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

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for ultrafiltration and subsequently adding cream to

the retentate may overcome this problem.

Effect on Proteins

0009 Under normal operating conditions, casein and whey

proteins are not normally affected by ultrafiltration

process. Air incorporation into the retentate may

however lead to denaturation of whey proteins at

the air–water interface. Though low-temperature

processing does not affect the whey proteins, ultrafil-

tration processing at high temperature (> 55



C) even

for a short period like 2 h may cause complexing of

b-lactoglobulin with casein. Such complexing in-

creases with residence time, concentration level, tem-

perature, and amount of air entrapped. Diafiltration

of retentate may also contribute to whey protein

denaturation.

Effect on Starter Activity

0010 Milk proteins and insoluble salts of calcium and

phosphate, responsible for buffering action, are con-

centrated by the ultrafiltration process. Increased buf-

fering capacity causes technological problems in the

manufacture of cheese from highly concentrated

retentate because a relatively large amount of lactic

acid must be produced to obtain the desired pH.

Consequently, the use of very active starter culture is

necessary to produce the desired level of lactic acid;

failure to reduce the pH would enhance the risk of

growth of undesirable microorganisms in the cheese.

(See Starter Cultures.)

Effect on Rennet Coagulability

0011 The renneting time, in general, decreases as the

concentration of ultrafiltration increases. The faster

and more effective collision of micelles, due to the

increase in protein content or increased calcium

concentration, may result in more secondary-phase

interactions and a decrease in clotting time.

Protein Standardization by the

Ultrafiltration Technique

0012 Protein standardization has now become an

important international issue mainly because of the

following reasons:

0013 Seasonal and regional differences in protein con-

tents of milk are inherent features which affect the

quality and composition of products made there-

from, hence the need for equalizing protein.

0014 Fortification of milk with total protein to increase

the nutritional value.

0015 Manufacture of total milk protein concentrates

for use in special and dietetic foods.

Ultrafiltration can be used with great success for

upward standardization of milk proteins in all the

above-mentioned situations.

Cheesemaking with the Ultrafiltration

Process

0016Several varieties of cheese are commercially produced

employing the ultrafiltration process. Ultrafiltration

helps to obtain a retentate with a composition identi-

cal to that of the desired cheese. Ultrafiltration tech-

nology offers the following advantages:

0017The increase in cheese yield is the most attractive

benefit. In the traditional cheesemaking process, all

the whey proteins and some casein fines, which

account for nearly 20% of total milk proteins and

some fat particles, are lost into whey. Ultrafiltration

processing helps to retain all these constituents in

the cheese. Though the actual increase in the yield

depends on the level of concentration achieved

during ultrafiltration and the type of cheese made,

about 8% higher yield for hard cheese (e.g., Ched-

dar cheese) and up to 30% for semihard and soft

varieties of cheeses is commercially obtainable.

0018Mechanization and automation of cheesemaking

are possible.

0019The requirements for starter culture and rennet are

reduced.

0020The amount of whey to be disposed of is either

substantially reduced or completely eliminated,

and the byproduct of the ultrafiltration process,

the permeate, has many useful applications.

Thus the biochemical oxygen demand (BOD) of

the cheese waste steam is considerably reduced.

(See Effluents from Food Processing: Composition

and Analysis.)

0021The milk-handling capacity of existing cheese-

making equipment can be increased without

increasing the vat size or floor area.

0022The overall energy requirements are low for the

concentration of milk, as well as for heating and

cooling the retentate.

Classification of Ultrafiltration Methods for

Cheesemaking

0023Based on the levels of concentration achieved, the

manufacture of cheese by the ultrafiltration process

can be broadly divided into three categories.

0024Low-concentration factor (LCF) method Milk is

usually concentrated up to twofold by ultrafiltration

followed by cheesemaking employing traditional pro-

cesses and equipment. Alternatively, milk is concen-

trated up to fivefold, and then used to supplement

3844 MEMBRANE TECHNIQUES/Applications of Ultrafiltration

whole/skim milk intended for cheesemaking to the

extent that the concentration of solids in the supple-

mented milk does not exceed twofold the original

level. The method can be used for most varieties of

cheese without difficulty. The quality of cheeses pro-

duced from LCF retentate is generally identical to the

traditional cheese. Better utilization of existing cheese

vats and production of cheese of identical protein

content throughout the year are two of the advan-

tages of the LCF process. Since the drainage of whey

occurs just as in the traditional cheesemaking process,

the benefit of higher yield is not achieved. (See

Cheeses: Chemistry of Gel Formation.)

0025 High-concentration factor (HCF) method In the

HCF process, milk is concentrated between three-

and sixfold. Beyond sixfold it is not possible to

concentrate milk with the present generation of mem-

branes. Since many changes in composition and other

properties of the retentate take place during high

concentration, modified process and equipment are

required for cheesemaking. This method is used for

the manufacture of some hard and semihard varieties

where partial drainage of whey is essential to achieve

the desired total solids and/or for texturizing the

product. The most successful commercial application

of this process is in the manufacture of Cheddar

cheese. Based on the fivefold concentration of milk,

the CSIRO Dairy Research Laboratory, Australia and

APV Ltd have jointly invented a commercial process

for making Cheddar cheese (known as APV Siro curd

process). Cheddar cheese made by this method is

identical to traditional cheese.

