Food Microstructure and Starch Digestion - Advances in Food and Nutrition Research - page 153

drying could not be ruled out. The cells stayed mainly intact during the
enzymatic action up to 30 min ( Fig. 4.8 ). Figure 4.8 B shows the inside of
the tuber cell which appears like a honey comb structure from where starch
might have been digested during simulated small intestinal digestion.

3.2. Case II: Microstructural characteristics of navy
beans and starch digestion
3.2.1 Microstructural characteristics of navy beans
The critical point dried, fractured and cut sections of raw and cooked beans
were observed under the scanning electron microscope by Berg et al. (2012) .
Within the raw bean cotyledon cells, the starch granules were observed to be
embedded in and surrounded by thick proteinaceous matrix derived from
the cell contents ( Fig. 4.10 A). A similar morphology for the cellular contents
of other legumes has been described by Daussant et al. (1983) . The size of the
bean cotyledon cells ranged between 50 and 100 m and they were hexag-

onal or angular in shape. The interaction of the cell wall materials such as
cellulose and noncellulosic polysaccharides is responsible for their stability
and resistance toward turgor pressure ( Carpita & Gibeaut, 1993 ) . The cut
surface of the beans cooked for 15 min showed swollen cotyledon cells
due to hydration during cooking ( Fig. 4.10 B). The cotyledon cells stayed
intact during the cooking process. Strands of dried soluble material were
observed on the top surface of cotyledon cell walls. This soluble material
might consist of soluble starch containing mainly amylose, soluble sugars,
and nonstarch polysaccharides which oozes out of the cotyledon cells during

m

A B

Figure 4.10 (A and B) Scanning electron micrographs showing sections of cotyledon
cells. (A) Raw navy beans and (B) cooked navy beans. Reproduced from Berg et al.
(2012) with permission from Elsevier.