The global market for food additives is expected to ex- ceed $33.9 billion by 2015. The major constituents of ad- ditives market include acidulants, fat replacers, sweeteners, vitamins, minerals, colorants, flavors, flavor enhancers, hy- drocoloids, emulsifiers, preservatives inclusive of antimicro- bial, antioxidants, and enzymes (www.prweb.com 2011). The market trend shows a growth trajectory toward low-calorie, low-fat, natural foods that contain natural additives or no ad- ditives. The strongest growth section will include vitamins and minerals. There is an increasing demand for natural fla- vors and colors at the expense of synthetics. Similarly, the demand for natural antioxidants over synthetic ones is grow- ing. The use of hydrocolloids as fat substitutes along with enhanced growth in artificial sweeteners may dominate the proceedings in the food industry based on food additives. As far as the preservatives are concerned, the sector may further grow from its current position of 2%, as Latin American, Asian, and Eastern European countries may continue their quest toward foods with longer shelf life. There is a grow- ing demand for ethnic flavors, particularly as ingredients in preprepared dressings for salads to restrict microbiological contaminants otherwise originating from spice ingredients (Mannikes 1992).
The demand for food additives in various sectors varies considerably depending on consumer requirements of differ- ent countries. The level of utilization also differs within vari- ous food-manufacturing sectors depending on the functional requirements of such applications, viz, solubility, thermal and light stability, and compatibility with human metabolism (Robach 1980).
The demand for food additives is primarily distributed among the three sectors: commodity processing sector, phar- maceuticals and drugs sector, and the food manufacturing sector (Fig. 12.1). The blenders and bulk suppliers play a major role in coordinating the overall blending, repackag- ing, and distribution to the utility sectors. The commod- ity suppliers are the sources of primary and secondary- processed, value-added commodities such as purees and juice concentrates for the manufacturing sector as such, which may be termed as tertiary processing, during which fruit ingredients are used as per the standards of identity (21 CFR 150.160).
Of the two phases of fruit product manufacturing, i.e., com- modity processing and ultimate fruit product manufacturing,
the use of additives is more in the second phase, accounting for nearly 60–70% of total food additives used in the fruit- based industries. Among unit operations carried out in com- modity processing, operations such as extraction/refining, clarification, and concentration require the bulk of the ad- ditives, while formulating, extrusion, freezing, dehydration, and fermentation involve their intensive use for the product manufacture (Somogyi 1996).
The use of additives in fruit processing is expected to grow especially in the areas such as artificial sweeteners, flavors, and texturizing agents. However, the regulations are expected to be more stringent, necessitating the need for more empha- sis on the use of natural ingredients, such as natural colors, flavors, and preservatives, which qualify to be in the GRAS list (Robach 1980). The nutritional additives may gain an increased demand, as fruit-based functional foods are likely to constitute a major food category.
Acidulants
Fruit processing as such involves physical, biochemical, and microbial stabilization of the processed products. Acidifica- tion has been in practice and its origin dates back to the onset of human civilization. Oriental preserves, such as fermented vegetable products and pickles, indicate the preservation po- tential of acidulants. Fruit and vegetable products are the major ones to use acidification, as the sensory value of the product is not impaired and the taste is improved as a result of flavor enhancement (Gardner 1972). In fruit products, acid- ification is usually accompanied by adjustment of the total soluble solids so that the Brix/acid value is comparable to that of fresh fruits. An adjustment in the Brix–acid ratio has been found to take care of the sensory perception, enabling a variety of fruit products to undergo acidification and have the advantages such as preservative and antioxidative effects.
The oriental vegetable products such as pickles require a characteristic sourness/tartness to attain an optimal sensory value. The advantages of acidification can be best utilized by an understanding of product profile and an appropriate acidu- lant can be selected to obtain the optimal sensory perception and shelf life of the finished product (Dziezak 1990).
Selection of Acidulants Regulatory Considerations
1. The GRAS nature of the acidulant needs to be ascer- tained. The GRAS substances may be used in foods not covered by standards of identity and which do not have restrictions on their usage levels, provided GMPs are followed.
2. If the acidulant is covered as a food additive, as in the case of fumaric acid, it has to be regulated by the food additive regulation.
Pharma &
cosmetic manufacturers
Food additive manufacturer
Primary processing
Secondary processing (Fruit-based processed ingredients) Concentrates Stabilized purees Colors
Flavors Flavoring agents
Stabilizers Emulsions Acidulants Preservatives Colorants
Bulk suppliers of additives
Export & domestic markets
Allied food industry (confectionery &
dairy) Value-added fruit
product manufacturers (Tertiary processing) Dehydrated & glazed fruits
Fruit preserves Canned fruits Fruit-flavored carbonated beverages Squashes & nectar Jams, jellies &
marmalades Frozen fruits Structured fruits Fruit pies
Catering service Export market Domestic market Figure 12.1. Utility profile of additives in fruit processing.
