Normal Rice Starch Research Articles

Physical aging of glassy normal and waxy rice starches: effect of aging time on glass transition and enthalpy relaxation

Physical aging and glass transition characteristics of amorphous normal and waxy rice starches (11 and 15% moisture contents) were investigated under differential scanning calorimetry as function of aging time. Normal rice starch showed higher T g than waxy rice starch. The T g and Δ C p at glass transition gradually increased with aging time, whereas fictive temperature was slightly reduced regardless of moisture content and starch type. The relaxation enthalpy and relaxation peak temperature increased with aging time until structural equilibrium was reached. Enthalpy increase was more significant in the early stage of aging whereas temperature increase was constant during the aging period tested (120 h). Aging kinetic analysis using Cowie and Ferguson model revealed that the amorphous normal and waxy rice starches behaved in different modes for the physical aging. Relaxation distribution parameter ( β) of both starches was in a range of 0.3< β<0.7, but higher at a lower moisture content, and for normal starch than for waxy starch. Maximum relaxation enthalpy for normal starch (1.10 and 2.69 J/g, respectively, at 11 and 15% moistures) was higher than those of waxy starch (0.77 and 2.48 J/g). Based on the characteristic time ( t c), normal starch has slower progression toward an equilibrium than waxy starch. Overall results proved that physical aging kinetics were highly dependent on starch structure and composition.

Rice starches. I. Structural aspects provide insight into crystallinity characteristics and gelatinisation behaviour of granular starch

To gain an understanding of the contribution of structural aspects to the gelatinisation behaviour of rice starch, five waxy and 10 normal rice starches, isolated from 15 milled rice samples, were analysed for structural features [absolute (AAM), free (FAM) and lipid-complexed (LAM) amylose contents, amylopectin chain length distribution and relative crystallinity] and gelatinisation behaviour as evaluated by differential scanning calorimetry. In doing so, the normal rice starches were classified according to their peak gelatinisation temperatures (Tp) as low, intermediate and high Tp rice starches. Higher AAM and FAM contents went hand in hand with decreased onset (To), Tp and conclusion (Tc) gelatinisation temperatures and increased gelatinisation range (Tc−To) of normal intermediate and high Tp starches, whereas LAM contents increased with To, Tp and Tc and decreased with Tc−To of all investigated starches. For all starches, the relative amounts of amylopectin chains with degree of polymerisation (DP) 6–9 were negatively correlated with To, Tp and Tc and positively with Tc−To. On the contrary, chains of DP 12–22 increased gelatinisation temperatures and decreased Tc–To. Furthermore, To, Tp and Tc of the normal rice starches increased with relative crystallinity.

Physical aging of glassy normal and waxy rice starches: effect of aging temperature on glass transition and enthalpy relaxation

Effect of physical aging at different temperatures ( T a) on the amorphous transitions of normal and waxy rice starches has been investigated using differential scanning calorimetry (DSC). Glass transition temperature ( T g) increased, but ΔC p at the T g decreased, as the difference ( T g− T a) between T g and T a increased, because the molecular mobility was reduced as the aging temperature was farther from T g. The extent of relaxation was analyzed by determining the limiting relaxation enthalpy (Δ H ∞) at various aging temperatures. The Δ H ∞ versus T g− T a revealed the two different roles by kinetic and thermodynamic controls for the relaxation. When T g− T a was low (0∼30 °C), Δ H ∞ increased with T g− T a, whereas when T g− T a was high (above 30 °C), it decreased with T g− T a. At a constant T g− T a, the residual moisture raised Δ H ∞ due to plasticization effect. The effect of aging temperature on the relaxation temperature range was opposite to that on Δ H ∞, and the peak range became narrower as the moisture content increased. The Δ H ∞ and peak temperature range were different between normal and waxy rice starches. The normal rice starch had a higher Δ H ∞ and a narrower peak temperature range than did waxy rice starch.

