Processed citrus juices

There is much that can be said in favor of the consumption of fresh fruits and vegetables in the daily diet. In much of the world, citrus is consumed primarily as the fresh fruit, but in the United States processed products are consumed as the major source of citrus in the diet. The main staple of processed citrus juices in the U.S. is frozen concentrated orange juice (FCOJ). 

The market for chilled citrus juices is one of the fastest growing segments of the domestic retail market, and now is second only to FCOJ in terms of volume consumption. Since its inception in the mid-fifties, this category for processed citrus juices has... 

Flavor changes that occur in citrus juices are the result of heat input into the product over time i.e., they are a function of temperature and time. It is for this reason that canned and bottled juices are generally less preferred by consumers than other processed citrus juices, e.g., frozen concentrates or chilled juices. The canned juices receive more heat input during pasteurization and they remain at relatively high temperatures for extended periods of time because they are discharged from the water coolers at temperatures near 40°C to facilitate drying and to inhibit rusting of the cans. It is well known that the rate of flavor deterioration increases with temperature, so canned juices are stored at a temperature as low as is economically practical before distribution at the retail level to extend their shelf life as much as possible. 

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. 

Citrus (oranges, lemons, grapefruit) is processed into juice and oil for human uses and into molasses and dried pulp for use as animal feed. The fruit is first washed with a detergent and rinsed with water. The oil is localized in oil sacs on the surface of the fruit. The surface is scarified under a water spray to form an emulsion of oil and water. The oil is recovered by centrifugation. Altered to remove high melting point fats, and dried with sodium sulfate, which is removed by filtration. 

Lee, H. S., and Coates, G. A. (1997). Vitamin C contents in processed Elorida citrus juice products from 1986-1995 survey. /. Agric. Food Chem. 45, 2550-2555. 

The main renewable resource for L-carvone is spearmint oil (Mentha spicata), which contains up to 75% of this flavour chemical. There also exists a synthetic process for the manufacturing of L-carvone, which is based on (-t)-limonene, which is available as a by-product of the citrus juice industry as a major component of orange peel oil (Scheme 13.4). The synthesis was developed in the nineteenth century and starts with the reaction of (-t)-limonene and nitrosyl chloride, which ensures the asymmetry of the ring. Treatment with base of the nitrosyl chloride adduct results in elimination of hydrogen chloride and rearrangement of the nitrosyl function to an oxime. Acid treatment of the oxime finally results in l-carvone. 

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... 

Nearly 3/4 of all vitamin C in an orange and 5/6 in a grapefruit is found in the peel (56b however, citrus juices and their products provide a major portion of the vitamin C in the American diet. Considerable variations in vitamin C content can be found in different citrus products due to such factors as varietys, maturity and cultural practices of the fruit (57J from which the products originate and to the processing practices and storage conditions of these products before they reach the consumer. 

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. 

Several postharvest treatments to citrus fruits have been tested in an effort to improve the quality of the extracted juice. Bruemmer and Roe subjected citrus fruits to anaerobic conditions for periods of 20 to 32 hours at 32.2 to 43°C (228, 229). This treatment reduced the titratable acidity and increased the Brix-acid ratio by about 10%. The decrease in acidity was accompanied, however, by a 20-fold increase in ethanol (229). Since the soluble solids-acid ratio is a major criterion of citrus juice quality, this procedure, if perfected, could allow earlier harvesting of fruit and a more consistent supply of fruit during the processing season. Bitterness of products from navel oranges, lemons, and grapefruit is related to limonin content. A 3-hour treatment of fruit with 20 ul ethylene/1 of air lowered the limonin content, reduced bitterness, and the juice was judged more palatable than juice from untreated fruit (230). 

Citrus Juice Processing as Related to Quality and Nutrition... 

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. 

Removal of citrate ion by an anionic ion-exchange process can be accomplished by exchange with hydroxyl ion and the subsequent formation of water, which is a component of juice and which can be removed by evaporation hence, it should be preferable to a method that relies on the addition of a neutralizing substance to a citrus juice. The ion-exchange process is illustrated in the following equation ... 

Citrus juices that are pasteurized at the lower temperatures, 65-66°C, can undergo clarification, i.e., a process of separation that results in a lower layer of liquid and sediment and an upper layer of clear liquid. This process is brought about by the natural enzyme, pectinesterase, that occurs in citrus fruits. Studies have shown that processing of the juice at temperatures of 170-210°F (76.7-99°C) for a fraction of a second to 40 seconds will destroy the pectinesterase activity in citrus juices (7-10). The temperature necessary to stabilize the juice is pH dependent. Juices at higher pH require higher temperatures for stabilization. With the new high-temperature short-time techniques and equipment, stabilization can usually be effected in a fraction of a second. Flash pasteurization can be accomplished in either a plate-type or a tube-type heat exchanger. 

Canned and bottled citrus juices are examples of products that are packed aseptically, and these processes have been used in the industry for many years. One of the newer processes for aseptic packaging employs a paperboard package that is sterilized with hydrogen peroxide prior to the form, fill, and seal operation. This process, developed by Tetra Pak Ab of Lund, Sweden, is in use in many parts of the world, but it has not yet been approved by the U.S. Food and Drug Administration for domestic use. 

The sugars, which contribute much to the acceptability of citrus juices, under adverse conditions can play a major role in the formation of off flavors that reduce the acceptability of the citrus juices and their products. The sugars, primarily the hexoses, can participate in "browning" reactions that cause darkening of the juice and these reactions give rise to components that are described generally as apricot-like or pineapple-like in flavor. In general,the more processed flavor that a citrus product exhibits, the less acceptable it becomes to the consumer. 

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