Starch, roots and tubers

Native starch granules exhibit three main types of X-ray diffractogram. The A type is characteristic of most starches of cereal origin the B t5q)e of potato (Figure 8.3), other root and tuber starches, and amylomaize starches and retrograded starch the C type of smooth pea and various bean starches. 

Plants and some algae store food in the form of starch. In plants, starch is mainly found in seeds, roots, and tubers as well as in stems, leaves, fruits, and even pollen. Grain seeds, such as corn kernels, contain up to 75% starch. Therefore, it is an important component of the carbohydrates in the diet and a very good source of energy for the body. Starch is found in foods such as cereal, pasta, and potatoes, and cornstarch is used to thicken sauces. Laundry starch is a liquid form of starch used to stiffen the collars and sleeves of shirts. An advantage of using it is that dirt and sweat will stick to the starch instead of the shirt textile fibers, with the result that collar rings are easily washed away with the starch. 

Table 10.6 compares the average size (DPn) and size distributions of six laboratory-purified amyloses and one commercial sample of potato amylose, which were determined by classic colorimetric and fluorescent-labeling techniques using 2-ami-nopyridine. The data by the two techniques are consistent and show that wheat and other cereal amyloses are smaller in size than those from root and tuber starches. The molar distribution technique indicated that wheat amylose contained two molecular species, compared with one for rice and com amyloses.209,210 Moreover, the molar size distributions for the cereal amyloses are much narrower than those of the tuber amyloses, and the cereal amyloses contain a preponderance of molecules of DPn < 1000 whereas the tuber amyloses contain 78-95% of molecules with DPn > 1000, and even 3-5% above DPn 10000. None of the amylose samples in Table 10.6 showed molecules with less than DPn 200, possibly because they had been purified as alcohol-inclusion complexes.209... 

Frese, L., Schittenhelm, S., and Dambroth, M., Development of base populations from root and tuber crops for the production of sugar and starch as raw material for industry, Landbauforschung Volkenrode, 37, 213, 1987. 

It is formed also by the hj drolysis of iiiulhi, a [lolysae-eharide which takes the jilacc of starch as a reserve material in the roots and tubers of many plants. Among these nuiy be mentioned decanijiaue Inula Ildcnium), dahlia. 

CGTase from B. clausii strain El 6 was specific for P-CD formation displaying a P-CGTase action. The distributions of a-, P-, and y-CDs were 0, 89, and 11%, respectively, on soluble starch. The starches from different botanical sources influenced quantities and types of CD formed. It was also observed that root and tuber starches were more accessible to CGTase action. The process of starch homogenization can interfere whit the CGTase action and, consequently, on the CD formation. The gelatinization of starches by the autoclave process improves the CD production, mainly for cereal starches. 

Weiss, R.F. and Finkelmann, A. 2000. Herbal Medicine , 2nd Ed. Thieme, Stuttgart Wheatley, C.C. and Bofu, S. 2000. Sweetpotato starch in China Current status and future prospects. In Cassava, Starch and Starch Derivatives (R.H. Howeler, C.G. Oates, and G.M. O Brien, eds), pp. 201-205. Proceedings of the International Symposium held in Nanning, Guangxi, China, November 11-15, 1996, A CIAT Publication, CIAT Re onal Cassava Program for Asia. Wheatley, C.C., Scott, G.J., Best, R., and Wiersema, S. 1996. Adding Value to Root and Tuber Crops , p. 166. CIAT, Cali, Colombia. 

As noted there are major differences between the root and tuber starches (potato and tapioca) and the cereal starches. Waxy starches are special varieties containing little or no amylose, e.g. waxy maize. Substances other than amylose and amylopectin are also present in starch, notably proteins, phosphorons, fats and lipids. 

Phosphoras structures and contents in starches vary with the botanical source, maturity and growing conditions of the plant. Most normal cereal starches contain phosphorus in the form of phospholipids, whereas phosphorus in root and tuber starches is in the form of starch phosphate monoesters [2],... 

The primary function of starch is to serve as energy storage and as a carbon source for de novo biosynthesis of macromolecules. Starch can accumulate temporarily in the chloroplast of cells found in photosynthetic tissue. Most starch is found in the storage organs such as the endosperm of seeds or in roots and tubers. 

The ratio of the two polysaccharides varies according to the botanical origin of the starch. The so-called waxy starches contain less than 15% amylose, normal starches 20-35% and high amylose starches more than about 40%. The moisture content of air-equilibrated starches ranges from about 10-12% (cereal) to about 14-18% (some roots and tubers). 

Starch is a polymer of glucose and is found mainly in the seeds, roots, and tubers of plants. Corn, wheat, potatoes, rice, and cassava are the chief sources of starch whose principal use is for food. 

Starch is a polyglycoside composed of glucose residues linked by alpha-glucosidic bonds. Starch is typically a reserve plant polysaccharide it is the form in which glucose is stored in the roots and tubers of plants. In animals, the reserve polysaccharide is a starch-like substance called glycogen. 

Starch occurs widely as a storage carbohydrate and is present in large amounts in some root and tuber vegetables. In Compositae (e. g., artichoke, viper s grass, bot. Scorzonera), inulin, rather than starch, is the storge carbohydrate. 

Cassava tubers are rich in carbohydrates (mostly starch), but low in proteins and most other nutrients. The raw roots are lower in water content and higher in calories than the other leading roots and tubers. Also, the various dried forms of cassava tubers are about as rich in food energy as the common cereal flours. Nutritional deficiencies may result if cassava is the predominant food in the diet unless the missing nutrients are obtained by consuming adequate amounts of certain other foods. For example, the Brazilians, who can afford to do so, mix cassava flour with meats and vegetables. 

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