Attokaran M. Natural Food Flavors and Colorants

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36 General

Apart from these, many liquids usually used in food can be diluents. They include

ethyl alcohol, acetic acid, and glycerol. Even chemical liquids not associated with

natural foods but regarded as reasonably safe such as ethyl acetate, benzyl alcohol,

and isopropyl alcohol are used as a diluent in special cases.

Emulsiﬁ ers

Heterogeneity can appear due to the presence of lipophilic and hydrophilic com-

ponents. A similar case is when one wants to make an oily extract into a water - soluble

or water - dispersible emulsion. In some cases, emulsiﬁ ers can help solve the problem.

Emulsiﬁ ers are surfactants, which are useful as detergents, wetting agents, anti-

foaming agents, and so on. Such molecules will have a hydrophilic end (e.g., sodium

of a soap) and a lipophilic end (e.g., aliphatic end of a fatty acid). The hydrophilic/

lipophilic balance based on the structure of the molecule determines its efﬁ ciency to

function as an emulsiﬁ er. In an oil - in - water dispersion, the lipophilic end will be

attached to the oil droplet. Micelles are formed with oil droplets with surrounding

molecules of emulsiﬁ er with the hydrophilic ends outside in water. Such a system can

form a stable dispersion.

Emulsiﬁ ers are either oil - in - water or water - in - oil type. Based on the molecular

mass of the hydrophilic end and the mass of the whole molecule, the hydrophile/

lipophile balance (HLB) value of an emulsiﬁ er is ﬁ xed on an arbitrary scale of 0 – 20,

with 0 corresponding to a completely hydrophobic molecule and 20 corresponding to

a completely hydrophilic molecule. A good emulsiﬁ er for a water - in - oil type of emul-

sion will have an HLB value of 4 – 6, while an oil - in - water type will have an HLB

value of 8 – 18.

Some commonly used emulsiﬁ ers are presented below.

Polysorbates are excellent emulsiﬁ ers, which can be used to bring about water

solubility for spice oleoresins. It can be described as polyethylene glycol sorbitan

monooleate when it is supplied as polysorbate 80. While it is also supplied as deriva-

tives of saturated fatty acids for use in liquid spice extracts, the oleic acid derivative

is the most satisfactory. With unsaturated fatty acids, the HLB will be 10 – 16. The

oleic acid derivative is a yellowish viscous liquid. In recent years, some countries in

Europe, as well as Japan and Korea, have raised doubts about its safety, although it

is still legal to use it. (Polysorbate 80: FEMA 2917; CAS: 9005 - 65 - 6; US/CFR:

172.515; E - no. 432.)

DATEM , or diacetyl tartaric acid esters of mono - and diglycerides of fatty acid,

are partially soluble emulsiﬁ ers, which make oleoresins water dispersible. HLB for

DATEM will be 7 – 8.

Fatty acid esters of many polyhydric compounds are also emulsiﬁ ers. Of these,

sucrose esters of fatty acids are good emulsiﬁ ers with a high HLB value (7 – 16) and

polarity. (FEMA 4092; US/CFR: 182.1101; E - no. 472e.)

Glyceryl monooleate is a good emulsiﬁ er, especially to make lipid products more

dispersible in oil. During esteriﬁ cation of glycerol with a limited quantity of fatty

acids, generally about 20% will come as diglycerides and the rest as monoglycerides.

Therefore, these are sometimes referred to as mono - and diglycerides. For oleoresins

that are liquids, oleic esters are more suitable than esters of saturated acids. HLB for

10 Homogenization of Extracts 37

glyceryl monounsaturated fatty acid will be 3 – 4. (FEMA: 2526; CAS: 111 - 03 - 5; US/

CFR: 172.515; E - no. 471 [unsaturated].)

Glycerol - polyethylene glycol oxystearate (macrogol - glycerol hydroxyl stearate)

produced from hydrogenated castor oil is a new class of emulsiﬁ er, which is very

effective in making oily extracts water - soluble. Food laws of major countries have not

allowed this as yet. It is manufactured by BASF with the name Chremophor and by

ICI/Uniquema (now by Creda Chemical Co.) with the name Cresmer.

