Chemical Composition of Olives

The main components of olive flesh are water, oil, sugars, proteins, pectins, organic acids, tannins, aleuropein and inorganic components. The composition of the olive varies according to the variety, the cultivation area, the year and the development stage. This is why some olives contain a small percentage of olive oil and a large percentage of sugars, as is the case with large-fruited varieties, and usually they are used for eating. On the contrary, the small-fruited varieties contain more percentage of olive oil and for this they are intended for oiling.

Moisture

Moisture is the most important component of fresh fruit. The moisture in the mesocarp fluctuates in a percentage of 50-70% and in the core 8-16% of the weight of the core. The lower the percentage of moisture in the mesocarp, the higher the nutritional value. Dissolved in the water of the cellular juice are sugars, eleuropein, organic acids, tannins and other cellular components. The moisture contained in the fruit is responsible for its non-shrinkage under extreme conditions. The percentage of humidity depends on the harvesting period of the olive fruit, i.e. on its ripening and if the arable land is dry or irrigated. During the processing of the fruit moisture decreases.

Fatty Substances

Low oil content is considered an advantage for the table olive. The oil content of the fresh fruit of table olives ranges from 18-30% mainly in the mesocarp while small amount is found in the endocarp at about 0.8% of the weight of the kernel. The fatty ones substances, being non-polar, are not extracted into the brine. Thus the fat content of the fruit at the end of processing is the same as that of the raw material or slightly increased. This increase is virtual and is usually due to the loss of other water-soluble components of the flesh. The main fatty acids contained are oleic, linoleic, linoleic, palmitic and stearic, their ratio changes during ripening. Percentages of oil content may differ even in fruits derived from same tree.

Sugars

Sugars such as glucose, fructose, mannose, galactose, sucrose and xylose are present in the olive fruit. The main ones are fructose and glucose which make up the 90-95% of sugars. The green fruit of the Cannervolia variety contains only 2 grams of reductant sugars (glucose, fructose) per 100 grams of fresh weight. Experimental fermentations of of the Kalamon variety report reducing sugars of 1.6 grams per 100 grams of fresh weight. The corresponding measurements for the main Spanish varieties Gordal and Manzanilla are 6 and 3 grams, respectively per 100 grams of fresh weight. The sugars and oil in the olive fruit are inversely related. In industrial practice it has been shown that the higher the content of fermentable components in the mesocarp, the easier the olive ferments but also is preserved during the storage stages and trading.

Proteins

The olive fruit of all table olives contains a small percentage of proteins. In particular, the Canned green olive was found to contain 1.38% crude protein. The percentage of of proteins on a fresh basis in Spanish table olives of different varieties and of different processing ranges from 0.72-1.42%. Despite their small percentage, the olive proteins are important because in the structure of their molecules, essential amino acids for human nutrition are involved. In the same study it was found that among the amino acids of olive proteins, the predominant ones are glutamate, aspartic acid followed by the basic amino acids valine, leucine, arginine, tyrosine, phenylalanine, alanine, lysine, glycine. The protein that is extracted into the brine supports the growth of lactobacilli. Therefore, the amino acids of proteins are important for the smooth progress of the lactic acid fermentation of the natural black olive.

Vitamins

Vitamins are divided into water-soluble vitamins, which include vitamins C, B1, B2 and B6 and oil-soluble to which belong the precursors of vitamin A and Vitamin E (tocopherols). Table olives are rich in tocopherols and tocotrienols. These substances play an important role in antioxidant mechanisms of the human body. Vitamins can be increased by microbial activity during olive fermentation. During the processing of the table olive, the water-soluble vitamins are lost, while the fat soluble remain. Generally the olive fruit is not considered as a good source of vitamins for human nutrition, but together with the other valuable ingredients it contains certain amounts of vitamins with special nutritional value for humans.

Pectins – Pectinolytic enzymes

Pectin participates in building the cell wall and occupies the space between two adjacent cells known as the middle lamella. The pectins are macromolecules which may cross-link with the intervention divalent cations, such as calcium, making the flesh of the olive becomes more cohesive. Immersion of the olives in a bath containing calcium chloride for a few hours increases the cohesiveness of the flesh. Its pectin content in the mesocarp of the olive is about 2% of fresh weight expressed in anhydrous form of galacturonic acid. As the ripening of the olive fruit progresses, the protopectin and total pectins are being reduced. With the reduction of protopectin the flesh become softer and soluble pectin is increased progressively. The degradation of protopectin, by any means, results in a soft texture. The pectinolytic enzymes that interest the table olive belong to two categories: in esterases (pectinesterases, methylesterases, etc.) and in polygalacturonases (endo-, exo-polygalacturonases, etc.). The first ones break up the ester bonds and release methanol and the latter cleave the 1,4-a glycosidic bond and release galacturonic acid molecules or dimers, trimers, derivatives.

Polyphenols–Tannins

The phenolic substances that have been isolated from time to time from the olive fruit are: ligustroside, hydroxyphenylethanol, eleuropein, glycosylated oleanolic acid, dimethyl-eleuropein, the isomer securidoide, oleoside, verbaxide and caffeic acid. Phenolic substances are responsible for the appearance of bruises in the raw material, of either green or black olives. In the first case the bruises remain after fermentation while in black olives in the places where the olive was bruised it is softer when fermented. The olive fruit is rich in polyphenols. The polyphenols in alkaline environment oxidize and give an artificial black color. The color is due to polymerization of polyphenols, including eleuropein. Greek table olives have phenolic substances from 0.29-2.3 mg per 100 grams of gallic acid.

Eleuropein

Eleuropein belongs to the phenolic substances, it is found in all the tissues and mainly in the mesocarp of the olive. It is a polar substance and therefore water-soluble, so that it is extracted with the water or brine from the flesh along with other water-soluble substances. In addition, it is an inhibitor of lactic fermentation. It is responsible for the bitter taste of the olive fruit and for this reason it should be partially or completely removed, depending on the variety of olive. The antimicrobial effect of eleuropein in the growth of pathogens and the growth of toxin-producing fungi is important. Eleuropein is obstracting the growth and production of enterotoxin B of Staphylococcus aureus and Salmonella enteriditis. It also has antimicrobial activity on vegetation and growth of Bacillus cereus spores. In addition, Eleuropein is completely obstracting the growth of Escherichia coli.

Pigments

The pigments of the fruit are of particular importance for its industry table olives, despite the fact that they have no nutritional value for humans. However, in the table olive, as in other foods, the color is the main thing determinant of quality. Olive pigments are divided into two categories: in the fat-soluble ones which are chlorophylls and carotenes, and in water-soluble which are mainly anthocyanins. Chlorophylls are synthesized in the former stages of fruit development and gradually recede over ripening to be replaced initially by carotenes (yellow color) and finally by anthocyanins at the stage of partial or full ripening (color pink, violet, melanovirus, black).