Attokaran M. Natural Food Flavors and Colorants

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236 Individual Flavors and Colorants

leaves can vary from 2 to 30 cm in length and 1 – 15 cm in breadth. Leaves at the bottom

are larger than those at the top. The ﬂ owers are yellow - green in color and are small,

with a diameter of 3 – 4 mm, and mature into a small, hard, dry, lumpy cluster, which

contains many seeds.

Spinach is rich in various vitamins and some minerals especially iron. There are

many varieties of spinach, as it is a favorite food all over the world, mainly for its

nutritive value. It is the leaf that is the valuable product.

Recently, a method to produce chlorophyll a from spinach leaves has been devel-

oped using solvent extraction and column chromatography. From 100 g of freeze - dried

leaves, 23 – 24 mg of chlorophyll a can be obtained (Dikio and Isabirye 2008 ).

Alfalfa

Alfalfa is a ﬂ owering plant belonging to the pea family and used as an important

forage crop. Its primary use is for the feeding of dairy cattle because of its nutritive

value. It is an important legume and is even harvested as hay. It is considered to be a

crop that encourages lactation. The tender shoots are sometimes consumed as a leafy

vegetable. Like other legumes, its root systems have nodules that house bacteria

capable of nitrogen ﬁ xing.

Plant Material

Alfalfa is a cool season perennial plant with a life of 3 – 12 years depending on variety

and climate. The plant grows to a height of 1 m. Its deep root system makes it very

adaptable in drought conditions. The crop exhibits autotoxicity and is therefore rotated

with other plants like corn or wheat.

Mulberry

Fresh mulberry leaves are eaten by silkworms. In the early twentieth century, silk

production ceased in Europe, though it has spread to Asia, in China, India, and

Thailand. The Chinese used mulberry leaves a source of chlorophyll, since they are

available because of silkworm culture. India also has a thriving silk industry, but

production of chlorophyll is somewhat limited. Use of mulberry leaves has brought

down the cost of chlorophyll. When silkworms consume the leaves, they metabolize

only protein, carbohydrates, and fat. The chlorophyll is excreted out. The excreta yield

chlorophyllin with a higher concentration and greater purity. Some Chinese producers

have incorporated this into their technology, but the idea of using excreta as raw mate-

rial is not well accepted. Fresh leaves are the best raw material. Mulberry seems to

be replacing other sources, such as spinach and alfalfa, as a cost - effective raw

material.

Plant Material

Mulberry is a genus of several species of deciduous tree grown in tropical and sub-

tropical regions of the world, particularly in Asia. The mulberry tree grows very fast

at ﬁ rst but growth slows; a height of 10 – 15 m is attained. The leaves are alternate and

simple. They are serrated on the edge and are lobed, more so while young.

59 Green Leaves 237

The fruit of the mulberry tree is really a multiple fruit which when immature is

white, pale yellow, or green, but turns red when ripening and dark purple when fully

ripened. The fruits, which are 2 – 3 cm in length, are edible, sweet, and have a good

ﬂ avor. The fruit contains anthocyanins, which give its color. There are also white

mulberry fruits. Although Morus alba is the most common plant, there are several

plants in the same genus. Naturally, there are some variations in the description of

plant material. It is the leaf that is used as a source of chlorophyll.

Chlorophyll: Chemistry

Chlorophyll is responsible for the green color of plants, especially the leaves. It helps

the plant synthesize carbohydrates by absorbing energy from sunlight. The building

units of these carbohydrates are carbon dioxide and water. For this purpose, in the leaf

chlorophyll is positioned between layers of lipids and proteins, all of which form the

chloroplast. The chloroplast is held close to the cell wall along with some carotenes

and xanthophylls.

