Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

Подождите немного. Документ загружается.

substances from the detector. An ion exchange resin

can be used for this purpose. (See Chromatography:

Gas Chromatography.)

0058 ECD permits the detection of 0.1 pg of chromium

injected as Cr(TFA)

chelate but, at these levels, ser-

ious complications arise in the separation of the metal

chelate from interfering electron capture impurities.

For this reason, several other detectors have been

evaluated, among them the nitrogen-phosphorus de-

tector, atomic absorption spectroscopy and MS. The

hyphenated GLC-MS techniques provide a positive

identification for the very small amounts of chro-

mium compounds. (See Mass Spectrometry: Prin-

ciples and Instrumentation.)

0059 GLC application to foods is more difficult than in

biological fluids. For instance, in liver, many of the

metals present, such as iron, copper, cobalt, and

nickel, tend to emerge shortly after the solvent peak

in large trailing peaks. These are probably thermal

decomposition products, and any chromium peak

present is masked.

0060 The introduction of the mass spectrometer as a

detector in food testing meant a substantial improve-

ment over the ECD, in particular the compatibility of

monitoring a peak which can be identified with a

single metal, and freedom from interferences. The

detection limit is around 0.5 pg.

Neutron Activation Analysis

0061 Neutron activation analysis (NAA) is based on the

formation of radioactive isotopes, when a sample is

irradiated with neutrons from a nuclear reactor or

from other neutron sources. The elements of interest

are identified and quantified by g-spectroscopy.

0062 It is generally used as a reference method to test the

accuracy of other analytical methods, because it is

highly specific and accurate. One of its main advan-

tages is that it is a nondestructive method. The chief

limitations to widespread use of this technique are the

need for a neutron source and the very high cost of the

analysis, that preclude the use of this method for

routine analysis.

0063 Moreover, in the case of chromium, the low abun-

dance of

Cr (4.31%), a small thermal neutron

section (17 barns), a low level of g-decay and a half-

life for

Cr of 27.8 days make it necessary to apply

long irradiations with a high-density flux of electrons,

especially when chromium concentrations are low.

Cr is separated by distillation of chromyl chloride.

0064 NAA has also been used to investigate the behavior

of chromium during drying or when the matrix is

subjected to high temperatures in dry ashing, because

it allows the direct determination of the sample with-

out previous destruction of the organic matter.

0065Another application of NAA (radiochemical

method) is to measure chromium in biological refer-

ence materials for certification purposes.

Chromium (III) and (VI) speciation

0066Metal speciation refers to the identification and quan-

tification of organometallic, chelated, or free metal

ion forms or their oxidation states.

0067As has already been mentioned, differences be-

tween the toxicity and bioavailability of Cr(III) and

Cr(VI) make it necessary to ascertain not only the

total chromium content but also the species present.

Cr(III) plays an essential role in the maintenance of

the glucose tolerance factor, while Cr(VI), because of

its high oxidation potential and its relatively small

size, enables it to pass through cell membranes, is

toxic, and carcinogenic.

0068Trace metal speciation is achieved by combining

two different techniques: one providing an efficient

and reliable separation procedure and the other de-

tection and quantification. Since liquid chromatoga-

phy is suitable for the separation of ionic, polar, and

nonpolar compounds, it is recognized to be specific-

ally efficient in the speciation of organometallics. At

trace levels the chromatographed species are usually

quantified by atomic absorption or emission tech-

niques. Among the latter, most applications are

based on ICP-AES or ICP-MS. When coupled with

separation procedures, ICP-MS is one of the most

powerful techniques for speciation analysis, and,

when ICP is used as a detector for high-performance

liquid chromatography (HPLC), it offers good

sensitivity, a dynamic range of over five orders of

magnitude and multielement detection capabilities.

Moreover, in comparison with ICP-AES, ICP-MS

offers the advantages of lower limits of detection

(sub-ng to sub-pg levels), wide linear ranges, isotope

analysis capability, and good precision values

(0.1–5.0% RSD). AAS is also a sensitive detector

after chromatographic separation.

0069A review of the literature reveals a large number

of procedures for chromium speciation in water

and soils. These include the Cr(VI) determination

methods based on three main procedures – a selective

chelation/extraction technique, coprecipitation and

column separation, together with Cr speciation by

hyphenated HPLC methods.

0070However, chromium speciation has rarely been

performed in complex matrices such as foodstuffs.

In these products total chromium is usually deter-

mined and then Cr(VI) or Cr(III) is separated and

measured. Examples of these determinations have

been reported in milk and in solid food samples.

1306 CHROMIUM/Properties and Determination

0071 A method has been reported for determining total

chromium directly by ETA-AAS in milk after the

addition of a surfactant and Pd-Mg as a chemical

modifier. To extract Cr(VI) quantitatively and select-

ively a solid-phase extraction method using a silica

column modified with NH

is applied to the super-

natant obtained by protein precipitation.

0072 On solid samples alkaline digestion is followed by

coprecipitation with iron (III) hydroxide, redissolu-

tion with HCl and determination of Cr(III) by FAAS.

This is used together with total chromium determin-

ation after a wet digestion of the sample. The amount

of Cr(VI) is then calculated by substracting Cr(III)

from total Cr. A positive interference was reported

when the content of Cr(VI) was 10 times larger than

Cr(III).

