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VPH > Food technology > Flashcards

Food technology Flashcards

1
Q

What are the main intrinsic factors of food that affect the microbial behaviour?

A
  • Nutrient availability
  • pH and buffering capacity
  • Natural antimicrobials
  • Redox potential and poising capacity
  • Food matrix
  • Water activity (Aw)
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2
Q

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

A
  • Water
  • Source of energy
  • Source of nitrogen
  • Vitamins and related growth factors
  • Minerals
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3
Q

Outline the water requirements of food microorganisms

A
  • Essential for like
  • Higher requirement for moulds
  • Then Gram -ve, then yeasts, then Gram +ve
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4
Q

What are potential sources of energy for food microorganisms?

A
  • Sugars
  • Alcohols
  • Amino acids
  • Starch
  • Cellulose
  • Fat (small number of bacteria)
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5
Q

What are sources nitrogen for food microorganisms?

A
  • Amino acids

- Other nitrogenous compounds

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6
Q

Give examples of natural antimicrobial compounds in food

A
  • 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
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7
Q

Outline how pH affects microbial growth in food

A
  • 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
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8
Q

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

A
  • Hazard analysis for different microorganisms being present in a certain food
  • Some foods inherently resistant due to inherent acidity e.g. fermented milks, pickles
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9
Q

What is redox potential (Eh)?

A
  • The ease with which the substrate loses (is oxidised) or gains (is reduced) electrons
  • The potential difference measured and expressed as mV (milli-volts)
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10
Q

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

A
  • Aerobic require positive Eh values

- Anaerobic require negative Eh values

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11
Q

What is the redox potential of a food determined by?

A
  • 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
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12
Q

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

A

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

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13
Q

Outline the importance of Water Activity in food preservation

A
  • 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
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14
Q

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

A

Skin, often left on fermented meat products

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15
Q

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

A
  • Relative humidity
  • Temperature
  • Heat (D-value, Z-value)
  • Atmosphere
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16
Q

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

A
  • Grow well at or below 7degreesC
  • Optimum between 20-30degreesC
  • e.g. Listeria, Yersinia, can grow at refrigeration temperature
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17
Q

Outline what is meant by psychrophiles

A

Optimum growth temperature is 15degreesC or lower

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18
Q

Outline what is meant by mesophiles and their importance

A
  • Grow well between 20-45degreesC
  • Optimum between 30-40degreesC
  • Most bacteria are mesophiles
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19
Q

Outline what is meant by thermophiles and their importance

A
  • Grow well at an above 45degreesC
  • Optimum between 55-65degreesC
  • Important for food stored at high temperatures or cooked
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20
Q

What is the D-value?

A

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.

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21
Q

What is D121?

A

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

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22
Q

What affects D-value?

A
  • The pathogen

- The food type

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23
Q

Give an example of how food type can affect D value

A

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

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24
Q

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

A
  • Need to remove 99.99% of the microorganism

- For spores need to get down to 0.1 spore/gram of food

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25
Q

What is the Z value?

A

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

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26
Q

Why might the Z-value not always be useful?

A

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

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27
Q

What are the main gaseous atmospheres used in food preservation?

A
  • Carbon dioxide (aka modified atmosphere packaging)
  • Ozone
  • Vacuum packing
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28
Q

Outline the use of ozone in gaseous atmosphere packaging of food

A
  • Strong oxidising agent

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

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29
Q

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

A

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

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30
Q

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

A

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

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31
Q

Which aspects of food production are particularly time sensitive?

A
  • Time of storage of ingredients
  • Time for preparation and handling
  • Intermediate product storage
  • Final product storage
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32
Q

What is the role of vets in food production?

A
  • Inspection of animal origin food establishments
  • Microbiological testing
  • Legislation
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33
Q

What is meant by food technology?

A

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

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34
Q

What is the main aim of food preservation?

