32 EFFECT OF FOOD PROCESSING AND PREPARATION ON MINERAL UTILIZATION

Phyllis E. Johnson USDA, ARS, Grand Forka Human Nutrition Research Center PO Box 7166, University Station, Grand Forks, NO 58202

ABSTRACT While effects of various nutrients and certain non-nutrient components of food on mineral utilization have been intensively studied, less. is known about the effects of food processing and preparation procedures. Fermentation during the production of beer, wine, yogurt, and African tribal foods affects bioavailability of Zn and Fe. Baking affects the chemical form of Fe in fortified bread products and these changes can affect its bioavailabillty. Availability of Fe in milk-based infant formula depends on whether Fe is added before or after heat processing. Food packaging (e.g., tin cans) can alter food composition and thus potentially affects mineral bioavailability. Maillard browning has been reported to cause slight decreases in Zn availability both in vitro and in humans. However, we found that feeding of highly browned casein-glucose products to rats as 5% of diet produced no effect on Zn absorption (59.5 ± 8.2% vs 54.1 ±7.3%) or Fe absorption (45.6 ± 7.7% vs 46.9 ± 12.6%) for brownedvs control, respectively; nor did we find any of the adverse health effects reported by others. Ve found no effect on stable Zn or Cu absorption in seven men when browned foods were fed, compared to the same diets without browning. Zinc absorption was 34 ± 13% (browned) vs 24 ± 15% (unbrowned), and Cu absorption was 55 ± 5% vs 55 ± 8% (p>O.05). INTRODUCTION Many factors relating to food composition l\ave been intensively studied with regards to their effects on mineral absorption and utilization. For the most part, the factors that have received the most attention are variables in food composition, whether they are nutrients or non-nutrients such as phytates, fiber, tannins, etc. Food processing and preparation can also have marked effects on the composition or nature of a food, yet the effects of these processes on mineral bioavai1ability have been studied to a much lesser extent. Indeed, one review of the effects of food production and processing methods on nutritive value of foods did not even mention effects on mineral content or bioavailabillty (Hollingsworth & Martin, 1972) • Processes such as fermentation, heat processing, and extrusion, contamination from packaging, or formation of Maillard products during cooking all have the potential of affecting mineral utilization. This paper will briefly review the effects of some

M. Friedman (ed.), Nutritional and Toxicological Consequences of Food Processing © Springer Science+Business Media New York 1991

483

of these processes on mineral bioava11abillty from food and will also present some original data from ~ laboratory concerning the effects of Maillard products on Zn, Cu, and Fe absorption in animals and humans. FERMENTATION Fermentation occurs during the production of alcoholic beverages, of yogurt and similar foods, and during the leavening of bread by yeast. Although the specific chemical transformations occurring during production of these foods differ, all seem to result in effects on the availability of minerals. When bread is leavened with yeast, the phytate content may be decreased as much as 60 to 80X (Nlvert et al., 1985). Reduction of the phytate content by leavening resulted in increased Zn absorption (Nlvert et al., 1985). Fermentation of sorghum during preparation of sceds, an African tribal food, resulted in higher '5Zn absorption by rats than from unfermented sorghum foods (Stuart et al., 1987). Fermentation of the sorghum to produce aceds also resulted in a reduction of the phytate content by approximately one-third, compared to non-fermented sorghum foods. There was no effect of fermentation of sorghum on absorption of Fe by rats in the same experiment. Fermentation of pearl millet, another staple food in Asia and Africa, improved extractability of Ca, Zn, Fe, Mn, and Cu (Mahajan & Chauhan, 1988), and presumably improved availability of these minerals. Fermentation of milk to produce yogurt affects the bioavailability of different minerals to varying degrees. Calcium is absorbed equally well from m11k and yogurt (Smith et aI., 1985; Schaafsma et aI., 1988). However, the apparent absorption ([intake - fecal excretion]/intake) of phosphorus by rats was higher from yogurt than from m11k or lactase-treated milk (Schaafsma et al., 1988); apparent absorption of Kg and Fe was less from yogurt than from milk, and apparent of absorption of Zn was the same from yogurt and milk. Although the differences between yogurt and milk in their effects on Fe and Kg availability were statistically significant, they were very small and may not be biologically important. In rats fed high phytate diets, growth and food efficiency were greater when either yogurt or inactivated yogurt were added to the diet; bone, plasma, and tissue levels of Zn were not increased by dietary yogurt, however (Toleman, 1987). Fermentation of soybean meal by lactic acid-producing bacteria or by

