Production of fruit juices

A large spectrum of berries and fruits are used in the production of fruit juice products. The range of products is substantially extended by an additional (fermentation) process to produce alcohol, and transform the fruit into wine. Enzymes, some of them proteolytic, are used to increase the yield of fruit juice during extraction, and to produce the required degree of clarity for the final product. 

Pectinases These enzymes carry out the hydrolytic degradation of the D-glycosidic linkage in pectins. The latter substances, also known as pectic substances, are polymeric components of plant cell walls and. like starch, are composed of sugar residues linked by glycosidic bonds. The chemistry is the same as that shown for the amylases previously described. The main application of pectinases is in the production of fruit juices, wines, and certain other food products. 

This chapter will not provide the background to the production of fruit juices and nectars, as that is dealt with elsewhere in this volume. However, fruit juices and nectars represent the largest volume of non-carbonated beverages that are sold in almost every marketplace. It is therefore appropriate that some aspects of these products, particularly those relating to processing and packaging, are mentioned here. 

An inexpensive oil which may have been produced by a variety of methods. An inferior qualitf essential oil is produced in large quantities from the by-products of fruit juicing processes. 

One of the most useful methods involves the use of L-ascorbic acid as a reducing agent. This is practiced extensively in the commercial production of fruit juices and purees. The ascorbic acid reacts with the o-quinones and changes them back into o-diphenols (Figure 10-14). 

The application of ceramic membranes in the production of fruit juices is a well established technique [3,6,12,14,44-50]. A very wide range of fruit juices is designated (apple, pear, peach, orange, grapefruit, pineapple, kiwi fruit, strawberry, cranberry, carrot, beet) the clarification of apple juice seems to be the main application [6,14,44r-49]. 

Osmotic distillation is a relatively new membrane separation process, which is used primarily for the dewatering of liquid food products. The majority of reported applications have involved the production of fruit juice concentrates. The main advantage of OD over vacuum distillation, which is the conventional method for concentrate production, is the preservation of product integrity. Osmotic distillation is operated at mild temperatures (typically ambient), and thereby produces concentrates that are free from the effects of thermal degradation. Also, the delicate volatile flavor and fragrance components that are essential to consumer acceptance of fruit juice concentrates are largely retained. 

In the production of fruit juice, wine, beer, and other beverages, the raw juice is in a slurry (known as a mash ) with solid fruit. The juice is separated from the fruit by a combination of filtration and/or centrifugation. The separation operation is a cost trade-off the more powder, time, and wash water used, the higher the yield of juice, but the more costly the process. There are also trade-offs of clarity and yield. 

The industrial production of fruit juices entails a number of technological treatments that can affect the phenolic compounds of the processed products and their antioxidant potential. These treatments include enzymatic digestion, concentration, heat treatment, filtration, etc. 

Pectin esterase from Aspergillus niger Pectin methyl ester —r Pectinic acid + CH3OH Removal of pectin sheaths from plant fibers removal of cloudiness in fruit juices and beer production of fruit juices and purees. 

Production of fruit juice involves the processing steps fruit preparationn and the extraction, treatment and preservation of the juice. 

Pomace is the residue from the production of fruit juices. Citrus fruits and apple pomace are used for... 

Pectins are also responsible for the consistency of sterilised fruits and vegetables, for the pressabiUty of oilseeds, the filterabiUty of fruit juices and the formation of hazes in fruit juices. Some manufacturing processes, for example in the canning industry, use pectolytic enzymes of microbial origin to increase the yield in the production of fruit juices and to maintain their clarity. Pectolytic preparations have also found use in the oenological industry, sugar industry and other sectors. 

Juices. There has been a great increase in the production of fruit juices since the end of World War II. The large volumes of these products have tended to keep prices down, so... 

The production of fruit juices involves (1) extraction of the juice by various types of cmshing or squeezing processes, (2) removal of undesired fmit parts (pulp, rind, se s, etc.) from the juice by passage through screens and/or other equipment, and (3) treatment of the refined juice by filtration, heat, or other means to prevent clouding, fermentation, and other types of deterioration during storage. 

