Quality aspects of heated-air drying of soybeans

J .sturrd Prod. Printed

Krs. Cal.

III Great

19. No.

I, pp. 31-41,

1983

0022-474X/83/010031-I

Britain

Pergamon

I $03.00/O Press

Ltd

QUALITY ASPECTS OF HEATED-AIR DRYING OF SOYBEANS T. F. GHALY CSIRO

Agricultural

Engineering (Receioed

and Group,

J. W. SUTHERLAND P.O. Box 26. Highett.

in ,jmlfom

Victoria

3190, Australia

IO August 1982))

Abstract--Samples of 300g of soybean seed, variety Forrest, conditioned to 14, 16 and 18% moisture content (m.c.; w.b.), were dried for 4 hr in a small batch fluidized-bed rig with a test section of l:!O mm diameter and air flow rate set at 0.03 kg/s. Air inlet temperatures of 40, 50, 55. 60. 65. 70 and 8O’C were used to determine the effects on quality. Conditioned and unconditioned samples, tog;ether with samples dried in the bed for 4 hr at room temperature, served separately as controls. Samples of 25 g of the conditioned seed, sealed in test tubes, were heated for 4 hr in an air oven at 40. 45, 50, 55 and 60°C to study the effect of heating at a constant m.c. Seed germination and seedling v&our clearly indicated the onset of heat damage and showed that no single criterion was more sensitive than any other. Safe drying air temperatures of 65, 60 and 55 C were obtained for initial moisture contents of 14. 16 and 18% respectively. Heating soybeans up to 60°C at a fixed m.c. increased the susceptibility to heat damage. Oil yield, free fatty acid ccntent and fatty acid composition were not affected by any of the heat treatments. The peroxide value, however. showed some increase at temperatures above 50°C. Fluidizing at room temperature did not affect germination. The colour of crude oil, after heat bleaching, for 5G8O’C heat treatments was paler than the controls. while 4O’C gave a very dark colour. Degumming of oils followed by refining removed all detectable phospholipids from all samples and produced oils paler in colour, when heat bleached, except for 80 C at 16 and 189, m.c. which produced oils slightly but noticeably darker. Soybeans were found to dry slowly compared to sunflower seed and rapeseed. and the logarithmic drying model was fitted to the various drying curves. Computer program DRIER was modified to be applicable to soybeans and some runs were carried out for a farm batch radialflow drier. Results indicated the advantage of using a high inlet air temperature provided that seed qualit) is not affected.

INTRODUCTION

production in Australia has increased in the last decade more than 16-fold and has a good market locally and overseas. On a world basis, soybean is probably the largest source of vegetable seed oil and protein, and contributes more than any other oilseed to human food needs. Soybean oil is used widely in the edible and industrial fields. The meal derived from crushing has become the principal protein supplement for livestock in ma.ny countries. Soy protein has a high biological value and is processed to produce a wide range of human foods. The soybean plant dries quickly in the final stages of maturity, hence shattering and pod burst are very common especially when seed moisture content falls below l&11% (MATHESON, 1976). Dry seeds are also brittle and subject to mechanical injury if care is not taken to select correct machine settings. Therefore, harvesting at higher moisture levels is favoured by some producers to avoid considerable yield losses. This must be followed by arlificial drying to a moisture level acceptable by the industry (a maximum of 12:/;, w.b.-A.O.F., 1980). Other advantages of drying include an increase in the number of useful harvesting hours per day, and the reduction of losses from wind, rain, insects and birds. Drying, however, must not impair the viability of the seed or the quality of the extracted oil. Overheating is known to damage seed viability (NELLIST, 1978). Oil from overheated seed is normally high in free fatty acid content and generally does not produce a satisfactory refined oil (MOYSEY, 1973). Therefore, this work was undertaken to study the effecl of drying conditions on some quality aspects of soybeans, and also to determine parameters necessary for drier design, in a similar manner to earlier work for sunflower seed and rapeseed (SUTHERLAND and GHALY, 1982). SOYBEAN

