International Jm~rnal of F(~d Micrt~bitdo,~.. 16 (19921337-342
~37
0~ 1992 Elsevier Science Publishers B.V. All rights reserved 0168-1~15/92/$05.fl0 FOOD 0052~
Short communication
Antibacterial activity of essential oil components Venkataramana Moleyar and Pattisapu Narasimham Area of Fruit aml Vegetable l'et'hnfdogy, (¥1~trul Fot~l Tt~chntdog~cal Research Inslitutc. M)'sore, brdia
(Received 2 October 1991; revision received 24 March 1~2: accepted 19 May 1992)
Antibacterial activity of ill'teen es.scntial oil components towards f~x~l borne Slaphylt~'tR't'lrs sp., Micrta'ta'cus sp.. Bacillus sp. and Eutend~aeter sp. was studied by an agar plate technique. Cinnamie aldehyde was the most active compound followed by eilral, guraniol, eugenol and menthol. At 51111 p.g/ml, cinnamic aldehyde completely inhibited the bacterial growth G~rmore than ~) days at ~i¢C that was comparable to 2[XI izg/ml of butylated hydroxy anistfle (BIIAk At lower temperatures. 25 and 21PC. antlbacteriul activity of the five essential oil ¢omponems increased. Addition of sodium chloride at 4% level (w/v) in the medium had no effec! on the inhibitory activity of cinnamie aldehyde. In mixtures of einnamic aldehyde and eugenol or BllA an additive effect was observed. Key words: Antibacterial activity; Essential oil comlxmcnt: Cinnamic aldehyde
Introduction T h e r e is an i n c r e a s e d n e e d for s a f e r antimicrobial food preservatives which a r e m o r e a c c e p t a b l e t h a n the p r e s e n t preservatives whose safety in f o o d is s o m e t i m e s q u e s t i o n e d . Essential oils a n d t h e i r c o m p o n e n t s which a r c widely u s e d as f o o d flavours, a n d a r e also classified u n d e r G R A S , offer m u c h scope in this r e g a r d . T h e antimierobial activity o f spices a n d essential oils is well r e c o r d e d (Pruthi, 1980; Shelef, 19831. Essential oils of thyme, c i n n a m o n , b a y a n d clove w e r e f o u n d to be strongly antimierobial a m o n g the m a n y tested ( R a m a d a n c t a l . , 1972 a, b; D e a n s a n d Ritchie, 19871. However, o p i n i o n s vary r e g a r d i n g the extent o f t h e i r antimierobial action d u e to differences in the m e t h o d o l o g y a d o p t e d for assaying, the differences in the e x p e r i m e n t a l c o n d i t i o n s ( M o l e y a r a n d N a r a s i m h a m , 1986, 19871 a n d also d u e to the use of essential oil as test material w h o s e c o m p o s i t i o n varies ( M o l e y a r a n d N a r a s i m h a m , 19881. T h e r e f o r e , it is desirable to assay the c o m p o n e n t s o f essential oils r a t h e r t h a n essential oil as a whole, for antimicrobial activity. J a y a n d Rivers (19841 r e p o r t e d t h a t a m o n g the 21 food flavours assayed f o r antimicrobial activity, di-acetyl followed by e u g e n o l were most active. A m o n g the essential oil c o m p o n e n t s tested for inhibiting activity (thyme, e u g e n o L m e n t h o l a n d
Correslumdeace address: Dr V. Moleyar, Area of Fruit and Vegetable Technolo~. Central Food
Technological Research Institute, My~)re - 570 013, India.
338 anethole) towards food-borne bacterial pathogens, eugenol was the most active (Karapinar and Aktu~, 1987). The present study deals with the antibacterial activity of the essential oil components as compared to that of BHA towards four food-borne bacteria. The effect of temperature and sodium chloride on the inhibitory activity and behaviour of essential oil components in mixtures is also studied.
