Fruit puree is the edible part of the fruit, pulped, homoge- nized, or manufactured by a similar process (Anon 1996). It is a semiprepared product; it contains the fruit in a sieved, ho- mogenous form, and contains no recognizable fruit pieces.
Fruit puree is not suitable for direct consumption by most people except infants, elderly, and individuals under medi- cal care. However, it is the raw material for production of jams, marmalades, fruit juices, and bakery fillings, and it is used as an ingredient in many food products. Industri- ally processed fruit purees can be preserved by preservatives, by cooling, freezing, heating, concentration, and addition of sugar. The best way to preserve it is with aseptic tech- nology. Properly ripen and good-quality fruit is suitable for puree production. Exceptions can be made in the case of fruits containing a high concentration of pectin (e.g., apple, gooseberry, etc.).
The typical fruit puree processing steps would include preparatory steps of fruit selection, washing, sorting for de- fects, dicing, etc. Blanching is usually necessary prior to pulping to decrease losses, energy requirement, and mechan- ical stress on the sieve. Crushing of the blanched fruit is performed gradually by passing through a crusher, a coarse sieve, a fine sieve followed by homogenization. The homog- enized fruit puree can be preserved by adding preservatives such as SO2(max. 2 g/kg), benzoic acid (max. 1.5 g/kg), sor- bic acid (max. 1.0 g/kg), or by pasteurization of puree (filled in 5-liter jars with hermetic seal) at 94–96◦C.
In the modern fruit processing industry, fruit purees are preserved by aseptic technology. In this case, a continuous, so-called “scratched-wall” heat exchanger (type ␣-Laval, Crepaco, Manzini, APV, etc.) is used for inactivating yeasts and molds. The sterile product is filled under aseptic con- ditions into sterile packaging (laminated foil bags, bag-in- box, barrels, containers, etc.), hermetically closed, and stored until further usage (K¨ormendy and T¨or¨ok 1990, Potter and Hotchkiss 2001).
Single-strength apple puree can be concentrated to 20◦–25◦Brix in a multistage vacuum evaporator or film evaporator with scraper. These evaporators are suitable for production of a concentrate of 40◦Brix. Concentrated fruit purees not only enrich the product with valuable extracts, characteristic taste, flavor, and color, but they also contribute to the product’s functional properties because of their high pectin and fiber content (Hegenbart 1994).
In great demand for fruit preparations are berries and cher- ries because of their high vitamin and mineral content, and attractive taste and color. The vitamin content of fruits can be protected by use of mild processing parameters. In this case, the processing of fruits with high vitamin content (elderber- ries, rosehip, sea buckthorn, etc.) results in fruit preparations with valuable composition; and when used as ingredients, in-
creases the nutritive value of the combined product (Lampe 1999, Barta et al. 2002).
The above-mentioned berries and red-grape-vine are pro- cessed to give anthocyanin extracts and concentrates as well, which are used as natural food colorings. The stability and intensity of elderberry anthocyanins are increased by the fact, that the high anthocyanin content is coupled with high vita- min C content of the fruit (St´eger-M´at´e et al. 2001).
A similar synergic effect between anthocyanins and vita- min C was proved in case of blackberries as well (St´eger-M´at´e et al. 2002). The antioxidative effect of the anthocyanins helps to protect the vitamin C content (Gardner et al. 2000).
Selected Fruit Purees 1. Banana puree
Banana puree is by far the most important processed product from the pulp of ripe bananas. The puree has a creamy white to golden yellow color, free from musty or off-flavors. Banana puree is an important infant food.
Puree canned in drums by an aseptic canning process, it is a good ingredient for bakery products and ice creams.
The puree can be successfully canned by the addition of ascorbic acid to prevent discoloration and used as an ingredient for dairy desserts, bakery items, drinks, processed foods, and sauces and as a part of special diets in hospitals and nursing homes. In canned banana puree, it is important to lower the pH approximately to 4.2 with citric acid. Sugar is added to balance the sugar/acid ratio.
