browning in foods - enzymatic, non enzymatic.pptx

Browning in foods
Browning is a common colour change seen in food
during processing or storage. The colour
produced during browning ranges from cream or
pale yellow to dark brown or black.
Browning reactions observed in food may be
classified as
1. Enzymatic browning
2. Non-enzymatic browning

Non-enzymatic browning
Non-enzymatic browning is a chemical process
that produces a brown colour in foods without
the activity of enzymes
Types
A. Maillard reaction: The reaction between reducing
sugars (ex: glucose and fructose) and proteins by the
application of heat ex: Toasted bread
B. Caramelization: Caramelization is a slow cooking
process that occurs when sugar is cooked over low heat,
causing a change in both appearance and flavor
ex: 5-star

Enzymatic browning
Fruits such as apples, pears, peaches, apricots,
and bananas, and vegetables such as potatoes
quickly turn brown when their tissue is exposed
to oxygen
Such oxygen exposure occurs when the food is
sliced or bitten into or when it has sustained
bruises, cuts or other injury to the peel
This “browning reaction” is related to the work of
an enzyme called phenolase

The phenolase changes the phenols into melanin,
which has a brown colour
To stop the reaction, the phenolase enzymes need
to be denatured
Denaturation of enzymes can be done
 By acid treatment - Lemon juice contains an
acid which can stop enzymes working properly
as enzymes often work best at a certain pH
 By heat treatment (blanching) – surface
inactivation of enzymes

Post-harvest changes in fruits and
vegetables
• The word ‘harvest’ comes from the Old English word
‘haerfest’, which meant ‘autumn’ or ‘the time of
gathering crops’.
• Harvest: The activity of cutting and collecting crops.
• Harvesting: Harvesting is the activity of picking and
collecting crops, or of collecting plants, animals, or fish as
food.
• Post-harvest = After harvest.
• Post-harvest is relating to or occurring in the period after
harvest.

• Post harvest technology is the application of scientific
and engineering principles to the handling, storage,
Packaging, distribution, and sale of agricultural produce
after it has been harvested.
• Post harvest technology is used to improve the quality
and extend the shelf-life of food. It also helps to reduce
wastage and improve the food safety.
• Post harvest technology is immensely important in
ensuring that crops are stored and transported properly.
• The steps or processes of handling crops right after harvest
is referred to as ‘Post-harvest management’.
• Post harvest changes are the physical, chemical, and
biological transformations that occur in crops after they are
harvested.

• Post-harvest changes refer to the alterations that
occur in agricultural products after they have been
harvested from the field. These changes can affect the
quality, nutritional value, and shelf life of the harvested
crops.
• Some of the factors that influence post harvest changes
are temperature, humidity, light, oxygen, carbon dioxide,
ethylene, microorganisms, insects, and rodents.

Post harvest changes include:
• Respiration: Respiration is the process of converting
sugars and oxygen into carbon dioxide, water, and energy.
Respiration is essential for maintaining the metabolism and
viability of plant cells, but it also consumes the stored food
reserves and releases heat. After harvesting, fruits and
vegetables continue to respire, consuming oxygen and
producing carbon dioxide.
• Ripening: Many fruits undergo ripening after harvest, a
process characterized by changes in color, texture, flavor,
and aroma. Ethylene gas, produced by some fruits, plays a
significant role in triggering and accelerating the ripening
process.

• Senescence: This is the natural aging process that all
fruits and vegetables undergo after harvest. Senescence is
the process of aging and deterioration of plant tissues due
to the loss of water, nutrients, and chlorophyll. Senescence
can cause wilting, yellowing, browning, and decay of
leaves, flowers, and stems.
• Transpiration (water loss): The process of losing water
vapour from the surface of plant tissues. Transpiration
helps to cool the produce and regulate the internal water
balance, but it also causes weight loss and shrinkage.
• Physical Damage: Bruising, cuts, and other physical
injuries can occur during harvesting, transportation, and
handling. Minimizing mechanical damage is crucial to
reduce post-harvest losses.

• Microbial Spoilage: Bacteria, fungi, and other
microorganisms can grow on the surface of harvested crops,
leading to spoilage.
• Enzymatic Activity: Enzymes present in fruits and
vegetables can cause changes in color, flavor, and texture.
Blanching, freezing, and other preservation methods can help
inhibit enzymatic activity.
• Nutrient Loss: Some nutrients may degrade or be lost
during storage and processing. Proper processing, handling
and storage practices can help minimize nutrient loss.
• Ripening is a complex process that occurs in climacteric
fruits, such as bananas, avocados, and tomatoes. During
ripening, the fruit softens, its color changes, and its flavor and
aroma become more pronounced. This is due to the
breakdown of starch into sugars, the production of ethylene
gas, and other biochemical changes.

