juice (cool) Filling
Treatment of mash
Treatment of juice
Clarification
Filtration
Concentrate (filtered)
Concentration Heating
Juice (filtered)
Homogenization Sieving Blanching
Puree (with fiber)
Filling Heat- treatment
Figure 13.1. Process flow diagram of fruit beverages.
production, and processing technology can often change the composition, resulting in quality problems. The further devel- opment of this system led to the publication of the European Economic Commission’s Association for Juice and Nectar Production (AIJN), called “Code of Practice.” In this publi- cation, RSK values are supplemented with other analytical features that are generally accepted of apple, grapefruit, or- ange, and grape juices. Besides consumption value, quality, genuineness, raw material, and technological deficiencies, these criteria comprise factors concerning the environmental pollution of the land close to the production unit with arsenic and heavy metals. Technological deficiencies usually result in high concentration of biogenic acids, hydroxymethylfurfural (HMF), ethylalcohol, and patulin; thus, their maximum levels are under regulation (Wiesenberger 1997). Complying with these stringent fruit juice quality criteria is the responsibility of fruit processors, raw material suppliers, and producers.
The values determined by the RSK system and the AIJN Code of Practice are primarily used in Europe but significant deviations may endanger the competitiveness of products in the world market.
PRODUCTION OF FILTERED AND CLOUDY FRUIT JUICE
Filtered and cloudy fruit drinks are made of mechanically pressed and cleaned juice directly or from the dilution of concentrated semifinished products. As it can be seen in the flow chart, production technology comprises five main oper- ations (Fig. 13.1).
Juice extraction—the elimination of the juice from fibrous, solid particles—is a basic technological step of fruit juice production. The fruit has to be prepared prior to juice extrac- tion, which is then followed by juice clarification and drink completion. Subsequently, the finished drink is packed and preserved.
Preparation Steps Raw Material Reception
Only those raw materials are allowed for fruit drink pro- duction that meet the following criteria: appropriate ripeness
and flavor, no signs of deterioration, and free from foreign ingredients, pathogenic organisms, and their effect. More- over, raw materials have to conform to the regulations and standards in force. Because of the change in quality criteria and permitted ingredients of fruit juices, general raw ma- terial properties are completed by an increasing number of special requirements. Processing companies expect, for ex- ample, that apple intended for juice production possesses the following paramteres: sugar–acid ratio in the 12:1–14:1 range, sugar content above 12 or 13 Brix◦, and acid level above 7g/L. Products with proper sensory traits can only be produced from such high-quality raw materials. Dur- ing reception, attention is paid to the cleanliness of berries in which washing may cause substantial damages (Szenes 1991).
The conformity of each batch should correspond to the methods and examinations of the relevant descriptions. Then, it has to be labeled for further identification and traceability.
In addition, conformity to the production technology require- ments also has to be checked (crop spraying records).
Washing
The aim of this step is to remove every contamination from the surface of the fruit, i.e., to increase physical, chemical, and microbiological cleanliness.
The surface of raw materials is strongly contaminated by microorganisms; it can attain 105–109 microorganisms per gram. Even with effective washing, it can be decreased only by 3–5 orders of magnitude. Therefore, washing efficiency has a significant impact on the heat treatment necessary for preservation.
Physical and chemical surface contaminations are elim- inated by water soaking, since these substances are water soluble or their adhesion properties decrease in aqueous so- lution. The efficacy of the dissolving process can be increased with higher water flow. The latter can be achieved by stream- ing, air injection, and by mechanical means. Because of the water flow, close contacts between fruit particles increase washing efficiency but potentially leading to damages to the fruits. Thus, the texture of the raw material is taken into consideration when choosing washing equipment. Vulnera- ble juice raw materials or berries are preferably not washed but rinsed with dipping or spraying methods. Fruits, with lower density than water, usually arrive at the processing plant via a floating channel, where surface contamination dis- solves in the soaking water. Nozzles, which are positioned at the end of the transportation system, spray clean water onto the fruits and eliminate contaminated water, contamina- tion residues, and other impurities. If destemmer needs to be used, it performs a spray wash of the relatively clean fruits.
