Juliano et al. - 1993 - Grain Quality Evaluation of World Rices

Materials and methods
S
amples were obtained through national rice breeding programs.
Wild rice samples were grown at IRRI and at the International
Institute of Tropical Agriculture (IITA). Rough rice samples
were dehulled in a Satake dehuller or McGill sheller, with the resulting
brown rices milled either in a McGill miller (no. 2 or 3), a Satake TM-
05 grain testing mill, a laboratory test tube rice miller, or a Kett Pearlest
micromill.
Milled rice for protein and amylose assays and amylography was
ground in a Wiley or Udy cyclone mill with a 40-mesh sieve. Samples
for GC were ground in 10-grain lots for 40 s in a Wig-L-Bug amalgamator
(Crescent Dental Mfg. Co.) or in a Udy cyclone mill with 60-mesh
sieve.
We measured the length and width of 10 whole grains to the nearest
mm using a photoenlarger calibrated to enlarge exactly 10 times the
original size (Khush et al 1979). IRRI classifies brown rice grain length
into extra long, >7.50 mm; long, 6.61-7.50 mm; medium, 5.51-6.60 mm;
and short, 15.50 mm. IRRI classifies brown rice grain shape based on
length-width (L-W) ratio as slender, >3.0; medium, 2.1-3.0; bold, 1.1-
2.0; and round, 11.0. We used these classifications for milled rice
samples without correction.
Protein content
The microKjeldahl method was used to measure protein in 50 mg rice
flour manually digested with HgO or Se catalyst. We used the automated
colorimetric procedure (indophenol blue after reaction with
hypochlorite and alkaline phenol, using AutoAnalyzer modules [Juliano
and Pascual 1980]) to determine the ammonia content in the digest.
Kjeldahl N was multiplied by 5.95 to convert it to crude protein. This
factor, expressed as wet weight, is based on the 16.8% N in rice protein.
Since 1967, rice powder (50 mg) was digested in 10-ml Kjeldahl
flasks with 2 ml concentrated H 2 SO 4 and 1 g K 2 SO 4 -catalyst mixture