2. Mango puree
Mango puree is the most common semiprocessed prod- uct of this fruit. Mango puree, prepared from ripe fruits is particularly relished for its succulence and exotic flavor. It can be used for making jams, jellies, bever- ages, and various dairy and bakery products that contain mango as an ingredient. Mango puree in fresh, pro- cessed, or chemically preserved form appears promising because of the ease of handling and the low cost of pro- duction. The puree requires a heat treatment sufficient for inactivation of enzymes. A plate heat exchanger is usually used to heat the product to 108–112◦C for 2 minutes, and then the puree is cooled rapidly. Sucrose and corn syrup are acceptable sweeteners in the prepa- ration of mango puree. The puree can be stored under suitable conditions (freezing or chemical preservation) for 6–8 months.
3. Peach puree
Fruits are washed, trimmed, and cooked, and the pulp passed through a continuous rotary unit with perfora- tion, followed by the addition of ascorbic acid (0.14%).
Clingstone peaches are preferable for the preparation of baby food because of the yellow color of the puree, better storage ability, nonmelting flesh, and thicker con- sistency. The peach pulp is blended with sugar syrup,
sterilized at 110◦C and deaerated. It can either be canned or preserved in jars. The peach baby food has soluble solids of 21%–22%, a pH of 3.0–4.1 and 0.35%–0.45% acidity as citric acid.
4. Some other fruit purees
Subtropical fruit puree such as kiwifruit puree, plum puree, and some tropical fruit purees such as guava and papaya purees are available on the market.
r Guava puree, also known as guava pulp, is a relatively liquid product. Guava puree is an excellent source of ascorbic acid, niacin, thiamine, riboflavin, calcium, iron, phosphorus, and dietary fiber. The ascorbic acid contents range in guavas from 100 to 1000 mg/100 g fruit. It is commonly used for the preparation of nectars, various juice-drink blends, ice-cream toppings, jams, and jellies.
r Kiwifruit puree is used as a fruit topping and in yogurts.
The product has a fresh green color and high natural flavor.
r Papaya puree is a liquid product with a light yellow color and sweet flavor, which is prepared by the mac- eration of papaya flesh into a semifluid-like product.
Much papaya products, such as juices, nectars, jams, jel- lies, syrups, toppings, and dried fruit rolls can be made from papaya puree.
r Avocado puree is often used as a filling for several kinds of sushi, including California rolls. It is also popular in chicken dishes and as a spread on toast. In Australia and New Zealand, it is commonly served in sandwiches, on toast, or with chicken.
A puree of the fruit was used to thicken and flavor the liqueur Advocaat in its original recipe, made by the Dutch population of Suriname and Recife, with the name deriving from the same source. The fruit has a markedly higher fat content than most other fruits, mostly mo- nounsaturated fat, and as such serves as an important staple in the diet of various groups. About 75% of an Avocado’s calories come from fat, most of which is monounsaturated fat. Avocados also have 60% more potassium than bananas. They are rich in B vitamins, as well as vitamins E and K. They have high fiber content among fruits including 75% insoluble and 25% soluble fiber (Naveh et al. 2002).
r Plum puree is used in ice-cream mixes, confectionery products, and meat sauces. The product has a light yel- low color and tart–sweet flavor (Anon 1999).
Fruit Pulps
Pulp is the edible part of the fruit, possibly without the skin, shell, stones, etc., sliced or crushed, but not sieved (Anon 1996). It is a semiprepared product, containing crushed fruit flesh with recognizable pieces, processed of washed and se- lected raw material. It is not suitable for direct consumption.
Fruit-processing industry is producing jams from fruit pulp and fresh fruit as well.
Fruit pulps differ from the previously mentioned fruit purees. “Pulping” means to crush washed and selected fruit flesh after separation of the peel, shell, stones, and stalks as needed, by a cog-crusher, fruit-milling machine, or ham- mer grinder, without crushing it by a sieve. These machines crush the fruit flesh to coarse ground, recognizable pieces.
The provisional preservation of the cleaned and crushed fruit flesh can be performed by preservatives, heat, cooling, or freezing. In the case of chemical preservation, the pulp is mixed with a given preservative (e.g., 0.03% SO2, 0.15%
benzoic acid, 0.1% sorbic acid, or with their Na or K salts).