0026Precheese method Skim milk or whole milk is con-

centrated up to the solids equivalent desired in the final

cheese. There is usually no production of whey, which

enables 100% utilization of whey proteins and casein

in the final product. This process is based on completely

new cheese technology and new equipment. A true

precheese ultrafiltration process is most successful

for the preparation of soft and semihard varieties,

i.e., those cheeses containing more than 45% moisture,

e.g., cream cheese, quarg, ricotta, feta, mozzarella, and

camembert. (See Cheeses: Types of Cheese.)

Other Uses of Ultrafiltration Retentate

0027The ultrafiltration retentate can also be used in the

manufacture of some other fermented dairy products

like yogurt, shrikhand, and ymer. The ultrafiltration

retentate can be spray-dried in the flush reason and

utilized in the lean season for manufacturing cheese.

Ultrafiltration in combination with diafiltration helps

to produce highly purified food-grade proteins with

low lactose content, and having highly improved

functional properties such as emulsion capacity and

foaming stability (Table 2). Such functional proteins

are finding increasing applications in the food

industry. (See Drying: Spray Drying.)

tbl0002 Table 2 Composition and functional properties of skim milk, ultrafiltered (UF) retentate (5 ) and whole-milk protein isolates (WMPI)

of cow and buffalo milk

Components Skimmilk UFretentate WMPI

Cow Buffalo Cow Buffalo Cow Buffalo

Total solids (%) 8.85 9.67 24.33 24.24 18.46 19.69

Total nitrogen (%) 0.534 0.642 2.85 2.93 2.61 2.85

Total protein (%) 3.20 3.66 18.00 18.55 16.44 18.06

Total protein (DM) (%) 37.30 39.92 73.95 76.53 89.06 91.72

Casein (DM) (%) 32.40 34.95 64.88 66.79 77.31 79.23

Whey protein (DM) (%) 4.90 4.95 9.12 9.74 11.75 12.49

Casein/WP 6.60 7.06 7.11 8.86 6.58 6.34

Lactose (DM) (%) 56.50 48.60 18.10 17.90 6.70 8.70

2þ

(DM) (%) 1.66 2.07 2.67 3.65 2.26 3.09

Alcohol stability (%) 82 75 75.7 62.5 52.3 41.8

Solubility (%) 92.7 93.5 86.7 88.6

Clotting time (min) 4.9 1.47 2.1 0.67 3.1 2.55

Curd firmness (K20) (min) 2.1 0.93 0.9 0.40 1.8 1.0

Emulsion capacity (m

1

) 61.2 102.8 59.74 114.23

Foaming capacity (%) 120 110 120 110

Foam stability

30 min 31.0 58.8 32.95 58.8

60 min 24.0 41.8 25.75 41.0

90 min 19.0 33.3 19.0 34.0

Data from El-Shibny S, Shahein NM and Sheikh M (1996) Preparation and functional properties of ultrafiltered milk protein isolates. Bulletin of

International Dairy Federation 311: 28–30.

MEMBRANE TECHNIQUES/Applications of Ultrafiltration 3845

Treatment of Whey

0028 Whey is a byproduct of cheese and casein manufac-

ture, and of the 6.5% solids present in whey, the

proportions of protein, lactose, and minerals are 12,

75, and 9%, respectively. Small amounts of fat

and some organic acids are also present. Whey is a

heavy pollutant with a BOD as high as 50 000 p.p.m.

Until the advent of membrane technology, whey

had to be either drained into the sewers or given

to livestock growers. Because of its very high water

content, the processing of whey employing conven-

tional evaporators and driers is highly uneconomical.

The high lactose-to-protein ratio is another factor

limiting the proper utilization of concentrated and

dried whey. (See Whey and Whey Powders: Produc-

tion and Uses.)

0029 The development of the ultrafiltration process

has undoubtedly proved a boon for the cheesemakers

in the treatment of whey. The use of ultrafiltration

to fractionate and concentrate whey proteins, fol-

lowed by evaporation and spray drying, is now a

well-established commercial process for the manufac-

ture of whey protein concentrate (WPCs). WPCs pre-

pared by ultrafiltration technology, having 35–80%

protein, are now available commercially. WPC can

be further separated into b-lactoglobulin and

a-lactalbumin fractions, or used for the manufacture

of casein macropeptide, a compound that may have

pharmatherapeutic value. The main attraction of

ultrafiltration for processing whey includes an almost

100% recovery of whey proteins for edible and other

useful applications, with a simultaneous reduction in

lactose content. It is possible to concentrate protein

up to 20 times with a 95% reduction in volume;

further increases in protein and reductions in lactose

content are possible employing the diafiltration tech-

nique. The energy requirements for removing water

from whey using the ultrafiltration process are min-

imal compared with any other dewatering techniques.

Since ultrafiltration is carried out at low temperatures

(about 50



C), the native and functional properties of

whey proteins are kept intact. The pollution load

of whey is remarkably reduced and, in combination

with reverse osmosis, the BOD value of whey can be

reduced by about 98%.

0030 Decline in the flux rate due to fouling of the mem-

branes is the main limitation in processing of whey by

ultrafiltration. In fact, whey is one of the most notori-

ous foulants of all the fluid milk products. Some

remedial steps to alleviate fouling problem are given

below:

0031 Whey should be separated and clarified before

processing in order to remove suspended casein

fines and lipid constituents.

