Sources of Lipids

All naturally occurring lipids from botanical sources (plants) or zoological sources (animals and humans) could potentially be used in the production of bioplastics. They have the same chemical structure and function in a very similar manner. Cholesterol (and its related esters) and fatty acids are commonly found in zoological sources, although the fats tend to be of a heavily saturated nature. It is feasible to create other products such as biodiesel from extreme sources including liposuction fat. However, a lack of volume and more importantly ethical approval have prevented their uptake further. The remainder of this chapter will focus on the use of triglycerides from plants and their related compounds for bioplastics production. 

Plants are used as the main sources of lipids for bioplastics production. Often used as energy storage in plants [1], triglycerides are mainly found in the seeds although they can also be observed in other parts, such as tubers [2], although this is a rare case. Some bioplastics have been synthesized from fish oils [3] but the lack of reliability in supply, cost and questions of the true sustainability of this route have restricted investigations in this area. 

In other cases, it is possible to find lipids as a waxy coating of leaves for example, cutin or in peanuts, where the entire plant is approximately 50% peanut oil [4]. 

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Various sources of lipid have been incorporated into ruminant diets to increase the energy density and provide the large amount of energy needed for slaughter animals to achieve market weight or for dairy cows to produce milk (see Milk and milkproducts). Fats also reduce the dustiness of feeds, increase the feedstuffs abiUty to pellet, and improve feed acceptabiUty. 

Intravenous lipid emulsions differ in their concentration (10%, 20%, and 30%), caloric density, natural source of lipids, and ratio of phospholipids to triglycerides (PL TG). Table 97-2 shows a comparison of commercially available intravenous lipid emulsions in the United States. The 10%, 20%, and 30% lipid emulsions provide 1.1 kcal/mL (4.6 kJ/mL), 2 kcal/mL (8.4 kJ/mL), and 3 kcal/mL (12.6 kJ/mL) with a PL TG of 0.12, 0.06 and 0.04 respectively. The lower PL TG indicates a lower phospholipid content and translates to abetter clearance of the 20% and 30% lipid emulsions compared with the 10% lipid emulsion.9 The 30% lipid emulsion is only approved for infusion in a TNA and should not be infused directly into patients. 

Identifying a specific natural source of lipids after GC/MS analysis is not always straightforward. The occurrence of mixtures, the unspecific FA composition of many lipid materials, the fact that materials may be physically handled during pretreatment before use and the deep changes induced by ageing, mean that extreme caution is required when interpreting FA profiles. 

Potatoes are not regarded as an important source of lipids, because the lipid content of the tuber is very low, ranging from 0.2 to 2 g (1.2 g on average) per kg on a fresh weight basis (OECD, 2002). The flesh of boiled potato cooked in skin without salt contains about 0.1 g total lipids, 0.03 g total saturated fatty acids, 0.002 g total monounsaturated fatty acids, and 0.043 g total polyunsaturated fatty acids per 100 g (USDA, 2007). The Adequate Intake determined for the essential n-6 and n-3 polyunsaturated fatty acids is for adults 11-17 and l.l-1.6g per day, respectively (Food and Nutrition Board, 2005). 

When trans-fatty acids are fed to rats with adequate amounts of essential fatty acids, they have little effect on growth, longevity, or reproduction, but when fed as the sole source of lipids they exaggerate the symptoms of essential fatty acid deficiency (111). An effect on the metabolism of long chain polyunsaturated fatty acids was noted however. 

The mechanisms behind lipid oxidation of foods has been the subject of many research projects. One reaction in particular, autoxida-tion, is consistently believed to be the major source of lipid oxidation in foods (Fennema, 1993). Autoxidation involves self-catalytic reactions with molecular oxygen in which free radicals are formed from unsaturated fatty acids (initiation), followed by reaction with oxygen to form peroxy radicals (propagation), and terminated by reactions with other unsaturated molecules to form hydroperoxides (termination O Connor and O Brien, 1994). Additionally, enzymes inherent in the food system can contribute to lipid oxidization. 

Five cases of hyperlipidemia have been reported in 12 patients who received propofol infusions 3-8 mg/kg/hour for 10-187 hours for sedation in an intensive care unit (946). Propofol was their only source of lipids. 

Lipids As the capacity of the stomach of newborns is very limited, lipids and fat are necessary to provide the large amounts of energy required by the newborn s high body growth rate. Milk fat is the major source of lipid that mammalian newborns use for accumulating body adipose tissue and for the development of their nervous system. The major lipids in milk fat are triglycerides, which represent more than 98 percent of the neutral lipids. From a quantitative point of view, there is no difference in the fat content in cow s (3.8 percent) and human milk (3.7 percent), but they do differ in their qualitative composition in fact, in cow s milk the predominant fatty acids are saturated acids, while polyunsaturated acids are the main fatty acids in human milk, as shown in Table 13.3. 

