Journal of Microwave Power
ISSN: 0022-2739 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/tpee19
Microwave Drying of Microorganisms:I. influence of the Microwave Energy and of the Sample Thickness on the Drying of Yeast A. M. F. Gomes, G. F. Leonhordt, M. Torloni & W. Borzoni To cite this article: A. M. F. Gomes, G. F. Leonhordt, M. Torloni & W. Borzoni (1975) Microwave Drying of Microorganisms:I. influence of the Microwave Energy and of the Sample Thickness on the Drying of Yeast, Journal of Microwave Power, 10:3, 265-270, DOI: 10.1080/00222739.1975.11688962 To link to this article: http://dx.doi.org/10.1080/00222739.1975.11688962
Published online: 17 Jun 2016.
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Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tpee19 Download by: [Iowa State University]
Date: 15 April 2017, At: 15:54
A . M. S\ Gomes, G.
¥.. Leonhardt M. Torloni and W. Borasamt
ABSTRACT
77/c w,ye of microwave energy for the rapid drying of yeasts is described. The influences of the microwave energy and of the sample thickness are studied. The advantages of the method over the conventional drying techniques are presented. Introduction
The economical production of single-cell protein and its utilization for food and feed will undoubtedly play a very important role, in the near future, to the solution of the world's protein problem. The microbial cells obtained by suitable culture techniques are usually dried in order to avoid considerable deterioration. Only recently has the study of the drying of microoigartisms, from a chemical engineering point of view, been carried out. Kachan et at. [1] and Silva et al. [2] studied, in this respect, the influence of several factors on the drying rates of Penicillium chrysogenum mycelium. No information regarding the use of microwave energy for the drying of single-cell protein has been found in the literature. This study was initiated in order to ascertain whether microwave heating could be used to dry yeast cells. Experimental Procedure
A Microvac-2000\ 2450 MHz microwave oven, with an input power varying from 1.2 to 4.2 kW, was used in the experiments. Its cavity is a horizontal cylinder of 64 cm diameter and 100 cm length. A horizontal stainless steel plate divides the cylinder in two equal parts. In the geometric center of this plate, a cylindrical brass tray (diameter 23 cm; height 5 cm) was placed containing the sample to be dried. Commercial pressed yeast (Saccharomvces cerevisiae), in 500 g tablets was used in the drying tests. The pressed yeast was classified through Tyler screens * Manuscript received August 26, 1975. Invited paper. This paper is open to correspondence, t Department of Chemical Engineering, Escola de Engenharia Maua, C.P. 5657, Sao Paulo, Brazil. t Les Microcodes Industrielles France.
Copyright © 1975 by IMPI Ltd., Edmonton, Canada.
Journal of Microwave Power, 10(3), 1975
JOURNAL OF MICROWAVE POWER, 10(3), 1975
number 6, 9. 20 and 48, leading to three fractions with different mean diameters (0,57 mm; 1.42 mm and 2.68 mm). Several measurements (Table 1) lead to the conclusion that the apparent density of the sample, and consequently its porosity, is not influenced by the particle mean diameter. Table II shows the values of the input power, the sample thickness and the particle mean diameter used in the experiments. TABLE 1 APPARENT DENSITY OF THE PRESSED YEAST SAMPLE AS A FUNCTION OF THE MEAN DIAMETER Mean Apparent Standard 1 Diameter Test Density Deviation (mm) Number (g»em/) (%) 1 0.445 3.6 2 0.445 2.8 0.57 3 0.450 3.8 4 0.440 3.9 5 0.437 2.2 1 0.489 2.7 2 0.504 1.8 1.42 3 0.483 1.5 4 0.486 2.1 5 0.496 0.6 1 0.484 2.6 2 0.481 1.6 2.68 3 0.481 2.4 4 0.491 6.7 5 0.494 1.6 1 Average of six measurements.