0032In general, the flux is lowest at the isoelectric point

of protein and becomes higher as the pH deviates

from this point. A combined treatment of heating

to 80–85



C for 15 s followed by pH adjustment to

about 3 or 7 is very useful for acid whey (casein

whey); pH adjustment is not necessary for sweet

whey (e.g., Cheddar cheese whey).

0033Complexing of proteins (e.g., casein micelles with

b-lactoglobulin) by heat treatment or solubiliza-

tion of proteins by either enzymatic treatment or

the use of carboxymethyl cellulose is reported to

increase the flux.

0034Salts, particularly calcium phosphate, exagge-

rate the fouling problem. Addition of sequester-

ing agent, e.g., ethylenediaminetetraacetic acid

(EDTA) or sodium hexamataphosphate, to an

acid whey has a very beneficial effect on the flux.

Partial replacement of calcium with sodium or its

removal by a demineralization process may also be

adopted.

Clarification of Fruit Juices and

Beverages

0035Many juices and beverages contain colloidal and sus-

pended solids which need to be removed before the

product is marketed. It is economically feasible to

use an ultrafiltration process for the commercial

production of many ‘single-strength’ beverages. The

principle behind the ultrafiltration clarification pro-

cess is that the beverage flows over the membranes,

and while the clarified beverage passes through the

membrane in the form of permeate, the colloidal and

suspended solids are rejected into the retentate

stream. Hence, the permeate is the desired stream

and the retentate is discarded.

Fruit Juices

0036Traditionally, press juice is subjected to pasteuriza-

tion followed by enzymatic hydrolysis of pectin. Then

a fining agent (gelatin) is added to the juice, and the

suspension is held for about 20–30 h. After decanting,

the juice is passed through a filter aid. The application

of ultrafiltration to fruit juice clarification helps re-

place the holding, decantation, and filtration steps.

All the undesirable components, such as pectin, large

carbohydrates, and tannin protein complexes, which

are responsible for cloudiness and sedimentation, are

retained by the ultrafiltration membrane. Polyphenol

oxidase, which causes browning of fruit juices, is also

not allowed to permeate along with the clarified juice.

0037So far, the largest application of ultrafiltration in

the juice industry has been in the production of

apple juice; a flow diagram of the process in given in

3846 MEMBRANE TECHNIQUES/Applications of Ultrafiltration

Figure 1. Since microorganisms are larger than the

pore size of the membranes, these are retained in

the residue and the clarified juice is essentially sterile.

The aseptic handling of this juice can either com-

pletely eliminate or substantially reduce the subse-

quent heat treatment prior to storage and bottling.

It is also possible to minimize the losses of sugar and

low-molecular-weight solutes by diafiltration of the

retentate and blending of the permeate, after concen-

tration, into the clarified juice. Other fruit juices that

can be clarified by ultrafiltration include citrus,

grape, cranberry, and pear.

0038 Some of the potential benefits of ultrafiltration

over the traditional processing of fruit juices are:

0039 a superior-quality juice in terms of organoleptic

properties and clarity can be produced;

0040 it is possible to develop a continuous and auto-

mated process, thereby lowering production cost;

0041 a marginally higher recovery of juice in the ultra-

filtration process (95–98%) is possible in compari-

son with traditional processing (90–93%);

0042 enzyme requirements can be reduced by more than

half (as compared with the traditional process)

because of partial depectinization;

0043 waste disposal can also be minimized.

A major drawback of the ultrafiltration system is that

it can only handle clear juices. Other problems such

as reduction in flux, primarily due to fouling, is less in

ultrafiltration than in microfiltration, which can be

rectified by selecting the correct membrane material

and configuration, and pretreating the feed.

0044Some vegetable juices, such as tomato, carrot,

celery, and cucumber, can also be clarified by the

ultrafiltration process with most of the advantages

discussed above for fruit juices.

Wine and Beer

0045The application of ultrafiltration improves the

organoleptic properties and stability of wine and

beer. In wine production, a clear quality product is

insured by treating either the must or the finished

wine with ultrafiltration so as to remove undesirable

microorganisms, stabilize proteins, and reduce the

decolorizing and astringent-tasting polyphenol com-

pounds, such as tannins. Other undesirable compon-

ents, which otherwise require more expensive and

time-consuming steps in conventional methods, are

also removed by ultrafiltration membranes. (See

Beers: Chemistry of Brewing; Wines: Production of

Table Wines; Production of Sparkling Wines.)

0046Vinegar is produced by fermenting wine into acetic

acid. After fermentation vinegar shows a slight tur-

bidity due to low levels of polysaccharide and protein.

Ultrafiltration is an ideal process for producing clari-

fied vinegar with yield more than 97%. (See Vinegar.)

Biotechnology-Oriented Applications

0047Lately, membrane technology has been applied to the

biotechnological processes. Ultrafiltration can be used

to harvest microorganisms from fermentation broths

with much higher recoveries than traditional filtration

and centrifugation processes. For example, hollow-

fiber ultrafilters can give 100% rejection of Lactobacil-

lus bulgaricus cells in whey permeate fermentation

broth. The fouling problem with ultrafiltration mem-

branes during cell harvesting is less than with the

microfiltration process. Ultrafiltration can be used for

numerous applications related to the preparation of

enzymatic hydrolysates from milk proteins, including:

0048the removal of enzyme and unhydrolyzed proteins

from a reaction mixture;

0498the adjustment of the molecular-weight distribu-

tion profile of peptide mixture;

0050other compositional adjustments related to salts or

free amino acids;

0051the removal of bitterness and antigenic molecules

from casein and whey protein hydrolysate; and

0052the selective concentration of highly functional

peptides.