RhLzopus 01 Lgosporus in tempeh fermentation significantly increased

bioavailability of Zn to rats (Moeljopawiro et al., 1988). Both destruction of phytate and production of Zn-binding ligands during fermentation were suggested as the reason for the increased Zn availabillty. Beer made in South Africa from maize and sorghum undergoes two sequential fermentations. The first is a lactic acid fermentation; this is followed by the alcoholic fermentation (Derman et al., 1980). Iron absorption from beer prepared by this process was more than twelve-fold greater than from a gruel made from the ingredients used to prepare the beer (Derman et al., 1980). Three factors were responsible for the enhanced Fe absorption; these were removal of solids during fermentation and the presence of ethanol and lactic acid in the beer. Wine contains various kinds of organic Fe(II) complexes, and wine has often been said to have a hematopoeic effect. Tabata & Tanaka (1986) studied the Fe complexes produced in wine when grape juice was fermented 484

by Saaaccharomyces cerevlslae. They found that Fe absorption and incorporation into hemoglobin were higher in rats given wine than in rats given FeC1 3 or FeS04' LIQUID MILK PRODUCTS Heat processing of milk-based products or milk substitutes during sterilization and canning can significantly affect the chemical form of Fe in the product and its bioavailability. This is of particular interest in the production of infant formulas, which are normally fortified with Fe. Theuer et al. (1973) found that heat sterilization of milk-based infant formulas containing ferric pyrophosphate and sodium iron pyrophosphate increased Fe availability substantially. Heat processing of soy isolatebased infant formulas increased the bioavailability of Fe from ferric pyrophosphate and sodium pyrophosphate two- to four-fold, but did not increase bioavailability from ferrous sulphate (Theuer et a1., 1971). When cow's milk was fortified with a citrate phosphate iron complex before pasteurization, bioavailability of the Fe to rats was unaffected (Ranhotra et al., 1981). When slurried chick diets were processed with heat and pressure, bioavailability of Fe from sodium ferric pyrophosphate and ferric pyrophosphate was increased, but processing did not change the bioavailability from ferrous sulfate or ferric orthophosphate (Wood et a1. , 1978). Clemens and Mercurio (1981) found that retort processing of liquid milk-based products significantly. increased the bioavailability of carbonyl Fe and electrolytic Fe, but not ferric orthophosphate. The improvement in bioavailability was related to oxidation and solubilization of the elemental Fe. Differences in heat treatment of infant formula (spraydried, UHT [ultra-high temperature), or sterilized) did not affect Ca absorption in infant monkeys (Rudloff & LOnnerdal, 1990) or rats (Weeks & King, 1985). Changes in the form of Fe can also occur during storage of liquid milk-based products. Iron added to liquid formulas marketed for weight control as ferric orthophosphate is largely insoluble and suspended rather than dissolved at the time of addition (Hodson, 1970). Hodson found that after two to five months of storage, all or most of the ferric Fe was converted to more soluble ferrous Fe, which is presumably more available for absorption (Hodson, 1970). In contrast, Clemens (l98l) found that none of the Fe from ferric orthophosphate in a liquid milk-based product was soluble after 6 or 12 months, and the relative biological value of this Fe was low. There were no changes in the solubility or valency of Fe added to a liquid milk-based product between between 6 and 12 months of storage (Clemens, 1981). Evidently, most of the change in bioavailability of elemental Fe added to liquid milk-based products takes place during the thermal processing and during the first six months of storage. It is clear that measuring the bioavailability of Fe from the salt used for food fortification is not enough to determine the bioavailability of a mineral in the food to which it is added. Changes in bioavailability depend on both the chemical form of the added fortification Fe and on the type of processing. Storage after processing may also affect Fe bioavailability. HEAT PROCESSING OR COOKING OF OTHER FOODS Many non-liquid foods are processed by methods that also involve heat. These include processes such as extrusion, puffing, or flaking. Carlson and Miller (1983) studied the effects of processing on the dialyzable Fe in various breakfast cereals. The dialyzable Fe in several Fe-fortified wheat and corn cereals ranked as puffed> extruded> flaked. Differences in the conditions of heat treatments such as time, temperature, 485

