Main uses in food processing and medicine 1441 General

Oregano is used in meat, sausages, salads, stewings, dressings and soups. The food industry uses oregano oil and oregano resin both in foods and in beverages and also in cosmetics. Oregano oil is used in alcoholic beverages, baked goods, meats and meat products, condiments and relishes, milk products, processed vegetables, snack foods, and fats and oils. It is the most common spice for pizza. Along with black pepper, it is a common ingredient of dressings and a good substitute for table salt. Marjoram, too, is used in many foods and beverages in food industry; meat sauces, canned foods, vinegar, vermouths and bitters are often seasoned with marjoram. It increases aroma in such vegetable dishes as pea soup and other pea dishes, squash and stews made from mixed vegetables, mushrooms and asparagus.

14.4.2 Dietary value

The dietary value of oregano is quite high: it contains significant amounts of vitamins E, B6, riboflavin, niacin, folate, pantothenate and biotin (Holland et al., 1991). Relatively high values (expressed as mg/100 g fresh leaves) have also been reported for vitamin C (45), thiamin (0.07) and carotene (0.81). Lagouri and Boskou (1996) detected a-, P-, y- and 8-tocopherol in a non-polar fraction of oregano extracts, with the y-tocopherol content being significantly higher than other tocopherol homologues. Oregano is also rich in mineral elements such as potassium, calcium, magnesium, phosphorus, zinc, manganese, iron, copper, sulphur, chlorine, iodine and selenium, whereas its sodium content is low. However, Brune et al. (1989) reported that oregano inhibits iron absorption and the effect is caused by its galloyl substances and the inhibition is in proportion to its content of galloyl groups. Oregano also has a relatively modest energy and fat content (66 kcal/100 g and 2 g fat/100 g, respectively). According to Gray et al. (1997), the concentration of oregano in food can increase or reduce its palatability and intake compared with an unseasoned control food.

14.4.3 Food-preserving properties

Apart from its dietary value, oregano is an effective antioxidant additive in different types of foods, such as mayonnaise and French dressing (Chipault et al., 1956; Nakatani and Kikuzaki, 1987; Baratta et al., 1998). This property is usually attributed to the high carvacrol content of the spice (Tsimidou and Boskou, 1994), although additional compounds, such as flavonoids may also be responsible (Vekiari et al., 1993).

14.4.4 Medicinal uses

There are various reports on the traditional medicinal uses European oregano has as a carminative, diaphoretic, expectorant, emmenagogue, stimulant, stomachic and tonic. In addition, it has been used as a folk remedy against colic, coughs, headaches, nervousness, toothaches and irregular menstrual cycles. Turkish villagers have traditionally used kekik water, the aromatic water obtained after removing essential oil from the distillate of oregano herbs, which has in recent years become a commercial commodity (Baser, 2002; Kintzios, 2002a). Although the monograph documentation of O. vulgare was submitted to the German Ministry of Health, the staff responsible for phytotherapeutic medicinal domain -Commission E - evaluated Origani vulgaris herba negatively (Banz. No. 122 from 6th July 1988), because of lack of scientific proof for a number of indication areas (Blumenthal, 1998). Nevertheless, many of the studies confirmed benefits of oregano for human health and its use for the treatment of a vast list of ailments, including respiratory tract disorders such as cough or bronchial catarrh (as expectorant and spasmolitic agent), in gastrointestinal disorders (as choleretic, digestive, eupeptic and spasmolitic agent), as an oral antiseptic, in urinary tract disorders (as diuretic and antiseptic) and in dermatological affections (alleviation of itching, healing crusts, insect stings), viral infections and even cancer (for a detailed review, see Baricevic and Bartol, 2002).

14.4.5 Microbiological quality and safety considerations

Although oregano can cause aversion symptoms during pregnancy (Hook, 1980), its consumption is considered safe from the chemical point of view. However, considerations have been frequently raised on the microbiological quality of preserved oregano. For example, Makinen et al. (1986) and Malmsten et al. (1991) tested the microbiological quality of marjoram and of oregano and detected moulds and aerobic spore-formers, especially Bacillus cereus, in most samples (although at concentrations not high enough to cause food poisoning). Coliforms and faecal streptococci were found in both freeze-dried and air-dried samples, but only sporadically and at very low counts. Moulds and yeasts were found in almost all samples, while increasing the storage time from one year to two increased tenfold the number of aerobic spore-formers in freeze-dried and in air-dried oregano. However, as demonstrated below, microbial contamination of oregano is not a common source of concern, owing to the antimicrobiological properties of the herb.

