1) High-methoxyl (above 7% methoxyl) will form jams and jellies with the proper proportion of sugar and acids.
2) Low-methoxyl pectins (3 to 7% methoxyl) will form stable gels with small quantities of polyvalent cations such as calcium without the additional soluble solids and acids.
Jellying power depends upon: a) the type of fruit used to make the pectin; b) the extraction system and c) the various ripening degrees of the actual fruits. The jellying power is the ability of solid pectin or pectic extract to turn sugar, under prescribed conditions, into jelly of suitable characteristics. The best pectin is extracted from lemons. For all dispersed pectins in water, viscosity is dependent on concentration, PH, salts and size of the plygalacturonic acid chain. The higher the polymerization of the pectin molecule, the greater is its jelly grade; the lower its methoxyl degree, the greater wll be its jelly grade.
Pectin changes during maturation, as the fruits ripen, the insoluble protopectin of mersitematic and parenchymatous tissue changes into water-soluble pectin and pectinates; as the fruits continue to ripen and become over-ripe these products are converted into low-grade pectin and insoluble pectates. Furthermore, juices and other by-products of the fruit processing need to be kept under control to prevent anomalous changes due to lack of control over processing parameters.
Pectin changes may be enzymatic or chemical. Because enzymes are an important factor in the pectic changes that occur in citrus, only two pectic enzymes will be considered:
1) Pectinestarase (PE) is an enzyme capable of demethylating pectin and 2) Polygalacturonase (PG) is a pectic depolymerizing enzyme. Only PE occurs naturally in citrus. PG is used as a technological adjuvant to decrease viscosity in concentrated juices and bases. PE is a very important factor to be taken into account during citrus product manufacturing. Its capacity to demethylate pectin causes viscosity increase that has to be controlled during orange juice evaporation in order to avoid product gelation. Moreover, enzymes act on cloud stability and decrease turbidity up to clarification of the juice. Pectin, in fact, is the natural colloidal stabilizer of citrus juices, giving them their “body”. If pectin is affected by PE activity, juice clarifies and all suspended colloids will flock down. The best way for inactivating PI activity is heat. The ratio of temperature-time to be used in the process varies from one citrus species to another. It depends as well on juice acidity and on its concentration. The rule of thumb is that the higher the juice concentration, the lower the temperature needed for PE inactivation and the higher the acidity, the lower the inactivation temperature. For example: for a single strength orange juice, one needs 99 degrees Celsius for 3 seconds or 88 degrees Celcius for 12 seconds, whilst for a 65 BX juice, the ratio is 71 degrees C for 15 sec. By comparison, for single strength lemon juice it is enough to use 74 degrees C for 122 sec or 88 degrees C for 1 sec, whist for very sweet mandarin juice one need 91 degrees C for 1 sec. PE activity is strictly linked to suspended
Let's consider now organic acids. They are key in both fruit growth and citrus products sales. Total acidity and total sugar content are criteria to evaluate the ripening degree of oranges and grapefruits, whilst in the case of lemon juice, they are the primary factor for price determination. Acidity is a critical point for consumer’s acceptance; it would be impossible to trade an orange juice having grapefruit juice acidity, for example. Organic acids are: 1) Citric Acid; 2) L-Malic Acid. 3) D-Isocitric Acid (found in small concentration, but determining quality and purity). Oxalic Acid, Succinic Acid, Malonic Acid, Quinic Acid, Tartaric Acid, Adipic Acid, 2-ketogluratic Acid are found only in small traces. Total acidity range has an extremely wide range between different species and different locations of the orchards. Mediterranean orange juices are more acid by comparison with the ones produced in US, Brazil and Cuba. Organic acids are found in the juice mainly, and to a lesser extent in other parts of the fruit.
The isocitrico acid is contained in small succinico, malonico, chinico, tartarico, adipic, 2-chetoglutarico and benzoic concentration while they are present ossalico acid traces. The acidity total differs largely between several the species and also in the various varieties of the same species, also in function of the climatic characteristics of the increase area.
The Mediterranean juices of orange are, in kind, more acids than those products in the USA, in Brazil or to Cuba. The organic acids, finally, are localize to you in the juice essentially and are contained in low concentration in the others leave of the fruit.
