Estimation of alkali spreading value and gelatinization temperature of some Philippine rice varieties using digital photometry
2018
Tuaño,A.P.P. | Ricafort, C.H. | del Rosario, E.J.
Gelatinization temperature (GT) is an important property of the rice grain which affects its cooking and eating qualities. The most reliable method for determining GT needs expensive equipment, namely differential scanning calorimeter (DSC). An alternative method is digital photometry (DP) which uses an inexpensive digital camera and free-access image processing software to determine the alkali spreading value (ASV) and GT of milled rice. The starch gel area of the images of alkali-gelatinized grains was measured after a given gelatinization time; the images were then taken with a digital camera outside a fabricated light box and analyzed using image J. Literature GT values based on DSC (GT sub DSC) for eight rice varieties were correlated with experimental values of relative increases in gel area after gelatinization, i.e., RIA sub i and RIA sub f based either on initial area or final area, respectively. The natural logarithm of RIA sub i (In RIA sub i) was found to be highly correlated with GT sub DSC values and was numerically equal (within experimental uncertainty) published ASV values. The correlation equation of In RIA sub i versus GTD sub DSC allowed determination of GT values for three additional rice varieties and correctly predicted GT values for 29 rice varieties based on literature ASV data. Thus, DP can be used as a cheap and rapid method of estimating ASV and GT.DP values were similar to the conventional visual scoring method for ASV determination, but is less subjective, more precise and provides a permanent record of data.
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