1. Food preservation methods 1-Physical methods 2-Chemical methods 3-Biopreservation

2. Food processing
All the operations by which raw foodstuffs (animal and plant tissue) converted into forms that
will not spoil as quickly as the fresh, whole foods (raw materials) from which they were made
is convenient and practical to consume.
includes basic preparation of food, alteration of a food product into another form and preservation and packaging techniques.

3. Why foods are processed?
to reduce or eliminate harmful microbes from growing in foods so that they remain fresh, wholesome, nutritious, safe, and free from the effects of spoilage for a certain length of time
manufacture specific desirable food products that exhibit a certain shelf life

4. Physical methods
Those methods that utilize physical treatments to inhibit, destroy, or remove undesirable M.O or endogenous enzymes without involving antimicrobial additives or products of microbial metabolism as preservative factors.

5. 1- Heat Treatments.
A- High- heat treatments
B- Low - heat treatments
2-Drying
3-Radiation
4-Filtrations

6. High-Heat Treatments
It is the most effective method for inactivating M.O and enzymes
It is either applied to foods in their final container or prior to packaging.
It is depend on time-temperature relationship

7. Effect of heating on M.O
Sufficient heating cause irreversible denaturation of cell proteins and metabolic enzymes and cause death.
If heat is not severe it will cause cell injury

8. Types of high-heat treatment
1-Blanching
The food substance, usually
a vegetable or fruit, is
plunged into boiling water,
removed after a brief, timed
interval and finally plunged into iced water
or placed under cold running water
(shocked) to halt the cooking process.

9. Primarily used for fruits & vegetables
Deactivates natural food enzymes
Kills some bacteria

10. Blanching time is crucial and varies with the vegetable and size of the pieces to be frozen.
Under blanching speeds up the activity of enzymes and is worse than no blanching.
Over blanching causes loss of flavor, color, vitamins and minerals.

11. Carrots Mushrooms Okra Small, whole - 5 min
Diced, sliced or lengthwise strips - 2 min
Mushrooms
Whole (steamed) - 5 min
Buttons or quarters (steamed) - 3½ min
Slices (steamed) - 3 min
Okra
Small pods - 3 min
Large pods - 4 min

12. Resistance of M.O to Heat
Psychrophiles are the most heat sensitive; thermophiles are the most heat resistant
Sporeformers are more heat resistant compared to vegetative
Cocci more resistant than rods
Spores produced by mold are more heat resistant than the bacterial spores

13. D value = decimal reduction time or time ( sec, min, hr) it takes to kill 90% of a population ( 1 log cycle) at a certain temperature under given conditions ( pH, food type etc.)
Z-value = the increase in temperature required to reduce the thermal death time 10-fold

14. F-value = Time in minutes needed to destroy a specific number of microbial cells or microbial spores at a reference temperature (121.1 ºC)

15. Determine the D value for a M
Determine the D value for a M.O in a particular food at a specified temperature by assessing the number of survivors over a specified time. Construct a thermal death time curve

18. Example :
Start with a population of 1,000,000 bacteria
1,000,000 x 90/100 = 900,000 killed
1,000, ,000 = 100,000 survive
( 1/10 survive; 9/10 killed)
1 D =90 % kill

19. 100,000 x 90/100 = 90,000 killed
100, ,000 = 10,000 survive
(1/100 survive; 99/100 killed)
2 D = 99% kill
10,000 x 90/100 = 9,000 killed
10, ,000 = 1,000 survive
( 1/1000 survive; 999/1000 killed)
3 D = 99.9%

20. Example : D72C = 1.2 sec for a bacterium
When heating a food at 72C, 90% of the bacterial population will be killed every 1.2 sec.
After 1.2 sec 90 % killed
2.4 sec 99 % killed
3.6 sec 99.9 killed
4.8 sec killed
The higher the D value the more resistant the MO.

21. Pooled raw milk at the processing plant has bacterial population of 4x106/mL.
It is to be processed at 79°C for 21 sec.
The average D value at 65°C for the mixed population is 7 min.
The Z value is 7°C.
How many organisms will be left after pasteurization? What time would be required at 65°C to accomplish the same degree of lethality?

23. Factors influencing the heat resistance of MO
1.Water activity
Decreasing relative humidity, moisture or aw increases heat resistance ( when heated in water versus air)

24. Wet heat
Heat treatment in the presence of water where M.O killed by denaturation
Dry heat
It is less lethal and kills M.O by dehydration and oxidation

25. 2. Fat content
Increasing the fat content of a food generally increases the heat resistance (may protect the cell against moisture loss).
3. Carbohydrate content
Increasing the CHO content of foods generally results in an increase in heat resistance ( resistance varies depending on nature of CHO)

26. 4.Salts
The presence of certain salt may either increase (NaCl) or decrease (CaCl2) heat resistance ( some salts may decrease water activity thereby promoting heat resistance)
5. Proteins
Increasing the level of protein in a food results in increased heat resistance

27. Most MO are maximally heat resistant at their optimum pH.
An increase or decrease from this value normally results in an increase in heat sensitivity
7. Initial number of MO in a food. Increasing the levels normally result in greater survivors ( some bacteria may release protective substances in the food or liquid, menstruum , they are heated in).