Lecithins are a complex mixture of phosphatides and glycolipids. They are obtained

from soy, corn, sunﬂ ower, and rapeseed. It comes as a cream - to brown - colored

viscous liquid. It increases miscibility in oil. The HLB will be around 3 – 4. (US/CFR:

184.1400; E - no. 322.)

Mechanical Homogenizers

Homogenization is a process that makes a solution or extract become uniform.

Chemical emulsiﬁ ers can do this to a point, but even when they are used, mechanical

homogenizers can complete the process more efﬁ ciently. Homogenizing can also help

to reduce the quantity of emulsiﬁ ers used.

In homogenization, pressure is used on liquids to subdivide the particles or droplets

present into even smaller particles. By breaking down liquid coagulates and globules

to submicron size, a stable dispersion can be created. In an ordinary household, the

same techniques are used when working with an egg beater or mortar and pestle. The

following are some of the techniques used in the food industry to obtain a stable

suspension of a dispersed liquid, generally thick, in the main product.

Colloid Mill

When a thick extract is heterogenous, the best way to bring it to homogeneity is by

passing it through a colloid mill. The action of a colloid mill is like the size reducing

of solids in a plate mill.

In a colloid mill, ﬂ uid shear is caused by a high - velocity stream to disperse particles

or liquid droplets. Small particles so formed will give a stable dispersion or emulsion.

Sometimes in addition to size reduction, weakly bonded agglomerates are disrupted.

The particle size of the globules will usually be below 5 μ g when stability is attained.

In a typical colloid mill, the feed liquid is fed through a hopper to pass through

closely spaced surfaces, one of which will be moving at a speed greater than that of

the other surface. One design involves liquid passing through a disk - shaped rotor and

casing, with the clearance being adjusted to below 20 μ m. To avoid heating due to

friction, cold water is circulated.

Ball Mill

This type of mill is generally used to reduce the size of hard brittle materials, like

minerals. However, moderate - sized mills can also be used to break the globules in

food extract into a small size to obtain homogenization. The action is more like a

mortar and pestle.

Since the materials handled are food items, a stainless steel drum has to be used

with heavy ceramic balls. A typical ball mill used for homogenization of black pepper

38 General

oleoresin consists of a stainless steel horizontal drum, which can rotate on a horizontal

axis. A large opening is provided for introducing the ceramic balls inside. From a point

opposite to the main opening, another opening with a tap is provided to withdraw the

homogenized liquid product. A convenient size is about 1000 - L capacity, ﬁ lled to

about one - third capacity with 1000 kg of ceramic balls of 30 - mm diameter. About

500 – 600 kg of oleoresin is poured from the main opening, which will ﬁ ll about half

the drum containing the balls. The drum and its contents are rotated using a motor.

The speed and duration of revolution can be adjusted according to the nature of the

extract to be homogenized.

Sand Mill

The modern pressurized horizontal sand mill is a natural extension of the ball mill for

use as a homogenizer. In a sand mill, there are a series of disks rotating at high periph-

eral speed. The centrifugal force transmits the power, making small glass beads (1.5 - to

2.0 - mm size) rotate inside a jacketed chamber. The movement of beads closer to the

disk is greater than that of those further inside. When the slurry passes through such

a system, the globules are broken down by shear caused by differential rotational

velocities of the beads. The speed of rotation and packing of beads can be adjusted

according to the viscosity of the product slurry and nature of the globules. The equip-

ment can also be used to homogenize fractions of different densities.

Pressure Homogenizer

Various well - known brands of pressure homogenizers of different capacities are avail-

able. In this, the product to be homogenized is passed at a very high pressure through

a specially designed homogenizing valve with an adjustable gap. The design will

include a single - acting reciprocating multiple pump to force the liquid through the

valve. The pressure created on striking a stationary surface is able to break globules

to micron - sized droplets.