Enzyme extracted from plant and animal tissues

can also be purified by the ultrafiltration process.

Ultrafiltration membranes containing immobilized

enzymes or whole microbial cells function as

continuous bioreactors. These bioreactors have been

Fruit

Fruit press

Clear juice

Pasteurization

Depectinization by enzyme addition

Residue (retentate)

Clarified juice

(permeate)

Bottling

Ultrafiltration

fig0001 Figure 1 Flow diagram for clarification of apple juice.

MEMBRANE TECHNIQUES/Applications of Ultrafiltration 3847

reported to provide an opportunity for greatly im-

proving the performance and productivity of fermen-

tation. Ultrafiltration is also used for the production

of high-quality water suitable for pharmaceutical and

biotechnology purposes. The most efficient removal

of pyrogens, bacteria, and particulates at low energy

are the main advantages of ultrafiltration over

other water treatment techniques. (See Water Sup-

plies: Water Treatment.)

Other Applications

0053 Other useful applications of ultrafiltration in the food

industry include production of concentrates and isol-

ates from soya, sunflower, and cotton seeds; removal of

glucose from egg white and its partial concentration

prior to drying; refining of sugar solutions; fraction-

ation and concentration of gelatin, and many more.

See also: Beers: Chemistry of Brewing; Cheeses: Types

of Cheese; Chemistry of Gel Formation; Drying: Spray

Drying; Effluents from Food Processing: Composition

and Analysis; Milk: Dietary Importance; Starter Cultures;

Vinegar; Water Supplies: Water Treatment; Whey and

Whey Powders: Production and Uses; Wines: Production

of Table Wines; Production of Sparkling Wines

Further Reading

Cheryan M (1986) Ultrafiltration Handbook. Lancaster,

PA, Technomic.

Cheryan M (1998) Ultra-filtration and Micro-filtration

Handbook. Lancaster, PA: Technomic.

EI-Shibiny S, Shahein NM and Sheikh M (1996) Prepar-

ation and functional properties of ultrafiltered milk pro-

tein isolates. Bulletin of International Dairy Federation

311: 28–30.

Fukumoto, LR, Delaquis P and Girard B (1998) Microfil-

tration and ultrafiltration ceramic membrane for apple

juice clarification. Journal of Food Science 63: 845–850.

Gauthier SF and Pouliot Y (1996) Use of ultra-filtration for

the preparation of enzymatic hydrolysates from milk

proteins. Bulletin of International Dairy Federation

311: 31–32.

Glover FA (1985) Ultrafiltration and Reverse Osmosis for

the Dairy Industry. Technical Bulletin no. 5. Reading,

NIRD.

Horton BS (1997) Whatever happened to the ultrafiltration

of milk? Australian Journal of Dairy Technology 52(1):

47–49.

Kosikowski FV (1986) New cheese making process utilising

ultra-filtration. Food Technology 40(6): 71–77.

Lelievre J and Lawrence RC (1988) Manufacture of cheese

from milk concentrated by ultra-filtration: a review.

Journal of Dairy Research 55: 373–392.

Novak A (1996) Application of membrane filtration in the

production of milk protein concentrates. Bulletin of

International Dairy Federation 311: 26–27.

Pal D and Cheryan M (1987) Membrane technology in

dairy industry. Part II. Ultrafiltration. Indian Dairyman

39(8): 373–392.

Puhan Z (1996) Protein standardization. Bulletin of Inter-

national Dairy Federation 311: 4–6.

Renner E and Abd El-Salam MH (1991) Application of

Ultra-filtration in Dairy Industry. Barking: Elsevier.

Vasiljevic T and Jelen P (1999) Temperature effect on

behaviour of minerals during ultrafiltration of skim-

milk and acid whey. Milchwissenchaft 54(5): 243–246.

Menaquinone See Vitamin K: Properties and Determination; Physiology

MENSTRUAL CYCLE: NUTRITIONAL ASPECTS

F Ford, University of Sheffield, Sheffield, UK

Background

0001 The effects of dietary intake on the menstrual cycle

have been the subjects of a great deal of research, but

many aspects are still poorly understood. The rela-

tionship between nutritional status and menarche will

be reviewed, together with the influences of: body

weight, body fat, dietary restraint, dietary fat and

energy intake, lignans, isoflavones, vegetarianism,

and PCB residues on the menstrual cycle.

Nutritional Status and Menarche

0002Some research shows that girls who experience early

menstruation reach their mature height sooner than

girls who experience late menarche (the onset of

3848 MENSTRUAL CYCLE: NUTRITIONAL ASPECTS

menstrual periods). In one study, girls who ate pri-

marily protein foods were shown to reach menarche

sooner, and girls who eat primarily carbohydrates

reached menarche later. However, in other studies of

all the dietary variables analyzed, only energy intake

was related to age at menarche. In a longitudinal

study, girls who consumed more (energy-adjusted)

animal protein and less vegetable protein at ages

3–5 years had an earlier menarche, and girls aged

1–2 years with higher dietary fat intakes and girls

aged 6–8 years with higher animal protein intakes

became adolescents with earlier peak growth. Con-

trolling for body size, girls who consumed more

calories and animal protein 2 years before peak

growth had a higher peak growth velocity. These

findings may have implications regarding adult

diseases whose risks are associated with adolescent

growth and development factors.