Materials and Methods
Test organi.~ms Cultures of Gram-positive bacteria, viz. Staphylococcus sp., Micrococcus sp. and Bacillus sp., and the Gram-negative Enterohacter sp., were obtained from Microbiology and Sanitation Department of the Central Food Technological Research Institute, Mysore, and were maintained on nutrient agar at 31) + 1°C.
ChemicaLs Essential oil components were obtained from Fluka Chemische Fabrik, Switzerland. They are listed in Table 1 with their purity. Standard solutions of these were prepared in ethanol. Butylated hydroxy-animle (BHA) was obtained from Sigma Chemical Co. (USA).
Culture media and h~ocula Nutrient agar (NA) made up in our laboratory from local ingredients was u~d. The ingredients of NA were: beef extract 3 g, sodium chloride 5 g, agar 15 g, distilled water ! I. The pH was adjusted to 7.2-7.4 with 1).! N NaOH. About 16-18 h old culture of the test bacteria in nutrient broth (NB) incubated at 30°C with optical density adjusted to 0.1 at 550 nm with NB was used as inoculum.
Determblation of the antibacterial activity Antibacterial activity of essential oil components was measured as their capacity to inhibit the growth of the bacteria on NA. Each compound was assayed at IIXl, 2511, 500, 750 and 1000 ttg/ml. Test chemicals were incorporated in medium maintained at 50°C. Twenty-ml aliquots of this medium were poured into petriplatcs and cooled. Plates were inoculated with I1.1 ml of the inoculum {about 3 x l0 s colony forming units) which was spread uniformly on the solidified medium. Five replicates were maintained for each treatment. The ethanol content in the medium did not exceed 0.6%. Media containing only ethanol (0.6%) served as control. Plates wcre incubated at 3(1 +_ I°C and were observed daily for visible bacterial growth. The growth inhibitory activity of cinnamic aldehyde was studied in mixtures both with eugenol and BHA. Ethanolic solutions of the test chemicals were incorporated separately into the molten medium to get the desired total concentration. The procedure was similar to the one followed above.
339 Effect o f temperature and sodiam chlortde o~a the antibacterial actit'ity o] :'innamic aldehyde Cinnami," aldehyde was incorporated intt the medium at (I, 3(11), 4111)and 5{10 p.g/ml. For each treatment three sets of petriplates were prepared. They were incubated at 30 + I°C, 25 +_ I°C and 20 _+ I°C, for 31) days. Sodium chloride at 4% level (w/v, excluding the (I.5% in the medium) was incorporated in the medium before autoclaving. Cinnamic aldehyde was ineorpt-,rated into the medium and the antibacterial activity was determined at 0, 100, 25(, and 500 p,g/ml as described above.
Results and Discussion
Anisaldehydc, anisolc, a- and/J-pincne, a- and y-tcrpinenc did not inhibit the test bacteria even at 1(~10/,tg/ml, the highest level tested (Table 1). Citronellal, eucalyptol, D-limonene and linalool had slight antibacterial activity, inhibiting the bacteria for I - 4 days at 100{) p,g/ml. At the same concentration menthol inhibited the bacteria for 3-1{) days, while citral, eugenol and gcraniol were moderately active in inhibiting the organisms for more than 31} days at 750-1000 ~ g / m l . Cinnamic aldehyde was most active, amoag the essential oil components tested, in completely inhibiting the bacteria for more than 30 days at 5(10 p.g/ml. BHA, the anti-microbial antioxidant, whose activity was also studied for comparison, completely inhibited the test organisms at 200 p.g/ml as has been reported earlier (Klindworth et al., 1979: Shelef and Liang, 1982). In general the essential oil components were more inhibitory to the three Gram-positive bacteria than to the