Food Preservation Techniques Quiz

Designing Food Products Using Steam or Wet Heat Processing

• This chapter covers different methods of heat processing food using steam or water.
• The course outline includes blanching, pasteurization/UHT, and heat sterilization/retort processes.
• Heat processing uses steam or water, hot air, and/or hot oils as well as direct and radiated energy (dielectric, ohmic, infrared).
• Also included are methods for the removal of heat (chilling), controlled/modified-atmosphere storage and packaging, freezing, and freeze drying.

Thermal Processing Introduction

• Thermal processing combines temperature and time to eliminate a specific number of microorganisms in a food product.
• Heating food is an effective method to preserve it.
• The main purpose of thermal processing is to reduce or inactivate microbial activity, enzyme activity, produce physical or chemical changes, and meet a required food quality standard.

Heat Treatment in Food Processing

• Positive effects include improved eating quality, preservation, easier control of processing, more shelf-stable foods, destruction of anti-nutritional factors, and enhanced availability of nutrients.
• Negative effects include alterations or destruction of food components.

Blanching

• Blanching is a pre-heat treatment method used in food preservation.
• It's used when preparing fruits and vegetables for freezing or canning.
• The goal is to maintain quality (color, texture, and nutritional content) of the product.
• Methods include wet blanching and dry blanching (high-pressure blanching, microwave blanching, and infra-red blanching).
• Blanching serves to inactivate enzymes.

Blanching Principle

• Heat transfer occurs via conduction and convection.
• Maximum processing temperature during freezing and dehydration often is insufficient to inactivate enzymes, causing undesirable changes during storage.
• Canning in particular, large cans, needs sufficient heat to disrupt tissues but inactivate only some enzymes in food.

Blanching Heating Method

• Food is heated rapidly to a pre-set temperature and held for a set duration, then quickly cooled.
• Heating method depends on the type of fruit/vegetable and the size of the food to be blanched.

Blanching Mode

• Blanching inhibits enzyme activity, specifically lipoxygenase and polyphenoloxidase.

Blanching Methods

• Wet blanching uses water (hot water, steam or hot gas). This contrasts with dry blanching which uses hot air or other energy source (high pressure, microwave, infrared).

Industrial Applications of Blanching

• Blanching finds uses in frozen foods (broccoli, carrots, peas, berries), seafood (shrimp, crab, lobster), canned foods, ready-to-eat meals, and nut processing.
• It is also used in the production of baby food, pre-cut vegetables, snacks, prepared salads, and deli items.

Blanching Equipments

• Industrial blanching methods typically involve saturated steam (steam blanchers) or hot water baths (hot-water blanchers).
• The steam blanchers include stages of preheating, steam injection and cooling.
• Some variations include drainage, drying, and Packaging.

Blancher-cooler

• Pre-heating, blanching, and cooling stages are present in blancher-coolers.
• The food is moved on a belt for consistent throughput and avoids food damage, particularly during water blanching.

Steam Blanchers

• These are used for foods with large surface areas for their efficiency in leaching losses.
• Conveyor systems (with water sprays at inlet & outlets) allow food to fully absorb steam.
• Food can also be processed using alternative methods (rotating valves, hydrostatic seals) to reduce steam losses and improve energy efficiency.

Individual Quick Blanching (IQB)

• A two-stage process achieving better uniform heating of food.
• The first stage involves heating food in thin layers to a high temperature.
• The second stage (adiabatic holding) involves sufficient time for the heat to distribute evenly throughout the food product.

Batch Fluidized-bed Blanchers

• A mixture of air and steam fluidizes the food and heats it simultaneously
• This results in more uniform heating, faster processing times, less loss of vitamins and other heat-sensitive components.

Equipment: Hot-Water Blanchers

• These devices hold food in hot water (70-100˚C) for a set time.
• Food is then moved to a dewatering/cooling section

Pipe Blanchers

• Use a continuous insulated metal pipe with feed and discharge ports.
• Hot water circulates through the pipe to heat the food.
• A versatile design with large capacity and minimal floor space.

Blancher-cooler

• Food is continuously processed through the heating, blanching, and cooling sections
• This reduces physical damage due to turbulence during blanching/heating.
• Re-circulated water and steam mixtures are used to heat and cool simultaneously.

Advantages & limitations of conventional steam and hot-water blanchers

• Conventional steam blanchers result in reduced losses of water-soluble components and lower disposal costs.
• Hot-water blanching may result in higher water treatment expenses and potential risk of contamination from thermophilic bacteria.
• Blanching outcomes may differ as uniformity can be uneven, with higher food piles leading to inconsistent blanching across the conveyor.

Advantages of Blanching

• Preservation of texture
• Color Preservation & ease of peeling
• Improved nutrient retention
• Reduction of microbial load
• Enzyme control in fermentation
• Reduction of non-enzymatic oxidation
• Extended shelf-life

Disadvantages of Blanching

• Damage to tissue cells
• Loss of colour
• Nutrient loss
• Protein denaturation
• Changes in flavour

Effect of Blanching on Foods

• Changes in sensory and nutritional qualities due to heat.
• The time/temperature application is a compromise and must consider enzyme inactivation to prevent excessive softening and flavour loss.

