Lipid complexed amylose

Lipid-complexed amylose chains interfere with amylose-iodine (If and If) complex formation. Therefore, extraction of complexed lipids with 75% n-propanol is necessary prior to determination of total amylose content. 

The amylose of native wheat starch granules consists of lipid-complexed amylose11 and lipid-free amylose.195 Lipid-free amylose and lipid-complexed amylose represent... 

Iodometric assay of amylose on cereal starches is most often done on lipid-extracted starch, and the amylose content from that assay is termed apparent amylose 145 or total amylose. 123 When the iodometric assay is performed on a lipid-extracted starch and the amylose content is corrected for interference from extra-long chains on amylopectin, the assay gives absolute amylose or real amylose. 145 Iodometric assay of starch that has not been lipid-extracted gives lipid-free (uncomplexed) amylose. Subtraction of total amylose from lipid-free amylose gives lipid-complexed amylose.123 The use of the term apparent amylose to designate lipid-free amylose is avoided in this chapter. All amylose percentages are calculated based on starch. 

Retrograded amylose Amylose-lipid complex Amylose-rich phase... 

Morrison, W.R., Tester, R., Snape, C.E., Law, R., Gidley, MJ. 1993. Swelling and gelatini-zation of cereal starches. IV. Some effects of lipid-complexed amylose and free amylose in waxy and normal barley starches, Cereal Chem., 70(4), 385. 

Potato starch contains fewer lipids than the cereal starches. Free latty acids in rice and maize starches result in amylose-lipid complex formation, thereby contributing to their higher transition temperatures and lower retrogradation. 

Shogren, R. L., Fanta, G. F., Felker, F. C. (2006). X-ray diffraction study of crystal transformations in spherulitic amylose/lipid complexes from jet-cooked starch. Carbohydrate Polymers, 64, 444 51. 

Lalush, I., Bar, H., Zakaria, I., Eichler, S., Shimoni, E. (2005). Utilization of amylose-lipid complexes as molecular nanocapsules for conjugated linoleic acid. Biomacromolecules, 6, 121-130. 

In summary, therefore, substantial information regarding the location and state of amylose has been obtained. Individual amylose chains are believed to be randomly located in a radial fashion among the amylopectin molecules. The concentration of amylose (and lipid) increases towards the surface of the granule, with smaller (leach-able) amylose chains predominating near the surface. Amylose chains are believed to be in a single helical state, although a small proportion may be involved in lipid complexes.147 Some of the larger (non-leachable) amylose chains may be involved in double helical interactions with amylopectin.159... 

Figure 8.5 Schematic diagram of state and phase transitions ofstarch note the effect of moisture content and time on the various states. Tg1 Tg2 and Tg3 represent the glass transition at different moisture content levels. A-L and V-structures denote short- and long-range order of amylose-lipid complexes, whereas d.h. order corresponds to short-range B-type structures.

All wheat starches give the same A-type crystal pattern, but their degree of crystallinity is inversely proportional to amylose content. In addition, the intensity of one reflection of an amylose-lipid complex at 2 20-23° (d 4.4A) increases proportionally to the amylose level.265,271,281,284,289 The lipid content of waxy wheat starch is much lower (0.02-0.17%) than that in non-waxy wheat starch (0.6-0.7%).286,291 However, the crude fat content of waxy wheat flour is elevated by 20-40% (3-glucan and pentosan are increased by 30%.291,292 The degree of crystallinity of waxy wheat starch is reported to be 18-21% versus 13-16% for the wild type.284,289 Increases of 35% for waxy wheat starch, 23-28% for double nulls, 20-23% for single nulls and 22% for the wild type have also been reported.271... 

The high lipid content of oat starch is reflected in the high value of the transition enthalpy (AHCX) measured for the amylose-lipid complex (Table 15.4). This transition is reversible, and on a rerun greater AHCX, as well as Tcx (endotherm peak temperature), was found.26 When the oat starch was defatted, the endotherm assigned to the amylose-lipid complex disappeared from the DSC thermogram.26 Extraction at room temperature with 1-propanol water (3 lv/v) did not influence the thermogram of the starch, but if the starch was refluxed in the same solvent, a decrease in AH and a complete elimination of the endotherm ascribed to the amylose-lipid complex occurred.28 For oat starches with a lipid content of 1.1-1.7%, it was possible to... 

Table 15.4 DSC parameters for the transition of the amylose-lipid complex of oat starch in excess water...

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