This type of homogenizer is particularly useful to homogenize liquid slurries of

water, ﬂ avor extracts, and hydrocolloids used for spray drying. When oily extracts

are made water - soluble or dispersible by use of an emulsiﬁ er, passing through a pre-

ssure homogenizer will improve efﬁ ciency and decrease the quantity of emulsiﬁ er

required.

Sediments and Impurities

Sometimes oily extracts may contain unwanted thick globules. If these globules tend

to settle to the bottom, then a super centrifuge will be useful. In a super centrifuge,

slightly heavier globules will be collected in the central collection tube, while clariﬁ ed

material will pass through the outlet. In capsicum and paprika oleoresins, this is a nice

way to get a clear product free of sediments. In aqueous coffee and tea extracts, there

can also be sediments that can be clariﬁ ed by super centrifuge.

When the impurities are of solid nature and in larger quantity, they can be ﬁ ltered

away. A basket centrifuge with appropriate ﬁ lter cloth will be satisfactory. Filtration

by basket centrifuge will be considerably cheaper than a super centrifuge where the

separation is based on gravity.

10 Homogenization of Extracts 39

Water Solubilization

Many natural ﬂ avors and colors obtained by extraction with organic solvents are

mostly lipid in nature and have very low dispersibility in water. Water solubility or

dispersibility can be introduced using emulsiﬁ ers. Polysorbates are satisfactory for

this purpose. In some cases, only a temporary dispersibility is required, since after

this, the intermediate product is taken for secondary processing. In such cases, a lesser

quantity of emulsiﬁ er is required, or a less efﬁ cient one like DATEM can be used.

Needless to say, in all these cases, mechanical homogenizing will be beneﬁ cial.

When the lipid extracts are required to be in an aqueous phase with plenty of solids,

as in bread dough, oily extracts can be used without emulsiﬁ ers, because the solids

will help in making the dispersion stable.

In the past, constituents that have a carboxylic or hydroxyl group were converted

to a potassium or sodium derivative to introduce water solubility. With efﬁ cient emul-

siﬁ ers available today, the trend is to avoid the use of alkali in food processing.

Size reduction of the dispersed phase by mechanical homogenization is the key to

obtaining a stable colloidal solution. Additionally, the use of an emulsiﬁ er will be very

beneﬁ cial.

Diluents such as propylene glycol with solubility in both water and oil are not

emulsiﬁ ers, but they can be used judiciously to reduce the quantity of more expensive

emulsiﬁ er to be used.

Many extractives like essential oils, oleoresins, and color extracts are oily liquids. For

some applications, these must be made into a solid powder. Two methods of suspen-

sion in solid matrix are plating and microencapsulation by spray drying.

Plating

When an oleoresin has to be made into solid suspension for use in solid food products

like cookies, cakes, or other bakery items, it can be mixed with an appropriate percent-

age of a solid that will not interfere with the ﬁ nal food. Sugar, dextrose, salt, corn or

other cereal ﬂ our, and rusk powder can be used. The appropriate amount of ﬂ avor

extract is mixed with any of the above in powder form. The ﬂ avor strength will be

lower per unit weight.

If a mild water dispersibility is desired, then maltodextrin or other modiﬁ ed starch

will be helpful. An emulsiﬁ er like polysorbate can also be added to increase the water

solubility of the plated powder. Mixing is very important for uniform spread and

avoidance of lumps.

Microencapsulation by Spray Drying

Microencapsulation is a process in which tiny particles or droplets are surrounded by

a coating to produce very small capsules with many useful properties. It is a special-

ized form of edible packaging of a food ingredient. Of course, the material used to

form the protective packaging must be safe for eating.

In its simplest form, a microcapsule is a tiny sphere having a uniform wall and

with a hollow inside to hold a droplet of the desired ingredient. The material inside

is referred to as the “ core ” and the protective outside sphere as the “ wall. ” Generally,

the particle size ranges between 1 and 200 μ m.

Many ﬂ avors and extracts used in candies, soup powders, other foods, and cosmet-

ics are liable to be subjected to oxidative deterioration and loss due to evaporation.

