17 Questions
What is the reason why spore-forming bacteria cannot proliferate in fruit juices despite surviving pasteurization?
The acidic environment of fruit juices makes it impossible for spore-forming bacteria to grow.
What is the primary difference between the batch/low temperature method and the high temperature/short time method of pasteurization?
The temperature and time duration; the batch method uses a lower temperature (63°C) for a longer time (30 minutes), while the HTST method uses a higher temperature (71.5-76°C) for a shorter time (15-30 seconds).
Why is flash pasteurization (HTST) preferred for preserving the color and flavor of food products?
Because it uses a higher temperature for a shorter time, which helps to minimize the loss of nutrients and flavor.
What is the typical temperature and time duration used for pasteurizing fruit juices?
85°C for 25-30 minutes, depending on the nature of the juice.
Why is it necessary to rapidly cool the liquid to 4-5.5°C after pasteurization in the HTST method?
To prevent the growth of bacteria and spoilage.
What is the primary advantage of the batch/low temperature method of pasteurization?
It is more suitable for low-volume items.
What is the primary objective of pasteurization?
To destroy enzymes and relatively heat sensitive microorganisms (non-spore forming bacteria, yeast and moulds)
How does the pH of the product affect the severity of the pasteurization process?
In Low acid foods (pH > 5.3), destruction of pathogenic bacteria is the priority, while in high acid foods (pH < 3.7), destruction of spoilage microbes/enzymes are the priority.
What is the purpose of the guaiacol/peroxide test in blanching?
To detect enzyme activity and adequacy of blanching
What are the consequences of under blanching and excessive blanching?
Under blanching doesn't thoroughly inactivate enzymes, leading to quality loss, while excessive blanching causes quality loss due to overheating
How does thermal processing affect the quality of fruit juices?
Heat resistance in fruit juices can be affected by thermal processing, leading to quality loss if not optimized
What is the difference between hot water blanching and steam blanching?
Hot water blanching uses water as the heat transfer medium, while steam blanching uses steam
What is the primary goal of thermal processing in food preservation?
Reduction of the number of microbes present to statistically small levels
Which vitamins are particularly susceptible to thermal degradation during food processing?
Vitamin C and B vitamins (especially thiamine B1 and pantothenic acid B5)
What is the significance of creating a hermetic environment during thermal processing?
To prevent recontamination during storage
At what temperature does Vitamin C begin to degrade, and at what temperature does the degradation increase significantly?
Vitamin C begins to degrade at 30°C, and the degradation increases significantly at 60°C
What is the objective of thermal processing in terms of microbial control?
Selective destruction of microbes of public health concern
Study Notes
Thermal Processing - Blanching
- Blanching is a thermal processing method that inactivates enzymes to prevent quality loss due to overheating or underheating.
- Excessive blanching causes quality loss, while under-blanching doesn't thoroughly inactivate enzymes, leading to quality loss.
- The Guaiacol/Peroxide test is used to detect enzyme activity and adequacy of blanching, which involves adding a few drops of 1% guaiacol solution and 0.03% hydrogen peroxide solution to cut portions of vegetables.
- Peroxidase activity is indicated by the development of a rapid brown-red color.
Thermal Processing - Pasteurization
- Pasteurization is a relatively mild heat treatment that destroys enzymes and heat-sensitive microorganisms (non-spore forming bacteria, yeast, and molds).
- The objective is to heat food to < 100°C in combination with other preservation methods like refrigeration and fermentation, as the food products are not sterile after processing.
- The severity of the process depends on the pH of the product, with low acid foods (pH > 5.3) prioritizing the destruction of pathogenic bacteria and high acid foods (pH < 3.7) prioritizing the destruction of spoilage microbes/enzymes.
Objectives of Thermal Processing
- Reduce the number of microbes present to statistically small levels, with the goal of selective destruction of microbes of public health concern.
- Create a hermetic environment to prevent recontamination during storage by removing oxygen, creating a vacuum, and preventing microbial/oxygen ingress.
- For fruit juices, pasteurization aims to destroy most bacteria, mold, spores, and yeasts, taking advantage of the acidic environment that inhibits the growth of heat-resistant spores and spore-forming bacteria.
Methods of Pasteurization
- Batch/Low Temperature Method (Vat/Holding Method): Heats the food product/juice to 63°C and holds it for 30 minutes before swiftly cooling.
- Done in batches, making it a slow process.
- Heating/cooling is relatively expensive.
- More effective for low-volume items.
- High Temperature/Short Time (HTST) Method: Heats the liquid to 71.5-74°C for 15-30 seconds or 74-76°C for 15-20 seconds before rapid cooling to 4-5.5°C using a continuous heat exchanger.
- Preserves color and flavor better.
- Expensive.
- Faster than batch pasteurization.
Learn about the pasteurization process of fruit juices, including the temperature and time required to destroy bacteria, mould, spores, and yeasts. Understand how acidic environments affect spore-forming bacteria and how thermal processing is applied.
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