June,
191-1
T H E JOCR.V.4L
O F I * V D C S T R I A L d.VD E-VGI-VEERI-VG C H E M I S T R Y
PHYSICAL FACTORS WHICH INFLUENCE THE PERCENTAGE OF WET AND DRY GLUTEN IN WHEATEN FLOUR By B . H. KEPNES Received J a n u a r y 2 8 , 1914.
The determination Of crude IYet and gluten is affected b y S O m a n y physical conditions a n d is S O t h a t it has been given a n d t h e proteins are now determined in most laboratories by the more accurate Kjeldahl method. I n exceptional cases when i t is necessary t o know t h e quality of t h e gluten. a qualitative determination is made. Xrpinl recognizes t h e fact t h a t there are numerous sources of error in t h e separation of t h e gluten. Jago2 states t h a t i t is difficult a n d in m a n y cases impossible t o wash away t h e whole of t h e starch from flour without also washing a w a y some of t h e more soluble p a r t s of t h e gluten itself. In consequence, gluten determinations v a r y according t o t h e thoroughness of washing a n d this differs in different hands. I n spite of this assertion Jag0 still continues t o a t t a c h importance t o properly conducted gluten determinations. holding t h a t t h e estimation of t h e q u a n t i t y a n d quality of t h e TTet gluten determines t h e quality of t h e resultant dough a n d bread. I t has been m y experience t h a t . within t h e same grade, Straight. P a t e n t , Bakers. etc.. t h e higher t h e percentage a n d t h e better t h e quality of t h e wet gluten, t h e better baking results are obt ained. Because there is no standard method, each laboratory a t present uses a method which is t h e most suitable for its use. Results are affected by t h e conditions a n d methods of manipulation by which t h e y are obtained. T h e y are not absolutely comparable from different laboratories because of t h e difference i n physical conditions. T h e following method we ha\-e adopted as being especially suitable for routine work: Weigh o u t t h i r t y grams of flour in a large size coffee cup. Mix in enough water, a b o u t 1 7 cc.. n-ith a stiff bladed knife t o make a dough of s t a n d a r d stiffness a n d continue t h e mixing until a n absolutely uniform dough is obtained. Cover t h e dough with cold xvater, let s t a n d strealn of n.ater one hour and then l\7ash in a a t exactly 65 O C . ( o \ ~ e ra sixty-mesh sieve) until nearly all t h e starch is Tyashed away. R e t u r n gluten t o cup, cover with cold vrater, let s t a n d one-half hour longer a n d t h e n wash until free from starch. T h e wash water should be clear a n d not milky, Cover t h e gluten ITTith cold Water until it is ready t o weigh. then d r y betTveen the hands, wiping t h e excess of water on a clean, lintpaper 2 ' 1 x 2'1 and f r e e towel, place on \\:hite a t 1 7 0 0 c, t o expand the gluten lveigh, place in t o a porous mass a n d bake i t . t h e n dry f o r twenty-four hours a t ~ o j "a n d again weigh. I t was f o u n d very difficult t o check t h e determinations f r o m d a y to d a y , hence, the effect of t h e different physic a1 conditions were deter mined . I t is necessary t o make an absolutely uniform dough of t h e Ivater and flour, otherwise portions of flours are Jvashed a w a y like starch. Poorly mixed samples 1
Jour. SOC.Chem. I n d . , 1902, pp. 1417 a n d 1560.
"Technology of Breadmaking." p . 296.
