Plant Composition

Hundreds of compounds have been identified in Vaccinium. They are divided into several main classes, which are discussed in this section.

Sugars

Two main carbohydrates occur in Vaccinium berries, glucose (1-3%) and fructose (0.5-2%) (1,2). In cranberry, glucose occurs in a much higher amount than fructose; this is unusual because usually fructose and glucose occur in equal amounts.

Acids

Major organic acids in Vaccinium spp. are citric, malic, quinic, and benzoic acids (3,4). Quinic acid (1,3,4,5-tetrahydroxycyclohexanecarboxylic acid) and benzoic acid are the most important and characteristic acids of cranberry (V. macrocarpom). The mean benzoic acid content is 0.01%, occurring mainly as 6-benzoyl-d-glucose (vacci-nin).

Phenolic Compounds

Phenolic compounds (4-6) are water-soluble compounds, sometimes present in glycosidic form, characterized by the occurrence of one or more hydroxyl residues in the molecule. They occur in monomeric or polymeric structures. They provide a high antioxidant potential in foods because they scavenge free radicals such as O^, HO", and ROO'. Phenolic compounds are also responsible for the color, taste, flavor, and astringency of foods.

Polymeric Phenols. The tannins comprise much of the phenolic content in Vaccinium. They have a molecular weight of up to 5000 and are characterized by their astringency, brown color, and ability to precipitate by bonding with proteins. Two types occur in vegetables, hydrolyzable and condensed. In Vaccinium they occur as condensed tannins.

Oligomeric Phenolic Compounds. Oligomeric (ie, of intermediate molecular weight that ranges from 500 to 1500) phenolic compounds (OPCs) (7,8) are dimeric, trimeric, or tetrameric forms of flavan-type phenols, such as catechin and epicatechin. They are called procyanidins or proanthocyanidins because they yield anthocyanidins after acid degradation. They occur as copolymer of all the possible combinations of the stereoisomer form of the monomeric flavans and are distinguished by an alphabetic letter (ie, B1( B2, B3, and B4 for the four-dimeric forms of [d,l]-catechin and [d,l]-epicatechin). With three monomers, the number of possible trimers would be 27, etc. A typical pro-cyanidin, procyanidin B1; that occurs in Vaccinium berries is represented in Figure 1.

Anthocyanins. The anthocyanins (5,6,9) are the pigments responsible for the red to dark blue color of the Vaccinium berries and their juice. Anthocyanins are flavonoids (a C6-C3-C6 molecule) and occur in glycosidic form. The nature and the type of the attachment of the sugar may be different. The sugar can be also acylated, generally with an aromatic or an aliphatic acyl moiety. A typical an-thocyanin is shown in Figure 2. The anthocyanin composition characterizes Vaccinium species with qualitative and quantitative differences. In highbush blueberry (V corymbosum L.), the total anthocyanin content varies from 25 to 495 mg/100 g fresh weight (FW). In the lowbush blueberry (V. angustifolium L.), the anthocyanin content ranges from 120 mg/100 g in the variety Bloomingdon and 260 mg/100 g in the variety Chignecto. In V. angustifolium, it is important to observe the occurrence of up to 35% of anthocyanins acylated with acetic acid and the genetic relationship among varieties (10). In rabbiteye blueberry

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