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Some chemical and physical properties of proso millet (Panicum milliaceum) starch
Joumal of Cereal Science 13 (1991) 299-305
Some Chemical and Physical Properties of Proso Millet (Panicum milliaceum) Starch G. A. YANEZ,* C. E. WALKER,t§ and L. A. NELSON:::
* Universidad de Sonora, Centro Coordinador de la lnvestigacion Alimentos, Hermosillo, Sonora, 83000, Mexico, t Kansas State University, Department of Grain Science and Industry, Shellenberger Hall, Manhattan, Kansas 66506-2201, U.S.A. and ::: University of Nebraska, Agronomy Department, Panhandle Station, Scottsbluff, Nebraska 69631, U.S.A. Received 12 January 1989 and in revised form 30 January 1990 Preso millet (Panicum milliaceum) starch extracted from four cultivars had an apparent amylose content slightly higher (29'2-32'6 %) than that of normal maize. Proso starch digestibility was similar to that of maize. Gelatinization temperatures and enthalpy values for proso starch were found to be significantly higher, (P < 0'05) than those of maize, suggesting that proso starch has a more ordered and uniform granular structure. The freeze-thaw stability of proso starch gels was less than that of maize starch. but the proso starch gels demonstrated an unusual ability to re-absorb water.
Introduction Relatively little information has been reported on proso millet starches, though they tend to compare with the other cereal grains. Becker and LorenzI studied the saccharides of proso and foxtail millets. Rachie 2 reported caloric contents for different millet species and other selected cereal grains. Proso. at 341 kcal (1427 kJ) per 100 g, was comparable with other grains. Proso millet starch content may vary from 59-80 %3. Hulse 4 provided an extensive review of proso millet chemical composition and reported an average of 52·1 % starch, 0·4 % reducing sugar, and 0·2 % non-reducing sugars. Hulse also reported amylose contents as low as 2 to 6 % of the starch. Yanez and Walker 5 reported on a proso millet that contained 64 % starch of which 29·1 % was amylose. Lorenza, and Lorenz and Hinze 7 have reported data for proso and foxtail millet starch functionalities. The objective of our study was to determine if some chemical and physical characteristics of proso millet starches varied among four different cultivars that had been grown at the same location and in the same year.
§ To whom correspondence should be addressed.
Abbreviations used: DSC: differential scanning calorimetry; SEM = scanning electron microscopy.
0733-5210/91/030299 + 07 $03,00/0
© 1991 Academic Press Limited
300
G. A. YANEZ ET AL.
Experimental
Proso millet samples Four cultivars of Panicum milliaceum (Dawn, Cope, Minco and Cerise) were grown at the Panhandle Research and Extension Center, High Plans Agricultural Laboratory of the University of Nebraska, near Sidney in 1985. Dawn is an unusually white proso, Cope and Minco are more typical cultivars with higher yields, and Cerise is a red-seeded cultivar.
Starch isolations Starches were isolated by an acidic aqueous wet-milling method 5 with a total steep time of 24 h.
