Thermal Processing of Food Flashcards
There are two main temperature
categories employed in thermal processing:
Pasteurization and Sterilisation
The basic purpose for the thermal processing of foods
reduce or destroy microbial activity
The primary purpose of blanching
is to destroy enzyme activity in fruit and
vegetables.
Other functions of blanching
include:
- Reducing surface microbial
contamination - Softening vegetable tissues to
facilitate filling into containers - Removing air from intercellular
spaces prior to canning
This is the preferred method for foods
with large cut surface areas as lower
leaching losses. Normally food material
carried on a mesh belt or rotatory cylinder
through a steam atmosphere, residence
time controlled by speed of the conveyor or rotation.
Steam Blanchers
involves a first stage in which a single layer of the food is heated to suffcient temperature to inactivate enzymes and a second stage in which 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.
Individual Quick Blanching (IQB)
The blancher-cooker has three sections
preheating stage, a blanching stage, and
a cooling stage
is a relatively mild heat treatment in which food is heated to <100°C.
Pasteurization
organisms that can survive exposure to relatively high temperatures but do not necessarily grow at these temperatures e.g. Streptococcus and Lactobacillus.
Thermoduric
organisms that not only survive relatively high temperatures but require high temperatures for their growth.
Thermophilic
In this method the heating of every particle of milk to at least 72°C and holding for at least 15 seconds. Carried out as a continuous process.
High-Temperature-Short-Time (HTST)
a sterilisation treatment, can also
be performed using higher temperatures
and shorter times e.g. 1 s at 135°C
Ultra Heat Treatment (UHT)
Typical Equipment employed for this
method includes:
- Plate heat exchanger (PHE)
- Holding tube – sized to ensure the
correct treatment time is achieved - Holding tanks – for storage of the
raw and pasteurised milk - Balance tank – to assist in
maintaining full flow, and to take
returned milk if temperature not
achieved - Control and monitoring system
sized to ensure the correct treatment time is achieved
holding tube
for storage of the raw and pasteurised milk
Holding tanks
to assist in maintaining full flow, and to take returned milk if temperature not
achieved
balance tank
Maximum temperature between
the container and the liquid are
20°C for heating and 10°C for cooling.
the destruction of all bacteria including
their spores.
aim of sterilization
are processed so that they are
shelf stable. They should be ‘commercially
sterile’.
canned foods
Conditions Affecting the Growth of Microorganisms:
Water
Temperature
Oxygen requirements
Micro-organisms can be classified into
three general groups regarding their
oxygen requirements.
- Aerobes – can only grow in the
presence of oxygen - Anaerobes – Can only grow in the
absence of oxygen - Facultative Anaerobes – adaptable.
Grows best aerobically but can grow
anaerobically
Thermophilic Spore Formers:
Flat Sours - B.sterothermophilus
Thermophilic Anaerobes –
C.thermosaccharolyticum
Sulphide types –
Desutfomotomaculum nigrificans