Biology Reference
In-Depth Information
microorganisms are usually used in the in vitro systems that attempt to simulate
the digestive process that occurs in the gastrointestinal tract of human beings.
The mammalian enzymes are very similar to human enzymes, whereas the
enzymes from microorganisms may work differently even though they are
similarly classified.
3. MICROSTRUCTURE OF NATURAL FOODS
AND STARCH DIGESTION
The microstructure of natural foods (e.g., potato, beans, rice, etc.)
including characteristics of their cell wall polymers (parenchyma cell size,
nature of pectic materials, etc.) has been reported as an important factor,
which can influence the deformation occurring during mastication or
mechanical processing ( Waldron et al., 1997 ) . Depending on the middle
lamella characteristics of parenchymatous tissue, the cells can either separate
or burst at the point of minimum resistance ( Singh, Kaur, Ezekiel, &
Gurraya, 2005 ). Raw foods generally show cell rupturing, whereas cooked
ones show cell separation due to destabilization of pectic materials during
thermal processing ( Aguilera & Stanley, 1990 ) .
The microstructural characteristics of natural foods (e.g., raw potatoes)
such as parenchyma cell size, cell wall composition, and thickness have been
reported to have a considerable effect on the final texture (mealy, waxy, etc.)
after cooking ( vanMarle, Recourt, van Dijk, Schols, &Voragen, 1997; van
Marle, Stolle-Smits, et al., 1997 ). Starch is the major component of the dry
matter, sometimes accounting for
70% of the total solids in some natural
plant foods. Singh et al. (2005) reported higher fracturability and hardness
values for the potato tuberswith closelypacked cell arrangements andhigher
starch content. The abundance of starch in the cells and the shape and size of
the starch granules are also important for the final texture of cooked aswell as
raw natural foods ( Andersson,Gekas,Lind,Oliveira, & Oste, 1994;
Martens & Thybo, 2000; McComber, Horner, Chamberlin, & Cox,
1994;vanMarle,Stolle-Smits,etal.,1997 ). Therefore, a good understand-
ing of texture requires sufficient knowledge of microstructural features such as
cell shape and size and cell wall characteristics. Cultivar type, physicochemical
composition, and postharvest storage are the important factors, which can
influence the cooking characteristics of potatoes and potato products
( Kaur, Singh, Singh, & Ezekiel, 2007; Liu, Tarn, Lynch, & Skjodt, 2007;
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