Chemical analysis Starch contents were determined by enzymic analysis of the whole proso grains, and starch apparent amylose contents (as a percentage of total starch) were determined following previously described methods B• Starch, protein and ash were by standard methodso. In vitro starch digestibility was determined as by Frels 10 using porcine pancreatic alpha-amylase (Sigma Chemical Co., Missouri, U.S.A.). Gelatinized starch was not reduced with sodium borohydride and no inhibitor was added. Digestion was monitored during a 40 min period by spectrophotrometric analysis of the maltose released 1o •
Physical properties The size distribution of 500 starch granules was measured by optical microscopic observation at 400 x, using a calibrated eye·piece reticule. Starch granules were also observed by scanning electron microscopy (SEM) by placing the starch on a stub previously coated with a thin layer of silver paste. The starch was then coated with gold-palladium by vacuum evaporation to provide good conductivity, preventing charging. The samples were observed and photographed using a Cambridge S4019 SEM (Cambridge Scientific Instruments, Inc. Cambridge, U.K.) at an accelerating voltage of 20 kV and a magnification of 5000 x . Gelatinization temperature (by loss in birefringence) was measured with the Kofler microscope hot stage l l (Arthur H. Thomas Co., Philadelphia, Pennsylvania, U.S.A.). Data for the initial and final gelatinization points were recorded. Thermal analysis was performed using a Perkin-Elmer differential scanning calorimeter (model DSC-2) with an FTS flexicooler with temperature controller (FFS Systems Inc., Stone Ridge, New York, U.S.A.). Samples were prepared according to the instrument manual by weighing approximately 3 mg of starch with a micro balance into an aluminum sample pan. Enough water was added with a micro-syringe to reach 73 % moisture (wet basis), and the pans were hermetically sealed with a Perkin-Elmer sample sealer. The samples were allowed to equilibrate for at least I h before analysing at J0 0 fmin heating rate, beginning at 280 OK and ending at 400 oK. The DSC was calibrated using indium as the standard. The enthalpy change (t:.H), onset temperature (1;,), peak temperature (J;,), and conclusion temperature (1;,) were determined. Starch pasting properties were determined with the Viscoamylograph (Brabender O. H. G., Duisberg, West Germany). Wet-milled Argo Maize cornstarch (CPC International Inc., Englewood Cliffs, New Jersey, U.S.A.) was used as a reference. The procedure given in the Amylograph Handbook 12 was followed, using 35 g (dry basis) for each determination. Freeze-thaw stability was estimated according to the method of Schoch 13 , using distilled water to prepare a 5 % (w Iv) starch paste and subjecting it to five freeze-thaw cycles. Duplicate samples (30 m!) of the starch paste were poured into 50 ml plastic centrifuge tubes. The tubes were centrifuged at 940 g for 20 min after thawing.
PROSO MILLET STARCH
301
TABLE I. Starch content of the grain, amylose content and proximate analysis of prosa millet starches" Cultivar Starch (%) Amylose b (%) Protein C (%) Cope Minco Cerise Dawn
65·0 (0'86) 63·5 (0'74) 61·8 (0'75) 68-2 (0'46)
32·0 (1'37) 32·6 (0'65) 31·9 (0'56) 29'2 (1'53)
1·13 (0' IS) 1·07 (0'15) 1·55 (0'22) 2'10 (0'74)
Ash (%) 0·48 (0'03) 0'60 (0'09) 0'76 (0'05) 0·83 (0'08)
"Dry weight basis; averages of three samples in duplicate. (S.D. in parenthesis). b As a percentage of total starch content. C Kjeldahl N x 6·25.
TABLE II. In vitro digestibility (per cent hydrolysis) of proso millet" and maize b starches Extent of analysis (%)C Sample/time (min) Maize Proso millet cv. Cope cv. Dawn cv. Minco cv. Cerise
10
20
30
40
10'91 A
25'31 A
36'58 A
42·82 A
8·92 B 11·15 A 10·34 A 9·03 B
22·92 C 26·11 A 24·77 AB 23·35 BC
3H4C 36·10 AB 34·75 BC 33·22 C
39·05 B 41·45 AB 40·34 AB 38·66 B
"Average or nine determinations; means with the same letter, in a column, are not significantly different at
P < 0·05. b C
Average or three determinations. Expressed as mole (%) or maltose released.
Statistical analysis Results for all experiments were tested by analysis of variance (ANOVA), followed with the Duncan multiple range test (DMRT), at alpha 0·05 level for mean comparison.
