CHEMICAL ANALYSIS AND ASSAY

III. CHEMICAL ANALYSIS AND ASSAY

A variety of factors dictates the effective use of acidulants not only in the food product, but also by the physical properties of the acidulant. Information on each of the acids discussed in this chapter is given in the Food Chemicals Codex (National Research Coun- cil, 1996). Supplements to the Codex are issued periodically to update contents. For each acid, the Codex provides its chemical description, specifications for identification and purity, guidelines for good manufacturing practices, general test methods, and notes on functional use in foods. Physical and chemical properties of the acids are presented in Table 1 .

The Official Methods of Analysis of the Association of Official Analytical Chemists International are used as the basis for conducting many assays for the various acids in foods (Cunniff, 1995; Helrich, 1990; Williams, 1984). Assays for organic acids in food- stuffs are generally carried out for three reasons: (1) the organic acid is a natural compo- nent of the product and therefore the assay is a quantitative or qualitative measure of wholesomeness or lack of adulteration or is a confirmation of the standard of identity for that product; (2) the acid is not normally present in the food product or is present at levels lower than that normally detected in a standard assay and serves as a measure of adultera- tion either through addition of the acid or fermentation of the substrate to form acidic byproducts; or (3) the organic acid is added to achieve a desired effect as regulated by good manufacturing practice.

In general, methods in common depend on the ease of separation of a specific acid from the food, the food product itself, and the desire for quantitative or qualitative results. For example, it is desirable to know the levels of acetic and propionic acids in breads and cakes, eggs, and seafood; citric, malic, and tartaric acids in wines, nonalcoholic beverages, fruit, and fruit products; lactic acid in wines, eggs, milk and milk products, fruits, and

Table 1 Physical and Chemical Properties of Organic Acids

Molecular

Solubility pK A. Acetic (monocarboxylic acid) (etha-

Acid (chemical name)

weight

Formula

60.05 C 2 H 4 O 2 Water, alcohol, glyc- 4.75 noic acid)

erol B. Acetate Salts

C 4 H 6 CaO 4 Water, sl. alcohol Calcium acetate Potassium acetate

98.14 C 2 H 3 KO 2 Water, alcohol Sodium acetate

82.03 C 2 H 3 NaO 2 Water, alcohol C. Dehydroacetic acid (methylaceto-

C 8 H 8 O 4 Sl. water, sl. alcohol 5.27 pyranone) D. Sodium diacetate (sodium hydrogen

C 4 H 7 NaO 4 Water 4.75 diacetate) E. Adipic (1,4-butane dicarboxylic

C 6 H 10 O 4 Sl. water, alcohol 4.43 acid) (hexanedioic)

5.41 F. Ascorbic acid

C 6 H 8 O 6 water, sl. alcohol 4.17 11.57 G. Caprylic (octanoic acid)

C 8 H 16 O 2 Sl. water, alcohol 4.89 H. Citric (2-hydroxy 1,2,3-propanetri-

C 6 H 8 O 7 Water, alcohol 3.14 carboxylic acid) ( β-hydroxytricar-

4.77 ballylic acid)

6.39 Calcium citrate

C 12 H 10 Ca 3 O 14 Sl. water Potassium citrate

C 6 H 5 K 3 O 7 H 20 Water Sodium citrate

C 6 H 5 Na 3 O 7 Water I. Fumaric (2-butenedioic acid)

C 4 H 4 O 4 Sl. water, alcohol 3.30 (trans-1,2-ethylenedicarboxylic

4.44 acid) Sodium stearyl fumarate

C 22 H 39 NaO 4 Almost insoluble, water J.

Lactic acid (2-hydroxypropionic 90.08 C 3 H 6 O 3 Water, alcohol 3.08 acid) (2-hydroxypropanoic acid) (1-hydroxyethane 1-carboxylic acid)

Water K.

Calcium lactate

C 6 H 10 CaO 6 H 2 O

Malic (1-hydroxy 1,2-ethanedicar-

C 4 H 6 O 5 Water, alcohol 3.4 boxylic acid) (hydroxy succinic

5.11 acid) (hydroxybutanedioic acid) L.

Propionic acid (propanoic acid) 74.08 C 3 H 6 O 2 Water, alcohol 4.87 Calcium propionate

C 6 H 10 CaO 4 Water Sodium propionate

96.07 C 3 H 5 NaO 2 Water, alcohol M. Succinic (1,4-butanedioic acid)

C 4 H 6 O 4 Water, alcohol 4.16 5.61

C 4 H 4 Na 2 O 4 Water N.

Sodium succinate

Tartaric (2,3-dihydroxysuccinic

C 4 H 6 O 6 Water, alcohol 2.98 acid)

4.34 Potassium acid tartrate

C 4 H 5 KO 6 Water, alcohol Sodium potassium tartrate

Water Sodium tartrate

C 4 H 4 KNaO 6 .4H 2 O

C 4 H 4 Na 2 O 6 Water Source : Budavari, 1996.

Enzymatic analysis for acetic, citric, dehydroacetic acid, isocitric, L- and D-lactic, L-malic, and succinic acids can be conducted to identify the acid (Bergmeyer, 1983). Acids can also be quantitated using thin layer chromatography (Tijan and Jansen, 1971), gas chromatography (Martin et al., 1971; Tsuji et al., 1986), high-performance liquid chro- matography (HPLC) (Bouzas, 1991; Marsili et al., 1981), and titrimetric or colorimetric methods (Nollett, 1996).