Other juice raw materials undergo three washing steps. The first phase is soaking, which breaks up surface contamina- tion and eliminates soil particles. In the case of fruits covered with wax layer or oleaginous skin, warm water (50–60◦C) is
applied. Warm water soaking or a long soaking period may result in substantial loss of valuable fruit components (Barta and K¨ormendy 2007).
The active phase of washing is intended to remove contam- ination and is followed by a clean water rinse. Washing means water flows all around the fruit, meanwhile rinsing means wa- ter spraying in order to remove washing water residues from the fruit’s surface.
Stem Removal
To prepare fruits for juice extraction, in the case of certain fruit species (e.g., cherry, sour cherry, plum, etc.), long green peduncle parts are removed. Otherwise, they will spoil the color and other quality traits of the juice. Mechanized stem elimination can only be carried out in raw materials of ho- mogenous size that do not tend to damage and burst. The most frequently used equipment is the belt-based solution, but in Eastern Europe roller-based machines are still widely used.
Selection
This step, which usually follows washing, separates every- thing from the raw material that is unsuitable for processing.
These can be foreign substances, stem and leaf particles, or moldy, deteriorated fruits. This activity is performed man- ually and requires close attention. Therefore, the necessary job environments (e.g., proper lighting and reasonably posi- tioned waste containers) must be provided for the workers.
The selection table on which this operation is done should be able to roll the fruits, enabling the workers to observe the entire fruit surface. Both the roller-based and belt-based machines comply with this requirement. In order to achieve better efficacy, proper adjustments must be made for single layer fruit flow and optimal belt speed (Parker 2003).
Juice Extraction
Juice extraction from prepared fruits includes more techno- logical steps. It comprises crushing, juice separation from solid fruit flesh particles or juice extraction, juice treatment, and preparation for filling. Crushing prior to pressing can be further divided to chopping and preparation for pressing.
Chopping
The aim of this step is to smash, cut the fruit, increase its sur- face, and launch cell-fluid elimination. Raw materials with more solid texture (e.g., apples) are chopped by crushing;
meanwhile, soft fruits (e.g., red currants) are only cracked.
The extent of chopping is determined by the type of the subsequent juice extraction procedure. Pressing preparation should result in crushed fruits that release the juice to rela- tively low pressure applied. Properly prepared crushed fruits
are not pulpy. It should be the mass of uneven shaped par- ticles of appropriate homogenous size, “roof”-shaped slices and tissue particles that form channels to drain the juice. In case the particle size is too small or it is pulpy, it tends to spread and its structure becomes massive when pressed, so the juice cannot pass through. If diffusion-based juice extrac- tion is performed, fruits have to be chopped in a way that the thickness of slices or strips is the smallest achievable. How- ever the size of these particles should enable the formation of masses where the flow of extraction liquid is ensured.
There are several devices for crushing the fruits. They can be designed for one specific fruit such as different apple mills.
However, there are machines that can be generally applied like hammer and barrel crushers. Their common features are the rotation system and the pressing, tearing, pulling, and striking forces applied.
Cracking, crushing, and smashing the tissue structure of fruits can lead to the damage of valuable compounds or ini- tiate enzymatic processes, which result in the formation of nondesired substances. Therefore, crushed fruits have to be processed immediately (Horv´ath 2007).
Chopped Fruit Preparation
Procedures designed to prepare chopped fruits are to increase juice yield and prevent undesirable changes (chemical, bio- logical, mechanical, etc.) to achieve better aroma, flavor, and color properties. The type of preparation will depend largely on the type of fruit and production technology.
There are several methods for this operation, such as heat treatment, enzymatic, freezing, vibration, ultrasonic, electro- plasmolytic, and ion-radiation procedures (Szenes 1991).
Heat treatment and enzymatic procedures can lead to 5–10%
increase in juice yield.
Heat treatment is mainly performed on berry fruits, such as raspberry and elder berry, prior to pressing. This step means heating the crushed fruit rapidly up to 80–85◦C, then cooling it back very quickly. Under this short heat impact, different physical, chemical, and microbiological processes take place.
