Encapsulation and Controlled Release of Food Ingredients - American

Chapter 5

Acacia Gums Natural Encapsulation Agent for Food Ingredients

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F. Thevenet Colloides Naturels International, 129 Chemin de Croisset, BP 4151, 76723 Rouen, France

Gum acacia, also called gum arabic, is a natural hydrocolloid produced by natural exudation of Acacia trees. This hydrosoluble gum has the unique property of being soluble at very high concentration in water, up to 50%. Recent studies have confirmed the presence of three fractions in the gum structure, each with its own properties. Studies have been conducted to investigate acacia gum as a protective film in citrus oil encapsulation. The stability and volatile compound retention after accelerated oxidation are shown. Also discussed are the analytical results on a citral and linalylacetate emulsion that was dried on acacia gum using two different drying techniques.

Acacia gums, also known as gum Arabic, are defined as "the gummy exudate flowing naturally or obtained by incision of the trunk and branches of Acacia Senegal and other species:. There are many acacia species (over 700) of which few are able to provide the amount of gum required for industrial production (25,000 to 30,000 tons/year). Acacia gums which are used as food additives belong to two botanical complexes following the Bentham and Vassal classification. These are the Series Gummiferae (Acacia Seyal Complex) and Series Vulgares (Acacia Senegal Complex).

Structure of Acacia Gum The chemical structure of these two families shows a comparable quantitative analysis. After hydrolysis in acidic medium, the high pressure liquid chromatography

0097-6156/95/0590-0051$12.00/0 © 1995 American Chemical Society In Encapsulation and Controlled Release of Food Ingredients; Risch, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

52

ENCAPSULATION

reveals the presence of the same simple sugars, galactose, arabinose, rhamnose and glucuronic acids. The percentages are slightly different from Gummiferae and Vulgares. Low rhamnose content and a ratio of arabinose: rhamnose higher that one are characteristic from Seyal complex. Although the protein content of Seyal complex is lower than the Senegal complex, the amino acid composition is the same. The amino acids present in the largest percentages are serine and hydroxyproline. The viscosity of the Seyal complex is normally lower than that of the Senegal Downloaded by STANFORD UNIV GREEN LIBR on September 23, 2012 | http://pubs.acs.org Publication Date: March 24, 1995 | doi: 10.1021/bk-1995-0590.ch005

complex. The highly ramified structure of acacia gums makes the gum Arabic soluble in water at up to 50% concentration. This is very rare for this type of hydrocolloid. Comparative viscosities between various colloids (1% concentration) using a Brookfield R V T at 20 RPM are shown in Table I (7). Table I. COMPARATIVE VISCOSITIES B E T W E E N VARIOUS COLLOIDS Solution at 1% concentration in water Brookfield R V T 20 R P M Guar

3,500 cps

Locust bean

3,000 cps

Xanthan

3,000 cps

Gum arabic

5 cps

The latest structural studies indicate the multimolecular structure of acacia gum.

It is an association of various fractions with different molecular weights. The 5

arabinogalactan (AG) fraction is the low molecular weight fraction (3.0 χ 10 ) and has a low protein content (0.5%). A G represents about 90% of the gum molecule. The 6

arabinogalactan protein fraction (AGP) has a high molecular weight (1.5 χ 10 ) and a high protein content (10%). It makes up less than 10% of the molecule. The glycoprotein (GP)fractionhas a very high protein content (50%) and a low molecular 5

weight (2.5 χ 10 ). It makes up about 1% of the molecule. The proposed structure of gum acacia Senegal is shown in Figure 1. The representation of the acacia gum molecule following the Wattle Blossom model (2) is supported by the gel permeation chromatography (GPC) profiles published by Osman et al (5). The Wattle Blossom model depicts a long chain protein support that serves as the linkage between arabinogalactan units.

Structure and Properties Relationship For the emulsifying properties, the most interesting parts of the molecule are the AGP and GPfractionscontaining a high percentage of proteins. These proteins act as an interface between oil and water. It should be noted that the amino acid composition (serine and hydroxyproline) of the proteins is hydrophobic. In Encapsulation and Controlled Release of Food Ingredients; Risch, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

In Encapsulation and Controlled Release of Food Ingredients; Risch, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

•

GAL —

ARA — •

•

GAL

X

X

\

G A L - — G Le A - — RHA f ARA — ARA

\

ARA

GAL

ARA

GAL — - GAL — * GAL — GAL — GAL — GAL — • • V G A L — - ARA — • G A L - — ARA X ARA — - G A L - — ARA f GAL V GLcA f '** G A L — ARA — G A L GLcA f ARA t RHA RHA Fig. 1-Modern hypothesis of the structure of gum Acacia Senegal.

