ALVIN ERICK C. BALES, M.SC.
FACULTY, BSFT
• "thermal" refers to processing using heat
• the application of heat to reduce or eliminate the
microbiological contamination (pathogens or spoilage
microorganism) and enzymatic activity of the food
thereby extending its shelf-life and making it safe for
consumption.
• combination of temperature and time
• the extent of heat treatment required depends
on the acidity of the food product
⚬ (An acid food product is one with a natural
pH of less than 4.6)
pH
4.6
Clostridium botulinum
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To reduce or destroy microbial activity
Reduce or destroy enzyme activity
Produce physical or chemical changes
Make the food meet a certain quality standard
(a) heat transfer;
(b) heat resistance of microorganisms of concern;
and
(c) bacterial inactivation.
• water retorts (batch or continuous)
• direct heating systems (steam injection or steam
infusion)
• indirect heating systems (tubular heat exchangers,
shell and tube heat exchangers, plate heat
exchangers, scraped surface heat exchangers)
• volumetric heating systems (microwave or ohmic
heating)
Retorts (batch or continuous)
Direct Heating Systems (direct steam injection)
• The heating of the containers is done by steam
injected directly into the retort chamber through
perforated pipes, for a uniform temperature
distribution throughout the vessel.
• Better food safety
Indirect Heating System (Indirect Steam Injection)
• The heating of the containers is carried out by
means of a shower (spray or rain) of superheated
water.
• The heating is done in an external heat exchanger.
Blanching
Pasteurization
Hot Filling
Heat Sterilization
• mild heat treatment commonly applied to fruits
and vegetables
• inactivate enzymes, enhance drying and
rehydration, remove tissue gases, enhance
color of green vegetables, and reduce microbial
load
• evaluated by assaying for peroxidase and
catalase activity
• carried out at up to 100°C using hot water or
steam at or near atmospheric pressure and
followed by a quick cooling in vry cold ice water
hot water blanching - 70-100 °C
steam blanching
screw-type blanching
fluidised bed blanchers - mixture of air
and steam
• pipe blanching
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• relatively mild heat treatment in which food is
heated to <100°C
• usually used for liquids and liquid particulates
• inactivate vegetative pathogenic microorganisms
• no guarantee that all spoilage-causing vegetative
cells or heat-resistant spores will be inactiveted
• LTLT (Low Temperature Long Time) - 63 °C for 30 min
⚬ milk for cheeses
• HTST (High Temperature Short Time) - 72 °C for 15 sec
⚬ more suitable for making yogurt
• Ultra Pasteurization or Ultra High Temperature - 138 °C
or above for at least 2 sec
⚬ milk production (canned milks)
⚬ fruit juices, cream, soy milk, yogurt, wine, soups, honey, and
stews
• also known as “hot fill and hold"
• refers to filling unsterilized containers with a sterilized
acid/acidified food product that is hot enough to
render the container commercially sterile.
• usually applied to acidic/acidified juices and beverages
• product is heated at 90 - 95°C then cooled to 80-85°C
then filled into the containers and sealed immediately
• refers to killing of all living microorganisms, including
spores, in the food product
• Commercial sterility - the application of heat, which
renders the food free of microorganisms capable of
reproducing in the food under normal non-refrigerated
conditions of storage and distribution
• shelf-stable with a long shelf life (1–2 years)
• 110°C - 121°C at 15psi
• Commercial sterility can be achieved by:
⚬ in-container sterilization - retorting process
⚬ in-flow (continuous) sterilization - aspetic
processing
Aseptic processing
Conventional Retorting (Batch Type)
⚬ involves filling of the product in metal cans, glass
jars, retortable semi-rigid plastic containers or
retortable pouches, double seamed or heat sealed,
followed by heating, holding, and cooling in a
pressurized batch
Conventional Retorting (Batch Type)
⚬ heating media used in various batch retorts include:
steam, water, steam-air, water cascading, water
spray, or water immersion (Lund, 1975; Weng, 2005).
Clark, S., Jung, S., & Lamsal, B. (Eds.). (2014). Food processing:
principles and applications. John Wiley & Sons.
Park, S. H., Lamsal, B. P., & Balasubramaniam, V. M. (2014). Principles of
food processing. Food processing: principles and applications, 2.
Holdsworth, S. D., Simpson, R., & Barbosa-Cánovas, G. V. (2008).
Thermal processing of packaged foods (Vol. 284). New York: Springer.
Sandeep, K. P. (Ed.). (2011). Thermal processing of foods: Control
and automation. John Wiley & Sons.
Safefood 360, Inc. (2014). Thermal Processing of Food
Simpson, R., Nuñez, H., & Ramírez, C. (2020). Principles of thermal
processing of packaged foods. Introduction to biosystems
engineering. Virginia Tech, 23pp. https://vtechworks. lib. vt.
edu/bitstream/handle/10919/93254/Food_Thermal_Processing. pdf.