Apple juice is a fruit juice made by the maceration and pressing of an apple. The resulting expelled juice may be further treated by enzymatic and centrifugal clarification to remove the starch and pectin, which holds fine particulate in suspension, and then pasteurized for packaging in glass, metal or aseptic processing system containers, or further treated by dehydration processes to a concentrate.
Apple juice is processed and sold in many forms. Fresh apple juice or sweet cider is considered to be the product of sound ripe fruit that has been bottled or packaged with no form of preservation being used other than refrigeration. This type of fresh juice is normally sold in markets not too distant from the producer. Apple juice has been treated by some method to prevent spoilage. Shelf-stable or processed apple juice can be natural juice, clarified juice, crushed juice or frozen apple concentrate.
Natural juice comes from the press and generally only ascorbic acid is added to preserve color. It is then bottled and heat processed. Some forms of natural apple juice are produced with the use of heat pasteurization only.
Apple juice production begins with fruit harvesting, transport and washing facilities. However, all fruit must be sound and free from gross damage or contamination. In particular, it should be free from mould or rot which can lead to tainted juices and microbiological instability.
Product quality and stability will be influenced by the cleanliness of the ingredients and sanitation in the processing plant. Most fruits accumulate some dust in the field or during trasportation. They should be rinsed thoroughly by sprays of water before crushing.
The fruit should be picked at the proper stage of maturity for the preparation of juice. The flavour, sugar content and pectin levels of the juice will vary with the maturity of the fruit.
Ideally, fruit should have been picked when fully ripe, with dark brown seeds and no residual starch as detected by an iodine test. Fruit which is picked slightly under-ripe for the dessert market or for controlled atmosphere storage should therefore be allowed to mature for a few days at ambient temperature before pressing.(Hicks)
A diagram depicting the processing steps for apple juice and juice concentrate is shown in figure ….. .
Since apple juice concentrate is so widely available, it is relatively easy to set specifications for a juice in terms of its sugar and acid levels and to ensure consistency by blending different concentrates with water or fresh juice to required spesification. The blending and dilution of concentrates must be carried out before final filtration or the juice may become turbid on storage. The aroma essence, however, should be dosed into the juice line after the final mixing and filtration stages, to avoid losses by evaporation and adsorption by filter aids which have a high affinity for many of the small polar molecules which are responsible for volatile flavour. (Hicks)
Pressing Pomace disposal
or Flash Heating
Storage and Shipping
Rough Filration or Centrifugation
CLOUDY JUİCE CLEAR JUİCE
Figure … Flow chart for the processing of apples into clear or cloudy juice
Before pressing, whole apples are ground into a mush or pulp for extaction. This mashing process is accomplished with either a disintegrator, hammer, or gating mill. These mills crush or cut the apple to proper consistency, depending on the maturity of fruit. When milling firm fruit for juice, small particles are desired. As the season progress and apples become softer, pressing becomes more difficult, thus, bigger particles of pulp are preferred for pressing.
Equipment used to press or exract juice from fruit are of several types and many variations. The pressing process can be batch or continious depending on the type of press used. Undue aeration must be avoided during the exraction of juices from fruit that has not been heated to destroy enzymes, since destruction of vitamin C and oxidative changes in flavour are very rapid. These changes are catalyzed by traces of copper and iron in solution.(Macrae) Juice yields from the different types of presses vary greatly (70-90%) and depend on the type of equipment, maturity of the fruit,press aid, press time, and in some instances the addition of pecric enzymes to apple mash.
