Bitterness units

A qualitative theory on the relationship between bitterness and chemical structures of bitter Rabdosia diterpenoids has been proposed 143). To be bitter a substance must have at least one bitter unit it consists of a hard acid and a hard base which are located within 1.5 A of each other so that intramolecular hydrogen-bonding is possible. Cleavage of this hydrogen bond and concomitant formation of a new hydrogen bond to the receptor site are responsible for bitterness 150). For instance, isodonal (71) which possesses an a-orientated 11-OH is very bitter, while trichodonin (70), its 11 P-epimer, is not. In bitter isodonal, the distance between the 11-hydroxy proton, the donor proton, and the 6-aldehydic oxygen, the proton acceptor, is ca. 1 A, while in tasteless trichodonin it is ca. 3 A. 

This method gave a better correlation with tasting trials than the second method of Rigby and Bethune [110]. In order to avoid assumptions about the chemical nature of the bittering principles in beer the EBC Analysis Committee simplified the regression equation and expressed the results as Bitterness Units [111]. 

Beer-spoilage ability was evaluated using the degassed pilsner-type beers (pH 4.2, bitterness unit 20 B.U., ethanol content 5.0%(v/v)). 

As a quantitative criterion for the degree of bitterness the European Bitterness Unit (EBU) is accepted by the European Brewery Convention (90-93). These EBU values are obtained by measuring the absorbance of a beer iso-octane extract at 275 nm, the absorption maximum of the iso-alpha acids. In practice this value is determined as follows 10 ml degassed beer is acidified with 1 ml HCI 3 N and extracted with 20 ml iso-octane. Subsequently, the absorbance of the extract is measured at 275 nm in a quartz tube of 10 mm length the bitter degree according to the EBC norms is found by application of the formula ... 

Celery Seed. Celery spice is the dried ripe fmit of y piumgraveolens L. (UmbeUiferae) a biennial, sometimes aimual, herb native to southern Europe and grown extensively in India, China, Mexico, and the United States. The seed is 0.42 cm long and brown. The odor of the seed is characteristic and warm and the taste somewhat bitter. It is used in tomato ketchup, sauces, soups, pickles, pastries, salads, and certain cheeses. 

Stevioside and rebaudioside A are diterpene glycosides. The sweetness is tainted with a bitter and undesirable aftertaste. The time—intensity profile is characteristic of naturally occurring sweeteners slow onset but lingering. The aglycone moiety, steviol [471 -80-7] (10), which is the principal metaboHte, has been reported to be mutagenic (79). Wide use of stevia ia Japan for over 20 years did not produce any known deleterious side effects. However, because no food additive petition has been presented to the FDA, stevioside and related materials caimot be used ia the United States. An import alert against stevia was issued by the FDA ia 1991. In 1995, however, the FDA revised this import alert to allow the importation and use of stevia as a diet supplement (80), but not as a sweetener or an ingredient for foods. Several comprehensive reviews of stevia are available (81,82). 

Another notable glycoside is amygdalin, which occurs in bitter almonds and in the kernels or pits of cherries, peaches, and apricots. Hydrolysis of this substance and subsequent oxidation yields laetrile, which has been claimed by some to have anticancer properties. There is no scientific evidence for these claims, and the U.S. Food and Drug Administration has never approved laetrile for use in the United States. 

Studies on the bitterness of other compoundsdo not, however, support this model. The bitter amino acids and sugars, for example, do not possess an AH,B unit of this dimension. As already mentioned, there is some evidence suggesting that there is more than one type of bitter-taste quality and receptor. If this is the case the diterpenes probably interact with a receptor showing a steric requirement difierent from that involved with the other classes of compounds. 

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