Gram-negative bacterium. Entertd~acter sp. Such difference in the sensitivity of bacteria to the spices has been noted earlier (Shelef et al., 1980). For the control plates visible growth was seen after ! day. A mixture of cinnamic aldehyde and cugenol at 250 and 500 p,g/ml, respectively, completely inhibited the growth of the four bacteria for more than 30 days, whereas the components of the mixtures at the same concentration individually failed to inhibit the bacteria (results not shown). Similarly a mixture of cinnamie aldehyde and BHA at 250 and 100/zg/ml completely inhibited the four bacteria whereas individually both compounds could not. However, with ,sodium chloride at 4% level cinnamic aldehyde did not show any increased inhibitory action (results not shown). Temperature affected the inhibitory activity of cinnamic aldehyde. At 25°C and 20°C complete inhibition was observed at 40{) p,g/ml as against 50{) /zg/ml at 30°C (results not shown). Cinnamic aldehyde has GRAS status and is permitted up to 700 ppm in food (MAFF Food Additives and Contaminants Committee, 1976). This means, the level of cinnamic aldehyde required for complete inhibition of microorganisms in f o o d appears to be within the permitted limit. Because of its characteristic flavour the use of cinnamic aldehyde as food preservative may be restricted to flavoured foods and to those containing spices. The dosage of cinnamic aldehyde required for complete inhibition of microorgan-
340 TABLE I Antibacterial activity of essential oil components Test compound a (purity)
Anisaldehyde (99%) Anisole (99%) Cinnamic aldehyde (98%)
Citral (85-90%)
Citronellal (85-90%)
Eugenol (99%)
Eucalypto| (99%) Geraniol (96%)
D-Lir, onenc (98°/~T Linalool (97%) Menthol (98%)
a-Pinene (99%) ~-Pinene (80-90%) a-Terpinene (90%) y-Terpinene (95%) BHA
Concentra-
No. of days for visible growth
t/on in Nutrient Agar (~g/ml)
Staphylococcus sp.
Micrococcus sp.
Bacillus sp.
Enterobacter sp.
1000 WOO 100 250 500 750 1000 100 250 500 750 WOO 500 750 WOO 250 500 750 1000 750 WOO I00 250 500 750 1000 "/50 I000 750 1000 250 500 750 IQ(]O IG00 1000 1000 WOO 50 I00 150 200
I I 1 3 >30 >30 >30 I 1 5 15 >30 I 2 4 I I 15 >30 I I I I 21 > 30 >30 1 I 1 3 I 4 6 6 I I 1 1 1 3 >30 >30
I I 1 4 >30 >30 >.30 I 1 9 20 >30 1 1 3 I ll) > 30 >30 t I I 2 21 > 30 >30 ! I 1 2 1 3 4 6 I I I 1 I 2 >30 >30
1 I I 3 >30 >30 >30 I I 3 8 >30 I I 2 I Q > 30 >30 1 3 I 2 11 > 30"40 >30 I 2 I 2 I 3 6 10 1 1 I I I 3 >30 >30
I 1 I 3 >30 >30 > 30 I 1 I 2 > 30 I I I I 2 10 15 I I I 1 I I0 >30
= All compounds were obtained from Fluke Chemische Fabrik, Switzerland.
10 > 30
341 isms, c a n be lowered by using it in c o m b i n a t i o n with o t h e r essential oil c o m p o n e n t s as mixtures. S u c h mixtures m a y be desirable as food preservatives for t h e i r mixed flavour instead of a n intense single flavour w h e n only o n e c o m p o u n d is u s e d ( M o l e y a r a n d N a r a s i m h a m , 1988). F u r t h e r r e d u c t i o n in the d o s a g e s o f the essential oil c o m p o n e n t s r e q u i r e d for the control o f m i c r o o r g a n i s m s in f o o d systems m a y be a t t a i n e d by m a k i n g use o f the a d d e d inhibitory effect o f low t e m p e r a t u r e storage. Such use o f m o r e t h a n o n e f a c t o r to inhibit m i c r o o r g a n i s m s in f o o d is desired (Scott, 1989). Use o f essential oil c o m p o n e n t s as f o o d preservatives has the a d d e d a d v a n t a g e t h a t they n e e d not u n d e r g o the r i g o r o u s testing t h a t is c u r r e n t l y r e q u i r e d by the F D A for a p p r o v a l since these have b e e n in use as f o o d flavours.
