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Flashcards in Food technology Deck (100)
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What are the main intrinsic factors of food that affect the microbial behaviour?

- Nutrient availability
- pH and buffering capacity
- Natural antimicrobials
- Redox potential and poising capacity
- Food matrix
- Water activity (Aw)


What nutrients are required in order for microorganisms of food to grow?

- Water
- Source of energy
- Source of nitrogen
- Vitamins and related growth factors
- Minerals


Outline the water requirements of food microorganisms

- Essential for like
- Higher requirement for moulds
- Then Gram -ve, then yeasts, then Gram +ve


What are potential sources of energy for food microorganisms?

- Sugars
- Alcohols
- Amino acids
- Starch
- Cellulose
- Fat (small number of bacteria)


What are sources nitrogen for food microorganisms?

- Amino acids
- Other nitrogenous compounds


Give examples of natural antimicrobial compounds in food

- Essential oils in some plant species (eugenol in cloves, allicin in garlic)
- Lactoferrin, conglutinin, lactoperoxidase system and a rotavirus inhibitor in cow's milk
- Lysosyme in eggs and milk


Outline how pH affects microbial growth in food

- Specific ranges in which different microorganisms grow best (most between 6.6-7.5, few below 4.0)
- Some foods better able to resist change than others e.g. meats better buffering capacity


Why is it useful to know the pH range of different microorganisms?

- Hazard analysis for different microorganisms being present in a certain food
- Some foods inherently resistant due to inherent acidity e.g. fermented milks, pickles


What is redox potential (Eh)?

- The ease with which the substrate loses (is oxidised) or gains (is reduced) electrons
- The potential difference measured and expressed as mV (milli-volts)


What are the specific redox requirements of anaerobic and aerobic microbes?

- Aerobic require positive Eh values
- Anaerobic require negative Eh values


What is the redox potential of a food determined by?

- Characteristic Eh potential of the original food
- Poising capacity of the food
- Oxygen tension of the atmosphere around the food
- Microorganisms effect on the Eh of the food
- The pH of the food


What is meant by Water Activity (Aw) of a food?

A measure of how efficiently the water present can take part in a chemical (physical) reaction


Outline the importance of Water Activity in food preservation

- Reducing water available for microbial growth important
- Can have high moisture but low water e.g. solution saturated with salt
- Below Aw 0.79, few pathogens are of concern


What is an important mechanical barrier of food to microbial growth?

Skin, often left on fermented meat products


What are the main extrinsic factors that affect microbial behaviour in foods?

- Relative humidity
- Temperature
- Heat (D-value, Z-value)
- Atmosphere


Outline what is meant by psychotrophs and give examples and their importance

- Grow well at or below 7degreesC
- Optimum between 20-30degreesC
- e.g. Listeria, Yersinia, can grow at refrigeration temperature


Outline what is meant by psychrophiles

Optimum growth temperature is 15degreesC or lower


Outline what is meant by mesophiles and their importance

- Grow well between 20-45degreesC
- Optimum between 30-40degreesC
- Most bacteria are mesophiles


Outline what is meant by thermophiles and their importance

- Grow well at an above 45degreesC
- Optimum between 55-65degreesC
- Important for food stored at high temperatures or cooked


What is the D-value?

Decimal reduction time, the time taken for the population to pass through a log cycle (i.e. 90% of population is killed) at a certain temperature.


What is D121?

The time required to kill 90% of a population of microorganisms at 121degreesC


What affects D-value?

- The pathogen
- The food type


Give an example of how food type can affect D value

Salmonella is 90x more resistant in chocolate vs milk, due to presence of fats and proteins in chocolate that protect the cell


How is the number of cycles at the D value determined?

- Need to remove 99.99% of the microorganism
- For spores need to get down to 0.1 spore/gram of food


What is the Z value?

The temperature change that is rquired to change the D value by a factor of 10
- i.e. treating food at 90degreesC for 30 min is the same as 100degrees for 3 min or 110degrees for 0.3min


Why might the Z-value not always be useful?

Increasing the temperature may affect the quality of the food or may damage the equipment


What are the main gaseous atmospheres used in food preservation?