The mass variation of the sample was checked in the following way: the input power was turned off, the oven was opened and the tray was rapidly weighted; the tray was then replaced into the oven and the power turned on. The total time for a complete weighting operation lasted 30 sec. The moisture content of the pressed yeast was determined by drying 1.5 g of the sample in a conventional oven at 100- 105 C during 5 hr. [3]. Each microwave-dried sample was checked regarding its carbonization degree. When a sensible darkening could be visibly noticed, the sample was classified as not satisfactory. Results and Discussion
Figure 1 shows typical drying curves. Table 2 presents the results obtained; the drying time needed to achieve a final moisture content of 0.05 g of H 2 0/g of dry yeast, as well as the drying rate during the constant rate period, were obtained from the experimental curves shown in Figure 1. Figure 2 shows that a fairly good linear correlation exists between the power input and the drying rate calculated during the constant rate period, independent of the particle mean diameter.
67 GOMES, LEONBARBT, TORLONI, BORZAM: MICROORGANISMS TABLE 2 DRYING TIME, DRYING RATE, AND CLASSIFICATION OF THE DRIED PRODUCT AS A FUNCTION OF THE INPUT POWER, SAMPLE THICKNESS, AND PARTICLE MEAN DIAMETER Particle Input Sample Drying Mean Test Power Diameter Thickness Constant Time2 Product Number (kW) (cm) (mm) (mill) Classification3 Rate1
1 2 3 4 5 6 7 8 9 10 11
12 13
14 15 16 17 18 19 20 21 22' 23 24 25 26 27
1.2 1.8 2.4
3.0
3,6
4.2
0.57 2.88 0,57 1.42 0.57 2,68 2.68 1,42 0.57 2.68 2.68 1.42 1.42 0.57 2.68 2.68 0.57 1.42 0.57 2.68 2.68 1.42 E42 2.68 2.68 1.42 1.42
1.0 2.0 4.0 5.0 1.0 2.0 3,0 4.0 1.0 2.0 3.0 4.0 5,0 0.4 0.8 1.2 1.6 2.0 0.4 0.8 1.2
1.6 2.0 0.8 1.2 1.6 2.0
3.94 7.38 8.30 10.02 4.46 13.94 14.10 13.69 9.06 22,50 21.57 21,08 20.41 4.00 12.27 19.41 28.49 24.74 6.57 12.41 27.89 32,63 29.79 20.95 33.44 35.94 36.52
92.0 97.5 120.0 108.0 53.0 60.0 63.0 83.0 38.0 37.5 — ,
52.0 60.0 27.0 25.0 38.0 20.0 33.0 27.0 25.0 16.0 17.0 21.0 18.0 17.5 23.0 16.0
S S NS NS S
NSs NS c NSK? NS NS NS S
s
NSs
NS S
NSs NS NS S NSs NS
1 Calculated in kg of water per hour per m'i during the constant rate period. 2 To achieve a moisture content of 0,05 grams of water per grain of dry yeast. 3 S: Satisfactory NS: Not satisfactory.
Figure 3 shows the influences of the sample thickness on the drying rate during the constant rate period. The curves of Figure 3 seem to indicate that for a sample thickness larger than 2.0 cm there is no significant variation of the constant drying rate. The results presented in this paper, when compared with the data published by Kachan el al. [1] and Silva et al. [2] (see Table 3), suggest a real possibility of using microwave energy for drying single-cell protein.
268
JOURNAL OF MICROWAVE POWER, 10(3), 1975
Figure 1 Typical drying curves. Moisture content measured in grams of water per gram of yeast. Sample thickness = 2,0 cm. Power input: 1.2 kW (Curve 1, 1.8 kW (Curve 2), 2.4 kW (Curve 3), 3.0 kW (Curve 4), 3.6 kW (Curve 5), and 4.2 kW (Curve 6).
40
- 2.66 r = 0.990
R = 9.31P
Figure 2 Drying rate (R) during the constant rate period (kg of water per hour per m2) vs. input power (P). Sample thickness = 2.0 cm. ( • ) particle mean diameter = 2.68 mm; (4) particle mean diameter = 1.42 mm. r = correlation coefficient.
1.2
2.4
3J6
INPUT POWER, P(kw)
4S
GOMES, LEONHARDT, TORI.ON I, BORZANI: MICROORGANISMS
269
Figure 3 Drying rate during the constant rate period (R) (kg of water per hour per m 2 ) vs. sample thickness. Input power: 1.2 kW (Curve 1), 1.8 kW (Curve 2), and 2.4 kW (Curve 3).