Results and Discussion
Chemical characteristics
Three separate batches, isolated on different days, of each variety were used to prepare the starch samples. Starch and amylose content average values and proximate analysis are reported in Table I. All proso millet cultivars tested were found to contain starch with apparent amylose contents ranging from 29·2 to 32'6 % of total starch. All amylose values, with the exception of Dawn, appear to be slightly higher than values usually reported for normal starches of other cereals (17-27 %)14. It has been reported that starch granules vary widely in digestibility, depending upon the source, processing and storage conditions, but cereal starches and some root/tuber starches are considered to be highly digestible 1D • In this study, proso cultivars had hydrolysis rates similar to that of maize (Table II). Statistically significant differences in
G. A. YANEZ ET AI.
302
FIGURE 1. Prasa millet starch granules by SEM from cultivar Cope. Bar length = ]0
~lm.
digestibility were observed between Dawn (similar to maize), and Cope and Cerise. The differences were small however, and all samples should be considered to be digestible, for all practical purposes. Physical characteristics Proso starch granules have a bimodal distribution with two basic shapes and sizes, small spherical and large polygonal (Fig. 1). Many large polygonal granules show indentations due to the dense packing of the endosperm. Starch granules sizes ranged from 1·8 to 13·5 J.l.m; mean diameters varying from approximately 4 to 5 11m, varying slightly among the cultivars (Fig. 2). Proso starch granules resemble those of rice, which have a mean granule size ranging from 4 to 6 11m 16. Data on the thermal characteristics of the starches are summarized in Table HI. Only slight variations in hot stage and DSC gelatinization temperatures were observed among proso cultivars. DSC transition temperatures were higher (P < 0,05) for proso starches as compared to maize starch. Amylograph peak viscosities were substantially lower (by 150 to 200 BU) for the proso starches than for maize starch. Cope and Dawn had similar viscosities at 95°C, higher than did Minco and Cerise. They were also higher at 50 °c setback. However, these latter two had apparently not reached a maximum, and were still increasing in viscosity at 95°C. Proso starch demonstrated a very interesting behavior following the freeze-thaw stability test. This stability of a starch gel is evaluated by the amount (%) of water
PROSO MILLET STARCH
303
40 35
o Cope 12 Down
30
£9
--; 25
...
~
!
Inca
• Cerise
20
~
.::
15
'0 5 0
',8
4·5
2'9
5·9
7·2
9·0
10'8
11·9
13'5
Particle SIZe (flm)
FIGURE 2. Granule size distribution for four proso millet starch cultivars. TABLE 3. Summary of thermal characteristics of proso millets starches Amylograph visco (BU)b
Gelatinization temp. (Qq" Sample Maize Proso Millet cv. Cope cv. Dawn cv. Minco cv. Cerise
1'"
T,.
Dsce'
Amylograph
61·3 64·0 72-5
69·0 94'0
Microscopy DSC Amylograph Microscopy DSC Amylograph Microscopy DSC Amylograph Microscopy DSC Amylograph
66'6 69'0 74·0 65·3 68·5 72-5 65'3 67·8 73'0 65·7 68·2 74·5
Method Microscopy"
Gelatinization temperatures: 1;,. onset; " Brabender units. " Koner hot stage microscopy. " Differential scanning calorimetry. •' No peak; viscosity still rising at 95°C, a
73-9 93·0 73·9 93·0
1;, 71-0 75·5 73-6 81·8 73-6 81·0
~H
cal (J)/g
3·\0 (12'98)
50 QC
359
750
223
388
218
363
167
263
183
307
3'56 (14'90) 3'57 (14'69)
72-5
72-4 80'3
3·51 (14'69)
73-6
72-9 80·3
3'57 (14'94)
-"
95 QC
~- .. _,-('
I;,. peak; and 7;" conclusion temperatures.
304
G. A. YANEZ ET AL. 80
r--------------------......,
70
. ---::
---~ . . ----------1// //
J/
/1
60
//
// //....
(J
I
50 .....
I' IP /'U
Ql
3:
"0
40
Ql
+-
e 0
0.