Because of the denaturation of proteins and the hydrolysis of protopectin, enzymes are inactivated, cell walls become permeable, and the diffusion of water-soluble substances ac- celerates. If heat treatment gets too long, due to improper technology, the tissue becomes soft, it falls apart, the fruit will be difficult to press, and the taste of the juice changes. In case of berries rich in color, this step aims to improve color, besides yield increase.
There are different heat exchangers that can be applied to perform heat treatment depending on the production line.
Enzymatic treatments are also frequently used before pressing, to make the process easier and to increase the yield.
Fruit raw materials possess different amounts and types of pectin, depending on the species and the variety. Pectins are complex polysaccharides; chemically they can be described as a polygalacturonic acid chain esterified with methanol.
Pectins play a pivotal role in plants’ structure and their sta- bility. Pectin can be found between the cell wall layers con- necting the solid shells that contain cellulose and hemicellu- lose. These pectin types are beneficial for pressing, because they ensure the solidity of shaped particles and increase the formation of juice channels. Other pectins are dissolved in tissue fluids, increasing fluid density and sticking properties.
These latter pectins hinder juice extraction and increase the risk of plugging in the pressing device. Therefore, the level and the composition of pectin have to be decreased or mod- ified according to the quality criteria of the finished product or the production technology. The change of pectin level is generally achieved by enzyme addition to the crushed fruit.
Enzymes are macromolecular biocatalysts with high activ- ity. These are substances of protein origin that are essential parts of the living world, regulating the building and degra- dation processes of plant and animal organisms. Their typical features come from their protein origin. One of the most sig- nificant traits is their substrate specificity, which means that one enzyme can catalyze only one specific reaction. Another important property is their pH and temperature dependence.
Each enzyme has an optimal pH and temperature range, where their catalyzing effect and activity is maximized. De- viations from these optimal values in both directions result in a radical decrease of their activity.
All living organisms synthesize enzymes that regulate bio- chemical procedures within their body. Therefore, enzymes can be extracted from animal and plant tissues, and mi- croorganisms. However, the most economic way to produce enzymes is fermentation with rapidly multiplying microor- ganisms under controlled industrial environments. Because of their substrate specificity, enzymes produced by different bacteria, yeast, and mold extracts mainly catalyze the reac- tion of one specific substrate, for example, pectin. Complex enzyme mixtures are produced by the combination of en- zymes coming from different sources. Most commercially available pectinase products consist of at least 20 enzymes with different activity. “Enzyme cocktails” that can success- fully treat fruits of different species, varieties, composition, ripeness, and properties are made by this method. Enzyme mixtures are specifically designed for a certain raw material and its processing steps.
Molecular genetics opened new perspectives in the de- velopment of enzyme production. Increased efficiency and development of new properties can be attained by better se- lection of microbial strains. However, the combination of different microorganism species by protoplast fusion or in- serting DNA sections into the genome of another cell may lead to significant changes in the features of the enzymes pro- duced by such modified microbes. In case of enzymes applied in fruit juice processing, the most important results of these techniques are efficiency, pH and temperature tolerance, and increased stability (Biacs 2007).
The three most significant pectin-degrading enzymes are pectin lyase or pectin transeliminase, polygalacturonase, and
O O
OH OH COOCH3
O
O O O O O O
OH COOCH3
O OH CO OCH3
O Pectinesterase
Pectin lyase OH COOH
O OH COOCH3
O OH COOCH3
OH OH OH OH OH
O O
OH OH
COOH COOH
O O O O O O O
OH
O OH COOCH3
O
Polygalacturonase OH COOH
O OH
COOH COOH O
OH
OH OH OH OH OH
Figure 13.2. Activity points of pectin-degrading enzymes.
pectinesterase. They are effective on different parts of the pectin molecule and are depolymerizing or ester-degrading enzymes (Fig. 13.2).
Pectin lyase and polygalacturonase break down the chains.
