There are a number of semi-tropical and strictly tropical fruit both with recognized and unrecognized juice, puree or pulp potential. Processing technology, including juice products from the better-known fruits such as pineapple, guava, mango, papaya and passion fruit have been well covered by Jagtiani, et al., (1988) and Nagy, et al., (1993). The semi-tropicals, such as citrus and kiwi, can grow in tropical highlands to freeze-limiting elevations. Most others are strictly tropical as their commercial production is severely limited by temperatures close to freezing and actual freezes are devastating. Even tropical highlands may be impractical, except in protected microclimates (Popenoe, 1920; Martin, et al., 1987; Mortonnes, 1987).
Some products such as pineapple juice, banana puree, mango and papaya puree and, increasingly, guava puree and passion fruit juice are commercially important. Others are:
Fruit includes lychee, rambutan, mamay, carambola, acerola, mangosteen, naranjilla, pitaya, babaco, guanabana (and other members of the Annonceaea family) and a host of other fruit recognized and consumed only locally and sporadically.
Many undoubtedly possess sensory, nutritional, nutraceutical/phytochemical and other desirable quality features as yet under exploited. Compared to the shelves of a health food store, there are many with food and dietary supplement value awaiting discovery. When prepared and stabilized in liquid form these exotics can provide additional value and diversity to juices.
At one time the Tropical Plant Introduction Station at Lancetilla, Honduras, operated by the United Fruit Company, had the start of a comprehensive, growing selection of tropical fruit germplasm. Sadly this international resource, now owned by the Honduran government is comparatively unrecognized, under-funded and depleted in germplasm. The Inter-American Institute for Cooperation on Agriculture (IICA) in Trinidad is encouraging tropical fruit utilization (IICA, 1998). It will take a global effort, considerable international cooperation, increased funding and many decades to put tropical horticultural crops in proper perspective.
The manufacture of pineapple juice is a good example of the interaction of plant breeders, horticulturists, food technologist and engineers in an industrial process that evolved over many decades (Tressler and Joslyn, 1961 and 1971; Nelson and Tressler, 1980; Mumaw, Somogyi, et al., 1996b). Peeling and coring equipment was predicated on a cylindrical pineapple, figuratively the shape and diameter of a number 21/2 can (~99 mm diameter by ~109 mm height). The `Smooth Cayenne' (Figure 15.1) was well suited to the Ginaca machine that, in a series of operations turned a cleaned, crown and root-free, whole pineapple into an intact cylinder (subsequently sliced into rings), core and extracted flesh from the residual side peel and 2 ends. Several sizes of Ginacas accommodate inspected and sized uniformly cylindrical fruit at the rate of over 90 fruit/minute, while off shape fruit are routed to other uses for instance juice or vinegar.
Figure 15.1: Smooth Cayenne pineapple.
The juice was and to some extent still is a by-product of solid pack operations. Table 15.1 shows the partitioning of processed pineapple products in roughly descending order. A fresh whole fruit or the cored and peeled flesh has the highest market value, but a limited shelf life, up to three weeks under proper conditions. Large slices in syrup or juice are next in value. Broken slices and smaller fruit can be cut into spears and chunks. The odd pieces are diced into ~1 cm cubes as crush. These operations generate a large amount of juice. The eradicator flesh (scooped from the peel or shell and ends), together with peeled off-size/shape fruit and core, are comminuted and passed through a finisher or screw press. Screening and centrifugation of these fractions is necessary to remove skin specks or eyes and adjusts the pulp level for blending with other juice streams.
Table 15.1: Hierarchy of pineapple products.