14.5 Functional properties 14.5.1 Antioxidant properties

Oregano extracts have documented antioxidant and antimicrobial properties (Dorofeev et al., 1989; Mirovich et al., 1989; Deighton et al., 1993), which have been presumably attributed to phenylcarboxylic acids, such as cinnamic, caffeic, p-hydroxybenzoic, syringic, protocatecholic and vanillic acids. Dietary supplies of antioxidants from Origanum species have been considered as effective scavengers of the free radicals that are generated by metabolic pathways in the body; however, limited industrial applications are often ascribed to the characteristic oregano aroma and flavour that influence the sensorial characteristics of processed food, so deodorization steps would be required (Nguyen et al., 1991; Moure et al., 2001).

Taking these limitations into consideration, practical considerations on the use of oregano as stabilizers of edible oils or of finished meat products have been made by several research groups (Baricevic and Bartol, 2002). Dry leaves of Origanum vulgare ssp. hirtum showed a high antioxidant activity in olive oil and, besides their stabilizing effect, the organoleptic quality of the olive oil was significantly improved by addition of oregano, as assessed by Mediterranean consumer acceptability studies (Antoun and Tsimidou, 1997; Charai et al., 1999). A significant increase in the oxidative stability of fried chips, measured as the rate of peroxide formation during storage at 63°C, was achieved both by addition of ground oregano or its petroleum ether extracts (Lolos et al., 1999). In contrast with the significant antioxidative and stabilizing effects of oregano extracts in lard and various oils, no effect on the quality or shelf-life of the fat obtained from animals fed with oregano additives or of meat and fat-containing food was observed (Vichi et al., 2001).

14.5.2 Antimicrobial properties

In conjunction with the antioxidant properties of the herb, there are abundant reports on the microbial inhibitory effects of oregano essential oil or its components. These effects are generally classified either as antifungal or antibacterial. According to general consensus, there is a relationship between the chemical structure of the most abundant essential oil components and their antifungal and anti-aflatoxigenic potency, which is, in addition, strongly correlated with the concentration of the essential oil or active ingredient and pH of the testing medium in vitro (Deans and Svoboda, 1990; Thompson, 1990; Biondi et al., 1993; Baricevic and Bartol, 2002). Phenols are believed to be the most potent antimicrobials, followed by alcohols, ketones, ethers and hydrocarbons (Bullerman et al., 1977; Hitokoto et al., 1980; Hussein, 1990; Daw et al., 1994; Charai et al., 1996). In more practical terms, ground oregano (at 2% concentration) was found to possess a strong antifungal potential against several food-contaminating moulds, such as Alternaria alternata Keissler, Fusarium oxysporum Schlecht, Penicillium citrinum, P. roqueforti, P. patulum, Aspergillusflavus and A. parasiticus (Azzouz and Bullerman, 1982; Schmitz et al., 1993).

Phenolic compounds are probably responsible for the high inhibitory activity of carvacrol/ thymol chemotypes of oregano against fungal growth, conidial germination and production of Penicillium species, such as P. digitatum (Daferera et al., 2000). In particular, monoterpene components seem to have more than an additive effect in fungal inhibition. Phenolic derivatives, present in essential oils, may also be involved in inhibition of yeast sporulation through depletion of cellular energy by reduction of respiration (Baricevic and Bartol, 2002). Curtis et al. (1996) reported that carvacrol or thymol, when applied in concentrations of more than 100 ppm led to a complete inhibition of fungal growth in vitro.

Although the antibacterial properties of oregano extracts are far less documented, Hammer et al. (1999) found that O. vulgare (Australian origin) yielded one of the most potent antibacterial agents among 52 investigated essential oils, which considerably inhibited the growth of all tested microorganisms. Other reports (Biondi et al., 1993; Izzo et al., 1995) demonstrated the inhibitory effects of oregano extracts against a number of Gram-positive (such as Staphylococcus aureus and Bacillus subtilis) and Gram-negative bacteria (such as Proteus vulgaris and Escherichia coli). These activities have been mainly attributed to thymol and carvacrol. However, as also shown for the antifungal properties of the species, it seems more appropriate to combine the antimicrobial efficacy of different food-preservative compounds, creating synergistic effects, such as those reported by Pol and Smid (1999) for carvacrol and nisin (a bactericidal peptide, used as a biopreservative in certain foods) against Bacillus cereus and Listeria monocytogenes in vitro.

The antimicrobial value of oregano may exceed its scope of applications beyond the food industry: a therapeutic potency of essential oil of Origanum vulgare L. subsp. hirtum against experimentally induced dermatophytosis in rats (infection with Trichophyton rubrum) was found by Adam et al. (1998). Other studies demonstrated the promising applications of oregano, its essential oil or isolated compounds, in plant protection, in post-harvest crop/ fruit protection or in apiculture, where species-specific fungi endanger the production systems (for an extensive and detailed review, see Baricevic and Bartol, 2002).

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