The nitrogenous compound in citrus are contained in rather low concentration but are important for assessing purity of the juices. Within of the nitrogenous substances without doubt more important ones are free amminoacids, representing approximately 70 % of the total nitrogenous substances. Citrus juices contain almost all important amminoacids, with the only exception of tryptophane. The most abundant are praline, asparagines, aspartic acid, serine, glutamic acid and arginine. Citrus contains small amounts of proteins which are basically enzymes (oxidoreductases, transferases, hydrolases and lyases, isomerases and ligases). Nitrogen bases and nucleic acids contents are extremely low.
There are three classes of Citrus lipids: non-polar, polar not ionic and polar ionic. Between non-polar lipids there are aldehydes, ketones and alcohols with long chain, carotins and their esters and some triglycerides. Non-ionic polar lipids usually contain sugars like glucosilglucerides. Polar ionic lipids contain reactive functional groups like aminic, carboxylic or phosphoric; free fatty acids and phosphatidic acid belong to this group. Despite their small content, lipids are important because they are involved in “off-flavors” development during juices storage. It is believed that oxidative changes produce hydroxyacids and other break-down products. We need to include the seed oil, one of the citrus by-products in the discourse about lipids. Seed oil extraction is hindered by the difficulty in separating the seeds from skins, segments and pulp. A single citrus processing plant may not be adequate to maximize seed oil extraction, therefore a consortium plant should be considered. Dry citrus seeds contain between 28 to 35% oil, which, in its unrefined form, has a pale-yellow color and an almond-like fragrance. Seed oil contains 95% tryglicerides and a small amount of free fatty acids, carbohydrates, sterols, tacoferols, phospholipids, limonin. The main characteristic of the seed oil is the distribution of fatty acids: the six main ones: palmitic, palmitoleic, stearic, linoleic, oleic and linoleic. The ration between saturated and non-saturated ranges between 1/3 and 1/5, comparable to corn oil.
Carotenoids derive their name from the main representative of their group, beta-carotene and pigments widely spread in nature responsible for bright shades ranging from yellow to deep red. Carotenoids are tetraterpenes formed by joining together of eight C5 isoprene units; the units are linked in a regular head to tail manner, except in the center of the molecule where the order is inverted tail to tail, thus making the molecule symmetrical.
From its basic structure, almost all other carotenoids can be formally derived by hydrogenation, cyclization, oxidation or any combination of these processes. From a classification standpoint, carotenoids can be divided in hydrocarbons C40H56 and their oxygenated derivatives, xanthofills which contain oxygen in the form of epoxy – (5.6 and 5.8 epoxy), hydroxyl – (monols, diols and poliols), keto – (oxo), methoxy – and carboxy groups. Other carotenoid groups are: the aromatic carotenoids with one or both end droup aromatic; allenic carotenoids with C=C=C grouping at one end of the central chain; and acetylenic carotenoids with triple link in 7.8 or 7’, 8’. The most important physiological role of carotenoids is to act as Vitamin A precursors in animal bodies. Almost all animals are able to enzymatically convert plant carotenoids of a special structure into Vitamin A. Beta-carotene, the most abundant provitamin supplies two molecules of Vitamin A; other more limited in number carotenoids with provitamin activity have an intact beta-iononering at only one-half of the molecule, e.g. alpha –carotene, gamma – carotene, 5,6-epoxy-beta-carotene, criptoxanthin and its monoepoxides and apo-beta-carotenals. Carotenoids are used as food colors and pigments. They are located in the plastids both of the flavedo and of the internal juice vesicles. In the early stages of the fruit ripeness, external color is masked by chlorophyll; with advancin maturity the yellow color appears in various tints from light yellow to deep orange, largely depending upon type and amount of carotenoids found. Carotenoid level and type vary widely. This variation depends on a multitude of factors such as environment, growing conditions, seasonal variations and stages of maturity. Accoridng to phenotypic interspecies differences, the overall carotenoid pattern in fruits varies from relatively simple mixtures to extremely complex ones.
A group of complex chemically related substances, triterpene derivatives, have been named limonoids; all components have a furan ring attached to the D-ring at C-17.
Between limonoids, the most important is limonin, known as citrus constituent since 1841.
