Apr., 1921
3 19
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
Studies of Wheat FIour Grades.
Conductivity of Water
I-Electrical
By C. H. Bailey and F. A. Collatz DIVISIONOF AGRICULTURAL BIOCHEMISTRY, MINNESOTAAGRICULTURAL EXPERIMENT STATION, ST. PAUL, MINNBSOTA
The ash content of wheat flour is almost universally employed a t t h e present time as an index of grade. High-grade or patent flours contain the least ash, occasionally as low as 0.35 per cent, while t h e lower or clear grades sometimes contain over 2 per cent. These differences are due t o t h e fact t h a t t h e Iower grades contain more of t h e branny and embryo structures, which structures contain a higher percentage of ash t h a n t h e floury portion of t h e wheat kernel. Swanson3 determined t h e ratio of total t o watersoluble phosphorus in different streams and grades of commercial flours. He found t h a t when the flour was extracted with water a t 40" there was generally a parallelism between t h e percentage of phosphorus in the water extract and t h a t in t h e original flour. He suggested t h a t a t least part of t h e phosphorus in the flour extract is probably in t h e form of phosphates of pot assi um. I n view of this observation of Swanson's, i t appeared probable t h a t t h e electrical conductivity of water extracts of flours would increase with the percentage of ash. To ascertain whether or not such a relation existed, a series of preliminary experiments was conducted, and in a note by Bailey4 i t was indicated t h a t the parallelism was apparently fairly exact. METHOD O F S T U D Y
The d a t a secured in the preliminary study were not adequate for drawing any definite conclusions, and recently a more comprehensive study was made of t h e factors determining t h e conductance of such extracts. Two samples of flour, representing a high-grade or patent flour containing 0.43 per cent of ash, and a clear or lower grade containing 0.92 per cent, were extracted with conductivity water a t different temperatures, and for various lengths of time. The general details of t h e procedure were as follows: 10 g . of t h e flour were weighed into a d r y Jena flask, and 100 cc. carefully prepared conductivity water having t h e desired temperature were added. The flour was suspended in t h e water by vigorous agitation, care being taken t h a t no lumps were formed. The flask containing this mixture was partially submerged in a water thermostat, which was maintained a t the desired temperature. The flour was kept in suspension b y intermittent shaking during t h e extraction period, and was then thrown out of suspension by whirling for 5 min. in a centrifuge. The clear decant a t e was passed through a filter t o remove any floating particles, and its electrical conductivity determined. APPARATUS FOR CONDUCTIVITY MEASURENEKTS
A special dip electrode was employed, which was similar t o t h e ordinary Freas cell with t h e bottom cut off. The glass walls of t h e cell extended far enough December 1, 1920. Published with the approval of the Director, as Paper No. 213, Journal Series, Minnesota Agricultural Experiment Station. a THISJOURNAL, 4 (i912),274. 4 Sczence 47 (1918),645. 1 Received
1
below the platinum electrodes t o protect them from mechanical injury. I n using this cell, t h e extract was placed in a glass vial and brought t o temperature (30°), and t h e electrodes were then immersed in t h e contents of t h e vial. This made i t possible t o work rapidly by transferring t h e dip electrode from one vial t o another. I n actual practice i t was found advisable t o place portions of t h e extract in a t least two vials, in the first of which t h e electrode was rinsed off, while t h e measurements were made with t h e electrode in the second of the two vials. A constant speed, high frequency generator furnished a current of 1000 alternations per second, which was used with a tunable telephone receiver. A balance was secured b y means of a resistance box, and a 10meter wire bridge calibrated in t h e middle for 50 cm. I N F L U E N C E O F TIbIE A N D T E M P E R A T U R E O F E X T R A C T I O N
The patent and clear flours were extracted for periods of time ranging from 15 t o 960 min. a t O " , 25", 40", and 60". I n Table I are given t h e specific conductivities of t h e extracts thus prepared, data which are given graphically in Fig. 1. I n t h e case of t h e patent flour CONDUCTIVITY (Kso x O F THE WATER EXTRACTS PATENTAND CLEARFLOURS EXTRACTED AT DIFFERENT TEMPERATURES FOR DIFFERENT LENGTHSOF TIME Time of TEMPERATURE OF EXTRACTION Extraction 00 26O 40' 60O Min. R8o X 10-4 Kso X 10-4 Rs4 X 10-4 Kio X 10-4
TABLZ I-SPECIFIC OF
16 30 60 120 240 480 960 16
30 60 120 240 480 960
..... 4.601
Patent Flour 6.161 6.253 6.272
4.600 6.264 6.615 6.609 6.780
i:ij7
6 770 7.378 8.041 8.890 9.333
6.847
6.444 6.443 Clear Flour 8 789 9.167 R. 367 9 999 10.160 10.401 10.693
.....
