8
Oyster 4.8 - 6.3
Fruits < 4.5 (most < 3.5)
Vegetables 3.0 – 6.1
13. cont
• Microorganisms that are able to grow in acid
environment are called acidophilic
microorganisms.
• These microorganisms are able to grow at pH
of around 2.0
• Yeasts and molds grow under acidic this env’t.
14. cont
• Other microorganisms such as Vibrio cholerae
are sensitive to acids and prefer alkaline
conditions.
• Most bacteria are killed in strong acid or
strong alkaline environment except
Mycobacteria.
15. Minimum and maximum pH for growth of some
specific microorganism
Microorganism Minimum Maximum
Escherichia coli 4.4 9.0
Salmonella
enterica serovar
typhi
4.5 8.8
All bacteria 4.0 9.0
Molds 1.5 11.0
Yeast 1.5 8.5
16. cont
o Examples of high-acid foods include
jams and jellies, pickles and most fruits.
o This type of foods has PH value less or equal
to 4.5.
o Low acidic foods include:
vegetables, legumes, beas,peas,carrot,corn,onion and
egg white
o which has greater or equal to 4.5.
17. Types of Water in Food
Most natural foods contain water up to 70% of their
weight or greater unless they are dehydrated.
Fruits and vegetables contain water up to 95% or greater.
Water in foods and biological materials can be grouped
in three categories:
free water
entrapped water, and
bound water
18. cont
o Free water- is easily removed from foods or
tissues by cutting, pressing, squeezing or
centrifugation.
• Entrapped water is- immobilized within the
lattices of large molecules, capillaries, or cells,
but it is released during cutting or damage, it
flows freely.
19. cont
• It may be entrapped in foods such as pectin
gels, fruits, vegetables, and so on.
o Entrapped water- although not free flowing,
does have the properties of free water.
o Free and entrapped water together may be
considered bulk water.
20. cont
• Entrapped water has properties of free water and
no properties of bound water.
• Bound water usually is defined in terms of the
ways it is measured; different methods of
measurement give different values for bound
water in a particular food.
21. cont
o This water will behave almost like pure water
during food processes.
o It is easily removed by drying, easily
converted to ice during freezing, and available
as a solvent.
22. Some characteristics of bound water include:
– It is not free to act as a solvent for salts and sugars.
– It can be frozen only at very low temperatures
(below freezing point of water).
– It exhibits essentially no vapor pressure.
– Its density is greater than that of free water
23. Moisture content
o The amount of free water in a food medium.
o The amount of free water is important for
growth of microorganisms.
24. cont
• If there is lack of free water microorganisms
will not grow.
• Water activity is defined as the vapour
pressure of a food substance to that of water at
the same temperature.
• (Aw = VPFood/VPWater)or Aw = P/P0
25. cont
o The water activity of pure water is equal to 1.0
o Food products have a water activity of less than 1.0.
o A saturated salt solution has a water activity of 0.75.
o Salting and drying reduces the water activity of a food
product
26. Water activity of some food products
Food Product Water activity
Raw meat and milk 0.99- 1.0
Luncheon meat 0.95
Boiled ham, sliced bacon 0.90
Dried grains 0.80
27. cont
• Growth of microorganisms is greatly affected by
the level of water activity (Aw) in the food.
• Inhibition of growth occurs if the water activity
for food is lowered beyond an organism’s
minimum level of water activity that is
necessary for growth.
28. cont
• Microorganisms have varying minimum water
activity requirements that supports their
growth in food.
29. Minimum water activity that supports growth of
some microorganisms
Microorganism Water activity
Clostridium botulinum,
Bacillus cereus,
Pseudomonas aeruginosa,
Salmonella spp.
0.95
0.95
0.95
0.95
Staphylococcus aureus (anaerobic),
Candida spp., Saccharomyces
0.90
Staphylococcus aureus (aerobic) 0.86
Penicillium spp. 0.82
Most spoilage yeast 0.88
Most spoilage molds 0.80
Osmotic yeast 0.70
30. cont
o Water activity is a measure of how efficiently the
water present can take part in a chemical or
physical reaction.
o If half the water is so tightly bound to a protein
molecule that it could not take part in a hydrolysis
reaction the overall water activity would be
reduced.
31. cont
o The tightly bound water has no tendency to
escape from a food as a vapor and therefore
exerts no partial pressure and has an effective
water activity of zero.
32. cont
• Concentration and dehydration processes are
conducted primarily for the purpose of:
– decreasing the water content of a food
– simultaneously increasing the concentration of
solutes and
– decreasing perishability.
33. cont
o Water activity refers to the water in the food
that is available (free) to support microbial
growth.
o It is measured with a water activity meter in a
scale from 0 to 1.
34. cont
o Foods with values below 0.85 are non-
hazardous regardless of their acidity, because
they do not support the growth of harmful
bacteria.
Examples are dried and semidried products.