—

ARA

J

—

GAL - —

\

ARA

GAL

GAL

\

— - GAL — -

ARA

MoGLcA

GAL

I

ARA

I

GAL


GAL

54

ENCAPSULATION

The glucuronic acids which are partially salified and partially nephylated, develop negative charges that surround an oil particle in an emulsion. The ideal diameter of the oil droplet is one micron. There is a charge repulsion which helps stabilization. The AGP fraction has a high viscosity which slows down the motion of oil particles and will help prevent agglomeration of the oil droplets. The film forming properties of acacia gum comesfromthe arabinogalactan fraction. The low viscosity and consequently high solubility of this portion is likely Downloaded by STANFORD UNIV GREEN LIBR on September 23, 2012 | http://pubs.acs.org Publication Date: March 24, 1995 | doi: 10.1021/bk-1995-0590.ch005

responsible for the barrier film that is formed after the evaporation of water.

Applications of Gum Acacia Acacia gum is widely used in the food and pharmaceutical industries. It is the know how of the gum industry to develop special varieties of acacia exudates that will have an internal structure that will be best for the final use of the gums. A wide variety of acacia gums in purified form are now availble, each having its own application. Texturizing, film forming, emulsifying and binding properties are the main characteristics specific to acacia gums. They are also used as a carrier when it is desired to have a product that is non-cariogenic, low in calQric value and/or is a good source of soluble fiber. In confectionery, the acacia gums are used as texturizing agents in products such as gum drops, gum pastilles and wine gums. They can also be used in association with modified starches or gelatin to modify the final texture. All types of texture can be obtained with the acacia gums giving a product that will not stick to peoples' teeth in addition to having a long lasting good flavor release. As a film forming colloid, acacia gum is used to isolate the centers in dragées. Peanut or chocolate centers in candy can be coated with a gum syrup to avoid oxidation of the fat or migration of the fat through the sugar coating. Either hard or soft coatings can be made. In the flavor industry, acacia gums are used for two primary applications. These are as a stabilizer for the concentrate used for soft drink manufacture (oil in water emulsion) and as a protective carrier for spray drying liposoluble and sensitive products. The process summary for soft drink applications is shown in Figure 2. The association of the tensoactive properties of the gum in combination with the mechanicalfractionationof the oil phase are keys for a good stability of the concentrate and the final dilute beverage.

Recent Research Different types of products including citrus flavors, vegetable fat, oleoresins, coloring agents and vitamins can be encapsulated. Analytical work on orange oil encapsulated with various acacia gums has been published by Risch and Reineccius (4). This work has been continued by Colloïdes Naturels International and Reineccius In Encapsulation and Controlled Release of Food Ingredients; Risch, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.


tests for stability microscopic centrifugation dilution —

Fig. 2-Emulsion for soft drinks.

soft drink

oil globules = 1μ

-conceLate

homogeneization under pressure - 180-230 Kg/cm2

dilution (1 to 1.5 g/liter) with carbonated water-sugar (100 to 130 g/liter) citric acid (2 g/liter) (color possible).

oil-flavors (4 to 8%) + resin (4 to 8%) + / - color +/- weighting agent

water (qs 100%) + acacia gums (5 to 20%)

