Nutritional Bioavailability of Zinc - American Chemical Society

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G. S. RANHOTRA and J. A. GELROTH American Institute of Baking, Nutrition Research, Manhattan, KS 66502

Under the current dietary practices, the intake levels of phytate, fiber, plant proteins, etc., which may possibly i n h i b i t zinc absorption, are not a source of undue concern for the majority of the population. However, as our awareness of the concepts of nutrient economics and nutrient density, and of matters of health as they might relate to foods of plant origin increases, more of the zinc i n our diet could originate from cereal-based and other plant foods. Consequently, the t o t a l and b i o available zinc content of our diet may become compromised. This may have serious health implications especially when a steady decline i n our c a l o r i c intake i s being witnessed. Health measures encompassing f o r t i f i c a t i o n of foods with zinc, the processing of foods to control the levels of suspected inhibitors of zinc absorption, and long-term studies to examine the effect of "adaptation" (to changed dietary regimens) are some of the areas which demand our immediate attention. Zinc deficiency i n man was f i r s t recognized i n the early I960 s (1). Since that time, research concerning the role of zinc in health and disease has been intense. Evidence that a sizable segment of the U.S. population may be deficient i n zinc, at least marginally (2), has contributed to the interest i n zinc research. Although the major sources of zinc i n the diet are foods of animal o r i g i n , p a r t i c u l a r l y meats, shellfishes and cheese (3,b), cereal-based foods also make important contributions. 1

Cereal-Based Food Products Zinc content. Table I l i s t s the zinc content of some cereal-based food products 03*4·). Substantial zinc loss occurs during refinement of cereal grains, e . g . , m i l l i n g of wheat to produce white flour. Therefore, products which are less refined or which contain the bran 0097-6156/83/0210-0185$06.00/0 © 1983 American Chemical Society Inglett; Nutritional Bioavailability of Zinc ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

186

NUTRITIONAL

BIOAVAILABILITY

OF

and germ f r a c t i o n s of grains are p a r t i c u l a r l y good sources zinc. Table I. Zinc content of some cereal-based Product Cake, white Sweet corn, b o i l e d Hamburger r o l l White bread Oatmeal bread Graham crackers Oatmeal cookies Cake, chocolate White r i c e , dry Brown r i c e , dry Macaroni, dry wholewheat bread Breakfast c e r e a l s shredded wheat bran f l a k e s , 40% germ, toasted a

Murphy et a l . (3) and Freeland Cousins (4)

foods

ZINC

of

a

mg/100 g 0.2 0.4 0.6 0.6 1.0 1.1 1.3 1.3 1.3 1.8 1.8 1.8 2.8 3.6 15.4 and

Zinc f o r t i f i c a t i o n . The current c e r e a l f o r t i f i c a t i o n (enrichment) p r a c t i c e r e stores some of the n u t r i e n t s (zinc not included) l o s t during m i l l i n g . In 1974, however, the Food and N u t r i t i o n Board (5) proposed an expansion of the current program to i n c l u d e a t o t a l of 10 micron u t r i e n t s (zinc i n c l u d e d ) . The proposed l e v e l of z i n c (Table II) would almost completely r e s t o r e z i n c to the l e v e l present i n whole grains. Although great changes i n d i e t a r y h a b i t s are c u r r e n t l y being witnessed, r e f i n e d products are l i k e l y to remain the mainstay of our d i e t . This and the f a c t that our c a l o r i c intake has been dec l i n i n g i n recent years, n e c e s s i t a t e s that the d i e t a r y adequacy of c e r t a i n n u t r i t i o n a l l y c r i t i c a l n u t r i e n t s such as z i n c be ensured. F o r t i f i c a t i o n provides a mean to accomplish t h i s . Zinc f o r t i f i c a t i o n sources. Should the n u t r i t i o n a l and other c o n s i d e r a t i o n s permit f o r t i f i c a t i o n , a number of z i n c sources can be used to f o r t i f y g r a i n products. These sources, u n l i k e p o t e n t i a l i r o n sources, appear not to d i f f e r a p p r e c i a b l y i n t h e i r r e l a t i v e b i o l o g i c a l v a l u e ( 6 ) . This was observed i n r a t s fed submarginal (9.5 ppm) z i n c d i e t s (Table I I I ) . Femur z i n c content was used to assess b i o l o g i c a l values (BVs). I n d i r e c t l y , t h i s means that product c o m p a t i b i l i t y and cost are l i k e l v to be more important than n u t r i t i o n a l c o n s i d e r a t i o n s i n choosing the z i n c source to be used i n c e r e a l f o r t i f i c a t i o n .