For example, if cardamom oil is blended with tea to be ﬁ lled in a tea bag, the volatile

oil will be lost gradually by evaporation. If the oil is protected by microencapsulation,

this will not happen during a speciﬁ ed shelf life. When the bag is dipped in hot water

at the time of consumption, only then will the volatile oil be released, giving the rich

ﬂ avor of cardamom to the tea.

One of the most successful methods of microencapsulation is spray drying. The

ﬁ rst step in microencapsulation is to make a colloidal suspension of the core material

Suspension in Solids 11

Natural Food Flavors and Colorants Mathew Attokaran

42 General

in an aqueous solution of wall material. Two classic wall materials are maltodextrin

and gum acacia. Both of these give emulsion with low viscosity capable of being

pumped through the atomizer of the spray dryer. Of the two wall materials mentioned

above, gum acacia is more efﬁ cient; maltodextrin is cheaper. In fact, among the natu-

rally occurring gums or hydrocolloids, gum acacia has the lowest viscosity in solution

form. Recently, some specialized starch - based gums have been made available for use

in spray drying with greater efﬁ ciency.

A typical mixture of various ingredients taken for homogenization can be as

follows: water 70 L, gum acacia 22.5 kg, and oil (such as cardamom oil) 7.5 kg. Oil

represents 25% of the mixture other than water, which will be evaporated. In the ﬁ nal

spray - dried powder, oil will be less than 25% due to loss. Maltodextrin gives a much

lower loading in the ﬁ nal powder, while higher loading can be obtained by special

modiﬁ ed starch designed for spray drying. This mixture, after being stirred with a

ladle, is passed through a pressure homogenizer where a stable colloid will be formed.

Each colloid particle will consist of a droplet of core material surrounded by an

aqueous solution of the wall material. When such a suspension is passed through the

atomizer of the spray dryer, each colloidal particle will dry into a powder. As explained

earlier, the powder will consist of a central core of volatile oil surrounded by a spheri-

cal dry wall formed by the evaporation of water during the passage through the hot

zone of the spray dryer.

Lipophilic materials like essential oil and oleoresins when spray dried with modi-

ﬁ ed starch or gum acacia will become easily water - soluble. When viscous products

like oleoresin are to be spray dried, for the stability of colloid suspension, it may be

necessary to add an emulsiﬁ er such as polysorbate, in addition to the hydrocolloid, to

the slurry.

In some materials like coffee extract, which is soluble in water, there is no

colloid formation. Very small quantities of coffee extract, in the form of tiny droplets,

when sprayed will dry to tiny particles. In this case, there is no wall or core to be

discerned.

Spray Drying

A spray dryer is a device used for converting a liquid solution or suspension of an

extract or other ingredient into a dry powder. Usually, since the liquid passes through

the drying zone as spray particles, drying will be effected in only a few seconds.

The main part of the spray dryer is a tall metallic cylindrical chamber with a conical

bottom. The upper zone is kept hot by admitting hot air from an external furnace. The

inlet temperature will be around 185 – 195 ° C and the outlet temperature generally

around 90 – 95 ° C, depending on the material to be dried. At the top end, there is an

arrangement to spray a water solution or a suspension of the material to be spray dried.

Spraying is done using a pump, which will allow liquid to be sent through a nozzle

in the form of a spray. Depending on the material to be sprayed and ﬁ nal particle size

desired, there are many designs of nozzles. As the sprayed drops fall down and pass

through the hot zone in the upper section of the chamber, they are dried by the removal

of moisture to form solid particles. Other features of the equipment are an opening at

the bottom for removal of dried particles collected at the conical section, insulation

11 Suspension in Solids 43

of the chamber to avoid heat loss, and a tapping or vibrating device to encourage

particles to fall into the bottom of the cone. An outlet is provided at the bottom for

an airstream carrying moisture to escape through a cyclone or a bag ﬁ lter to recover

any escaping spray - dried product. Instead of two points of collection of the product,

modiﬁ cations can be made to have a single point of collection. It may be a good idea

to make an air - conditioned or dehumidiﬁ ed enclosure around the withdrawal opening

at the bottom to protect the hygroscopic powder.

