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Smoke, Flash and Fire Point
The smoke point also known as burning point is the temperature at which the oil or
fat begins to produce a bluish smoke under specified conditions. They are measured
by pouring lipid on a metal container and applying heat at a controlled rate in an
oven. The test reflects the amount of volatile organic material in oils and fats such
as free fatty acids. Also, smoke test helps to select lipids that will be used at high
temperatures, e.g. during baking or frying. Fat is considered no longer good for
consumption once it has exceeded its smoke point, due to the large quantity of free
radicals. Similar to smoke point, the flash point and fire point is determined based
on the volatile organic material in a lipid. The appearance of flash on the surface of
the sample due to the ignition of volatile gaseous products, at a particular temperature denotes the flash point. The fire point denotes the temperature at which continuous combustion occurs (a fire) due to the thermal decomposition of the volatile
lipids. Oils like pongamia (Pongamia glabra)oil and nahor (Mesua ferrea L.,
Guttiferae) oilused to produce bio-diesel has a flash point of 134 and 142 °C respectively (De and Bhattacharyya 1999).
Rheology
The rheology of lipids is important in many food applications. Rheology is the science that deals with the deformation and flow of matter. The rheology is measured
by applying a force to a material and measuring its flow or change in deformation
of shape. Rheological models for oil fields are classified as Newtonian or nonNewtonian. Newtonian fluids shows a linear relationship when shear rate plotted
against shear rate against shear stress, whereas a non-linear relationship obtained
for non-Newtonian fluids that are sensitive to shear rate. Plasticity is one of the
significant rheological characteristics to determine the spreadability of lipids.
Plasticity of any lipid rises when the fat crystal forms a three-dimensional network
giving the product solid-like characteristics. The flow properties of liquid oils are
determined based on their critical stress limits. The product behaves like a shearthinning liquid above the critical stress (known as the “elastic modulus”) due to the
disruption of crystal network. At the same time, below the critical stress limit
(known as the “yield stress”), where the crystal network is not disrupted, and the
product remain a solid. Rheological techniques are hence needed to measure the
change in deformation of a lipid under applied stress. The stiffness of an emulsion
filled gel is determined by the hardness of fat and its structural organization (Oliver
et al. 2015). Increasing the hardness of fat stiffens the emulsion filled gels with high
rigidity. Thus, the gel stiffness increases as a function of the solid fat content, due to
inhomogeneous distribution of the fat droplets, droplet aggregation and/or concentration of the droplets.
Lipids and Oils: An Overview
Smoke, Flash and Fire Point
The smoke point also known as burning point is the temperature at which the oil or
fat begins to produce a bluish smoke under specified conditions. They are measured
by pouring lipid on a metal container and applying heat at a controlled rate in an
oven. The test reflects the amount of volatile organic material in oils and fats such
as free fatty acids. Also, smoke test helps to select lipids that will be used at high
temperatures, e.g. during baking or frying. Fat is considered no longer good for
consumption once it has exceeded its smoke point, due to the large quantity of free
radicals. Similar to smoke point, the flash point and fire point is determined based
on the volatile organic material in a lipid. The appearance of flash on the surface of
the sample due to the ignition of volatile gaseous products, at a particular temperature denotes the flash point. The fire point denotes the temperature at which continuous combustion occurs (a fire) due to the thermal decomposition of the volatile
lipids. Oils like pongamia (Pongamia glabra)oil and nahor (Mesua ferrea L.,
Guttiferae) oilused to produce bio-diesel has a flash point of 134 and 142 °C respectively (De and Bhattacharyya 1999).
Rheology
The rheology of lipids is important in many food applications. Rheology is the science that deals with the deformation and flow of matter. The rheology is measured
by applying a force to a material and measuring its flow or change in deformation
of shape. Rheological models for oil fields are classified as Newtonian or nonNewtonian. Newtonian fluids shows a linear relationship when shear rate plotted
against shear rate against shear stress, whereas a non-linear relationship obtained
for non-Newtonian fluids that are sensitive to shear rate. Plasticity is one of the
significant rheological characteristics to determine the spreadability of lipids.
Plasticity of any lipid rises when the fat crystal forms a three-dimensional network
giving the product solid-like characteristics. The flow properties of liquid oils are
determined based on their critical stress limits. The product behaves like a shearthinning liquid above the critical stress (known as the “elastic modulus”) due to the
disruption of crystal network. At the same time, below the critical stress limit
(known as the “yield stress”), where the crystal network is not disrupted, and the
product remain a solid. Rheological techniques are hence needed to measure the
change in deformation of a lipid under applied stress. The stiffness of an emulsion
filled gel is determined by the hardness of fat and its structural organization (Oliver
et al. 2015). Increasing the hardness of fat stiffens the emulsion filled gels with high
rigidity. Thus, the gel stiffness increases as a function of the solid fat content, due to
inhomogeneous distribution of the fat droplets, droplet aggregation and/or concentration of the droplets.
Lipids and Oils: An Overview