Conclusion

0073 ETA-AAS with Zeeman background correction and

matrix modification appears to be the most useful

method for routine, and relatively rapid determin-

ation of the total chromium content of foods. Special

precautions should be adopted to avoid sample losses

and/or contamination throughout the period of an-

alysis, i.e., from sampling to measurement. There-

fore, accurate chromium determination requires the

use of clean room facilities, filtered air and water, and

ultrapure reagents to control environmental pollu-

tion. The daily use of appropriate reference materials

is essential to check analytical accuracy. At the

moment NAA remains useful as a reference method.

0074 In the future the hyphenated HPLC techniques may

contribute to chromium speciation.

See also: Chromatography: High-performance Liquid

Chromatography; Gas Chromatography; Fish Farming;

Mass Spectrometry: Principles and Instrumentation

Further Reading

Boumans PWJM (ed.) (1987) Inductively Coupled Plasma

Emission Spectroscopy. Part II: Applications and

Fundamentals. New York. John Wiley.

Fishbein L (1984) Overview of analysis of carcinogenic and/

or mutagenic metals in biological and environmental

samples. 1. Arsenic, beryllium, cadmium, chromium

and selenium. International Journal of Environmental

Analytical Chemistry 17: 113–170.

Hoenig H and De Borger R (1983) Particular problems

encountered in trace metal analysis of plant material by

atomic absorption spectrometry. Spectrochimica Acta

38B: 873–880.

Maslowska J (1996) Metal contamination. In: Nollet

LML (ed.) Handbook of Food Analysis, vol. 2,

pp. 1665–1682.

Rollinson CL (1975) In: Trotman-Dickenson AF (ed.) Com-

prehensive Inorganic Chemistry, vol. 3, pp. 631–637.

Oxford: Pergamon Press.

Rubio R, Sauquillo A, Rauret G and Quevauvillier PH

(1992) Determination of chromium in environmental

and biological samples by atomic-absorption spectros-

copy: a review. International Journal of Environmental

Analytical Chemistry 47(2): 99–128.

Sarzanini C (1999) Review: liquid chromatography: a tool

for the analysis of metal species. Journal of Chromatog-

raphy A 850: 213–228.

Slavin W (1984) Graphite Furnace AAS: A Source Book.

Perkin Elmer.

Sperling M (1995) Chromium. In: Townshend A (ed.)

Encyclopaedia of Analytical Science, vol. 2, pp.

729–743. Academic Press.

Torgrimsen T (1982) Analysis of chromium. In: Biological

and Environmental Aspects of Chromium, pp. 65–

97.Amsterdam: Elsevier.

Physiology

R A Anderson, Beltsville Human Nutrition Research

Center, Beltsville, MD, USA

Background

0001Chromium in the trivalent form is an essential nutri-

ent that functions in carbohydrate, lipid, and nucleic

acid metabolism. Dietary intake of Cr by humans and

farm animals is often suboptimal. Insufficient dietary

intake of Cr is associated with increased risk factors

associated with type 2 diabetes mellitus (DM) and

cardiovascular diseases. Chromium functions in glu-

cose and insulin metabolism primarily via its role in

the regulation of insulin. Adequate dietary Cr leads to

a normalization of insulin leading to decreased blood

glucose in subjects with elevated blood glucose, in-

creased blood glucose in subjects with low blood

sugar, and no effect on subjects with near optimal

glucose tolerance. Improved insulin function is also

associated with an improved lipid profile. Chromium

in foods and dietary supplements is trivalent, whereas

Cr often found in paints, welding fumes, and other

industrial settings is hexavalent and is severalfold

more toxic than the trivalent nutritional Cr.

Absorption, Transport, Storage, and

Excretion

0002Absorbed Cr is excreted primarily in the urine, and

only small amounts of Cr are lost in the hair,

CHROMIUM/Physiology 1307

perspiration, and bile. Therefore, urinary Cr excre-

tion can be used as an accurate estimation of

absorbed Cr. At normal dietary Cr intakes (10–40 mg

per day), Cr absorption is inversely related to dietary

intake. Chromium absorption is approximately 0.5%

at a daily intake of 40 mg and increases to 2% when

intake drops to 10 mg. Therefore, the amount of

absorbed Cr over this range is approximately 0.2 mg

and is reflected in the urinary Cr losses of approxi-

mately 0.2 mg per day. This inverse relationship of Cr

intake and absorption appears to be a basal control

mechanism to maintain a minimal level of absorbed

Cr. Intakes above 40 mg result in corresponding in-

creases in total Cr absorbed.

0003 Chromium absorption in young and old normal

subjects is similar, but people with type 1 DM absorb

two- to fourfold more Cr than other groups of sub-

jects tested. People with diabetes appear to have an

impaired ability to convert inorganic Cr to a useable

form. Diabetic mice also lose the ability to covert Cr

to a useable form. People with diabetes require add-

itional Cr, and the body responds with increased ab-

sorption, but the absorbed Cr cannot be utilized

effectively and is excreted in the urine. The chromium

content of tissues of people with diabetes is also

lower.

0004 Chromium absorption and incorporation into

tissues are also dependent on the form of Cr ingested.

An accurate estimation of Cr absorption and utiliza-

tion in animal studies can be achieved by measuring

Cr incorporation into tissues. The tissue with the

greatest Cr concentration is the kidney, followed by

the spleen, liver, lungs, heart, and skeletal muscle.