Ql
(f)
30
/
I
/1 //
/
- - - - - Minco - - - - - - Cerise Dawn
~'//
~ I V
0
//
I,'
/p // I; //
20
10
I '
Ii
~
....0
(
... . . .----
----------
Cope
-------
Maize
,I ,I
,I
I I
I
2
3
4
5
Freeze-thaw cycles
FIGURE 3. Freeze-thaw stability of maize and four proso millet starch cultivars.
separated during the freeze-thaw cycles. After centrifugation, some separated water was noted from all starch gels. However, maize starch gels re-absorbed the water more slowly than proso, and tended to break more easily, while proso gels were more easily compressible. Higher percentages of separated water were obtained from proso than from maize gels (Fig. 3). The proso starch gel structure, after removal of the water, was quite different from that of maize starch. It had a fibrous appearance, whereas that of maize was very short, with a mushy, fragile texture. Cope starch (more than the other proso varieties) resembled maize starch in its pattern of water separation. Maize gels, when allowed to dry, shrank and turned yellow, while most of the proso gels retained a white porous structure that re-absorbed water totally, and rapidly increased to their original size.
PROSO MILLET STARCH
305
Conclusions Proso millets contain a starch with smaller granule sizes but higher amylose contents, gelatinization temperatures, and enthalpy values than common maize starch. There were statistically significant differences among the four cultivars tested in total starch and in starch amylose content, in digestibilities and in gelatinization/pasting properties. Proso starch appeared to be less freeze-thaw stable than maize starch, but a partly dried gel also had the interesting ability to re-absorb water rapidly and to expand to its original shape. This property may be important and may have applications in fields other than food. This observation, as well as an apparent difference in pasting properties of some cultivars (Minco and Cerise), might lead to profitable future research. References I. Becker, R. and Lorenz, K. J. Food Sci. 43 (1978) 1412-1414. 2. Rachie, K. O. 'The Millets: Importance, Utilization, and Outlook', International Crops Research Institute for the Semi-Arid Topics Hyderabad, India. (1975). 3. Casey, P. and Lorenz, K. Bakers Digest 50 (1977) 45-51. 4. Hulse, J. H., Laing, E. M. and Pearson, O. E. 'Sorghum and the Millets: Their Composition and Nutritional Value', Academic Press. New York, (1980) Chapters 2, 3, and 5. 5. Yanez, G. A. and Walker, C. E. Cereal Chem. 63 (1986) 164-167. 6. Lorenz, K. Lebensm. Wiss. u. Technol. 10 (1977) 324-327. 7. Lorenz, K. and Hinze, G. J. Agric. Food Chem. 24 (1976) 911-914. 8. Yanez, G. A., Messinger, J. K., Walker, C. E. and Rupnow, J. H. Cereal Chern. 63 (1986) 273-276. 9. Association of Official Analytical Chemists.• Official Methods of Analyses,' 12th edn, The Association, Washington, DC. (1975). 10. Frels, J. M. and Rupnow, J. H. Food Biochem. 8 (1984) 281. II. Schoch, T. J. and Maywald, E. C. Anal. Chern. 28 (1956) 382-387. 12. Shuey, W. C. and Tipples, K. H. 'The Amylograph Handbook', Am. Assoc. Cereal Chem. St. Paul, Minnesota (1980). 13. Schoch, T. J. 'The Freezing Preservation of Foods, Vol. 4.' (D. K. Tressler, W. B. Van Arsdel and M. J. Copely, eds.), Westport, Connecticut (1968) p 44. 14. Pomeranz, Y. 'Modern Cereal Science and Technology', VCH Publishers, New York, (1987) p. 403. IS. Dreher, M. L., Dreher, C. J. and Berry, J. W. Cril. Rev. Food Sci. Nlltr. 20 (1984) 47-66. 16. Juliano, B. O. 'Starch: Chemistry and Technology' 2nd edn. (R. L. Whistler, J. N. BeMiller and E. F. Paschael, eds.), Academic Press, Orlando, Florida (1984) pp 513-517.