SAMPLE
THICKNESS ( c m )
TABLE 3 COMPARISON OF RESULTS PRESENTED IN THIS PAPER WITH UNPUBLISHED EXPERIMENTAL DATA OBTAINED BY KACHAN ET AL. (1975) AND SILVA ET AL. (1975) Drying Drying cl Reference rate( time Kachan(a> 0.38 to 1.74 7 hr(d) Silvafb) 0.53 to 2.12 7.5 hr(d) This paper 3.94 to 36.52 16 to 120 min(e) (a) (b) (c) (d) (e)
Experiments carried out with Penicillium chrysogenum mycelium in a conventional tray convection dryer, Experiments carried out with Penicillium chrysogenum mycelium in a conventional tray vacuum dryer, Calculated in kg H.G/hr/m 2 during the drying constant rate period, To achieve a moisture content of 0.10 grams H,0/gram of dry mycelium, To achieve a moisture content of 0.05 grams H.O gram of dry yeast.
270
JOURNAL OF MICROWAVE POWER, 10(3), 1975
A c k n o v n i^mt-M >
Tlii? - • ported, in part, by grants from the Fundagao de Amparo a Pesqiusa do Estaao de Sao Paulo (FAPESP), Sao Paulo, Brazil. References
1 Kachan, G. C., Silva, G, A. and BorzanI, W. (1975). "Drying of Penicillium chrysogenum mycelium. I. Tray dryer," (In press, Lat. Am. 1. Cfaem. Eng. and Appl. Chem., 5, 2.) 2 Silva, G. A., Kachan, G. C. and Borzani, W. (1975), "Drying of Penicillium chrysogenum mycelium. II. Vacuum dryer." (In press, Lat. Am. I. Chem. Eng. and Appl, Chem,, 5, 2.) 3 White, I. (1954), Yeast Technology, p. 144. Chapman and Hall, London.
ISSN: 0022-2739 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/tpee19
Microwave Drying of Microorganisms:I. influence of the Microwave Energy and of the Sample Thickness on the Drying of Yeast A. M. F. Gomes, G. F. Leonhordt, M. Torloni & W. Borzoni To cite this article: A. M. F. Gomes, G. F. Leonhordt, M. Torloni & W. Borzoni (1975) Microwave Drying of Microorganisms:I. influence of the Microwave Energy and of the Sample Thickness on the Drying of Yeast, Journal of Microwave Power, 10:3, 265-270, DOI: 10.1080/00222739.1975.11688962 To link to this article: http://dx.doi.org/10.1080/00222739.1975.11688962
Published online: 17 Jun 2016.
Submit your article to this journal
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tpee19 Download by: [Iowa State University]
Date: 15 April 2017, At: 15:54
A . M. S\ Gomes, G.
¥.. Leonhardt M. Torloni and W. Borasamt
ABSTRACT
77/c w,ye of microwave energy for the rapid drying of yeasts is described. The influences of the microwave energy and of the sample thickness are studied. The advantages of the method over the conventional drying techniques are presented. Introduction
The economical production of single-cell protein and its utilization for food and feed will undoubtedly play a very important role, in the near future, to the solution of the world's protein problem. The microbial cells obtained by suitable culture techniques are usually dried in order to avoid considerable deterioration. Only recently has the study of the drying of microoigartisms, from a chemical engineering point of view, been carried out. Kachan et at. [1] and Silva et al. [2] studied, in this respect, the influence of several factors on the drying rates of Penicillium chrysogenum mycelium. No information regarding the use of microwave energy for the drying of single-cell protein has been found in the literature. This study was initiated in order to ascertain whether microwave heating could be used to dry yeast cells. Experimental Procedure
A Microvac-2000\ 2450 MHz microwave oven, with an input power varying from 1.2 to 4.2 kW, was used in the experiments. Its cavity is a horizontal cylinder of 64 cm diameter and 100 cm length. A horizontal stainless steel plate divides the cylinder in two equal parts. In the geometric center of this plate, a cylindrical brass tray (diameter 23 cm; height 5 cm) was placed containing the sample to be dried. Commercial pressed yeast (Saccharomvces cerevisiae), in 500 g tablets was used in the drying tests. The pressed yeast was classified through Tyler screens * Manuscript received August 26, 1975. Invited paper. This paper is open to correspondence, t Department of Chemical Engineering, Escola de Engenharia Maua, C.P. 5657, Sao Paulo, Brazil. t Les Microcodes Industrielles France.