Acknowledgements T h e a u t h o r s t h a n k Shri B.S. R a m a c h a n d r a , A r e a C o o r d i n a t o r , Fruit a n d Vegetable T e c h n o l o g y for his s u g g e s t i o n s d u r i n g the course o f the investigation. V.M. is grateful to C S I R - N e w Delhi for the a w a r d o f a R e s e a r c h Associateship.
References Deans, S.G. and Ritchie, G. (1987) Antibacterial properties of plant essential oils. Int. J. Food Microbiol. 5, 165-180 Jay, J.M. and Rivers, G.M. (1984) Amimicrobial activity of some flavoring compounds. J. Food Safety 6, 129-139. Karapinar. M. and Aktu~, S.E. (1987) Inhibition of food-home pathogens by tbymol, eugenol, menthol and anethole. Int. J. Food Microbiol. 4, 161-166. Klindworth, K.J., Davidson, P.M., Brekke, CJ. and Branen, A.L, (1979) Inhibition of CIostddium per[ringens by Butylated hydro~ anisole. J. Food Sci. 44, 564-567. MAFF, Food Additives and Contaminants Committee (1976) Report on the Review of Flavorurings in Food, HMSO, London, p. 72. Moleyar, V. and Narasimham, P. (1986) Antifungal activity of some ~sential oil components. Food Micmbiol. 3. 331-3.36. Moleyar, V. and Narasimham, P. (1987) Detoxification of Essential oil components (citral and menthol) by Aspergillus niger and Rhizopus stolonifer. J. Sci. Food Agric. 39, 239-246. Moleyar, V. and Narasimham, P. (1988) Fungitoxicity of binary mixtures of citral, cinnamic aldehyde, menthol and lemon grass oil against Aspergillns niger and Rhizopus stolonifer. Lebensm. Wi~. TechnoL 21, 100-102. Prnlhi, J.S. (1980) Spices and condiments: chemistry, microbiology, technology. Adv. Food Res. (Suppl.) 4, 32-68. Ramadan, F.M., EI-Zahfaiy, R.T., EI-Wakeil, F.A. and Alian, A.M. (1972a). On the antibacterial effects of some essential oils. L Use of agar diffusion method. Chem. Mikmbiol. Technol. Lebensm. 2. 5t-55. Ramadan, F.M., EI-Zahfaly, R.T.. Allan, A.M. and EI-Wakeil, F.A. (1972b). On the antibacterial effects of some e~ential oils. I1. Studies on semi-solid Agar phase. Chem. Microbiol. Teehnol. Lebensm. I, 96-102. Scott, V.N. (1989) Interaction of factors to control microbial spoilage of refrigerated foods. J. Food Protect. 52, 431-435.
342
Shelef. L.A., Naglik, O.A.. and Bogen, D.W. (1980) Sensitivity of some common food borne bacteria to the spices sage, ro~mary and allspice. J. Food Sei. 45, 1042-1044. Shelcf, L.A. and Liang, P. (1982) Antibacterial effects of Butylated hydroxy anionic (BHA) against Baolhts species. J. Food Sei. 47. 796-799. Shelef, L.A. (1983) Antimicrobial effects of spices. J. Food Safety 6, 29-44.