Some Chemical and Physical Properties of Proso Millet (Panicum milliaceum) Starch G. A. YANEZ,* C. E. WALKER,t§ and L. A. NELSON:::
* Universidad de Sonora, Centro Coordinador de la lnvestigacion Alimentos, Hermosillo, Sonora, 83000, Mexico, t Kansas State University, Department of Grain Science and Industry, Shellenberger Hall, Manhattan, Kansas 66506-2201, U.S.A. and ::: University of Nebraska, Agronomy Department, Panhandle Station, Scottsbluff, Nebraska 69631, U.S.A. Received 12 January 1989 and in revised form 30 January 1990 Preso millet (Panicum milliaceum) starch extracted from four cultivars had an apparent amylose content slightly higher (29'2-32'6 %) than that of normal maize. Proso starch digestibility was similar to that of maize. Gelatinization temperatures and enthalpy values for proso starch were found to be significantly higher, (P < 0'05) than those of maize, suggesting that proso starch has a more ordered and uniform granular structure. The freeze-thaw stability of proso starch gels was less than that of maize starch. but the proso starch gels demonstrated an unusual ability to re-absorb water.
Introduction Relatively little information has been reported on proso millet starches, though they tend to compare with the other cereal grains. Becker and LorenzI studied the saccharides of proso and foxtail millets. Rachie 2 reported caloric contents for different millet species and other selected cereal grains. Proso. at 341 kcal (1427 kJ) per 100 g, was comparable with other grains. Proso millet starch content may vary from 59-80 %3. Hulse 4 provided an extensive review of proso millet chemical composition and reported an average of 52·1 % starch, 0·4 % reducing sugar, and 0·2 % non-reducing sugars. Hulse also reported amylose contents as low as 2 to 6 % of the starch. Yanez and Walker 5 reported on a proso millet that contained 64 % starch of which 29·1 % was amylose. Lorenza, and Lorenz and Hinze 7 have reported data for proso and foxtail millet starch functionalities. The objective of our study was to determine if some chemical and physical characteristics of proso millet starches varied among four different cultivars that had been grown at the same location and in the same year.
§ To whom correspondence should be addressed.
Abbreviations used: DSC: differential scanning calorimetry; SEM = scanning electron microscopy.
0733-5210/91/030299 + 07 $03,00/0
© 1991 Academic Press Limited
300
G. A. YANEZ ET AL.
Experimental
Proso millet samples Four cultivars of Panicum milliaceum (Dawn, Cope, Minco and Cerise) were grown at the Panhandle Research and Extension Center, High Plans Agricultural Laboratory of the University of Nebraska, near Sidney in 1985. Dawn is an unusually white proso, Cope and Minco are more typical cultivars with higher yields, and Cerise is a red-seeded cultivar.
Starch isolations Starches were isolated by an acidic aqueous wet-milling method 5 with a total steep time of 24 h.