Body Weight and the Menstrual Cycle

0003 It is well established that starvation and emaciation

are almost invariably associated with amenorrhea

(lack of menstrual periods), the most profound

disturbance of the menstrual cycle. The work of

Frisch in the USA identified the link between body

composition and ovulation in the human female.

She suggested that fat must comprise at least 22%

of body weight for the maintenance of ovulatory

cycles and also observed that in normal postpubertal

women, fat is about 28% of body weight. It is

well recognized that the relationship is to the fat

content of the body rather than absolute body weight.

Trained athletes of average or above average body

weight may have a very low body fat content and

may be oligo- or amenorrheic. Frisch observed

that amongst trained athletes who became fit after a

normal menarche, 60% continued regular cycles, but

40% had irregular cycles and presumably associated

subfertility.

0004 Eating disorders such as anorexia nervosa and

bulimia nervosa are also causes of oligo- or amenor-

rhea. In anorexia nervosa, amenorrhea and failure to

maintain a body weight within 15% of that expected

are both diagnostic criteria. However, many women

engage in pathologic dieting behaviors without meet-

ing the current diagnostic criteria for anorexia or

bulimia nervosa. Clinical eating disorders are only

the most extreme form of pathologic eating attitudes

and behaviors that are present in many young

women. Specific food choices and nutrient intakes

may be associated with altered gonadal hormone

status of these dieters.

0005 Extreme weight loss is not a prerequisite for men-

strual cycle disturbances because dieting can induce

missed cycles before substantial weight loss occurs.

Even a very short-term (i.e., 4-day) acute energy

shortage can interfere with luteinizing hormone

pulsatility and thereby affect cycle function. In

humans, dieting with minor or moderate weight loss

has been shown to cause menstrual cycle disturbances

or may be a risk factor for the development of repro-

ductive dysfunction in normal weight healthy

women. Cognitive factors may also be associated

with the stability of the menstrual cycle. One such

factor is cognitive dietary restraint, the perception

that food intake is constantly being limited in an

effort to control body weight. Menstrual differences

between women with high and low restraint scores

were detected in a number of studies. One study

found that women with high restraint scores had

significantly shorter cycle lengths, shorter luteal-

phase lengths, and lower mean luteal-phase proges-

terone concentrations. In a group of women with

a wide range of physical activity levels who were

initially confirmed to ovulate normally, it was found

that the luteal-phase length was shorter, without

alteration of cycle length, in women with high re-

straint scores.

0006Cycle disturbances are associated with obesity as

well as with energy shortages. A high prevalence of

obesity among amenorrheic women was reported

many years ago, and anovulatory cycles appear to

be more common in obese women. Weight loss in

obese women results in improved ovulation and

pregnancy rates. It has been suggested that high

androstenedione concentrations observed in obese

women may activate the conversion of estradiol to

estrone in adipose tissue. Estrone in turn may

trigger higher luteinizing hormone concentrations,

leading to ovarian hyperstimulation, thus increasing

testosterone concentrations, resulting in anovulatory

cycles.

0007The Nurses Health Study in the USA has also

produced some interesting information about the

relative risk of menstrual cycle irregularity not only

in the underweight but also in the overweight

woman. For women with a body mass index (BMI)

below 20, at the age of 18 years, ovulatory infertility

was found with a relative risk of about 1.2 compared

to women with a BMI of 20–25. Interestingly,

however, the relative risk of ovulatory infertility

was 1.5 in those with a BMI of 28 and more than 2

in the obese group with a BMI above 30. About half

of the risk is associated with polycystic ovarian

syndrome, in which ovulatory infertility and obesity

coexist, but there is still a doubling in relative risk of

ovulatory infertility in women with a BMI above 30

who do not have ultrasonically detectable polycystic

ovaries.

MENSTRUAL CYCLE: NUTRITIONAL ASPECTS 3849

Energy Intake and the Menstrual Cycle

0008 The biological regulation of appetite is currently

an important topic in nutrition, because of its

relationship with the increasing burden of obesity.

Cyclical fluctuations in food intake occur in women

across the menstrual cycle, with a periovulatory nadir

and a peak in the luteal phase. These alterations in

food intake, in response to ovarian steroid hormone

changes, may be more than 2.5 MJ per day, with the

mean reported changes shown in 19 separate studies

of 1.0 MJ per day. Hormonally induced fluctuations

in food intake could, therefore, contribute to energy

imbalance and consequent weight gain. The regula-

tion of food intake by menstrual cycle hormones

suggests that it is essential to consider the phase of

the menstrual cycle in studies of nutrient intake per-

formed in women.

Vegetarian Women and the Menstrual

Cycle

0009 The question of whether menstrual disturbances are

more common in vegetarian than in nonvegetarian

women in complex. Three general mechanisms that

could contribute to menstrual disturbances that may

differ between vegetarians and nonvegetarians in-

clude energy imbalances associated with body-weight

disturbances or exercise, psychosocial and cognitive

factors, and dietary components. Although results

from several cross-sectional studies suggest that clin-

ical menstrual disturbances may be more common in

vegetarians, a prospective study that controlled for

many potential confounders found that subclinical

disturbances were less common in weight-stable,

healthy vegetarian women. Because the sample stud-

ied may not be representative of all vegetarian

women, however, these results cannot be generalized.

