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Title: CHANGES IN PROTEIN AND STARCH CONFORMATION DURING VARIABLE TEMPERATURE PARBOILING OF RICE: FT-RAMAN AND 13C CP-MAS NMR SPECTROSCOPIC ASSESSMENT

Author
item Himmelsbach, David
item MANFUL, JOHN - FOOD RESEARCH INST., GHAN
item COKER, RICHARD - UNIV. OF GREENWICH, UK

Submitted to: American Association of Cereal Chemists Meetings
Publication Type: Abstract Only
Publication Acceptance Date: 6/10/2005
Publication Date: 9/1/2005
Citation: Himmelsbach, D.S., Manful, J.T., Coker, R.D. 2005. Changes in protein and starch conformation during variable temperature parboiling of rice: FT-Raman and 13C CP-MAS NMR spectroscopic assessment [abstract]. American Association of Cereal Chemists Meetings. Paper No. O-52 p. 79.

Interpretive Summary:

Technical Abstract: FT-Raman and solid-state 13C cross polarization magic-angle spinning (CP-MAS) NMR spectroscopies were employed to assess the conformational changes to protein and starch in paddy rice under variable conditions of parboiling. Rice variety, TOX 3108 from Ghana, was parboiled by the soaking-steaming-drying method under conditions that mimicked various local conditions employed in Ghana. Variable temperature soaking (bringing to 30 degrees C, 50 degrees C, 70 degrees C, and 90 degrees C cooling, and then holding at 30ºC in an oven for 16 hr) followed by variable steaming times (4, 8,12 min) at each of the soaking temperatures and subsequent air-oven drying was employed. Spectral analyses were performed on the samples after de-husking, milling and grinding. The results of these treatments were compared to raw (non-parboiled) rice and a proprietary parboiled rice product. FT-Raman spectroscopy was useful in ascertaining the protein conformations. Principal component analysis (PCA) of the Raman data indicated that the conditions employed did not generate parboiled rice similar to the fully parboiled proprietary product yet was much different from raw rice. Curve fitting applied to the Amide I region of the Raman spectrum indicated increased conversion of the protein to beta-sheet and beta-turn from alpha-helix conformation upon parboiling with as little as 4 minutes of steaming, regardless of the soaking temperature. Solid-state 13C NMR spectroscopy indicated that starch did not become completely gelatinized (amorphous), even under the 90 degrees C - 12 minutes parboiling conditions as it did with the high-pressurized-heat treatment utilized in the commercial parboiling process. Thus it can be concluded that under the conditions investigated, only mildly parboiled rice is produced. However, these processes may be sufficient to impart beneficial properties to the rice such as denaturization of the enzymes and annealing of the rice to prevent disintegration.