The German scientist Richard Martin Willstatter won the 1915 Nobel Prize for his

pioneering work on chlorophyll ’ s structure and properties. The total synthesis of

chlorophyll by Nobel laureate Robert Burns Woodward about 50 years ago was a

signiﬁ cant milestone in the history of synthetic organic chemistry. Chlorophyll is a

large molecule consisting of tetrapyrrole unit chelated by a magnesium iron placed in

the center of the molecule. It has a long side chain phytol esteriﬁ ed to the tetrapyrrole

unit. In addition, the central unit has small side groups including a methyl ester and

some carbon side chains. There are two types of chlorophyll. In chlorophyll a, R is

methyl, while in b, it is an aldehyde group.

This chapter is primarily limited to chlorophyll ’ s use as a food color. For further

details of this chemistry and function in photosynthesis, readers are advised to refer

to the large number of books and reviews available on the subject.

Extractives

Chlorophyll extraction reached its zenith during the days when chlorophyll toothpaste

was very popular. The earlier raw material of spinach, which is a human food, was

replaced by alfalfa, mainly a cattle feed and a cheaper raw material. But with the

decline in chlorophyll toothpaste, the pigment lost its purpose. Chinese and, to a

limited extent, Indian manufacturers have started making the pigment at a much

cheaper price by using mulberry leaves as the starting material.

Chlorophyll extract, being a natural pigment, is approved in the food laws of many

countries. A satisfactory extraction solvent is a mixture of acetone and hexane in the

ratio of 70:30. Acetone enables the solvent to enter the cells and the mixture can be

extracted from dried ground leaves fairly well. Unfortunately, chlorophyll has poor

stability. It was in the days of chlorophyll toothpaste that copperization was developed

as a way of obtaining stability and intensity of green color. In fact, the present method

of making chlorophyll extract is mainly based on the steps developed in the United

States in the ﬁ rst half of the twentieth century (Judah 1954 ). These steps include

extraction, saponiﬁ cation, and reaction with copper sulfate to produce copper

chlorophyllin.

238 Individual Flavors and Colorants

A simple, general method of making copper chlorophyllin is given as follows.

Dried, cut mulberry leaves are extracted by gravity percolation at ambient temperature

using a mixture of acetone and hexane in the ratio 70:30. The combined miscella is

desolventized at a temperature not exceeding 60 ° C to obtain chlorophyll extract.

The extract is saponiﬁ ed using 1 N methanolic potassium hydroxide at 70 ° C by

reﬂ uxing for 1 hour. The amount of 1 N alkali used is 75% by weight of the chlorophyll

extract. The resultant mass is neutralized with 1 N hydrochloric acid. The neutralized

material is made into a copper derivative by stirring well with 5% aqueous copper

sulfate. The mixture is kept for 24 hours to complete the reaction. The watery layer is

removed to obtain copper chlorophyllin as a deep green, thick mass (Fig. 59.1 ). This

may be washed with water to remove excess free copper.

The result is a dark green, oily liquid with a mild herbaceous odor. The product is

soluble in oil. It can be made water - soluble by using additives such as propylene glycol

and polysorbate. Chlorophyll, after extraction and saponiﬁ cation, can be made into

iron or magnesium chlorophyllin by using ferric chloride or magnesium chloride,

respectively. Magnesium treatment is done for the latter because of possible distur-

bance during saponiﬁ cation.

There are minor variations in the procedure, adopted by different people. In the

early U.S. process, there was a provision to recover the xanthophylls that invariably

associate with chlorophyll. The Chinese currently recover phytol, which is a raw

material for the synthesis of vitamins such as tocopherol and vitamin K.

Uses

Chlorophyll has a unique natural green color which can be used in foods, especially

those which do not need heat treatment, such as ice cream and other chilled food

products. Chlorophyll ’ s limitation is its poor stability and low intensity of color.

Figure 59.1. Chlorophyllin.

59 Green Leaves 239

Copper chlorophyllin has excellent intensity of color and stability. Wherever food

laws allow, it can be used as a green color. Copper chlorophyllin is only a seminatural

color because of copperization. It has an E - number and is approved for use in the

United States. Copper chlorophyllin can be used in food, cosmetics, and toiletries,

including toothpaste.

