Novel Technologies and Systems for Food Preservation by Dinis Gaspar Pedro;IGI Global;Silva Pedro Dinho da;

Author:Dinis Gaspar, Pedro;IGI Global;Silva, Pedro Dinho da;
Language: eng
Format: epub
Publisher: IGI Global

Milling

Most rice is milled for direct consumption or for subsequent utilization as an ingredient in end-use products. The primary purpose of milling is to remove the germ and bran layers from the kernel endosperm. The extent to which bran has been removed from the kernel endosperm is referred to as the “degree of milling” (DOM). To a large extent, the milled-rice customer and the intended use of the rice dictate the target bran removal level (e.g., most rice milled for breakfast cereal processing is not milled to the same extent as that used for “table” rice).

Figure 1 indicated four morphological layers surrounding the rice kernel endosperm (the pericarp, seed coat, nucellus, and aleurone layers (Luh, 1980)) and the germ (embryo) which are collectively referred as “bran”. The bran contain approximately 18-20% lipids and 14-15% protein, while milled rice, comprising primarily the kernel endosperm, is generally much lower in lipids (approximately 0.3-0.5%) and protein (approximately 7%). These values can vary greatly due to varietal, environmental, or processing variability. Because of these stark differences in composition between the bran and endosperm, the DOM can affect the functionality of milled rice. In addition to having functional effects, the bran remaining on kernels after milling can affect sensory characteristics. As milling removes the outer protective layers of the rice caryopsis, the endosperm of milled rice becomes relatively more prone to moisture sorption from its surrounding environment. This is particularly true for rice that has just been milled, since rice exiting a mill is typically at higher temperatures than the surrounding air. A situation often experienced in the milling industry that can be very costly in terms of broken rice and mill downtime is the fissuring and subsequent breaking of kernels during post milling operations, often referred to as “residual breakage”.

Figure 1. Rice kernel structure

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