Retrogradation of Starch Mixtures Containing Rice Starch

ABSTRACT: Different starches often coexist in food systems. Starch retrogradation is the primary reason for quality deterioration of a food system during storage. This article addresses the retrogradation behaviors of several starch mixtures containing normal rice starch (NRS). Potato starch, tapioca starch, waxy corn starch, hydroxypropylated potato starch, hydroxypropylated tapioca starch, and acetylated tapioca starch were mixed with NRS. Starch suspensions were gelatinized and the relative solid content, (S′) measured by pulsed nuclear magnetic resonance, was used to characterize the retrogradation behavior of starch systems. The retrogradation behaviors of starch mixtures can be divided into two categories according to the additive or non‐additive nature of S′, for which the concept “regional moisture content” was introduced.

Roles of Water-Soluble and Water-Insoluble Carbohydrates in the Gelatinization and Retrogradation of Rice Starch

The roles of water-soluble carbohydrates leached from starch granule and water-insoluble ones left in starch granule in the gelatinization were studied relating to gel hardness in the retrogradation. In the case of whole starch gel, hardness of rice starch gel was lower in the presence of lipids than it was in the absence of lipids, and an increase in hardness during storage at 5°C was retarded by the presence of lipids. The characteristic of water-insoluble fraction paste of gelatinized normal rice starch was the opposite to that of whole starch gel. This seems to be due to the shortage of amylose in the paste. When the proportion of amylose was high in the mixture of normal rice starch and waxy one, both the water-solubility and the gel hardness were strongly affected by lipids. On the contrary, the effects of lipids were hardly seen when the proportion of amylopectin was high in the mixed starches. Amylopectin of rice starch in the presence of amylose showed a considerable increase in complex formation.

Effects of Granular Structures on the Pasting Behaviors of Starches

ABSTRACTJaponica (Tainung 67 [TNu67]) and waxy (Taichung 70 [TCW70]) rice, normal and waxy corn, and cross‐linked waxy rice and corn starches were used in an investigation of the influence of the granular structure on the pasting behavior of starch, using small amplitude oscillatory rheometry. Both normal corn and normal rice (TNu67) starches had the highest storage moduli (G′), followed by their cross‐linked versions; native waxy corn and rice starches had the lowest. Native waxy starches showed paste characteristics (G′ &lt; 500 Pa; tan δ &gt; 0.2) at concentrations of up to 35%. However, cross‐linked waxy starches exhibited gel behavior at 10% concentration (cross‐linked TCW70) or higher (cross‐linked waxy corn starch). The degrees of swelling power were in the order: TCW70 &gt; native waxy corn &gt; TNu67 ≅ cross‐linked TCW70 ≅ normal corn ≅ cross‐linked waxy corn starches. Solubilities were in the order: normal corn &gt; TNu67 &gt; native waxy &gt; cross‐linked waxy starches. The addition of 2% purified amylose from indica rice (Kaohsiung Sen 7) did not induce gelation of waxy corn starch. Swelling powers of normal corn, TNu67, and crosslinked waxy starches were similar, but normal corn and TNu67 had much higher G′ value. Such results implied that the formation of gel structure was governed by the rigidity of swollen granules and that the hot‐water soluble component could strengthen the elasticity of the starch gel or paste.

Structures of indica rice starches (IR48 and IR64) having intermediate affinities for iodine

The amyloses of rice starches (IR48 and IR64) having intermediate affinities for iodine (i.a.) had number- and weight-average d.p. values of 930 and 1200, and 3300 and 3420, respectively, and average chain-lengths ( c.l. ) of 380 and 450. They comprised branched (∼6 chains on average) and unbranched molecules in the molar ratios 1:2 and 1:3, respectively, and the former appeared to be larger. The amylopectins had i.a. of 0.63 and 0.87 g/100 g and c.l. of 20 and 21, respectively, and were composed of long, medium, and short chains in the weight ratios 9:21:70. The amylose contents were 17.0 and 18.3%, respectively. The normal rice starches contained similar amounts of amyloses with similar structures, regardless of their i.a., but the amylopectin from the higher-i.a. starch had a higher i.a. and a larger proportion of long chains.