moisture, and the final degree of browning may influence Fe availability. Maillard browning products have not been found to have much effect on Fe availability in J.n vJ.vo studies (see below). However, processing conditions may also affect the relative amounts of ferrous and ferric Fe in the products and thus alter Fe availability. Extrusion processing did not affect Zn bioavailability from egg white- or soy-based diets fed to rats (Hess et aI., 1984). Although total Fe concentration decreased slightly, Fe diffusibility J.n vJ.tro increased during the manufacture of a maize-based snack food, from 2.3% (whole maize) to 5.0% (maize grits) to 14.7% (pre-extrusion mix) to 18.4% (extruded mix) to 21.8% (final product) (Hazell &Johnson, 1989). In vJ.vo studies showed no significant influence of extrusion processing on Fe availability in rats (Fairweather-Tait et al., 1987) or humans (Kivisto et al., 1986). Heat treatment of egg white did not affect J.n vJ.tro Fe bioavailability until the heating was sufficient to cause pronounced Maillard browning (Leahey & Thompson, 1989). Various food preparation procedures that involve heat can affect mineral bioavailabil1ty in ways other than the formation of Maillard products, which will be discussed later. When enriched flour is used to prepare baked goods, a marked effect of the baking process is the formation of insoluble forms of Fe (Lee & Clydesdale, 1980). Bioavailability of Fe is generally lower from poorly soluble forms of Fe than from soluble forms (PIa et al., 1976) so that these changes in the solubility of Fe after cooking might reduce the bioavailability of the Fe in the food. However, in vJ.tro estimation of Fe availability in breads fortified with various forms of Fe showed no effect of baking on Fe bioavailability (Schricker & Miller, 1982). Baking did not affect bioavailability of the endogenous Fe in wheat bran muffins (Buchowski et al., 1988). Frying of a soy-hamburger patty resulted in marked reductions in the percent soluble Fe at simulated intestinal pH values (Rizk & Clydesdale, 1985). In contrast, compared to raw beef, boiling or baking of beef did not result in any change in Fe bioavailability to rats (Jansuittivechakul et al., 1985). Copper in cooked beef is more available for absorption than Cu in raw beef (Moore et al., 1964). Food cooked in iron utensils contains more Fe than food cooked in non-iron utensils. Cooking in iron utensils can more than double the amount of Fe in foods (Burroughs & Chan, 1972; Brittin & Nosseman, 1986: Mistry et al., 1988). The amount of increase in Fe depends on the type of food (Mistry et al., 1988) and the amount of prior use of the iron utensil (Brittin & Nossaman, 1986). Both in vivo studies in rats (Martinez & Vannucchi, 1986) and in vJ.tro studies (Mistry et al., 1988) showed that Fe added to food by cooking in an iron pot was as available as native food Fe. EFFECT OF CURING AND COOKING OF MEAT ON FE BIOAVAILABILITY Although bioavailability to ratA of Fe in meat was not changed by boiling or baking (Jansuittivechakul et al., 1985), rats do not discriminate between heme and non-heme Fe as humans do. There is evidence that both cooking and curing of meat affect the proportion of heme and nonheme Fe in the meat. Because heme Fe is more available for absorption by humans than is non-heme Fe (Monsen et al., 1978), these changes may affect the bioavailability of Fe from meat. Slow heating of muscle extracts resulted in the release of more non-heme Fe than did fast heating (Chen et al., 1984), but nitrite stabilized the heme Fe and prevented the increase in non-heme Fe levels. Both baking and microwave cooking increased nonheme Fe in ground beef, and a linear relationship was observed between nonheme Fe in meat and the time of exposure to heat treatment (Schricker & Hiller, 1983). Changes in the amount of heme Fe were felt to be large 486

