PISA BASE QUESTION SERIES
TEST ITEM :- 1
SUBJECT :- SCIENCE
Name of the Teacher: AJAY KUMAR BARHOLIYA
Subject : CHEMISTRY
Email: ajaykumarbarholia@gmail.com
Teaching Experience ; - 28 years
Rancidification is the process of complete or incomplete oxidation or HYDROLYSIS of fats and oils when exposed to air, light, or moisture or by bacterial action, resulting in unpleasant taste and odor.
Specifically, it is the hydrolysis or autoxidation of fats into short-chain Aldehyde, ketones and
free fatty acids, which are
objectionable in taste and odor. When these processes occur in food,
undesirable odors and flavors can result
Rancidity
refers to the oxidation of unsaturated fats or oils in food that results in bad
smells and bad taste. In simple words, when food has become unpleasant, it is
termed rancid. When oxygen molecules interact with food and oil, the normal
composition of the food is damaged which results in a change in taste and
smell, and thus the food is not suggested to be consumed.
Rancidity is also known as Rancidification. It is a condition that is produced by the aerial oxidation of unsaturated fat which is present in food and other products that are noticeable by their terrible smell or taste.
When unsaturated fats are exposed to sunlight, it then converts to a hydroperoxide and breaks down to volatile aldehydes, esters, alcohols, hydrocarbons, ketones, etc., of which some of them have an unpleasant odor.
For
e.g-
- An expired
packet of chips smells different.
- The taste
and smell of butter get changed when it is kept open for a long time.
Types of Rancidity
Rancidity is divided into three types:-
- Hydrolytic Rancidity
- Oxidative Rancidity
- Microbial Rancidity
Hydrolytic
Rancidity
Hydrolytic
Rancidity is defined as the smell or odor that occurs when free fatty acids are
released and triglycerides are hydrolyzed. It generally causes an unpleasant
smell. Triglyceride is a combination of three fatty acids, present in oily
food. They release free fatty acids and produce glycerol when they react with
water. These fatty acids form toxic compounds and may further undergo oxidative
rancidification. Hydrolytic Rancidity occurs more quickly in the presence of
enzymes like lipase and with moisture and heat. It results in the hydrolysis of
the fats with the liberation of either one or more volatile fatty acids.
Oxidative
Rancidity
Oxidative
Rancidity is defined as a reaction that causes oxygen damage to a food
substance. It occurs with unsaturated fats. The natural oil structure is
damaged and interrupted by oxygen molecules in such a way that it changes its color,
taste, and smell. It leads to the formation of toxic compounds like peroxides
that damage Vitamin A and E in foods. In Oxidative Rancidity. The unsaturated
fatty acids of glycerides are oxidized at their double bonds. Thus, this
reaction causes the release of ketones, volatile aldehydes, and acids. It can
be prevented by an oxygen-free atmosphere, light-proof packaging, and the
addition of antioxidants.
Microbial
Rancidity
Microbial
Rancidity is that type of rancidity where microorganisms such as molds or
bacteria use their enzymes like lipases to break down chemical structures of
fat in oil-producing unwanted smells and taste. This process can be reduced by
inhibiting microorganisms or by destroying them. It can also be reduced by
pasteurization and the addition of antioxidant ingredients like vitamin E.
Prevention of Rancidity
There
are many possible ways to prevent Rancidity. Some of them are:
The free
radical pathway
for the first phase of the oxidative rancidification of fats.
Antioxidants are often used as preservatives in fat-containing foods to delay the onset or slow the development of rancidity due to oxidation. Natural antioxidants include ascorbic acid (vitamin C) and TOCOPHEROLS (vitamin E).
Synthetic
antioxidants include BUTYLATED HYDROXY ANISOL (BHA), BUTYLATED
HYDROXY TOLUENE (BHT). The natural antioxidants tend
to be short-lived so synthetic antioxidants are used when a longer
shelf-life is preferred. The effectiveness of water-soluble antioxidants is
limited in preventing direct oxidation within fats, but is valuable in
intercepting free radicals that travel through the aqueous parts of foods. A
combination of water-soluble and fat-soluble antioxidants is ideal, usually in
the ratio of fat to water.
Antimicrobial agents can also delay or
prevent rancidification by inhibiting the growth of bacteria or other
micro-organisms that affect the process
Oxygen
scavenging technology
can be used to remove oxygen from food packaging and therefore prevent
oxidative rancidification
The Rancimat method is
carried out using an air current at temperatures between 50 and 220 °C.
