Digital Image Analysis Method for Rapid Measurement of Rice Degree of Milling

Abstract

Cereal Chem. 75(3):380-385A digital image analysis method was developed to quickly and accurately measure the degree of milling (DOM) of rice. The digital image analysis method was statistically compared to a chemical analysis method for evaluating DOM, which consisted of measuring the surface lipids concentration (SLC) of milled rice. The surface lipid area percentage (SLAP) obtained by the image analysis method and the SLC obtained by chemical analysis had a high coefficient of determination using a quadratic model (R 2 = 0.9819) and using a logarithmic model (R 2 = 0.9703). The quadratic model and the logarithmic model were validated using the test data set and it received high coefficients of determination (R 2 = 0.9502 and R 2 = 0.9459, respectively).Rice millers grade rice quality for nutritional and economic considerations and, thus, need a fast and accurate grading system as part of their milling assessment operations. The primary physical grading factors are head rice yield, which is the weight percentage of rough rice remaining as head rice (kernels that are 75% or more of their original length after milling), and degree of milling (DOM), which indicates how much bran remains on milled kernels (USDA 1979). Generally, milled rice with a high DOM level has less kernel bran than does milled rice with low DOM levels. The current methods for grading rice quality are subjective and time-consuming. This study developed a digital image analysis method that can quickly and accurately determine DOM.DOM is an important factor in terms of the nutritional value and the economic return of the milled rice. Low DOM level rice contains more protein, vitamins, minerals, and lipids than does high DOM rice (Wadsworth et al 1991). Although low DOM level rice has greater nutritional value, it often has a lower market appeal because most consumers prefer the taste and appearance of well-milled rice. Additionally, the degree to which rice is milled inversely affects head rice yield (Sun and Siebenmorgen 1993). Therefore, adjusting DOM during the rice milling operations is essential for optimizing quality and economic return. DOM can be measured by several methods, including visual inspection, chemical analysis, and optical measurements. Traditionally, DOM has been determined through visual inspection by trained personnel. For official grading, this judgment is made by comparing a sample to one of four official samples representing the four DOM grades (undermilled, lightly milled, reasonably well-milled, and well-milled) defined by the United States Standards for Milled Rice (USDA 1979). The closest similarity between the official representative sample and the inspection sample determines the DOM grade. Visual inspection is not only subjective but also is lacking in terms of quantitatively assessing the milling degree. For accurate measurement, more objective and quantitative methods must be employed to determine DOM.Chemical methods of assessing DOM include the differential dye-staining procedure and the compositional analysis...

Determination of the size distribution and percentage of broken kernels of rice using flatbed scanning and image analysis

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Influence of Milling Parameters on Head Rice Recovery: A Review

“…It was hypothesized that the overall whiteness of milled rice could be estimated simply from the mean value of the gray level distribution obtained from the digitized image of the bulk sample. Digital image analysis has been used to estimate the area of the bran layer on the surface of rice kernels and correlated with the surface lipids concentration determined by chemical analysis (Liu et al, 1998).…”

Quality Inspection and Grading of Agricultural and Food Products by Computer Vision-a Review

“…Liu et al, [33] developed a digital image analysis method for measuring the degree of milling of rice. They compared the method with conventional chemical analysis and obtained a coefficient of determination of R 2 =/0.9819 for the 680 samples tested.…”