Citrus

Citrus species belongs to a large family Rutaceae, sub-family Aurantoideae. The family contains 140 genera and 1,300 species distributed throughout the world. Rutaceous plants are often aromatic by virtue of scented oils in leaves, flowers and fruits. The leaves characteristically contain oil glands. Another unique feature is a raised nectary disc subtending the ovary in flowers. The Aurantoideae sub-family is further distinguished by having a unique fruit type- the hesperidium, which basically a berry-like fruit with a leathery rind.

  • Uses of Citrus
  1. Production of single strength fruit juices and concentrates
  2. Squashes
  3. Citrus fruits powder
  4. Marmalade and other flavouring agents
  5. Production of citric acid, lactic acid, feed yeast and vinegar.
  6. Production of insecticide
  • Soil and Climatic Conditions required for Citrus Production

An average citrus tree requires about 100 – 112mm per annum. Our prevailing climatic condition of a distinct dry hot season in November through February, both months inclusive, suggests that supplementary irrigation is necessary during this period of great water stress for sustained tree vigour, high yield and premium fruit quality.

  • Planting Materials

Hitherto most of the local farmers in Nigeria use seedlings, which are not budded for planting. With the establishment of the National Horticultural Research Institute (NIHORT), Ibadan, budded citrus were produced for the establishment of citrus orchards. These budded seedlings have the advantage of coming into fruiting early (3 – 4years), develop less thorns which make harvesting difficult and also are higher yielding than seedling trees.

For the southern ecology, Cleopatra mandarin is recommended as rootstock while Rough lemon should be used in the Northern zones of the country because of the low rainfall, which is spread within 4 to 5 months of the year.

Nearly all internationally acclaimed varieties of citrus have been introduced at one time or the other into Nigeria. These varieties are found in scattered plantings in the orchards of most of the missionary schools, hospitals, State’s Ministries of Agriculture and Natural Resources and most recently in the progeny orchard collections of the National Horticultural Research Institute (NIHORT) in Ibadan, Mbato and Bagauda.

  • Citrus Processing

In the citrus processing industry, the raw juice, the peel residue and the seeds are the major product or by-products and from these sources a lot of industrial products are derivable. The raw juice itself, single strength {natural} fruit juice (orange, lime/grapefruit, etc.), concentrated juice, citrus fruit powders and fruit (orange) flour are some of the major industrial products. The peel residue, the pressed peel, citrus pulp and meal, peel oil, citric and lactic acids, brandy spirit, feed yeast, vinegar, marmalade, candied peel, citric pomade, etc. are some of the products.

Products derivable from the seeds are seed oil and meal. The level of sophistication of the citrus fruit utilization therefore depends on the technology available within the various citrus producing countries, and the dynamics of the cost of derivable products locally or internationally.

  • Orange Juice Production (Single Strength)

The basic industrial and domestic processing of citrus fruit for juice production is simple in that both processes (industrial and domestic) tend to ensure that the juice content of wholesome fruits are extracted without crushing the seeds nor allow contamination by the orange essence contained in the peel. The following constitute the steps in the processing:

  1. Cleansing
    The citrus fruit e.g. orange, the raw material is cleaned in a rotary washer, which is a propelling screw with a water injection pipe built in.
  2. Warm Water Heating
    Peeling of orange is easy if it is preparatory warmed by sending it through hot water. Therefore cleaning takes place in hot water rotary brusher.
  3. Peeling and Trimming:
    Orange is peeled manually on a trimming table, where inferior fruits are eliminated.
  4. Juice Extraction
    Peeled orange is fed into a hopper, at the entrance of which it is cut up into small fragments, which go into a cylindrical screen. It is scraped against the inner wall of the screen with a rotary scoop, so that the juice may be ejected from the holes of the screen and the waste from the outlet of the cylinder. The juice then goes into a tank after been strained through a secondary cylindrical screen.
  5. Preheating and Cooling
    The juice is heated to a temperature of 90°C for inactivation of enzymes as well as pasteurization, after which it is cooled to a temperature of about 40°C. The preheater and cooler are designed for mutual heat exchange for effective utilization of heat.
  6. Centrifugal Separation:
    A centrifuge is employed in order to remove any pulp contained in the juice.
  7. Desecration:
    In the course of the various treatments earlier discussed, a fairly large amount of air is bound to mix up with the juice. It is for the elimination of such air that the juice is made to fall in a form of thin film, in cylindrical equipment, which is subject to a pressure of 60 – 100 mm/Hg on the inside. Air is eliminated during the fall of the juice.
  8. Formulation
    This is done to adjust the concentration and the sugar contents of the juice. Addition of essence colours, activators, citric acid, etc. may also be done.
  9. Bottling/sterilization:
    The juice is bottled and sterilization done at temperature of 90°C for 30 seconds.

process flow sheet for the manufacturing of fruit juice

 

