Fruit clarification

There are many ancillary uses of cellulase in food processing. I need only mention a few examples involving the extraction of essential oils and flavoring materials, tenderizing fruits, clarification of juices, and improvement of filterability of vanilla extracts. Many other examples are given in this volume. 

Papain is a cysteine protease isolated from the latex of the immature fruit and leaves of the plant Carica papaya. It consists of a single 23.4 kDa, 212 amino acid polypeptide, and the purified enzyme exhibits broad proteolytic activity. Although it can be used as a debriding agent, it is also used for a variety of other industrial processes, including meat tenderizing and for the clarification of beverages. 

PM seems to occur in small amounts in the vegetative tissues of all higher and lower plants investigated. It is very abundant in the tomato fruit,60 orange flavedo and albedo,21 the tobacco plant,61 eggplant62 and alfalfa it usually occurs in the commercial fungal pectinase preparations that are manufactured for the clarification of fruit juices.25 In the natural products in which the enzyme is found, the major portion of it is usually strongly adsorbed on the water-insoluble cellular components of the tissue macerates.60 62 68... 

The super-centrifuge is used for clarification of oils and fruit juices and for the removal of oversize and undersize particles from pigmented liquids. The liquid is continuously discharged, but the solids are retained in the bowl and must be removed periodically. 

Two broad areas of application for xylanolytic enzymes have been identified (1). The first involves the use of xylanases with other hydrolytic enzymes in the bioconversion of wastes such as those from the forest and agricultural industries, and in the clarification and liquification of juices, vegetables and fruits. For these purposes, the enzyme preparations need only to be filtered and concentrated as essentially no further purification is required. Several specific examples of applications involving crude xylanase preparations include bioconversion of cellulosic materials for subsequent fermentation (2) hydrolysis of pulp waste liquors and wood extractives to monomeric sugars for subsequent production of single cell protein (3-5). Xylose produced by the action of xylanases can be used for subsequent production of higher value compounds such as ethanol (6), xylulose (7) and xyIonic acid (8-9). 

Some, but not all, fruits that are regarded as nonclimacteric are characterized by low respiratory activity.543 It should be noted that Trout and coworkers545,546 expressed doubt of the generally accepted classification of citrus fruits as nonclimacteric. Clarification of whether these and other fruits, such as fig, grape, strawberry, and pineapple, exhibit a truly nonclimacteric pattern of ripening may come from further study. 

Laties and associates589-592 provided evidence for an alternative, cyanide-resistant path of respiration in avocado mitochondria. Uncouplers were considered to stimulate glycolysis to the point where the glycolytic flux exceeds the oxidative capacity of the cytochrome pathway, with the result that the alternative pathway is engaged. However, these authors concluded that the alternative pathway is not required in order to sustain the elevated rate of respiration that characterizes the climacteric. Clarification of the role, if any, of this alternative pathway in fruit ripening awaits further study. 

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. 

Pectinase fungi pressing clarification wine, fruit juice... 

Figure 6.24 Ultrafiltration flux in apple juice clarification as a function of the volumetric feed-to-residue concentration factor. Tubular polysulfone membranes at 55 °C [27]. Reprinted from R.G. Blanck and W. Eykamp, Fruit Juice Ultrafiltration, in Recent Advances in Separation Techniques-III, N.N. Li (ed.), AIChE Symposium Series Number 250, 82 (1986). Reproduced by permission of the American Institute of Chemical Engineers. Copyright 1986 AIChE. All rights reserved...

Krystynowicz A, Bielecki S, Czaja W, Rzyska M (2000) Prog Biotechnol 17 (Food Biotechnology) 323 Application of bacterial cellulose for clarification of fruit juices... 

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