enough to cause significant changes in absorbable Fe in the meat. Again, nitrite appeared to protect against heat-induced changes in non-heme Fe. In the same study (Schricker & Miller, 1983), ascorbic acid was found to significantly increase non-heme Fe levels in ground beef even when heating was mild. Another study, however, showed only a very small decrease in hemoglobin Fe (not total Fe) absorption with cooking; hemoglobin Fe absorption by three human subjects was l5.7X from uncooked hemoglobin and l4.4X from cooked hemoglobin (Turnbull et al., 1962). Heme Fe levels in sausages were unchanged after curing with sodium nitrite or sodium erythorbate (Lee & Shimaoka, 1984). More of the non-heme Fe was in an ionic form in erythorbate-cured sausage than in sausage cured with nitrite. More of the Fe in the erythorbate-cured sausage was in a soluble ferrous form. There were no changes in vacuum-packed meats after 14 days at SoC, but ferrous Fe was depleted when sausages were exposed to air at 5°. Atmospheric oxidation of beef decreased Fe bioavailability to rats (Mahoney et al., 1979). GERMINATION The consumption of bean sprouts, alfalfa sprouts, and other sprouted seeds has become more prevalent in recent years. Germinstion of pea seeds increased the bioavailability of Zn to rats (Beal et al., 1984); the increased Zn bioavailability was attributed to a twelve-fold increase in phytase enzyme content which resulted from germinstion and a concomitant reduction in phytate content of the geminsted peas. Germinstion of peas reduced phytate to a much greater extent (75X) than did cooking (25X); 1015% of Zn in peas was lost to cooking water (Beal & Mehta, 1985). PROCESSING OF SOY PRODUCTS Conditions involved in the processing of soy protein have been thought to be partially accountable for the poor bioavailability of minerals froll soy protein products. Rackis (1979) suggested that Zn bioavailability in isoelectric (acid-precipitated) soy isolates is high, while isolates processed with alkaH exhibit low Zn bioavaUabUity. Erdman et al. (1980) found poorer growth in rats fed neutral soy than rats fed acid soy, but there was no significant difference in tibia Zn or Mg between rats fed acid or neutral soy. In a subsequsnt study based on measurement of 6'Zn retention, bioavailability of Zn was significantly higher from acid-precipitated soy products than from neutralized products (Ketelsen et al., 1984). The bioavailability of Fe was also found to be affected by the form of soy product in the diet (Picciano et al., 1984). Rats were able to discriminate among soy products, and Fe bioavailability was ranked as soy concentrate> soy flour> soy beverage, although all three products were considered good plant sources of Fe. Thompson & Erdman (1988) found that when various radiolabeled test meals were fed in either acid or neutralized fOrll to rats, neutralization of soy protein isolate, but not of casein, resulted in less retention of 5'Fe from the meal. However, the difference between the acid and neutralized soy products was not present after the products were subjected to heat treatment. In addition to pH and heat treatment, other differences among soy products may also have an effect on Fe bioavailability. Thompson & Erdaan (1988) also compared 59Fe retention from casein test meals in rats fed diets based on soy flour, acidprecipitated soy concentrate, ethanol-washed soy concentrate, water-washed soy concentrate, tofu analogue concentrate, or soy protein isolate. For two of the soy products, the acid precipitsted concentrate and the ethanol487