0005Tissue Cr is an accurate method to assess Cr ab-

sorption and utilization and is also a measure of Cr

storage. The kidney, which is one of the primary sites

of tissue Cr storage, is also one of the best sources of

insulin potentiating forms of Cr. Chromium is trans-

ported to the tissues primarily bound to transferrin,

the same protein that transports iron. There are two

metal-binding sites on transferrin, one primarily for

iron and a second involved in Cr transport. During

conditions of high iron excess or iron overload such

as in iron storage diseases (hemosiderosis; hemochro-

matosis), all the metal transport sites on transferrin

are occupied by iron. This may explain the high inci-

dence of diabetes in hemochromatosis patients that

may be induced by Cr deficiency.

Metabolic Functions and Essentiality

0006The essentiality of Cr in human nutrition was docu-

mented in 1977 when diabetic signs and symptoms

of a patient on total parenteral nutrition (TPN) were

reversed by supplemental Cr. Diabetic symptoms, in

addition to elevated blood glucose, included weight

loss, impaired nerve conduction, brain disorders and

abnormal respiratory quotient that were refractory to

exogenous insulin. Upon daily addition of supple-

mental Cr to her TPN solution for 2 weeks, diabetic

symptoms were alleviated, and exogenous insulin re-

quirement dropped from 45 units per day to zero.

tbl0001 Table 1 Signs and symptoms of Cr deficiency

Function Animals

Impaired glucose tolerance Human, rat, mouse, squirrel monkey, guinea-pig, cattle

Elevated circulating insulin Human, rat, pig, cattle

Glycosuria Human, rat

Fasting hyperglycemia Human, rat, mouse

Impaired growth Rat, mouse, turkey

Hypoglycemia Human

Elevated serum cholesterol and triglycerides Human, Rat, mouse, cattle, pig

Increased incidence of aortic plaques Rabbit, rat, mouse

Increased aortic intimal plaque area Rabbit

Nerve disorders Human

Brain disorders Human

Corneal lesions Rat, squirrel monkey

Ocular eye pressure Human

Decreased fertility and sperm count Rat

Decreased longevity Rat, mouse

Decreased insulin binding Human

Decreased insulin receptor number Human

Decreased lean body mass Human, pig, rat

Elevated percentage body fat Human, pig

Impaired humoral immune response Cattle

Increased morbidity Cattle

Adapted from Anderson RA (1998) Chromium glucose intolerance and diabetes. Journal of American College of Nutrition 17: 548–555.

1308 CHROMIUM/Physiology

These findings have been repeated and documented in

the scientific literature on several occasions.

0007Signs and symptoms of Cr deficiency listed in

Table 1 are not limited to subjects on total parenteral

nutrition. Improvements in glucose and/or lipid con-

centrations have been reported in children with pro-

tein-calorie malnutrition, the elderly, people with

type 1 and type 2 DM, hypoglycemia, and marginally

impaired glucose tolerance, and numerous animal

species have also been shown to be improved by

increased Cr intake.

0008The hallmark sign of marginal Cr deficiency is

impaired glucose tolerance. The effects of Cr on

people with high, low, and normal glucose tolerance

as well as diabetes are illustrated in Figure 1. Chro-

mium leads to a decrease in blood glucose in people

with elevated blood sugar and an increase in those

with low blood sugar owing to its role in normalizing

insulin. In the presence of Cr in a physiologically

active form, insulin is more efficient, and much

lower levels of insulin are required. During periods

of elevated blood glucose, more efficient insulin leads

to a decrease in blood glucose. In people with low

blood sugar, reactive hypoglycemia, more efficient

insulin leads to a rapid rise in response to a glucose

challenge and a more rapid return to baseline values.

This leads to less of a drop or a raising of the

hypoglycemic glucose values. Supplemental Cr also

leads to increased insulin binding and increased

insulin receptor number, and recent evidence suggests

that Cr may be involved in the phosphorylation–

dephosphorylation of the insulin receptor proteins

(Figure 2). Chromium activates insulin receptor

kinase, the enzyme that phosphorylates the insulin

receptor leading to activation of insulin function,

and appears to inhibit the phosphatase enzyme that

deactivates insulin function.

Assessment of Chromium Status

0009There are no accurate methods for reliable a priori

detection of marginal Cr deficiency. Chromium

Hyper

lycemia

Blood glucose (mmol l

−1

)

Hypo

lycemia Control Type 2 DM

fig0001 Figure 1 Response to supplemental Cr of people with hyper-

glycemia, hypoglycemia, optimal glycemia (control), and type 2

DM. The minimal amount of Cr usually showing beneficial effects

in people with high or low blood sugar is 200 mg per day. People

with diabetes require 400 to 600 mg per day or more.

Insulin

Alpha subunit

Cell membrane

IRS-1

PI 3-Kinase

Cr Activates receptor kinase

Cr Inhibits protein tyrosine p'ase

COOH

Beta subunit

fig0002 Figure 2 Postulated mechanism of action of chromium. When

insulin binds to the a subunit, phosphorylation is increased,

leading to increased insulin sensitivity and action. Chromium

increases insulin binding to cells by increasing the insulin recep-

tor number, which varies depending upon the type of cell, and

also increases insulin sensitivity by increasing insulin receptor

phosphorylation. IRS-1 denotes the insulin receptor substrate 1,

and PI 3-kinase denotes phosphoinositol-3-kinase. For original

references and details see Anderson RA (1998) Chromium, glu-

cose intolerance and diabetes. Journal of American College of Nu-

trition 17: 548–555 with permission.

tbl0002 Table 2 Daily intakes of chromium from various food groups

Food group Average daily intakes (mg) Comments

Cereal products 3.7 55% from wheat

Meat 5.2 55% from pork; 25% from beef

Fish and seafoods 0.6

Fruits, vegetables, nuts, and mushrooms 6.8 70% from fruits and berries

Dairy products, eggs, and margarine 6.2 85% from milk

Beverages, confectionaries, sugar, and condiments 6.6 45% from beer, wine, and soft drinks

Total 29.1

From Anderson RA (1988) Chromium. In: Smith K (ed.) Trace Minerals in Foods, pp. 231–247. New York: Marcel Dekker.

