Starch cell wall preparation

Despite the elaborate washing procedures usually employed, cell-wall preparations may also frequently be contaminated with cytoplasmic constituents that sediment with the walls after tissue homogenization. Starch grains and proteins are particularly difficult to remove in this respect. Both incubation with purified alpha amylase (EC 3.2.1.1)55,101 and extraction with chloral hydrate118 have been utilized for removal of starch from cell-wall preparations. Pronase57,101 has been used to remove proteins. 

Grain legumes have also been processed into refined starch (10,11) and protein isolates (12,13,14) by procedures derived from the traditional corn starch and soybean protein industries (15). However, comparative data on product yields, composition and losses have not been published. A commercial plant for the wet processing of field pea into refined starch, protein isolate and refined fiber has been established in Western Canada. Little is known about the characteristics of the protein isolate or refined fiber product. Water-washed starch prepared from the air-classified starch fractions of field pea (16,17) and fababean (6) have been investigated for certain physico-chemical and pasting properties. Reichert (18) isolated the cell wall material from soaked field pea cotyledons and determined its fiber composition and water absorption capacity. In addition, the effects of drying techniques on the characteristics of pea protein Isolates have been determined (14). 

With the exception of starch, many biopolymers cannot provide nutrition for humans and other omnivorous animals. In human foods biopolymers are used as additives that can improve texture, viscosity, fiber content, and other properties of prepared foods, without providing direct nutritional values. Examples of such utilization are the addition of pectins, agar, and other gums to foods to achieve thickening and gelling effects. Another example of potential large-scale utilization of cell wall biopolymers is the dramatic improvement in the texture and rising of breads prepared from com and other starches by the addition of xylans (78). 

Rice endosperm cell walls have been prepared by grinding the rice flour (obtained from the milled grains) to pass through a 50-mesh sieve and then treating the flour sequentially as follows (1) with cold water and then 1 1 ethanol/ether to defat the flour, (2) with a-amylase to remove starch and isolate the water-soluble polysaccharides from the supernatant fluid,... 

In this chapter an attempt has been made to discuss the methods available for the isolation and analysis of higher plant cell walls. Because the structures and properties of the cell wall polymers from various tissue tyjDes show considerable differences, it is emphasized that, where possible, separation of the tissues in a plant organ prior to preparation of the cell walls is desirable. Attention is drawn to the problems associated with coprecipitation of intracellular compounds with cell wall polymers, particularly in view of the occurrence of small amounts of proteoglycan and proteoglycan-polyphenol complexes in the walls and the covalent attachment of phenolics and phenolic esters with some of the cell wall polymers of parenchymatous and suspension-cultured tissues. The preparation of gram quantities of relatively pure cell walls from starch- and protein-rich tissues is discussed at some length because of the importance of dietary fiber in human nutrition and an understanding of the composition, structure, and properties of dietary fiber would be hampered without such methods (Selvendran, 1984). 

Figure 2. Immunolocalization of carbonic anhydrase. Sections of the anterior region of Chlamydomonas. prepared as described previously, show the same pattern of gold particle distribution. Significant staining of the cell wall (cw) even in the region of flagella (fl) attachment is apparent. Some non-specific staining of the starch grains was also found to occur with either pre-immune serum or with the polyclonal antibody directed against carbonic anhydrase.

NSP, by definition, includes all the plant polysaccharides other than starch. For the reasons given above, NSP are divided into two broad classes in the classification and measurement scheme described here (Table 1) (1) the cell-wall NSP, which impart rigidity, and encapsulate and control the release of other nutrients, and (2) other NSP, including gums and refined preparations of cell-wall material, which occur in foods mainly as additives. There is no endogenous human enzyme for the hydrolysis of NSP, which are therefore nonglycemic, and all become available for fermentation in the large intestine. 

The purity of the wall preparations that have been studied can also be questioned. Even though elaborate washing of the wall preparations is customary, the walls may be contaminated by some of the cytoplasmic components which attach to or sediment with the walls following tissue homogenation. Starch grains are an example of a difficult to remove cell wall contaminant. 

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