Chemical analysis Starch contents were determined by enzymic analysis of the whole proso grains, and starch apparent amylose contents (as a percentage of total starch) were determined following previously described methods B• Starch, protein and ash were by standard methodso. In vitro starch digestibility was determined as by Frels 10 using porcine pancreatic alpha-amylase (Sigma Chemical Co., Missouri, U.S.A.). Gelatinized starch was not reduced with sodium borohydride and no inhibitor was added. Digestion was monitored during a 40 min period by spectrophotrometric analysis of the maltose released 1o •
Physical properties The size distribution of 500 starch granules was measured by optical microscopic observation at 400 x, using a calibrated eye·piece reticule. Starch granules were also observed by scanning electron microscopy (SEM) by placing the starch on a stub previously coated with a thin layer of silver paste. The starch was then coated with gold-palladium by vacuum evaporation to provide good conductivity, preventing charging. The samples were observed and photographed using a Cambridge S4019 SEM (Cambridge Scientific Instruments, Inc. Cambridge, U.K.) at an accelerating voltage of 20 kV and a magnification of 5000 x . Gelatinization temperature (by loss in birefringence) was measured with the Kofler microscope hot stage l l (Arthur H. Thomas Co., Philadelphia, Pennsylvania, U.S.A.). Data for the initial and final gelatinization points were recorded. Thermal analysis was performed using a Perkin-Elmer differential scanning calorimeter (model DSC-2) with an FTS flexicooler with temperature controller (FFS Systems Inc., Stone Ridge, New York, U.S.A.). Samples were prepared according to the instrument manual by weighing approximately 3 mg of starch with a micro balance into an aluminum sample pan. Enough water was added with a micro-syringe to reach 73 % moisture (wet basis), and the pans were hermetically sealed with a Perkin-Elmer sample sealer. The samples were allowed to equilibrate for at least I h before analysing at J0 0 fmin heating rate, beginning at 280 OK and ending at 400 oK. The DSC was calibrated using indium as the standard. The enthalpy change (t:.H), onset temperature (1;,), peak temperature (J;,), and conclusion temperature (1;,) were determined. Starch pasting properties were determined with the Viscoamylograph (Brabender O. H. G., Duisberg, West Germany). Wet-milled Argo Maize cornstarch (CPC International Inc., Englewood Cliffs, New Jersey, U.S.A.) was used as a reference. The procedure given in the Amylograph Handbook 12 was followed, using 35 g (dry basis) for each determination. Freeze-thaw stability was estimated according to the method of Schoch 13 , using distilled water to prepare a 5 % (w Iv) starch paste and subjecting it to five freeze-thaw cycles. Duplicate samples (30 m!) of the starch paste were poured into 50 ml plastic centrifuge tubes. The tubes were centrifuged at 940 g for 20 min after thawing.
PROSO MILLET STARCH
301
TABLE I. Starch content of the grain, amylose content and proximate analysis of prosa millet starches" Cultivar Starch (%) Amylose b (%) Protein C (%) Cope Minco Cerise Dawn
65·0 (0'86) 63·5 (0'74) 61·8 (0'75) 68-2 (0'46)
32·0 (1'37) 32·6 (0'65) 31·9 (0'56) 29'2 (1'53)
1·13 (0' IS) 1·07 (0'15) 1·55 (0'22) 2'10 (0'74)
Ash (%) 0·48 (0'03) 0'60 (0'09) 0'76 (0'05) 0·83 (0'08)
"Dry weight basis; averages of three samples in duplicate. (S.D. in parenthesis). b As a percentage of total starch content. C Kjeldahl N x 6·25.
TABLE II. In vitro digestibility (per cent hydrolysis) of proso millet" and maize b starches Extent of analysis (%)C Sample/time (min) Maize Proso millet cv. Cope cv. Dawn cv. Minco cv. Cerise
10
20
30
40
10'91 A
25'31 A
36'58 A
42·82 A
8·92 B 11·15 A 10·34 A 9·03 B
22·92 C 26·11 A 24·77 AB 23·35 BC
3H4C 36·10 AB 34·75 BC 33·22 C
39·05 B 41·45 AB 40·34 AB 38·66 B
"Average or nine determinations; means with the same letter, in a column, are not significantly different at
P < 0·05. b C
Average or three determinations. Expressed as mole (%) or maltose released.
Statistical analysis Results for all experiments were tested by analysis of variance (ANOVA), followed with the Duncan multiple range test (DMRT), at alpha 0·05 level for mean comparison.