The chemical preservatives are effective below pH 3.5. If the pH value is higher, a combination of acid and preservatives is used. This step requires careful mixing of the pulp in a mixer of moderate revolution per minute and continuous in- jection of preservatives. Attention is given not to crush fruit pieces.
The advantage of the heat-preserved fruit preparation is that it does not contain preservative; however, a consider- able demand on package materials is a disadvantage, as the pasteurization of the pulp is often performed in 5-liter jars.
The slow rate of cooling following pasteurization can affect color, flavor, and nutrients. In case of pulps, use of aseptic technology is difficult because of the lumpy character of the product. The cleaned and crushed fruit flesh is blanched in water (added water cannot be more than the water quantity evaporated during the blanching) before pasteurization in a duplicator kettle or continuous blancher. The acidity of the blanched product can be adjusted to about 1% by adding citric acid, and the hot pulp is filled in glass jars and pasteur- ized without delay. The temperature at the center should be 86–90◦C for effective pasteurization.
Pulps of Exotic Fruits
1. As an example for the processing of fruit pulp of ex- otic fruits, see later, the pulping process of the fruit of the multipurpose tree from Nepal known as Lapsi.
It is a potential agro-forestry tree species for income generation and nutrient supplementation in the hills of Nepal. Farmers normally process the fruits for their household needs as pickles and chutney by crushing and boiling the fruits, whereas entrepreneurs purchase the fruits from growers and produce varieties of edible pulp cake indigenously called Titaura for selling in the market of Nepal as well as neighboring countries. This practice has been instrumental in raising the socioeco- nomic status of rural communities in Nepal (Chhetry and Gauchan 2007)
2. Baobab dried fruit pulp is derived from the fruits of the Baobab tree (Adansonia digitata), also known as the “upside down tree.” On pollination by fruit bats, this tree produces large green or brownish fruits.
The baobab tree is found primarily in South Africa, Botswana, Namibia, Mozambique, and Zimbabwe.
In July 2008, “Phytotrade Africa” was granted autho- rization to market Baobab dried fruit pulp in the EU by Commission Decision of the Advisory Committee on Novel Foods and Processes according 2008/575/EC [(ACNFP), Anon 1996]. There is a proposal to market baobab dried fruit pulp as a novel food ingredient for use in a range of food products, namely, smoothies, cereal bars, and other similar food products. The level of baobab dried fruit pulp would be between 5% and 15%. Marketing of a depectinized baobab fruit pulp as a novel food ingredient for use in biscuits, con- fectionery, and related food products is also envisaged.
Desiccated Fruits
Dehydration of food is one of the most ancient ways of preser- vation, and it is based on the limit of water activity (aw) for microbial growth. A aw of 0.65 and below is effective in controlling microbial spoilage.
Only healthy and ripen fruits are desirable for drying. Qual- ity requirements for fruits as raw material for drying include:
solid fruit flesh, easy separation of pits and skin, and small pits. Washed and cleaned fruit flesh is treated with SO2, if necessary to prevent enzymatic browning. This treatment gives some protection against microbial deterioration, pests, and nonenzymatic browning (Maillard reaction).
Withdrawal of water from the prepared fruit flesh can be performed in two different ways:
r Under tropical climate, people take advantage of the sunshine, and dry fruits in thin layer by slow, natural drying (figs, bananas, peaches, and apricots).
r Dehydration means treatment in tunnel or band dryers by blowing through warm air of 60–70◦C (apples and plums).
Residual water content of dehydrated fruits is about 18%–24%, and when adequately packaged they are long last- ing without any damage because of their high-sugar content and low (aw=0.72–0.75) water activity.
Quality requirements related to the dried product are the following:
r Solid, plastic, and creamy but not sticky consistency and leather-like surface of dried prunes and apricots.
r Bright color of dried apple rings, light color of peaches, and other fruits.
r High-sugar content, harmonic sugar/acid ratio, easy dis- connection of the stones.
r Bigger size, thin skin, and a pleasant, pliable consistency (dried figs).
Dried grapes are taken in trade as “raisins,” “sultanas,” and
“korinths.” Raisins have a brown color, and do not contain any pits. Sultanas have a light color without pits; korinths are smaller than raisins and sultanas, and are dark colored.