The apple mash has many natural enzymes but at rather low concentrations. Enzymes are substrate spesific, which means a given enzyme can catalyze only one particular reaction. Pectolytic enzyme products contain the primary types of pectinases: pectinmethylesterase (PME), polygalacturonase(PG), pectinlyase and pectin transeliminase (PTE). PME deesterifies the galacturonic acid, liberating methanol from the side chain, which then allows
PG to hydrolyze long pectin chains. Enzymatic mash treatment has been developed to improve the pressability of the mash and, therefore, the throughput and yield. The enzymes added at about 80-120 ml per ton of apple mash break down the cell structure. High molecular weight constituents of cell walls,like protopectin, are insoluble and inhibit the exraction of the juice from the fruit and keep solid particles suspended in the juice. Pectinase used in the apple process is extracted from the mold Aspergilus niger group of organisms, a commonly occuring natural product. Pectinase developed for apple mash pretreatment acts mainly on the cell wall, breaking the structure and freeing the juice. Also the viscosity of the juice is lowered, and it can emerge more easily from the mash. The high content of pectin esterase (PE) causes the formation of deesterified pectin fragments, which has a low water-binding capacity and reduces the slipperiness. These pectins consist of chains of galacturonic acid joined by α-glycoside linkage. Xylose is covalently bound as a monomer and galactose and arabinose as polymers. These polymers form a link with the cellulose. The entire system forms a gel that retains the juice in the mash. Even if the pectins are partially broken down by the pectinase enzyme, more juice is released from the mash, and pressing or exraction becomes easier. By inexpensive pretreatment of mash with enzymes and heating to 50 (C, the press throughput can be increased about 30-40% and juice recovery by over 20%. Mash pretreatment will also increase the flux rate of ultrafiltered apple juice up to 50%.
The enzyme treatment usually includes a pectin pectinmethylesterase (PME) in order to improve the activity of the polygalactronase(PG). It is important to have right balance of
PME and PG activites in the enzyme preperation and that they should be active at juice pH.
Two methods of enzyme treatment are commonly used: °1) hot treatment where the enzymes are added to 54 °C juice, mixed and held for 1 to 2 hours. °2) cold treatment where the enzymes are added to cold, room temperature, 20 °C juice and held for 6 to 8 hours
After juice extraction by pressing and before the filtration process, apple juice is treated to remove suspended solid material. The soluble pectin in the juice has colloidal properties and inhibits the seperation of the undissolved cloud particles from the clear juice. Pectinase enzyme hydrolyzes the pectin molecule so it can no longer hold juice. Enzyme treatments are widely used to remove pectinaceous material and clarify the juice. This material, if not removed, will clog the filters, reduces production, and can result in a haze in the final product.. A very useful additional activity in enzymes for apple juice work is that of an amylase, which helps to break down the starch often found as granules in early season fruit.
For the production of a clarified single strength juice the use of pectolytic enzymes is hepful but not absolutely essential, particularly when working with firm fruit in good condition, since much removal of debris may be achieved by fining alone. For the production of 70°Brix concentrate, however, the use of pectolytic enzymes on the juice is mandatory, sice the pectin otherwise form a gel in the presence of the high levels of acid and sugar once the solids content exceeds 60°Brix or so .
The fractured pectin chains and tannins are removed from apple juice with the use of gelatin (fining agents) treatments which can be used in combination with enzyme treatment, bentonite, or by itsef. The positively charged gelatin at the pH of apple juice(approx. 3,5) will facilitate removal of the negatively charged suspended colloidal material from the juice. The action of gelatin in clarifying apple juice is slow and it can take many hours for the insoluble floc from the slurry. Such a delay may be unaccaptable from the standpoint of flavour quality and microbial spoilage. In such cases tannic acid addition to the juice before gelatin treatment will prevent color and flavor changes by speeding up the process. Bentonite, another fining procedure, can be added along with the heat treatment to remove excess protein.
After the enzyme treatment, fining and settling process, the apple juice is pumped from the settled material (lees) and further clarified by filtration. Many types of juice filters are available. Pressure, vacuum and membrane filters are available and all can produce an acceptable product. The use of filter aids in filtration operations is one of the most traditonal techniques to achieve a clarified juice.This filter aid helps prevent blockingof the filters.
As the fruit matures, more filter aid will be required. Most commonly used filter aid is diatomaceous earth or cellulose type materials. Before filtration, centrfifugation may be used to remove a high percentage of suspended solids. In some juice plants centrifugation is used instead of filtration. This centrifugation process produces a product that is not clear as filtered juice, this process alows more or less continuous production. Centrifugation with filtration reduces the amount of filter aid required. The type of filter used must match the capacity to maintain plant production. The filtration process is critical, not only from production consideration, but the quality of the end product.
