7. PROCESSING AT
8.2 Floating pulp
Premium pulp production has become more im por tant because adding pulp to juice prod- ucts is thought by many people to give a fresher ap pear ance and better mouthfeel to juice. Pulp can also add value to products because many con sum ers are prepared to pay more for a juice con tain ing pulp.
Floating pulp consists of the larger solid par ti cles in juice comprising mainly ruptured cell sacs and segment walls. It is separated from the juice in fi nishers. Pulp contains mostly car- bo hy drates, pectin and crude fi bres. The crude fi bres are built up of hemicellulose and cel lu lose polysaccharides and give stability to the tis sue forming individual juice sacs.
For many years orange pulp was a by-prod uct of little value used for the production of pulp wash or cattle feed. This has changed in re cent years. Today, more pulp is processed for sale as fl oat ing
pulp for addition to juice.
Section 5 describes the different ways pulp is processed. This section deals with the quality and characteristics of the commercial pulp prod uct sold for addition to orange juice.
8.2.1 USEFUL TERMS
In talking about orange pulp, it is of great help to know the correct meaning of terms com mon ly used to describe raw materials and prod ucts. Pulp, juice sacs, juice cells and fi bres are all terms used to describe the same thing. Add ing to the confu- sion is the fact that many terms have different meanings when used in fruit process ing and with reference to the end prod uct at the juice packers.
Terpeneless oils
Folded oils Top-note com pounds
Aroma fractions
Fig. 8.5 The basic components of a fl avour system. 8.2 Floating pulp
AT THE FRUIT PROCESSOR
Pulp
The by-product stream at different process steps within the plant and also the product sold com- mer cial ly.
Finished pulp
The pulp stream leaving the fi nal fi nisher with a very high concentration of solid particles. This is the product sold as “frozen pulp”.
“Dry” pulp
Another term used for fi nished pulp. The name is misleading because the “dry” pulp contains juice adsorbed to solid particles
Pulpy juice
Used in Florida for the pulp stream to the pulp pasteuriser and to the aseptic bag-in-box fi ller. The concentration of solid particles is about 500 g/litre.
Solid particles in pulp
These are mainly cell walls and segment walls. The cell walls are fragmented during extraction. The length of particles varies from <0.5 mm up
to 25 mm.
Bottom pulp (= sinking pulp)
Very small solid particles which fl ow with the juice through the fi nisher screens.
Washed pulp
Solid particles which have been washed with wa- ter to remove juice. Used for cattle feed or sold in frozen form after removing most of the water. Pulp wash
Sugars and other juice solubles recovered from pulp by washing it with water. Sold as 65 °Brix concentrate in frozen form. Sometimes added to orange juice before evaporation.
Pulp concentration
A confusing term which means the amount of solid particles in the pulp stream. Methods to measure pulp concentration vary.
FOR TRADING
Frozen pulp
Finished pulp sold in frozen form. Frozen cells
Same as frozen pulp. Aseptic pulp
Pulp sold in aseptic bag-in-box containers. Con- tains considerably more juice than frozen pulp.
AT THE JUICE PACKERS (END PRODUCT)
Pulp
Used by some people to mean “sinking pulp” and by others to mean “fl oating pulp”.
Sinking pulp (suspended pulp)
Very small solid particles (<0.5 mm) which set tle from the juice with time (or spin down in a cen- trifuge). Sinking pulp is part of all citrus juic es, even those without added fl oating pulp.
Floating pulp
Larger solid particles. Most fl oat to the top after juice is stirred.
Floaters
Used mainly in Florida for fl oating pulp. Fibres (= fl oating pulp)
Sometimes used to mean large solid par ti cles. Added cells (= fl oating pulp)
Frozen or aseptic pulp added to juice. Added pulp (= fl oating pulp)
Frozen or aseptic pulp added to juice. Sacs or whole cells
Intact citrus cells which still contain juice. These liquid-fi lled cells cannot be obtained by normal extraction methods. A product often sold canned in syrup and added to juice drinks.
Floatability
The proportion of added cells that fl oat to the top when added to juice.
Unless otherwise stated, in this text the ex pres sion
Oil content
The concentration of oil is an important quality parameter when fl oating pulp is added to juice. This is because the oil level in the pulp stream is of ten higher than in the corresponding juice stream. Hydrophobic (not mixing easily with water) oil droplets and hydrophobic cell mem- branes are naturally attracted to each other, par- tic u lar ly when present together in a hydrophilic (mixing easily with water) juice environment. An ex ces sive oil content in the fi nal juice gives it a harsh and burning taste.
A reamer-type ex trac tor normally gives an oil content of 0.03–0.06 % v/v, whereas pulp from a squeezer-type ex trac tor may contain oil levels from 0.05 % v/v up wards. To minimise the oil content from squeez er-type extractors, so-called low-oil ex trac tors can be used.