31

32

T.F. GHALY and J. W. SUTHERLAND EXPERIMENTAL

DESIGN

One variety of soybean was conditioned to 3 moisture contents (m.c.). 14, 16 and 18?, (w.b.) and dried with air at 6 temperatures (40, 50, 60, 65, 70 and SO’C). Conditioned and unconditioned samples together with conditioned samples fluidized at room temperature were analysed to study the effect of conditioning and mechanical damage. Replicates were made of 40, 60 and 80°C heat treatments, the conditioned controls and the unconditioned seed. This gave a total of 38 samples which were fully randomized. In addition. 3 samples of 14, 16 and 18”/; m.c. were dried at 40°C. then reconditioned back to study the effect of m.c. Three extra runs at an air temperature of 55°C were carried out later with appropriate controls. All samples were tested for m.c., germination, vigour criteria, oil yield, free fatty acid (FFA) content, fatty acid composition, peroxide value (PV) and colour of the extracted oil, except the 55°C samples which were tested for germination and vigour criteria only. A further 3 runs at 3O’C were performed for m.c. determination only. A total of 14 selected heat treatments were repeated at 14, 16, 18 and 207; m.c. to study the effect of drying on the colour of refined oil, and the effect of degumming and refining on phospholipid content of the extracted oil. A simple factorial experiment was also carried out to study the effect of heating the seeds at a constant m.c. Conditioned soybeans of 14, 16 and IS:,, were heated in sealed tubes at 40, 45, 50, 55 and 6O”C, then tested for germination only.

MATERIALS

AND METHODS

The drying apparatus The fluidized-bed drying rig is the same as that used for earlier work on sunflower seed and rapeseed (SUTHERLAND and GHALY, 1982). It is almost identical to the apparatus illustrated and described by EVANS and DERMOTT (198 1). The only significant differences are that a larger fan of the same type was used (flow rate 25 l/s at 6 kPa static pressure), and the bed diameter was 120 instead of 100 mm. Temperatures in the fluidized bed were measured by 4 copper/constantan thermocouples spaced at 10 mm intervals along the centre line. The rig simulates the layers of seed near the air inlet in fixed batch driers, i.e. the region most likely to be damaged by high-temperature drying. The seed and operating

procedure

The soybean seed, variety Forrest, grown in New South Wales in 1980. was of 9.8% m.c. (w.b.). Batches of 300g were conditioned to the required m.c. by thorough mixing with a calculated quantity of distilled water, then storing in sealed jars for a minimum of 2 weeks at l-3°C to allow for moisture equilibration. Seed m.c. was determined by the air oven method (130°C for 3 hr) on whole seeds (A.O.C.S., 1969). When the required air flow rate and inlet air temperature were established for each drying run, the seed was poured quickly into the fluidizing chamber. Samples of 300g were then dried for a period of 4 hr with an air mass flow rate of 0.03 kg/s. This flow rate gave a vigorous fluidization for all inlet air temperatures. For the range of temperature from 40 to 80°C the air velocity through the bed varied from 2.4 to 2.7 m/s respectively. The depths of soybeans were 35 and 55 mm in the unfluidized and fluidized states respectively. Small samples were taken initially and from the bed during drying (at 0.25. 0.5, 1, 2, 3 and 4 hr) for m.c. determination and sealed in air-tight jars. At the conclusion of each run, the remainder of the seed was cooled rapidly to ambient temperature and then stored at l-3°C until quality assessment was carried out. The effect of heating soybeans at a constant m.c. was assessed by sealing 25 g samples in test tubes and heating in an air oven at the required temperature for 4 hr. The seeds were then cooled rapidly to ambient temperature and stored at l-3°C until germination tests were carried out.