Limonin is not directly present in fruit tissues, it is contained in the aslimonoic acid A-ring lactone, that is not bitter. When the fruit is macerated, during juicing, the combined action of fruit acids and an enzyme converts the aslimonoic acid info limonin, which is extremely bitter. In citrus products this is usually known as “delayed bitterness”. The absence of bitterness in the intact fruit and the delay in the onset of bitterness after juicing differentiate limonin bitterness from that due to the flavone neohesperidosides, such as naringin of grapefruit or bitter orange. In the latter case, the intact fruit is bitter and so is the fresh squeezed juice from it. Flavone neohesperidosides do not occur in many citrus species like sweet oranges (Citrus Sinensis), lemons (Citrus Lemon), limes (Citrus Aurantifolia) and in mandarins and tangerines (Citrus Reticulata); limonin, on the other end, is ubiquitous in all citrus species, although it may not be present in sufficient quantity at maturity to cause delayed bitterness of the juice. Delayed bitterness is most noticeable in the juice of the Navel orange and the Shamouti orange. There is no way, after juicing, to stop the reation. There is a direct relationship between limonin concentration and bitterness; generally speaking less than 6 ppm = not bitter; more than 9 ppm = bitter; 24 to 30 ppm = extremely bitter. Obviously, variations in acidity amd sweetness influence subjective responses to bitterness. In fact, a 1 ppm solution of limonin in water is considered bitter.
Flavenoids
Flavonoids are very abundant in Citrus and have a very complex pattern. Three types of flavonoids occur in Citrus: flavones (including 3-hydroxyflavanones), flavones (including 3-dydroxyflavones) and anthocyanins. Depending upon whether or not a glucosyl residue is present, the flavanones and flavones are further divided in O-glycosyl, aglycones and C-glycosylflavones. Anthocyanins are only known as constituents of blood oranges. The most important flavanones are hesperidin, naringin, poncirin, neoheriocitrin and neohesperidin. Between flavones, the most important are rhoifolin, rutin and diosmin. Between aglycones, of mention are sinensetin, auranetin, tangeritin. Without taking into account anthocyanins, there are 56 flavonoids in citrus. Some are bitter. Some, like diosmin, hesperidin and rutin, show pharmacological activity. In fact, Vitamin P, a very effective factor for reducing capillary permeability was discovered in 1937 by Szent and Gyorgyi while working on lemon peels. Pharmacological use is important in vascular and trombotic diseases like varicose veins. Diosmin, in particular, reduces capillary damage induced by histamine. Often crude flavonoids extracts are employed in drug formulas. Recent research shows that some flavonoids act as regulators in 1) prostaglandins synthesis (prostaglandins are a class of natural compounds physiologically very active at the level of muscles and involved in the inflammatory processes), 2) platelets aggregation, as well as other processes. Some flavonoids act as inhibitors and others as enhancers of enzymatic biosynthesis. Some flavonoids, like hydroxyethylrutinosideres are anti-inflammatory, others are immunosuppressive and other show antiallergenic properties. New research points to anticancerous properties of tangeritin by delaying metastasis of a primary cancer to a secondary or tertiary stage. Hesperidin, naringin and nobiletin have lower therapeutic potential. Dihydrochalcones derivatives of flavonoids are low calorie sweetners. Flavonoids are found mainly in the albedo and their concentration in juices depends upon the juicing technology. Due to their bitterness, it is desirable to remove flavonoids (such as limonin) through a process known as absorber resins.
With respect to anthocyanins, the most abundant is cyanidin-3-glucoside, then cyanidina-3.5-diglucoside, peonidin-5-glucoside, delphinidin-3-glucoside and petunidin-3-glucoside.
The un-organic elements of citrus fruits and products comprise the material (ash) remaining after all organic matter has been destroyed. The percentage of ash and the relative concentration of un-organic constituents depend upon growing conditions (fertilization, soil type, climate, temperature and rainfall), tree health, cultivars, state of maturity, season of harvest and geographic location. Likewise, the percentage distribution of un-organic elements in processed products depends upon several processing parameters such as pressure used in juicing the fruits, pulp control, finishing and pulp washing. Main un-organic elements are potassium, phosphor, calcium and magnesium. Also found but in smaller concentration are: sodium, chlorine, nitrogen and iron.
