Hurdle technology uses a combination of preservation methods to make foods shelf-stable while maintaining quality and safety. It involves using multiple hurdles like reduced moisture, increased acidity, refrigeration, or addition of preservatives that microorganisms must overcome to grow. The hurdles work synergistically so that microbes cannot adapt to or overcome all of the preservation factors simultaneously. This allows foods to be processed more gently and minimally while still achieving a long shelf life.

1. PALLVI DHOTRA
ROLL No. 06
FOOD SCIENCE & TECHNOLOGY

2. Hurdle technology is the combined use of several
shelf-
preservation methods to make a product shelf-stable,
to improve quality and to provide additional safety.
Also known as “combined method technology”.
Leistner in 1976, introduced the term “hurdle effect”.
NEED FOR HURDLE TECHNOLOGY
Consumers are demanding for fresh, natural and
minimally processed food products.
Ongoing trend has been eat out and to consume ready
to eat foods.
New ecology routes for microbial growth have emerged.
emerged.

3. Preservative factors or hurdles disturb the
homeostasis of microorganisms.
Microorganisms should not be able to “jump over”
all the hurdles present in the food product.
Preservative factors prevents microorganisms from
multiplying and causing them to remain inactive or
even die.
The hurdle concept illustrates that complex
interactions of temperature, water activity, pH etc
are significant to the microbial stability.

4. High Temperature
i. Pasteurization
mild heat treatment (e.g., 63oC for 30 min; 100oC for 12
sec)
high product quality
destroys vegetative pathogens (disease-causing microbes)
(disease-
shelf-
reduces total microbial load, increases shelf-life
does not destroy spores (dormant stage of some bacteria)
usually combined with other hurdles (e.g., refrigeration)

5. ii. Sterilization
complete destruction of microorganisms
severe heat treatment (equivalent to several
min at 121.1oC)
destroys spores
gives "shelf-stable" product
"shelf-
some nutrient, quality destruction (colour,
flavour, texture)

6. iii. Blanching
blanching is a kind of pasteurization
generally applied to fruits and vegetables
primarily applied to inactivate natural
enzymes
commonly practiced when food is to be
frozen
depending on its severity, also destroys
microorganisms

7. Vegetative cells, as well as, viruses are
60° 80°
destroyed at temperature 60°C to 80°C
Higher temperature may be needed for
killing of thermophilic microorganisms
Vegetative cells are killed in 10 minutes at
100°
100°C and many spores in 30 minutes at
100°C
100°

8. Low Temperature
i. Refrigeration
ideally 0oC to 4oC for most foods
short-
short-term preservation (days to weeks)
high product quality (fresh, minimally processed,
sous vide)
slows down microbial growth, respiration,
enzyme/chemical reactions
some pathogens can grow (e.g., C. botulinum (type
E), Listeria)

9. ii. Freezing
generally -18oC to -30oC
quality depends on product, time,
temperature
long-
long-term preservation (months to years)
stops microbial growth, respiration
slows down chemical reactions
must have good packaging

10. Reduced Water Activity (aw)
aw is water "availability"
water is required for microbial growth,
enzyme/chemical reactions
pathogenic microorganisms cannot grow at aw <
0.86
yeast & moulds cannot grow at aw <0.62
free water can be removed by concentration,
dehydration and freeze drying
in general, the lower the aw, the longer the storage
life

11. Glucose
Fructose
Sucrose
Sodium chloride
Potassium chloride

12. Increased Acidity (lowered pH)
acidity slows down growth of spoilage
organisms and pathogens
pathogens won't grow, spores won't
germinate at pH<4.5
(e.g., fruit juices, sauerkraut)
above pH 4.5, must sterilize for shelf
stability
below pH 4.5, can pasteurize

13. Organic acids
citric acid
malic acid
tartaric acid
benzoic acid
lactic acid
propionic acid
Inorganic acids
by-
Fermentation by- products

14. Controlling Oxygen
low oxygen inhibits growth of many
spoilage organisms
but:
anaerobic conditions required by some pathogens
(e.g., C. botulinum)
Preservatives
inhibit bacteria, yeasts, moulds
used at low levels (mg/kg) for specific applications
e.g., benzoate (soft drinks), propionate (baked
goods),
nitrites (meats), sulfites (wine), ascorbate (juices)

15. Sulphur dioxide and Sulphites
Nitrites and Nitrates
Sorbates
Propionates
Sodium benzoate

16. Competitive Microorganisms
"good" bacteria inhibit "bad" (spoilers, pathogens)
May act by:
by:
"crowding out"
producing acid
producing antibiotics (bacteriocins)
e.g., lactic acid bacteria (sauerkraut, yogurt)

17. Sequence of hurdles ensures stability at each
stage. All hurdles decline with time except aw.
Nitrite inhibits pathogens
growth of other bacteria depletes oxygen
acid-
Low oxygen favours acid-producing
competitive flora
Acid decreases pH
Aw hurdle gradually increases due to drying.

18. These products have pH > 4.5 and aw > 0.85.
Should have to comply with the low-acid
low-
canned food regulations (i.e., commercial
sterilization).
However, for quality reasons, these products
cannot be given a sterilization process.
Instead, the spreads are stabilized by moderate
levels of salt, decreased pH and moisture.

19. Improves product quality and microbial safety.
Save Money, Energy & Several other Resources.
Foods remains stable & safe, high in sensory &
nutritive value due to gentle process applied.
Doesn't effects the integrity of food pieces (fruits).
Applicable in both Large & Small Industries.
Manufacture of new products according to the need
of processors and consumers.

20. BOOKS-
BOOKS-
A text book of food preservation - BY
NEELAM KHETARPAL.
Food microbiology - BY
Food science – BY
WEBSITES-
WEBSITES-
<http://www.ifrn.bbsrc.ac.uk/safety/comicro
/Culture_25.pdf>
<http://ars.usda.gov/Services/docs.htm?doci
d=6786