Quality Aspects of Heated-Air Drying of Soybeans

33

Germination was carried out according to INTERNATIONAL SEED TESTING ASSOCIATION methods (1976) using duplicates of 50 seeds germinated in two rolled crepe filter papers saturated with a measured quantity of distilled water. Five and eight day counts were taken. The average mass of seedling and length of radicle were also measured at the final count. Oil yielcl was measured by petroleum-ether extraction of the oil at room temperature, in accordance with the A.O.C.S. specifications (1969). from amounts of soybeans of fixed mass of dry matter. Free fatty acid (FFA) content. peroxide value (PV) and oil colour using a photometric method, were also measured according to the A.O.C.S. A full description of the colour measurement was given by SUTHERLAND and GHALY (i982j. Fatty acid composition of the oil was measured by gas-liquid chromatography of methyl esters. using a similar method to the A.O.C.S. procedure (1969). Phospholipids were determined by thin-layer chromatography on 0.25 mm thick silica gel plates (Merck Silica Gel 60 F‘254 with concentration zone). The plates were developed with a solvent mixture comprising chloroform, methanol and water in the proportions 30: 15:2. Spots were detected using iodine vapour. Degumming and refining were achieved by treating the crude oil first with 10”; sodium chloride solution and centrifuging, then with 9.47, sodium hydroxide solution followed by washing with boiling water, centrifuging a few times and finally drying the oil (B. LATHLEAN, 1981. personal communication).

RESULTS AND DISCUSSION

Inlet air temperature was controlled to within O.YC for all drying runs, the air being heated electrically. Upon examination of the bed thermocouple temperature readings it was found that all bed temperatures were within 1’C of the set inlet air temperature in less than 10 min for each run. Therefore the seed and inlet air temperatures were almost equal for the major part of each 4 hr drying run. The average ambient air state for the drying runs was 19 C dry-bulb temperature (range 17-22°C) and 5300 r.h. (range 45- 6O”J. The air oven used for the sealed tube heating experiments maintained a constant temperature to within O.YC, and seed temperature was within 1’C of the desired temperature after approximately 1 hr for each run. Moisture contmt Soybean drying characteristics are different from other oilseeds such as sunflower and rapeseed. The time-temperature effect on the drying of soybean from 14”, (w.b.) is illustrated in Fig. 1. together with some sunflower seed curves for comparison (SUTHERLA&D and GHALY, 1982). It is clear that sunflower seed dries faster and to lower m.c.‘s in 4 hr than soybean. At an inlet air temperature of 4O”C, for ‘example, the m.c. of soybean seed decreased by 4”, in 4 hr while that of sunflower seed decreased by more than 9p,. However, increasing the air temperature from 40 to 80°C increased the drying rate of soybeans considerably as the m.c.‘s achieved after 4 hr were 9.9 and 3.5”” respectively (Table 2 and Fig. 1). It is of interest to note that after 2 hr the drying of soybean achieved using an air temperature of 80°C was similar to that for sunflower using air of 40°C only. The logarithmic drying model was fitted to all the drying curves in the same manner as for sunflower seed and rapeseed (SUTHERLAND and GHALY, 1982). Unlike sunflower and rapeseed where a marked variation of drying constant (li) with inlet air temperature was observed, the values of Ccfor soybeans averaged over the three initial m.c.‘s were quite uniform. For air temperatures between 30 and 80°C the values of k (hr- ‘) can be taken average as 1.0 and 0.5 for drying times of 2 and 4 hr respectively. The corresponding values of equilibrium m.c. (IV,,) for the various air temperatures are given in Table 1.

34

T.F.

01 0

GHALY

and J. W. SUTHERLAND

I

I

I

I

1

2 ( HOURS 1

3

1

TIME

FIG. 1. Time-temperature

effect on the m.c. of soybean seed heated in a fluidized bed for 4 hr (with data for sunflower for comparison).