  • Concentrated Juice Production
  1. Vacuum Concentration:
    The deaerated juice (as described earlier) is concentrated to 1/5 – 1/6 of the volume/capacity under reduced pressure. The temperature of concentration differs somewhat according to the amount and temperature of cooling water. However it is normally about 30°C.
  2. Seasoning:
    The concentrated juice is adjusted in terms of concentration and sugar content.
  3. Sterilization:
    The concentrated juice is subjected to a 30 second heat treatment at a temperature of 90 – 95°C.
  4. Bottling/Canning:
    The concentrated juice is then bottled or canned (tinned).

process flow chart of the concentrated juice

 

  • Orange Squash Juice Preparation

Cleansed oranges are cut into halves either by hand or machine. The halves are pressed by hand against a revolving burr of ross fitted to a rosing machine. The juice is collected into a vessel. The juice is then filtered through a net cloth or passed through a sieving, machine (pulper), in which the juice gets brushed through a stationary cylindrical sieve by revolving stainless steel, wooden or brush paddles.

  1. Syrup Preparation:
    Sugar, citric acid and water are mixed together, heated(if necessary) cooled and filtered through cloth.
  2. Mixing:
    The filtered syrup is mixed with the juice and to improve flavour, peel emulsion of 2 – 4 oranges for every 100 oranges used or an appropriate quantity of essential oil or orange essences are added. Colour can be improved upon by adding edible colours like sunset yellow, edicol orange A.G. etc. (this must be resistant to the action of sulphur dioxide).
    Chemical preservative like potassium metabisulphite is added at the rate of one once/100 lbs of squash. This corresponds to approximately 350 ppm of SO2 in the squash (permitted by law).
  3. Bottling:
    The juice is bottled, capped, labeled and stored in a cool and dry place. The juice has a shelf-life of 1 – 1 year 6months without much change in colour or taste.

Process Flow Sheet for Fruit Beverage Manufacturing

  • Fruit Juice Powder

Dried fruit juice powders are largely in demand because of their high nutritive value compared to liquid juice if processed suitably. They are highly economic in space management, consideration and handling compared to the fresh fruit itself or the liquid (juice) derivative. The removal of water enables the product (powder) to be used in case of products where the pulp or juice would be unsatisfactory.

  1. Manufacturing Process
    The main raw materials for the fruit juice powder may be the fruit of second quality or the concentrates of the fruit juice.
  2. Juice Preparation
    If fruits are the basic starting materials, they are cleansed, peeled, cut and the juice extracted under strict hygienic conditions. Juice extracts are carefully and properly filtered.
  3. Evaporation
    Filtered juice is subjected to multi-stage evaporation to get concentrated juice. Such fruit concentrate is less prone to fermentation and occupies very less space. Reducing processing temperature through vacuum processing can minimize darkening of colour and the “cooked” taste of concentrate.
  4. Drying
    Drying of the concentrated juice to powdery form is accomplished through spray dryers. The resulting powder obtained is recovered in the settling chambers or bags beyond the drying chambers.

Process Flow Sheet of Fruit Juice Powder

  • Selected Products from the Citrus Peel

Dried citrus pulp finds its main use as feed for dairy and beef cattle. It is considered to be a desirable bulk carbohydrate concentrate that is fairly high in energy and a good source of calcium but low in phosphorous and carotene. It also exerts a mildly laxative action upon the digestive track, gives the hair coats sleek glossy appearance and is often the most economical local source of total digestible nutrients in some countries.

Citrus Peel Oils:
After juice removal from the fruit, the citrus pulp as with most animals feed is dried up to moisture content of approximately 8% to prevent microbial spoilage and spontaneous combustion in some cases. The demand for a year-round supply of citrus pulps requires that the product be placed in storage where insect infestation may not be a problem. Appropriate measures such as cleanliness of the warehouse and application of insecticides keep such insect infestation at minimum level.

Process Technology:
The cannery residues ejected by citrus fruit extractors is the raw material for the production of dried citrus pulp.

  1. Juice Extraction:
    Juice extracted from the fruit by citrus fruit extractors.
  2. Residue Accumulation:
    Large tonnage of the residue are accumulated and held in unprotected open pits or on cement slabs.
  3. Milling/Shredding:
    The peel residue is moved by slide conveyors or elevators to a hammer mill or shredder, where high speed rotating hammers or knives cut it into pieces (1/4 x 3/4 inch). Lime Ca(OH)2 or calcium oxide (CaO) (0.3 to 0.5%) is proportioned on the moving residue as powder or slurry. The lime reacts with the acidic component of the residue, which slowly turn from bright yellow to straw coloured product. This brings about a rapid degrading and demethylation of pectins in the peel. The mixture becomes more liquid and much less slimy and is ready for pressing and drying.
  4. Pressing:
    The limed residue is pressed in the continuous presses and the moisture content reduced from 82% to 72%. The pressed residue and press liquor are then further processed independently.
  5. Drying:
    The curried and pressed residues, containing from 65 to 75% moisture is conveyed to a rotating drier and dried up to 6% – 8% moisture level.
  6. Separation of products:
    The dried pulp is separated into 3 products:
  • Fines or dust (1%).
  • Citrus meal (14%).
  • Dried citrus pulp (85%)

 

 

 

 

 

 

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