The fruits of Strawberry-tree contain several groups of secondary metabolites; some simple phenolics such as Gallic Acid, |
ProtoCatechuic Acid, Gentisic Acid, para-
Vanillic Acid and meta-
Anisic Acid (aka m-
MethylSalicylic Acid), several flavonol glycosides such as the 3-O-glycoside of Quercetin and the 3-O-Rhamnoside of both Myricetin and Quercetin. Galloyl derivatives and Elagitannins present include
Strictinin (an elagitannin) and the Rhamnoside of Ellagic Acid. Also present are
ProAnthoCyanidin B3 and
ProAnthoCyanidin B7 which are dimers based upon Catechin.
GalloCatechin is also present.
There are also the AnthoCyanins
Cyanidin-3-O-Arabinoside and many other derivatives. The Vitamin E Tocopherols also feature widely in the fruits, as well as the related carotenoids β-Carotene,
Lycopene and Lutein.
The fruits also contains many simple organic acids such as Oxalic Acid,
Malic Acid, Fumaric Acid, Lactic Acid,
Suberic Acid and
Quinic Acid where the concentrations of each depend upon the ripeness of the fruits, and upon the country in which it is grown.
Lactic Acid is present in St Ivel Lactic Cheese, if that can still be purchased anywhere; your Author has not seen it in the shops for several decades. There are 2 optical isomers of Lactic Acid, the S- and R- forms. Lactic Acid (actually L-lactate) is produced within hard-working muscles as they metabolise glucose to produce work, but they must strive to rid themselves of it, otherwise muscle fatigue sets in. The bacteria Lactobacillus also produces Lactic Acid by a fermentation process. It is now also used in some commercial de-scalers and soap-scum removers by the detergent industry, for it is much more environmentally friendly that other (noxious) descalers. The polymeric form,
PolyLactic Acid is used to make some biodegradeable plastics.
Oxalic Acid, by contrast, is a dicarboxylic acid, and is present in several plants with a highly astringent taste, such as Rhubarb where its concentration in the leaves (which contain much more than the stalks) is 0.52% by weight, but the highest concentration is found in Parsley at 1.7%. It is mechanically toxic in its crystalline form due to the needle-like crystals it forms called raphides, which puncture cell walls killing the cells. It is usually found as hydrated crystals, COOH)2˙2H2O. In its anhydrous state, due to hydrogen bonding, it exists as two polymorphic forms; one bonded in a linear string, the other in a planar sheet array.
Fumaric Acid is an unsaturated dicarboxylic acid isomeric with Maleic Acid (not to be confused with Malic Acid). Fumaric Acid is the trans form, Maleic Acid the cis-form. Fumaric Acid has a fruity taste. Found in species of Fumitory such as
Common Fumitory (Fumaria officinalis) some bolete mushrooms, and lichens such as
Iceland Moss (Cetraria islandica) It is used as an acidity regulator in foods and is designated E297. It is also used as a vinegar substitute, such as in 'salt and vinegar' flavour crisps. Use is also found as a mordant in the dying process. Fumaric Acid is practically non-toxic, indeed, it is used as a key intermediate in mammals (and all other aerobic organisms) during the
TriCarboxylic Acid Cycle (
KREBS cycle) - a metabolic pathway involving the recycling of
Citrate and back to OxaloAcetate in a continuous circle, all the while consuming
Adenoside TriPhosphate (
ATP) as the energy source.
Malic Acid is an intermediate moiety in the
Citric Acid Cycle (
CAC) which is also known as the TriCarboxylic Acid Cycle aka KREBS cycle (ses above). It seems biochemists are just as prolific with alternative names as are botanists. See Citric Acid Cycle. Malic Acid comes as two stereoisomers, L- and D- enantiomeric forms, but only the L-form is produced biologically. Apples are a well known source of Malic Acid, indeed, the
Apple Tree genus (Malus) gives its name to malic acid, although it can also be found in many other fruits such as
Quince, Rhubarb (in which the taste of Malic Acid is very pure). Like Fumaric Acid, it is also used as a vinegar-like flavouring in Salt and Vinegar flavour crisp under E296. It is also present in wine.
Citric Acid is present in most citrus fruits, such as Lemon, Orange and Grapefruit, hence the name, and is also used (mainly as the citrate salt), as a preservative in all sorts of tinned foods, even tinned tomatoes (which don't originally contain citric acid, so it makes them taste awful).
Suberic Acid (aka
Octanedioic Acid) is another Dicarboxylic Acid, as are all shown here except Lactic Acid and Quinic Acid. Suberic Acid itself is a colourless crystalline solid used in the manufacture of plastics and in drug synthesis. It is found in Cork, the thick soft phellem layer of bark tissue usually derived from
Cork Oak (Quercus suber). The cork itself is made of
Suberin, a cross-linked somewhat-rubbery substance consisting of both polyaromatic (such as hydroxycinnamic acids and their derivatives) and polyaliphatic moieties (such as
α-Hydroxy Acids and diacids ) with somewhat variable cross-links between them. The variable substance called
Phlobaphen also occurs as one of the polyaromatic components of suberin.
Cork Oak is the tree used to make cork bottle stoppers. Under the microscope cork is found to have an irregular lattice framework full of holes, which is why cork is so light and springy. Suberin is also the biopolyester found in specialised plant cell walls to be found wherever protection from water or gas exchange is paramount, for it is impervious to both water and gasses. It is also created in plants to repair any tissue damage, for instance leaf abscission or any wounding of the plant. Both
Cutan are similar random waxy polymers. Cutin covers all aerial surfaces of plants like a cling-film layer to protect them from fungi, bacteria and other pathogens by being a physical barrier. Cutan is rarer in plants but is much more likely to preserve plant material over historical timescales than is cutin.
Lignin is another random polymer film produced by plants for the purpose of protection.
Quinic Acid, is a cyclic polyol found in Coffee Beans, Chinchona Bark. It has a perceived acidic and astringent presence in a cup of coffee. Quinic Acid is found Tobacco leaves, Carrot leaves, apples, pears, peaches, plums, vegetables and in the bark of Eucalyptus globulus, a Blue Gum tree. It resembles a sugar compound.