Use in juice clarification

Enzymes are used also in fruit juice manufacturing. Addition of pectinase, xylanase, and ceUulase improve the liberation of the juice from the pulp. Pectinases and amylases are used in juice clarification. Similarly enzymes are widely used in wine production to obtain a better extraction of the necessary components, and thus improving the yield. Enzymes hydrolyze the high molecular weight substances like pectin. 

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 enzymes used for juice clarification are almost exclusively pec-tolytic. The reasons for the clarification effect are as follows. Pectin stabilizes the suspended solids in the juice. Through addition of the enzyme, the pectin is converted to a dissolved form and broken down. This is associated with a significant decrease in viscosity. In addition, pectins that have been made soluble act as protective colloids for many of the suspended particles. As soon as the protective effect of pectin is lost, these suspended particles coagulate and are precipitated. A significant decrease in viscosity is accompanied by a significant increase in filtration performance. 

Sterilization and Particle Removal (Beverages). MF has been used extensively in the filtration of wine and beer. It is also currently used in the clarification of cider and other juices. 

These polymers are mostly applied in the paper industry for wet-strength papers usable in neutral of alkaline systems instead of the urea-formaldehyde resins requiring acid conditions for crosslinking. PolyEI increases retention of dyes, pigments and fillers. PolyEI is known as a powerful flocculant used in the clarification of fruit juices and in water treatment. It removes effectively clays, colloidal acids, pectines and tannines from water. Commercially available polyEI have molecular weights in the range Mn = 600 to 100000 60). 

A reactor with such a configuration was used in the clarification of fruit juice by elimination of pectin by the enzyme pectinase. The pectin, which is present in colloidal form, aggregates in the presence of the enzyme and settles, leading to easy physical clarification (Shao et al., 1989). 

Rhamnogalacturonase may be useful in the prevention of haze formation in apple Juice concentrates. In combination with other enzymes it mi t improve liquefaction, resulting in increase juice yield and clarification. 

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). 

Decanters are frequently used in conjunction with disc-stack-type centrifuges in the pre-preparation of clear juices and juice concentrates, where the initial decanter treatment results in a partially clarified juice with a low level of suspended solids. This is followed by a clarification stage using a disc-stack whereby the solids are thrown outwards from the through-flow juice stream into a solids-holding space and automatically discharged therefrom as and when an optimum level of solids is reached (see Figure 3.6). 

Juice solids have a critical effect not only on wine quality (discussed under juice clarification) but also on yeast activity. A juice that is too clean, from excessive pectic enzyme treatment, filtration, or centrifuging, may have difficulty completing fermentation. Groat and Ough (24) and others have reported that juice solids levels below 0.1 to 0.5 percent resulted in slower fermentations. Levels of 0.5-2.5 percent solids are used commonly in the North Coast. 

Such applications appear to be more attractive for the use of bioreactors than traditional uses of endopeptidases for chillproofing beer, juice clarification, and curd formation in cheesemaking which currently use well established soluble enzyme processes. In the case of curd formation, hydrolysis of micellar k-casein by immobilized chymosin is questionable (56). 

Pectic enzymes are used commercially in the clarification of fruit juices and wines and for aiding the disintegration of fruit pulps. By reducing the large pectin molecules into smaller units and eventually into galactur-onic acid, the compounds become water soluble and lose their suspending power also, their viscosity is reduced and the insoluble pulp particles rapidly settle out. 

ENZYMATIC HYDROLYSIS OF STARCH. Starch is a substance used for storing energy reserve in plants, where it is deposited in the form of starch granules. Starch may be noticed in fruit juice as a milky haze. This haze disappears when the juice is heated, but re-appears after it is cooled to less than 10°C. Like pectin, starch has a protective colloid effect on suspended particles and thus makes juice clarification more difficult. 

Mud. The material removed from the filters during clarification of the juice contains the settled insoluble solids. The mud is returned to the fields as fertilizer. Some sugar factories extract a crude wax from the filtered mud, which is used in the manufacture of polishes. 

Amino acid production by fermentation started around 1960 in Japan. Initially glutamic acid was the main product. It was sold as sodium salt, monosodium glutamate (MSG), a flavor enhancer on oriental cuisine. Other amino acids soon followed. They are used in food and feed to increase the efficiency of low protein substrates. Microbiologically produced enzymes were introduced around 1970. They are used in grain processing, sugar production, fruit juice clarification, and as detergent additives (Table 9.1). 

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