481
give results which are I per cent lower in wet gluten a n d 0 . 2 t o 0.jper cent lower in dry gluten t h a n a well mixed sample. T h e poorer t h e mixing. as a rule, t h e greater t h e loss. If a n excess of water is used for making t h e dough, t h e yield of %vetgluten is increased from I t o 3 per cent f o r t h e different grades, while insufficient water causes t h e percentage of gluten obtained t o be lower. T h e percentage of d r y gluten is not affected b y this contlition, showing t h a t t h e higher or lower percentage of wet gluten is due LTholly to water held by it,
If t h e doughs are kept covered with cold water before washing t h e percentage of wet gluten obtained in most cases increases with t h e length of time they are allowed t o s t a n d up t o eight hours. They are kept cold in order t o offset t h e influence of temperature and a n y fermentation. -4rpin' shows t h a t t h e wet gluten is increased 1.66 per cent b y standing four hours, while t h e percentage of d r y gluten remains unaltered. I find t h a t very short p a t e n t s and flours which have aged a t least nine months are exceptions t o this because there is only a < very slight increase for even eight hours. Bakers a n d straight grades, when freshly ground, showed a n increase of I. jo to 3. j o per cent on standing eight hours. Low grades show an increase of only 0.3 per cent on standing one hour a n d a decrease of 2 . j per cent on standing eight hours. T h e low grades being high in n a t u r a l ferments or bacteria suffer a loss by their action. T h e aged flours a n d short patents are unaffected because t h e y contain less of these natural ferments t h a n t h e freshly ground bakers a n d straight grades. A11 grades begin t o decrease a t t h e end of sixteen hours v h i c h would strengthen this supposition. T h e percentage of dry gluten remains t h e same up t o sixteen hours on all flours with t h e exception of t h e low grade, which suffers a loss. After glutens are washed a n d allowed t o s t a n d for even twenty-four hours there is n o change in weight. This shows t h a t t h e increase or decrease in weight on standing eight hours before washing is due t o some agency in t h e flour which is not included in t h e crude wet gluten. The thoroughness of washing affects t h e results t o a great degree. When glutens are washed in t h e usual manner, weighed, a n d t h e n vigorously washed for five minutes more there is a loss of j per cent on t h e low grades, 3 t o 4 per cent on t h e straights a n d bakers and 2 . 5 Per cent O n the high patents and Old flours. There is also a loss Of d r y gluten. This loss varies with t h e manipulation and t h e vigorousness of t h e Operation. .%rpin2 states t h a t t h e yield of gluten is increased 1.16 per cent XTith a n increase of 10' in temperature of t h e water used f o r washing. T e find t h a t wet gluten increases i . j o per cent for t h e same increase of temperature f o r all grades except t h e low grade, which shows a slight decrease. This can perhaps also be explained by t h e more active action of natural higher temperature. f e r m e n t s caused found a n increase of 1.16 per cent f o r t h e same range of temperature in t h e dry gluten. This point we have Jour. SOC.C k e m . Ind.,1902, 1 4 1 i a n d 1560. Chem. C e n t r . , 2 (1902). 1019 and 134i.
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T H E J O U R N A L OF I N D Y S T R I A L A N D E L V G I N E E R I N G C H E M I S T R Y
482
carefully investigated a n d a t no time did we find a n increase in t h e percentage of t h e dry gluten due t o t h e increase in temperature. I n order t o test t h e effect of temperature on t h e washed glutens t h e y were allowed t o s t a n d twelve hours a t 2 5 ' C., having veen washed a t 15' C. T h e glutens had become very sticky a n d hard t o dry. T h e low grades all showed t h a t fermentation had started. T h e low grades showed a marked decrease while t h e high grades showed only a slight decrease. This was also t r u e of t h e dry glutens. Whatever agency causes t h e increase in weight, when t h e temperature of t h e wash water is higher t h a n ordinary, is within t h e flour itself a n d is not contained in t h e wet gluten. A higher percentage of gluten is obtained by washing i n hard water t h a n i n s o f t . Hardy' is of t h e opinion t h a t electrolytes or salts, which may be organic or inorganic, impress t h e property of tenacity a n d ductility on t h e gluten. Wood's2 researches also prove t h a t inorganic salts have a binding effect on gluten. All authorities agree t h a t gluten cannot be washed from flour with pure distilled water because t h e gluten will not hold together. At first i t forms a coherent mass b u t as soon a s t h e salts, natural t o t h e flour, are dissolved, t h e gluten scatters a n d cannot be collected again. If it be submerged in h a r d water when it first s t a r t s t o scatter it forms again a coherent mass. There was a n increase of I t o 2 per cent in wet gluten for all grades when t h e glutens were washed in very hard water. There was only a slight change of a b o u t 0 . 2 5 per cent for t h e d r y gluten a t t h e most, showing t h a t t h e hard water usually increased the waterabsorbing capacity of t h e gluten. C 0N CLUS10 N S
It can readily be seen t h a t conditions may be so different in various laboratories t h a t t h e determinations of wet gluten are n o t comparable. E r e n for ordinary routine work, where comparative results alone are required, unless t h e utmost care is taken, t h e determination is unreliable. Since t h e percentage of d r y gluten is very slightly affected by these same conditions i t is more reliable. I-Thoroughness of mixing affects both t h e per cent of wet a n d dry gluten. 2-An excess of water used in making t h e doughs increases, a n d insufficient water decreases t h e per cent of wet gluten. The d r y gluten is t h e same. 3-The length of t i m e t h e dough is allowed t o stand increases t h e percentage of wet gluten up 50 eight hours. High patents, old flours a n d low grades are exceptions. T h e d r y gluten remains unaltered except in t h e low grade where some fermentation has t a k e n place. 4-Overwashing decreases t h e percentage of both t h e wet a n d dry gluten. 5-A larger per cent of wet gluten is obtained with warm wash water t h a n with cold. T h e d r y gluten is unaffected. 6-More wet gluten is obtained with "hard" wash 1 2
Supplement J o u r , 4 (1910), 5 2 ; Jour. Board of A g r t c . Jour. A g r i c . S c i e n c e , I (1907). 267.