Dehydrated cherries and dehydrated apple products are widely used in foods such as pastry, confectionery products,
ice cream, frozen desserts, sweets, fruit salads, cheese, and yogurt (Somogyi et al. 1996).
Dried plums are available in many forms suitable for bak- ery use. Diced and extruded dried plum bits can be used to enhance fruit breads, pastries, muffins, and cakes. Gaining in popularity are the extruded bits, which are guaranteed pit free. These bits can also be modified by adding other flavors, fruits, and colors to extend the use of more expensive fruits.
The relatively low cost of dried plum paste makes it an ideal base to create various fruit-filling flavors for Danish pastry and bar cookies. The flavor of dried plums is compatible with other fruits, spices, and chocolate. In fact, dried plums act in a manner similar to vanilla to round out and enhance other flavors. Thus, dried plums can be used to reduce the cost and improve the quality of fillings. For example, strawberries can be used as the characterizing fruit in a high-quality filling us- ing dried plum paste as the base fruit. The high pectin content in dried plums provides added stability to heat processes, and can eliminate the need for added stabilizers.
Dried plum purees are available which contain approxi- mately 45%-dried plums, pureed with added water and/or corn syrup. Dried plum puree has the advantage of being soft and easily incorporated into batters and doughs. As will be illustrated later, it has been found to be an excellent fat replacer in bakery products (Scott 1993).
Sweetened and Candied Fruits
Sweetened fruits, soughs, candied fruits, and dehydrated- sweetened fruits belong to the above-mentioned product fam- ily. The sugar content of these products is increased to a degree, which prevents the growth of microorganisms. The important point here for preservation is to achieve a low water activity with the addition of sugars. The significant increase of sugar content of the fruit preparation can be performed by soaking in sucrose or glucose solution of gradually increas- ing concentration, under atmospheric pressure or in vacuum.
The concentration difference between the sugar syrup and fruit cells will be equalized in consequence of the difference in osmotic pressure. The saccharose content of 70%–80% of the fruit flesh can be achieved by soaking in concentrated sugar syrups. Its water content is decreased to 12%–21% by careful drying. Cherries and sour cherries, pineapples, pears, quinces, peaches, apricots, plums, figs, green almonds and nuts, chestnuts, gooseberries, strawberries, and raspberries can be processed to candied fruits of good quality.
The surface of sweetened fruits is coated with sugar glazing or with a thin layer of crystallized sugar for confectionery use.
The first-mentioned procedure is called glazing and the sec- ond is candying. A special group of this type of fruit prepara- tions is produced by treating the blanched peel of citrus fruits with sugar syrup, by glazing and drying it carefully. Prepara- tory steps of the technology are similar in the case of all types of sweetened products, but they are adapted to the charac- teristics of the raw material (e.g., washing, cleaning, pitting,
peeling, separation of the stems if needed, crushing, and blanching). Ready-made fruit preparations (sweetened fruits, soughs, candied fruits, and dehydrated-sweetened fruits) dif- fer from each other in finishing and final appearance. The raw material of all those products is the so-called “egute”—the cleaned, blanched fruit, soaked in syrup of starch or saccha- rose or in high-fructose corn syrup.
In case of fruits with high-fructose content (pears, quinces, melons, etc.) fruit preparations of low caloric content can be prepared. In this case, concentrated syrup of Jerusalem artichoke juice with high-fructose content (75%–80%) can be used as a sweetener (Barta 1993, Bray et al. 2004).
The aim of soaking in syrup is to saturate the cells opened during blanching with sugar. The form and consistency of the fruits can be stabilized as a consequence of this treat- ment. Following the above-mentioned preparative steps the fruit pieces should be fed in a flat vessel and filled with hot sugar syrup of 28◦–30◦Brix. The product being filled with the syrup stays in the syrup for 2–3 days, after that the syrup will be poured off, heated, and sweetened with sugar to a concentration value of 35◦Brix. This procedure is repeated five to six times, gradually increasing the concen- tration of the syrup to 60◦Brix. After having achieved this value the hot, sweetened fruit pieces are dripped, filled in 5-liter jars, and filled up with high-fructose corn syrup or starch at a concentration of 68◦–70◦Brix and hermetically packed. This semiprepared product (egute) can be stored and used.