\

liposoluble phase

hydrosoluble phase

- prm-emulsion mix oil globules = 5u



56

ENCAPSULATION

(University of Minnesota, 1990, personal communication) using a more complex oil system encapsulated with conventional spray drying on a blend of acacia gum and maltodextrins. The tests conducted included emulsion stability, spray dry flavor retention and oxidative stability of the orange oil. A modified starch was used for comparisons. Four different ratios of acacia gum to maltodextrin were used. These were 1:0, 1:1, 1:3 and 1:5. The blends were hydrated overnight to make 40% solutions. A flavor blend comprised of 2% each of ethyl propionate, ethyl butyrate, ethyl caproate, benzaldehyde and cinnamic acid in orange oil was prepared just before making the emulsion. Prior to spray drying, emuslions were prepared by mixing 20% flavor blend into the hydrated gum/maltodextrin blends with a high shear mixer. Spray drying was done using a Niro spray drier with an inlet air temperature of 200 ± 5 C and an exit air temperature of 100 ± 5 C. Emulsion Stability. The stability of the emulsions was determined by centrifugation. Spray dried powder we diluted in water (3 g per liter) and centrifuged. After centrifugation, the absorbance at 400 nm was determined. The results are shown in Figure 3. The addition of maltodextrins to the acacia gum tends to result in a small decrease in the initial absorbance and this trend held generally throughout centrifugation. It is known that the acacia gums suitable for stabilization of a liquid emulsion are not the best for encapsulation and vice versa. Acacia gum behavior in liquid form (oil in water emulsion) and in powder form (coating in dry film) is not the equivalent for the same gum. Flavor Retention During Spray Drying. The flavor retention was determined by a gas chromatographic method. The more volatile compounds (ethyl propionate and ethyl butyrate) were lost to a greater extent than the less volatile compounds as shown in Figure 4. The blend of one part spray dried gum acacia and one part maltodextrins showed excellent retention of volatiles. There was a general trend that retention of volatiles decreased as the proportion of maltodextrins increased. The modified starch gave flavor retention that was inferior to the 1:1 blend of acacia gum and maltodextrins. Oxidative Stability. The oxidative stability of orange oil was monitored using gas chromatography to measure the formation of limonene oxide with time. Samples were stored in an incubator at 37 C. The results are shown in Figure 5. The modified starch shows significant oxidative changes in the orange oil during storage. The orange oil was stable to oxidation in the pure gum acacia as well as in the gum acacia/maltodextrin blends. This agrees with the previous work which has been done to compare the protective effect of various species of acacia gums. It appears that a 1:1 ratio of acacia gum to maltodextrin will yield a flavor in the powder form that has almost the same stability as pure acacia gum as the carrier. In Encapsulation and Controlled Release of Food Ingredients; Risch, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

Acacia Gums


THEVENET

Fig. 4-Flavor retention of spray drying.


58

ENCAPSULATION


4 Π

Storage

Time

(days)

Fig. 5-Oxidative stability of orange oil prepared from different matrices.

Alternative Drying Technique The use of maltodextrins decreases the cost of the carrier and allows spray drying at higher infeed solids because of the lower viscosity of the emulsion. In view of spray drying at a higher solids concentration, Bhandri et al (5) have recently studied a spray drying system able to dry liquids at very high viscosity. This is referred to as the Leaflash technique. In Leaflash spray drying, hot air flows at a very high velocity in the dryer. This hot air converges at the dryer head and simultaneously atomizes and dries the resultant atomized droplets. This system uses very hot air (300 to 400 C) and is able to dry very viscous liquids at high dry solids contents. In the work, they used various emulsions that were prepared using blends of acacia gum and maltodextrins into which a mixture of citral and linalyl acetate (80/20) was emulsified using homoginization under pressure. The emulsion was prepared at 50% dry solids. The air temperature of the Leaflash was 350 C and the outlet temperature was 105 C. The viscosity of the emulsions is shown in Table II. Table II. Viscosity of Gum Acacia and Maltodextrin Blends % Gum Acacia

% Maltodextrins

Viscositv

100

0

10,000 cps

60

40

3,000 cps

40

60

1,700 cps

20

80

255 cps

0

100

105 cps

SOURCE: Adapted from ref. 5.


5. THEVENET

Acacia Gums

59


They reported that the retention of volatiles, as determined by hydrodistillation, was higher in the samples with a higher gum content. (5) Acacia gums have been used in the food industry for many years for their unique texturizing, film forming and stabilizing properties. A better knowledge of the botanical species in conjunction with a sophisticated purification process allows a selection of the harvested grades to provide a continuity of quality of the gum. The research in the past few years into the complex structure of the acacia gum molecule has led the way to development of gums for specific needs. Literature Cited 1. Thevenet, F. In Flavor Encapsulation; Risch, S.J and Reineccius, G.A., Eds.;ACS Symposium Series 370; American Chemical Society: Washington, D.C., 1988; pp 38-44. 2. Stene, G.B.; Clarke A.E. Annual Rev. Plant Physiol. 1983, vol 34, pp. 47 - 70. 3. Osman, M.E.; Williams, P.E.; Menzies, A.R.; Phillips, G.O. J. Ag. Food Chem. 1993, vol. 41, pp. 71-77. 4. Risch, S.J.; Reineccius, G.A. Perf.Flav. 1990, vol. 15, no. 4, pp 55-58. 5. Bhandari, B.R.; Dumoulin, E.D.; Richard, H.M.J.; Moleau, I.; Lebert, A . M . J. Fd. Sci. 1992, vol. 57, pp 217-221. RECEIVED November 17,

1994


Encapsulation and Controlled Release of Food Ingredients - American

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