Analytical Method

Chlorophyll content including that of raw material can be determined by the AOAC

method of spectrophotometric measurement after extraction.

For copper chlorophyllin, one method that is used for chlorophyll toothpaste

involves mixing the samples with polysorbate 80 so it is in water - soluble form, then

measuring the absorbance at 405 wavelength.

Chlorophyllin content

Absorbance 1000 5

565 weight (g) 2

××

Identiﬁ cation Numbers

FEMA No. CAS US/CFR E - No.

Spinach extract – 68917 - 48 - 6 – –

Alfalfa extract 2013 84082 - 36 - 0 182.20 –

Chlorophyll – – – E140

Copper chlorophyll – – – E141

Chlorophyll copper complex – – – E141 (i)

Chlorophyll copper complex

}

– – – E141 (ii)

Sodium and potassium salt

References

Dikio , E.D. and Isabirye , D.A. 2008 . Isolation of chlorophyll a from spinach leaves . Bull. Chem. Soc.

Ethiop. 22 ( 2 ), 301 – 304 .

Judah , Melvin A. 1954 . Chlorophyll. A staff industry collaborative report . Ind. Eng. Chem. 46 ( 11 ),

2262 – 2271 .

Introduction

Hops are the female ﬂ ower cluster referred to as cones or strobiles of a plant generally

grown in the northern hemisphere. The extract of hops is used as a ﬂ avor and stabilizer

of beer.

It is believed that over 2000 years ago, Germans began using hops as a beer ﬂ avor,

an art which they learned from the tribal people of Finland. About 1000 years ago, an

Arabian physician claimed that use of hops helps to induce sleep and improve the

nervous system. This is a belief still prevalent among some people. Benedictine monks

used to cultivate the hops plant to be used as a spice and in salads. Many early

Europeans found hops to be a useful vegetable for salads. There are historical records

of its cultivation and use in beer in sixteenth - century England. Later, it was introduced

to the United States (Farrell 1990 ).

Plant Material

The hop plant is a vigorous, climbing, herbaceous perennial usually grown on strings

or wires. A commercially cultivated ﬁ eld is called a hop ﬁ eld, hop garden, or hop yard.

Although it is sometimes referred to as a vine, the hop plant does not use tendrils or

sucker roots to attach itself to the support. It has stout stems with stiff hairs that help

it climb on the support. The length of the climber can be as high as 10 – 15 m, always

twisting clockwise on the support, though the height is also dependent on the support

that is available.

The peculiarity of the plant is that female and male ﬂ owers are borne on separate

plants. The female ﬂ owers are important for ﬂ avoring purposes. Leaves are opposite

with a petiole that is 6 – 12 cm in length. The leaves are palmately lobed blades of

12 – 25 cm in length. The leaves are broad, with edges which are vaguely toothed. When

there is no more support for climbing, horizontal shoots sprout between leaves of the

main stem to form a complicated network of stems, which wind around each other.

Because female ﬂ owers are important and the plant is vegetatively propagated, the

male plants are often cut off if plants are grown using seeds. This way the pollination

and seed formation can be avoided. Seed formation is regarded as undesirable for

ﬂ avoring in beer. Harvesting of female ﬂ ower cobs is labor - intensive, so today harvest-

ing is done mechanically.

Hops

Humulus lupulus L ( Urticaceae )

241

Natural Food Flavors and Colorants Mathew Attokaran

242 Individual Flavors and Colorants

The major producers of hops in the world are Germany (about 38%), the United

States (about 26%), and China (about 12%), of the total annual production of

90,000 tonnes. East European countries, especially the Czech Republic (about 9%),

and the United Kingdom and Spain are other producers.

Varieties

Each variety of hops gives the beer of the region speciﬁ c organoleptic characteristics.