8.2.2 FLOATING PULP PROPERTIES
The two main types of orange pulp on the mar ket originate from squeezer-type and reamer-type ex- tractors. The two extraction methods pro duce pulp with somewhat different prop er ties and therefore affect pulp quality. Pulp from reamer-type extrac- tors has longer cells and low er oil levels than pulp produced in standard squeezer-type extractors.
Due to the increased demand for high-qual- i ty pulp, some plants have extractors adjusted to optimise pulp quality rather than to maximise juice yield.
Pulp properties
The properties of fl oating pulp are not very well defi ned in the juice industry or by juice pack ers. However, some properties are more im por tant than others. These are discussed be low. See also Table 8.3.
Cell length
Generally, pulp with longer and less damaged cells has better fl oatability and provides a mouth- feel closer to fresh juice.
A reamer-type extractor produces a pulp with longer fi bres and less fragmented cells com pared with pulp from a standard squeez er-type extrac- tor. Pulp from reamer-type extractors can contain fi bres up to 25 mm long. In pulp from a standard squeezer-type ex trac tor, most cells are shorter than 5 mm and about 40 % are short er than 1 mm. However, a new system of squeeze extraction that yields longer cells has been in tro duced.
The visual difference between pulp from the two types of extractor is illustrated in Figure 8.6.
TABLE 8.3 FACTORS EFFECTING SELECTED QUALITY PARAMETERS FOR PULP PRODUCTION
Cell length Oil level Brix/acid ratio Defect rate Microbial status Extraction method • •
Fruit variety • • • Time of season • •
Fruit size •
Pulp recovery process • • Extractor settings •
Operation of fi nishers •
Fig. 8.6 Illustration of relative pulp Reamer-type extractor
Standard squeezer-type extractor 8.2 Floating pulp
In calculating the total oil content in the fi nal prod uct, the con tri bu tion from both the fl oat ing pulp and the juice must be taken into ac count. Other properties
Apart from cell length and oil levels, quality pa- ram e ters such as taste, colour, °Brix, ratio and microbial status are also important. The °Brix and ratio values strongly depend on what orange variety the fl oating pulp comes from, but they should be similar as for orange juice. Flavour and colour are often specifi ed as “typ i cal”.
8.2.3 FLOATING PULP CONCENTRATION It is important to know the fl oating pulp con- cen tra tion both at the juice processor and at the pack er. There are several dif fer ent meth ods of an a lys ing the pulp con cen tra tion de pend ing on whether it is a pulpy juice stream, fi n ished pulp or fi nal single-strength juice.
The pulp stream or fi nal juice can be an a lysed by pouring it onto a screen with de fi ned hole size. Excess juice is drained from the screen, with or without shaking, and the screen plus pulp is weighed. The result is expressed as grams pulp per litre (or quart) juice. Al ter na tive ly, juice is poured into a glass beaker to see how much set- tles and how much fl oats after a certain time. A method used by many proc es sors in Flor i da and Brazil uses screens and a cer tain shak er that shakes the screens at a de fi ned fre quen cy and am pli tude. This is an at tempt to stand ard ise the screening method.
Screens with different mesh numbers are used to analyse fl oating pulp con tent in the laboratories of juice plants. In Flor i da the 20 mesh screen is the norm, where as some Bra zil ian producers use a 40 mesh screen. The hole size of screens can have a signifi cant effect on analysis results. When small er screen holes are used, the pulp re leas es more water dur ing anal y sis. There fore, exactly the same meth od must be used if meas ure ments are to be com pared.
Mesh number Hole size, m 20 850 40 425
QUICK FIBRE (QF)
Quick Fibre is an analysis method used to de- termine the “dryness” of fi nished pulp. 200 g of pulp is mixed with 200 ml of water and stirred for 1 min, left alone for 3 min and then stirred again for 1 min. Thereafter, the mixture is screened and shaken for 3 min. A QF value equals the weight of the liquid (g) drained from the screen. A high Quick Fibre value means that the pulp analysed has a high juice content. A low QF indicates that the fi nished pulp an a lysed is dry and has ab- sorbed some of the add ed wa ter.
The QF method is mainly used during fruit processing to de ter mine the correct fi nisher set- tings. Typical clas si fi ca tions of QF val ues are listed below.
Classifi cation of Quick Fibre (QF)
Finisher Brazil Florida settings (40 mesh (20 mesh
screen) screen) QF value QF value Very tight <130 Tight 130-150 <150 Moderate 150-180 150-180 Loose 180-210 180-200 Very loose >210
Source: 1) E. A. Nonino 2) Dan A. Kimball
A special method called Quick Fibre (QF) is used to analyse commercial pulp (fi nished pulp) leaving the producer. It determines the dryness of fi nished pulp and this method also uses a FMC shaker and a screen. The dryness of the pulp is set in the fi nishers and is an important process parameter because it determines not only the juice yield but also the qual i ty of both juice and pulp.