The most commonly used acidulants are acetic acid, citric acid, malic acid, phosphoric acid, fumaric acid, and tartaric acid. The physical and functional char- acteristics of the commonly used acidulants are de- scribed in Table 9.2. Except fumaric acid, the other acidulants are generally recognized as safe (GRAS).
Table 9.2. Physical and Functional Characteristics of Major Acidulants Used in Fruit Processing
Range of Appln in
Physical Fruit
No. CFR Form PKa Industry Taste Type of Products
1. Citric acid 184.1033 (GRAS)
Crystalline powder
3.14 Very high A burst of tartness Carbonated and noncarbonated beverages 4.77 6.39
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 Low Tart Frozen
concentrates 4.44
Cider and apple drinks 3. Malic acid 184.1069 (GRAS) Crystalline powder 3.4 Medium Smooth tartness Fruit-flavored sodas 5.11 4. Phosphoric acid 182.1073 (GRAS)
Liquid 2.12 Low Acrid Buffering agent in
jams and jellies 7.21 12.67 5. GDL 184.1318 (GRAS) White crystalline powder
3.7 Medium Neutral taste acidic paste upon hy- drolysis Salad dressings 6. Tartaric acid 182.1073 (GRAS) Crystalline powder 2.98 Medium Extremely tart Cranberry and grape-flavored fruits 4.34
Jams and jellies 7 Acetic acid 184.1009
(GRAS)
Clear colorless liquid
4.75 High Tart and sour
Pickled fruits
Citric, malic, and acetic acids are widely used in a va- riety of fruit products inclusive of canned and frozen products, fruit-flavored carbonated and noncarbon- ated beverages, jams, jellies, and pickled fruits. Sud- den burst of tartness is a major characteristic of acidu- lants such as citric acid, and the use of GDL is gaining increasing popularity to overcome the problem. Glucono-Delta-Lactone (GDL)
It is an inner and neutral ester of gluconic acid and gets hydrolyzed in aqueous solutions to form glu- conic acid (Fig. 9.2). Gluconic acid is a natural
constituent of juices and honey and an intermedi- ate in glucose oxidation. The functionality involves slow hydrolysis under moist conditions, resulting in a gradual and continuous 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 with tempera- ture and the intensity of acidification depend 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
9 Food Additives in Fruit Processing 155 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 OH C H CH2OH
Glucono-deltalactone Gluconic acid
Figure 9.2. Hydrolysis of glucono-delta-latone.
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 extensive use in lieu of acidulants such as citric and malic acids (Montinez et al., 1997).
PRESERVATIVES
The preservative category of food additives is a large group encompassing a number of functionali- ties. Though the basic understanding of preservatives is about their antimicrobial activity, it encompasses other functions such as antioxidation and antibrown- ing activities. Chemical preservatives are defined by FDA (1979) as “any chemical that when added to food tends to prevent or retard deterioration but does not include common salt, sugars, vinegars, spices and oils extracted from spices, substances added to food by direct exposure thereof to wood smoke, or chemi- cals applied for their respective insecticidal or herbi- cidal properties.” The antioxidants and antibrowning agents constitute the preservatives responsible for re- stricting the chemical deterioration of the products, whereas the antimicrobials are responsible for the protection from biological hazards. Often the syn- ergistic effects of antioxidants with antimicrobials could give the best result in terms of shelf life (Bra- nen et al., 1980).
During fruit processing a number of antimicro- bials, antioxidants, and antibrowning agents are used as additives. The number of antimicrobials approved for use in food is remarkably limited. The primary
food additives cited in FDA are (1) sodium ben- zoate, (2) calcium and sodium propionates, (3) sorbic acid and potassium sorbate, and (4) parabens. These preservatives are often used in combination with other methods of preservation such as refrigeration, freezing, and dehydration to obtain better control of deleterious organisms. Certain important preserva- tives such as organic acids and sulfites are multifunc- tional and their functionalities include preservation as well as antioxidation and antibrowning activities.
Antimicrobials
Selection of Antimicrobials
The selection of antimicrobials has to be carried out appropriately to obtain the best possible preservative function. The following criteria need to be followed for the selection of approximately 30 compounds, which can legally be used as antimicrobials in food products (Fulton, 1981):
1. Antimicrobial and chemical properties of the com- pound.
2. Composition of the target food.
3. The type of preservation technique adopted for the product.
4. The type and quantum of microbiological load. 5. The safety and regulatory aspects of the antimi-
crobial for use in the specific product. 6. Cost effectiveness of the antimicrobials.
Mode of Action
1. The mode of action of antimicrobials can be either bactericidal or bacteriostatic and generally falls into one of the following categories (Davidson et al., 2002).
2. Reaction with the cell membrane causing in- creased permeability and loss of cellular con- stituents.
3. Inactivation of essential enzymes. 4. Destruction of functional activity.