Faced with the current economic realities, producers worldwide are searching for new options of surviving, as well as expanding their business. One of the many opportunities to grow markets, turnover and profits is by adding value to farm produce through further processing.
Agro-processing of field crops
Two types of processing methods may be performed on raw materials:
Primary processing: This type of processing includes the simplest of processes such as washing, peeling, chopping, ageing, milling of wheat for flour production and the processing of sugar cane.
Secondary processing: This type of processing involves the conversion of primary processed products into more complex food products, and includes procedures such as mixing, depositing, layering, extruding, drying, fortifying, fermentation, pasteurisation, heating, etc.
Avocado
Avocado oil from soft fruit: Avocado oil can be extracted from the soft fruit or dehydrated product. The oil recovered from the soft fruit is more desirable as it is free from solvent residues or flavour deterioration due to ultra-high temperatures. This oil is highly prized for use in soaps and cosmetics.
Guacamole is a dish consisting of mashed avocado’s mixed with chopped onions, tomatoes, chilli peppers and seasoning.
Banana
Banana purée is the crushed and pasteurised liquid that can be used in confectionery products, beverages, sauces, flavourings and fillings as well as in fruit juices. The product is preserved by aseptic packaging or freeze storage.
Banana concentrate: Banana purée is concentrated by evaporation. The concentrate is used as base fillings, beverages, sauces and puddings.
Banana flour is the dried product produced from mashed green bananas.
Frozen bananas. Fresh bananas are individually quick frozen (IQF) to produce a ‘fresh fruit’ which maintains individual identity and is just right for integration into muffins and other bakery products. Frozen bananas can also be used in fruit cocktails and breakfast cereals.
Dehydrated banana slices are prepared from ripe, peeled bananas by an air-drying or vacuum-drying process. The slices are dehydrated using air convection dryers such as tunnel dryers to a moisture content of between 4 and 7%. Vacuum drying produces a superior product, and is able to reduce the moisture content to below 3,5% to produce a crisp chip-like snack that retains its original colour and flavour for over a year.
Solar-dried bananas (small scale) have a moisture content of 15%, a soft, leathery texture and characteristic banana flavour. Ideally the colour should be as light as possible. Solar drying makes maximum use of solar heat to dry a food product. It can be used as a replacement for sun drying since it causes fewer losses, dust contamination and reduces the drying time. It does, however, still require fair weather conditions to be effective.
Sun-dried bananas: Banana slices are dried in direct sunlight, on racks on the ground for 5–7 days. Hot, dry climates are required for the successful drying of any fruit. Sun drying reduces the moisture content of the bananas to 15%. The end product is soft and leathery with a characteristic banana flavour.
Banana flakes are a dried product produced from banana purée. Drying is performed on drum (roller) dryers. The flakes can be ground to produce banana powder. Banana flakes and powder are used by the baking and confectionery industry.
Figs
Sun-dried figs are eaten as a fruit snack or used as an ingredient in baking. It has a soft, chewy texture and characteristic fig flavour. Ideal cultivars for drying should have a strong flavour, high density and solid-to-acid ratio to produce a dried product with the required taste.
Tunnel-dried figs: Fresh figs are dried in tunnels to a final moisture content of between 12–17%. The product is eaten as a fruit snack or used as an ingredient in baking.
Frozen figs: Fresh figs are sliced and frozen in sugar syrup for later use in processed foods and baked goods.
Guava
Guava purée is prepared from whole, fresh guavas by means of a maceration or pulping and screening process. It is preserved by freezing, canning or aseptic packaging. It may also be concentrated. The purée is used to prepare guava nectar and other beverages, syrups, sauces, toppings, jams and jellies.
Guava fruit leather: Guavas do not dry well in the form of pieces, but can be dried fairly well in a purée to produce a fruit bar or fruit leather. It is further recommended that guava purée be mixed with that of other fruits such as mango, banana or papaya to improve the flavour of the product.
Guava juice is the liquid expressed from the edible portion of the fruit, by pressing or other mechanical means. It is naturally turbid due to cellular components in suspension. Clarification can be accomplished by centrifugation. Guava juice is mainly used as a breakfast food, in punch or bakery products. It also serves as the packaging medium for many other canned guava products. The juice can be used to manufacture guava jelly. Guava juice is prepared from fresh guavas or guava purée.
Guava purée concentrate: Guava purée is concentrated to reduce the volume and thus transportation and storage costs of the product. Concentration is also a method of preservation since it reduces the water activity of the product.
Guava fruit bar: Guavas do not dry well in the form of pieces, but can be dried fairly well in a purée to produce a fruit bar or fruit leather. A fruit bar is a dried form of fruit purée that has been sweetened with sugar. It has a moisture content of between 15–20%, a soft, chewy texture and sweet taste characteristic to the particular fruit used. Both pink and yellow guava cultivars can be used to produce a fruit bar. Approximately 400g of fresh guavas are necessary to produce 100g fruit bar, i.e. a yield of 25%.
Kiwi fruit
Kiwi fruit juice (clarified) is the liquid expressed from sound, mature kiwi fruit. It has a sweet-tart flavour and high acid content. The juice is clarified by a combination of separation, filtration and enzyme treatments.