The volatile oxidation products are
carried by the air current into the measuring vessel, where they are absorbed
(dissolve) in the measuring fluid
- Antioxidants
can be added to foods that contain oils and fats to slow down oxidative
deterioration.
- To slow
down the process of rancidification, food can be stored in airtight
containers.
- Vacuum
packing can be done to keep oxygen out.
- By adding
inert gas such as nitrogen to the bag to replace oxygen.
- Food items
can be kept in the refrigerator. It will reduce the rate of most reactions
that take part in rancidity.
- By storing
food in dark places.
Factors that affect Rancidity:
There
are various factors that affect rancidity. Some of the factors are discussed
below:
- Oxygen: The primary cause of
rancidity is exposure to oxygen. Oxygen is more soluble in fats, which
leads to food damage and oxidation by releasing free radicals.
- Microorganisms: Many microorganisms release
an enzyme known as lipase which leads to hydrolysis of lipids. These
microorganisms use their enzyme on food materials and destroy their
chemical composition.
- Physical
factors: Physical
factors like Heat, light, temperature plays an important role in
rancidification. Heat and light stimulate the process of oxidation and are
the main source for the production of free radicals. Light promotes the
decomposition of unsaturated fatty acids.
- Trace
elements: The rate
of rancidity can be increased by trace elements like Fe and Zn. This is
another important factor that affects rancidity.
COMPETENCY BASED QUESTIONS
Ques
. 1 Food items containing fats and oils give foul smell when left for a long
time because of …………………….
Answer: -
………………………………………………………………………………
Ques
.2 potato chips manufacturers usually flush bags of chips with Carbon dioxide
gas. (True or False)
Answer: -
………………………………………………………………………………
Ques.
3 oil and fat containing food items are flushed with nitrogen. (True or False)
Answer: -
………………………………………………………………………………
Ques.4
fats and oils are oxidized and they give
foul smell because of corrosion (True or
False)
Answer: -
………………………………………………………………………………
Ques.
5 : Name
the gas that is used in the storage of oil and fat-containing foods for a long
time?
Answer: -
…………………………………………………………………………………………………………………………………………………………………...
Ques.6: Oil and fat
containing food items are flushed with nitrogen. Why? (1 Marks)
Answer: -
………………………………………………………………………………………………………………………………………………………………………………………………………………
Ques.
7: Name
the chemical that is added to the oil and fat-containing food to prevent
rancidity?
Answer:
-……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………...
Ques.
8: What
happens when food is kept for a very long time?
Answer: -
…………………………………………………………………………………………………………………………………………………………………………………………………………….
Ques.
9: Why are food items preferably packed in aluminum foil? (1 Marks)
Answer: - ………………………………………………………………………………………………………………………………………………………………………………………………………………
Ques.10:
What type of rancidity results from the exposure of fat to oxygen?
Answer: -
…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………...
Ques.11
:You must have tasted or smelt the fat containing food material left for a
longtime. Such foods taste and smell bad. What is the reason for this? Name to
the phenomenon responsible for it.. (1 Marks)
Answer 1 :-……………………………………………………………………………………………
(i)………………………………(ii)…………………………………………………
Ques.12:
(a) Explain two ways by which food industries prevent rancidity.
(b)
Discuss the harmful effect of corrosion in the metal industry with three points. (1+1
Marks)
Answer: (a) :-
…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….
(b)
:- ……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………...
Q13 :- .....
Rubrics
Template
for preparation of Practice Items for Scientific Literacy
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Domain: Scientificliteracy
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Theme: RANCIDITY Unit
name: … |
Class :
…. Expected
time: ..min Total
Credit: .. |
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Description
of item:
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Learning
Outcome: |
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Scientific Literacy
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FRAMEWORK |
CHARACTERISTICS |
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Competency |
Scientific knowledge |
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Knowledge –system |
Physical system |
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Context |
GLOBAL |
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Cognitive demand |
Medium |
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Item Format |
open ended question |
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Proficiency Level |
4 |
Credit
Pattern :
Full
credit : …..
Partial
credit : ….
No
credit : 0
Description
of answer key and credits :
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Q1 Full credit – ( ) ……….
No credit – any other answer /
missing. |
