Antimicrobial Potential of Agro-Industrial Wastes
14.5.3.1 Extraction of Polyphenolic Compounds from Mango Seed Kernels
Huge quantities of peel and kernel by-products are generated during processing of mango. This waste has high content of phenolic compounds and saturated fatty acids. Mango kernels are good source of phospholipids, phenolic compounds, campesterol, β-sitosterols, stigmasterol, and tocopherols (Soong and Barlow 2004). Mango seed kernel enhances oxidative stability and shelf life of fresh cheese and ghee (Parmar and Sharmar 1990). Good antioxidant property of mango seed kernel
is attributed to the presence of polyphenols, sesquiterpenoids, phytosterols, and microelements, such as selenium, copper, and zinc (Schiber et al. 2003). Maisuthisakul (2008) found phenolic compounds like phenolic acids and flavonoids in the extract of Thai mango (Mangifera indica Linn.) seed kernels.
14.5.3.2 Extraction of Tannins from Agricultural By-Products
Huge amount of agricultural wastes of tannin-containing plants are generated. Tannins, a polyphenolic compound, showed antimicrobial (Doughari et al. 2008) and antioxidant activities (Zargham and Zargham 2008). Sung et al. (2012) investigated wastes from green tea processing, acorn, chestnut, and persimmon hulls for extraction of tannin and their antibacterial and antioxidant activities. Tannin content in the ethanol, acetone, and aqueous extracts was determined. They found tannin concentrations in the extracts of chestnut hull, green tea waste, acorn hull, and persimmon hull. Tannin concentration for green tea waste was highest in ethanol extracts, whereas for chestnut hull it was highest in ethanol and acetone extracts. Antibacterial activities of various extracts were screened against Staphylococcus aureus, E. coli, S. flexneri, L. monocytogenes, and B. coagulans. Tannin extracts from green tea waste showed higher antibacterial activity than the extracts of acorn, chestnut, and persimmon hulls.
14.5.3.3 Biological Activity of Jojoba Hull Extracts
Simmondsia chinensis, better known as jojoba, is commercially cultivated in many countries all over the world. It is grown commercially for its seed oil. It is also used as food by many animals. Jojoba seed oil has medicinal properties useful for treatment of cancer, kidney disorder, obesity, sore heart, warts, and wounds (Leung and Foster 1996). Wagdy and Taha (2012) evaluated antimicrobial activity of phenolic extracts of jojoba hulls using different extracting solvents against five bacterial strains Escherichia coli, Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes, and Salmonella typhimurium. They used five different extracts: methanol, ethanol, acetone, isopropanol, and ethyl acetate. Different extracts of jojoba hulls inhibited growth of the test microorganisms through varying degree. Maximum inhibition of B. cereus and S. typhimurium was exhibited by ethyl acetate extract. Highest inhibition of B. cereus was achieved with ethyl acetate. S. aureus was inhibited most by methanol extract. Highest inhibition of L. monocytogenes and E. coli was obtained with ethanol and acetone extract, respectively. Wagdy and Taha (2012) suggested that jojoba hull is a very promising source of bioactive compounds with very good antioxidant, antimicrobial, and anticancer properties.
14.5.3.4 Antimicrobial Compounds from Olive Oil Mill Waste
Olive fruit is a rich source of phenolic compounds, such as phenol acids, phenol alcohols, catechol, methylcatechol, phenyl alcohols (tyrosol, hydroxytyrosol), flavonoids (luteolin-7-glucoside, apigenin-7-glucoside, rutin and quercetin), and several anthocyanin pigments (cyaniding-3-glucoside and cyaniding-3-rutinoside) (Ragazzi et al. 1973; Andary et al. 1982; Romero et al. 2002). Hydroxytyrosol is one of major phenolic compound present in olive fruit with remarkable pharmacological and antioxidant activity (Visioli et al. 2004; Fernandez et al. 2006). Oleuropein is another valuable compound with certain antiviral, antibacterial, antifungal, antioxidant, and anti-inflammatory properties (Aziz et al. 1998; Visioli and Galli 2002). Phenolic compounds derived from olives have shown antibacterial activities against pathogenic bacteria, such as Salmonella spp., Staphylococcus aureus, Clostridium botulinum, and Listeria monocytogenes (Payne et al. 1989; Nychas et al. 1990; Tassou and Nychas 1995).
It is a known fact that olive oil mill waste contains polyphenols in considerable amount. Concentration of polyphenols has been reported to be so strong that phytopathogenic bacteria like Pseudomonas syringae and Corynebacterium michiganense fail to grow in it (Capasso et al. 1995). Ciafardini and Zullo (2003) studied the effect of polyphenols present in the olive oil mill wastewater (OMWW) on the crucifer seed-borne phytopathogen Xanthomonas campestris. They reported that polyphenols in contact with the bacterial cultures react with the protein of the bacterial cell walls and disrupt them. OMWW was able to control the seed-borne phytopathogen Xanthomonas campestris completely without damaging the germinability of the crucifer seeds and the metallic greenhouse structures. Therefore, Ciafardini and Zullo (2003) suggested that polyphenols from OMWW are a natural substitute for commercial corrosive chemicals like sodium hypochlorite, which is currently used to disinfect seeds and greenhouses.
14.5.3.5 Other Agrowastes
Martin et al. (2012) assessed the antimicrobial potential and chemical composition of guava bagasse (Psidium guajava), Cabernet Sauvignon, Pinot Noir (Vitis vinifera) grape marc, Isabella grape marc (Vitis labrusca) wastes, Petit Verdot Verdejo grape marcs, Syrah and Verdejo grape stems, Petit Verdot grape seed and red grape fermentation lees (Vitis vinifera), tomato bagasse (Solanum lycopersicum) wastes, and vegetable wastes, kale (Brassica oleracea), beet (Beta vulgaris), broccoli (Brassica oleracea) and turnip stems (Brassica rapa), carrot (Daucus carota) and radish leaves (Raphanus sativus), pumpkin (Cucurbita sp.) and peanut peel, and passion fruit hulls (Passiflora edulis) against pathogenic microorganisms of importance in food. Samples were immersed in ethanol and methanol solutions to prepare extract. Beet stalk, peanut peel, Pinot Noir grape marc, Petit Verdot grape seed and marc, red grape fermentation lees, and guava bagasse wastes showed antimicrobial activities against Gram-positive bacteria Staphylococcus aureus and Listeria monocytogenes. Methanol extract of peanut peels and ethanol extract of guava bagasse extracts showed the lowest MIC against S. aureus and L. monocytogenes. Guava bagasse extract showed the highest antimicrobial activity against L. monocytogenes.