Among flavonids we point out Rhoifolina, Rutina, Diosmina.
Among the agliconi we cite the Sinensetina, the Auranetina, the Tangeritina. Excluding the anthocyanin, have been recognized and isolates at least 56 flavonoidi have been identified. The flavonoidi presents in the citruses are bitters not as some of the Diosmina, the Rutina, the Esperidina, possess attività' phaarmacological. It does not have to forget, in fact, that the P Vitamin, extremely effective factor for the reduction of the permeability of is gone capillary was discovered in from Szent and 1937 Gyoryi working on the lemon rind. I use farmacologico is important for the vascular syndromes (hemorrhoidses) and in the trombotiche diseases (varicose veins), the Diosmina, in particular, drastically reduces the induced capillary lesions from the istamina. Often crude extracts of flavonoidi come employ to you for druggist formulations. In rather recent times it has been also demonstrated that some flavonoidi act from regolators in the syntheses of prostaglandins, of the natural substances physiologically many assets that act on many types of smooth musculature and that they are been involved in the inflammatory states, the piastrinica aggregation and other physiological processes. E' be observed as some flavonoidi act from inhibitors and others from goaders del complex enzymatic engaged nella synthesis of these substances. Some flavonoidi, like the idrossietilrutinosidi, also are of the anti-inflammatory ones not possessing prostaglandinica activity. Finally, some flavonoidi show soppressiva activity of the immune system towards the so-called the not specific factors, and others possess attività' anti-allergic and anticancer for this last activity it has been studied above all the Tangeretina that is able to block the beginning of the tumorali metastases through which a primary tumor passes to is made secondary and terziarie. The Esperidina, the Naringina and the Nobiletina have been also heads that, but, possess proprietà' inferior to the Tangeretina. Some flavonoidi of the citruses have been heads also for antiviral activity but with insufficient it turns out to you. It does not have to be forgotten, finally, that it derives to you diidrocalconici of some flavonoidi are upgrades them dolcificanti without calories. The Flavonoidi is localizes to you in the Albedo above all and their concentration in the juice depends in determining way from the extraction technology. Their removal can be obtained for means of adsorption systems. Their bitter taste is lighter regarding that one of the limonina and to the contrary of this last one it stretches to disappear from the palate.
Antioxidants
As far as the anthocyanin, more abundant is the cianidyn-3-glucoside, follows the cianidyn-3,5-diglucoside, the peonidina-5-glucoside, delfinidina-3-glucoside and the petunidina-3-glucoside. The anthocyanin are present in variety of peculiarly Italian oranges: the Moro, the Tarocco and the Sanguinello. This class of substances, because of the instability inborn in their structure of knows them of 3-idrossiflavilio is extremely subject to phenomena oxidized caused to you from the light and the heat. They have had to make large technological efforts for being able industrially to produce juice of red orange concentrated of good quality maintaining lessened the oxidation phenomena during the production process. From the farmacologico point of view the antociani seem to possess property similar to those of the flavonoidi. The inorganic components of the citruses comprise ashes, that is what she remains after that all the organic components have been destroyed with the heat. The percentage of ashes and their composition depend on the increase conditions (climate during the increase of the fruits, type of land, rainfall) and from the cultivar, the conditions of health of the plant and from the geographic origin moreover, the distribution several percentage of constituent the inorganic ones is dependent from various parameters of working like the pressure of spremitura, and the control of the pulp.
With respect to vitamins, the most important is Vitamin C (Ascorbic Acid). A glass of orange juice supplies 60 units of RDA. Other vitamins are: Pholacine, Vitamin B6, Thiamine, Riboflavin, Biotin, Pantotenic acid and products with Vitamin A activity. Average quantities in freshly squeezed orange juice are reported to be as follows in the table below:
Comparison |
| Vitamin | Unit/100 ml | Value |
| Ascorbic Acid | mg | 35 - 56 |
| Tiamin | mg | 60 - 145 |
| Riboflavina | mg | 11 - 90 |
| Niacina | mg | 200 - 300 |
| B-6 | mg | 25 - 80 |
| Folacina | mg | 120 - 330 |
| Pantotenic Acid | mg | 130 - 210 |
| Biotina | mg | 1 - 3 |
| Vitamin A (attività) | IU | 190 - 400 |