Fresh fruit, whole
Careful selection with refrigerated holding
Fresh peeled and cored
Refrigerated cylinder, slices, or spears
Frozen or thermally processed in No.21/2 to No.1 cans
Spears and chunks
Odd or broken rings, frozen or thermal processed
Eradicator flesh, frozen or thermal processed
Canned single strength or frozen concentrate
From combined process waste streams
The pineapple thus goes from intact fruit to at least five separate product streams within several minutes in a high throughput, labour efficient, capital intensive system. Many pineapple cultivars are ideally suited for juice, including some with exceptional flavour, but lighter in colour than the typical "pineapple yellow" of `Smooth Cayanne'. Of course, odd sized, noncylindrical-shaped cultivars and fruit with deep seed pockets are not amenable to a Ginaca machine. In these cases, other mechanical or even hand peeling/coring devices are used. Yet, given the commercial effectiveness of ginaca type operations, it is hard to compete with anything less than a highly mechanized operation.
Thorough comminution of pineapple flesh and cores followed by passing the slurry though finishers with ~0.5 to 1-mm screens produces a pulpy juice of 12 to 15ºBrix and °Brix/A around 20. Decanting centrifugation then adjusts the pulp (insoluble solids) level to 12 to 24 percent (Hooper, Ashurst, 1995).
Pineapple juice with a pH of ~3.5 can tolerate moderate thermal processing. A fill temperature of 70ºC followed by rapid heating to 95ºC or a hot fill at ~90ºC with rapid cooling in both cases maintain quality. Major quality defects are: excessive heating or slow cooling, resulting in a dark, scorched juice; too little or too much pulp creating a thin or thick consistency; excessive shell material yielding dark specks and harsh flavour. Home or village processing operations exist where under/over ripe or spoilt fruit are juiced with poor results. The juice can be concentrated to 72ºBrix with or without essence recovery and add-back. The frozen concentrate has a global market as reconstituted juice or a major blending stock. Pineapple is either the base or component of many juice and beverage blends. The trade demands a bright yellow colour, however, some pale yellow, even whitish-fleshed cultivars, when fully ripe can have an excellent flavour, although only appreciated locally.
Despite the impressive efficiency and automation of all pineapple operations, from production through juice processing and shipping, competitive pressure from low labour and land cost Pacific Rim countries have largely decimated the Hawaiian pineapple processing industry. Since the early 1960s when Ginacas and other high throughput equipment became available outside the United States, efficient, low cost producers have captured the majority of global markets for processed pineapple.
These lines rapidly replaced hundreds of workers manually performing mundane preparation steps. Migration of the Hawaiian pineapple industry and ongoing shifts of citrus processing from Florida to Brazil and elsewhere serve as both an inducement and challenge to entrepreneurs interested in exploiting a region's juice potential. Given an adequate infrastructure, sufficient capital and skilled labour, developing regions can compete effectively against industrialized countries, but so can their evolving competitors.
Mango (Mangifera indica L.) is the prototypical tropical fruit, available globally in many forms. The puree can be the co-product of the fresh fruit or canned slice packing operations. In addition, some cultivars and mango seedlings are extremely fibrous but very flavourful. The fibre content precludes their use for fresh market, so juicing is the logical alternative. As long as this texture defect is not accompanied by the characteristic terpene-like flavour of many chance seedlings, the fruit has beverage value.
Mangos for puree should be fully mature, even soft, but not overripe. Ease of handling is quite variety-dependant. Mechanical peeling presents some difficulty due to the thick, leathery peel and the presence of bitter substances in the skin, requiring careful and complete removal. Heat treatment and lye peeling have been used successfully (Brekke, et al., 1975). A paddle pulper fitted with brushes and 0.040 to 0.20 screens can effectively remove the pulp, provided that the discharge throat is large enough to eject the intact seed (Figure 6.6). It must be emphasized that success of mechanical peeling is highly cultivar dependent. Thick peel with the attendant latex and bitter compounds cannot be mechanically separated without contributing off-flavour to the puree.
