Eucalyptus is well reputed for its use as medicinal plant around the globe. The present study was planned to evaluate chemical composition, antimicrobial and antioxidant activity of the essential oils (EOs) extracted from seven Eucalyptus species frequently found in South East Asia (Pakistan). EOs from Eucalyptus citriodora, Eucalyptus melanophloia, Eucalyptus crebra, Eucalyptus tereticornis, Eucalyptus globulus, Eucalyptus camaldulensis and Eucalyptus microtheca were extracted from leaves through hydrodistillation. The chemical composition of the EOs was determined through GC-MS-FID analysis. The study revealed presence of 31 compounds in E. citriodora and E. melanophloia, 27 compounds in E. crebra, 24 compounds in E. tereticornis, 10 compounds in E. globulus, 13 compounds in E. camaldulensis and 12 compounds in E. microtheca. 1,8-Cineole (56.5%), α-pinene (31.4%), citrinyl acetate (13.3%), eugenol (11.8%) and terpenene-4-ol (10.2%) were the highest principal components in these EOs. E. citriodora exhibited the highest antimicrobial activity against the five microbial species tested (Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Aspergillus niger and Rhizopus solani). Gram positive bacteria were found more sensitive than Gram negative bacteria to all EOs. The diphenyl-1-picrylhydazyl (DPPH) radical scavenging activity and percentage inhibition of linoleic acid oxidation were highest in E. citriodora (82.1% and 83.8%, respectively) followed by E. camaldulensis (81.9% and 83.3%, respectively). The great variation in chemical composition of EOs from Eucalyptus, highlight its potential for medicinal and nutraceutical applications.

Cell wall of various plants contains an organic polymer lignin. Lignin makes significant structural constituents that support of vascular plants tissues, some types of algae and makes plants stiff and woody. Chemically lignin composed of cross-linked phenolic polymers and Kraft lignin dissolved in the unsaturated resin system. Lignin is a vastly available and well-studied antioxidant. They work as antioxidant against the biological, chemical and mechanical stress on plants. The substance that removes potentially damaged oxidizing agents in a living organism is regarded as antioxidant. Lignin contains a huge amount of phenolic constructions that enable it to act as an effectual antioxidant. Infrared spectroscopy (IR) observed decreases in some oxidative aging products and maintained the idea that lignin play role as an effective antioxidant. It was discovered that antioxidant action of lignin varies with the molecular characteristics, isolation method and genetic origin. Capacity of lignin to scavenge the radicals that are involved in the oxidation is affected by partial dispersion into polymer matrix. Antioxidant activities of various technical lignins are determined. Chemical changes in lignin could result in products with characteristics that can be used in special industrial divisions.

The plant biomass and agro-industrial wastes show great potential for their use as attractive low cost substrates in biotechnological processes. Wheat straw and corn cob as hemicellulosic substrates were acid hydrolyzed and enzymatically saccharified for high xylose production. The hydrolysate was concentrated and fermented by using Saccharomyces cerevisiae and Kluyveromyces for production of xylitol. Acid hydrolysis of wheat straw and corn cob in combination with enzymatic hydrolysis showed great potential for production of free sugars from these substrates. Kluyveromyces produced maximum xylitol from acid treated wheat straw residues with enzymatic saccharification. The percentage xylitol yield was 89.807 g/L and volumetric productivity of 0.019 g/L/h. Kluyveromyces also produced maximum xylitol from corn cob acid hydrolyzed liquor with xylitol yield 87.716 g/L and volumetric productivity 0.018 g/L/h. Plant and agro-industrial biomass can be used as a carbohydrate source for the production of xylitol and ethanol after microbial fermentation. This study revealed that wheat straw acid and enzyme hydrolyzed residue proved to be best raw material for production of xylitol with S. cerevisiae. The xylitol produced can be utilized in pharmaceuticals after purification on industrial scale as pharmaceutical purposes.

Medicinal plants Ficus religiosa, Citrus paradisi, Vitis vinifera, Ficus benghalensis, Gardenia radicans, Ziziphus Jujuba, Morus alba, Punica granatum, and Psidium guajava were evaluated for their anti-aflatoxigenic activities. The layer hens feed contaminated with A. flavus was treated with plant leaves at different concentrations and feed was stored at 28°C and 16% moisture level for 6 months and subjected to aflatoxins B1 and B2 (AFB1, AFB2) monitoring. P. granatum and M. alba showed 100% inhibition. Both types of AFs were not detected up to 180 days. Z. Jujuba, V. vinifera and F. benghalensis controlled AFB2 completely; however, at the end of 180 days, a small amount of AFB1 was observed. P. guajava, C. paradise, G. radicans and F. religiosa also controlled AFB1 and AFB2, but at higher concentration. In comparison to the European Commission and FAO standards for AFB1, at the end of the storage period, the AFs detected were within permissible limits. In view of considerable antifungal activities, the AFs produced by A. flavus can be controlled by P. granatum and M. alba plants to protect feed from fungal attack and AFs production during storage.