The principle problem of algae as sources of lipids is their high water (70-90%) and low lipid content. Despite their lipid content (-7%), the fatty acids of marine algae have aroused considerable interest among researchers for their nutritional value to other marine organisms, occurrence of bioactive conjugated fatty acids, and potential medical applications. The annual production of carotenoids from seaweeds is estimated to be approximately 100 million tons, of which fucoxanthin, the main carotenoids from brown seaweed, contributes more than 10% (Matsuno, 2001). 

Figure 2-5 Chromatogram of Milk Fat Fatty Acid Composition Analyzed as Butyl Esters on a 30-m Capillary Column. Source Reprinted from R.G. Ackman, Animal and Marine Lipids, in Improved and Technological Advances in Alternative Sources of Lipids, B. Kamel and Y. Kakuda, eds., p. 298, 1994, Aspen Publishers, Inc.

J. L. Weihrauch and B. B. Teter, Fruit and Vegetable By-product as Sources of Oil, in Technological Advances in Improved and Alternative Sources of Lipids, B. S. Kamel and Y. Kakuda, eds., Blackie Academic Professional, London, 1994, pp. 178-180. 

PhosphattdykhoHne (PC) and phosphatidylethanolamine (PE) are the major phospholipids of cell membranes. Table 6.1 lists the amount of lipid in cell membranes expressed as micrograms of lipid per milligram of membrane-bound protein. The membranes were isolated from cells of adipose tissue from rats that had been raised on a diet containing sunflower oil (100 g oil/kg diet) as the source of lipids. The diet was essentially free of cholesterol and phospholipids because plants do not contain cholesterol and the phospholipids of vegetable oils are removed during the refining process. 

The negative effects of LCTs on immune function have stimulated a search for new sources of lipids." " Medium-chain triglycerides (MCTs) may offer several advantages, especially for critically ill patients. MCTs are hydrolyzed and cleared more rapidly than... 

Our dietary intake comprises three macronutrients (protein, carbohydrate and lipid) and a large but unknown number of micronutrients (vitamins, minerals, antioxidants, etc.). Good health rests, in part, on an adequate and balanced supply of these components. This book is concerned with the major sources of lipids and the micronutrients that they contain. 

From these studies it emerges that the lipid biosynthetic pathways of the African trypanosomes are complex, differing both from the host and the malaria parasite, and rely heavily on an external source of preformed lipid. Host complex lipids bound to serum proteins, most likely lipoproteins and particularly HDL, are a source of lipid for African trypanosomes as they appear to be for Plasmodium. 

Reactions catalyzed by CYPs require several elements and generally, although not always, result in oxygenated metabolites. Successful in vitro reactions using microsomal tissues require NADPH and oxygen as essential cofactors. Purified CYP isoforms require a source of lipid, such as phosphatidylcholine, and the ncccs.sary coenzyme NADPH cytochrome P450 reductase. In some cases, other microsomal components, such a.s cytochrome bs, may also be required for optimal metabolic activity. 

Source of Lipids in the Diet Digestion and Absorption of Lipids Food Lipids as the Source of Energy... 

Edible nut seeds are a rich source of lipids and therefore they are calorie-dense (-500-700kcal/lOOg edible portion). In addition to lipids, nut seeds are a good source of quality proteins, certain minerals (such as selenium in Brazil nut) and vitamins (such as vitamin E in almond and hazelnut), and depending... 

Lipid oxidation is a major pathway for the formation of volatile compounds in roasted tree nuts. After the enzymes in the nuts (e.g., lipoxygenase) are inactivated by the high temperatures used for roasting, autoxidation becomes the principal source of lipid breakdown [66]. Lipid degradation reactions are not necessarily deleterious to flavor [67], and some aldehydes and ketones (e.g., n-aldehydes and 2-aIkanones) produced during roasting may impart desirable sweet, fruity, and pungent aroma notes to roasted tree nuts. 

LA), or y-linolenic acid (18 3n-3, group ALA) (Nu-Chek-Prep, Elysian, MN) as the only source of lipids. These fatty acids were esterified according to Bordeaux et al. (8) and added to the diet just before feeding. The stability of the ethyl esters, under conditions including exposure to air, was confirmed by gas-liquid chromatography (GLC). Food intake was measured daily and body weight weekly. After 15 d of this regimen, the rats were killed, and liver, kidney, and brain preserved. 

A6-Desaturase Gene Expression. In liver, A6D gene expression (Fig. 4) increased, irrespective of the source of lipids. Oleic acid provided in the diet as the only source of lipids yielded the highest induction of A6D gene expression. LA had a greater effect than ALA on this gene. However, in brain (Fig. 5) and kidney (Fig. 6), A6-desaturase expression did not change, irrespective of the fatty acid provided. 

Together, these results point out that purified oleic acid, linoleic acid, and a-linolenic acid, provided as the only source of lipids, modulate A6-desaturase activities and ex-... 

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