Inglett; Nutritional Bioavailability of Zinc ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

13.

RANHOTRA AND GELROTH

Zinc Bioavailability from Cereal Foods 3

Table I I . Expanded c e r e a l f o r t i f i c a t i o n p r o g r a m '

b

Fortification(enrichment) Current Expanded(1974) (mg/100 g) (mg/100 g) Vitamin A (ret.eq.) 0.29 Thiamin 0.64 0.64 Riboflavin 0.40 0.40 Niacin 5.29 5.29 Vitamin B-6 0.44 Folic acid 0.07 Iron 2 .86-3.63 8.81 Calcium 211 ( o p t i o n a l ) 198.20 Magnesium 44.04 -Zinc 2.20 Food and N u t r i t i o n Board (5) b Wheat f l o u r , corn g r i t s , corn meal and r i c e L e v e l proposed (FDA) i n 1981: 4.41 mg/ 100 g ( l e v e l proposed i n 1974 was disallowed) c

a

c

Zinc B i o a v a i l a b i l i t y D i e t a r y adequacy of z i n c i s s t r o n g l y l i n k e d to z i n c b i o a v a i l a b i l i t y , p a r t i c u l a r l y i n foods r e p r e s e n t i n g the bread and cer e a l group. Cereal products c u r r e n t l y provide about o n e - f i f t h of our energy need ( 7 ) . Various d i e t a r y g u i d e l i n e s proposed i n recent years t o improve h e a l t h have recommended that we i n c r e a s e our consumption of c e r e a l foods to i n c l u d e more complex carbohydrates i n the d i e t . These and other c o n s i d e r a t i o n s have l e d to an impressive increase i n our consumption of some g r a i n products such as v a r i e t y breads ( 8 ) . This means more and more of the z i n c i n our d i e t o r i g i n a t e s from foods which a l s o c o n t a i n n a t u r a l l y o c c u r r i n g or added components suspected to i n h i b i t the a b s o r p t i o n of z i n c . The components most widely i n v e s t i g a t e d and which w i l l be discussed i n clude (a) phytates, (b) f i b e r , (c) p r o t e i n and (d) c e r t a i n micron u t r i e n t s . Other f a c t o r s (Table IV) are a l s o important but w i l l not be discussed. E f f e c t of phytates. A number of s t u d i e s have shown that z i n c , as compared to other m i n e r a l s , i s p o o r l y u t i l i z e d from p h y t a t e - c o n t a i n i n g foods. The r e l a t i v e BV of z i n c i n a number of p h y t a t e - c o n t a i n i n g foods was r e c e n t l y examined by Franz et_ a l ( 9 ) . Each product was prepared as f o r human consumption and incorporated i n t o a s e m i - p u r i f i e d d i e t f e d t o r a t s . Whole corn and brown r i c e had a low r e l a t i v e BV (0.58 or l e s s compared to 1.00 f o r z i n c i n z i n c s u l f a t e ) w h i l e wholewheat f l o u r and unleavened wholewheat bread had medium values (0.63-0.74). Refined c e r e a l products such as white f l o u r , leavened and unleavened white bread and white r i c e ( a l l low i n phytate) had high r e l a t i v e BV (0.89-1.08) as d i d leavened wholewheat bread


187


44.7 9.5 154+12 29.6+3.5 766+36 89+3 87

36.1 9.5 140+24 34.2+2.8 730+43 87+4 100

11.2 9.5 144+20 35.0+2.9 751+57 89+2 102

Source ( d i e t ) Stéarate Sulfate

79.5 9.5 165+19 34.4+4.1 775+58 87+4 101

Oxide

30.0 9.5 144+18 35.8+3.4 729+58 87+5 105

Acetate

Table IV. F a c t o r s a f f e c t i n g the b i o a v a i l a b i l i t y of z i n c i n food

Ranhotra et a l . (6) R e l a t i v e ( z i n c i n z i n c s u l f a t e = 100%) b i o l o g i c a l v a l u e based on femur z i n c .