CHROMIUM/Physiology 1309

concentrations in hair, urine, blood, tissues, etc. can

be used to assess recent Cr exposure but are not long-

term measures of Cr status. The only reliable indica-

tor of Cr status is to monitor glucose, insulin, lipid

and/or related variables before and after Cr supple-

mentation. Response in blood glucose can often be

seen in 2 weeks or less, whereas effects on blood lipids

may take longer. One study reported no effects of

supplemental Cr on blood lipids after 3 months but

significant effects after 7–16 months.

Requirements

0010The estimated safe and adequate daily dietary intake

(ESADDI) for chromium for children 7 years to adult

of 50–200 mg per day was established by committees

of the US National Academy of Sciences in 1980 and

affirmed in 1989. The ESADDI is similar to an RDA

and is usually established prior to the RDA. The Food

and Drug Administration proposed a Reference Diet-

ary Intake for Cr effective in 1997 of 120 mg per day.

However, the new committee of the National Acad-

emy of Sciences representing North America has pro-

posed that the normal intake of Cr should serve as the

adequate intake, which is 20 mg for women and 30 mg

for men over 50 and 25 for women and 35 mg for men

aged 19–50 years. The French Conseil National

d’Etudes et de Recherche sur la nutrition et l’Alimen-

tation has proposed daily intakes of 55 mg for adult

French women 19–65 years (60 mg per day for those

over 65 years) and 65 and 70 mg, respectively, for the

men.

0011Chromium requirement is related to the degree of

glucose intolerance and diabetes. Glucose tolerance

of subjects with mild glucose intolerance declines

when consuming diets containing less than 20 mg per

day of Cr for 5 weeks, whereas glucose tolerance of

subjects with near optimal glucose tolerance is not

altered by these low Cr intakes. People with diabetes

also have a higher requirement for Cr. Chromium

supplementation with 200 mg of Cr per day to people

with mild glucose intolerance results in significant

improvements, whereas the blood glucose of people

with diabetes often does not respond. However,

tbl0003 Table 3 Chromium content of selected foods

Cr (ng g

1

)