washed concentrate, there was no significant depression in 5'Fe retention relative to casein. They suggested that the lack of effect by the ethanolwashed product might have been caused by removal of some non-protein factors during ethanol extraction. Differences in bioavailability from various soy products are probably unimportant in a practical sense if the soy products make up a small portion of the total diet. On the other hand, if soy products comprise a major portion of the diet, as infant formula or as meat substitutes or extenders, for example, processing technology may have an impact on the nutritional quality of the diet. FOOD PACKAGING Composition of food may be affected by its packaging. Migration of nutrients or other substances into or out of food can result in changes in food composition that have the potential of affecting mineral utilization from the food. Elkins (1979) found that the canning process may cause loss of minerals from green beans to blanching water and canning brine. After 12 months of storage, however, beans showed a 131% increase in Fe, a 94% increase in Zn, and a 25% decrease in Cu. Peaches also decreased in Cu content during storage. Henriksen et a1. (1985) found significant changes in trace element content of canned tomatoes and green beans, but not peaches, during storage. Changes ranged from a 14% increase in Zn content to a 630% increase in Fe in tomatoes and from a 307% increase in Mg to a 555% increase in Cu in green beans. Schmitt and Weaver (1982) also found losses of Zn and Cr from kale and bush beans after canning or blanching and freezing. Canning, but not blanching, reduced Mg in peas by 18%; Fe and Ca were not affected by either process (Lee et al., 1982). Storage of food in tin cans, especially storage after opening the can, was found to increase concentrations of Sn and Fe in foods (Greger & Baier, 1981). Storage or canning of foods in glass does not affect trace element content (Greger & Baier, 1981; Theriault & Fellers, 1942). Tin has been reported to decrease Zn retention significantly (Johnson et aI., 1982). Food Fe which originates from tin cans is soluble and seems to be nearly 100% available for absorption (Theriault & Fellers, 1942). Because trace element interactions can affect bioavailabi1ity, changes in mineral content of foods may affect bioavailability of minerals in addition to those whose concentrations are changed. MAILLARD BROWNING It is well known that Maillard browning can affect the protein quality of foods (Dworschlk, 1980). The effect of Maillard products on mineral nutrition is unclear. Copper can form complexes with Maillard products (Petit, 1956). On the other hand, Rendleman (1987) found that me1anoidins In model systema, toasted bread, or coffee did not bind Ca; toasted bread and coffee did bind Ca, but binding was to various organic acids in these foods. Maillard products in heat-sterilized solutions for parenteral nutrition were found to increase urinary excretion of Zn, Cu, and Fe when administered intravenously, but not when administered nasogastrically (Freeman et aI., 1975; Stegink et aI., 1981). This stimulated research into the effects of Maillard products on mineral availability from foods. In my laboratory, we found that corn flakes (browned) bound more Cu and less Fe than did corn grits (unbrowned) (Johnson et aI., 1983). Camire and Clydesdale (1981) also found an effect of toasting on binding of Zn, 488

Kg, and ferrous Fe by wheat bran. We found that adult men fed a single meal containing either corn grits or corn flakes at breakfast absorbed significantly less Zn from corn flakes than from corn grits (corn grits, 48%; cornflakes, 36%) (Lykken et al., 1986). When subjects were fed diets with cornflakes or corn grits for 42 days, there were no significant differences in absorption of Fe, Zn, or Cu measured with stable isotopes (Johnson, 1983), suggesting that perhaps some adaptation to the diets occurred. Subjects fed the corn flakes diet excreted higher molecular weight Zn-binding substances in urine, whUe low molecular weight Znbinding substances predominated in urine of subjects fed corn grits (Johnson et al., 1983). In a subsequent study, we fed "browned" and "unbrowned" diets to adult men for four months in a crossover design. The "browned" diets contained cookies, crackers and quick breads cooked in a conventional oven, toasted bread, meats browned with flour, tortillas, and browned spaghetti. The unbrowned diets contained the same foods, but foods were untoasted and bread was served without crust. Foods were prepared with moist heat processes or in a microwave oven to minimize browning. Zinc and Cu absorption were measured by giving oral doses of the stable isotopes 67Zn and 6SCu. Neither Cu nor Zn absorption was significantly affected by the dietary treatment in this study, but mean Zn absorption was about one-third higher when browned diets were fed (Table 1) (PE Johnson, unpublished data). Table 1. Absorption of Zinc and Copper from Browned and Unbrowned Diets by Adult Ken Vol. I

% Zn Absorption Unbrowned Browned

% Cu Absorption Browned Unbrowned

2104 2109 2110 2118 2119

49.2 35.8 9.3 40.4 24.0

43.0 11.8 39.2 20.2 5.5

58.5 49.5 47.5 63.1 52.5

63.5 55.0 65.5 43.9 44.4

2123

41.3

34.8

57.7

59.2

mean ± SD

34.1 13.3

23.9 14.9

54.8 5.4

55.4 8.5

2122

38.5

13.1

54.6

56.6

There were no significant differences between browned and unbrowned diets for either Zn or Cu absorption (p>O.05). Recent in vitro studies showed that Maillard browning products formed from amino acid/glucose solutions bind Zn and decrease apparent Zn availability compared to an unheated control (Whitelaw & Veave r, 1988). Toasting of corn meal also reduced apparent Zn availability compared to unbrowned corn meal (Whitelaw & Weaver, 1988), and the authors commented that the degree of Zn binding observed seemed to be related to the extent of browning. In contrast, we found that Zn binding seemed to depend not only on the degree of protein browning but also on the nature of the protein (PE Johnson and TC Lee, unpublished data). Browned proteins (casein, albumin, gluten) were prepared by mixing three parts protein with two parts glucose and adjusting the moisture to 15%. The samples were then stored for 0, 5, 489

