Biology Reference
In-Depth Information
3.1. Case I: Microstructural characteristics of potato
and starch digestion
3.1.1 Microstructural characteristics of potato
Microscopic and rheological techniques provide important information
on the structural organization of foods and some researchers have applied
these techniques to study the microstructure and rheological properties of
potatoes ( Singh et al., 2005; Singh, Kaur, & McCarthy, 2009; Singh,
Kaur,etal.,2008 ;) Singh, Kaur, McCarthy, Moughan, & Singh, 2009 .
In a recent study carried out on different potato cultivars, light micros-
copy was used to reveal apparent differences in the microstructure of
tuber parenchyma ( Bordoloi,Kaur,&Singh,2012 ; Fig. 4.1 ) . The cultivar
Red Rascal tuber parenchyma cells were observed to be elongated and
hexagonal, whereas those from Agria appeared roughly spherical. Agria
and Nadine tuber parenchyma cell size was found to be generally larger
than those from other two potato cultivars. Moonlight and Red Rascal
parenchyma showed a very regular and defined arrangement of cells in
contrast to Agria, which had an irregular cellular arrangement. Raw
parenchyma cellular compartments were generally filled with a range
of different shape and size starch granules. Each cell also showed few
mature starch granules and numerous tiny structures ( Fig. 4.1 A, C, and G),
resembling to the “immature starch granules” as explained by Singh et al.
(2005) . The number and size of mature starch granules per cell also varied
from cultivar to cultivar. Mealy potatoes have been reported to contain
higher starch and amylose contents as well as a higher percentage of large
starch granules
m) than the waxy cultivars ( Barrios,
Newson, & Miller, 1963 ). Potatoes with larger cell size have been reported
to exhibit larger mean starch granule size and vice versa ( Singh et al., 2005 ) .
Confocal laser scanning microscopy (CLSM) allows direct visualization of
the potato tissue and the micrographs of raw and cooked potato tuber cells
( Fig. 4.2 ) . Figure 4.3 shows scanning electron micrograph of a fracture
surface of raw potato parenchyma from cultivar Agria. Raw potatoes
( Fig. 4.3 A and B) presented cell rupture revealing the starch granules, in
contrast to the starchy matrix observed in cooked potato ( Fig. 4.3 D).
Cavities, tiny holes and remnants of the cell wall material were observed
on the surface of many of the raw starch granules present inside the cells
( Fig. 4.3 C ).
The swelling and gelatinization of starch granules during cooking exert
pressure on the cell walls and thus play an important role in determining
potato texture after cooking. Cooking of potatoes also affects noncellulosic
(diameter > 50
m
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