53.8 9.5 167+18 31.8+2.5 694+92 76+5 93

Chloride

100.0 9.5 161+11 33.0+2.6 698+97 88+4 95

Elemental

1

-Form and chemical nature of z i n c - D i e t a r y i n t e r a c t i o n s ( z i n c v s . p r o t e i n , l i p i d s , carbohydrates such as f i b e r , other m i n e r a l s , v i t a m i n s and c h e l a t o r s such as phytates) -Food processing c o n d i t i o n s (leavening, e t c . ) - D i g e s t i b i l i t y of food -Body s need f o r z i n c / e f f e c t of " a d a p t a t i o n " -Health status of the i n d i v i d u a l -Intestinal microflora - E f f e c t of age, sex, m e d i c a t i o n , e t c . -Environmental and other f a c t o r s

a

b

Zinc content source (%) d i e t (ppm) Serum z i n c (μ%/ά1) Femur z i n c (pg) Zinc intake (ug) Zinc absorbed (%) RBV of z i n c

Carbonate

Table I I I . B i o a v a i l a b i l i t y of z i n c i n p o t e n t i a l f o r t i f i c a t i o n sources

13.

RANHOTRA AND


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( 1 . 0 4 ) . The authors conclude that r e l a t i v e BV appeared to be i n v e r s e l y r e l a t e d to phytate contents of the foods. Another study ( 1 0 ) tested cookies made with egg albumin with phytate added or not. The a d d i t i o n of phytate (Table V) s i g n i f i c a n t l y reduced the b i o a v a i l a b i l i t y of zinc as determined based on the z i n c content of femur (Table V I ) . The reduced BV was comparable to BVs obtained with cookies made with the soy p r o t e i n products. In these s t u d i e s , the l e v e l of p r o t e i n and z i n c i n a l l t e s t products was e q u a l i z e d . In the albumin-based cookies, however, the zinc o r i g i n a t e d almost e n t i r e l y from the added source (zinc c h l o r i d e ) , while i n the soybased cookies the added source made only a p a r t i a l c o n t r i b u t i o n . In these s t u d i e s , very l i t t l e phytate was hydrolyzed during the Table V. Cookie f o r m u l a Cookie A Β C

3

Cake f l o u r (g) Other i n g r e d i e n t s ( g ) P r o t e i n source* (g) egg albumin soy f l o u r (def.) soy concentrate soy i s o l a t e Zinc (mg) added (as chlo.) i n p r o t e i n source Phytate (mg) added (as Na s a l t ) i n p r o t e i n source Phyt. h y d r o l y z e d ( % )

100 58

D

Ε

100 58

100 58

100 58

33

-

-

50

-

-

3 9 . ,9

-

-

30. 9

100 58

3

c

a

D

c

33

4.49 0.07

100

2 .,20 2 .,36

4.49 0.07 1107

19.6

2 . 24 2 . 32

3 ., 4 0 1, . 1 6

-

66

1107 7,.3

1041 9,.8

448 659 18. 4

Ranhotra et a l . ( 1 0 ) Amount added provided 26 g p r o t e i n In cookie-making

cookie-making process (Table V ) . In cereal-based products where appreciable phytate h y d r o l y s i s occurs during p r o c e s s i n g , b i o a v a i l a b i l i t y of z i n c seems to improve. T h i s was observed i n a study ( 1 1 ) where breads, made with or without soy (Table V I I ) , contained added phytate. In these breads, phytate was almost completely hy drolyzed during processing. The breadmaking process a l s o s i g n i f i c a n t l y improved the apparent absorption of zinc (Table V I I ) . Rein hold et_ a l . ( 1 2 ) studied the a v a i l a b i l i t y of z i n c i n leavened and unleavened wholemeal wheaten breads and concluded that leavening (hydrolyzes phytate) markedly increased the b i o u t i l i z a t i o n of z i n c i n bread. Morris and E l l i s ( 1 3 ) examined the e f f e c t of d e p h y t i n i z ing wheat bran on z i n c u t i l i z a t i o n by r a t s and demonstrated that i t i s f e a s i b l e to g r e a t l y overcome the phytate e f f e c t through dep h y t i n i z a t i o n (Table V I I I ) . In humans, Sandstrom et a l . ( 1 4 ) r e ported r e d u c t i o n i n the a v a i l a b i l i t y of zinc added to wholemeal



