thermal processing Flashcards
Why the maximum processing temperature in freezing and dehydration is insufficient to inactivate enzymes and does not substantially reduce the number of microorganisms in unblanched foods?
It is because freezing and dehydration (drying) do not kill microorganisms. It is just used to
inhibit and inactivate them. Both processes are also unable to totally get rid of heat resistant
microorganisms and enzymes. Hence, these microorganisms are able to grow on thawing or
rehydration
Why it is necessary to blanch foods prior to canning operations?
because the time taken in order to reach sterilising temperature in canning may be
longer especially in larger can. Hence, this condition will provide enough and sufficient time for enzyme and microbial activity to take place and occur
How under-blanching may cause more damage to food than the absence of blanching does?
Under-blanching may cause more damage because heat provided during blanching is
sufficient to disrupt and break down the tissue and cause the release of intracellular
enzymes. Actually, the enzyme released needs to be inactivated in order to reduce microbial
and enzyme activity. In this case, under blanching provides insufficient heat to inactivate and denature the all enzyme it releases.it just inactivate partially of the enzyme causing the remaining enzyme to mix with substrate during storage. The remaining enzymes cause an increase in enzyme activity and speed up deterioration and reduce quality of foods
)What are the enzymes that cause loss of colour or texture, production of off-odours
and off flavours, or breakdown of nutrients in vegetables and fruits?
lipoxygenase, polyphenol oxidase, polygalacturonase and
chlorophyllase.The heat resistant enzymes are catalase and peroxidase.
)How to evaluate the efficiency of a blanching process?
The efficiency of the blanching process can be evaluated through the Peroxidase Test. It is
because this peroxidase enzyme is heat-resistant and easily detected. Peroxidase Test
occurs by adding guaiacol solution and hydrogen peroxide solution and observing the
development of a brown colour indicating peroxidase activity.
Why peroxidase and catalase are used as marker enzymes to determine the success
of blanching although they do not cause significant deterioration during storage?
Why peroxidase is preferable as marker enzymes compare to catalase?
Peroxide and catalase are the most heat-resistant enzymes. Hence, their presence and
absence will indicate the effectiveness and success of blanching. For example, absence of
both enzymes mean other less heat resistant enzymes have been removed and destroyed.
Peroxidase is more preferable than catalase because peroxidase are more heat resistant. If
the testing showed the indication of peroxidase enzyme is low or absence means other less
heat resistant enzyme (catalase) ia also being destroyed.
Blanching: Aim and purposes = enzyme deactivation
Blanching helps deactivate enzymes present in food.
Enzymes are natural substances that can cause food to ripen or deteriorate. By briefly exposing the food to high temperatures, blanching stops enzymatic reactions, which can help preserve the color, flavor, and texture of the food.
Blanching: Aim and purposes= cleaning and sanitaiton
Blanching can be used to clean and sanitize food. It helps remove dirt, bacteria, and other contaminants from the surface of the food. This is especially important for fruits and vegetables that may have been exposed to soil or other impurities during harvesting.
Blanching: Aim and purposes= pre cooking
Blanching partially cooks the food, making it easier to handle in subsequent cooking or processing steps. It can be especially useful when preparing certain recipes like stir-fries or for canning and freezing, as it can reduce
cooking times and help maintain the food’s quality during storage. It also removes air from intercellular spaces prior to canning
Blanching: Aim and purposes = pre cooking for skin removal
peeling and skin removal: Blanching is often used to facilitate the peeling of certain foods, such as tomatoes and peaches. After blanching, the skin can be easily removed.
Blanching: Aim and purpose = reducing bitterness
For some bitter vegetables, like certain greens or bitter melon, blanching can help reduce bitterness by removing some of the compounds responsible for the bitter taste
Hot water blanching
Includes various designs which hold the food in hot water (70 to 100°C) for a specified time
* Food are then moves it to a dewatering/cooling section.
* In blanchers of this type the food enters a slowly rotating drum, partially submerged in the hot water
Steam blanching
Food materials are carried on a mesh belt or rotatory cylinder
through a steam atmosphere
* Residence time is controlled by speed of conveyor
- Individual Quick Blanching (IQB)
- First stage → a single layer of the food is heated to sufficient temperature to inactivate
enzymes - Second stage → a deep bed of the product is held for suffcient time to allow the temperature
at the centre of each piece to increase to that needed for inactivation.
pasteurization to destroy…
- To destroy enzymes and reduce relatively heat sensitive
micro-organisms (e.g. non spore forming bacteria, yeast
and molds).
