Foods, carbohydrates cellulose

Simple carbohydrates (cellulose, starch, glucose, fructose, inulin, chitin, etc.) extracted from biomass, oligo- and polysaccharides of microbial or algal origin and derivatives thereof play a very important role in many sectors ranging from textiles and specialty chemicals to cosmetics, and food and feed industries. Large-scale carbohydrate-based processes in these sectors are well established and based on relatively simple chemical or biotechnological... 

Much current research focuses on the formation of bioethanol from cellulosic plants, plants that contain the complex carbohydrate cellulose. Cellulose is not readily metabolized and so does not compete with the food supply. However, the chemistry for converting cellulose to ethanol is much more complex than that for converting corn. Cellulosic bioethanol could be produced from very fast-growing nonfood plants, such as prairie grasses and switchgrass, which readily renew themselves without the use of fertilizers. 

It is well known that even complex carbohydrate mixtures (found in food or urine samples) can be separated by TLC [10]. Although many different stationary phases are nowadays commercially available, there are in practice only three suitable layers for the separation of carbohydrates cellulose, silica, and aminopropyl bonded silica [3]. 

There are three chemical compounds that form the building blocks of food carbohydrates, hits (or hpids), and proteins. Carbohydrate molecules, which are found in fruits, vegetables, starches, and dairy products, consist of atoms of carbon, hydrogen, and oxygen, chemically bonded in a ratio of 1 2 1. Monosaccharides and disaccharides such as glucose, fructose, and sucrose have just one or two molecules of this kind and are known as simple sugars. Polysaccharides like starch, glycogen, and cellulose (an important component of dietary fiber) have several carbohydrate molecules and are known as complex... 

Historically, dietary fiber referred to iasoluble plant cell wall material, primarily polysaccharides, not digested by the endogenous enzymes of the human digestive tract. This definition has been extended to iaclude other nondigestible polysaccharides, from plants and other sources, that are iacorporated iato processed foods. Cellulose [9004-34-6] (qv) is fibrous however, lignin [9005-53-2] (qv) and many other polysaccharides ia food do not have fiberlike stmctures (see also Carbohydrates). 

Carbohydrates occur in every living organism. The sugar and starch in food and the cellulose in wood, paper, arid cotton are nearly pure carbohydrates. Modified carbohydrates form part of the coating around living cells, other carbohydrates are part of the nucleic acids that carry our genetic information, and still others are used as medicines. 

At one level, life can be regarded as a collection of hugely complex reactions taking place between organic compounds in oddly shaped containers. Many of these organic compounds are polymers, including the cellulose of wood, natural fibers such as cotton and silk, the proteins and carbohydrates in our food, and the nucleic acids of our genes. 

Heterogeneous catalysts, particularly zeolites, have been found suitable for performing transformations of biomass carbohydrates for the production of fine and specialty chemicals.123 From these catalytic routes, the hydrolysis of abundant biomass saccharides, such as cellulose or sucrose, is of particular interest. The latter disaccharide constitutes one of the main renewable raw materials employed for the production of biobased products, notably food additives and pharmaceuticals.124 Hydrolysis of sucrose leads to a 1 1 mixture of glucose and fructose, termed invert sugar and, depending on the reaction conditions, the subsequent formation of 5-hydroxymethylfurfural (HMF) as a by-product resulting from dehydration of fructose. HMF is a versatile intermediate used in industry, and can be derivatized to yield a number of polymerizable furanoid monomers. In particular, HMF has been used in the manufacture of special phenolic resins.125... 

Both in the USA and the EU, the introduction of renewable fuels standards is likely to increase considerably the consumption of bioethanol. Lignocelluloses from agricultural and forest industry residues and/or the carbohydrate fraction of municipal solid waste (MSW) will be the future source of biomass, but starch-rich sources such as corn grain (the major raw material for ethanol in USA) and sugar cane (in Brazil) are currently used. Although land devoted to fuel could reduce land available for food production, this is at present not a serious problem, but could become progressively more important with increasing use of bioethanol. For this reason, it is important to utilize other crops that could be cultivated in unused land (an important social factor to preserve rural populations) and, especially, start to use cellulose-based feedstocks and waste materials as raw material. 

Humans lack enzymes to hydrolyse cellulose, and some odier carbohydrates in food. However, bacteria in the intestine can hydrolyse and ferment some of this carbohydrate to produce short-chain fatty acids, which are used by the colon and the liver. It is estimated that for each gram of unavailable carbohydrate in the diet, 8.4 kJ of energy is made available in this way, although this is influenced by factors such as ripeness of fruit or the way leguminous seeds are cooked. Nonetheless, these effects will be small and can be ignored unless the amount of such carbohydrate is high or very accurate results are required. (The subject of unavailable carbohydrate and fibre in the diet is discussed in Chapters 4, 6 and 15). 

Natural feedstocks must serve many human purposes. Carbohydrates are valuable raw materials due to their actual or potential value. For example, protein plants are already utilizing rapidly reproducing reengineered bacteria that metabolize cellulose wastes converting it to more protein-rich bacteria that are harvested and then used as a protein source feed-meal for animals. Further, natural materials can be used in applications now largely reserved only for synthetic polymers. Sufficient natural materials are available for the supply of both food and polymer needs. 

Many of the molecules that make up living organisms are polymers, including DNA, proteins, the cellulose of plants, and the complex carbohydrates of starchy foods. We leave a discussion of these important biological molecules to Chapter 13. For now, we focus on the human-made polymers, also known as synthetic polymers, that make up the class of materials commonly known as plastics. 

Carbohydrates are of tremendous importance to all of us. They make up a large part of our food supply in the form of sugars and starches. Another carbohydrate called cellulose helps to clothe us (cotton. linen) and shelter us (wood). 

Dietary Fiber. Dietary fiber is a broad term that encompasses the indigestible carbohydrate and carbohydrate-like components of foods that are found predominantly in plant cell walls (see Carbohydrates). It includes cellulose lignin, hemicelluloses. pentosans, gums, and pectins. 

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