b

c

D

3

3

9.5 185+11 105+10 57.6+4.9 1168+87 82+3 100

—

9.5 190+11 109+43 50.1+5.9 1242+64 65+6

9.5 189+11 174+26 55.7+6.5 1234+84 80+3 92.2

Phytate added^ Soy added (12%) Bread Ingredients Bread

Ranhotra e t a l . (11) F l o u r contained 2.2 mg added zinc/100 g; z i n c a d d i t i o n adjusted f o r z i n c i n soyAs sodium s a l t . Phytate added to provide 77 mg Ρ (phytate i n soy considered).

—

9.5 188+12 106+32 53.4+6.3 1168+64 61+9

No soy Ingredients

b

content.

Ε 9.0 165+12 86+13 32.4+4.1 3132+296 81+3 73

3

Table V I I . Tissue c o n c e n t r a t i o n and a b s o r p t i o n of z i n c i n r a t s f e d b r e a d >

D i e t a r y z i n c (ppm) Body weight gain (g) Serum z i n c (pg/dl) Femur z i n c fag) Z i n c i n t a k e (Mg) Z i n c absorbed (%) Phytate hydrolyzed (%)

D

a

Cookies (Table V) D Β C 9.0 9.0 9.0 165+9 166+14 160+9 100+11 87+15 90+14 33.4+3.0 34.2+2.7 33.6+2.9 3188+182 3204+258 2995+296 83+3 85+2 83+3 77 77 76

D i e t a r y z i n c (ppm) Body weight gain (g) Serum z i n c (pg/dl) Femur z i n c (pg) Z i n c i n t a k e fag) Zinc absorbed (%) RBV Ranhotra et a l . (10) R e l a t i v e ( z i n c i n cookie A=100%) b i o l o g i c a l value based on femur z i n c

A 9.0 163+10 98+14 45.5+2.8 3197+162 89+2 100

Table V I . Tissue c o n c e n t r a t i o n and a b s o r p t i o n of z i n c i n r a t s f e d c o o k i e s

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Zinc Bioavailability from Cereal Foods