3. For foods covered by standards of identity, the maxi- mum levels prescribed need to be followed.
4. If any local regulations exist, they should be considered while selecting an acidulant.
Functional Considerations
1. Effect of acidulant on the overall product profile.
2. Matching of solubility characteristics with the process conditions and acidulant concentrations required.
3. Hygroscopic characteristic requirements of dry mixes.
4. Suitability of the acidulant to impart an optimal level of tartness at the functional pH.
5. Physical form and particle size for application in dry mixes.
6. Screening of several acidulants based on feedback from the market/user for optimum product applications.
Functions
Different acidulants offer a host of functional diversity in var- ious food applications, but primarily as antimicrobial (Levine and Fellers 1940) and flavoring (Hartwig and McDaniel 1995). The major functions of acidulants are
1. Flavoring to provide a desired taste and intensity, which enhances, blends, or modifies the overall flavor of the product?
2. Reduction in pH to prevent or retard the growth of mi- croorganisms as well as germination of spores and to increase the lethality of the process.
3. Maintenance or establishment of pH through buffering action. Usually, a combination of free acids and salts are used.
4. Chelation of metal ions to assist in minimizing lipid oxidation (Cu and Fe), reducing color changes, and controlling texture of some fruits and vegetables.
5. Alteration of the structure of foods including gels made from gums (pectin and carrageenan) and proteins.
6. Modification of sugar crystallization in hard candy manufacture.
Mechanism of Action
At equal concentrations, the acidulants vary in their ability to depress pH and the degree/intensity of the tartness pro- duced. The percentage required to replace anhydrous citric acid varies from 55% to 60% in case of phosphoric acid, 67–72% for fumaric acid, 80–85% for tartaric acid, 78–83%
for malic acid, and 110–115% for adipic acid. The use of glucono-delta-lactone (GDL) is gaining popularity due to the novel features such as slow hydrolysis and mild acid flavor.
In fruit processing, acidulants are used extensively and the Brix–acid ratio is maintained at appropriate levels to opti- mize the sensory perceptions. The products include nectars, squashes, jams, and jellies (Seiferi 1992).
The other function of acidulants is preservation and safety assurance. In 1970s, considerable research took place on the action of organic acids on the microbial cell at the molecular level. The mode of action of an acid was related to the undis- sociated portion of the molecule (Huntur and Segel 1973).
This action is deemed more important than any other exter- nal change in pH brought about by the addition of acids.
The undissociated moiety of a weak acid penetrates rapidly to the interior of the cell because of its lipid solubility and discharges the gradient diffusion through the plasma mem- brane and dissociates internally. The dissociated forms of weak acids, on the other hand, could not be absorbed by microorganisms to any great extent.
Murdock (1950) found that citric acid inhibited the flat- sour organisms isolated from tomato juice, and this inhibition appeared to be related to the inherent pH of the product. Cit- ric acid, rather than acetic or lactic acids, also inhibited ther- mophilic bacteria (Fabian and Graham 1953). In addition to the pH-lowering effects of citric acid, a secondary inhibitory effect is attributed to the chelation of essential minerals. It is believed that inhibition may have been attributable to chela- tion of essential metal ions by citrate rather than inherent acid inhibition. Chelation has also been believed to be an influencing factor in inhibiting the growth ofStaphylococcus aureus(Rammell 1962). There have been a number of studies that have attributed the antimicrobial activity of citric acid to the chelation of metal ions, which are essential for microbial growth (Beuchat and Golden 1989).
Citric acid is also used conventionally as a synergist for antioxidants and to retard browning reaction. Usage levels for citric acid have been found to be 0.1–0.3% with an antioxi- dant level of 100–200 ppm (Dziezak 1986). The specialized uses include the function as a gelling agent. The structured fruits can be taken as an example to illustrate the specific aspect. Alginates are gelled with calcium salts under acidic pH (Kaletunc et al. 1990). Pectinacious fruits are largely sub-
jected to structuring using a variety of acidulants, especially GDL.
Range of Products
A wide variety of fruit-based products possess acidulants as a direct food additive:
1. Beverages
a. Fruit-flavored carbonated beverages b. Fruit-flavored noncarbonated beverages c. Beverage powders
d. Low-calorie beverages (diet beverages).
Among the above mentioned products, fruit- flavored carbonated beverages are the recent ones.
Usually, these beverages are made with 10% nat- ural juices for health-conscious consumers. Citric and malic acids are used in fruit-flavored carbonated beverages. Tartaric acid is generally used in lime- flavored beverages. The noncarbonated beverages include fruit drinks, nectars, and isotonic beverages as “thirst quenchers.” Fruit-flavored dry beverages make use of acidulants such as citric, malic, and fumaric acids for imparting tartness along with the release of carbon dioxide from carbonate salts of sodium and calcium. Fruit-flavored diet beverages yielding 50% fewer calories than comparable prod- ucts make use of acidulants to control pH of the beverage so that desired sweetness characteristics can be achieved (Dziezak 1990).