~37
0~ 1992 Elsevier Science Publishers B.V. All rights reserved 0168-1~15/92/$05.fl0 FOOD 0052~
Short communication
Antibacterial activity of essential oil components Venkataramana Moleyar and Pattisapu Narasimham Area of Fruit aml Vegetable l'et'hnfdogy, (¥1~trul Fot~l Tt~chntdog~cal Research Inslitutc. M)'sore, brdia
(Received 2 October 1991; revision received 24 March 1~2: accepted 19 May 1992)
Antibacterial activity of ill'teen es.scntial oil components towards f~x~l borne Slaphylt~'tR't'lrs sp., Micrta'ta'cus sp.. Bacillus sp. and Eutend~aeter sp. was studied by an agar plate technique. Cinnamie aldehyde was the most active compound followed by eilral, guraniol, eugenol and menthol. At 51111 p.g/ml, cinnamic aldehyde completely inhibited the bacterial growth G~rmore than ~) days at ~i¢C that was comparable to 2[XI izg/ml of butylated hydroxy anistfle (BIIAk At lower temperatures. 25 and 21PC. antlbacteriul activity of the five essential oil ¢omponems increased. Addition of sodium chloride at 4% level (w/v) in the medium had no effec! on the inhibitory activity of cinnamie aldehyde. In mixtures of einnamic aldehyde and eugenol or BllA an additive effect was observed. Key words: Antibacterial activity; Essential oil comlxmcnt: Cinnamic aldehyde
Introduction T h e r e is an i n c r e a s e d n e e d for s a f e r antimicrobial food preservatives which a r e m o r e a c c e p t a b l e t h a n the p r e s e n t preservatives whose safety in f o o d is s o m e t i m e s q u e s t i o n e d . Essential oils a n d t h e i r c o m p o n e n t s which a r c widely u s e d as f o o d flavours, a n d a r e also classified u n d e r G R A S , offer m u c h scope in this r e g a r d . T h e antimierobial activity o f spices a n d essential oils is well r e c o r d e d (Pruthi, 1980; Shelef, 19831. Essential oils of thyme, c i n n a m o n , b a y a n d clove w e r e f o u n d to be strongly antimierobial a m o n g the m a n y tested ( R a m a d a n c t a l . , 1972 a, b; D e a n s a n d Ritchie, 19871. However, o p i n i o n s vary r e g a r d i n g the extent o f t h e i r antimierobial action d u e to differences in the m e t h o d o l o g y a d o p t e d for assaying, the differences in the e x p e r i m e n t a l c o n d i t i o n s ( M o l e y a r a n d N a r a s i m h a m , 1986, 19871 a n d also d u e to the use of essential oil as test material w h o s e c o m p o s i t i o n varies ( M o l e y a r a n d N a r a s i m h a m , 19881. T h e r e f o r e , it is desirable to assay the c o m p o n e n t s o f essential oils r a t h e r t h a n essential oil as a whole, for antimicrobial activity. J a y a n d Rivers (19841 r e p o r t e d t h a t a m o n g the 21 food flavours assayed f o r antimicrobial activity, di-acetyl followed by e u g e n o l were most active. A m o n g the essential oil c o m p o n e n t s tested for inhibiting activity (thyme, e u g e n o L m e n t h o l a n d
Correslumdeace address: Dr V. Moleyar, Area of Fruit and Vegetable Technolo~. Central Food
Technological Research Institute, My~)re - 570 013, India.
338 anethole) towards food-borne bacterial pathogens, eugenol was the most active (Karapinar and Aktu~, 1987). The present study deals with the antibacterial activity of the essential oil components as compared to that of BHA towards four food-borne bacteria. The effect of temperature and sodium chloride on the inhibitory activity and behaviour of essential oil components in mixtures is also studied.
Materials and Methods
Test organi.~ms Cultures of Gram-positive bacteria, viz. Staphylococcus sp., Micrococcus sp. and Bacillus sp., and the Gram-negative Enterohacter sp., were obtained from Microbiology and Sanitation Department of the Central Food Technological Research Institute, Mysore, and were maintained on nutrient agar at 31) + 1°C.
ChemicaLs Essential oil components were obtained from Fluka Chemische Fabrik, Switzerland. They are listed in Table 1 with their purity. Standard solutions of these were prepared in ethanol. Butylated hydroxy-animle (BHA) was obtained from Sigma Chemical Co. (USA).