• Ethylene gas, a natural plant hormone that acts as a
ripening agent. Exposure to ethylene can accelerate the
ripening process in certain fruits and vegetables, leading
to color changes, softening, and flavor development.
• Even after they’re picked from the field, fruits and
vegetables are still living things. They continue to
respire, releasing water vapor and carbon dioxide, and
they undergo various biochemical changes that affect
their quality. These post-harvest changes can be
desirable, such as the ripening of fruits, or
undesirable, such as spoilage.

Here are some tips for minimizing post-harvest
changes in fruits and vegetables:
• Harvest fruits and vegetables at the proper stage of maturity
• Store fruits and vegetables at the proper temperature and
humidity.
• Keep fruits and vegetables away from direct sunlight and
heat.
• Handle fruits and vegetables carefully to avoid bruising and
damage.
• Store fruits and vegetables separately from other foods, such
as meat and poultry, to prevent the spread of bacteria.
• Use proper packaging to prevent water loss and spoilage.
• Wash fruits and vegetables just before eating them, not
before storing them.

• Fruits are generally divided in two categories:
climacteric and non-climacteric fruits.
• In general terms, climacteric fruits can ripen after
harvest, whereas non-climacteric fruits cannot
ripen after harvest.
• Climacteric fruits having the ability to continue to ripen
when they are harvested at the time that they are
horticultural mature but not yet ripe. Example: Apple,
Banana, Avocado
• Non-climacteric fruits only ripen while still attached to
the parent plant. Example: Grapes, Strawberries

• Climacteric fruit ripening is characterized by an increased
rate of respiration, and then a burst of ethylene biosynthesis
during ripening. The production of ethylene in climacteric fruits
is also known as autocatalytic, which means an initial
concentration of ethylene causes an increase in production of
ethylene. This means once ethylene production starts, the fruit
naturally increases the amount of signal made accelerating
ripening. Some examples of climacteric fruits include
peaches, mangoes, bananas, apples, papaya, guava, sapota, water
melon, custard apple and avocados,
• Non-climacteric fruits have a different ripening pattern.
They do not have a peak of ethylene production or respiration
during ripening; thus, they need to be harvested when they are
fully ripe. Some examples of non-climacteric fruits
include cherries, grapes, lemons, oranges, pomegranate,
pineapple, strawberries, cucumber, and blueberries.

Climacteric rise:
• Climacteric rise is the term used to describe the sudden
increase in respiration and ethylene production that
occurs in some fruits during ripening. It is associated
with changes in color, flavor, texture, and aroma of the
fruits.
• Climacteric fruits, such as apples, bananas, tomatoes,
and mangoes, can ripen after harvest and show a
climacteric rise.
• Non-climacteric fruits, such as citrus, grapes, and
strawberries, do not show a climacteric rise and need
to ripen on the plant.

There are several methods to control climacteric rise during storage
and transportation of fruits. Some of them are:
• Reducing the temperature: Lowering the temperature can slow
down the respiration and ethylene production of fruits, thus
delaying the ripening and senescence processes.
• Reducing the oxygen and increasing the carbon dioxide:
Modifying the atmosphere around the fruits can also reduce the
respiration and ethylene production rates. This can be achieved by
using controlled or modified atmosphere storage, where the oxygen
level is lowered and the carbon dioxide level is increased, either by
using gas generators or by using gas-permeable films or containers.
• Reducing the ethylene exposure: Ethylene is a major factor
that triggers and accelerates the ripening and senescence of fruits.
Therefore, reducing the exposure of fruits to ethylene can delay the
climacteric rise. This can be achieved by using ethylene scavengers
or inhibitors, such as potassium permanganate, sodium bisulphite,
or 1-methylcyclopropene (1-MCP), which can either absorb or block
the action of ethylene.

Maturity and types of maturity:
• Maturity in fruits and vegetables is the stage of
development when they are ready for harvest and
consumption.
• Maturity is the stage where any part of the plant attains full
growth and development. So it is the stage of fruit
development beyond which no further growth take place.
• After maturity of any part of the plant it starts its decline
stage i.e. called as ‘ripening’.
• Maturity is the basis for determining the exact stage to pick
a crop.
• Maturation is indicative of the fruit being ready for harvest.
At this point, the edible part of the fruit or vegetable is fully
developed in size, although it may not be ready for
immediate consumption.