Copyright © 1975 by IMPI Ltd., Edmonton, Canada.
Journal of Microwave Power, 10(3), 1975
JOURNAL OF MICROWAVE POWER, 10(3), 1975
number 6, 9. 20 and 48, leading to three fractions with different mean diameters (0,57 mm; 1.42 mm and 2.68 mm). Several measurements (Table 1) lead to the conclusion that the apparent density of the sample, and consequently its porosity, is not influenced by the particle mean diameter. Table II shows the values of the input power, the sample thickness and the particle mean diameter used in the experiments. TABLE 1 APPARENT DENSITY OF THE PRESSED YEAST SAMPLE AS A FUNCTION OF THE MEAN DIAMETER Mean Apparent Standard 1 Diameter Test Density Deviation (mm) Number (g»em/) (%) 1 0.445 3.6 2 0.445 2.8 0.57 3 0.450 3.8 4 0.440 3.9 5 0.437 2.2 1 0.489 2.7 2 0.504 1.8 1.42 3 0.483 1.5 4 0.486 2.1 5 0.496 0.6 1 0.484 2.6 2 0.481 1.6 2.68 3 0.481 2.4 4 0.491 6.7 5 0.494 1.6 1 Average of six measurements.
The mass variation of the sample was checked in the following way: the input power was turned off, the oven was opened and the tray was rapidly weighted; the tray was then replaced into the oven and the power turned on. The total time for a complete weighting operation lasted 30 sec. The moisture content of the pressed yeast was determined by drying 1.5 g of the sample in a conventional oven at 100- 105 C during 5 hr. [3]. Each microwave-dried sample was checked regarding its carbonization degree. When a sensible darkening could be visibly noticed, the sample was classified as not satisfactory. Results and Discussion
Figure 1 shows typical drying curves. Table 2 presents the results obtained; the drying time needed to achieve a final moisture content of 0.05 g of H 2 0/g of dry yeast, as well as the drying rate during the constant rate period, were obtained from the experimental curves shown in Figure 1. Figure 2 shows that a fairly good linear correlation exists between the power input and the drying rate calculated during the constant rate period, independent of the particle mean diameter.
67 GOMES, LEONBARBT, TORLONI, BORZAM: MICROORGANISMS TABLE 2 DRYING TIME, DRYING RATE, AND CLASSIFICATION OF THE DRIED PRODUCT AS A FUNCTION OF THE INPUT POWER, SAMPLE THICKNESS, AND PARTICLE MEAN DIAMETER Particle Input Sample Drying Mean Test Power Diameter Thickness Constant Time2 Product Number (kW) (cm) (mm) (mill) Classification3 Rate1
1 2 3 4 5 6 7 8 9 10 11
12 13
14 15 16 17 18 19 20 21 22' 23 24 25 26 27
1.2 1.8 2.4
3.0
3,6
4.2
0.57 2.88 0,57 1.42 0.57 2,68 2.68 1,42 0.57 2.68 2.68 1.42 1.42 0.57 2.68 2.68 0.57 1.42 0.57 2.68 2.68 1.42 E42 2.68 2.68 1.42 1.42
1.0 2.0 4.0 5.0 1.0 2.0 3,0 4.0 1.0 2.0 3.0 4.0 5,0 0.4 0.8 1.2 1.6 2.0 0.4 0.8 1.2
1.6 2.0 0.8 1.2 1.6 2.0
3.94 7.38 8.30 10.02 4.46 13.94 14.10 13.69 9.06 22,50 21.57 21,08 20.41 4.00 12.27 19.41 28.49 24.74 6.57 12.41 27.89 32,63 29.79 20.95 33.44 35.94 36.52
92.0 97.5 120.0 108.0 53.0 60.0 63.0 83.0 38.0 37.5 — ,
52.0 60.0 27.0 25.0 38.0 20.0 33.0 27.0 25.0 16.0 17.0 21.0 18.0 17.5 23.0 16.0
S S NS NS S
NSs NS c NSK? NS NS NS S
s
NSs
NS S
NSs NS NS S NSs NS
1 Calculated in kg of water per hour per m'i during the constant rate period. 2 To achieve a moisture content of 0,05 grams of water per grain of dry yeast. 3 S: Satisfactory NS: Not satisfactory.