The extracted puree is susceptible to browning and should be processed immediately. The pH will generally range from 4.5 to greater than 5.0. Thus acidification with citric acid to ~4.0 pH is necessary, if the puree is to be pasteurized. A hot fill temperature of ~95ºC for 2 min is adequate for sanitary puree or nectar, followed by rapid cooling. Canned or glass packed products should be heated and cooled carefully to prevent scorched flavour and browning. For optimum flavour and colour, rapid blanching at ~90ºC for 1 minute followed by cooling to about 30ºC and freeze preservation is recommended (Nagy, et al., 1993).
Mango nectar is produced by mixing the puree with citric acid, sugar and water to a proscribed Brix/acid ratio, dependent upon raw material and desired use. Puree is blended with other juices that complement mango flavour, lower the pH and provide thinner viscosity. Various pulp dehydration methods can be employed to produce dried powders. The additional expense incurred by dehydrating mango puree must be balanced against the saving in transportation and storage.
One of the more easily processed fruits, passion fruit (Passiflora edulis and flavicarpa) is more readily consumed as the juiced flesh than in the whole seed-containing pulp form. Yellow (edulis) and purple (flavicarpa) cultivars are popular, although many under exploited members of the Passiflora genus exist and are popular in tropical regions (Nagy, et al., 1990). Although morphologically similar, the yellow is more acid and with a pH of less than 3.0, generally requires dilution and sweetening for consumption.
Parallel commercialization in Hawaii and Australia has resulted in fruit processing lines that efficiently separate the gelatinous pulp from the seed and rind. In Hawaii this is accomplished by a centrifugal extractor where the pulp and some seeds of mechanically sliced fruit pass through holes in the spinning centrifuge. The Australian system lightly crushes the whole fruit between rotating disks popping the placenta away from the rind. More recently an Italian compression roller system has been developed industrially (Somoygi et al., 1996b). In all cases a finisher with a 0.8 to 0.3-mm screen separates seeds from the juice. Other systems employing a vacuum to remove the pulpy interior of halved fruit or an oversized pitting device have been mentioned (Jagtiani, et al., 1988).
Single strength yellow passion fruit juice at ~17ºBrix and 2.8 pH is too strong for direct consumption. The nectar base, consisting of 55 to 60 parts sugar to 100 parts juice, is best preserved by freezing and reconstituted 1:3 or 4 with water for consumption. The purple cultivar and newer introductions are less acid and require correspondingly less sugar and dilution as nectar bases. Where freezing is not practical, rapid pasteurization or aseptic processing produces acceptable but flavour-diminished nectar.
Passion fruit juice is unique in containing from 0.5 to over 3 percent starch, resulting in an increase in viscosity upon pasteurization or concentration as the starch gels, unless pretreated with amylase or separated by centrifugation. The delicate flavour is diminished by pasteurization and even aseptic processing or gentle concentration systems cannot approach the fresh or frozen product in flavour. Despite the heat labile flavour, passion fruit is a major component in many processed tropical fruit beverage blends and popular with those unaware of the exquisite flavour of analogous unheated (fresh or frozen) products.
Acceptable passion fruit concentrate to greater than 60ºBrix can be produced with attention to low temperature or short residence time evaporators - centrifugal or falling film evaporators. Essence recovery and add-back approximate (but do not match) the original flavour. The concentrate, packed in 200L barrels (Figure 15.3) and frozen, can be held at -20ºC and used in tropical juice/beverage blends.
Figure 15.2: Passion fruit concentrate filling into 200Litre drums.
Although the rind is high in quality pectin and seeds are a source of protein and oil, no major co-product industry has developed. Despite the extensive research and industrial developments with passion fruit, there is much to be done. Probably the diffuse, mixed cultivar and comparatively small-scale cultivation has hampered more widespread investigations. And many other Passiflora genus merit development.