28. 8. Heat resistance tends to increase with an increase in growth temperature ( especially for spore forming MO)
9.The heat resistance of a MO decrease when heated in the presence of an inhibitory compound ( acid, bacteriocin, NO2, etc)

29. Holding time:
the food should be heated at specific temperature for a specific time
Cold point:
the centre of can filed with solid food

30. 2-Pasteurization
The process of heating food to ensures destruction of all non spore forming pathogens (bacteria, viruses, protozoa, molds, and yeasts) and a large number of spoilage M.O (99 to 99.9%) and heat sensitive enzymes

31. Products that can be pasteurized : eggs, sports drinks, canned food, water , juice, honey, apple cider, milk
Time/temperature kills all pathogens or reduces them to levels which are safe; incapable of growing in milk under proper storage conditions.

32. A - High temperature, short time (HTST)
72C for16 sec. and then immediately cooled to less than 10°C
B - Low temperature, long time (LTLT)
63C for 30 min. and then immediately cooled to less than 10°C

33. Small number of spore forming MO survive and cause spoilage
Two groups can survive milk pasteurization
a- Thermoduric
Can survive exposure to relatively high temperature but do not necessary grow at these temp.
b- Thermophilies
They requires high temperature for their growth and metabolic activity

34. 3- Sterilization
Destruction of all microorganisms vegetative and spores
Commercial sterility
No viable MO can be detected by conventional cultural methods or that the number of survivors is too low to be significant under condition of storage

35. 12-D concept
minimum heat process that should reduce the probability of survival of the most heat resistant Cl. botulinum spores to
In other words, minimum heat that would allow for the survival of one Cl. botulinum spore in 1012 cans (1 billion cans).
Processing for 2.52 min at 121C will achieve this effect.

36. Holding time
the food should be heated at specific temperature for a specific time
2.52 min at 121C
Cold point
the centre of can filed with solid food

37. Time-Temperature Combinations
From thermal death curves, the following time/temperature treatments yield the same microbe killing effect:
oC oC
oC oC
oC oC
oC oC

38. Thermocouple Placement at Cold Point in Can

39. Protective Effects of Food Constituents
Sugar protects bacterial spores in canned fruit
Starch & protein protect spores
Fats & Oils protect bacterial spores

40. Every food particle inside a can must reach the critical temperature for the required time
Factors affecting heat penetration include:
size of can
shape of can
consistency of the food item (thick or thin)
nature of the food (particulate vs liquid)

41. From a microbiological point of view canned foods are divided into groups depending on the final pH of their product in order to prevent food poisoning results from Clostridium botulinum

42. 1) low acid: pH > 4.6
meats, some vegetables (corn and lima beans)
2) medium acid to acid: pH
tomatoes, pears
3) high acid: pH < 3.7
sauerkraut, pickles , grapefruit

43. Infrequently canned food undergoes microbial spoilage due to:
1- Underprocessing:
Inadequate time/temperature applied; incorrect calculation used for determining the heat process.
In acid canned foods this is largely due to spores that survive then germinate.
In hot filled foods spoilage may result from yeast and mold and aciduric bacteria.

44. 2- Post process leakage ( PPL):
Most common form of spoilage.
Can is contaminated ( leakage at the ‘canners end’) following retorting perhaps during water cooling.
Most of the MO causing this problem are viable ( since the can has already been heated).
From a ‘lot’, only a few cans show this condition.

45. 3. Pre-process spoilage (incipient spoilage)
Product is canned but held too long before retorting especially at abusive temperatures ( perhaps due to a power failure).
Microscopic inspection of the retorted can contents will show evidence of a mixed microflora of dead MO.
All cans in the lot will be effected and soft swells are common.

46. Flat-sour bacteria
Endo-spore forming bacteria that produce acid but little or no gas in canned food and usually there are more resistant than Cl. botulium spores and they need 4 to 5 min at 121 ºC.
Temperature abuse > 40 ºC but not < 30 ºC
Bacillus sterothermophilus

47. Aseptic Packaging Food is sterilized outside the can
Placed into a sterile container and sealed under aseptic conditions
Paper and plastic packaging materials most commonly used
Most suitable for liquid-based food products

48. Hot Pack/Hot Fill
Filling unsterilized containers with sterilized food that is still hot enough to render the package commercially sterile.