Results and Discussion
Chemical characteristics
Three separate batches, isolated on different days, of each variety were used to prepare the starch samples. Starch and amylose content average values and proximate analysis are reported in Table I. All proso millet cultivars tested were found to contain starch with apparent amylose contents ranging from 29·2 to 32'6 % of total starch. All amylose values, with the exception of Dawn, appear to be slightly higher than values usually reported for normal starches of other cereals (17-27 %)14. It has been reported that starch granules vary widely in digestibility, depending upon the source, processing and storage conditions, but cereal starches and some root/tuber starches are considered to be highly digestible 1D • In this study, proso cultivars had hydrolysis rates similar to that of maize (Table II). Statistically significant differences in
G. A. YANEZ ET AI.
302
FIGURE 1. Prasa millet starch granules by SEM from cultivar Cope. Bar length = ]0
~lm.
digestibility were observed between Dawn (similar to maize), and Cope and Cerise. The differences were small however, and all samples should be considered to be digestible, for all practical purposes. Physical characteristics Proso starch granules have a bimodal distribution with two basic shapes and sizes, small spherical and large polygonal (Fig. 1). Many large polygonal granules show indentations due to the dense packing of the endosperm. Starch granules sizes ranged from 1·8 to 13·5 J.l.m; mean diameters varying from approximately 4 to 5 11m, varying slightly among the cultivars (Fig. 2). Proso starch granules resemble those of rice, which have a mean granule size ranging from 4 to 6 11m 16. Data on the thermal characteristics of the starches are summarized in Table HI. Only slight variations in hot stage and DSC gelatinization temperatures were observed among proso cultivars. DSC transition temperatures were higher (P < 0,05) for proso starches as compared to maize starch. Amylograph peak viscosities were substantially lower (by 150 to 200 BU) for the proso starches than for maize starch. Cope and Dawn had similar viscosities at 95°C, higher than did Minco and Cerise. They were also higher at 50 °c setback. However, these latter two had apparently not reached a maximum, and were still increasing in viscosity at 95°C. Proso starch demonstrated a very interesting behavior following the freeze-thaw stability test. This stability of a starch gel is evaluated by the amount (%) of water
PROSO MILLET STARCH
303
40 35
o Cope 12 Down
30
£9
--; 25
...
~
!
Inca
• Cerise
20
~
.::
15
'0 5 0
',8
4·5
2'9
5·9
7·2
9·0
10'8
11·9
13'5
Particle SIZe (flm)
FIGURE 2. Granule size distribution for four proso millet starch cultivars. TABLE 3. Summary of thermal characteristics of proso millets starches Amylograph visco (BU)b
Gelatinization temp. (Qq" Sample Maize Proso Millet cv. Cope cv. Dawn cv. Minco cv. Cerise
1'"
T,.
Dsce'
Amylograph
61·3 64·0 72-5
69·0 94'0
Microscopy DSC Amylograph Microscopy DSC Amylograph Microscopy DSC Amylograph Microscopy DSC Amylograph
66'6 69'0 74·0 65·3 68·5 72-5 65'3 67·8 73'0 65·7 68·2 74·5
Method Microscopy"
Gelatinization temperatures: 1;,. onset; " Brabender units. " Koner hot stage microscopy. " Differential scanning calorimetry. •' No peak; viscosity still rising at 95°C, a
73-9 93·0 73·9 93·0
1;, 71-0 75·5 73-6 81·8 73-6 81·0
~H
cal (J)/g
3·\0 (12'98)
50 QC
359
750
223
388
218
363
167
263
183
307
3'56 (14'90) 3'57 (14'69)
72-5
72-4 80'3
3·51 (14'69)
73-6
72-9 80·3
3'57 (14'94)
-"
95 QC
~- .. _,-('
I;,. peak; and 7;" conclusion temperatures.
304
G. A. YANEZ ET AL. 80
r--------------------......,
70
. ---::
---~ . . ----------1// //
J/
/1
60
//
// //....
(J
I
50 .....
I' IP /'U
Ql
3:
"0
40
Ql
+-
e 0
0.