Effect on food - Nutrients

• Blanching can lead to losses of minerals, water-soluble vitamins, and other water-soluble components. This loss is mostly due to leaching, thermal destruction, and oxidation.

Effect on food - Texture

• Blanching typically softens the texture of vegetables.
• Insoluble calcium pectate complexes can aid in maintaining firm tissues.

Effect on Food - Colour and Flavour

• Blanching aims to brighten colors and remove dust particles
• Sodium carbonate or calcium oxide are used to protect chlorophyll and retain the color, while preventing enzymatic browning in specific products.

Modern Trends of Blanching

• Development of hybrid technologies (e.g., ultrasound, vacuum, and radio-frequency heating combined with thermal methods) in blanching aims to achieve more uniform heating minimizing nutrient loss and energy efficiency.

Evaluation of Sustainability Using Life Cycle Assessment (LCA)

• LCA aims for a more energy-efficient approach to food processing by minimizing CO2 emissions.
• Modified atmosphere packaging should be combined with blanching

4.2 Pasteurization/UHT

• To inactivate bacterial pathogens (target organisms like Coxiella burnetti).
• Two main industrial pasteurization methods: i. Low Temperature Long Time (LTLT): Holding the product at a specific temperature for a long period. Example: 62°C-36°C for 30-35 mins. ii. High Temperature Short Time (HTST): Heating the product to a higher temperature for a shorter duration. Example: 72˚C for 15 seconds. iii. Ultra-High Temperature (UHT): A continuous process using high temperatures for a short time to sterilize a product that is then packaged.

Factors Affecting Pasteurization

• Factors affecting pasteurization results include product pH, particle size, equipment used, method used, and product viscosity.

High-temperature short-time (HTST)

• Designed to kill 99.999% of viable microorganisms in milk using controlled high temperatures and shorter durations. Example 161°F/161˚C for 16 seconds.

Ultra-heat Treatment/Ultra-High Temperature (UHT)

• Continuous process packaging products after sterilization.
• High temperatures (130-150˚C) and short durations (1-3 seconds) achieve sterilization

Results of UHT

• Improved nutrient, color, flavor & texture retention.
• UHT treatment is effective in minimizing product damage during sterilization.

Difference between HTST and UHT

• HTST uses a lower temperature and longer duration than UHT.
• UHT offers a longer shelf life after pasteurization.
• UHT causes fewer chemical changes but the product may appear cooked and have a slightly browned color.

4.3 Heat Sterilization/Retort Process

• In excess of 100°C to destroy most microorganisms and spores in food.
• High temperatures are important to destroy microorganisms that form spores, which have the ability to survive high temperatures.
• Failure to reach the required temperature will result in the possibility of spores germinating and growing, leading to food poisoning.
• Some microorganisms, like Clostridium botulinum, may survive if not processed under appropriate times/temperatures

Sterilization Process Stages

• Phase 1: Heating
• Phase 2: Holding
• Phase 3: Cooling (introduces cold water to autoclave)

Sterilization Methods

• Heat, chemicals, radiation, high pressure, and filtration

Heat Sterilization

• Most widely used, reliable sterilization methods that destroy enzymes and other essential components.
• Can be applied to products suitable for high temperatures, but also products sensitive to moisture are also processed. Methods include: i. Dry heat (160-180°C) ii. Moist heat (121-134°C)

Dry Heat Sterilization

• High temperatures (160-180°C) used over longer durations (up to 2 hours), depending on the targeted temperature.
• Good penetration and non-corrosive nature, suitable for sterilizing glass/metal surgical instruments.

Moist Heat Sterilization

• Employing steam under pressure (121-134°C) to generate high temperatures for sterilization.
• Saturated steam serves as an effective sterilising agent.

Home-Based Retort

• Devices for domestic use to achieve home-based commercial-scale retorting

Retort Types (Industrial)

• Various types include pressurized steam, water immersion, and water spray.

Factors Affecting Sterilization

• The application of time/temperature depends on the microorganisms and product properties, initial product temperature, pH, microbe counts, and container size.

Methods of Sterilization

• Physical Methods (heat, radiation, filtration)
• Chemical Methods (gaseous agents)

Packaging Considerations

• Product is packaged either before or after heat treatment into air-tight containers.
• Packaging must be sterilized prior to use and filling must be done in aseptic conditions.

Labeling Post Sterilization

• Product labels include:
• Content/Ingredients
• Manufacturing Details
• Instructions for Use
• Storage Information (temperature etc)
• Expiry date

Do's and Don'ts: Pouch Packaging

• Proper pouch conditions for handling food to avoid breakage, ballooning, and maintaining quality. 

Test your knowledge on food preservation methods, including pasteurization and the operation of retorts. This quiz covers various techniques, mechanisms, and technological advantages in the context of food safety and preservation. Ideal for students studying food science or culinary arts.