9.365 9.880
10.018
10.260 10 347 10.680 10.770
9.780 9.872 9.936 10.182 10 195 10.474 io.474
t h e conductivity increased with time and temperature within certain limits. A t temperatures of 40" and 60" there were slight increases in conductivity of the extract after 240 min., while a t 25" equilibrium was reached a t t h e end 3f 480 min., and a t 0 " it was not reached until after a t least 960 min. Moreover, there was a difference in t h e shape of t h e curves a t the four temperatures. A s the temperature increased t h e initial rise in conductivity per unit of time became more abrupt, b u t equilibrium mas reached much sooner, and t h e curve consequently flattened out in a shorter time. The clear flour gave somewhat different results. Equilibrium was not reached so quickly a t any of the temperatures, and what is even more significant, the conductivities of the extracts prepared a t 60" were lower, with the exception of t h e one taken a t the end of 15 min., t h a n were extracts prepared a t 40". Thus the values a t 6 0 " were intermediate between the 25' and 40" extracts. The explanation of these curves is probably t o be
T H E J O U R N A L OF IlVDUSTRIAL A N D ENGINEERING C H E M I S T R Y
320
found in the conclusions reached from observations made on phytase activity. I n t h e preceding paper by Collatz and Bailey1 the progress of t h e hydrolysis of phytin by phytase was discussed, and d a t a were presented showing much the same response t o temperature as is exhibited b y these flours. Phytase from wheat bran was found t o have a n optimum tempera-
FIG. GRAPHS SHOWING EFFECTOF TIMEAND TEMPERATURE O F ExTRACTION O F PATENT A N D CLEARFLOURS UPON SPECIFIC
flours marketed by t h e mill. These contained from 0.35 t o 1.73 per cent of ash. The flours in Series A a n d B were extracted in t h e ratio of 1 part of flour t o 10 parts of water a t 25' for 30 min. This temperature was employed primarily because it was easy t o maintain. This being about t h e mean laboratory temperature, i t follows t h a t there is little likelihood of significant variation in t h e temperature of t h e digest resulting from exposure of t h e materials either before or after combining t h e flour and water. The temperature of t h e mixture consequently changes very slightly during t h e clarification and filtration processes. It is probable t h a t t h e deviation from t h e means observed in t h e preliminary studies reported by Bailey, in which t h e flours were extracted a t O " , may be attributed t o t h e varying rate of temperature change in t h e mixtures from t h e time they were removed from t h e ice bath until t h e clarification was completed. Again, a small variation in t h e length of t h e period of extraction results in less error when t h e extraction is conducted for 30 min. a t 25' t h a n when conducted for t h e same length of time a t Oo. Temperatures above 25" are open t o t h e same objections as are those materially lower, namely, t h e difficulty of maintaining t h e mixture a t a uniform temperature throughout t h e operation TABLEI ~ - - ~ l % I . A T r O N O F I
_j
II
TO
SPECIFIC CONDUCTIVITY OF WATER
ASH CONTENTOF WHEATFLOURS
CONDUCTIVITY OF THE EXTRACTS
ture of 55"; t h e initial rate of change in conductivity of a phytin-phytase solution increased with t h e temperature, and reached equilibrium more quickly a t t h e higher temperatures. The difference in t h e behavior of t h e patent and t h e clear flours a t 60" may possibly be attributed t o t h e ratio of substrate t o enzyme in the several grades. From t h e available d a t a we conclude t h a t t h e electrolytes of the water extract of wheat flours are chiefly phosphates which are produced as the result of hydrolysis of phytin by t h e phytase in t h e natural tissues of the kernel. Since t h e activity of phytase, a n d t h e consequent appearance of electrolytes i n t h e phytase-phytin solution in water, is affected b y temperature, and increases t o a point of equilibrium with lapse of time, i t follows t h a t there are variations in t h e conductivity of water extracts of any flour dependent upon t h e conditions of extraction. It is necessary, therefore, t o maintain uniform conditions with respect t o time, temperature, and ratio of flour t o water, i n comparing several flours by t h e electrical conductivity of their water extracts. ELECTRICAL
C O N D U C T I V I T Y OF W A T E R E X T R A C T S D I F F E R E N T FLOUR GRADES
OF
To afford a wide range of quality, and of percentages of ash, t h e flour streams from two different mills were secured. The series of flours from one mill, designated as Series A, comprised four break flours, and five middlings flours, containing from 0.44 t o 1.62 per cent of ash. T h a t from another mill, designated as Series B, included five break flours, a sizings, stone stock, seven middlings, three tailings, and a dust flour, in addition t o the patent, first clear, and second clear 1
Tars
JOURNAL,
13 (1921).317.