Germination the results of germination criteria of heat-treated samples as a Figure 2 summarizes percentage of the conditioned controls. The final count of these controls ranged from 82-84% and the unconditioned seed gave an average of 7696. It is clear from Fig. 2 that all the measurements indicated the onset of heat damage and that no single criterion was more sensitive than any other, with the exception of severely damaged samples. Results showed that soybeans of 14-18% initial m.c. can be dried for 4 hr, using air temperatures of 40-55”C, without significantly damaging the seed. An air temperature of 80°C killed all the seeds at the three moisture levels as did 70°C at 16 and 187, m.c. It is also clear from Fig. 2 that soybeans became more sensitive to heat damage as the initial m.c. increased from 14 to 187,. Thus the maximum safe temperatures for drying seeds of 14, 16 and 18”: m.c. were 65, 60 and 55°C respectively. Heating soybeans up to 60°C at a fixed m.c. (the sealed tube runs) increased the susceptibility to heat damage, as was observed with sunflower seed and rapeseed (SUTHERLAND and GHALY, 1982). At 14 and 16% m.c., 60°C caused considerable damage as did 55°C at 187, m.c., whereas 60°C at IS:/, m.c. killed almost all the seeds (Fig. 2). The sealed tube results apply to seed near the air outlet of a fixed batch drier which can remain at a high m.c. for a long period. However, it can be shown (SUTHERLAND. 1975) that a temperature of 4O”C, which was safe for each m.c. cannot be reached by high m.c. seed near the outlet of a batch drier even with an inlet air temperature of 80°C. Statistical analysis also revealed that conditioning the soybean from 9.8 to 14, 16 and 18% improved the 8 days count significantly and the 5 days count slightly, but had no TABLE 1. EQUILIBRIUM MOISTURE CONTENTS FOR SOYBEANS

Inlet air temp. (“Cl 30 40 50 55 60 65 70 80

Equilibrium m.c. w,, (% w.b.1 2 hr

4hr

12.8 11.7 10.1 9.5 8.6 7.5 6.5 4.9

11.9 9.9 8.0 7.2 6.2 5.3 4.5 3.0

Quality

Aspects

of Heated-Air

14% m.c. (w.b.

.

lB%m.c.

(w.b.

Drying

50 AIR

FIG.

2.

Effect of air temperature

35

)

1

e

ow 40

of Soybeans

10

50

TEMPERATURE

on germination criteria for 4 hr.

(W

’

-T80

)

of soybean

seed heated

in a fluidized

bed

effect on seedling mass or length of radicle. However, samples of 14 and 16% m.c. which were dried at 4O”C, then reconditioned to their initial m.c. were slightly lower in germination than the 40°C heat-treatments, but the 18% m.c. heat-treatment improved slightly when reconditioned. Samples that were fluidized at room temperature, to investigate mechanical damage, were in general lower in germination than the conditioned controls, but the effect was not significant except at 14% m.c. where the length of radicle was slightly affected. It is possible that the high m.c. of the seeds enhanced germination but had little effecl on growth performance, i.e. seedling mass and length of radicle. Oil yield The yield of crude oil from heat-treated samples revealed no significant differences between them. However, results showed that the yield of crude oil from the conditioned controls was significantly higher than from the unconditioned controls or from treated samples (Table 2). Results also showed that the higher the m.c. of the conditioned control the higher the yield. This, together with the fact that oil yield from heated samples was similar to that from the unconditioned controls, suggests that conditioning to higher m.c. rather than heat treatment affected oil yield. It was also observed that the speed of oil extraction from unheated and the 40°C heated sample,3 was considerably faster than from other heat treatments; the higher the temperature the slower it was with 70 and 80°C in particular being very slow to extract.

T. F. GIIAL~ and J. W.

SLITHERLAW

PhotometrIc Bed temp.

Seed m.c.

( C)

I’),)\\.h.)

Control*

IA.0

Room temp. 30* 50 60’ 65 71) x0* -ro+ Control* Room temp. -lo* 50 60’ 6.5 70 SO’ 109 Control* Room temp. -to+ 50 60* 65 70 x0* 4OQ llnconditioned control

11.x

Oil ~xld

FFA ‘” olric (I’,,d.b.) acid

3.9 Il.9

17.0 17.7

0.20 0.20 (1.I4 II. 17 0.0s 0.09 0.07 0.n9 0. I X 0.2 I 0.24 0. I5 0.07 lJ.13 0.12 0.13 0.15 0.21 0.30 0.2X 0.19 0.12 0.15 0. I4 0. I4 0.11 Cl.30