Culture media and h~ocula Nutrient agar (NA) made up in our laboratory from local ingredients was u~d. The ingredients of NA were: beef extract 3 g, sodium chloride 5 g, agar 15 g, distilled water ! I. The pH was adjusted to 7.2-7.4 with 1).! N NaOH. About 16-18 h old culture of the test bacteria in nutrient broth (NB) incubated at 30°C with optical density adjusted to 0.1 at 550 nm with NB was used as inoculum.
Determblation of the antibacterial activity Antibacterial activity of essential oil components was measured as their capacity to inhibit the growth of the bacteria on NA. Each compound was assayed at IIXl, 2511, 500, 750 and 1000 ttg/ml. Test chemicals were incorporated in medium maintained at 50°C. Twenty-ml aliquots of this medium were poured into petriplatcs and cooled. Plates were inoculated with I1.1 ml of the inoculum {about 3 x l0 s colony forming units) which was spread uniformly on the solidified medium. Five replicates were maintained for each treatment. The ethanol content in the medium did not exceed 0.6%. Media containing only ethanol (0.6%) served as control. Plates wcre incubated at 3(1 +_ I°C and were observed daily for visible bacterial growth. The growth inhibitory activity of cinnamic aldehyde was studied in mixtures both with eugenol and BHA. Ethanolic solutions of the test chemicals were incorporated separately into the molten medium to get the desired total concentration. The procedure was similar to the one followed above.
339 Effect o f temperature and sodiam chlortde o~a the antibacterial actit'ity o] :'innamic aldehyde Cinnami," aldehyde was incorporated intt the medium at (I, 3(11), 4111)and 5{10 p.g/ml. For each treatment three sets of petriplates were prepared. They were incubated at 30 + I°C, 25 +_ I°C and 20 _+ I°C, for 31) days. Sodium chloride at 4% level (w/v, excluding the (I.5% in the medium) was incorporated in the medium before autoclaving. Cinnamic aldehyde was ineorpt-,rated into the medium and the antibacterial activity was determined at 0, 100, 25(, and 500 p,g/ml as described above.
Results and Discussion
Anisaldehydc, anisolc, a- and/J-pincne, a- and y-tcrpinenc did not inhibit the test bacteria even at 1(~10/,tg/ml, the highest level tested (Table 1). Citronellal, eucalyptol, D-limonene and linalool had slight antibacterial activity, inhibiting the bacteria for I - 4 days at 100{) p,g/ml. At the same concentration menthol inhibited the bacteria for 3-1{) days, while citral, eugenol and gcraniol were moderately active in inhibiting the organisms for more than 31} days at 750-1000 ~ g / m l . Cinnamic aldehyde was most active, amoag the essential oil components tested, in completely inhibiting the bacteria for more than 30 days at 5(10 p.g/ml. BHA, the anti-microbial antioxidant, whose activity was also studied for comparison, completely inhibited the test organisms at 200 p.g/ml as has been reported earlier (Klindworth et al., 1979: Shelef and Liang, 1982). In general the essential oil components were more inhibitory to the three Gram-positive bacteria than to the Gram-negative bacterium. Entertd~acter sp. Such difference in the sensitivity of bacteria to the spices has been noted earlier (Shelef et al., 1980). For the control plates visible growth was seen after ! day. A mixture of cinnamic aldehyde and cugenol at 250 and 500 p,g/ml, respectively, completely inhibited the growth of the four bacteria for more than 30 days, whereas the components of the mixtures at the same concentration individually failed to inhibit the bacteria (results not shown). Similarly a mixture of cinnamie aldehyde and BHA at 250 and 100/zg/ml completely inhibited the four bacteria whereas individually both compounds could not. However, with ,sodium chloride at 4% level cinnamic aldehyde did not show any increased inhibitory action (results not shown). Temperature affected the inhibitory activity of cinnamic aldehyde. At 25°C and 20°C complete inhibition was observed at 40{) p,g/ml as against 50{) /zg/ml at 30°C (results not shown). Cinnamic aldehyde has GRAS status and is permitted up to 700 ppm in food (MAFF Food Additives and Contaminants Committee, 1976). This means, the level of cinnamic aldehyde required for complete inhibition of microorganisms in f o o d appears to be within the permitted limit. Because of its characteristic flavour the use of cinnamic aldehyde as food preservative may be restricted to flavoured foods and to those containing spices. The dosage of cinnamic aldehyde required for complete inhibition of microorgan-
340 TABLE I Antibacterial activity of essential oil components Test compound a (purity)
Anisaldehyde (99%) Anisole (99%) Cinnamic aldehyde (98%)
Citral (85-90%)
Citronellal (85-90%)
Eugenol (99%)
Eucalypto| (99%) Geraniol (96%)
D-Lir, onenc (98°/~T Linalool (97%) Menthol (98%)
a-Pinene (99%) ~-Pinene (80-90%) a-Terpinene (90%) y-Terpinene (95%) BHA
Concentra-
No. of days for visible growth
t/on in Nutrient Agar (~g/ml)
Staphylococcus sp.