Candied Fruits
Definition. Fruits preserved by soaking and heating in sugar syrup. The fruit is usually boiled in the syrup, and then can be left in syrup for 4–14 days. During the candying process, the naturally occurring water in the fruit is replaced by sugar, resulting in fruits with firm textures, sweet flavors, and ex- tended keeping qualities. Fruits that are already firm, such as pineapple, apricots, cherries, and apples, are best for can- dying. Soft fruits, such as most berries, will not survive the extended soaking process. The fruit is first poached in water and then sugar is added to the mixture. During the prolonged soaking period, the sugar syrup is gradually concentrated by adding more sugar periodically. Finally, the candied fruit is left to dry outside of the syrup for several days. It can be finished by being sugared or glac´ed, or can be used as is for dipping in chocolate or incorporated in other recipes:
r Candied apples are whole apples covered in a hard candy coating. The topping varies from place to place.
r Toffee apples are popular in the United Kingdom. These products are coated with a hot toffee.
r Caramel apples or taffy apples are created by dipping or rolling the apples in hot caramel, sometimes then rolling them in nuts or other small savories or confections, and
allowing them to cool. They are always served with a stick of sorts in the middle, making them easier to eat.
Sweetened Fruit Products
Sweetened fruit products are made from egute after being dripped, dried in a warm current of air, rolled in crystalline sugar, and packed in cellophane. Sweetened berry prepara- tions are manufactured also by blending whole, sliced, or crushed fruits with sugar in ratios such as 4:1, 3:1, or 7:1 (berries:sugar). A usual procedure is to “cap” or sprinkle sugar onto the surface of the berries, after they have been filled into pails or drums. In the United States, the quality of the berries is US Department of Agriculture (USDA) Grade A or B. These products are typically used in ice cream, yogurt, bakery preparations, or fillings (Somogyi et al. 1996).
The sough (glazed egute covered with a shining fondant layer) is manufactured by soaking the semiprepared prod- uct in a hot, oversaturated sugar solution, finally put on a grating and dried in a hot room. A bright fondant layer crys- tallizes on the surface of the fruit pieces, which makes the product attractive and protects its fresh, plastic consistency.
This procedure is called “glazing.” Dripped, dried egute is also used to manufacture candied fruit (fruit pieces, coated with a thin layer of crystallized sugar). The semiprepared product will be soaked in cool sugar syrup of 59◦–60◦Brix.
The surface of the fruit pieces is covered with a thin layer of granulated sugar. After the sweetening treatment, the syrup will be racked from the vessel, which is equipped with an outlet and a grating on the bottom. The fruit layer remains on the grating, and can drip and dry. The sugar layer on the sur- face of the fruit pieces, consisting of closely united crystals, protects the product from drying out quickly. An attractive packaging is improving the protecting effect of the sugar layer and also the marketability of the product. To manufac- ture sweetened-dehydrated fruits, the raw material is prepared in a similar way to the procedure used in the technology of canned or bottled fruit processing: washing, cleaning, peel- ing, and pitting, destemming, halving, or slicing, treatment of the surface in the case of light colored fruits with diluted solution of citric acid or H2SO3. The prepared raw material should be soaked 10–20 minutes under vacuum in a sugar solution of 15◦–20◦Brix and 60◦C. Duration of the treatment depends on fruit ripeness. After the well-made sweetening treatment the fruits become transparent. Because of the vac- uum effect, the intercellular capillaries will be deaerated, and sugar solution will penetrate into the air space. The less the aroma the fruit contains, the lower sugar concentration has to be adjusted (apples, pears: 30◦Brix; apricots and peaches:
35◦Brix; quinces: 40◦Brix).
Sweetened fruits should be carefully placed on a sieve, slowly dried to a water content of 15%–17%, at the beginning at a temperature of 70–75◦C, and at the end at 65◦C. To decrease hygroscopicity, the sweetened-dried fruits should be rolled in sugar powder. The sugar surplus can be removed