Guava (Psidium guavajava L.) is represented by a number of commercial cultivars with flesh colour ranging from red to white. The delicate fruit is sensitive to postharvest damage; thus pulping is one logical strategy for utilizing the fruit. In many regions the fruit is a host to fruit flies and other penetrating insects, so careful inspection is necessary. Maturity grading can be accomplished by submerging the fruit in clean water. Immature fruit sink and the floating mature fruit are thereby separated. The clean, whole fruit may be pureed by passing though a paddle pulper. Care must be taken to exclude stones cells that contribute a grainy texture to the puree. These cells are distinct from the seeds and are easily removed by the pulper; 0.3 to 0.5-mm mesh screen is adequate. Guava is high in ascorbic acid (~100 to 200 mg/100g) and the red/pink contributing pigment is lycopene. The more acid cultivars produce fine nectar bases with added sugar.
Depending upon the acid level, nectar bases consisting of 40 to 50 parts puree and 100 parts sugar can be either frozen or flash pasteurized. Reconstitution with 21/2 to 3 parts water produces flavourful nectar from the frozen base and acceptable nectar from the pasteurized base. Clear guava juice is obtained by treating the pulp with a pectic enzyme followed by centrifugation. The straw yellow juice retains fair guava flavour and can be blended or concentrated more easily than the puree. However, the colour remains in the pulp residue and contains most of the lycopene. So, unless there is a value-added use for the pulp, utilization in the original puree form is logical. The pulpy nature and high pectin level of the puree favour jams, pastes and confectionery products.
One distinguishing feature of papaya (Carica papaya L.) is the unusually high pH of the flesh, ranging from 5.5 to almost 6.0 when at the eating ripe stage. The fruit come in many sizes from 300g to several kg and colour from light yellow to deep red-orange. The flesh is a good source of carotenoids, including beta-carotene with redder flesh associated with more lycopene. The thin skin and soft flesh requires careful handling with peeling best accomplished by hand to prevent off flavour pick up from the skin. Recent processing developments are well summarized by Chan, Nagy, et al., (1993). A surface steam treatment to coagulate latex and toughen the skin is a pretreatment for slicing and mechanical peeling by a crusher-scraper (Anagara, et al., 1969) in combination with a modified passion fruit centrifugal peel separator. The flesh is easily deseeded and pureed by finishing equipment. As emphasized, complete removal of skin and seeds is necessary to avoid off-flavour.
In view of the high pH, papaya puree is either frozen or acidified with citric acid or blended with acid juices prior to pasteurization. The flesh tolerates heat reasonably well during enzyme inactivation. Papaya is the source of papain, a protolytic enzyme with many
food uses. Papain is found in the peel latex, primarily in the immature fruit and industrially extracted, but absent from ripe fruit. Fruit from which latex is harvested are unsuitable for quality flesh or juice utilization. Another enzyme in papaya, pectinesterase, acts rapidly to demethylate pectin and form low methyoxide pectin gel with calcium. Hence, rapid heat inactivation, sweetening to 26ºBrix, or acidification to less than pH 3.6 is necessary to prevent gelation. Acidification followed by aseptic processing is an effective method for bulk handling the puree whose colour, bland flavour and high carotenoid content make papaya a popular blending stock for tropical drinks. Pectic enzyme treatment is necessary to thin the puree sufficiently to affect about a three-fold concentration to 24 to 36ºBrix.
Another species, Carica pentagona Babaco from northern South America merits mention. The fruit resembles a large papaya with orange flesh, but is much more acid, more flavourful and roughly similar in nutrient content. The juice is popular locally, but relatively unknown elsewhere. The dramatic flavour difference in these species suggests that there are intriguing opportunities to improve upon the Carica genus.
There are few fruits with a more appealing, delicate flavour than guanabana (Annona muricata L.); the fruit is a natural sherbet in its fresh state even before sherbet manufacture. This large oblong fruit with soft, white, fibrous cotton-like flesh is best separated from the large black seeds and consumed as a puree (Figure 15.4). The fragile skin defies mechanical peeling, although the seed-containing flesh can readily be pureed in a paddle pulper. The puree at ~15 ºBrix and 0.5 percent acid, pH 3.6 is moderately susceptible to darkening, prevented by application of sulphur dioxide, ascorbic acid or rapid handling and freezing.
