Cereal Chem. 74(2):163-167Starches of waxy rices that showed varietal differences in hardness testing of cooked rice after amylopectin staling and high-amylose content (AC) rices differing in gel consistency (GC) and starch gelatinization temperature (GT) were studied to determine the factors related to varietal differences in amylopectin staling of cooked rice. Intermediate-and high-GT starches showed greater amylopectin staling of gelatinized rice by hardness testing values or differential scanning calorimetry (DSC) endotherm than did low-GT starches in both waxy and nonwaxy rices. Isoamylase-debranched amylopectins of waxy rices differed in the ratio of weight-average degree of polymerization (DP w ) fractions, but these fraction ratios were not simply related to differences in amylopectin staling of cooked rice. Among high-AC rices, amylopectin from low-GT starch was confirmed to have higher iodine affinity (2.3-2.5%) than amylopectin from intermediate-GT starches (1.7-1.8%), regardless of GC. Within high-AC starch of the same GT type, soft-GC rice corresponded with more A + B 1 DP w 16-18 and less B 3 DP w 150-200 fractions of debranched amylopectin and low DP w of amylose. Amylopectin of amylose extender mutant of IR36 was confirmed to have a longer chain length than ordinary rice amylopectin: the debranched amylopectin has more B 2 DP w 47-51 fraction, less A + B 1 DP w fraction, but no B 4 fraction with DP w >200. Only high-AC amylopectin had debranched fraction with DP w >120.

Among three high‐amylose starches differing in gel consistency, the hard gel starch (IR42), corresponding to harder cooked rice, had higher amylograph consistency and setback, higher gel viscosity in 0.2 N KOH and higher alkali viscograph peak than starch with soft (IR32) or medium (IR36) gel consistency. IR42 starch had less extractable starch and amylose in boiling water than IR32 and IR36 starches. The three starches had similar amyloses; the differences in gel consistency were due to the amylopectin fraction. IR42 amylopectin had higher iodine affinity, more long‐chain linear fractions on isoamylase debranching and gel filtration or 1‐butanol precipitation, and less DPn 16–17 fraction than IR32 and IR36 amylopectins.

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Residual protein of rice starch granules prepared from milled rice by protein extraction with sodium dodecylbenzene sulfonate or alkaline protease treatment was related to amylose content. SDS‐polyacrylamide disc gel electrophoresis confirmed that the major protein in nonwaxy starch granules was the Wx gene product with subunit molecular weight of about 60,000 daltons. The Wx gene product was absent in waxy starch granules.

Starches of 40 rice varieties from different ecosystems and 2 amylose extender mutants were analyzed for their predominant waxy gene allele (Wx" or WX') through the amount of Wx gene product (60-kdal polypeptide) by SDS-polyacrylamide gel electrophoresis. Nonwaxy rices carrying the Wx" and Wxb alleles were clearly differentiated by two distinct regression equations correlating AC and the amount of Wx gene product. Indica, samba, and tropical upland rices hat the Wx" allele and contained about three times as much Wx gene protein at the same AC as japonica and long-grain US rices carrying the WX' allele. Indica-japonica, bulu, and basmati-type rices showed selection for either Wx" or Wxb. Identification of the predominant Wx allele provides an alternative method for classifying nonwaxy rice grains into indica or japonica type, and complements the embryo isozyme classification. Results of the two methods are generally consistent. Vergleichbare Hohen von wachsigemGenprodukt der Endosperm-Starkekorner verschiedener Reis-Okotypen. Die Starken von 40 Reisvarietaten aus verschiedenen Okotypen und 2 Amylose-Extender-Mutanten wurden hinsichtlich ihrer vorherrschenden wachsigen Gen-Allele (Wxa oder Wxb) anhand der GroBe an Wx-Genprodukt (Gl-kdal Polypeptid) durch SDS-Polyacrylgel-Elektrophorese analysiert. Nicht-wachsige, die Wxa-und Wxb-Allele tragende Reissorten wurden durch zwei bestimmte Regressionsgleichungen AC (Amylose-Gehalt) und die Menge an Wx-Genprodukt klar differenziert. Indica-, Samba-und tropische Hochland-Reissorten hatten das Wxa-Gen und enthielten etwa dreimal soviel Wx-Genprotein bei gleichem AC wie Japonica-und Langkorn-US-Reissorten, die das Wxb-Allel enthielten. Indica-, Japonica, Bulu-und Basmati-Reisarten zeigten eine Auswahl f i r entweder Wx" oder Wxb. Die Identifiziemng des vorherrschenden Wx-Allels setzt eine alternative Methode zur Klassifizierung von nichtwachsigen Reiskornern in Indica-oder Japonica-Sorte voraus und erganzt die Klassifizierung des Embryo-Isozymes. Die Ergebnisse beider Methoden sind allgemein ubereinstimmend.