Figure 3 shows the influences of the sample thickness on the drying rate during the constant rate period. The curves of Figure 3 seem to indicate that for a sample thickness larger than 2.0 cm there is no significant variation of the constant drying rate. The results presented in this paper, when compared with the data published by Kachan el al. [1] and Silva et al. [2] (see Table 3), suggest a real possibility of using microwave energy for drying single-cell protein.
268
JOURNAL OF MICROWAVE POWER, 10(3), 1975
Figure 1 Typical drying curves. Moisture content measured in grams of water per gram of yeast. Sample thickness = 2,0 cm. Power input: 1.2 kW (Curve 1, 1.8 kW (Curve 2), 2.4 kW (Curve 3), 3.0 kW (Curve 4), 3.6 kW (Curve 5), and 4.2 kW (Curve 6).
40
- 2.66 r = 0.990
R = 9.31P
Figure 2 Drying rate (R) during the constant rate period (kg of water per hour per m2) vs. input power (P). Sample thickness = 2.0 cm. ( • ) particle mean diameter = 2.68 mm; (4) particle mean diameter = 1.42 mm. r = correlation coefficient.
1.2
2.4
3J6
INPUT POWER, P(kw)
4S
GOMES, LEONHARDT, TORI.ON I, BORZANI: MICROORGANISMS
269
Figure 3 Drying rate during the constant rate period (R) (kg of water per hour per m 2 ) vs. sample thickness. Input power: 1.2 kW (Curve 1), 1.8 kW (Curve 2), and 2.4 kW (Curve 3).
SAMPLE
THICKNESS ( c m )
TABLE 3 COMPARISON OF RESULTS PRESENTED IN THIS PAPER WITH UNPUBLISHED EXPERIMENTAL DATA OBTAINED BY KACHAN ET AL. (1975) AND SILVA ET AL. (1975) Drying Drying cl Reference rate( time Kachan(a> 0.38 to 1.74 7 hr(d) Silvafb) 0.53 to 2.12 7.5 hr(d) This paper 3.94 to 36.52 16 to 120 min(e) (a) (b) (c) (d) (e)
Experiments carried out with Penicillium chrysogenum mycelium in a conventional tray convection dryer, Experiments carried out with Penicillium chrysogenum mycelium in a conventional tray vacuum dryer, Calculated in kg H.G/hr/m 2 during the drying constant rate period, To achieve a moisture content of 0.10 grams H,0/gram of dry mycelium, To achieve a moisture content of 0.05 grams H.O gram of dry yeast.
270
JOURNAL OF MICROWAVE POWER, 10(3), 1975
A c k n o v n i^mt-M >
Tlii? - • ported, in part, by grants from the Fundagao de Amparo a Pesqiusa do Estaao de Sao Paulo (FAPESP), Sao Paulo, Brazil. References
1 Kachan, G. C., Silva, G, A. and BorzanI, W. (1975). "Drying of Penicillium chrysogenum mycelium. I. Tray dryer," (In press, Lat. Am. 1. Cfaem. Eng. and Appl. Chem., 5, 2.) 2 Silva, G. A., Kachan, G. C. and Borzani, W. (1975), "Drying of Penicillium chrysogenum mycelium. II. Vacuum dryer." (In press, Lat. Am. I. Chem. Eng. and Appl, Chem,, 5, 2.) 3 White, I. (1954), Yeast Technology, p. 144. Chapman and Hall, London.