Population studies are needed to draw definitive

conclusions.

Effects of Exercise on the Menstrual

Cycle

0010 Several prospective studies have shown that men-

strual function does not change with exercise, pro-

vided that increases in activity are gradual, and body

weight is maintained. This suggests that adequate

energy availability may be a key factor in maintaining

normal hormonal function with exercise.

0011 A study was conducted to determine whether

rigorous exercise training adversely affects ovarian

hormone levels and bone health in cyclically menstru-

ating trained runners. Results indicated that lower

estrogen production, especially during the early

follicular phase, but not progesterone, was associated

with a lower whole body calcium per kilogram of soft

lean tissue and probably bone mineral density.

Dietary Components and the Menstrual

Cycle

0012Research suggests that concentrations of ovarian hor-

mones or their metabolites may be lower at various

points in the menstrual cycle in women consuming

diets high in fiber, low in fat, or both. This is con-

sistent with cross-sectional studies reporting inverse

associations between hormone concentrations and

fiber intake, direct associations between hormone con-

centrations and fat intake, and lower serum estrogen

concentrations with a faster intestinal transit. It also

corroborates the lower estradiol and progesterone con-

centrations observed in women 2 years after being

randomly assigned to a low-fat, high-carbohydrate

diet for a study in breast cancer risk reduction. How-

ever, the data must be interpreted cautiously because

many experimental studies were conducted over only

one or two menstrual cycles, and other data suggest

that changes observed acutely may not persist over

time. In addition, some subjects were free-living and

others were housed in metabolic wards, which could

affect the menstrual cycle differently.

0013Studies have been conducted to explore the effects

of two classes of phytoestrogens, lignans and isofla-

vones. One study examined the effects of flaxseed

powder, which is high in lignan precursors, in 18

women with normal ovulatory cycles using a ran-

domized, crossover design. Each women followed

her usual omnivorous, low-fiber diet for three cycles

and then followed her usual diet supplemented with

flaxseed powder for another three cycles. The last two

cycles of each dietary period were compared. During

flaxseed supplementation, luteal-phase lengths were

significantly longer, and the ratio of progesterone to

estradiol during the luteal phase was higher. More-

over, no anovulatory cycles occurred during flax-

seed supplementation, but three anovulatory cycles

occurred during the control diet period.

0014In another study, the effects of isoflavones were

examined in six women with regular ovulatory cycles.

It was found that diets containing 60 g of soy protein

per day (with 45 mg of isoflavones) significantly in-

creased follicular-phase length compared with con-

trol diets. Subsequently, they showed that a soybean

product from which the isoflavones had been ex-

tracted had no effect on the cycle. Thus, lignans and

isoflavones, two different classes of phytochemicals,

appeared to have different effects: flaxseed lignans

increased luteal-phase length and did not affect

follicular-phase length, whereas soybean isoflavones

3850 MENSTRUAL CYCLE: NUTRITIONAL ASPECTS

increased follicular-phase length but did not influence

luteal-phase length.

0015 Previous studies have suggested that high soybean

intakes are associated with lower concentrations of

serum cholesterol and may be related to decreased

rates of coronary artery disease, cancer, and osteopor-

osis. One of the postulated mechanisms of these

effects is that soy products, particularly the isofla-

vones in soy, act through changes in endogenous hor-

monal balance. Isoflavones significantly improved

the lipid profile across the menstrual cycle in normo-

cholesterolemic, premenopausal women. Although of

small magnitude, these effects could contribute to a

lower risk of developing coronary heart disease in

healthy women who consume soy over many years.

Relationship Between Diet, Menstrual

Hormones, and Breast Cancer

0016 There is compelling evidence linking ovarian hormo-

nal activity to breast cancer risk. Since the mid-1980s,

dietary fat intervention studies have been conducted

to investigate the effect of fat intake on endogenous

estrogen levels. A meta-analysis of dietary fat inter-

vention studies that investigated serum estradiol

levels reviewed the nature of the evidence provided

by prospective analytic studies of fat consumption

and breast cancer risk. Results indicated that dietary

fat reduction can result in a lowering of serum

estradiol levels and suggest that a low-fat high-

carbohydrate diet may reduce the risk of breast

cancer by reducing exposure to ovarian hormones

that are a stimulus to cell division in the breast.

0017 Intake of soybean protein is associated with a re-

duced risk of breast cancer in a case-control study. It

has also been demonstrated to increase menstrual

cycle length in an experimental setting.

0018 Most epidemiological studies of the relationship be-

tween alcohol consumption and breast cancer risk over

the past decade have shown that persons who consume

a moderate amount of alcohol are at 40–100% greater

risk of breast cancer than those who do not consume

alcohol. Dose–response effects have been observed, but

no causal relationship has been established. However,

it has also been shown that alcohol consumption in

premenopausal women is associated with increases in

total estrogen levels and amount of bioavailable estro-

gens. This may help to explain the relationship between

the risk of breast cancer and alcohol intake.

Dietary Contaminants and the Menstrual

Cycle

0019 Highly contaminated Lake Ontario sport fish re-

present an important human dietary exposure to

polychlorinated biphenyls (PCBs) and other toxic

contaminants that may disrupt endocrine pathways.