Polygalacturonase, which belongs to the group of hydro- lase enzymes, attacks the pectin molecule where a galac- turonic acid is located. Enzymes can break down the chain inside the molecule (endo-polygalacturonases) and can form oligopectins of different size besides water absorption. The nonreducing end of the chain can also be attacked (endo- polygalacturonases), splitting galacturonic acid monomers from the pectin molecule one by one.
Pectin lyase or pectin transeliminase breaks up the chain beside the galacturonic acid that is esterised with a methyl group. The highest efficiency can be achieved in fruits, where the metoxyl value of the pectin chain is high.
Ester-degrading pectinesterase enzymes break down methylester groups found on polygalacturonic acid chains.
Besides water absorption, they release methanol molecules (Pilnik et al. 1981). The increase of methanol level may cause problems in fruits that contain highly methylestered pectin (e.g., apples and citrus).
In concentrate production, it can increase the methanol content of the condensed aromas. In case of cloudy juice pro- duction, polygalacturonic chain, stripped of its methyl group, reacts with the potassium ions found in the fruit and forms precipitation. This reduces the natural cloudiness of the juice.
The activity of enzymes that depolymerize the pectin molecule and rapidly decrease the viscosity of the mash has a beneficial impact on juice yield. Therefore, it is important to be aware of the pectins’ properties found in the fruit to be processed. The optimal enzymes can be selected based upon this information to maximize yield and juice quality.
As written above, the increase of juice yield in fruits containing low level of estered pectins can be achieved by enzyme mixtures rich in endo-polygalacturonase, which
break down pectins at the galacturonic acids containing car- boxyl group. Meanwhile for the degradation of pectins with high degree of esterification, pectin transeliminase is the most efficient choice, since it breaks down glycoside bonds that are located next to methyl radicals (Reising 1990).
Besides depolymerizing enzymes, mixtures always con- tain pectin esterases. Cellulases and hemicellulases are also included to break down the cell wall and improve juice elim- ination.
Enzyme treatment can be carried out under cold and warm circumstances. Cold treatment at 20–25◦C takes more hours, which endangers the juice quality (Schmitt 1990). Mean- while, warm treatment takes place in 0.5–1 hour, at 50–55◦C.
As enzymes are protein-based molecules, these are heat sen- sitive and are only active at certain pH values. If the tempera- ture and pH conditions of the mash are not optimal, successful pectin decomposition requires longer time or higher enzyme concentration (Dietrich 1998). The pressing waste of high- pectin fruits (e.g., citrus, apple) is usually used for pectin production. In these cases, enzyme treatment should not be applied.
Enzyme pretreatment is not applied in the production of cloudy concentrates, because their main ingredients are dis- solved colloid substances in the liquid phase.
Juice Extraction
In this process, the liquid phase of fruits is expressed from solid particles. There are different methods for this separa- tion: pressing, diffusion, centrifugal procedures, and reverse- osmosis. The type of equipment applied depends on the fruit species, production line, and economy of scale. The most widely used solution is pressing.
Pressing separates a food system into two phases. In this case, fruit tissues are the solid phase, while the liquid between the particles is the liquid phase.
Pressing needs outside forces to create pressure in the sys- tem, drain liquid, resulting in shape modification. The equip- ment hinders the disposal of the solid phase and the liquid gathers in a vessel. The remaining material, with low liq- uid content, is called marc. The most important parameter of pressing is the liquid yield, which means the percentage of juice extracted, compared to the raw material at the beginning of the process. Juices extracted by pressing are mainly New- tonian fluids. The greater part of dry matter content is present in the form of real solution. Meanwhile large molecule size substances, for example, pectins and starch, form colloid so- lutions. Juice yield is basically determined by the type of the pressing device, and the quality and preparation of the raw material (Lengyel 1995). Fruit processing industry applies continuous extraction systems such as belt- and screw-based, and intermittent systems, such as the package and basket type pressing machines. In addition, decanters are based on centrifugal forces (Nagel 1992).