9.X

16.6

0.12

Y.Y

s.5 6.9

5.9 1.9 3.5 13.Y 15.X 12.‘) IO.‘) 9.0 7.’ 6.3 5.7 3.X

15.9 17.7 11.2 1I.5 Y.8 7.X 6.9 5.9

17.0 15.7

I h.4 16.6 IfI. I 16.2 15.9 lb.1 16.5 IX.2 16.7 16.4 16.1 17.0 I6.S 16.X 16.7 1X.X 17.2 16.X 16.5 16.7 16.5

16.9

PV (m-eyuiv kg)

Free,firttj, acid

C

Before heat bleach+

After heat bleach:

0.52 0.30 0.50 I.26 3.06 4.49 3.62 3.00 0.62 I .J’ 0.57 2.15 0.31 2.3X 2.4X 2.43 I.87 1.55 2.14 0.X8 0.17 0.96 4.4X 2.3 I 5.0I 3.46 3.07

.:.x7 3.36 4.15 7.X0 2.57 I.X? I .90 1.x-l 5.29 5. II 3.x9 3.97 3.16 2.70 1.55 4.46 7.36 5.44 6.78 4.4 4.30 3.39 3.10 2.x1 3.07 x.72

36.92 25.26 61.3.3 I.XI 1.93 2.01 1.,X2 3.w 26.12 21.6X 31.10 77.37 12.33 .3.47 ?.6Y 6.2 I 9.3’) 23.15 27.4x x.52 27.7X 7.51 6.3s 0.2-l s.05 14.54 32.76

0.60

3.X2

‘1.7X

* Values are averagesof replicates. t AH samples were deep yellow in colour. $ Photometriccolour C: ~3: very pale yelloN (almost yellow; 20-40: deep yellow: >-IO: rust red. s 30 C reconditioned to initial m.c.

This could be a result of protein denaturation drying at temperatures above 50°C.

colour

3.0x

white); 3 9: pale yellow;

combined

with other

Y 20:

interactions

during

cmtetlt

It can be seen from Table 2 that the conditioned controls (14.G17.7”, m.c.) and room temperature treatments (11.8&14.?“~, m.c.) produced crude oils significantly higher in FFA than the unconditioned controls (9.8?,, m.c.) or any of the heat treatments (3.5-l 1.5”,, m.c.). As with oil yield. high m.c. rather than heat treatment was associated with the high FFA, and the higher the m.c. the higher the FFA content. It is believed that the storage of these samples for approximately 3 months at 1&3-C was the main reason for the increase in FFA in the samples of high m.c. This is confirmed by the results of the 4O’C heat treatments which were reconditioned to the initial m.c. and had FFA contents close to those of the conditioned controls (Table 2). However, statistical analysis revealed that heat treatments had no significant effect on the FFA content of any of the samples analysed. This is in basic agreement with the findings of MORRISON and ROBERTSON (1978) and SUTHERLAND and GHALY (1983) on sunflower and rapeseed oil. It can be concluded, therefore. that drying soybeans for 4 hr using air temperatures of 40-80°C had no significant effect on the FFA content and that the storage of high m.c. seed ( > 1I”,) for lengthy periods ( > 2 months) could result in higher FFA content. even if the storage temperature is as low as lL3”C.

Quality

Aspects

of Heated-Air

Drying

of Soybeans

37

The main fatty acids (myristic. palmitic, stearic, oleic, linoleic, arachidic, linolenic and behenic) were measured in the crude oil from all heat-treatments and controls. The percentage of e,-lch in the unconditioned control was 0.06. 10.2. 3.7. 21.8, 54.8, 0.5. 8.4 and 0.4 respectively. No significant differences were found between any of the samples analysed. Hence. it can be concluded that heating soybeans up to 80°C for 4 hr is unlikely to alter their fatty acid composition.

The PV of crude oil from the controls showed an increase on increasing the initial m.c. from 14 to 18Y,, (Table 2). There were also increases in PV (though not all significant) at temperatures higher than 50°C. However, there was a high degree of variability between these results.