Micrococcus sp.
Bacillus sp.
Enterobacter sp.
1000 WOO 100 250 500 750 1000 100 250 500 750 WOO 500 750 WOO 250 500 750 1000 750 WOO I00 250 500 750 1000 "/50 I000 750 1000 250 500 750 IQ(]O IG00 1000 1000 WOO 50 I00 150 200
I I 1 3 >30 >30 >30 I 1 5 15 >30 I 2 4 I I 15 >30 I I I I 21 > 30 >30 1 I 1 3 I 4 6 6 I I 1 1 1 3 >30 >30
I I 1 4 >30 >30 >.30 I 1 9 20 >30 1 1 3 I ll) > 30 >30 t I I 2 21 > 30 >30 ! I 1 2 1 3 4 6 I I I 1 I 2 >30 >30
1 I I 3 >30 >30 >30 I I 3 8 >30 I I 2 I Q > 30 >30 1 3 I 2 11 > 30"40 >30 I 2 I 2 I 3 6 10 1 1 I I I 3 >30 >30
I 1 I 3 >30 >30 > 30 I 1 I 2 > 30 I I I I 2 10 15 I I I 1 I I0 >30
= All compounds were obtained from Fluke Chemische Fabrik, Switzerland.
10 > 30
341 isms, c a n be lowered by using it in c o m b i n a t i o n with o t h e r essential oil c o m p o n e n t s as mixtures. S u c h mixtures m a y be desirable as food preservatives for t h e i r mixed flavour instead of a n intense single flavour w h e n only o n e c o m p o u n d is u s e d ( M o l e y a r a n d N a r a s i m h a m , 1988). F u r t h e r r e d u c t i o n in the d o s a g e s o f the essential oil c o m p o n e n t s r e q u i r e d for the control o f m i c r o o r g a n i s m s in f o o d systems m a y be a t t a i n e d by m a k i n g use o f the a d d e d inhibitory effect o f low t e m p e r a t u r e storage. Such use o f m o r e t h a n o n e f a c t o r to inhibit m i c r o o r g a n i s m s in f o o d is desired (Scott, 1989). Use o f essential oil c o m p o n e n t s as f o o d preservatives has the a d d e d a d v a n t a g e t h a t they n e e d not u n d e r g o the r i g o r o u s testing t h a t is c u r r e n t l y r e q u i r e d by the F D A for a p p r o v a l since these have b e e n in use as f o o d flavours.
Acknowledgements T h e a u t h o r s t h a n k Shri B.S. R a m a c h a n d r a , A r e a C o o r d i n a t o r , Fruit a n d Vegetable T e c h n o l o g y for his s u g g e s t i o n s d u r i n g the course o f the investigation. V.M. is grateful to C S I R - N e w Delhi for the a w a r d o f a R e s e a r c h Associateship.
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