A
  • Minimise growth of microorganisms during storage period
  • Promote longer shelf life
  • Reduce hazard from eating the food
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35
Q

List reasons for rejection of food as spoiled

A
  • Organoleptic changes
  • Chemical changes
  • Physical damage
  • Freezer burn
  • Staling
  • Ripening
  • Presence of foreign bodies
  • Contamination with chemical agents
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36
Q

Describe organoleptic changes

A
  • 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
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37
Q

Give an example of food spoilage that can be passed vertically

A
  • Aflatoxin M1 and M2 in milk due to biaccumulation in the cow
  • Will persist after pasteurisation
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38
Q

List chemical changes that can occur in food spoilage

A
  • Chemical oxidation of fats producing rancidity

- Browning of fruits and vegetables in contact with air

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39
Q

Which fats go rancid faster?

A

Mono or polyunsaturated fats as these are oxidised faster

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40
Q

Explain the colour change that occurs in meat following slaughter

A
  • 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)
41
Q

Outline the importance of physical damage in food spoilage

A
  • Caused by improper handling somewhere along production chain
  • Can allow entry of microorganisms, insects or rodents causing biological risk
42
Q

Explain the process of freezer burn

A
  • 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
43
Q

Explain the process of staling

A
  • Chemical and physical process in bread and other foods (reduces palatability)
  • Loss of water
  • May require increase in water in recipe if occurs rapidly
44
Q

Explain ripening in food spoilage

A

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

45
Q

Describe the importance of foreign bodies in food spoilage

A
  • 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
46
Q

Explain the importance of contamination with chemical agents in food spoilage

A
  • 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
47
Q

What are the main food preservation methods for meat?

A
  • Fermenting
  • Canning
  • Smoking
48
Q

Outline the process of fermenting meat

A
  • Raw meat plus fat made into mince
  • Mixed with other ingredients
  • Starter culture added
  • Packed into casings
  • Fermented
  • Dried and ripened
49
Q

Outline the principles of meat fermentation

A
  • 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
50
Q

Describe the product formulation of fermented meats

A
  • Nitrite/nitrate added
  • 0.3-2% fermentable carbohydrate added
  • Lactic acid
51
Q

Why is the carbohydrate content important in meat fermentation?

A
  • 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
52
Q

Why is lactic acid important in meat fermentation?

A
  • Decreases the water binding capacity of meat proteins

- Aids the drying process

53
Q

Why is nitrite or nitrate added in meat fermentation?

A
  • 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
54
Q

Describe the starter culture used in meat fermentation

A
  • Traditionally was natural flora
  • Now use commercial starter culture as is faster, more predicatble drop in pH, earlier development of firmness and safer product
55
Q

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

A
  • Lactobacillus plantarum
  • Pediococcus acidilacti
  • Yeasts
  • Micrococcus if only nitrate (no nitrite) is added
56
Q

Describe the ripening process in meat fermentation

A
  • Protein hydrolysed by microbial proteinases producing amino acids and other breakdown products
  • pH drops
57
Q

What is the role of mincing in meat fermentation?

A

Increase the surface area for microbial activity and produces required texture

58
Q

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

A
  • 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
59
Q

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

A

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

60
Q

What may lead to spoilage of canned foods?

A
  • Underfilling
  • Quality of can seam
  • Improper handling
  • Hygiene of can transport system
61
Q

Outline why smoking can be used to preserve meat

A
  • Wood smoke contains number of substances with antimicrobial activity
  • Formaldehyde, higher aldehydes, phenols and methanol
  • Highly inhibitory to microorganisms
62
Q

What are the 3 main types of yoghurt?

A
  • Set
  • Stirred
  • Yoghurt drinks
63
Q

What is the basic chemical process that produces yoghurt?

A
  • Is a product of bacterial fermentation of milk
  • Lactose converted by bacteria into lactic acid
  • Decreases pH, denatures casein protein, sets protein and yoghurt
64
Q

Outline the steps for the production of set yoghurts

A
  • 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
65
Q

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

A
  • 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
66
Q

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

A
  • Increases the SNF content of the milk, producing a more viscous product
67
Q

What is the purpose of homogenisation in yoghurt production?

A

Reduces the size of the fat globules

68
Q

What is the importance of heat treatment in yoghurt production?

