8
swelling of the amorphous regions (Wani et al. 2012).Starch gelatinization is normally achieved by heating starch with water, but can also be achieved by heating
starch in the presence of plasticizers like glycerol, ethylene glycol, and 1,
4- butanediol, alkaline solutions like NaOH and KOH, in neutral salt solutions like
CaCl 2 and LiCl, and solvents like dimethyl sulfoxide (DMSO) (Ai and Jane 2015).
After gelatinization is complete, the amorphous starch readily absorbs water and
forms a paste. Upon cooling, some starch pastes can develop gels.
Gelatinization, an important functional property of starches, varies with respect
to the starch composition (amylose-to-amylopectin ratio, and the percentage of
phosphorus, lipids, proteins, and enzymes), the molecular structure of amylopectin,
granule architecture, granule morphology, and granule size distribution (Tester
1997; Hoover et al. 2010).The temperature of initial gelatinization and the range
over which gelatinization occurs depend on the method of measurement, on the
starch: water ratio and granule type. To determine the gelatinization temperature of
starch, many instruments have been used. These include differential scanning calorimetry (DSC), polarized light microscopy, thermomechanical analysis, and nuclear
magnetic resonance spectroscopy, and other methods for the degree of starch gelatinization, such as X-ray scattering and Fourier transform infrared spectroscopy.
However, DSC has emerged as the preferred method of choice for the measurement
of starch gelatinization and the properties that are reported using DSC include gelatinization onset (To), peak (Tp), and conclusion (Tc) temperatures, peak height
index (PHI), and enthalpy (ΔHg). The gelatinization properties of different starches
determined by differential scanning calorimetry are presented.
Cooling of gelatinized starch results in the re-association of the leached amylose
from gelatinized granules. This process is called retrogradation. Retrogradation
causes starch gels to become less soluble during cooling due to recrystallization of
starch molecules (BeMiller and Whistler 1996) and is of great interest to food technologists and industries since it profoundly affects quality, acceptability and shelflife of starch-containing foods (Karim et al. 2000).
Retrogradation, also referred to as setback, occurs with re-crystallization of amylose which is more susceptible to retrogradation than amylopectin. Amylopectin is
only minimally involved in starch retrogradation (Mua and Jackson 1998). The reassociation and re-crystallization of amylose causes release of the water absorbed
and bound during gelatinization, leading to the phenomenon known as syneresis.
Retrogradation of gelatinized starch involves formation and subsequent aggregation
of double helices of amylose and amylopectin chains, thus governing elasticity,
firmness, and textural staling of all starch-containing systems (Atwell et al. 1988).
Therefore, changes leading to retrogradation can restrict the starch functional properties making it less desirable for food industries. Cereal starches in general retrograde more slowly, and to a lesser extent, than tuber and root starches (Roulet et al.
1990). Differences in retrogradation behavior might be related to amylopectin fine
structure, lipid content, amylose/amylopectin ratio and molecular weights. Avarami
equation is frequently used to analyze retrogradation kinetics, however, this analysis implies a single step process. Since retrogradation is more complex, this analysis
has therefore limited applicability.
K. Gul et al.
swelling of the amorphous regions (Wani et al. 2012).Starch gelatinization is normally achieved by heating starch with water, but can also be achieved by heating
starch in the presence of plasticizers like glycerol, ethylene glycol, and 1,
4- butanediol, alkaline solutions like NaOH and KOH, in neutral salt solutions like
CaCl 2 and LiCl, and solvents like dimethyl sulfoxide (DMSO) (Ai and Jane 2015).
After gelatinization is complete, the amorphous starch readily absorbs water and
forms a paste. Upon cooling, some starch pastes can develop gels.
Gelatinization, an important functional property of starches, varies with respect
to the starch composition (amylose-to-amylopectin ratio, and the percentage of
phosphorus, lipids, proteins, and enzymes), the molecular structure of amylopectin,
granule architecture, granule morphology, and granule size distribution (Tester
1997; Hoover et al. 2010).The temperature of initial gelatinization and the range
over which gelatinization occurs depend on the method of measurement, on the
starch: water ratio and granule type. To determine the gelatinization temperature of
starch, many instruments have been used. These include differential scanning calorimetry (DSC), polarized light microscopy, thermomechanical analysis, and nuclear
magnetic resonance spectroscopy, and other methods for the degree of starch gelatinization, such as X-ray scattering and Fourier transform infrared spectroscopy.
However, DSC has emerged as the preferred method of choice for the measurement
of starch gelatinization and the properties that are reported using DSC include gelatinization onset (To), peak (Tp), and conclusion (Tc) temperatures, peak height
index (PHI), and enthalpy (ΔHg). The gelatinization properties of different starches
determined by differential scanning calorimetry are presented.
Cooling of gelatinized starch results in the re-association of the leached amylose
from gelatinized granules. This process is called retrogradation. Retrogradation
causes starch gels to become less soluble during cooling due to recrystallization of
starch molecules (BeMiller and Whistler 1996) and is of great interest to food technologists and industries since it profoundly affects quality, acceptability and shelflife of starch-containing foods (Karim et al. 2000).
Retrogradation, also referred to as setback, occurs with re-crystallization of amylose which is more susceptible to retrogradation than amylopectin. Amylopectin is
only minimally involved in starch retrogradation (Mua and Jackson 1998). The reassociation and re-crystallization of amylose causes release of the water absorbed
and bound during gelatinization, leading to the phenomenon known as syneresis.
Retrogradation of gelatinized starch involves formation and subsequent aggregation
of double helices of amylose and amylopectin chains, thus governing elasticity,
firmness, and textural staling of all starch-containing systems (Atwell et al. 1988).
Therefore, changes leading to retrogradation can restrict the starch functional properties making it less desirable for food industries. Cereal starches in general retrograde more slowly, and to a lesser extent, than tuber and root starches (Roulet et al.
1990). Differences in retrogradation behavior might be related to amylopectin fine
structure, lipid content, amylose/amylopectin ratio and molecular weights. Avarami
equation is frequently used to analyze retrogradation kinetics, however, this analysis implies a single step process. Since retrogradation is more complex, this analysis
has therefore limited applicability.
K. Gul et al.