There are different techniques for the preliminary extrac- tion of liquids that are easily released. The common feature of these methods is that some part of the juice is drained from the mash by gravity. It can be performed in buffer tank with perforated bottom, in screw conveyor with perforated coat- ing, or in continuous belt press. This latter can be applied as preliminary pressing equipment in case of using basket- type pressing devices. These solutions relieve the pressing machine, thus increasing its capacity (K¨ormendy and Vukov 2007).
The juice of fruits can also be detached with extraction.
It means that semipermeable cell walls are made permeable following a heat treatment, and the cell fluid is then dissolved with water.
This process is featured by the degree of extraction, ex- pressing the amount of extracted valuable substances, com- pared to the total valuable matter content of the fruit.
The amount of substances diffused is in direct proportion with the diffusion coefficient, the active surface, and the con- centration gradient.
In order to increase the diffusion coefficient and the permeability of the cell walls, diffusion fluid extraction is performed at 50–70◦C. Active surface can be increased by proper chopping. The concentration gradient is determined by the stream conditions and the solvent–cell fluid ratio. How- ever, the amount of solvent applied is limited by the concen- tration decrease of the liquid extracted. Diffusion juice extrac- tion is usually carried out in double-screw extractor devices.
In this equipment, fruits are extracted in continuous mode with water in counterstream. Chopped fruits, to be extracted, are fed continuously on one end of the device; meanwhile, leached slices continuously exit the other end. Extraction liq- uid is fed and pumped in counterstream. Therefore, fresh fruit slices get in contact with the solution containing high level of extracted material; on the other end, fresh water first contacts slices that are already extracted. The application of this tech- nology can lead to high extraction efficiency and sufficiently
concentrated juice (K¨ormendy and Vukov 2007). Pressing and extraction can be combined to achieve better extraction of the valuable compounds. In this combined step, soluble residue substances are extracted from the marc by the means of aqueous extraction. Warm condensed water formed from the vapor during the concentration step is usually utilized as extraction fluid. The double pressing method, which is a combination of pressing and extraction, can significantly in- crease liquid yield. However, this process is time consuming.
Moreover, extraction fluid cannot be mixed with the pressed juice; it has to be processed separately.
Juice Clarification
Extracted fruit juices are usually turbid, due to insoluble plant particles (fibers, cellulose, hemicellulose, protopectin, starch, and lipids) and colloid macromolecules (pectin, pro- teins, soluble-starch fractions, certain polyphenols, and their oxidized or condensed derivatives). Depending on the fin- ished product, these substances must be partially or entirely eliminated to avoid turbidity and precipitation and to improve sensory attributes (taste, flavor, and color). Juice clarification has to be suited to the type of finished product. Filtered (clarified) juices are real solutions that should not contain dissolved colloid substances, so these compounds have to be eliminated. In spite of this, the special turbidity of cloudy juices comes from the fine-size, shaped particles of original ingredients and dissolved colloid substances that are left in the finished product.
Juice clarification can be performed by physical–chemical methods, mechanical procedures, and their combinations.
A physical–chemical clarification is applied when elimi- nating all substances causing turbidity. In this step, clarifi- cation agents are added to form precipitation from insoluble chopped plant particles and macromolecules that can be sep- arated by mechanical methods afterward. As the first part of juice clarification, protective colloids (petcins, starch, and hemicellulose) have to be removed, because they hinder the settlement of floating substances and their gel-forming affin- ity inhibits concentration. Furthermore, they (starch, araban) can cause subsequent turbidity in concentrates during stor- age. This process also includes the addition of enzymes. The aim of enzyme treatment is to break down pectin molecules found in the juice. High quality, stable, filtered concentrates can only be produced if pectin decomposition is completed with the break down of starch, hemicellulose, and araban.
Therefore, the development and production of combined en- zymatic clarification agents, which possess pectinase, amy- lase, hemicellulase, and arabanase activity, is an important field for enzyme manufacturers. These products are not only specific to fruit species or varieties, but they take ripening stages of raw materials (e.g., apple), which can be pro- cessed within a longer period, into consideration as well (Dietrich 1998, Grassin 1990). Modern pectolytic clarify- ing enzyme products possess specific pectin transeliminase