The Granule Surface

Characterization of the state, nature and structure of the starch granule surface has been somewhat limited. Over the past few years, however, substantial progress in starch surface chemical analysis and surface imaging has been made. The following two sections detail recent developments in these two new areas of starch research. 

---

It is not possible here to present a full account of the interactions between these effects, so the reader is referred to standard texts dealing with this important topic [93], However, there may be an optimum mixing time and in such cases, prolonged mixing may result in an undesired product. In the special case of mixing in a lubricant, which is required at the granule surface, overmixing can be particularly detrimental. 

Figure 5.8 Agglomeration model view of the granule surface.

The ratio of total binder volume to total particle volume in the bed is denoted by y. If all granules are uniform fhis quantity must equal the binder volume to particle volume ratio for each granule. By defini-fion, the volume of parficles per granule is aVg and fhe volume of binder per granule isfWg less fhe deficiency of binder at the granule surface, AS sn Therefore y is given by... 

An important side effect of the glazing and blending operations is an increase in SLD, traceable to a general smoothing of the granule surfaces by attrition. A typical set of data is given in Figure 8. 

They concluded that these data supported Badenhuizen s17,18 suggestion that starch molecules are completely synthesized in the amyloplast stroma and are then deposited on the granule surface. Once the polysaccharides are part of the granule, there was no evidence of subsequent conversion of amylose to amylopectin.166 This is in contrast to conclusions drawn from long-term 14C-labeling studies of wheat starch.167,168 In results of these studies, amylose appeared to be synthesized first, and then transformed into amylopectin. These differences may be due to the different species used or to the widely different sampling times. 

The exact quantity of protein and lipid present depends on the species and variety of starch however, typical well washed cereal starch samples contain —0.3% protein and up to 1.0% lipid, while a typical root or tuber starch may contain —0.05% protein and 0.05-0.1% lipid.63 These values result from bulk analysis of starch in reality, the actual distribution of the components is not uniform, with both protein and lipid enrichment believed to be present towards and at the granule surface.58,64,65... 

Do the semi-amorphous growth shells have a local increase in amylose content (while respecting the general increase in amylose towards the granule surface) ... 

Figure 6.6 Surface of an osage-orange, reminiscent of the granulated surface of the sun (figure 6.4). [From Flarlow, Art Forms from Plant Life (New York Dover, 1976), 69.]...

---