Abstract
Antimicrobial activity of ethanolic extracts of Xylopia aethiopica, Aframomum melegueta and Piper guineense fruits were assayed against fourteen (14) microorganisms commonly associated with food poisoning and/or food spoilage. The microorganisms were Bacillus subtilis IAM1069, Bacillus cereus IFO 13494,Staphylococcus aureus FDA 209p, Escherichia coli NRIC 1023, Salmonella typhimurium IFO12529, Lactobacillus plantarum IAM 1041, Pediococcus acidilactici-M, Leuconostoc mesenteroides-M, Lactobacillus casei TISTR390, Saccharomyces cerevisiae OC-2, Hansenula anomala IFO 0140 (p), Pichia memb.IFO 0128,Penicillium funiclosum NBRC 6345 and Candida species. All the plant extracts exhibited selective antimicrobial activities on the test organisms. X. aethiopica extract exhibited the highest antimicrobial activity on the organisms with a minimum inhibitory concentration (MIC) of 50 ppm on Bacillus species and S. aureus. S. cerevisiae (MIC = 300 ppm), P. funiclosum NBRC 6345 and L. mesenteroides (MIC = 500 ppm) were also susceptible to X. aethiopica fruit extract but the MIC values for the other tested microorganisms were higher than 1000 ppm. This was followed by A. melegueta fruit extract with MIC of 100 ppm for B. cereus and S. aureus. Although P. guineense fruit extract inhibited the growth of B. cereus and S. aureus (MIC = 300 ppm); and B. subtilis (MIC = 1000), the MIC for the other microorganisms were higher than 5000 ppm. On the whole, all the plant extracts exhibited the least antimicrobial activities onLactobacilli and fungi species. X. aethiopica fruit extract was used to preserve fresh orange juice. The ability of 100 and 1000 ppm extract to preserve the orange juice was significantly greater (p<0.05) than 50 ppm. The microbial concentration in orange juice containing 100 ppm of X. aethiopica extract was 4 cfu/mL after 28 days of storage at room temperature. Key words: Food spoilage, food poisoning, microorganisms, spices, ethanolic extract, natural preservatives, orange juice.
Highlights
Food poisoning and food borne infections are very common all over the world, especially in tropical countries with elevated temperature and humidity that favour microbial growth (Adebajo, 1993)
P. guineense fruit extract inhibited the growth of B. cereus and S. aureus (MIC = 300 ppm); and B. subtilis (MIC = 1000), the minimum inhibitory concentration (MIC) for the other microorganisms were higher than 5000 ppm
The yield varied among the spices with X. aethiopica giving the highest extract yield of 20%, followed by P. guineense with 13.5%, while A. melegueta gave the lowest yield of 7.5%
Summary
Food poisoning and food borne infections are very common all over the world, especially in tropical countries with elevated temperature and humidity that favour microbial growth (Adebajo, 1993). The spices are used to give aroma and flavour to food and at the same time they can serve as food preservatives because they possess active ingredients which are either microbistatic or microbicidal (Adegoke and Sagua, 1993; Okeke et al, 2001; Okigbo et al, 2005; White, 2006; Okigbo and Igwe, 2007). Among these medicinal plants are Xylopia aethiopica (Negro pepper), Aframomum melegueta (Aligator pepper) and Piper gueenese
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