Crude filtered oil contains impurities such as phospholipids, gums, resins, free fatty acids and colour bodies. Most of these can be removed by degumming and refining. The refined oil is often treated with steam at 200-250°C under vacuum to remove products responsible for odour and taste or is heated to elevated temperatures in the manufacture of resins for surface coating (LATHLEAN. 1979). Hence a high quality refined oil must be pale in colour on heating to at least 25O’C. Therefore, the heat bleach test (heating 15 ml of the oil in a 150 ml beaker to 288°C over 5 min and holding the temperature for a further 5 min) i:j considered important to assess the potential of a particular oil. However, if a commercial crude soybean oil is heated to this high temperature, a very dark colour and black specks are normally produced in the oil as a result of the impurities present. Although the ultimate criterion is the colour of the refined oil after a heat bleach test, the first part of this study was devoted to the effect of drying conditions on the colour of crude oil. i.e. before degumming and refining. The main objective was to see if heat treatment led to different quantities of oil impurities being present in the extracted oils. These impurities are the main cause for darkening, if the oil is subjected to a heat bleach test as mentioned above. Results of this part of the work are summarised in Table 3 and Fig. 3 (rows 1 and 2). The crude oils extracted from the heat-treated and control samples (before the heat bleach test) were all of a bright deep yellow colour. In fact. it was difficult to differentiate visually between them (Fig. 3, row I), although the photometric colour C ranged from 1.83 to 6.78 (Table 2). Almost all heat treatments gave lower C values than the controls and in general, the higher the initial m.c. the higher were the values. When the heat bleach test was performed on these oils, a wide range of colours was produced (Fig. 3. row 2). ranging from very pale yellow (almost white) to a dark rust red. with colour values ranging from 1.81 to 77.37 (Table 2). Heat treatments of 50-C and above produced oils paler in colour compared to the controls while the 40 ‘C gave a very dark colour colour C is a measure of except at the 18”, m.c. It should be noted that the photometric the absorbance at different wavelengths of a particular oil rather than the colour as such. However, visual assessment of the colour of heat bleached oils, depending on the degree of paleness or ‘darkness, agreed very well with colour values; the lower the C value the paler the colotr. The results achieved here clearly demonstrated the significance of the heat bleach test in differentiating between samples, possibly containing different quantities of impurities. Results also suggested that oils produced from heat treatments of 50-80°C had less impurities than the controls, hence the paler colours. Similar observations were reported by SUTHERLAND and GHALY (1982), where heat treatments of rapeseed of 4&7O”C produced crude oil paler in colour than the controls when heat bleached. However, the 40 and some 50°C treatments of the present study gave very dark colours when heat bleached and l-his is believed to be mainly the result of liberation of impurities in the

T.F.GHALY

-

1

and J. W. SUTHERLAND

Quality Aspects of Heated-Air Drying of Soybeans TABLE3. EFFECTOFDEGUMMINGAND REFININGONPHOSPHOLIPIDS AND OFHEATED SOYBEANS

Initial mc. (“Gw.b.) Phospholipids*

40 40 40 50 50 50 60 65 70 70 80 80 80 80 Unconditioned control

OF EXTRACTEDOILS

Degummed and refined oil

Crude oil

Bed temp. (‘C)

COLOUR

39

Photometric colour C of heat-bleached oil?

Phosphohpids*

13.6 15.6 18.2 16.0 18.1 19.9 19.8 18.1 18.0 20.0 14.2 16.3 17.8 20.5

+++ +++++ +++++ ++ ++ ++t + ++ + ++ + + +++ +++

47.82 16.92 14.13 21.36 29.72 19.61 6.93 6.22 5.56 7.89 1.96 6.07 10.83 16.12

0 0 0 0 0 0 0 0 0 0 0 0 0 0

12.1

++++

24.05

0

Photometric colour C of heat-bleached oil? 0.96 0.69 1.85 1.04 2.21 1.65 2.20 1.32 3.23 2.09 2.99 4.40 3.50 1.83