Types of maturity:
There are three types of maturity in fruits and
vegetables, depending on the purpose and
criteria of harvesting and consumption. They
are,
• Harvesting maturity
• Physiological maturity
• Horticultural or commercial maturity

Harvesting maturity:
This is the stage of development when a plant part is ready
to be picked and collected from the field.
• Harvesting maturity depends on the horticultural
maturity and the post-harvest quality and shelf life of the
produce.
• For example, for local markets and processing, fully
coloured tomatoes are harvested, but for distant markets,
tomatoes that have started developing color are harvested.
• Harvesting maturity can be determined by various
maturity indices, such as days from fruit set, specific
gravity, lenticels number, oil content, and pressure tester.

Physiological maturity:
This is the stage of development when a plant part or the
whole plant has reached its maximum growth and
maturation.
• It is usually associated with full ripening in the fruits.
• For example, a seed is physiologically mature when it can
germinate and produce a new plant.
• The French bean or pod of okra is at its Physiological
maturity when seeds are fully developed and the pod is
which will split with little pressure.
• Physiological maturity is always followed by senescence.
• Physiological maturity is often measured by the rate of
respiration and the sugar/acid ratio of the produce.

Horticultural or commercial maturity:
This is the stage of development when a plant part possesses the
necessary characteristics for use by consumers for a particular
purpose.
• The horticultural maturity of fruits and vegetables depends
upon the purpose for which it is harvested.
• For example, a tomato is horticultural mature when it has the
desired color, size, shape, and firmness for the market.
• A papaya with green pulp and peel that has attained
maximum size is already commercially mature as a vegetable.
Still, a tinge of yellow colour has to develop when it is used for
dessert.
• Horticultural maturity is often assessed by visual, physical,
and chemical indicators, such as color, size, shape, texture,
aroma, flavor, sugar, acid, starch, and ethylene content.

Changes during the storage of fruits and
vegetables:
• Storage is a very important part after harvesting as it can
increase the product’s shelf life and slow down the post
harvest changes in fruits and vegetables.
• Most vegetables have a very short storage life because of
their rapid respiration.
• The storage of fruits and vegetables involves various factors
that can impact their quality, freshness, and shelf life.
• Fruits and vegetables are continue to undergo physiological
changes even after they are harvested. These changes can
affect their quality, nutritional value, and safety.

Physical changes
The physical changes that occur during the storage of
fruits and vegetables can vary depending on the type of
produce, storage conditions, and duration of storage.
However, some common physical changes include:
1. Moisture loss
2. Textural changes
3. Color changes
4. Flavor changes
5. Physical damage and color changes

Physiological changes:
• Bulbs, roots, tubers and seeds become dormant.
(Dormancy in plants is a state of reduced growth
and metabolic activity that allows them to survive
harsh environmental conditions such as cold
winters, hot summers, or droughts. It’s like a
plant’s way of taking a nap until conditions are
more favourable for growth and reproduction.)
• Flesh tissues undergo ripening after maturation.
• Senescence occurs quite rapidly with an
accompanying loss of palatability.

Key physiological changes that occur during the storage of
fruits and vegetables:
• Respiration
• Ethylene Production
• Ripening
• Water Loss
• Texture Changes
• Color Changes
• Nutrient Loss
• Acid degradation
• Sugar accumulation
• Senescence

Pathological changes
Alterations in their quality and safety due to the development
of diseases, infections, or microbial growth. These changes
can result in the deterioration of the produce, rendering it
unsuitable for consumption. Common pathological changes
include:
1. Fungal infections
2. Bacterial spoilage
3. Viral infections
4. Post harvest diseases
5. Mold growth

Fungal growth
Viral growth
Mold growth
Bacterial growth

Chemical changes
Chemical changes during the storage of fruits and
vegetables are influenced by various factors, including
enzymatic activity, respiration, and exposure to
environmental conditions. Some common chemical
changes include:
1. Enzymatic Browning
2. Conversion of Starch to Sugars
3. Changes in Organic Acids
4. Respiration and Ethylene Production
5. Changes in Nutrient Content
6. Production of Off-Flavors and Odors

Prevention of changes during storage of
fruits and vegetables
It is important to implement a combination of proper
postharvest handling practices and storage conditions.
1. Temperature Management
2. Humidity Control
3. Ventilation
4. Ethylene Management
5. Packaging
6. Sanitation
7. Controlled Atmosphere Storage

browning in foods - enzymatic, non enzymatic.pptx

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browning in foods - enzymatic, non enzymatic.pptx