|Monday, 04 July, 2016, 08 : 00 AM [IST]|
|Ramesh Kumar Sharma|
|Herbs and spices, the food flavouring substances, have been found to contain both microbials and antimicrobials. The microbial contamination of herbs and spices is due to the condition in which they are grown and harvested.
In 1986, J Pafumi attempted to assess the microbiological quality of spices and herbs and hinted at two microorganisms clostridium perfrigens and bacillus cereus as the main spores found. Needless to say that microbiologically contaminated herbs and spices, if consumed, cause foodborne diseases. Therefore cleaning and decontamination of herbs with irradiation or any suitable technique is quite essential. It is worth mentioning that generally the herbs which carry lower microbial load exhibit higher antimicrobial property or microorganism inhibitory effect and might be used as natural food preservatives to extend shelf life of food articles as well as medicine to cure particular diseases.
In India, cinnamon, cloves, mustard, garlic, onion and so on have been used in food preparations with both the view points of taste development and shelf life extension.
Ayurveda, the Indian system of medicine, too utilises herbs for treatment of patients. The drug action considerations in Ayurveda seem to be based on six tastes (as Charak classifies herbs as per their tastes) which also constitute the basis for culinary uses of herbs and spices.
Nowadays scientific investigations confirm that herbs and spices contain active antimicrobials due to which those act as Ayurvedic medicine and food preservatives. However food preservation property of herbs is correlated with its antimicrobial component but herbal medicinal property is the function of entire physiological action of herbs including taste.
The modern system of medicine (allopathic system) utilises herbal extracts and isolated herbal compounds. But Ayurveda normally employs combination of herbs and also sometimes herbal extracts. The modern culinary system has also initiated the use of active antimicrobial component isolated from herbs for food articles’ shelf life extension. But Indian culinary system believes in integrally utilising herbs in pure, ground and roasted forms. In both the cases of herbal applications, whether medicine or food preservation, the toxin load of herb or spice is sure an issue. And the herbs of low toxin load are generally preferred.
In 1974, L B Bullerman observed how effectively the aflatoxin (fungal toxin) production in foods is inhibited by cinnamon. In 1977, Bullerman, Lieu, and Seier studied the correlation between aflatoxin growth inhibition and presence of cinnamon and clove oils. In 1979, A Sharma, G M Tewari; A J Shrikhande and S R Padwal-Desai came forward with their study on ‘ Inhibition of aflatoxin producing fungi by onion extracts’ published in Journal of Food Science (44:1545-1547).
In 1980, C N Huhtanen conducted a study regarding inhibition of clostridium botulinum by spice extracts. In 1984, L A Shelef, E K Jyothi and M Bulgarelli studied the effect of sage on growth of enteropathogenic and spoilage bacteria in broths and foods. The application of essential oils as fumigants against fungi was also found effective as reported by N Paster, M Menasherov, U Ravid and B Juven in Journal of Food Protection (58; 81-85) in 1995 with title ‘Antifungal activity of oregano and thyme essential oils applied as fumigants against fungi attacking stored grain.’
In 1988, L L Zaika came forward with paper on ‘Spices and herbs: Their antimicrobial activity and its determination’ published in Journal of Food Safety (9:97-118) and concluded that inhibitory effect of different spices and herbs is varying. Cinnamon, cloves and mustard exhibit strong antimicrobial effect. Allspice, bay leaf, caraway, coriander, cumin, oregano, rosemary, sage, thyme show medium antimicrobial effectiveness while black pepper, red pepper and ginger exhibit weak inhibitory effect. In an important study on ‘Antimicrobial effects of spices’ published in Journal of Ford Safety (6:29-44) in 1983 LA Shelef concluded that higher levels of spices are necessary to inhibit growth in food than in culture media.
Cinnamaldehyde: Also called cinnamic aldehyde or cinnamyl aldehyde, it is structurally 3-phenylpropenal derived from cinnamon bark oil or synthetically prepared by condensation of benzaldehyde and acetaldehyde. The sweet spicy cinnamon bark oil or cinnamon oil which contains cinnamaldehyde up to 70 per cent and engenol up to 18 per cent and phellandrene, benzaldehyde and linalool in minor fractions is obtained via distillation of the bark of cinnamonum zeylanicum nees cultivated in tropical Africa, America and Asia. The essential oil content of cinnamon bark varies from 0.5 to 2.0 per cent. (Cinnamon leaf oil, meanwhile, contains more than 70 per engenol and 6 per cent cinnamaldehyde and bears pungent odour). The Ceylon (or Sri Lankan) cinnamon is considered to be the best quality cinnamon bark oil for its delicate flavour which is derived from inner bark of shoots of cinnamonum zeylanicum. Cinnamaldehyde, the major antimicrobial component of cinnamon essential oil, is yellowish oil with cinnamon odour (specific gravity 1,048 to 1.052, refractive index 1.618-1.623, m.p. -8°c, b.p. 248°c) and has strong inhibitory effect on fungi mycotoxigenic aspergillus and aspergillus parasiticus.
Eugenol: Also called caryophyllic acid or eugenic acid, is structurally 4-allyl -2 – methoxyphenol derived by extraction of clove oil with aqueous potash, liberation with acid and rectification in a stream of carbon dioxide. The pungent spicy clove oil which contains eugenol more than 85 per cent is obtained via distillation of cloves, the unexpanded flowers of eugenia aromatica. Eugenol, considered to be the major antimicrobial component of clove essential oil, is colourless or yellowish oily liquid with pungent spicy odour (Specific gravity 1.064-1.070, refractive index 1.5400-1.5420 at 20°c, b.p. 253.5°c) and has strong inhibitory effect on mycotoxigenic aspergillus.
Thymol: Also called thymic acid, is structurally 5-methyl – 2 – isopropylphenol derived from thyme oil or other oils or synthetically prepared from meta-cresol and isopropyl chloride by the Friedal Crafts reaction at – 10°c. The pleasant spicy thyme oil which contains phenolic compounds more than 40 per cent including thymol and carvacrol is obtained via distillation from flowering plant thymus vulgaris or thymus zygis. Thymol, considered to be the major antimicrobial component of thyme essential oil, is white crystalline solid with aromatic odour (specific gravity 0.979, m.p. 48-51°c, b.p.233°c) and has strong inhibitory effect on vibrio parahaemolyticus.
Allicin: This sulphur containing compound derived from garlic extract, has strong inhibitory effect on salmonella typhymurium, Escherichia coli, staphylococcus aureus, bacillus cereus, bacillus subtilis, mycotoxigenic aspergillus and candida albicans in descending order.
Allyl isothiocyanate: Also called artificial mustard oil, it is structurally 2 – propenyl isothiocyanate derived by distillation of dried ripe seeds of brassica nigra L (black mustard seed) or synthetically prepared by distilling sodium thiocynanate and allyl chloride. It is colourless to high yellow liquid having highly pungent mustard flavour which is blistering to skin and very harmful to lungs. It exerts strong inhibitory effect on mycotoxigenic aspergillus.
It is worth mentioning that onion essential oil strongly inhibits aspergillus flavis and aspergillus paraciticus, the fungi responsible for aflatoxins development in foods. The bay leaf essential oil selectively inhibits clostridium botulinum.
Toxin Load Considerations