mgper

serving

Dairy products

Whole milk, 1 cup ¼244 g <0.50 <0.12

Skim milk, 1 cup ¼244 g <0.50 <0.12

Butter, 1 pat ¼5g 12+ 2 0.06

Margarine, 1 pat ¼5g 3+ 1 0.02

American cheese, 1 oz. ¼28 g 20 + 1 0.56

Eggs, 1 egg ¼50 g 4 + 1 0.20

Meats, poultry, and fish

Beef cubes, 3 oz. ¼85 g 24 + 2 2.0

Chicken breast, 3 oz. ¼85 g 6 + 1 0.50

Turkey breast, 3 oz. ¼85 g 20 + 1 1.7

Turkey ham, 3 oz. ¼85 g 122 + 19 10.4

Ham, 3 oz. ¼85 g 42 + 4 3.6

Haddock, baked, 3 oz. ¼85 g 7 + 1 0.60

Grain products

Waffles, 1 waffle ¼75 g 89 + 6 6.7

Whole wheat bread, 1 slice ¼25 g 39 + 1 0.98

Whole wheat roll, 1 roll ¼26 g 23 + 1 0.60

English muffin, WW, 1 muffin ¼100 g 36 + 1 3.6

Dinner roll, 1 roll ¼25 g 25 + 3 0.62

Rye bread, 1 slice ¼25 g 37 + 6 0.92

Bagel, egg, 1 bagel ¼55 g 46 + 7 2.5

Crackers, trix, 2 crackers ¼14 g 9 + 2 0.12

Spaghetti, 1 cup ¼140 g 2 + 1 0.28

Rice, white, 1 cup ¼165 g 7 + 1 1.2

Rice, brown, 1 cup ¼165 g 4 + 1 0.66

Fruits and vegetables

Banana, peeled, 1 med ¼126 g 8 + 2 1.0

Grapes, 10 grapes ¼50 g 2 + 0 0.10

Apple, peeled, 1 med ¼135 g 3 + 1 0.40

Apple, unpeeled, 1 med ¼150 g 9 + 1 1.4

Orange, peeled, 1 med ¼131 g 3 + 1 0.39

Juice, grape, 1 cup ¼250 g 30 + 1 7.5

Juice, orange, 1 cup ¼248 g 9 + 2 2.2

Peas, 1 cup ¼160 g 5 + 1 0.80

Tomato, 1 med ¼135 g 7 + 1 0.94

Lettuce, 1 wedge ¼135 g 13 + 2 1.8

Celery, 1 stalk ¼40 g 3 + 1 0.12

Green beans, 1 cup ¼135 g 16 + 0 2.2

Carrots, raw, 1 carrot ¼72 g 4 + 1 0.29

French fries, 10 strips ¼50 g 24 + 1 1.2

Potatoes, mashed, 1 cup ¼210 g 18 + 1 2.7

Broccoli, 1 cup ¼185 g 118 + 0 22.0

Juice, tomato, 1 cup ¼240 g 6 + 1 1.5

Condiments

Dressing, Thousand Island, 1 tbsp ¼16 g 11 + 1 0.18

Dressing, French, 1 tbsp ¼15 g 12 + 0 0.18

Pepper, 1 packet ¼0.25 g 145 + 15 0.04

Salt, 1 packet ¼1g 5+ 1 0.01

Mayonnaise, 1 tbsp ¼15 g 2 + 1 0.03

Mustard, 1 tsp ¼5g 48+ 6 0.24

Ketchup, 1 tbsp ¼17 g 58 + 0 0.99

Barbecue sauce, 1 tbsp ¼16 g 108 + 8 1.73

Maple syrup, 1 tbsp ¼21 g 25 + 3 0.52

Jelly, grape, 1 packet ¼14 g 14 + 1 0.20

Vinegar, 1 tbsp ¼15 g 25 + 4 0.38

Sugar, 1 packet ¼6g 3+ 1 0.03

Miscellaneous

Fruit punch, 1 cup ¼200 g 3 + 1 0.60

Orange sherbet, 1 cup ¼193 g 7 + 1 1.4

Apple pie, 1/7 ¼136 g 11 + 1 1.5

Cookies, oatmeal raisin, 4 cookies ¼52 g 18 + 3 0.94

Cookies, vanilla sand., 4 cookies ¼42 g 16 + 4 0.64

Cookies, choc. chip, 4 cookies ¼42 g 82 + 30 3.4

Peanut butter, 1 tbsp ¼16 g 38 + 3 0.61

Soybeans, 1 tbsp ¼9g 22+ 6 0.20

Values are mean + SD of triplicate analyses.

From Anderson RA, Bryden NA, and Polansky MM (1992) Dietary

chromium intake – freely chosen diets, institutional diets and individual

foods. Biological Trace Element Research 32: 117–121.

1310 CHROMIUM/Physiology

daily Cr supplementation of 400 mg or more results in

significant improvements in many people with dia-

betes.

Dietary Sources and High Intakes

0012 Dietary Cr content of foods varies widely, and there

are no comprehensive databases to calculate dietary

Cr intake. The chromium content of foods is often

erroneously high owing to Cr contamination during

collection and analyses. For example, stainless steel

blender blades are often used in the homogenization

of foods, but stainless steel is approximately 18% Cr.

In the presence of acidic foods, more Cr may leach

from the blender blades than is present originally in

the foods. Chromium is present in several food

groups but at low levels. The distribution is similar

among fruits, vegetables, dairy products, beverages,

and meats, with lesser amounts from cereal products

and small amounts from fish and seafood (Table 2).

Specific Cr contents of selected foods are listed in

Table 3. The chromium content of foods is a combin-

ation of the endogenous Cr present in the foods and

the Cr introduced during the various stages of grow-

ing and processing. For example, fruit juices are often

high in Cr, since Cr may leach from containers during

processing and storage under acidic conditions. Pro-

cessed foods such as meats also often contain elevated

levels of exogenous Cr (Table 3).

0013 Trivalent Cr, the form of Cr found in foods and in

nutrient supplements, is one of the least toxic nutri-

ents. The reference dose established by an expert

panel of the US Environmental Protection Agency is

350 times the upper limit of the estimated safe and

adequate daily dietary intake. The reference dose is

defined as ‘‘an estimate (with uncertainty spanning

perhaps an order of magnitude) of a daily exposure to

the human population, including sensitive subgroups,

that is likely to be without an appreciable risk of

deleterious effects over a lifetime.’’ This conservative

estimate of safe intake has a much larger safety factor

for trivalent Cr than almost any other nutrient. The

ratio of the EPA reference dose to the ESADDI for

chromium of 350 compares to roughly two to five for

other trace elements such as zinc and manganese and

five to seven for selenium. Chromium in the form of

both Cr chloride and Cr picolinate fed to rats at

several thousand times the ESADDI for humans

(based on body weight) resulted in no detectable

signs of toxicity.

0014In summary, dietary intake of Cr is suboptimal for

most humans and farm animals. Increased intake of

trivalent Cr leads to improved glucose and lipid

metabolism. The physiological role of Cr appears to

be primarily though the improved function of insulin.

Increased intake of Cr leads to increased insulin bind-

ing, increased insulin receptor number, and increased

phosphorylation of the insulin receptor proteins

leading to increased insulin sensitivity and function.

There have been no documented negative effects of

supplemental Cr in any of the more than 40 Cr sup-

plementation studies involving daily Cr intakes of

1000 mg or more.

See also: Coronary Heart Disease: Etiology and Risk

Factor; Antioxidant Status; Intervention Studies; Diabetes

Mellitus: Etiology; Glucose: Glucose Tolerance and the

Glycemic (Glycaemic) Index; Trace Elements

Further Reading

Anderson RA (1988) Chromium. In: Smith K (ed.) Trace

Minerals in Foods, pp. 231–247. New York: Marcel

Dekker.

Anderson RA (1998) Chromium, glucose intolerance and

diabetes. Journal of American College of Nutrition 17:

548–555.

Anderson RA, Bryden NA and Polansky MM (1992) Diet-

ary chromium intake – freely chosen diets, institutional

diets and individual foods. Biological Trace Element

Research 32: 117–121.