Even if these liquefaction processes are still not accepted worlwide (for instance in Europe), they should grow within the next few years. We do really believe that they are the processes of the future, and especially the process of pressing / pomace liquefaction because it is an easy process, it allows the production of quality juice combined with high yields within a great flexibility. Such high yields, low production cost and flexibility to process different fruits make that fruit juice producers are more and more choosing the pomace liquefaction. 

Since many years, pectolytic enzymes have been widely used in industrial beverage processing to improve either the quality and the yields in fruit juice extraction or the characteristics of the final product [1,2]. To this purpose, complex enzymatic mixtures, containing several pectolytic enzymes and often also cellulose, hemicellulose and ligninolytic activities, are usually employed in the free form. The interactions among enzymes, substrates and other components of fruit juice make the system very difficult to be investigated and only few publications are devoted to the study of enzymatic pools [3-5], An effective alternative way to carry out the depectinisation process is represented by the use of immobilized enzymes. This approach allows for a facile and efficient enzymatic reaction control to be achieved. In fact, it is possible to avoid or at least to reduce the level of extraneous substances originating from the raw pectinases in the final product. In addition, continuous processes can be set up. 

Other assays have been used to evaluate the antioxidant activity against H202 of several plant-based products, namely, fruit juices from different cultivars of berries (Wang and Jiao 2000), fractions rich in phenolics isolated from the aqueous by-products obtained during the milling of oil palm fruits (Balasundram and others 2005), cherry laurel fruit and its concentrated juice (Liyana-Pathirana and others 2006), and strawberries and blackberries treated with methyl jasmonate, allyl isothiocyanate, essential oil of Melaleuca alternifolia, and ethanol (Chanjirakul and others 2007). 

Antioxidant capacity can be measured by several techniques, each of which has its own limitations. Antioxidant capacity of fruit juices and purees was evaluated by the DPPH method (which measures the radical-scavenging activity against a nonphysio-logical free radical), and treatment of these products with PEF or HHP resulted in losses... 

Pectin is used in foods in two forms, high methoxyl pectin and low methoxyl pectin. High methoxyl pectin is the form normally found in fruit while low methoxyl pectin is a chemically modified pectin. Pectins are acidic polysaccharides that occur in the cell walls of fruit. The commercial source of pectin is either citrus peel or apple pomace. The citrus peel is the residue from the production of citrus juices while apple pomace is the residue of cider production. Thus pectin is a by-product of either cider or fruit juice production. 

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... 

Crystallisation by freezing, or freeze crystallisation, is a process in which heat is removed from a solution to form crystals of the solvent rather than of the solute. This is followed by separation of crystals from the concentrated solution, washing the crystals with near-pure solvent, and finally melting the crystals to produce virtually pure solvent. The product of freeze crystallisation can be either the melted crystals, as in water desalination, or the concentrated solution, as in the concentration of fruit juice or coffee extracts. Freeze crystallisation is applicable in principle to a variety of solvents and solutions although, because it is most commonly applied to aqueous systems, the following comments refer exclusively to the freezing of water. 

Essential oils are to be distinguished from the so-called distillates which are ethanol-containing products that are obtained from plant materials by distillation with ethanol or with ethanol-water mixtures. Essence oils are defined as essential oils that separate from the aqueous phase in the distillation receiver during the distillative concentration of fruit juices (usually citrus juices). 

The aroma of intact black currant fruit is mostly produced by anabolic pathways of the plant, and production of fruit volatiles occurs mainly during a short ripening period [112]. The aroma profile of black currant shares similarities with that of other berry fruits, although terpenes are more abundantly present in black currant [107]. Black currant is mainly used for the production of juice. Over 150 volatile compounds have been reported from either black currant berries and/or juice, of which the major groups are monoterpenes, sesquiterpenes, esters and alcohols [107]. Processing of berries to juice has been shown to lead to major changes in the aroma composition [113-118]. 