* Phospholipid content estimated by thin-layer chromatography of oils before heat bleaching; the number of i-‘s corresponds to the relative amount of phospholipids. t Photometric colour C: <3:verv pale yellow (almost white); 339:pale yellow; 9920:yellow: 20-40:deep ,yellow; > 40lrust red.- _

extracted oils. fis far as drying is concerned, this is of no concern as the colour of these oils was very pale when refined as will now be discussed. Preliminary analysis showed that degumming and refining of control samples produced oils almost devoid of phospholipids and pale in colour when heat bleached. Therefore, heat treatments that gave dark crude oils on heat bleaching were repeated; part of the extracted oil was degummed and refined and then tested for heat bleach, and part was tested as crude oil. Results are summarised in Table 3 and Fig. 3 (rows 3 and 4) and showed that: (1) In general, the samples that produced crude oil pale in colour after heat bleaching had low phospholipid content (typical of 60-70°C and some of 80°C). It is possible that the impurities in crude oil (mainly phospholipids) were not all extracted with the oil but where held back in the meal as a result of protein denaturation, phospholipid hydration or other interactions during drying at temperatures between 50 and 80°C. (2) Degumming followed by refining removed all detectable phospholipids from all samples and produced oils paler in colour when heat bleached. The 40°C heat treatments produced oils very pale in colour. However, 70°C at 20% m.c. and 80°C at 16, 18 and 20% produced oils slightly but noticeably darker in colour. It is possible that the colour m the case of these 4 samples was partly due to components other than phospholipjds, as a result of drying at high temperature, and these could not be removed by, refining. SUTHERLAND and GHALY (1982) also reported that sunflower seed heated to 80°C produced oil dark in colour when heat bleached and that the colour could not be removed by a laboratory refining procedure. DRIER

Computer

program

DESIGN

DRIER (SUTHERLAND, 1975) has been modified to apply to soyin a similar manner to the programs developed for sunflower seed (DRYSUN) and rapeseed (DRYRAP), as described by SUTHERLAND and GHALY (1982).In developing program DRYSOY, moisture desorption data for soybeans obtained by PIXT~~N and WARBURTON (1971) was fitted by an equation proposed by SMITH

beans (program DRYSOY)

T. F. GIIALY and J. W. SCJTH~RLAND

40

TABLL 4. PR~DIUIONS FROM COMPLTI~K PROGKAM DRYSOY FOR A RADIAL-FLOW SOY&AN DRIFR

Inlet air temp.

t c-1

MISS of seed Initial moisture content Final average moisture content Drying time Radius of bin Radius of duct Air flow Pressure rate drop (kPa) (I’S) 3980 5560

60 50 40

* Assuming

12.040

0.33 0.58

2.20

= Xt = 18”” = = = =

1’” 4h; 1.25 m 0.63 m Fan power* (kw) 1.35 3.22 26.49

Heat input (kW1 217 213 3 IO

IOO”,, eticiency.

(1947). This equation was found to fit the experimental data to within 0.3”, m.c. (w.b.) over the air temperature range from 15 to 35°C and the air r.h. range from 25 to 85”,,, and was thus considered satisfactory. Runs of program DRYSOY were carried out simulating drying of soybeans in the CSIRO 8-t radial-flow wheat drier (WEDD and SUTHERLAKD. 1979). similarly to runs of DRYSUN and DRYRAP for sunflower seed and rapeseed (SUTHERLAW and GHALY. 1982). The results are given in Table 4, and it can be seen that the fan power and heat input required at 4O’C are approximately 20 and 1 times that at 60 C, in order to dry 8 t of seed from 18 to 129, m.c. (w.b.) in 4 hr. This indicates the advantage of using higher inlet air temperatures, but care must be exercised as it has been shown in this paper that at 18’?,, m.c. a seed temperature of 60°C can cause some damage to soybean germination criteria (Fig. 2). CONCLUSIONS