Ql
(f)
30
/
I
/1 //
/
- - - - - Minco - - - - - - Cerise Dawn
~'//
~ I V
0
//
I,'
/p // I; //
20
10
I '
Ii
~
....0
(
... . . .----
----------
Cope
-------
Maize
,I ,I
,I
I I
I
2
3
4
5
Freeze-thaw cycles
FIGURE 3. Freeze-thaw stability of maize and four proso millet starch cultivars.
separated during the freeze-thaw cycles. After centrifugation, some separated water was noted from all starch gels. However, maize starch gels re-absorbed the water more slowly than proso, and tended to break more easily, while proso gels were more easily compressible. Higher percentages of separated water were obtained from proso than from maize gels (Fig. 3). The proso starch gel structure, after removal of the water, was quite different from that of maize starch. It had a fibrous appearance, whereas that of maize was very short, with a mushy, fragile texture. Cope starch (more than the other proso varieties) resembled maize starch in its pattern of water separation. Maize gels, when allowed to dry, shrank and turned yellow, while most of the proso gels retained a white porous structure that re-absorbed water totally, and rapidly increased to their original size.
PROSO MILLET STARCH
305
Conclusions Proso millets contain a starch with smaller granule sizes but higher amylose contents, gelatinization temperatures, and enthalpy values than common maize starch. There were statistically significant differences among the four cultivars tested in total starch and in starch amylose content, in digestibilities and in gelatinization/pasting properties. Proso starch appeared to be less freeze-thaw stable than maize starch, but a partly dried gel also had the interesting ability to re-absorb water rapidly and to expand to its original shape. This property may be important and may have applications in fields other than food. This observation, as well as an apparent difference in pasting properties of some cultivars (Minco and Cerise), might lead to profitable future research. References I. Becker, R. and Lorenz, K. J. Food Sci. 43 (1978) 1412-1414. 2. Rachie, K. O. 'The Millets: Importance, Utilization, and Outlook', International Crops Research Institute for the Semi-Arid Topics Hyderabad, India. (1975). 3. Casey, P. and Lorenz, K. Bakers Digest 50 (1977) 45-51. 4. Hulse, J. H., Laing, E. M. and Pearson, O. E. 'Sorghum and the Millets: Their Composition and Nutritional Value', Academic Press. New York, (1980) Chapters 2, 3, and 5. 5. Yanez, G. A. and Walker, C. E. Cereal Chem. 63 (1986) 164-167. 6. Lorenz, K. Lebensm. Wiss. u. Technol. 10 (1977) 324-327. 7. Lorenz, K. and Hinze, G. J. Agric. Food Chem. 24 (1976) 911-914. 8. Yanez, G. A., Messinger, J. K., Walker, C. E. and Rupnow, J. H. Cereal Chern. 63 (1986) 273-276. 9. Association of Official Analytical Chemists.• Official Methods of Analyses,' 12th edn, The Association, Washington, DC. (1975). 10. Frels, J. M. and Rupnow, J. H. Food Biochem. 8 (1984) 281. II. Schoch, T. J. and Maywald, E. C. Anal. Chern. 28 (1956) 382-387. 12. Shuey, W. C. and Tipples, K. H. 'The Amylograph Handbook', Am. Assoc. Cereal Chem. St. Paul, Minnesota (1980). 13. Schoch, T. J. 'The Freezing Preservation of Foods, Vol. 4.' (D. K. Tressler, W. B. Van Arsdel and M. J. Copely, eds.), Westport, Connecticut (1968) p 44. 14. Pomeranz, Y. 'Modern Cereal Science and Technology', VCH Publishers, New York, (1987) p. 403. IS. Dreher, M. L., Dreher, C. J. and Berry, J. W. Cril. Rev. Food Sci. Nlltr. 20 (1984) 47-66. 16. Juliano, B. O. 'Starch: Chemistry and Technology' 2nd edn. (R. L. Whistler, J. N. BeMiller and E. F. Paschael, eds.), Academic Press, Orlando, Florida (1984) pp 513-517.