bread compared w i t h white bread. But they a l s o found that the " a b s o l u t e " a b s o r p t i o n of z i n c n a t u r a l l y - o c c u r r i n g i n wholemeal bread i s high. This may a l s o be true f o r a l l g r a i n products which are good sources of z i n c , unless these products have " i n h i b i t o r y " (on z i n c absorption) i n f l u e n c e s too great to be overcome during d i g e s t i o n and/or absorption processes. Added and n a t u r a l l y - o c c u r r i n g phytates may a f f e c t z i n c absorp t i o n d i f f e r e n t l y although M o r r i s and E l l i s (13) report that phy t a t e i n wheat bran a f f e c t s z i n c u t i l i z a t i o n i n r a t s i n n e a r l y the same manner as does phytate added at a s i m i l a r phytate : z i n c molar r a t i o . One can a r r i v e at a s i m i l a r conclusion i n examining the data i n Table VI where cookie Β c o n t a i n i n g added phytate compared w e l l w i t h cookie C which contained n a t u r a l l y - o c c u r r i n g phytate. Phytate : z i n c molar r a t i o s i n food products can be used to estimate the r e l a t i v e r i s k of having an inadequate intake of z i n c . Oberleas and Harland (2) propose that a d a i l y phytate : z i n c molar r a t i o of 10 or l e s s i s acceptable i n p r o v i d i n g adequate z i n c and that d a i l y r a t i o s above 20 may jeopardize z i n c s t a t u s . E f f e c t of f i b e r . U n l i k e phytates, the e f f e c t of f i b e r on z i n c a b s o r p t i o n r e mains more u n c e r t a i n . The information r e c e n t l y compiled (Table IX) by Kelsay (15) underscores t h i s . The u n c e r t a i n t y may, i n p a r t , be a t t r i b u t e d to (a) d i f f e r e n c e s i n preexperimental d i e t a r y regimen of t e s t s u b j e c t s , (b) d i f f e r e n c e s i n the l e v e l of f i b e r i n t a k e , (c) d i f f e r e n c e s i n the type of f i b e r t e s t e d , (d) d i f f e r e n c e s i n the time span of the study ( e f f e c t of "adaptation"), and most c r i t i c a l l y (e) the experimental d i f f i c u l t i e s i n d i s a s s o c i a t i n g the e f f e c t of other suspected i n h i b i t o r s from e f f e c t due to f i b e r . Conceivably, the nature of the z i n c complex ( i n v o l v i n g f i b e r , phy t a t e , p r o t e i n , etc.) e x i s t e n t at the s i t e of z i n c absorption may be more c r i t i c a l than the mere l e v e l s of p o t e n t i a l i n h i b i t o r s . The e f f e c t of " a d a p t a t i o n " may be p a r t i c u l a r l y s i g n i f i c a n t . Anderson et_ a l . (16) studied the z i n c status of long-term vegetar i a n women who obtained 77% of the t o t a l d i e t a r y z i n c from p l a n t products. Three-day d i e t a r y records showed that these subjects consumed 9.2 + 2.5 mg z i n c and 30.9 + 11.0 g d i e t a r y f i b e r o r i g i n a t i n g from f i v e d i f f e r e n t food groups. Their z i n c status (serum z i n c ( p g / d l ) : 98.3 + 23.9; h a i r z i n c fag/g)i 187 + 44) appeared w i t h i n the normal range d e s p i t e t h e i r h i g h intake of l e s s r a p i d l y absorbed z i n c and t h e i r h i g h intake of t o t a l f i b e r and phytate. a

Table V I I I . Femur z i n c c o n c e n t r a t i o n i n r a t s Femur z i n c (ppm) D i e t a r y z i n c source 177+10 Zinc s u l f a t e 69+3 Raw wheat bran 136+6 Low-phytate bran M o r r i s and E l l i s (13). D i e t a r y z i n c : 12 ppm a

E f f e c t of p r o t e i n . Many e a r l i e r studies have shown that z i n c i s l e s s e f f i c i e n t l y


191


balance

et a l .

3

Kelsay (L5)

Kelsay et a l . (1979)

Kies et a l . (1979)

Papakyrikos (1979)

Guthrie and Robinson (1978) Drews e t a l . (1979)

Decreased as f i b e r i n t a k e i n c r e a s e d ; negative w i t h h i g h e s t l e v e l of f i b e r Negative w i t h f r u i t s and vegetables

Tendency of a l l sources to increase f e c a l zinc loss

Not s i g n i f i c a n t l y a f f e c t e d by bran S i g n i f i c a n t l y lowered by hemicellulose

F r u i t s and vegetables (24 g of n e u t r a l - d e t e r g e n t f i b e r ) f o r 26 days F r u i t s and vegetables (10, 18, S i g n i f i c a n t l y lower on 25 g of NDF than on low f i b e r d i e t or 25 g of NDF) f o r 21 days or on 10 g of NDF

Became negative w i t h wholemeal bread Became negative w i t h wholemeal bread Negative w i t h a d d i t i o n of cellulose Not s i g n i f i c a n t l y a f f e c t e d by bran

Zinc

Kelsay et a l . (1979)

source

Unleavened wholemeal bread (350 g/day f o r 32 days) Leavened wholemeal bread (60% of c a l o r i e s ) f o r 20 days C e l l u l o s e (10 g) i n apple compote f o r 20 days Soft white wheat bran (26 g) or corn bran (26 g) f o r 28-30 days Wheat bran (14 g) f o r four weeks Cellulose, hemicellulose or p e c t i n (14.2 g) f o r four days C e l l u l o s e , h e m i c e l l u l o s e or wheat bran (10 or 20 g) f o r seven days H e m i c e l l u l o s e (4.2, 14.2, or 24.4 g) f o r 14 days