Soybean seed, conditioned to 14, 16 and 18”” m.c. (w.b.) was air dried in a fluidized bed for 4 hr without damaging the viability or the vigour of the seed at maximum air temperatures of 65, 60 and 55°C respectively. The damage occurring to soybeans at higher temperatures was enhanced at higher initial m.c.‘s, or by heating the seed at a constant m.c. (in sealed tubes). Oil yield, FFA content, fatty acid composition and PV of the extracted oil were not significantly affected by drying air of up to 80 C. The colour of extracted refined oil was not adversely affected at air temperatures of up to 80-C for 14”,, m.c. seed and up to 70 C for 16 and 18”,, m.c. Conditioned controls were of higher germination and oil yield than unconditioned controls. The FFA levels were also higher, possibly as a result of storing the seeds at higher m.c. Fluidizing the seed for 4 hr at room temperature did not affect viability. Experimental results from this work have been included in a design and performance prediction method for batch soybean driers, with an associated computer program which is available to external users. .4cknr)lclrd~rrt1r,lrs~This work forms part of a prolect on the drying of oilseeds supported by the Austrahan Oilseeds Research Committee. The assistance provided by Mr B. LATHLEA~ of Meg&t Ltd. Dr R. TIMMS of CSIRO Dairy Research Laboratory (now at Krmpas Edible Oil Co.. Johore Bahru. Malays~n) and Mr J. W. VAN DFR TOUW of CSIRO Division of Mathematics and Statistics is gratefully acknowledged.

REFERENCES A?IFRICA~ 011. C~I~MISTS’SOU~TY (A.0.C.S.I Sot.. Chicago. U.S.A.

(1969) O_tfic’iuIcotd Trrtturive

,tIetl~o&

3rd edn. Am. Oil Chem.

Quality

Aspects

of Heated-Air

Drying

of Soybeans

41

EVANS, D. E. and DERMOTT. T. (1981) Dosageemortality relationships for Rhyxperrh dominicu (F.) (Coleoptera:Bostrychidae) exposed to heat in a Ruidized bed. 1. srored Prod. Rrs. 17, 52364. INTERNATIOKAL SEE,DTwrri~c; ASSOUATIO~ (1976) International Rules for Seed Testing. Pror~. Ifir. Seed Test. Assoc. 4. 3349. LATHLEAN. B. (1979) What happens to your oilseeds after they leave your farm’? .4yric. Gu~ette qf N.S.W. 90, ‘-5. MATHESON. E. M. (1976) Vegetable Oil Srrd Crops irr Ausrrrrfirr. Holt, Rinehart & Winston, Sydney. MORRISON. W. H. and ROBERTSON,J. A. (1978) Effects of drying on sunllower seed oil quality and germination, J. Am. Oil Chm Sot. 2, 272-274. Mousru, E. B. (19’73) Storage and Drying of Oilseeds. In Grcrirt Storclye-Purr of’cl S~~stem (Edited by SINHA, R. N. and MUIR, W. E.), Section 3. Chap. 10. Avi. Wesport. CT. NELLISI.M. E. (1978) Sk/e Tetn~~r~ruws/or Dryiry Gram A report to the Home-Grown Cereals Authority. N.I.A.E.. England. Rep. 29. PIXTON. S W. and WARBURTOU. S. (1971) Moisture content relative humidity equilibrium, at different temperatures, of some oilseeds of economic importance. J. stored. Prod. Rrs. 7, 261-269. SMITH. S. E. (1947)The sorption of water vapor by high polymers. J. Am Chrrt~. Sot. 69, 646-651. SUTHERLAND. J. Vi. (19751 Batch gram drier design and performance prediction. J. c[+c,. Ehgr~g Rrs. 20. 413 -432. SUTHLRLANIXJ. W. and GHALY. T. F. (1982) Heated-air drying of oilseeds. J. srowd Prod. Rrs. 18. 43-54. Wtu~, S. and S~VHERLANU. .I. W. (1979) Buildi,y u Rudiul F/on Btrrch Gruitl Drier. N.S.W. Department of Agriculture. Farm Mechanisation and Engineering Bulletin ME7.