- Carbon dioxide (aka modified atmosphere packaging)
- Ozone
- Vacuum packing


Outline the use of ozone in gaseous atmosphere packaging of food

- Strong oxidising agent
- Not used on high-lipid foods as would cause increased rancidity


Outline the relationship between relative humidity and gaseous atmosphere of a food

By altering the gaseous atmosphere, it is possible to retard surface spoilage without lowering the RH
Removal of oxygen increases preservation


Which foods in particular should be stored under low relative humidity conditions?

Foods that undergo surface spoilage from moulds, yeasts and certain bacteria


Which aspects of food production are particularly time sensitive?

- Time of storage of ingredients
- Time for preparation and handling
- Intermediate product storage
- Final product storage


What is the role of vets in food production?

- Inspection of animal origin food establishments
- Microbiological testing
- Legislation


What is meant by food technology?

The application of food science in order to inform the production of food products


What is the main aim of food preservation?

- Minimise growth of microorganisms during storage period
- Promote longer shelf life
- Reduce hazard from eating the food


List reasons for rejection of food as spoiled

- Organoleptic changes
- Chemical changes
- Physical damage
- Freezer burn
- Staling
- Ripening
- Presence of foreign bodies
- Contamination with chemical agents


Describe organoleptic changes

- Brought about by growth of microorgansism
- Unacceptable changes in taste, odour, appearance, texture
- Some spoiled foods will still be safe to eat e.g. yoghurt containing yeasts


Give an example of food spoilage that can be passed vertically

- Aflatoxin M1 and M2 in milk due to biaccumulation in the cow
- Will persist after pasteurisation


List chemical changes that can occur in food spoilage

- Chemical oxidation of fats producing rancidity
- Browning of fruits and vegetables in contact with air


Which fats go rancid faster?

Mono or polyunsaturated fats as these are oxidised faster


Explain the colour change that occurs in meat following slaughter

- Colour change from initial dark to bright red following slaughter
- Oxygenation of myoglobin (mb) and formation of oxymyoglobin (mbO2) (bright)
- Oxidation of myoglobin and formation of MetMb (metmyoglobin) (brown)


Outline the importance of physical damage in food spoilage

- Caused by improper handling somewhere along production chain
- Can allow entry of microorganisms, insects or rodents causing biological risk


Explain the process of freezer burn

- Frozen food loses moisture due to poor packing/wrapping
- Molecules migrate from meat to coldest place they can find (sides of freezer)
- Meat becomes dehydrated


Explain the process of staling

- Chemical and physical process in bread and other foods (reduces palatability)
- Loss of water
- May require increase in water in recipe if occurs rapidly


Explain ripening in food spoilage

Spoilage can occur due to over-ripening e.g. fruits, vegetables, cheeses, fermented meats


Describe the importance of foreign bodies in food spoilage

- Food rejected as spoiled if contains foreign matter e.g. hair, soil, metal, nails etc
- Metal detectors important esp. with animal origin
- Hard or sharp foreign objects may cause consumer injury
- May introduce harmful bacteria into food


Explain the importance of contamination with chemical agents in food spoilage

- May occur through environmental pollution of air, water and soil
- Often occurs with chemicals used for cleaning so these need to be approved for use


What are the main food preservation methods for meat?

- Fermenting
- Canning
- Smoking


Outline the process of fermenting meat

- Raw meat plus fat made into mince
- Mixed with other ingredients
- Starter culture added
- Packed into casings
- Fermented
- Dried and ripened


Outline the principles of meat fermentation

- Type of meat used and product formulation depends on type of sausage
- Starter or natural flora used
- Organisms in starter can vary
- Temperature of fermentation can vary
Production may involve cooking, smoking, drying, mould ripening


Describe the product formulation of fermented meats

- Nitrite/nitrate added
- 0.3-2% fermentable carbohydrate added
- Lactic acid


Why is the carbohydrate content important in meat fermentation?

- Very little carbohydrate naturally in meat
- Is required for fermentation to occur as is energy source for desired bacteria
- Low levels lead to slow fermentation rates


Why is lactic acid important in meat fermentation?