Anderson RA, Cheng NC, Bryden NA et al. (1997) Elevated

intakes of supplemental chromium improve glucose and

insulin variables of people with type II diabetes. Dia-

betes 46: 1786–1791.

Lukaski HC (1999) Chromium as a supplement. Annual

Review of Nutrition 19: 279–302.

Morris B (1999) Chromium action and glucose homeo-

stasis. Journal of Trace Elements in Experimental Medi-

cine 12: 61–70.

Ravina A, Slezak L, Mirsky N, Bryden NA and Anderson

RA (1999) Reversal of corticosteroid-induced diabetes

mellitus with supplemental chromium. Diabetic Medi-

cine 16: 164–169.

Vincent JB (2001) The bioinorganic chemistry of chromiu-

m(III). Polyhedron 20: 1–26.

CHROMIUM/Physiology 1311

CIDER (CYDER; HARD CIDER)

Contents

The Product and its Manufacture

Chemistry and Microbiology of Cidermaking

The Product and its

Manufacture

B Jarvis, Ross Biosciences Ltd, Ross-on-Wye, UK

A Brief History of Cider

0001 The fermentation of apple juice to produce an alco-

holic beverage is believed to have been practiced for

over 2000 years. Cider is recorded as being a common

drink at the time of the Roman invasion of England in

55 bc. Celtic mythology revered the ‘sacred apple,’

and in his famous natural history (ad 77), Pliny

the Elder refers to a drink made from the juice of the

apple. Cider was drunk throughout Europe in the third

century ad, and in the fourth century, St. Jerome used

the term ‘sicera’ (whence the name cider was possibly

derived) to describe drinks made from apples. Re-

putedly, cider was a more popular drink than beer in

the eleventh and twelfth centuries in Europe. Cider is

produced throughout the temperate regions of the

world where apple trees flourish. Such localities in-

clude Austria, Belgium, England, France, Germany,

the Northern coastal area of Spain, Switzerland, and,

more recently, Argentina, Australia, Finland, New

Zealand, South Africa, Sweden, and the USA.

0002 There are many references to cider in writings from

the Middle Ages. The popularity of cider in fourteenth

century England was such that William of Shoreham

reflected the Church’s concern for the niceties of sac-

ramental rites by stating that ‘young children were not

to be baptised in cider’! William Langdon in Piers

Plowman and Shakespeare in A Midsummers Night’s

Dream make reference to the consumption of cider;

Daniel Defoe observed that Hereford people ‘boast

the richest cider in all Britain,’ and Samuel Pepys

noted in his Diary that on 1 May 1666 he ‘drank a

cup of Syder.’ From the seventeenth century onwards,

cider was praised in numerous poems and other liter-

ary works as an aid to good cheer and a homely cure

for almost every ailment known to man.

0003 Prior to the twentieth century, cider was a popular

rural drink, cheaper than beer and often more potent

(at c. 7% alcohol by volume (abv)). Farm workers

often had part of their wages paid as truck (i.e., in

kind), and every farmer would make his own cider for

consumption by his workers and his own family and

guests – although it is recorded that the best ciders

were retained for his personal use. Most farms in the

West of England and the West Country had their own

cider press, or used the services of a travelling cider

press that was hauled by horse from farm to farm. My

own cider mill and press (dated 1717) stand outside

my window as I write this account!

0004Commercial cider production commenced during

the nineteenth century in England (e.g., H Weston &

Sons of Much Marcle, 1880; H P Bulmer of Hereford,

1887; Whiteways Cyder of Whimple in Devon,

1894), although a few farms produced cider commer-

cially from as early as 1727 (e.g., Symonds Cider and

English Wine Co. Ltd., Stoke Lacey, UK). Cider pro-

duction in England was estimated as 250 10

(55 10

gallons) in 1900. By 1920 the level of

cider production had decreased significantly; al-

though some 73 10

l (16 10

gallons) were still

produced on farms only 23 10

l(510

gallons)

came from factory producers. By the late 1980s, cider

sales had risen to over 273 10

l (60 10

gallons)

per year and, in the 12 months to September 1999,

almost 500 10

l (109 10

gallons) were sold in

the UK by members of the National Association of

Cider Makers, a trade association formed originally

in 1920; a further 23 10

l(510

gallons) of

cider were exported from the UK. Since 1999, UK

cider sales have remained constant at 500 10

(109 10

gallons) p.a.

0005The significant increase in the volume of cider pro-

duced commercially each year in the UK up to 1999

followed a period when growth had been inhibited by

the imposition of Excise Duty in 1976 and results both

from the introduction of new cider products, linked to

increased marketing activity, and from changes in

drinking habits, especially of younger adults. In

2002, it is possible to obtain cider either on draught

or prepackaged in glass and PET bottles and in cans.

Products range in alcoholic strength from less than 0.5

to 8.5% (abv), and in sweetness from very dry to

sweet. In addition, cider products now include

‘white’ ciders, naturally colored ciders, and blends of

1312 CIDER (CYDER; HARD CIDER)/The Product and its Manufacture

cider with fruit juice or other ingredients. Some cider,

made from apples of a single crop, may be sold as a

defined year Vintage Cider, whilst others are made

from a single apple cultivar, e.g., Kingston Black.

