7.3 Chemistry of Agar
149
This lower viscosity and higher gel strength make processing of the gels easier by
allowing easier flow during processing of the product prior to gel formation.
7.3.4 Interaction with Sugars
Sugars are often used alongside agar-based products such as candies, icings and
creams. Other than acting as a sweetener, sugar also contributes to the physical properties of the food. When agar gel interacts with sugar in a fluid gel system, this has
an effect on the rheological properties of the resultant product and consequently the
nature of gels and foams formed in such systems. This property-related interaction
with sugar could be used as a means of reducing sugar contents of processed food
while giving consideration to the change in properties such as the texture, syneresis
and gel strength. These properties are important in food products, while the consumer and health agencies demand a lower sugar content for health reasons, and
they also demand appealing taste, texture and appearance. The producer therefore
needs to understand the agar–sugar interaction and how this affects the property of
the product. Recent studies which analyzed the effect of concentrations of different
sugars: glucose, sucrose and fructose which are commonly used in food products,
have significant effect on the viscosity, gel strength and foam stability. At concentrations above 50% w/v of sugar (either fructose, sucrose or glucose), the gel formed
is more elastic; at lower concentration below 50% w/v of sugar, the shear viscosity
and modulus of elasticity increase, thus indicating a stronger more rigid gel formed.
Increasing sugar concentration also increased the foam stability measured as foam
half-life (Ellis et al. 2019). Earlier studies using agarose extracted from Gelidium
amansii have established that stronger agarose gels with higher melting points are
formed when sugar is added to the agarose gel solution up to a critical concentration
(Watase et al. 1990). This relationship between the sugar concentration and physical
properties of the resulting gel of agar is attributed to the interactions between the
functional groups of the sugars and those of the agar. These interactions in turn affect
the conformations during gelation. In the same study, it was observed that urea and
guanidine hydrochloride resulted in a decreased young modulus.
7.3.5 Thermal Degradation of Agar
For a product to be considered safe, the products upon degradation should pose
no harm to health while in storage or in use. One of the advantages of agar as a
phycocolloid is its ability to withstand higher processing temperatures. This makes
it suitable for heat-sterilized food products such as canned fish and meat. However,
recent studies point to potential toxic effect of the degradation of agar within a food
product when heated (Ouyang et al. 2018). Stronger agar gels tend to have higher
thermal degradation temperature such that the chances of having toxic degradation
149
This lower viscosity and higher gel strength make processing of the gels easier by
allowing easier flow during processing of the product prior to gel formation.
7.3.4 Interaction with Sugars
Sugars are often used alongside agar-based products such as candies, icings and
creams. Other than acting as a sweetener, sugar also contributes to the physical properties of the food. When agar gel interacts with sugar in a fluid gel system, this has
an effect on the rheological properties of the resultant product and consequently the
nature of gels and foams formed in such systems. This property-related interaction
with sugar could be used as a means of reducing sugar contents of processed food
while giving consideration to the change in properties such as the texture, syneresis
and gel strength. These properties are important in food products, while the consumer and health agencies demand a lower sugar content for health reasons, and
they also demand appealing taste, texture and appearance. The producer therefore
needs to understand the agar–sugar interaction and how this affects the property of
the product. Recent studies which analyzed the effect of concentrations of different
sugars: glucose, sucrose and fructose which are commonly used in food products,
have significant effect on the viscosity, gel strength and foam stability. At concentrations above 50% w/v of sugar (either fructose, sucrose or glucose), the gel formed
is more elastic; at lower concentration below 50% w/v of sugar, the shear viscosity
and modulus of elasticity increase, thus indicating a stronger more rigid gel formed.
Increasing sugar concentration also increased the foam stability measured as foam
half-life (Ellis et al. 2019). Earlier studies using agarose extracted from Gelidium
amansii have established that stronger agarose gels with higher melting points are
formed when sugar is added to the agarose gel solution up to a critical concentration
(Watase et al. 1990). This relationship between the sugar concentration and physical
properties of the resulting gel of agar is attributed to the interactions between the
functional groups of the sugars and those of the agar. These interactions in turn affect
the conformations during gelation. In the same study, it was observed that urea and
guanidine hydrochloride resulted in a decreased young modulus.
7.3.5 Thermal Degradation of Agar
For a product to be considered safe, the products upon degradation should pose
no harm to health while in storage or in use. One of the advantages of agar as a
phycocolloid is its ability to withstand higher processing temperatures. This makes
it suitable for heat-sterilized food products such as canned fish and meat. However,
recent studies point to potential toxic effect of the degradation of agar within a food
product when heated (Ouyang et al. 2018). Stronger agar gels tend to have higher
thermal degradation temperature such that the chances of having toxic degradation