2. Candies, structured fruits, and fruit gums: A wide variety of acidulants are used in these fruit-based products. Fruit-flavored candies are popular products and several patents exist in this area (Dwivedi 2003).
The candied fruit products are extruded in a ribbon/belt format, capable of being extruded and rolled on to it to form a candy roll. The product as such includes sweeteners, fruit flavors, binders, water, stabilizers, and acidulants. Fassin and Bachmueller (2000) described the manufacture of fruit gum confectionary, based on the preparation of fruit gum mass by heating water, sweetener, gelling agent, acidulants, flavorings, and fruit/vegetable extracts.
In the case of structured fruits, GDL has been used as an acidulant to prepare structured hydrocolloid gels with fruit pulp and sugar as the major ingredients (Nussinovitch et al. 1991). Apple sauce and grape juice concentrates have been texturized to obtain gelled prod- ucts with excellent consistency using GDL as an acidu- lant and gelling agent to liberate calcium from calcium hydrogen phosphate that ultimately caused the gelation of the product (Kaletunc et al. 1990).
3. Thermal processed fruits: Acidulants are also widely used in thermally processed fruit and vegetable prod- ucts. In the canning process, citric, lactic, malic, and
Table 12.2. Physical and Functional Characteristics of Major Acidulants Used in Fruit Processing
No. CFR Physical Form Pka
Range of Application in
Fruit Industry Taste Type of Products 1. Citric acid 184.1033
(GRAS)
Crystalline powder
3.14 4.77 6.39
Very high A burst of tartness
Carbonated and noncarbonated beverages
Wines, jams, and jellies Desserts and fruit
squashes Canned and frozen
products 2. Fumaric
acid
172.350 (food additive)
White granules or crystalline powder
3.03 4.44
Low Tart Frozen concentrates
Cider and apple drinks
3. Malic acid 184.1069 (GRAS)
Crystalline powder
3.4 5.11
Medium Smooth
tartness
Fruit-flavored sodas 4. Phosphoric
acid
182.1073 (GRAS)
Liquid 2.12
7.21 12.67
Low Acrid Buffering agent in jams
and jellies
5. GDL 184.1318
(GRAS)
White crystalline powder
3.7 Medium Neutral taste
acidic paste upon hydrolysis
Salad dressings
6. Tartaric acid
182.1073 (GRAS)
Crystalline powder
2.98 4.34
Medium Extremely tart Cranberry and grape-flavored fruits Jams and jellies 7. Acetic acid 184.1009
(GRAS)
Clear colorless liquid
4.75 High Tart and sour Pickled fruits
other organic acids are used to lower pH to 4.6 or below. This addition allows lower temperatures and shorter processing times to be used for the inhibition of sporulation and growth of microorganisms without any loss of flavor, color, and texture in the finished product (Rajashekhara et al. 2000).
Commonly Used Acidulants
The most commonly used acidulants are acetic acid, citric acid, malic acid, phosphoric acid, fumaric acid, and tartaric acid. The physical and functional characteristics of the com- monly used acidulants are described in Table 12.2. Except fumaric acid, the other acidulants are GRAS. Citric, malic, and acetic acids are widely used in canned and frozen prod- ucts, fruit-flavored carbonated and noncarbonated beverages, jams, jellies, and pickled fruits. Sudden burst of tartness is a major characteristic of acidulants such as citric acid, and the use of GDL is gaining increasing popularity to overcome the problem.
Glucono-Delta-Lactone It is an inner and neutral ester of gluconic acid and gets hydrolyzed in aqueous solutions to form gluconic acid (Fig. 12.2). Gluconic acid is a natural
constituent of juices and honey and an intermediate in glu- cose oxidation. The functionality involves slow hydrolysis under moist conditions, resulting in a gradual and continu- ous decrease in pH. At the end of hydrolysis, equilibrium mixture exists, consisting of gluconic acid as well as delta- and gamma-lactones. The rate of acid formation increases
O
O C
O C C
H H
C
HO HO
OH
OH C
H H
H
OH OH
OH H C C C
CH2OH C H
Hydrolysis Dehydration
C OH H
CH2OH Glucono-delta-lactone Gluconic acid Figure 12.2. Hydrolysis of glucono-delta-lactone.
with temperature and the intensity of acidification depends on the concentration of GDL and the temperature.
The slow rates of acidification by GDL and its mild taste set it apart from other acidulants. The use of GDL is gaining increasing popularity. In case of fruit products apart from the juices, it is widely used in jellies and structured fruits. The relatively higher cost of GDL is a drawback for its exten- sive use in lieu of acidulants such as citric and malic acids (Montinez et al. 1997).