0006 Because of the significant growth in cider sales in

recent years, imitation ciders have appeared on the

market in several countries. Such products are pro-

duced by compounding distilled alcohol with apple

juice and artificial flavors. Such products are not

cider. In 1998, the European Association of Cider

and Fruit Wines Industries of the EU (AICV) defined

the acceptable procedures for production of cider and

related products. Fortification of cider or apple juice

by the addition of distilled alcohol is not an approved

process for a product to be sold as cider.

Cider Fruits

0007 Traditional ciders are made from the juice of cider

apples, believed to have been imported into Britain by

the Normans, although it is recorded in Gaulmier’s

Traite du Sidre (1573) that a Spaniard named Dursus

de l’Etre brought apple trees into France in 1486!

Traditional cider apples are of four main types: bitter

sweet – low in acidity but high in tannin; bitter sharp

– high acidity and high tannin; sharp – high acidity

but low tannin; and sweet varieties – low acidity and

low tannin. Examples of some cider fruit cultivars are

listed in Table 1.

0008 In some areas, especially Kent, Suffolk, and Nor-

folk in the UK, cider is made primarily from culinary

fruit varieties such as the Bramley, although blends of

bittersweet and culinary juices are frequently used to

develop particular flavor profiles in commercial cider

blends.

Cider Orchards

0009The traditional farm orchard of standard trees still

exists, and although generally declining in acreage,

many hundreds of such orchards provide both an

apple crop and grazing for livestock.

0010Modern cider apple orchards are largely intensive

bush orchards, where the trees are frequently planted

as closely as 2.4 m apart in rows some 5.5 –6 m apart.

After planting, staking, and protecting against rabbits,

using a wire guard, the grass under the trees is treated

with a suitable herbicide to reduce competition for

nutrients and water. Some growers cover the herbi-

cide strips with a mulch of straw or other suitable

material to ensure maximum retention of moisture.

Although it has become standard practice to retain

the herbicide strip into the productive years of an

orchard, this practice is currently the subject of

research to assess whether a grass sward may be

better in relation to the quality of harvested fruit.

0011During the growing season, it may be necessary to

spray the trees against pests, such as red spider mite,

and diseases such as mildew, apple scab, and canker.

In years of heavy potential cropping, chemical thin-

ning (e.g., using paclobutrazol, ‘Cultar’) is frequently

recommended, to reduce stress on the tree and

thereby minimize the risk of biennialism, a condition

that occurs significantly in cider fruit orchards.

Harvesting

0012In traditional orchards, fruits are generally allowed to

fall naturally, or shaken from the trees using long poles

(lugs), and then picked up either by hand or by

machine. Traditionally, fruit from standard trees

would be raked into piles or filled into sacks that

were stored under the trees until the fruit was in a

suitably ripe condition to be milled and pressed.

0013In intensive bush orchards, it is normal to shake the

trees mechanically to cause the fruit to fall. Such

shaking does not harm the tree and permits fruits to

be harvested mechanically immediately after falling,

so reducing the risk of rots that may occur if fruit are

left for any length of time on the ground. The col-

lected fruit is normally washed and then transported

by road to the cider mill where, after weighing, the

fruit is tipped into a fruit canal or on to a concrete pad

for holding prior to milling and juicing.

Processing the Fruit

Milling and Pressing

0014The fruit is generally transferred into the mill using

either a water flume, which provides additional

washing, on a conveyor belt or using screw conveyors.

tbl0001 Table 1 Characteristics of cider apple varieties

Type Typical varieties Typicaljuice composition

Acidity

(gper100 ml)

Tannin

(gper100 ml)

Sweet Northwood <0.45 <0.2

Sweet Alford

Sweet Coppin

Bitter sweet Ashton Brown <0.45 >0.2

Jersey

Dabinett

Michelin

Yarlington Mill

Sharp Brown’s Apple >0.45 <0.2

Frederick

Reinette Obry

Bitter sharp Bulmer’s Foxwhelp >0.45 >0.2

Brown Snout

Chisel Jersey

Kingston Black

CIDER (CYDER; HARD CIDER)/The Product and its Manufacture 1313

Detritus such as twigs, leaves, and stones is removed

mechanically, and the fruit is milled using a grater,

slicer, or hammer mill. The apple pulp is then

conveyed to a mechanical press where the juice is

extracted.

0015 Traditionally, the presses consist of a frame con-

taining a slatted board covered by a cloth into which

a measured amount of the pulp is transferred. The

corners of the cloth are folded over to form an envel-

ope, the frame is removed, and the next slatted board

is added together with the frame and another cloth.

This procedure is repeated some 10 –20 times to build

a ‘cheese,’ which is then pressed hydraulically to

remove the juice, under a ram pressure of some

14 MPa (c. 2 MPa on the ‘cheese’). This method

removes up to 80% of the juice. Sometimes, the

pomace residue (see below) is soaked in a small

volume of water and repressed to remove further

quantities of fermentable sugar.

0016 Such processes are very labor intensive and, except

for farmhouse production, have now largely been

replaced by automatic presses such as the Bu

cher-

Guyer, a horizontal cylinder press, or the Bellmer

continuous belt press. Such presses are more efficient,

often permit countercurrent extraction of the pomace

with warm water, and have little demand for labor

once properly set up. Processes such as electro-

acoustic dewatering have been claimed to release a

higher yield of juice by passing an electric current

through the pulp prior to pressing but have not

found application in the cider industry.

Pomace

0017 Apple pomace can be used for the extraction of the

natural gelling agent, pectin, used in the manufacture

of jam, dairy products, and other foodstuffs, and in

certain medical applications.

