Retrogradation

Retrogradation in rice is a trait that describes the hardening of cooked rice after storage or cooling, and it has significant implications for many consumers of rice, since many people cook rice in the morning and consume it several hours later or the next day. Tools to select against retrogradation in breeding programs are yet to be described. Here, we aim to determine the effect on retrogradation of storage time and temperature and the role of starch, protein, and lipids using gels made from Koshihikari grown in either Australia or Japan. Immediately after cooking, cooling from 60 to 40 °C had a minimal effect on firmness, but cooling to 20 °C led to significantly firmer gels. Storing the gels at low temperatures did not have an additional effect on the firmness as compared with storing the gels at 20, 40, or 60 °C. The removal of proteins led to significantly softer gels at all storage treatments but did not affect the change in firmness on cooling. The removal of lipids increased the rate of retrogradation and the firmness of gels significantly for all treatments. Koshihikari grown in Japan retrograded much less than Koshihikari grown in Australia. The amount of amylose that could be washed from gels made from Australian flour was much greater than for gels made from Japanese flour. After storage, only low molecular weight amylose chains were released from the gel and only after rewarming them to 60 °C. Despite the fact that flours from both origins were 18% amylose, the amount of long amylose chains that were complexed with lipids was much greater for the Japanese rice, and the unavailability of the complexed long amylose chains explained the lack of retrogradation in the Japanese rice. Once the long chains were released from amylose−lipid complexes, the Japanese rice retrograded. Thus, the environmental factor affecting retrogradation in this variety is type or amount of lipids synthesized, and the degree of retrogradation was determined by the availability of long chains of amylose.

Retrogradation behavior of waxy and normal corn starch gels stored at 5 and 21◦C were
investigated for 50 days by differential scanning calorimetry. The extend of retrogradation
can be expressed as the ratio of retrogradation and gelatinization enthalpy values and these
were 70–78% for normal corn starch and 39–68% for amioca stored at two temperatures.
Higher retrogradation rates were observed at 5◦C for both waxy and normal corn starch.
Kinetic data were evaluated by considering retrogradation as consecutive reactions in series
and by Avrami Equation. High R2 values (0.97–0.98) indicated that both models can be used
for prediction. The comparison of rate constants obtained by Avrami Equation indicated
that both temperature and amylose content of starch affected the recrystallization rate. By
the kinetic model based on consecutive reactions in series, it was proven mathematically that
the rate limiting step in recrystallization of starch gels is the nucleation.

ABSTRACT The physico-chemical, morphological, thermal, pasting, textural, and retrogradation properties of the starches isolated from four traditional Taewa (Maori potato) cultivars (Karuparera, Tutaekuri, Huakaroro, Moemoe) of New Zealand were studied and compared with starch properties of a modern potato cultivar (Nadine). The relationships between the different starch characteristics were quantified using Pearson correlation and principal component analysis. Significant differences were observed among physico-chemical properties such as phosphorus content, amylose content, swelling power, solubility and light transmittance of starches from the different potato cultivars. The starch granule morphology (size and shape) for all the potato cultivars showed considerable variation when studied by scanning electron microscopy and particle size analysis. Starch granules from Nadine and Moemoe cultivars showed the presence of large and irregular or cuboid granules in fairly high number compared with the starches from the other cultivars. The transition temperatures (To; Tp; Tc) and the enthalpies (ΔHgel) associated with gelatinization suggested differences in the stability of the crystalline structures among these potato starches. The Moemoe starch showed the lowest To, while it was higher for Tutaekuri and Karuparera starches. Pasting properties such as peak, final and breakdown viscosity and texture profile analysis (TPA) parameters of starch gels such as hardness and fracturability were found to be higher for Nadine and Huakaroro starches. The Nadine and Huakaroro starch gels also had lower tendency towards retrogradation as evidenced by their lower syneresis (%) during storage at 4 °C. Principal component analysis showed that the Tutaekuri and Nadine cultivars differed to the greatest degree in terms of the properties of their starches.

Starches separated from four potato cultivars were hydroxypropylated and their physico-chemical, morphological, thermal and rheological properties were compared. The extent of hydroxypropylation measured as molar substitution differed significantly among the ...

BACKGROUND: Tortillas were prepared from two (blue and regular white) maize varieties and compared with regard to chemical composition and in vitro starch digestibility, i.e., available starch (AS), total (RS) and retrograde (RRS) resistant starch contents, amylolysis rate and predicted glycemic index (pGI). The impact of cold storage (4 °C) on digestibility was also investigated.RESULTS: Despite its higher protein and lipid contents, pigmented tortilla exhibited lower AS content than the white product. AS in both types of tortilla decreased during the first 2 days of storage, and remained stable thereafter. Blue tortilla had lower RS content (21 g kg−1 dry matter basis) than the white tortilla (30 g kg−1 dry matter basis). RS values were slightly higher in 2 day-stored tortillas than in their fresh counterparts. Although the RRS content in recently made white tortillas was greater than in the colored preparation, stored blue tortillas exhibited double RRS values compared with freshly baked samples. α-Amylolysis of blue tortilla was slower than in the white sample. Consequently, blue tortilla exhibited a lower pGI value. pGI for the white tortilla decreased upon cold storage, a change that was not be observed for the colored preparation.CONCLUSION: Starch digestibility characteristics of blue tortilla make it suitable for people with special nutritional or metabolic requirements. Copyright © 2007 Society of Chemical Industry