From sucrose to starch granule to starch physical behaviour: a focus on rice starch

The diversity of the physical and consequently the functional behaviour of starches, isolated from different rice varieties, is related to their specific structures. The latter are directly related to the starch biosynthetic pathway. To fully take advantage of the different functionalities of starches from different rice varieties and to design tailor-made starches, it is important to gain insight into biosynthesis–structure–physical behaviour–functionality relations. In a first part of this review, starch composition is described with a focus on rice starch. Secondly, current knowledge on starch biosynthesis is discussed. This more specifically includes (i) the function of the rice biosynthetic enzymes (i.e. adenosine diphosphate glucose pyrophosphorylases, synthases, branching and debranching enzymes), (ii) the effect of mutations on rice starch structure and, (iii) models for amylose and amylopectin synthesis. Thirdly, starch structure [i.e. from granule (2–100 μm), to growth ring (120–500 nm), blocklet (20–500 nm), amorphous and crystalline lamellae (9 nm), and amylopectin and amylose chain levels (0.1–1.0 nm)] is dealt with. Finally, relations between rice starch structural aspects [i.e. amylopectin (core) chain length distributions] and physical behaviour (i.e. gelatinisation and amylopectin retrogradation as measured by differential scanning calorimetry) are studied.