Membrane(ultrafiltration) filtration has been used with good results to seperate, clarify, and concentrate various food products. Ultrafiltration of apple juice cannot only clarify the product, but depending on the size of the mebrane, can remove the yeast and mold microorganisms common in apple juice.
Preservation of apple juice can be by refrigeration, pausteurization, concentration, chemical treatment, membarne filtration or irradition. By far the most common is heat pateurization based on temperature and time of exposure. The juice is heated to over 83°C, held for 3min, filled hot into container, and hermetically sealed. The apple juice is held 1 min. and then cooled to less than 37°C. When containers are closed hot and then cooled, a vacuum develops, reducing the available oxygen that also aids in the prevention of microbial growth.
After the heat treatment, the juice product may also be stored in bulk containers, but aseptic conditions must be maintained to prevent microbial spoilage. Aseptic packaging is another common process where, after pasteurization, the juice is cooled and packaged in a closed, commercially sterile system under aseptic conditions. Aseptic juice processing is shown in figure …. Preservation by use of chemicals such as benzoic or sorbic acid and sulfir dioxide are not commonly practiced. If chemicals are used, it is only to increase the shelf-life of unpasteurized juice.
Commercial Sterilization of Foods- cooled to Ambient Temperature
Sterilization of the Container
Product Packaged in
Sterile Enviroment at
Figure…. A layout of the component steps for an aseptic operation (Somogyi and fri.)
Apple juice concentration °AJC) is another common method of preservation. The single strength apple juice is concentrated by evaporation or freeze concentration, preferably 70 to 71°Brix. (Somogyi vol2)
A juice which has been clarified before concentration will generally give a clear juice on re-dilution and requires only a final polishing before bottling. A concentrate made from cloudy juice, however particularly if stored for a long time, may be extremely tedious to clarify on re-dilution. At 5 °C or less storage temperatures, concentrates and aroma essences will remain essentially unchanged for at least 6 months and probably longer. At 15, 20 or 30 °C, however the rediluted juice becomes noticeably lower in quality, the effects being proportional to storage time and temperature; 2 weeks at 20 (C can produce detectable changes. Caramelised flavours develop and browning is increased because of Maillard reaction between reducing sugars and amino acids at high concentration. There is also a loss in apparent polyphenols and in titrable acid. Attempts have been made to define a single index to measure the overall quality loss, for instance by monitoring the increase in 5-hydroxymethylfurfural(HMF). This is known to be a product of Maillard reaction and is easily measured by high performance liquid chromatography (HPLC) or by colorimetric procedures. It is undetectable in fresh juices and present below 1ppm in fresh AJC. When concentrate is stored, however, HMF levels may rise as high as 700 ppm although levels of 100 ppm are more commonly encountered. HMf is generally useful guide to deterioration of any given juice. (HİCKS)
If AJC is not cooled to 5 °C on exist from the evaporator, loss of flavour quality can begin imediately. Because its viscosity slows convective cooling, AJC pipped into a large
uninsulated unstirred tank at 50 °C may take literally weeks to cool ambient temperature in center, during which time Maillard reactions can progress significantly. Although oxygen itself does not take part in the Maillard reaction, AJC should be handled and stored in an inert atmosphere to prevent oxidative changes which could otherwise occur. Concentrate stored at ambient temperature may slowly produce CO2 which must be vented. This can arise both from chemical decarboxylation of Maillard products and from the action of osmotolerant yeasts. (HİCKS)
It ıs possible to inhibit AJC deterioration by the use of SO2 at levels of approx. 250 ppm. The early Maillard products, including HMF, are characterised by carbonyl groupings to which the bisulphite will bind and so prevent further reaction. However, on dilution the juice will contain 30-40 ppm SO2 which is nowadays unacceptable to most juice processors. (HİCKS)
Apple essence is recovered during the concentration of apple juice. The aroma essence should be dosed into the juice line after the final mixing and filtration stages. The identification of volatile apple constituents, commonly known as essence or aroma, has been the subject of considerable research. It is generally agreed that there are six components contributing the most to the quality of apple essence or aroma. These can be divided into three desirable and three undesirable components as tabulated in table…. It was also confirmed that desirable volatiles in apples decrease significantly in storage. Apple juice produced from late season cold storage or CA stored apples will not produce the typical “fresh” apple aroma.