- Decreases the water binding capacity of meat proteins
- Aids the drying process


Why is nitrite or nitrate added in meat fermentation?

- Suppress natural Gram -ve flora
- Promote growth of Streptococci, Micrococci, Pediococci and Lactobacilli that normally occur in meat in low numbers
- Nitrite prevents decolourisation and oxidative rancidity


Describe the starter culture used in meat fermentation

- Traditionally was natural flora
- Now use commercial starter culture as is faster, more predicatble drop in pH, earlier development of firmness and safer product


What organisms are commonly used in starter cultures for meat fermentation?

- Lactobacillus plantarum
- Pediococcus acidilacti
- Yeasts
- Micrococcus if only nitrate (no nitrite) is added


Describe the ripening process in meat fermentation

- Protein hydrolysed by microbial proteinases producing amino acids and other breakdown products
- pH drops


What is the role of mincing in meat fermentation?

Increase the surface area for microbial activity and produces required texture


What are some common defects of fermented meat as a consequence of microbiological problems?

- Growth of green or black moulds on surface
- Surface bacterial slime
- Souring due to excess lactic acid production
- Gassiness due to heteroformative lactic acid bacteria
- Greening of meat pigment due to production of hydrogen peroxide by Lactobacillus viridans


What is the minimum heat process applied in canning of low acid foods?

A process that gives 12 decimal reductions of C. botulinum
- e.g. at 121degreesC, D value is 0.21 minutes so 12x0.21=2.52 minutes


What may lead to spoilage of canned foods?

- Underfilling
- Quality of can seam
- Improper handling
- Hygiene of can transport system


Outline why smoking can be used to preserve meat

- Wood smoke contains number of substances with antimicrobial activity
- Formaldehyde, higher aldehydes, phenols and methanol
- Highly inhibitory to microorganisms


What are the 3 main types of yoghurt?

- Set
- Stirred
- Yoghurt drinks


What is the basic chemical process that produces yoghurt?

- Is a product of bacterial fermentation of milk
- Lactose converted by bacteria into lactic acid
- Decreases pH, denatures casein protein, sets protein and yoghurt


Outline the steps for the production of set yoghurts

- Solids added to raw milk
- Homogenisation
- Heat treatment
- Cooling/starter addition
- Packaging
- Incubation (culture multiplies, pH drops to 4.4-4.6)
- Cooling and storage


Outline the steps for the production of stirred yoghurts (e.g. Greek yoghurt)

- Solids added to raw milk
- Homogenisation
- Heat treatment
- Cooling/starter addition
- Stirred
- Incubation (culture multiplies, pH drops to 4.4-4.6)
- Pakaging
- Cooling and storage


What is the importance of the addition of solids in yoghurt production?

- Increases the SNF content of the milk, producing a more viscous product


What is the purpose of homogenisation in yoghurt production?

Reduces the size of the fat globules


What is the importance of heat treatment in yoghurt production?

- Destroys pathogens (milk contains a variety of microorganisms)
- Stimulates culture activity as it provides starter with a clean environment
- Is a critical control point


Why is it important that milk is free from antibiotic residues in yoghurt production especially?

If antibiotic residues are present, culture will not multiply, pH will not drop and the yoghurt will not set


Outline the steps in the production of cheeses

- Raw milk pasteurised
- Starter culture added, incubated
- Rennet added and coagulation occurs
- Scalding
- Cheddaring
- Milling and salting
- Moulding and pressing
- Ripening
- Packaging and storage


What is contained in the starter culture for yoghurts?

Streptococcus thermophylus and Lactobacillus bulgaricus


What is contained in the starter culture for cheeses?

Lactococuus lactis spp. cremoris


What is the role of milk pasteurisation in cheese production?

Kills pathogens and allows clean environment for starter function


What is the importance of the incubation period in cheese production?

Fermentation and lactic acid development to produce the required pH drop


What occurs during ripening of cheeses?

Protease enzymes are released from starter organisms, producing amino acids, indole, sulphur compounds and phenol to enhance flavour


Describe the cheddaring phase in cheese production

- Squeezing and stretching of the curd
- Final lactic acid concentration 0.6-0.8%


What are common microbial problems in cheese?

