Citrus fruit processing

FIGURE 5.2 Some operations of citrus fruit processing in relationship with recovery of essential oils and essences. Adapted from Girard and Mazza (1998) and Braddock (1999). 

Dried by-product from citrus fruit processing for juice production or canning. It consists principally of the pulp and can include the skin and pips (n = 1413). 

An examination of the developments in the design of citrus fruit processing machinery shows quite clearly that the quality of the juice was more important than the quality of the oil, the only exception being oil of bergamot. Nevertheless, oil quality improved during the last decades and complies with the requirements of ISO standards. The expressed pulp of the more valuable kind fruit is very often treated with high-pressure steam to recover additional amounts of colorless oils of variable composition. The kinds of fruit treated in this manner are bergamot, lemon, and mandarin. 

Developments continue on citrus fruit processing. The membrane configurations most often used in juice clarification are tubular membranes or hollow fibre modules, as well as plate and frame systems using flat sheet membranes. The traditional method of concentrating juices and purees has been evaporation, but nowadays reverse osmosis is proving successful. Reverse osmosis plant performance depends on juice viscosity, the osmotic pressure of the solution, and the constraints imposed by the need for a particular product quality. 

The world demand for citric add around 1900 amounted to some 10,000 tonnes per annum. This was realised by pressing citrus fruits and precipitation of the citric add as calcium titrate. An Italian, government-led cartel had virtual monopoly of this process and as such the price of citric add was very high. 

Ascorbic acid is photosensitive and unstable in aqueous solution at room temperature. During storage of foods, vitamin C is inactivated by oxygen. This process is accelerated by heat and the presence of catalysts. Ascorbic acid concentration in human organs is highest in adrenal and pituitary glands, eye lens, liver, spleen, and brain. Potatoes, citrus fruits, blade currants, sea buckthorns, acerola, rose hips, and red paprika peppers are among the most valuable vitamin C sources [1,2]. 

Cold-pressed essential oils from the peel are some of the most important by-products recovered during the processing of Citrus fruits. The presence of limonene in the aqueous discharges, with its antimicrobial activity [1], decreases the effectiveness of the waste treatment system and increases the time necessary for the biological breakdown of the organic matter produced in the peel oil recovery system [2,3]. Additional recovery of essential oils from waste water would increase industry s returns and reduce the pollution problems associated with the disposal of waste water [4,5]. Several methods for reducing the levels of residual essential oils in the aqueous effluent have been developed over the years [6-11]. 

As compared with the residues of DDT present within citrus peel (2), the relative significance of surface residues of DDT on citrus fruits is diminished by the fact that these are readily removed in large proportion by the usual packinghouse processing (5). 

Pome Fruit Types. As with citrus fruit types, the method of sample preparation was modified for the parathion studies. In the earlier studies the DDT-treated apples and pears were scrubbed in a warm 10% solution of trisodium phosphate, and all the peel was removed from the water-rinsed fruit with a household-type potato peeler. The pooled samples of peel and pulp were then processed independently to recover the contained toxicant for subsequent estimation. 

Essential oils are organic compounds derived from flowers, seeds, leaves, roots, resins, and citrus fruits. The structures of many fragrant compounds have been studied, and processes for making these valuable compounds in a laboratory have been developed. There are now approximately 5000 synthetically produced chemicals that are available to a perfumer. These chemicals include vanillin, rose oxides, and the damascenes, or rose ketones. 

Citric acid, which prior to 1922 was made entirely from citrus fruits and mainly in Italy, is now produced almost exclusively by the fermentation of sucrose by means of a mold, Aspergillus niger. At first pure sucrose was used for this process but more recently molasses has been used instead. Practically the whole of the world production of citric acid is used as such in medicinal preparations, in making soft drinks and in certain foods. The textile industries use small amounts, and it is also... 