10, 20, 30, or 40 days at 37° in a sealed glass chamber. Relative humidity was maintained at 681 in the chamber. At the end of the treatment, 5- and 10-day browned proteins were Ught tan, 20- and 30-day proteins were darker tan, and 40-day proteins were dark brown. Subsequent to removal from the chamber, samples were stored at -20°. Adsorption isotherms for Zn with each browned protein were determined by a published method (Sarazinni, 1983) and the apparent stability constants for Zn were calculated (Table 2). Apparent stability constants for Zn and Cu with browned albumin using modified gel filtration chromatography (Evans et al., 1979) gave the results in Table 3. When we fed browned casein/glucose products (browned 40 days by the above procedure) to rats as 51 of a protein-adequate diet containing 12 ppm Zn and 35 ppm Fe, we found no effect on Zn or Fe absorption compared to feeding unbrowned casein and glucose (PE Johnson, TC Lee, TL Starks, unpublished data) (Table 4). Hemoglobin, hematocrit, plasma, liver, and femur mineral concentrations were also unaffected by feeding the browned casein (Table 4). This is consistent with the data shown in Table 2, which indicate that Zn binding by 40-day browned casein is less than Zn binding by unbrowned casein. Furniss et al. (1989) fed casein-lactose Maillard reaction products to rats and found little effect except a slight increase in urinary Zn excretion compared to rats fed unheated casein-lactose mixtures. Increasing the degree of browning increased the amount of urinary Zn excretion. Free fructose-lysine had no effect on urinary Zn excretion. In contrast, O'Brien et al. (1989) fed Maillard reaction products prepared Table 2. Apparent Stability Constants for Zn and Browned Casein and Gluten Days Browned

o

1.40 ± 0.29

10 20 30 40

1.14 ± 0.11 0.78 ± 0.31 0.46 ± 0.05 0.48 ± 0.11

5

Table 3. Days Browned 0 10 20 30 40

K

Casein

x

10-~

Gluten 1.10 0.93 2.86 3.03 1.53

± ± ± ±

0.14 0.18 1.06 1. 73

Binding of Zn and Cu by Browned Albumin

Zinc Atoms Zn/mole alb 4.3 5.7 4.5 5.8 4.2

log 8n

Copper Atoms Cu/mole alb

3.74 3.62 4.69 4.17 3.77

0.62 2.62 1.82 1.88 1.54

log

8n

4.18 3.12 3.19 3.21 3.15

from glucose and monosodium glutamate to rats and found increases in urinary excretion of Ca, Mg, Zn, and Cu. Retention of Zn, but not Ca, Mg, Fe, or Cu, was significantly less (62% vs 41%) in rats fed Maillard 490

reaction products than in control rats. In a similar study, rats fed fructose-tryptophan reflux products absorbed slightly, but significantly less, 5'Fe than rats fed diets with free fructose and tryptophan (Mahalko et a1., 1984). It seema that in vivo effects of Maillard products prepared from whole proteins on mineral bioavailability are minimal or non-existent. Thus, the nutritional impact of Maillard products on mineral availability from real diets is minimal. In situations where individual amino acids -y react to form Maillard products, as in parenteral nutrition solutions heated after amino acids and sugar are mixed, Maillard products may increase urinary losses of minerals. Table 4. Effect of 5% Casein-Glucose Maillard Product in the Diet on Zinc and Iron Absorption in Rats Control

Maillard

Diet % "Zn Absorption % "Fe Absorption Femur Fe ("gig) Femur Zn (lIglg) Liver Zn ("gig) Liver Fe ("gig) Hemoglobin (gldL)