Fiber

3

Reinhold et a l . (1973) Reinhold et a l . (1976) I s m a i l - B e i g i et a l . (1977) Sandstead et a l . (1978)

Investigator

Table IX. E f f e c t of f i b e r on z i n c b a l a n c e

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Zinc Bioavailability from Cereal Foods

193

absorbed i n animals fed p l a n t p r o t e i n r a t h e r than animal p r o t e i n (17). This may be a t t r i b u t a b l e to d i f f e r e n c e s i n the makeup of the two p r o t e i n s and/or to the e f f e c t due to a s s o c i a t e d components such as f i b e r and phytate. In s t u d i e s w i t h préadolescent g i r l s , P r i c e e£^ a l . (18) observed that the absorption of z i n c from mixed d i e t (plant and animal foods) was somewhat higher than that from p l a n t foods (Table X ) . The r e s u l t s may be somewhat confounded by the d i f f e r e n c e s i n d i e t a r y p r o t e i n l e v e l s . In a recent study, Sandstrom et^ a l . (14) showed a p o s i t i v e c o r r e l a t i o n between z i n c absorption and the p r o t e i n content i n meals c o n t a i n i n g m i l k , cheese, beef and egg i n v a r i o u s combinations w i t h wholemeal bread. In another study, Sandstrom eit a l . (19) compared the e f f e c t of hamburger, the bun and the combination of the two on changes i n p l a s ma z i n c i n human s u b j e c t s . They found that meat alone d i d not appear to i n h i b i t z i n c absorption but the bun (with or without meat) caused a r e d u c t i o n i n plasma z i n c response. The bun i s u s u a l l y q u i t e low i n f i b e r and phytate but contains about 10% p r o t e i n . E f f e c t of c e r t a i n m i c r o n u t r i e n t s . The e f f e c t of m i c r o n u t r i e n t s on z i n c u t i l i z a t i o n has r e c e i v e d l i t t l e a t t e n t i o n . Van Campen (20) demonstrated i n v i t r o that z i n c and copper are mutually a n t a g o n i s t i c during the absorptive process. Calcium a l s o aggrevates z i n c d e f i c i e n c y when added to d i e t s based on p l a n t products that might a l s o contain appreciable amount of phytate. For example, the r e l a t i v e BV of z i n c i n a l k a l i - t r e a t e d corn (calcium hydroxide) i s reported to be low compared to b o i l e d or raw corn ( 9 ) . When the d i e t i s f r e e of or low i n phytates, z i n c absorption i n humans consuming high or low calcium l e v e l s appears not to be a f f e c t e d (21). Solomons (22) r e p o r t s a s i g n i f i c a n t reduct i o n i n z i n c absorption i n humans i n the presence of nonheme ( i n organic) i r o n (Table X I ) ; heme i r o n seems to have no such e f f e c t . Duncan and Hurley (23) s t u d i e d the i n t e r a c t i o n between z i n c and v i t a m i n A i n pregnant and f e t a l r a t s and found that plasma v i t a m i n A i n both animals was s i g n i f i c a n t l y reduced by low i n t a k e s of e i ther z i n c or v i t a m i n A. Over the range of doses commonly consumed by man, a s c o r b i c a c i d was shown (24) to have no demonstratable e f f e c t , u n l i k e that on i r o n , on the absorption of i n o r g a n i c z i n c i n man. Table X. E f f e c t of p r o t e i n on z i n c absorption i n adolescent Dietary protein Amount Source (g/day) Plant 25 Plant 25 46 Mixed Mixed 46 a P r i c e et a l . (18)

Intake (mg) 4.83 4.53 6.93 6.83

Zinc F e c a l and urinary losses(mg) 4.29 3.72 4.94 5.09

Absorbed (%) 11.2 17.9 28.7 26.0


girls

a

194

NUTRITIONAL BIOAVAILABILITY OF ZINC Table X I . Zinc and i r o n (inorganic) i n t e r a c t i o n i n humans