Figure 15.3: Guanabana, fruit can exceed 5 kg each.
There are other Annonacea species with equally distinctive flavour appeal such as the Cherimoya (Annona cherimola) or custard apple (Nagy, et al., 1990). These are about as difficult to handle and puree as the bulky guanabana. All merit greater commercial development.
Acerola (Malpighia punicifolia L), known as Barbados Cherry due to the fruit's appearance, has the distinction of having exceptionally high ascorbic acid levels (Figure 15.5). Green mature fruit, although inedible, contain over 3 percent ascorbic acid and represent a natural source of vitamin C when harvested and extracted. The ripe fruit can have over 1 percent fresh weight of ascorbic as the major acid (Nieva, 1955). The red, cherry-shaped fruit are readily crushed and pureed in a paddle pulper to separate a thin orange pulp from the seeds. The acerola flavour is acid, ~5ºBrix, but bland and easily blended with other more flavourful juices. At 5 percent addition to other juices acerola contributes roughly the ascorbic acid equivalent of single strength orange juice, ~50mg/100ml.
Figure 15.4: Acerola fruit at various stages of maturity.
A popular frozen nectar base consisting of 45 percent passion fruit nectar (55:100 juice: sugar), 45 percent guava (48:100: puree: sugar) and 10 percent acerola nectar (juice: sugar 1:2) served as a well received example of tropical fruits for visitors to the University of Hawaii Manoa Campus. The product stored well at -20ºC and no change in colour or flavour was detected over a two-year period. With a reliable annual supply of fruits, it was unnecessary to carry frozen nectar base over one year.
Storage time is an important point to consider in juice sales. Even though processing and packaging technology can accomplish a lengthy shelf life, the goal is to sell the product to satisfied consumers who will promptly use it and generate repeat sales. All storage is expensive, particularly freezer space, so a very stable product that doesn't sell has no commercial advantage over a less stable but faster moving item. Stability simplifies inventory control and maintains quality, but sales appeal is most critical. Economics usually trumps technology; even mediocre products can survive and thrive over better items with less marketing support.
There are few fruits more aromatic than naranjilla (Solanum quitoense Lam), resembling an orange in size, shape and colour (hence the Spanish designation "little orange"). A ripe fruit in a room is readily detected and appreciated for the pleasant scent. Unfortunately this fragrance is diminished in the fresh juice and easily destroyed by heating. The flesh is a light green with the morphology of a tomato to which it is related. The fruit is easily juiced without peeling by passing though a paddle pulper with a ~1mm screen to separate the seeds, skin and pulp from the green juice. At a ºBrix of around 8 and over 1 percent acid (as citric), pH ~ 3.5, the juice is best used for blending (Ashurst, 1995).
The carambola (Averrhoa carambola) or star fruit, so called because of the 5-pointed star shape cross section of the fruit, has appeal in salads and as a garnish. The fruit is easily pureed to produce a thin yellow juice of ~6ºBrix and moderate acidity consisting primarily of oxalic acid. Single strength juice is weak, acidic and not very flavourful. Major products are a sweetened juice and a salted, fermented juice in the Orient (Nagy, et al., 1993). A locally popular carambola wine is produced in South Florida from sound culls from the fresh market.
Another popular Oriental fruit now grown widely in the Tropics is lychee (Litchi chinensis Sonn.) The white translucent flesh is also illusive to juicing, being protected by an attractive, inedible, red leathery skin and containing a large brown seed. The flesh and juice posses a fragrant pleasing flavour, greatly diminished by pasteurization. The ~16ºBrix juice is low in acid, has pH~4.6 to 5.0 and requires citric acid or blending with acid juices to optimize the B/A ratio and reduce the pH to around 4.0.
