Citrus fruit parts

Hydroxycinnamic acids (HCAs), comprising p-coumaric, ferulic, caffeic and sinapic, and their bound forms, are found in citrus fruit parts (d5). During processing and storage of citrus juices, vinyl phenols are produced from the free HCA by acid-catalyzed decarboxylation. The decarboxylation of all HCAs would potentially produce p-vinyl phenol (from p-coumaric acid), p-vinyl guaiacol (ferulic acid), p-vinyl catechol (caffeic acid) and 3,5-dimethyl-4-hydroxystyrene (sinapic acid). P-vinyl phenol and p-vinyl guaiacol have been identified in processed citrus juices, but p-vinyl catechol and 3,5-dimethyl-4-hydroxy styrene have yet to be reported. Vinyl phenols are unpleasant smelling compoimds with very low perception thresholds their presence adversely affects acceptability of citrus juice products. 

Polyterpenes. Polyterpenes is one of the first classes of non-polar tack-ifiers to be developed. Terpene monomers are a by-product in the extraction of rosin from wood stumps or tree sap, and from the extraction of oils from citrus fruits. The latter is the dominant source. As such, polyterpene prices generally mirror those of citrus fruits, which fluctuate substantially from one growing season to the next. Terpenes like rosin are cyclic, see Fig. 6, which is partly responsible for their excellent solvent properties. 

Rouse, A.H. 1953. Distribution of pectinesterase and pectin in component parts of citrus fruits. Food Technol. 7 360-362. 

When dissection of fruits was involved in the preparation of the samples, the values reported represent the parts per million of toxicant based on fresh weight of the indicated component only and not of the weight of the whole fruit. As separated in these studies the peel of most citrus fruits constitutes approximately one sixth the weight of the whole fruits. 

Consistent with the definition of terms adopted for the discussion in this series of papers of integral phases of the residue studies being conducted by the Division of Entomology, University of California Citrus Experiment Station (2, 13-15), the following distinctions are noted Residues may be specified as pretreatment, posttreatment, harvest, or ultimate. The latter refers to the residue on or in foodstuffs, whether fresh or processed, at the time of consumption (2, 13). The location of residues with reference to fruit parts may be extra-surface (external to the cuticle) or subsurface. Subsurface residues may be differentiated with reference to actual location as cuticular residues or specified intracarp residues. Residues in the cuticular layers or in any of the cellular structures or matrices are herein indicated as subsurface (penetrated) residues (2, 13). 

Essential oil, also defined as essence, volatile oil, etheric oil or aetheroleum, is a complex mixture of volatile constituents biosynthesised by living organisms. Essential oils can be liberated from their matrix by water, steam and dry distillation, or expression in the case of citrus fruits [1-5]. Their occurrence and function in nature is still a question and the subject of ongoing research. However, there is evidence that organisms produce essential oils for defence, signalling or as part of their secondary metabolism. As a consequence essential oils comprise an important bio resource for renewable natural products [1-25]. 

The use of terpenoids, usually as mixtures prepared from plants, dates from antiquity. The several essential oils produced by distillation of plant parts contained the plant essences. These oils have been employed in die preparation of perfumes, flavorings, and medidnals. Examples are oils of clove (local anesthetic in toothache), lemon (flavoring), lavender (perfume), and juniper (diuretic). Usually essential oil production depends on a simple technology which often involves steam distillation of plant material The perfume industry of Soudiem France uses somewhat more sophisticated procedures in the isolation of natural flower oils since these oils are heat sensitive. The separation of oils from citrus fruit residues m California and Florida is done by machine. 

Figure 3.3 Component parts of a typical citrus fruit.

Citrus fruit varieties are grown for commercial use in many parts of the world. Originating in the southern and eastern regions of Asia, China and Cochin China,... 

The energy-supplying nutrients are generally carbohydrates, protein and fat. While citrus products provide little protein and fat, their contribution of carbohydrate is an essential part of the nutritive value of citrus. The proximate composition of several kinds of citrus fruits (8) are shown in Table II. Because... 

Table VI. Percentage Distribution of Various Polysaccharide Fractions in Different Com-ponent Parts of Citrus Fruit ...

The organic acids of citrus fruit include a group of carboxylic acids (23) with different acids predominant in various component parts of the fruit. Citric acid is the main acid in the juice, representing from 80 percent of the total acidity in juice from ripened oranges, about 90 percent of that of grapefruit and nearly all of that of lemon. The pH of the juice greatly affects the sourness of the product (24) and is, in turn, affected by the cations, especially potassium. The major acids in citrus peel are malic, oxalic (25), malonic (26), and quinic (27). 

Citrus fruits, especially certain of their component parts, constitute one of the richest sources of pectin. On a dry weight basis, as much as 30% of orange fruit albedo may be pectin (8). The rag, comprising the fruit core and segment membranes after juice extraction, is also a rich source. Since pectin is a cell wall component, it follows that comparatively little would be present in juice expressed from fruit. For example, concentrations ranging from 0.01 to 0.13% in orange juice have been reported (15). Much of this would be present as cell wall fragments and particulate material in juice pulp and cloud. 

Were it not for the processing of citrus fruits, this rich source of nutritious food, in the forms of juices and drinks, would be available to us for only limited periods of time throughout the course of any year. Processing techniques practiced today in the citrus industry ensure the availability of a continuous supply of citrus juices and their allied products to people in all regions of the United States and, indeed, in many parts of the world. 

The increased awareness on the part of consumers about nutrition has led to an increased demand for citrus juices and products, a demand that is greater today than it has ever been. This has led to a tremendous growth within the citrus industry, and developing nations of the world that have climates suitable for the production of citrus fruits have benefitted tremendously from this consumer demand. Brazil is a prime example. The growth of the citrus industry in Brazil has been a great economic factor in... 

The species Cit us aurantium produces different essential oils depending upon which part of the plant is used. Expression of the outer peel of the almost ripe citrus fruit produces the Bitter orange essential oil, steam distillation of leaves and twigs produces Petitgrain, while steam distillation of the freshly picked flower produces Neroli or orange blossom essential oil. 

Ranganna S, Govindarajan VS, Ramana KV. Citrus fruits— varieties, chemistry, technology, and quality evaluation. Part 11. Chemistry, technology, and quality evaluation. A. Chemistry. Crit Rev Food Sci Nutr 1983 18(4) 313-86. 

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