Pale beers of Continental Europe (Germany, Austria, Czech) use “ Noble ” hop varieties

such as Saaz Hallertan, Spalt, and Tettnanger. They give the low bitterness reﬂ ected

in European beers and are primarily used for their aroma. On the other hand, English

varieties such as Fuggle and East Kent have resemblance to Noble hops, but they have

better bittering capacity as they age. Recently, seven varieties of hops cultivated in

China have been analyzed for α - acids, β - acids, cohumulone, and essential oil com-

position. Qingdaodahua and Qilinfenglu are bitter varieties, and Yulebite and Fubei - 1

are aroma varieties and have better brew qualities (Zhao et al. 1999 ). Similarly, a wide

range of varieties of hops have been analyzed in America. Their speciﬁ c characteristics

are studied with reference to trace compounds and characteristics (Hampton et al.

2002 ).

Bitterness and Aroma

Hops have two types of acids which inﬂ uence the bitterness and aroma they impart

to the beer. α - Acids contribute to bitterness. They are composed of humulone and the

related compounds of cohumulone, adhumulone, prehumulone, and posthumulone.

β - Acids, on the other hand, have lupulone and other allied compounds such as colu-

pulone and adlupulone (Leung and Foster 1996 ). α - Acids isomerize during boiling

with wort, making them soluble and capable of making the product bitter. On the other

hand, β - acids do not isomerize during boiling and therefore have a low effect on bit-

terness. High β - acid hops are used for their aroma.

There are two types of hops: bitterness - contributing and aroma - contributing.

Naturally, bittering hops have a higher α - acid content. Noble hops have an α - acid

content of 5 – 9%. The newly developed American hops have 8 – 19% α - acids. Aroma

hops with very mild bitterness have below 5% α - acid and contribute less to bitterness

and more toward aroma.

Essential Oil

Hops generally contain 0.3 – 1% of volatile oil. Compounds such as humulene, α -

caryophyllene, myrcene, β - caryophyllene, and farnesene account for 90% of the

essential oil. There are more than 100 compounds that ultimately contribute to the

aroma - giving oil (Leung and Foster 1996 ).

Harvested hops are dried in kilns at a temperature not more than 66 ° C. When dried,

hops will have a moisture content of about 10%. On steam distillation, a green, slightly

acrid oil of hops is obtained with a yield of about 0.5% (Farrell 1990 ). The main

constituents are myrcene and humulene, with low amounts of lupelone, xanthohumol,

ceryl alcohol, lactaric acid, dipentene, caryophyllene, linalool, and methyl nonyl

ketone.

60 Hops 243

According to the FCC, hops oil is a light yellow to green - yellow liquid with hops ’

characteristic aromatic odor. On aging, the oil darkens and becomes viscous. It is

soluble in most ﬁ xed oils and with opalescence in mineral oil. It is practically insoluble

in glycerin and in propylene glycol. It is a ﬂ avoring oil.

Physical constants as per FCC are as follows.

Optical rotation − 2 ° to − 2 ° 5 ′

Refractive index 1.470 – 1.494 at 20 ° C

Speciﬁ c gravity 0.825 – 0.926

Solubility 1 mL usually is not soluble in 95% alcohol; older oils are less

soluble than fresh oil

Extract

For convenience of handling, hops are available in extract form. One extraction pro-

cedure involves use of pure ethyl alcohol by percolation (Bisnel 1995 – 2009 ). The

extract, which is rich in lupulin, is then boiled in water for an hour followed by strain-

ing and washing. The alcoholic and water extract is freed of the solvent by evaporation

at low temperature into thick material.

Supercritical carbon dioxide extract of hops creates characteristics useful for the

production of beer. All useful ingredients, such as α - acid, β - acid, and aroma oil are

obtained very satisfactorily. One of the advantages of supercritical carbon dioxide

extraction is that speciﬁ city of extraction can be obtained by manipulating the pres-

sure. Since there are different valuable constituents and some undesirable constituents

such as resin, tannins, fats, and waxes, supercritical ﬂ uid extraction is especially suited

for hops.