In one study, women anglers were interviewed by

telephone to determine menstrual cycle length and

fish consumption in order to calculate a PCB expos-

ure index. Multiple regression analyses identified sig-

nificant cycle-length reductions with consumption of

more than one fish meal per month and a moderate/

high estimated PCB index. Women who consumed

contaminated fish for 7 years or more also had

shorter cycles.

Menstrual Cycle and Iron-deficiency

Anemia

0020Menorrhagia (heavy menstrual bleeding) is a benign

yet debilitating social and health condition. The

widely accepted clinical definition of menorrhagia is

blood loss of 80 ml or more per period. This figure is

derived from population studies that have shown that

the average blood loss is between 30 and 40 ml, and

90% of women have blood losses of less than 80 ml.

Excessive menstrual bleeding is the commonest cause

of iron deficiency in the UK, affecting 20–25% of the

fertile female population. Menorrhagia is a common

problem accounting for 12% of all gynecological

referral in the UK.

Conclusion

0021The evidence presented above appears primarily to

show associations between dietary factors and the

menstrual cycle rather than causation. What does,

however, seem clear is that the relationship between

normal ovarian hormone function and diet is com-

plex and needs further evaluation from prospective

rather than epidemiological research studies.

See also: Anemia (Anaemia): Iron-deficiency Anemia;

Anorexia Nervosa; Bulimia Nervosa; Exercise:

Metabolic Requirements; Obesity: Etiology and

Diagnosis; Vegetarian Diets

Further Reading

Barnard ND, Scialli AR, Bertron P, Hurlock D, Edmonds K

and Talev L (2000) Effectiveness of a low-fat vegetarian

diet in altering serum lipids in healthy premenopausal

women. Randomized Controlled Trial. American

Journal of Cardiology 85(8): 969–972.

Barr SI (1999) Vegetarianism and menstrual cycle disturb-

ances: is there an association? American Journal of

Clinical Nutrition 70 (3 supplement): 549S–554S.

Boyd NF, Lockwood GA, Greenberg CV, Martin LJ and

Tritchler DL (1997) Effects of a low-fat high-carbohydrate

diet on plasma sex hormones in premenopausal women:

MENSTRUAL CYCLE: NUTRITIONAL ASPECTS 3851

results from a randomized controlled trial. Canadian Diet

and Breast Cancer Prevention Study Group. British Jour-

nal of Cancer 76(1): 127–135.

Bruinsma K and Taren DL (1999) Chocolate: food or drug?

Journal of the American Dietetic Association 99(10):

1249–1256.

Campbell WS, Franz C, Kahle L and Taylor PR (1996)

Relation of energy, fat, and fiber intakes to plasma con-

centrations of estrogens and androgens in premeno-

pausal women. American Journal of Clinical Nutrition

64(1): 25–31.

Doll H, Brown S, Thurston A and Vessey M (1989) Pyrid-

oxine (vitamin B

) and the premenstrual syndrome: a

randomized crossover trial. Journal of the Royal College

of General Practitioners 39(326): 364–368.

Eck LH, Klesges RC, Meyers AW, Slawson DL and Winders

SA (1997) Changes in food consumption and body

weight associated with smoking cessation across men-

strual cycle phase. Addictive Behaviors 22(6): 775–782.

Frisch RE (1994) The right weight: body fat, menarche and

fertility. Proceedings of the Nutrition Society 53(1):

113–129.

Gendall KA, Bulik CM, Joyce PR, McIntosh VV and Carter

FA (2000) Menstrual cycle irregularity in bulimia ner-

vosa. Associated factors and changes with treatment.

Journal of Psychosomatic Research 49(6): 409–415.

Jones DY, Judd JT, Taylor PR, Campbell WS and Nair PP

(1987) Influence of dietary fat on menstrual cycle and

menses length. Human Nutrition – Clinical Nutrition

41(5): 341–345.

Kato I, Toniolo P, Koenig KL et al. (1999) Epidemiologic

correlates with menstrual cycle length in middle aged

women. European Journal of Epidemiology 15(9):

809–814.

Lu LJ, Anderson KE, Grady JJ, Kohen F and Nagamani M

(2000) Decreased ovarian hormones during a soya diet:

implications for breast cancer prevention. Cancer

Research 60(15): 4112–4121.

McLean JA, Barr SI and Prior JC (2001) Cognitive dietary

restraint is associated with higher urinary cortisol excre-

tion in healthy premenopausal women. American Jour-

nal of Clinical Nutrition 73(1): 7–12.

Mendola P, Buck GM, Sever LE, Zielezny M and Vena JE

(1997) Consumption of PCB-contaminated freshwater

fish and shortened menstrual cycle length. American

Journal of Epidemiology 146(11): 955–960.

Norman RJ and Clark AM (1998) Obesity and reproduct-

ive disorders: a review. Reproduction, Fertility, & De-

velopment 10(1): 55–63.

Thys-Jacobs S (2000) Micronutrients and the premenstrual

syndrome: the case for calcium. Journal of the American

College of Nutrition 19(2): 220–227.