Vol. 6, NO. 6
water t h a n with soft. The dry gluten is slightly increased by t h e hard water. FLOURTESTING LABORATORIES C o , LTD. MAPLELEAF MILLING PORTCOLBORNE. ONT.
XX-HEAT A N D
THE DETERMINATION OF THE ACETYL NUMBER OF OILS, FATS, ETC.' By EDWARD B HOLLAND Received January 13, 1914
Ih*TRODUCTIOX
T h e various hydroxy compounds t h a t occur in oils, f a t s a n d waxes form derivatives on heating with acetic anhydride, the acetyl radical displacing t h e hydrogen of the alcoholic hydroxyl groups. This property serves as t h e basis of analytical methods for t h e quantitative determination of these compounds. The proposed acetyl number indicates t h e milligrams of potassium hydroxide required for t h e saponification of t h e acetyl assimilated b y one gram of a n oil, f a t or wax on acetylation.2 On saponifying with alcoholic potash t h e acetyl is hydrolyzed t o acetic acid a n d combines with t h e alkali t o form potassium acetate. T h e results are expressed in terms of milligrams of potassium hydroxide t o conform with t h e general practice in f a t analysis. T h e compounds involved are mono- a n d dihydroxy acids a n d their glycerides, mono- a n d diglycerides a n d free alcohols. USE O F T H E TEST
I n t h e examination of oils a n d f a t s a determination of acetyl number is necessary, in most instances, for a thorough understanding of t h e n a t u r e a n d quality of t h e product. Some of t h e hydroxy compounds are natural a n d others are t h e result of hydrolysis or of oxidation. Glycerides of hydroxy acids are a natural constituent of certain oils a n d f a t s although t h e y d o not appear t o be very widely distributed in a n y considerable a m o u n t . Castor oil, composed largely of ricinolein, is a notable illustration. Hydroxy acids probably occur more frequently as t h e result of oxidation of unsaturated acids. Oleic acid has been shown repeatedly t o be comparatively u n stable. By t h e assimilation of oxygen a n d water i t may be converted into dihydroxystearic acid, a saturated compound. C1;HssCOOH H20 0 = Ci?H33(OH)gCOOH. Whether t h e oxidation takes place in t h e glycerides or in t h e f a t t y acids afte'r hydrolysis is uncertain, although t h e l a t t e r appears t h e more probable supposition. 5lono- a n d diglycerides result from the hydrolysis of triglycerides a n d free f a t t y acids condition their presence. T h e absence of free f a t t y acids in a commercial product, however, does not necessarily preclude t h e presence of mono- a n d diglycerides. Solid alcohols of t h e cyclic series (sterols) occur in oils a n d f a t s both in combination as esters a n d a s free
+
+
1 The writer is pleased t o acknowledge many suggestions and helpful criticisms by Dr. J S Chamberlain, Mr. F. W. Morse, Mr J. C Reed, and Mr. J. P. Buckley. 2 Benedikt and Ulzer and Lewkowitsch report on the basis of the acetylated product.