The world of aroma compounds is becoming more and more complex. In the early days people used aromatic products like fruit juices or fruit juice concentrates which were relatively weak and still close to the related foodstulf. Later, with more knowledge of separation techniques, infusions, extracts, oleoresins and absolutes ranging from weak to strong impact were used to impart aroma. Essential oils such as spice oils already had a very strong impact. Modern analytical technologies allowed the evaluation of the chemical compositions of extracts and essential oils, so that isolates either as powerful mixtures or even as single compounds could be obtained. 

From a number of pilot applications Fig. 1.4-8 shows the quasi-continuous train for the sterilization of fruit juices with pulp contents. The high pressure sterilization offers valuable advantages with respect to the quality of the final product compared to other sterilization procedures, especially if natural fractions of fruit pulp are desired by the consumers. 

Foods. The determination of antioxidants and food preservatives is a very active part of the gas chromatography field. Adaptations and sample types are almost limitless for example, analysis of fruit juices, wines, beers, syrups, cheeses, beverages, food aromas, oils, dairy products, decomposition products, contaminants, and adulterants. A detailed discussion of this field may be found in Chapter 9. 

Coppola, E., English, N., Provost, J., Smith, A., and Speroni, J. 1995. Authenticity of cranberry products including non-domestic varieties. In Methods to Detect Adulteration of Fruit Juice Beverages, Vol. 1 (S. Nagy and R.L. Wade, eds.) pp. 287-309. AgScience, Aubumdale, Fla. 

Previous chapters in this volume have been concerned with chemical reaction engineering and refer to reactions typical of those commonplace in the chemical process industries. There is another class of reactions, often not thought of as being widely employed in industrial processes, but which are finding increasing application, particularly in the production of fine chemicals. These are biochemical reactions, which are characterised by their use of enzymes or whole cells (mainly micro-organisms) to carry out specific conversions. The exploitation of such reactions by man is by no means a recent development—the fermentation of fruit juices to make alcohol and its subsequent oxidation to vinegar are both examples of biochemical reactions which have been used since antiquity. 

For fruits and their products, HPLC techniques for phenolics have been used to study the effect of processing, concentration, and storage on the phenolic composition of juices as well as a potential precursor for an off-flavor compound in juices. Phenolic analysis has been further applied to the detection of economic adulteration and especially to verify the authenticity of fruit juices. This is especially important when cheaper fruits can be added to more expensive ones in a fraudulent manner. In most fruits, the nonanthocyanin flavonoids consist mainly of flavonols and flavanols, with trace amounts of flavones. Glycosides are the predominant forms present. These most often are separated by reversed-phase HPLC on Cl8 columns with gradients consisting of acidified H20 and ACN, MeOH, or EtOH. 

PH Gamache, IN Acworth, ML Lynch, WR Matson. Coulometric array detection for HPLC in the analysis of juice products. In S Nagy, RL Wade, eds. Methods to Detect Adulteration of Fruit Juice Beverages. Auburndale, FL Agscience, 1995, pp 120-144. 

Enzyme and finishing treatments are widely used in the processing of fruit juices to obtain products of particular specification. 

Decanters are also of use in the production of fruit puree, where the aim is to remove only the undesired particles such as pips, stalk fragments, skin fragments and coarse tissue material, leaving the crushed fruit flesh evenly distributed throughout the juice. By setting the machine parameters accordingly, the undesired components can be selectively removed from the liquid stream output of puree. 

Although a combination of product quality and cost considerations will dictate the methods used for bulk processing of fruit juices, there are instances where the flavour components present in the juice at e vulnerable to any form of heating din ing concentration. Strawberry juice is perhaps the best example of this, being one of the most heat sensitive of fruits, and it works well with alternative processes for concentration such as freeze-concentration and hyperfiltration. 

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