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Institute of Technology of Cambodia
Department of Chemical Engineering and Food
Technology
Food Spoilage and Food preservation
Professor : Dr. Hul Seingheng
Group member:I3GCA-3
1.
Hun Lina
2.
Huot Syradeth
3.
Kak Mei
4.
Khuon Chann
5.
M. Kin Kimsok
2010-2011
I. How do microbes cause food spoilage?
II. How can food be preserved?
1.
Physical method
2.
Chemical method
Food spoilage is the process which damage
the food
Spoiled food is the food whose chemical
characteristic is destroyed, and it is smelly, bad
appearance, the unpalatable taste, odour or texture.
Why the food are spoiled?
Microbes, chemical reactions
food spoilage
Microbes break down Protein into amino acid,
amines, hydrogen sulphide and amonia.
. Hydrogen sulphide
smelly
. Sulphur
smelly
. Fats
. Carbohydrate
acid, alcohol, gas
Chemical reaction: oxidation, enzymatic activity
Microbes that cause food spoilage called
Proteolytic.
They are Enterobacteriaceae, staphylococci, micrococci, aerobic
Gram-positive sporing bacilli, pseudomonads, moulds…
For example:
Black spots on meat are caused by Cladosporium species.
White spots are caused by Sporotrichum carnis.
Yellow or green are caused by Penicillium species.
Milk is an excellent growth medium for bacteria, moulds, yeasts.
-Souring of milk is the result of acid fermentation by lactobacilli ( or
lacto bacteria or Clostridium septicum).
-Clostridium sordelii is a clostridium that causes milk proteins to clot
-Lactococcus cremoris and Enterobacter aerogenes causes the
formation of ‘ropy’ milk.
-Clostridium sporogenes break down milk proteins to produce
alkaline products.
-Clostridium novyi forms gas from milk.
In turn, moulds and yeasts may break this down.
II. How can food be preserved?
1. Physical method
a.
b.
c.
d.
e.
f.
g.
h.
i.
Pasteurize
Sterile
Cooking
Chilling
Drying
Osmotic protection
Filtration
Irradiation
Vacuum package
2. Chemical method
1. Physical method
a. Pasteurize
- The process that slow the activities of microbes
Condition: ~ 60 0C -70 0C for 15min
b. Sterile
- The process that almost completely kills microbes
Condition: >121 0C for about 5min
c. Cooking
- This process causes the denaturation of autolytic
enzymes, tenderises food, imparts desirable flavours
and odours to the food and it alters the microbial flora,
eliminating many heat-sensitive organisms.
Cooking does not always kill microorganisms.
Overcooking may produce an unacceptable food.
There may be a conflict between a desirable food and
one that is microbiologically safe.
The soft-boiled egg affords a good example of cooking.
d. Chilling is used to delay its decomposition, to slow the
growth of spoilage organisms and to retard the activities of
autolytic emzymes by storing food in the low temperature
(the refrigerater).
However, it is not without problems:
Listeria monocytogenes grow very well at the temperatures
found in refrigerators.
-cook-chill food : at the temperature above freezing
-strawberies: not suitable for freezing (flash freezing)
e. Drying
- The process of removing the water from the food.
NB: Dried fruits and vegetable often retain some
water that moulds can grow .
f. Osmotic protection
Two principal processes: salting or high sugar environment.
Most spoilage bacteria and yeasts cannot tolerate salt
concentrations of about 10%.
The sugar concentration in foods must be higher than 50%.
Despite this, condensed milk is conferred by the
moderately high concentrations of lactose.
g. Filtration is the process of separation of microbes
from liquid foodstuffs by using the filter sterilization.
Liquid foodstuffs: wine, beer, cider, fruits juices, maple
syrup and soft drink.
h. Irradiation is the process of preservation food by
using light. It does not involve food heating.
Food irradiation converts water to hydrogen peroxide and
by generating free radicals that react with cellular
components.
It may produce unacceptable changes (causing
odours and unpleasant tastes).
It has been employed to prolong the shelf life of soft
fruits such as strawberries.
Low-dose irradiation eliminate of salmonellas from
poultry and to suppress the spoilage flora found on
meats, poultry and fish.
i. Vacuum packaging
- Is another that can help preserve the food.
--absence of O2
--increase of CO2
2. Chemical method
--sage, rosemary, garlic, onion
--vinegar (pH too low for the growth)
--smoking (70 C for 30min)
--formaldehyde
--phenolic
--cresols
2. Chemical method
--sodium benzoate
--sulphur dioxide
--sodium metabisulphite
--salt of sorbic and propionic acid
--nitrate, nitrite
conclusion
Through the article, we know why and how the foods
are spoiled, then we can preserve them by various
methods such as pasteurization, filtration and chemical
substances.
Thanks for your attention