1'01. 13, NO. 4
Grade of Flour
Ash Per cent
EXTRACTS
Specific Conductivity of Water Sxtract KBD X lo-'
Series A
............ 1.34 ......... ........ 0.59 ........ 0.67 .................. 1.62 ......... ........ 0.44 ......... ............... 0.45 ........ 0.56 ........ 1.17 ...... ........ ........ ....... ........ 0.61 Series B First break.. ................... 0 . 5 6 Second break.. ................. 0.48 Third break.. .................. 0.58 Pourth break.. ................. 0.SO Fifth break.. ................... 0.96 Sizings.. ....................... 0.45 First middlings.. ................ 0 . 4 1 Second middlings.. .............. 0.38 Third mlddlings. ................ 0.42 Fourth middlings., .............. 0.46 Fifth middlings.. ............... 0.43 Sixth mlddlings.. ............... 0.42 Seventh middlings. .............. 0.47 Stone stack. .................... 0.35 First fine tailings. ............... 0.73 Second fine tailings. ............. 0.92 First coarse tailings. ............. 0 . 6 6 Dust flour ...................... 1.38 Patent 90 per cent.............. 0.44 First d e a r , . .................... 0.90 Second clear.. ................... 1.73 First break, Second break.. Third break.. Fourth break.. First middlings. Second middlings. Third middlings. Fourth middlings.. Fifth middlings..
10.563 6.647 7.690 11.969 5.395 6.647 6.438 10.242 0.177 6.803 5.971 8.838 8.483 9.187 5.564
5.270 4.744 5.002 6.514 5.192 5.075 5.870 4.643 7.624 8.650 7.450 10.610 5.815 8.850 12.678
The 30-min. period was selected in order t o reduce t o a minimum t h e time involved in completing t h e determination. A method of grading flour based on t h e conductivity of t h e water extract wi11 be more advantageous t h a n t h e determination of ash only in t h e event t h a t t h e time required is materially reduced. If a 30-min. extraction gives comparative results, t h e reduced time may be more important t h a n increased accuracy accompanying a longer extraction period. From t h e d a t a presented in t h e foregoing section i t is evident t h a t any procedure is more or less empirical and must be scrupulously followed t o afford any basis for comparison.
T H E J O U R N A L OF I N D L S T R I A L A N D ENGINEERING C H E M I S T R Y
Apr., 1921:]
32 1
For convenience in comparison, t h e flours are arranged in Table I11 in order of their ash content with t h e specific conductivity in a parallel column. The same arrangement is shown graphically in Fig. 2. I n addition, these data have been subjected t o mathematical treatment, a n d t h e ash content calculated which corresponds t o each unit of conductivity on a smoothed curve. I n parallel columns are given t h e results of these calculated percentages, and t h e differences between t h e actual and calculated percentages of ash. It will be observed t h a t u p t o 0.80 per cent of ash t h e differences are small, being in all b u t one instance within t h e limits t o be expected in ash determinations. The ratio of conductivity t o ash content is sufficiently exact t o permit of t h e determination of t h e former as a n index of flour grade.
2 4 6 8 /O JPCC/F/C CONDUCT/V/IY O F dXTClACT Mao X /O-*
FIG RELATION
O F ASH CONTENT TO SPECIFIC CONDUCTIVITY O F WATER I!XTR,4C!TS PRGPARED B Y EXTRACTING AT 2.5' F O R 30 MIN.
