doi:10.1016/j.biosystemseng.2005.09.008
Copyright © 2005 Silsoe Research Institute Published by Elsevier Ltd.
Pulsed Electric Field Assisted Pressing of Sugar Beet Slices: towards a Novel Process of Cold Juice Extraction
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A.B. Jemai
, 
and E. Vorobiev
Equipe des Technologies Agro-Industrielles, Département de Génie Chimique, Université de Technologie de Compiègne, Centre de Recherche de Royallieu, B.P. 20529, 60205 Compiègne, France
Received 17 April 2004;
accepted 14 September 2005.
Available online 28 November 2005.
The use of pulsed electric fields (PEF) as an intermediate treatment for the cold juice extraction from sugar beet ‘cossettes’ (i.e. long grated particles) has been investigated using a pilot scale multi-plate and frame pressing equipment (pressure of 5–15 bar; particles filling of 4·5–15 kg) and a pulse generator (1000 V–1000 A). It has been possible to validate laboratory-scale results (40 g of particles) by studying the feasibility and advantages of a PEF-assisted cold pressing of sugar beet cossettes on a much larger scale (4·5–15 kg). A best scheme scenario for an adequate PEF-assisted cold pressing of sugar beet cossettes consists of two initial pressing steps with an intermediate PEF treatment, followed by one or more washing steps and a final pulp pressing. A yield of about 80% in juice per initial mass of cossettes has been achieved before washing. By performing some washing and final pressing operations, losses of sugar in pulp could be significantly reduced to about 3% of the initial sugar content. The purity of pressed juices was systematically higher following PEF treatment compared to that of juices prior to PEF treatment (96–98% and 90–93%, respectively). Spectrophotometric colour measurements, reflecting impurities and fine suspended particles contents in juices, showed that purified PEF juices had colour values three to four times lower than those of purified factory juices, a difference confirmed by the colour of sugar crystals obtained from both types of juices. In addition, significant amounts of potassium, sodium and α-amino nitrogen were found to remain in PEF-treated particles, which explains why better purity juices are obtained following PEF treatment.
Fig. 1. Simplified schematic of filter-press equipment (Bouzrara, 2001): (1) membrane plates; (2) and (3), false plates; (4) moving head; (5) fixed head; (6) guiding rail; (7) tightening piston; (8) filter body; (9) liquid recipient
Fig. 2. Schematic of a one chamber configuration of plate and frame filter press
Fig. 3. Experimental procedure: PEF, pulsed electric field
Fig. 4. Typical juice extraction kinetics during a 3-press process; pulsed electric field (PEF) applied at the end of the 1st pressing stage
Fig. 5. Normalised accumulated mass of pressing
Fig. 6. Juice yield during a typical 3-press/3-wash process at 5 bar (error bars are standard deviation values based on 13 experiments)
Fig. 7. Juice yield (in normalised form) after the 3-press process as a function of energy input (optimisation experiments): —, model; 
, experiment
Fig. 8. Purity of different juices for a typical 3-press/4-wash process at 5 bar (error bars are standard deviation values based on 43 experiments)
Fig. 9. Purity difference between the juices from the 1st press and that of the 2nd press, 3rd press, and 1st wash, respectively (error bars are standard deviation values based on 43 experiments)
Fig. 10. Best scheme scenario for a pulsed electric field (PEF)-assisted cold pressing of sugar beet cossettes: MC, moisture content; NSS, non-soluble solid content; MC, moisture content; SC, sugar content; SS, soluble solids content; dW, dry weight
Fig. 11. Correlation between juice yield and cake dry weight after a 3-press process: —, model;
, experiment; r2, coefficient of determination
Table 1.
Electrical equipment parameters and characteristics
Table 2.
Scale-up performance of pilot scale results compared to laboratory scale data
Using 40 g of grated cossettes (
Bouzrara, 2001).
† Corresponding to 2nd+3rd juices with 3rd juice representing an average of 10% yield.
Table 3.
Characteristics of different juices for a 3-press/3-wash process at 5 bar
PEF, pulsed electric field.
Table 4.
Colour of factory and pulsed electric field (PEF) juices and final crystals in the international commission for uniform methods of sugar analysis (ICUMSA) Units
Summarised from SUBEEP report (
Anonymous, 2002).
† Béghin-Say factory at Chevrière, France.
Table 5.
Estimated residual contents of pulp (per 100 g) following pulsed electric field (PEF) versus extraction process (extrapolated at sugar content SC=2%)
Summarised from SUBEEP report (
Anonymous, 2002).
† Extrapolated values from experimental data.
‡ Common industry values.
Table 6.
Example of sugar loss reduction by one additional washing step using less wash water (three times 10% of initial weight of cossettes compared to four times 5%); process 1 versus process 2 corresponding to three and four washing steps, respectively
MC, moisture content; SC, sugar content; SS, soluble solids content; NSS, non-soluble solids.
Initial composition (per 100 kg beets):
MC=77·5%;
SC=17·5%;
;
NSS=4·32%.
† Initial compositions (per 100 kg beets):
MC=77·9%;
SC=17·5%;
;
NSS=3·77%.
‡ PEF, pulsed electric field.
§ Sugar extraction (overall sugar yield divided by initial sugar content) of 93·54% and 97·03%, respectively.
Table 7.
Effect of the pressure on the overall process performances; process 1† versus process 2‡ corresponding to 5 and 10 bar pressures, respectively
MC, moisture content; SC, sugar content; SS, soluble solids content; NSS, non-soluble solids.
PEF, pulsed electric field.
† Initial composition:
MC=77·5%,
SC=17·5%;
;
NSS=4·32%.
‡ Initial compositions (per 100 kg beets):
MC=77·7%,
SC=17·7%;
;
NSS=3·05%.
§ Sugar extraction (overall sugar yield divided by initial sugar content) of 93·54% and 96·30%, respectively.
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