MERCURY

Contents

Properties and Determination

Toxicology

Properties and Determination

C J Cappon, Cappon Associates, Henrietta, NY, USA

This article is reproduced from Encyclopaedia of Food Science,

Introduction

0001 Mercury is probably the most ubiquitous heavy metal

in the environment, resulting from natural geological

activity and industrial pollution. Although it is ex-

tremely useful, it is also highly toxic, depending on its

specific chemical form. The hazards of mercury and

its compounds have been long known and of much

concern. Its history as an occupational hazard has

been linked to its elemental and divalent ionic – inor-

ganic – forms, mostly due to volatility and skin

contact. However, there has been much recent con-

cern for widespread environmental contamination

from organic mercury species, namely the alkylmer-

curies – methyl, ethyl-, and phenylmercury. Alkylmer-

cury poisoning has been almost exclusively linked to

methylmercury pollution of waterways and aquatic

food sources, specifically in Japan, Sweden, and

Canada. This has initiated several comprehensive

worldwide analytical surveys of foods to assess

human mercury intake levels and potential adverse

health effects. It has also highlighted the critical need

for more accurate and reliable mercury analytical

methods for a variety of materials. Most modern

methods involve mercury speciation separation

schemes. This article discusses the environmental

sources and toxicological impact of mercury in

food, with special emphasis on analytical speciation

3852 MERCURY/Properties and Determination

methodology – sample preparation procedures and

instrumental techniques.

Uses of Mercury

0002 Mercury has been utilized since antiquity. Although a

comparatively rare element – ranking 16th from the

bottom of natural element abundance – almost 3500

applications for mercury compounds are currently

recognized. The major uses of mercury are summar-

ized in Table 1.

Environmental Input and Speciation

0003 Mercury in food can come from natural or human

activities. Mercury from natural activities can enter

air, soil, and water via weathering, dissolution, vapor-

ization, and biological processes. Three oxidation

states are possible in nature: metallic (Hg

), mercur-

ous (Hg

2þ

), and mercuric (Hg

2þ

). The two main

categories of human mercury release are: (1) agricul-

ture – run-off of excess pesticide application and

absorption by vegetation roots and foliage; and (2)

industry – waste-water discharge, disposal of solid

waste containing mercury residues (thermometers,

fluorescent lamps, labware, paints), burning of coal

and petroleum-based materials.

0004 Table 2 lists the specific mercury species that have

been identified in air, soil, and water. Water is the

most significant and direct source of food mercury

contamination. Of special importance are the factors

which favor highly toxic methylmercury formation in

soil and water (including sediment), resulting in sub-

sequent uptake by edible vegetation and animal food

sources. In addition, biotransformation of methyl-

mercury from inorganic mercury (and vice versa)

can occur in specific marine and terrestrial food

animal species.

Occurrence and Speciation in Food

0005Mercury occurs in a wide variety of foods, most

commonly fish and seafood, where the typical total

mercury concentration range is 0.05–3.0 p.p.m.

(fresh weight). Grain and dairy products, animal

meats, and certain vegetable crops usually have a

lower and narrower range (0.01–0.05 p.p.m.). There

is no reported evidence of external mercury contam-

ination of food during processing, packaging, or stor-

age, so that food mercury content results solely from

the natural and human sources previously identified.

0006In the mid-1960s, methylmercury was identified as

the major mercury species in fresh-water and marine

fish. Since the early 1970s, several comprehensive

analytical surveys of total, inorganic, and methylmer-

cury content of fish and other types of seafood have

been undertaken. Methylmercury levels in the edible

fillet of most fish species is typically 70–95% of the

total mercury content. Methylmercury contents below

50% have been reported for a limited number of fish

samples. A notable example is Pacific blue marlin, the

only pelagic species having a large amount (> 80%)

of total muscle mercury present as inorganic com-

pounds. Inorganic mercury also predominates in

shellfish (molluscs, crustaceans) and other nonfish

species (e.g., octopus, squid). Other common organo-

mercurials – ethylmercury and phenylmercury – are

generally not found in seafood. (See Fish: Spoilage of

Seafood; Shellfish: Contamination and Spoilage

of Molluscs and Crustaceans.)

0007Mercury content and speciation have also been

reported for other food sources. Some examples in-

clude marine mammals (seal, whale), terrestrial wild

and domestic animals (chicken, otter, beaver, deer),

and vegetable crops. Regarding edible vegetation,

mercury uptake and methylmercury percentage are

enhanced in the tuberous and leafy regions of crops

grown on sludge- and compost-treated soil. Com-

pared to the relatively low mercury concentrations

in edible vegetation, mushrooms and related fungi

accumulate higher amounts of total mercury and

methylmercury.

0008Table 3 summarizes mercury levels and speciation

in a variety of foods.

Impact of Mercury in the Environment

0009Knowledge of mercury speciation is very critical

when evaluating the impact of environmental mer-

cury pollution and consumption of mercury-contam-

inated food, since different chemical forms of

tbl0001 Table 1 Uses of mercury

Dissipative Paints, agriculture, dental, catalyst,

pharmaceuticals, pulp and paper, metallurgy

and mining

Recyclable Chlorine and caustic soda production,

electrical, measurement, laboratory

tbl0002 Table 2 Environmental mercury contamination: input sources

Agriculture Fungicides and seed preservatives

Industrial Chlorine and caustic soda production;

amalgamation, pulp and paper preservative;

catalyst for plastic production,

pharmaceuticals (drugs, antiseptics); prints

(fungicide), electrical and measurement

instruments (thermometers, switches, neon

lamps); power production (coal burning)

Geological Weathering of rocks, volcanic activity

MERCURY/Properties and Determination 3853