Uses

The main use of hops is to ﬂ avor beer. They contribute to bitterness and, in some

cases, to aroma. Generally, there are specialized varieties for this. However, dual - use

hops are now available.

Hops are also used in some soft drinks, as well as to ﬂ avor confectionery, tobacco,

baked products, chewing gum, and some pharmaceutical preparations. Hops are also

used in herbal medicines as a treatment for anxiety and restlessness. A pillow ﬁ lled

with hops is a popular folk medicine remedy for sleeplessness. Hop shoots are also

sometimes used in salads and soups where the bitterness is welcome.

Identiﬁ cation Numbers

FEMA No. CAS US/CFR E - No.

Hops oil 2580 8007 - 04 - 3 182.20 –

Hops extract 2578 8060 - 28 - 4 182.20 –

Hops extract solid 2579 8060 - 28 - 4 182.20 –

Hops absolute – 8060 - 46 - 5 – –

244 Individual Flavors and Colorants

References

Henriette Kress.

Farrell , Kenneth T. 1990 . Spices, Condiments and Seasonings . New York : Chapman and Hall , pp.

108 – 110 .

Hampton , Richard ; Nickerson , Gail ; Whitney , Peggy ; and Haunold , Alfred . 2002 . Comparative chemical

attributes of native North American hops, Humulus lupulus , var. lupuloids, E. Small . Phytochemistry 61

( 7 ), 855 – 862 .

Leung , Albert Y. ; and Foster , Steven . 1996 . Encyclopedia of Common Natural Ingredients . New York : John

Wiley and Sons , pp. 300 – 302 .

Zhao , Suhua ; Liu , Kuifang ; Liu , Gang ; Zhang , Lingyi ; and Li , Yanping . 1999 . Study on chemical constitu-

ents and nature of seven varieties of hop in Xinjiang . Shipin Yu Fajiao Gongye 25 ( 5 ), 11 – 14 (Chinese)

( Chem. Abstr. 132:264358).

Introduction

Hyssop is referred to in many ancient books and therefore must have been a highly

regarded herb and medicine. There is mention of it in quotes connected with Moses,

Solomon, and Christ. It has been in use in European Mediterranean countries long

before Christ. Hyssop is mentioned in the Torah and is believed to have been used in

early rituals of the Catholic Church. The name “ hyssop ” is probably derived from

Greek, although it may have Hebrew origins. Hyssop belongs to the mint family and

is grown in gardens as a decorative plant.

Plant Material

Hyssop grows wild in some Mediterranean countries. It is cultivated in Europe, espe-

cially in the south of France, as an herb. It is also cultivated in some Middle Eastern

countries and Himalayan slopes as a commercial crop.

The plant thrives in light, rich soils of temperate regions. It is propagated by seeds,

cuttings, and divisions. It is a hardy evergreen shrub which grows to a height of 60 cm.

The leaves are opposite and very narrow and oblong, 2 – 6 cm long. In the summer, the

plant produces purple - blue ﬂ owers which are borne on the upper parts of the branches

clustered around leaf axils. The herb has a camphor - like spicy aroma and has a bitter

but pleasant mint - like taste.

Harvesting is done best on a dry day when the herb has reached full maturity so

that it will have the highest oil content and aroma characteristics. The best time for

harvesting is just before the ﬂ owers open. They should be dried in the shade without

delay, so that their ﬂ avor is retained. With good air circulation at a temperature below

32 ° C, the herb should be dried within a week; longer duration may result in a loss of

color and aroma.

The herb contains fat, carbohydrates, and polyphenols. It has small amounts of

carotene, xanthophylls, and the antioxidant ursolic acid. The fresh herb is reported to

contain iodine.

Essential Oil

The aerial part of the plant, on steam distillation, yields an essential oil. The yield of

oil from the dried herb is only 0.3 – 0.8%.

Hyssop

Hyssopus ofﬁ cinalis L ( Labiatae )

245

Natural Food Flavors and Colorants Mathew Attokaran