When t h e extracts of t h e thirty flours in t h e two series were prepared in t h e manner described, i t was found t h a t their specific conductivities varied with t h e ash content. The variation was not direct, a n d t h e curve w a s not a straight line, b u t a simple parabola. The ash content and specific conductivity of t h e flours in Series A a n d B are given in Table 11, TABLEIII-SPECIFIC CONDUCTIVITY OF WATSR EXTRACT, ACTUALA N D CALCULATED PERCENTAGE OR ASH IN FLOURS OF SERIESA AND B Specific IN FLOUR Conductivity of ,------ASH Calculated Difference Water Extract Actual Per cent Per cent SAMPLE Koa X 10-4 Per cent 40.021 0.346 4.643 Stone stork.. -0.003 0.378 4.744 Second middlings. ... +0.012 0.409 5.270 First middlings. -0.014 0.417 5.075 Sixth middlings. 4.002 0.419 5.002 Third middlings. -4.013 5.192 Pifth middlings.. 40.017 5.590 Patentl.. -n _.nnQ .___ 5.395 First middlings? 40.032 5.815 Patent. -0.008 5.547 Second middlings'. -0.002 5.564 Sizings flour.. -0.016 5.514 Fourth middlings. 30.014 5.870 Seventh middlings. +0.013 5.971 Second break.. -0.021 6.338 Third middlings'.. -0.010 6.503 First break. +0.018 6.838 Third break.. -0.013 6.647 Second break'. -0.025 6.777 Fifth middlingsa. +0.021 7.450 First coarse tailings.. +0.051 7.690 Third break*. -0.017 7.624 First fine tailings., +0.045 8.483 Fourth break.. +0.014 8.850 Clear flour. -0.041 8.650 Second fine tailings.. +0.053 9.167 Clear flour'. +0.018 9.167 Fifth break., +o. 025 Fourth middlings%. 10.242 -0.077 10.563 First breaks. -0.109 10.610 Dust flour -0.014 11.970 Fourth break%. +0.066 Second clear flour.. 12.678 1 Flours used in preliminary experiments. _I
.......
..... .... .... ... .......... ..... ............ .. ...... ..... ..... ..
........ ...... ...... ...
...... .. ..... ......... ........ ......... ....... .......... ...... .
2
Series -4.
s u >I >I4 K Y Specific conductivity of t h e water extracts of wheat flour varies with t h e time and temperature of extraction. A temperature of 60' or somewhat less gives t h e highest values. From t h e similarity of t h e response of flour extracts t o temperature changes a n d t h a t of phytin-phytase preparations, i t appears t h a t t h e conductivity of water extracts of wheat flour is due chiefly t o inorganic salts of phosphoric acid, resulting from t h e hydrolysis of phytin through t h e activity of t h e enzyme phytase. When comparisons of different flours are t o be made i t is necessary t h a t a uniform procedure be followed in t h e preparation of t h e extracts. Specific conductivity of flour extracts parallels ash content a n d can be employed as a n index of flour grade. I n determining t h e grade of flour by this method i t has been found convenient t o extract 1 part of flour with 10 parts of water a t 25' for exactly 30 min., a n d measure t h e conductivity of t h e clear extract a t 30" with a dip electrode. Standardization of Petroleum Specifications The Interdepartmental Committee on Standardization of Petroleum Specifications, superseding the war-time committee on the same subject, was organized a t its first meeting a t the Bureau of Mines, Washington, D. C., February 19, 1921. The committee gave its approval to Bulletin 5 of the previous committee, continuing in force the specifications on gasoline, kerosene, fuel oils, lubricating oils, signal oils, etc., and decided to adopt the plan of adding a technical subcommittee to handle the details of drawing up and revising specifications and methods of testing. N. A. C. Smith has been appointed chairman of the technical committee. The Committee on Standardization consists of Dr. H. Foster Bain, Bureau of Mines, Chairman, representing the Department of the Interior; J. H. Vawter, Office of the Supervising Architect, representing the Treasury Department; Captain Wm. H. Lee, Q. M . C., Office of the Quartermaster General, representing the War Department; E. B. Cranford, Asst. Supt., Division of Post-Office Service, representing the Post-Office Department; B. A. Anderton, Bureau of Public Roads, representing the Department of Agriculture; Dr. C. W. Waidner, Bureau of Standards, representing the Department of Commerce; W. A. E. Doying, Inspecting Engineer, representing the Panama Canal; hf. W. Bowen, Assistant to the Chairman, representing the Shipping Board.