The seed that adheres to the flesh and the pliable, bitter skin require tedious hand peeling and separation. In view of the rapid discolouration accompanying juicing, the fruit must be handled gently and rapidly. Mechanization for peeling and deseeding has been reported on a commercial scale in Taiwan (Nagy, et al., 1993). The high value of the fruit dictates inclusion of lychee in nectars and beverage blends, instead of pure juice.
Lychee, along with close relatives, rambutan and pulisan, are highly prized as the fresh fruit in the Orient, so juice is still a comparatively minor co-product of fresh, canned and dried fruit operations. Canned nectars sampled in the mid-90s were overly sweet, but at least were not oxidized nor scorched, as they had been a decade previously. Curiously, lychee wine has a fairly harsh, sour flavour after fermentation requiring ageing and sweetening.
Banana is the highest volume tropical fruit in world trade. It is to the credit of horticulturists and post-harvest physiologists that ripe bananas are readily available year-round in remote reaches of the Northern Hemisphere. The fruit is primarily consumed fresh or as puree for baby food, bakery and confectionery uses. Harvesting and ripening
regimes dictate that a substantial volume of fruit cannot be shipped. Consequently, much is available for puree and other processed products.
The major restriction in manufacturing banana puree is its tendency to brown rapidly. Procedures for overcoming the enzymatic browning involve:
A juice can be made by enzymatic treatment of the puree according to the flow scheme depicted in Figure 15.6. Since enzymatic browning is very rapid, the procedure calls for peeling, acid adjustment to pH 4.2 with citric and ascorbic acids and rapid heating to 85ºC. The puree, now thickened due to starch gelatinization, is cooled to 60ºC, a macerating enzyme is added and held for 30 minutes. Afterwards, the thinned puree can be easily centrifuged and/or pressed to express the juice at about 22ºBrix. Yields average about 75 percent, puree basis. The juice can be clarified by centrifugation, filtered and concentrated to greater than 60ºBrix. Volatile essence recovery and add back reinforces the banana character of puree and juice.
Figure 15.5: Banana juice flowchart.
Single strength banana juice has a characteristic overly sweet, slightly salty, cloying taste, particularly if maintained at the initial banana pH of above 5.0. Acidification improves the flavour, but at such a high solids level, the clear yellow juice is best blended with more
acid juices for balance and colour. In view of the year-round abundance of bananas at
ripening facilities and substantial waste of fruit too ripe to ship, more uses for juice should be explored.
There are many other fruits of both tropical and temperate climate origins that merit exploitation as juice. These range from species and cultivars related to fruits already mentioned to those relatively unknown. Undoubtedly niche markets exist or could be developed for some. Most tropical countries have indigenous fruits with special local appeal. It is only a matter of time before those amenable to cultivation and processing scale-up appear on the world scene. Table 15.2 lists a few worth exploring.
Table 15.2: Some unique tropical fruits meriting juice evaluation.
Widely available and extensively utilized
Widely available and underutilized
Coffee and vanilla berries
Not exploited, but available
Cultivars exist with brilliant purple flesh
Longan, rambutan and pulisan
Related to lychee and as appealing
Flavourful, high Brix pulp
Sapote and sapodilla
Widespread, popular throughout the tropics
Exquisite flavour, very delicate fruit
Regional delicacy in parts of South America
Of some note is coconut water, a sterile filtered product developed and patented (pending) by FAO's Agro-industries and Postharvest Management Service, Agricultural Support Systems Division. The isotonnesic nature of coconut water makes it a natural oral rehydration fluid (sports drink). The water is quite perishable, but available as a by-product of coconut processing. Thermal processing adversely affects flavour, so sterile filtration represents a practical solution (FAO, 2000d). Coconut is also an ingredient in other juice beverage blends (Figure 15.7). The coconut component is probably coconut water. Although the milk, derived from comminution and pressing of the flesh and requiring stabilization of the emulsion also has beverage use (Somogyi, et al., 1996b).
Figure 15.6: Pineapple coconut drink.