Treatment a. b. c. d. a

25 mg Z n ^h a + 25 mg Fe* " a + 50 mg F e ^ a 4- 75 mg F e ^ 4

Fe : Zn ratio

1 hr

0 1:1 2:1 3:1

56+11 18+8 23+2 16+3

a

Plasma Zn Qug/dl) 4 hr 2 hr 3 hr 85+18 40+9 44+4 27+5

72+16 47+8 38+8 21+4

48+12 36+9 27+8 19+4

Solomons (22) R i s e above f a s t i n g plasma l e v e l s

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8.

9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

Prasad, A.S. "Zinc in Human Nutrition"; CRC Crit. Rev. Clin. Lab. S c i . : Boca Raton, FL., 1977; p. 891 Oberleas, D.; Harland, B.F. J. Am. Diet. Assoc. 1981, 79, 433 Murphy, E.W.; Willis, B.W.; Watt, B.K. J. Am. Diet. Assoc. 1975, 66, 345 Freeland, J.H.; Cousins, R.J. J. Am. Diet. Assoc. 1976, 68, 526 Food and Nutrition Board. "Proposed Fortification Policy for Cereal-Grain Products"; National Res. Council/National Acad. S c i . : Washington, DC, 1974; p. 2 Ranhotra, G.S.; Loewe, R . J . ; Puyat, L.V. Cereal Chem. 1977, 54, 496 Marston, R.M.; Peterkin, B.B. Natl. Food Rev. 1980, NFR-9, 21 Ranhotra, G.S.; Winterringer, G.L. "The Consumption Pattern of Variety Breads in the U.S. in Variety Breads in the United States (Miller, B. ed.); Am. Assoc. Cereal Chem.: St. Paul, 1981, p. 37 Franz, K.B. ; Kennedy, B.M.; Fellers, D.A. J. Nutr. 1980, 110, 2272 Ranhotra, G.S.; Lee, C.; Gelroth, J.A. Cereal Chem. 1979, 56, 552 Ranhotra, G.S.; Lee, C.; Gelroth, J.A. Nutr. Rep. I n t l . 1978, 18, 487 Reinhold, J.G.; Parsa, Α.; Karimian, N . ; Hammick, J.W.: Ismail -Beigi, F. J. Nutr. 1974, 104, 976 Morris, E.R.; Ellis, R. J. Nutr. 1980, 110, 2000 Sandstrom, B.B.; Arvidsson, Α.; Cederbald, Α.; Bjorn-Rasmussen, E. Am. J. Clin. Nutr. 1980, 33, 739 Kelsay, J.L. Cereal Chem. 1981, 58, 2 Anderson, B.M.; Gibson, R.S.; Sabry, J.H. Am. J. Clin. Nutr. 1981, 34, 1042 O'Dell, B.L. Am. J. Clin. Nutr. 1969, 22, 1315 Price, N.O.; Bunce, G.E.; Engel, R.W. Am. J. Clin. Nutr. 1970, 23, 258


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GELROTH


19. Sandstrom, B.; Arvidsson, Α.; Bjorn-Rasmussen, E . ; Cederbald, A. "Zinc Absorption from Bread Meals in Trace Elements Metabo lism in Man and Animals (Kirchgessner, M. ed.) III." Proc. Third Intl. Sym. Arpeitskeirs Fuhr Tierernahrungs Forschung: Weihenstephan, 1978; p. 129 20. Van Campen, D.R. J. Nutr. 1970, 97, 104 21. Spencer, H.; Vankinscott, V . ; Lavin, I . ; Samachon, J. J. Nutr. 1965, 86, 169 22. Solomons, N.W.J. Am. Diet. Assoc. 1982, 80, 115 23. Duncan, R . J . ; Hurley, L.S. J. Nutr. 1978, 108, 1431 24. Solomons, N.W.; Jacob, R.A.; Pineda, O.; V i t e r i , F.E. Am. J. Clin, Nutr. 1979, 32, 2495 RECEIVED October 5,1982


Nutritional Bioavailability of Zinc - American Chemical Society

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