59.5 45.6 99.3 253 68.3 289 15.2

± 8.2 ± 7.7

± 20.4

± 21 ± 5.7 ± 68

± 1.1

54.1 46.9 106.3 263 72.2 279 15.4

± 7.3 ± 12.6

± 16.5

± ± ± ±

14 7.8 59 1.2

FOOD ADDITIVES A variety of chemicals are added to foods during processing for several purposes: to _intain or improve nutritional value, to msintain freshness, to help in processing or preparation, and to make food more appealing. The addition of nutrients to enrich or fortify food obViously can affect bioavailability of minerals; discussion of these effects is outside the scope of this review. Preservatives and antioxidants include substances such as calcium lactate, calcium sorbate, citric acid, EDTA, lactic acid, potassium sorbate, sodium erythorbate, sodium nitrate, sodium nitrite, TBHQ (tertiary butyl hydroquinone), ascorbic acid, and tocopherols. Many of these substances are known to affect mineral metabolism. The effects of sodium erythorbate, sodium nitrate, and sodium nitrite have been discussed above in the section on curing meats. Calcium interacts with Fe and inhibits its absorption (Latunde-Dada & Neale, 1986; Dawson-Hughes et al., 1986). Citric acid and ascorbic acid improve Fe absorption (Gillooly et al., 1983; Monsen et a1., 1978). Iron is easily complexed by EDTA, and Fe(III)EDTA is well absorbed (MacPhail et al., 1981); £oTA also improves Zn availability (Oberleas et a1., 1966). TBHQ was reported to protect against some of the manifestations of Cu deficiency in rats (Johnson & Saari, 1989). Table 5.

Effe,t of Some Food Additives on Zn Absorption in Vomen % Zn Absorption

Zn only (control) PEG 4000 FD & C Blue No. 1 FD & C Red No. 40

25.9 26.4 30.5 19.9

± 12.0 ± 18.5 ± 10.6

± 9.3

n 7 7

5

5

491

Other food additives are used as emulsifiers, stabilizers, leavening agents, pH control agents, humectants, dough conditioners, and anti-caking agents. These include substances such as calcium alginate, calcium bromate, calcium phosphate, calcium sUicate, cellulose, lactic acid, lecithin, mannitol, pectin, polyethylene glycols (PEG), sorbitol, tartaric acid, and various types of gums. The effects of Ca on availability of other minerals were mentioned above. Cellulose and pectin improved Fe absorption in humans (Gillooly et al., 1984), but cellulose had no effect on Zn absorption (Turn1und et aI., 1984). Sorbitol improved Fe absorption in humans (Loria et aI., 1962) as did tartaric acid (Gillooly et aI., 1983). Adjustment of the pH of bread dough with lactic acid resulted in improved Zn availability from whole-meal bread (Harmuth-Hoene & Meuser, 1988) . We found no effect of PEG 4000 on Zn absorption in humans (PE Johnson, unpublished data) (Table 5). In vitro tests of Zn and Fe availability showed that locust bean gum and guar gum reduced Zn availability, but sodium alginate had no effect on Zn or Fe availability (Zemel & Zemel, 1985). Food additives which affect appeal characteristics of foods include flavor enhancers, flavors, colors, and sweeteners. Food dyes are complex organic molecules which have the potential of forming complexes with trace minerals. However, we found that neither FD & C Blue No. 1 nor Red No. 40 affected Zn absorption in humans (PE Johnson, unpublished data) (Table 5). Addition of flavoring (beef, cheese, or pickled onion flavors) increased in vitro Fe diffusibility from maize grits and a commercial maize product (Hazell & Johnson, 1989). OTHER TYPES OF PROCESSING Physical processing such as the milling of grain can also affect mineral bioavai1abi1ity. Pear1ing of sorghum to remove the outer layers of the grain reduced the polyphenol and phytate contents by 96% and 2%, respectively (Gillooly et a1., 1984). This resulted in an increase of Fe absorption frOlll 1.7% to 3.5%. It is well known that removal of bran during milling of wheat results in improved bioavaUabUity of Fe and Zn; this may be caused by the removal of fiber or by the reduction in phytate content of the flour (Davies, 1978; Elwood et a1., 1968; Andersson et a1., 1983). ACKNOWLEDGEMENTS The author wishes to thank Cheryl Stjern for mass spectrometric analyses, James Normandin for sample preparation, Lisa Hesse and Thad Bowman for stabUity constant determinations, Rodger Sims for mineral analyses, and LoAnne Mullen for metabolic diet preparation. REFERENCES Andersson, H., Nlvert, B., Bingham, S. A., Eng1yst, H. N., and Cummings, J. H., 1983, The effects of breads containing similar amounts of phytate but different amounts of wheat bran on calcium, zinc, and iron balance in man, Br. J. Nutr, 50:503-510.

Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the USDA and does not imply its approval to the exclusion of other products that may be suitable. 492

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