The antimicrobial activities of phenolics have been reported from various plant resources. Their modes of actions are well explained by many workers (Cowan 1999; Nohynek et al., 2006; Veldhuizen et al., 2006). However their basic mode of action is as follows.
1. The position and number of hydroxyl groups is related to the level of toxicity in case of some phenols e.g carvacrol.
2. In simple phenols such as catechol and epicatechin, inhibition is mainly due to substrate deprivation and membrane disruption.
3. Other mechanisms of action by phenolic acids, flavonoids and tannins involve enzyme inhibition, enzyme inactivation, formation of complexes with cell walls and metal.
4. Disruption of cell homeostasis leading to growth inhibition and cell death.
Phytomedicines from M.oleifera and J. curcas wastes:
Researchers are increasingly attracted for the development of phytomedicine and therefore, have aided the industry in this process to develop innovative biotechnology to look for new potential leads to combat against microbial pathogens (Kroyer, 1995). To comply with scientists have studied the antimicrobial activity from different organic wastes (Perez et al., 1992). For instance the food and cosmetic industry has opted for the use of natural alternatives for the maintenance of product shelf life (Riemer and Kristoffersen 1999). Agricultural wastes such as peel of various fruits and vegetables nowadays is applied in all these industries (Mohamed et al. 1994). Extensive research has been done on citrus peel. The peel of citrus fruit is a rich source of flavones and many polymethoxylated flavones showed potential antimicrobial activity (Ahmad et al., 2006). Researchers from different countries showed that different types of citrus peel exhibited broad spectrum antimicrobial activity (inhibition zone 11mm-22mm) with MIC in the range between 130μg/ml-50 mg/ml (Javed et al., 2011; Jwany et al., 2012). Other than peel, roots of citrus fruit also showed to have flavanoid content with antiinfective activity (Intekhab and Aslam, 2009). Peels of other fruits and vegetables such as Mangifera indica, Lagenaria siceraria, Solanum tuberosum Ananas comosus, Luffa acutangula, Momordica charantia, Moringa oleifera, Carica papaya, Raphanus sativa, Chrysophyllum albidum, Punica granatum have been reported to have broad spectrum antimicrobial activity with MIC ranging between 0.39-500 mg/ml, inhibition zone appeared between 9mm to 35mm (Kulkarni et al., 2005; Chanda et al. 2010; Kamba and Hassan 2010; Mohd et al. 2012; Janjua et al. 2013). Along with the antibacterial property of Egyptian banana peel the UV protection property was also detected and was tested on Egyptian cotton fabrics (Salah 2010). Banana peel was also found to be effective against skin and gastrointestinal tract diseases (Naveena and Sumathy 2011). Potato peel a vegetable waste was found to be fungicidal and bacteriostatic against Gram negative bacteria but at high concentrations (Deviprasad and Pushpa 2007; Rodrigues de Sotillo et al., 2007). Sphingolipids a kind of byproduct from the stems of cucumber (Tang et al., 2010) showed to have antimicrobial activity against phytopathogenic fungi having inhibition percentage between 23.4± 2.7 to 88.0± 0.6 and bacteria having inhibition zone between 13mm to 22mm.
The seeds of pumpkin (Chonoko and Rufai, 2010) used traditionally for various ailments was reported to have broad spectrum antibacterial activity having MIC between 500 mg/ml – 2000 mg/ml (Inhibition zone 7mm-11mm). The leaves of Psidium guajava, Averrhoa carambola, showed to have broad spectrum antimicrobial activity against Gram positive bacteria, Gram negative bacteria, yeast and fungi (Mohamed et al. 1994). Leaves and stems extracts of Ginja cherry plant the waste obtained in the production of the cherry liquor showed antibacterial activity, having MIC between 10-100 mg/ml (Piccirillo et al., 2010). Grape wastes obtained during the processing of wine have also been reported to exhibit broad spectrum antibacterial activity (Vasan, 2009).
Agricultural wastes such as acorn hull, chestnut hull, and persimmon hull contains tannins which were found to inhibit pathogenic bacteria - Listeria monocytogenes, Bacillus coagulans, Shigella flexneri, Methicillin-Resistant Staphylococcus aureus (Sung et al., 2012).
Oliveira (2008) showed that walnut green husks, a by-product of walnut production, has potential antimicrobial activity against both Gram positive and Gram negative bacteria (Inhibition zone 2mm-9mm). Other such wastes to be reported with antimicrobial activity are olive leaves (Pereira et al., 2007a), walnut leaves (Pereira et al., 2007b). Bokhari and Perveen (2011) showed that leaves of date palm inhibited fungal strains such as Fusarium oxysporum, Fusarium solani, Aspergillus flavus, Alternaria alternata and Trichoderma sp with MIC between
3.7mg/ml-6.7mg/ml. Osman et al., (2011) showed that agricultural wastes (rice straw, cotton waste, maize waste) has inhibitory effect against the fungi Rhizoctonia solani causing root rot in Glycine max (inhibition % 0-31.2±2.2). Whereas, the leaf waste and the juice of Agave sisalana (Santos et al 2009; Ade-Ajayi et al., 2011) a fibre producing agro product has broad spectrum antimicrobial activity against both fungi and bacteria having effective dose of 0.39 mg/ml (inhibition zone 18-20mm). Electrospun nanofibres a waste from cotton processing industry reported antibactetrial activity against Staphylococcus aureus (Kampeerapappun 2012). A significant amount of antibacterial activity has been reported from coffee and tea waste a byproduct from beverage processing industry. The in vitro and greenhouse trial with extracts of tea and coffee wastes showed inhibition of halo blight disease caused by the bacterial pathogen, Pseudomonas syringae and also showed improved plant growth (Alstrom, 2008).