36. cont
• A critical factor that determines the stability or
shelf life of foods.
• Most bacteria, for example, do not grow at
water activities below 0.91, including pathogens
such as Clostridium botulinum.
37. cont
• Below 0.80 most molds cannot be grown and
below 0.60 no microbiological growth is
possible.
• However, there remain a number of food
spoilage microbes that can grow within the
range 0.8 - 0.6
38. cont
• E.g. Staphylococcus aureus, a common food
poisoning organism, can grow down to this
relatively low water activity.
• Intermediate-moisture foods, which have aw
values between 0.6 and 0.9, have drawn
considerable attention because they are
palatable without the need to rehydrate them.
39. Table: typical growth limits function of wa
aw= 0.91-0.95 = most bacteria
aw = 0.88 = most yeast
aw = 0.80 = most mushroom
aw = 0.75 = halophile bacteria
aw = 0.70 = osmiophil yeast
aw = 0.65 = xerophile mushroom
40. cont
• Foods which have high level of water activity, the
shelf life is limited mainly by microbiological
activity.
• Products with aw levels below about 0.70 may well
be stable microbiologically and consequently have
a longer shelf life, but enzyme related breakdown
processes is occurred.
41. cont
• It is mainly determine chemical reactions that
affects the quality and stability of these foods.
• Water activity control is an important factor for
the chemical stability of foods.
42. cont
• Most foodstuffs contain carbohydrates and proteins
and are therefore subject to non-enzymatic browning
reactions (Maillard reaction).
• The Maillard reaction gets stronger at increasing aw
values and reaches its peak at aw = 0.6 to 0.7 with
further increase of aw this reaction gets rapidly
weaker.
43. cont
• Most enzymatic reactions are slowed down at aw
values below 0.8.
• Some of these reactions occur even at very low
aw values.
• However, as many foodstuffs are thermally treated
during their processing, enzymatic spoilage is
usually of very little importance.
45. SORPTION PHENOMENA
• Below moisture content of about 50 % the
water activity decreases rapidly and the
relationship between water content and relative
humidity (water activity) is represented by the
sorption isotherms.
46. cont
• Sorption is a physical and chemical process by which
one substance becomes attached to another.
• Absorption – the incorporation of a substance in one
state into another of a different state (e.g., liquids being
absorbed by a solid or gases being absorbed by a
liquid).
47. cont
• The adsorption isotherms are required for the
observation of hygroscopic products and the
desorption isotherms are useful for
investigation of the process of drying.
• The adsorption and desorption processes are
not fully reversible.
49. cont
• Sorption isotherms usually have a sigmoid shape and
can be divided in to three areas that correspond to
different conditions of the water present in the food.
• As water is added (resorption), sample composition
moves from Zone I (dry) to Zone III (high moisture)
and the properties of water associated with each zone
differ significantly.
.
50. Note:
– Water present in Zone I of the isotherm is most
strongly sorbed and least mobile
– Water present in zone II is slightly less mobile than
bulk water
– Zone III water is freezable, available as a solvent,
and readily supports the growth of microorganism.
– It is referred to as bulk-phase water.
51. Hysteresis
• The SI prepared by addition of water (resorption or
adsorption) to a dry sample will not necessarily be super
imposable on an isotherm prepared by desorption.
This lack of superimposability is referred to as
“hysteresis”.
• SIs of polymers, glasses of low molecular- weight
compounds, and many foods exhibit hysteresis.
52. cont
o The magnitude of hysteresis, the shape of the curves, and
the inception and termination points of the hysteresis loop
can vary considerably depending on factors such as:
– nature of the food,
– the physical changes it undergoes when water is
removed or added,
– temperature,
– the rate of desorption, and
– the degree of water removal during desorption.
54. aw and food stability
• aw is:
– A critical factor that determines the stability or shelf
life of foods.
– Most bacteria, for example, do not grow at water
activities below 0.91, including pathogens such as
Clostridium botulinum.
– Below 0.80 most molds cannot be grown and below
0.60 no microbiological growth is possible.
55. cont
– However, there remain a number of food spoilage
microbes that can grow within the range 0.8 - 0.6.
Eg. Staphylococcus aureus, a common food poisoning
organism, can grow down to this relatively low aw.
– By measuring aw, it is possible to predict which mos will
and will not be potential sources of spoilage.
– Further, aw can play a significant role in determining the
activity of enzymes and vitamins in foods and can have a
major impact on their color, taste, and aroma.
56. Note:
–Many preservation processes attempt to
eliminate spoilage by lowering the
availability of water to mos.
–Reducing the amount of free--or unbound--
water also minimizes other undesirable
chemical changes that occur during storage.
57. cont
– The processes used to reduce the amount of free
water in consumer products include techniques like
concentration, dehydration and freeze drying
(lyophilization).
– Freezing is another common approach to controlling
spoilage.
– Water in frozen foods is in the form of ice crystals
and therefore unavailable to mos and for reactions
with food components.