A moderately sized spray dryer will have a chamber of about 3 m in diameter and

6 m in height, half of which will be the conical bottom. The angle of the cone side to

perpendicular will be around 60 ° . The chamber must be made of stainless steel when

the spray - dried material is used in food.

The heart of the equipment is the nozzle through which the colloidal solution of

the slurry is sprayed. A high - speed rotary atomizer revolving at a speed of 15,000 –

35,000 revolutions per minute, with cocurrent swirling action, will yield a ﬁ ne powder.

A high - pressure nozzle at the top yields a coarser powder. Here, the spray is directed

downward with less swirling. For this, a much thinner and taller chamber will be

suitable. There are many specialized nozzles depending on the material and nature of

the powder required. One such is the two - ﬂ uid nozzle ﬁ xed at the middle portion of

the chamber. Here, air and slurry to be dried are sprayed upward.

The size of the powder particle is important. This depends on the food material

with which the microencapsulated product is to be mixed. For example, if the tea

particles are larger, a comparable size of spray - dried particles will be required to regu-

late the desired proportion during the ﬁ lling of the tea bags. Fine spray - dried instant

coffee tends to form lumps while dissolving in water. The above defects can be cor-

rected by increasing the size of particles by a technique known as agglomeration. In

this process, particles are critically wetted and made to stick together by collision

caused by the turbulence introduced. When particles adhere to form the desired size,

it is made into a nonsticky agglomerate by drying.

During the storage of plant products like spices, if drying is not carried out properly,

there is a chance of fungus contamination. This could lead to a musty ﬂ avor, which

will be transferred to the extractives. An even greater danger in the case of extensive

contamination is the possibility of formation of mycotoxins. When plant material is

partially dried and stored, there is the danger of loss of color in products like chili and

cardamom. Excessive exposure to sunlight can also cause loss of color, especially in

the case of curcumin of turmeric and chlorophyll. Carotenoid pigments are also

affected by light, though to a lesser extent.

During processing, there can also be chemical changes. Heat treatment of extract

of paprika, marigold, and tomato gives traces of toluene and m - xytene (Rios et al.

2008 ). A temperature of 80 ° C and below during processing ensures that these artifacts

are indeed very low. The presence of other compounds such as methyl benzaldehydes

or isophorones indicates carotenoid oxidation.

Formation of breakaway small molecules is a possibility when complicated mol-

ecules, such as those in ﬂ avoring materials, are subjected to processing. The presence

of toluene and acetone has been reported in ginger (Chen and Ho 1988 ). This may

not be a case of thermal degradation, as the study is on the extract of freeze - dried

ginger powder by liquid carbon dioxide. Benzene and toluene have been noticed in

another study on ginger oil (Erler et al. 1988 ). In turmeric extraction, acetone has been

detected even when no acetone was used for extraction (Binu et al . 2007 ). The damage

may be due to the heating carried out during estimation itself. Oleoresin analysts are

sometimes intrigued by the presence of an unaccounted - for quantity of residual

methanol.

In the case of ginger oleoresin, excessive heat, above 80 ° C, may result in gingerols

being converted to shogaols. Gingerol content is important when ginger oleoresin is

used for pharmaceutical purposes. In such cases, there is a need to restrict the tem-

perature of processing, preferably below 70 ° C, but never above 80 ° C.

When the two - stage extraction procedure was introduced in India, there was fear

that piperine would be lost due to prolonged heating during the ﬁ rst stage of the steam

distillation step to recover volatile oil. To remove the moisture prior to the second

stage of solvent extraction, some manufacturers resorted to sun drying. However,

experience has shown that if shade drying is used, there is no noticeable loss of

piperine.

Loss of xanthophylls occurs during heat treatment of extracts such as paprika and

marigold. Curcumin of turmeric is remarkably stable during the heating carried out

Deterioration During Storage

and Processing

Natural Food Flavors and Colorants Mathew Attokaran