Kiwifruit juice (cloudy) is also expressed from sound, mature kiwifruit, having a sweet-tart flavour and high acid content. Cloudy kiwifruit juice is partially clarified and may be concentrated to a soluble solids content of 20°Bx (degrees Brix). The juice is preserved by bottling or canning while the concentrate is frozen.
Kiwi fruit nectar is a cloudy kiwi fruit juice that contains added sugar, stabilisers and citric acid, as well as other optional ingredients such as preservatives. The nectar can be manufactured from fresh kiwi fruit of good quality or from frozen, deseeded kiwi fruit pulp. The finished nectar has a soluble solids level of 14°Bx and acidity of 0,75% (expressed as citric acid). Much of the appealing green colour is lost during the heat processing involved in producing the nectar, but this can be overcome by the addition of permitted artificial colours.
Kiwi fruit pulp is produced from ripe fruit that is washed, pulped and deseeded. It is preserved by freezing and has a maximum storage life of twelve months. It is mainly an intermediate product that is further processed into nectars, pie toppings, fruit yoghurt bases, ice-cream and other frozen dessert flavourings.
Concentrated kiwi fruit juice is produced from clarified juice that is concentrated to a soluble solids content of 60–70°Bx. The juice is preserved by bottling or canning while the concentrate is frozen.
Litchi
Litchi juice concentrate: Fresh litchis are used to produce a partial juice which is then concentrated by the process of water removal. The final product has at least double the strength of the standard ready-to-drink juice. Litchi juice concentrate is mainly used as a base for the preparation of beverages. The consumer simply adds and mixes a measured quantity of water or carbonated water with the concentrate to produce the beverage.
Mango
Dehydrated mango slices: Mangoes can be dehydrated in a firm, ripe or full-size green condition by air convection drying ovens, cabinets or tunnels. The final moisture content determines the use of the product. Mango cultivars with bright yellow/orange flesh that have minimum peeling and drip losses are ideal for dehydration.
Mango atchar: Green mangoes with premature soft seeds are suitable for atchar or oil pickles. Cured green mango slices are drained, mixed with spices and oil and filled into suitable containers and sealed. Extra oil is added at the top to prevent air entry. High acid mangoes (5–6%) were found to produce the best quality atchar.
Mango fruit leather: Fruit leathers are dried sheets of fruit pulp with a soft rubbery texture and sweet taste, characteristic of the fruit used. Most types of fruit can be used to produce fruit leathers, either alone or in mixtures. The most commonly used fruits are apples, various berries, mangoes, peaches, plums, mangoes, guavas, pineapples and passion fruit. Layers of different coloured leathers can be pressed together to form a sandwich. The single layers can be cut in various shapes or strips that can be rolled up.
Mango juice is the strained liquid extracted from ripe mangoes. It is thus free of skin, seed and coarse particles, but contains solids in suspension. Mango juice has a bright yellow colour with typical mango taste. It is preserved in a ready-to-drink form by acidification and a mild heat treatment followed by canning, bottling or aseptic packaging.
Mango purée is the crushed, sieved and pasteurised pulp obtained from fresh ripe mangoes. It can be used in confectionery products, beverages, sauces, flavourings and fillings and in fruit juices. The product is preserved by freezing, canning or aseptic packaging
Frozen green mango slices are a very popular dessert in Asia. Green mangoes with premature soft seeds are suitable for this process.
Canned mango pieces: Ripe, firm mangoes are used for the manufacturing of canned mango slices.
Papaya
Dried papaya pieces: Papaya pieces are dried to produce a sweet, fruit snack with a chewy texture. The final moisture content can be between 15–25%, depending on the desired texture. Firm ripe papayas of the red or yellow varieties are used. The shelf life of this product is about 90 days at ambient temperatures. Storage temperatures of below 7°C will extend the shelf life.
Papaya juice is the liquid extracted from papaya purée. Frozen or freshly prepared papaya purée can be used. The purée is diluted with water to produce a juice with a 12–15°Bx content, a bright yellow-orange or pink-orange colour, sweet taste and typical papaya flavour. There are two major problems facing the processor, namely gelation of the purée due to the liberation of enzymes upon pulping, and the development of off-flavours originating from the skin, latex or seeds.
Canned papaya pieces: The green mature or semi-ripe papayas are used in the preparation of canned papaya chunks or slices. Papaya pieces are often canned in mixtures of subtropical fruit, including mango and passion fruit.
Passion fruit
Passion fruit juice is the liquid expressed from the edible portion of the fruit by pressing or other mechanical means. It is yellow-orange in colour and is particularly fragrant. The juice is used as a beverage on its own or in a blend with other tropical juices.
Pineapple
Dried pineapple pieces: Pineapple slices are dried to produce a sweet fruit snack with a chewy texture and a characteristic pineapple flavour. The final moisture content can be between 20–25%, depending on the desired texture. Firm ripe pineapples are used. The shelf life of this product is roughly 90 days at ambient temperatures. Storage temperatures of below 7°C will extend the shelf life.
Canned pineapple pieces: Ripe pineapples are peeled, cored and cut into rings, pieces or crushed for canning. Sugar syrup or pineapple juice may be added as packaging liquor. – Theresa Siebert, ARC
| The manual on the Agro-Processing of Poultry contains complete information on the products discussed above as well as many other processing methods and products available to the poultry farmer and processor. The manual is available from the ARC-Institute for Agricultural Engineering. Contact: Elmarie Stoltz, 012 842 4017, stoltze@arc.agric.za |