0018 Pomace, either before or after depectinization, can

be fed to animals either as a wet slurry or after drying;

it can also be spread on to agricultural land as an

organic mulch or fertilizer. Although it aids the break-

down of clay soils, its acidity often poses problems.

Apple Juice

0019 The extracted juice is rich in malic acid, tannins, and

sugar; it will also be contaminated with a variety of

microorganisms derived from the fruit itself, from the

orchard floor, from the harvesting equipment, and

from the environment of the cider mill. Immediately

after pressing, juice is treated with sulfite, either as

sulfur dioxide (SO

) or in the form of potassium

metabisulfite. Sulfite acts both as an antioxidant, to

prevent browning of the juice (due to polyphenol

oxidase and chemical browning reactions), and as

an antimicrobial that destroys ‘wild’ yeasts and bac-

teria. The sulfite-treated juice will normally be stored

for some 24 h before being pumped into fermentation

vessels. The level of sulfite will normally be adjusted

to give 10–30 mg of free SO

per liter at the time of

pitching with yeast.

0020Generally, the juice will not be clarified prior to

fermentation. However, if the juice is to be concen-

trated by thermal evaporation, it will be treated with

a mixture of enzymes (pectinases and amylases) and

then clarified prior to concentration. Failure to

destroy pectins and starch results in a thick viscous

mass that neither concentrates effectively nor stores

adequately.

Fermentation of Cider

Fermentation Vessels

0021Traditionally, the apple juice would have been fer-

mented in oak vats. Although many such vats are

still used, they have been largely replaced in commer-

cial practice by vats of mild steel with a ceramic or

resin lining, by lined fiber-glass resin vats and, more

recently, by stainless steel vats. A few cider makers

use redundant brewing vessels such as tall conico-

cylindrical vats. However, there is evidence that tall

conicocylindrical vats inhibit effective fermentation

by creating excessive hydrostatic pressure on the

yeast, although squat conicocylindrical vats are excel-

lent. The Unitank-style vessel used frequently for the

fermentation of wine is also excellent for cider fer-

mentation. Figure 1 illustrates some of the styles of

fermentation vessels used in cider making.

Fermentation Substrate

0022Traditional cider making fermented the whole juice,

often with much of the apple solids remaining. Such

solids included the pips, which contain glycosides,

and so the cider would contain small quantities of

cyanide derivatives.

0023In many countries, the practice of chaptalization

has become increasingly common. Chaptalization

supplements the sugar content of the apple juice with

a suitable fermentation sugar (e.g., brewers’ dextrose)

and permits the production of strong cider with an

alcohol content of 11.5–12% abv. By comparison,

fresh juice fermentations, depending upon the sugar

content, will rarely exceed 5.5–6.5% abv. In France,

where the production of traditional cider is con-

strained by legislation, only the product of fermenta-

tion of fresh apple juice or fresh juice reinforced with

juice from concentrate, can be called ‘cidre.’ How-

ever, it is now permissible in France to produce a cider

1314 CIDER (CYDER; HARD CIDER)/The Product and its Manufacture

from juice and fermentation sugar, which must be

described as ‘un boisson alcoolise

base de pomme’

(sic an alcoholic beverage derived from apples) to

differentiate it from traditional cidre.

0024 In the preparation of cider, the apple juice may be

fresh or reconstituted from apple juice concentrate; in

many countries, pear juice (fresh or reconstituted)

may be added to a maximum of 25% of the apple

juice content. Other than fermentation sugars, the

only other primary addition will be a suitable yeast

culture. Fermentations originating wholly or largely

from concentrate normally need the addition of yeast

nutrients, such as ammonium phosphate, sodium

pantothenate and/or thiamine.

Fermentation Process

0025 Where a natural fermentation of the apple juice is

required, the pressed and sulfite-treated juice is trans-

ferred to suitable fermentation vessels and allowed

to ferment naturally. The process is monitored by

measurement of the specific gravity (SG) of the

juice; the fermentation is deemed to have gone to

completion when the SG is 1.0000 or less.

0026However, most commercial cider is inoculated with

a selected strain, or a mixture of strains, of a wine

yeast capable of growth at elevated alcohol levels.

The process consists of partially filling the vat with

juice at a temperature at or below 18



C, followed by

inoculation with the specific starter culture of yeast.

The use of a slightly reduced initial temperature is to

prevent excessive temperature development during

the initial exothermic growth of the yeast prior to

onset of fermentation. The starter culture may be

grown in the laboratory from a pure culture or

added either as a commercial dried yeast preparation

or as an aerated slurry of dried yeast – the latter is the

most efficient for commercial processing. Once fer-

mentation has started, additional substrate (i.e., apple

juice and/or fermentation sugar) is added from time

to time until the vat is filled. Although most cider

vats are typically of 45 10

– 9 10

l (10 10

–

2 10

gallons) capacity, much larger vats do exist.

(A)

(B)

(C)

(D1)

(D2)

fig0001 Figure 1 Schematic design of cider fermentation vessels. (A) Shallow angle conicocylindrical fermenter suitable for cider.

(B) Typical steep angle, tall conicocylindrical fermenter as used for brewing beer. (C) Unitank fermentation vessel, with sloping

base. (D) Oval cross-section (D1) horizontal fermentation vessel (D2).

CIDER (CYDER; HARD CIDER)/The Product and its Manufacture 1315