- Blowing
- Mould growth
- Bacteriophages attacking starter culture


Describe blowing in cheese

- Early: due to coliforms, indicates poor staff hygiene
- Late: due to gas producing Clostridia (can be transferred from cow feed to milk)


What is food poisoning from cheese usually associated with?

- Generally considered low risk food
- Associated with poor processing hygiene
- Unpasteurised milk


How is microbiology controlled in the food industry?

- HACCP based systems
- Risk assessment
- Raw material/ingredients
- Hygiene monitoring
- Process monitoring
- Finished products assessed
- Crisis management


Explain the importance of microbiology in developing the HACCP plan

- Examines raw materials and associated sources of supply
- Process points that influence the growth, death, survival or contamination with microorganisms
- Consequences of failure of any process stage


Outline risk assessment in food production

- Hazard identification and characterisation
- Exposure assessment
- Risk characterisation


Outline hygiene monitoring in food production

- Swabs (surfaces, pipes, equipment)
- Solid or liquid samples (soil, rinse water)
- Personnel (hand swabbing, hand rinsing)
- Air (exposure plates, air sampling machines


Which stages of the process of food production are monitored and what is assessed?

- Handling: cleanliness of equipt and people
- Packaging: swabs/rinse tests for aseptically filled packages
- Product: micobial load at end of production
- Transfer systems e.g. conveyors: cleanliness of equipt and microbial load developmet during time scale of operations
- Chill/freezer stores: microbial load development during storage


How is conformation to microbial criteria assessed in finished food products?

- Criteria drawn up in relation to specific foods
- Identification of organisms/toxins of concern
- Method to be used for detection and enumeration
- Sampling plan
- Limits for assessment of results
- Guidance on result interpretation
- Frequency of sample indicated, clear description of food/sample to be examined


What does microbial criteria for food products need to set limits for?

- Pathogens
- Microbial toxins
- Indicator microorganisms
- Spoilage microorganisms


What are the 2 types of sampling plan that can be used in food production?

- 2 class
- 3 class


What is included in a sampling plan for food production?

- Limits for organisms
- Sampling frequencey
- Organisms/toxins of concern
- Food/sample type to be examined clearly identified
- Interpretation guidance


What regulation covers microbiological criteria for foods?

EC 2073/2005


Outline product shelf life evaluations for food products

- Variety of parameters used to determine shelf life
- Deterioration in specific organoleptic qualities (flavour, aroma, appearance, texture)
- Microbial growth


Describe the process of microbiological challenge testing in food production

- Varying levels of organisms of concern inoculated into pack of food under consideration
- Food stored with un-inoculated food under controlled conditions
- Examination at various intervals to determine growth, death or survival


Describe what is meant by a 2 class sampling plan

- Consists of specifications n, c and m
- Mainly used for presence/absence assessment i.e. marginally acceptable from acceptable


Describe what is meant by a 3 class sampling plan

- Consists of specifications n, c, m and M
- Mainly for separating of marginally acceptable from good quality


In sampling plans, what is n?

The number of sample units from a lot that must be examined to satisfy a given sampling plan


In sampling plans, what is c?

The maximum acceptable number, or maximum allowable number of sample units that may exceed microbiological criterion (m). When c is exceeded, lot is rejected


In sampling plans, what is m?

The maximum number or level of relevant bacteria per gram. Levels above are either marginally acceptable or unacceptable.


In sampling plans, what is M?

A quantity used to separate marginally acceptable quality from unacceptable quality foods. Only used in 3 class sampling
Values at or above M are unacceptable relative to health hazard, sanitary indicators or spoilage potential


Describe the features of traditional food inspection systems

- Aims to combat classical foodborne diseases
- Fail to prevent contamination of foods with microorganisms of greater concern
- End product testing
- Reactive


Describe the features of risk based food inspection systems

- Risk used as predictor of disease
- Controls the design and manufacture, preventing failure
- Ongoing verification
- Proactive


What is the "Stable to Table" approach to food safety?

Biological and chemical agents which cause food poisoning vary but all accompany animal from stable to table