A
  • Destroys pathogens (milk contains a variety of microorganisms)
  • Stimulates culture activity as it provides starter with a clean environment
  • Is a critical control point
69
Q

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

A

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

70
Q

Outline the steps in the production of cheeses

A
  • Raw milk pasteurised
  • Starter culture added, incubated
  • Rennet added and coagulation occurs
  • Scalding
  • Cheddaring
  • Milling and salting
  • Moulding and pressing
  • Ripening
  • Packaging and storage
71
Q

What is contained in the starter culture for yoghurts?

A

Streptococcus thermophylus and Lactobacillus bulgaricus

72
Q

What is contained in the starter culture for cheeses?

A

Lactococuus lactis spp. cremoris

73
Q

What is the role of milk pasteurisation in cheese production?

A

Kills pathogens and allows clean environment for starter function

74
Q

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

A

Fermentation and lactic acid development to produce the required pH drop

75
Q

What occurs during ripening of cheeses?

A

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

76
Q

Describe the cheddaring phase in cheese production

A
  • Squeezing and stretching of the curd

- Final lactic acid concentration 0.6-0.8%

77
Q

What are common microbial problems in cheese?

A
  • Blowing
  • Mould growth
  • Bacteriophages attacking starter culture
78
Q

Describe blowing in cheese

A
  • Early: due to coliforms, indicates poor staff hygiene

- Late: due to gas producing Clostridia (can be transferred from cow feed to milk)

79
Q

What is food poisoning from cheese usually associated with?

A
  • Generally considered low risk food
  • Associated with poor processing hygiene
  • Unpasteurised milk
80
Q

How is microbiology controlled in the food industry?

A
  • HACCP based systems
  • Risk assessment
  • Raw material/ingredients
  • Hygiene monitoring
  • Process monitoring
  • Finished products assessed
  • Crisis management
81
Q

Explain the importance of microbiology in developing the HACCP plan

A
  • 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
82
Q

Outline risk assessment in food production

A
  • Hazard identification and characterisation
  • Exposure assessment
  • Risk characterisation
83
Q

Outline hygiene monitoring in food production

A
  • Swabs (surfaces, pipes, equipment)
  • Solid or liquid samples (soil, rinse water)
  • Personnel (hand swabbing, hand rinsing)
  • Air (exposure plates, air sampling machines
84
Q

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

A
  • 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
85
Q

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

A
  • 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
86
Q

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

A
  • Pathogens
  • Microbial toxins
  • Indicator microorganisms
  • Spoilage microorganisms
87
Q

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

A
  • 2 class

- 3 class

88
Q

What is included in a sampling plan for food production?

A
  • Limits for organisms
  • Sampling frequencey
  • Organisms/toxins of concern
  • Food/sample type to be examined clearly identified
  • Interpretation guidance
89
Q

What regulation covers microbiological criteria for foods?

A

EC 2073/2005

90
Q

Outline product shelf life evaluations for food products

A
  • Variety of parameters used to determine shelf life
  • Deterioration in specific organoleptic qualities (flavour, aroma, appearance, texture)
  • Microbial growth
91
Q

Describe the process of microbiological challenge testing in food production

A
  • 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
92
Q

Describe what is meant by a 2 class sampling plan

A
  • Consists of specifications n, c and m

- Mainly used for presence/absence assessment i.e. marginally acceptable from acceptable

93
Q

Describe what is meant by a 3 class sampling plan

A
  • Consists of specifications n, c, m and M

- Mainly for separating of marginally acceptable from good quality

94
Q

In sampling plans, what is n?

A

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

95
Q

In sampling plans, what is c?

A

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

96
Q

In sampling plans, what is m?

A

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

97
Q

In sampling plans, what is M?

A 
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
98
Q

Describe the features of traditional food inspection systems

A
  • Aims to combat classical foodborne diseases
  • Fail to prevent contamination of foods with microorganisms of greater concern
  • End product testing
  • Reactive
99
Q

Describe the features of risk based food inspection systems

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

VPH (13 decks)

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