About two thirds of the citrus produced worldwide is consumed as fresh fruit. Unfortunately, citrus utilised as fresh fruit cannot constitute a source of commercial flavours. However, in certain high-production countries such as the USA (Florida) and Brazil, the majority of the citrus crop is processed. In Florida over 90% of the orange crop is processed and is a major source for citrus flavouring material. Citrus fruits are processed primarily into juice, but oil from the outer layer of the peel, flavedo, and the condensate from making concentrated juice are also major sources of flavour products from citrus fruit. 

Exceptions to the simple definition of an essential oil are, for example, garlic oil, onion oil, mustard oil, or sweet birch oils, each of which requires enzymatic release of the volatile components before steam distillation. In addition, rhe physical process of expression, applied mostly to citrus fruits such as orange, lemon, and lime, yields oils that contain from 2-15% nonvolatile material. 

PMK Friar, SL Reynolds. The effect of home processing on postharvest fungicide residue in citrus fruit residues of imazalil, 2-phenylphenol and thiabendazole in home-made marmalade, prepared from late Valencia oranges. Food Addit Contam 11 57-70, 1994. 

M Runkel, M Bourian, W Legrum. Scopolin and skimmin as constituents of citrus fruits. Fruit Processing 7 213-216, 1997. 

In citrus fruits, where the outer skin or epicarp is a composite structure containing certain flavouring substances, it would be detrimental to juice quality if the fruit were subjected to direct pressure as is the case with the fleshy fruits, that is, soft fruits, pome fruits and stone fruits. Stone fruits, before being processed for juice separation, must first be separated from their stones, or pits, in order to facilitate ease of handling and to avoid unwanted notes in the finished... 

Comminutes. The process of comminution refers only to citrus products, where the oils that reside in the flavedo (coloured peel) have intense flavour characteristics. At its simplest, comminution involves taking a complete orange (or other citrus fruit) and making a pulp from it. This pulp will have a much more intense flavour than juice alone but because of the presence of much peel and albedo (pith) it would be unacceptable in taste to most consumers. Thus, the process of comminute production, developed in the immediate postwar years, is typically as set out in Figure 6.1. 

As citrus fruits and their products contribute substantially to the American diet and are consumed in great abundance, we believe the time is appropriate to review in detail some important nutritional and quality properties of this important fruit. Twenty-eight scientists joined with us to cover extensively subjects in the following areas nutrition and health quality as related to specific biochemical components effects of handling and processing quality control and evaluation regulatory implication and adulteration. 

The main sugars in the peel of citrus fruits are also sucrose, glucose and fructose, although a trace of free xylose was reported (13). The relative amounts of these sugars are shown in Table IV. These free sugars are also the major ingredients of cattle feed manufactured from citrus peel and processing residue, especially when citrus molasses is blended into the feed (14). 

Interest in pectin from a nutritional standpoint has increased with new evidence of its influence on several physiological processes. Long acknowledged as an effective antidote to diarrhea, pectin has now been found to be of possible benefit in control of cholesterol levels and in management of diabetes. As one of the richest potential sources of pectin, citrus fruits could enjoy enhanced nutritional status from these findings. 

The quality of extracted citrus juices depends on enzyme reactions that occur not only in the fruit during the development period, but also in the juice during processing. When juice is extracted from citrus fruit, enzymes are released from their normal restraint in the cell. Several of these enzymes catalyze reactions that adversely affect taste and appearance of the juice. Unless the reactions are controlled, the juice products will not meet the standards of quality set up by the USDA Food Safety and Quality Service. The two reactions of commercial importance are the hydrolysis of pectin to pectic acid, which clarifies juice, and the lactonization of limonoic acid A-ring lactone to the bitter compound, limonin. Research efforts to identify and characterize the reactions, to isolate and purify the enzymes, and to develop methods to control the reactions are described in this review. 

Mechanical harvesting. Efforts to develop systems to mechanically harvest citrus fruits, particularly oranges, have been in progress for several years. Usually, these systems have been developed to handle fruit destined for processed as opposed to fresh utilization. Some efforts, however, have been made to... 

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