ANTIOXIDANT ACTIVITY LITERATURE REVIEW

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4. Lignin

Lignin is a phenolic polymer in large amounts in plant cells and wood tissues. Lignin acts naturally as antioxidant against chemical, biological and mechanical stress in plants Kosikova, 2009. Coffee pulp contains the highest amount of lignin in coffee berry than the other parts Murthy, 2011. As antioxidant agent, lignin acts as a stabilizer of reaction induced by oxygen Kratzl et al., 1967.

E. ANTIOXIDANT ACTIVITY

Autoxidation is a spontaneous reaction between oxygen in atmosphere and organic compounds Chan, 1987. Autoxidation is responsible to rancidity and loss of nutritional value in foods and to condition of cellular damages and cytotoxicity. Autooxidation via free radical chain reaction proceeds into three steps: initiation, propagation and termination. These steps are generally addition of triplet oxygen to organic compounds. Besides free radicals which produced in autoxidation process, lipid hydroperoxides are also produced as primary products and decomposition of hydroperoxides such as aldehydes, ketones, alcohols, hydrocarbons, volatile organic acids, and epoxy compounds, known as secondary oxidation products Shahidi et al., 2002. Antioxidant defines as compounds which can delay, inhibit or prevent oxidation by scavenging free radicals and diminishing oxidative stress Dai et al., 2010. Oxidative stress is an imbalance condition where quantities of reactive oxygen such as ROS and superoxide anion, overcome capacity of endogenous antioxidant Ames et al., 1993. This process will impact on degenerative diseases in human body such as coronary disease and cancer. Phenolic compounds are majority compounds in plant which have antioxidant activity. Base on its chemical structures, phenolic compounds could have antioxidant free radical scavenging activities because of phenolic hydroxyl groups that donating a hydrogen atom or electron to a free radicals and its conjugated aromatic system that delocalizing an unpaired electron Dai et al., 2010. The antioxidant mechanism of pheolic was showed in the figure 3. Phenolic compounds in coffee have been studied as antioxidant agent. Coffee beans roasted by using microwave methods showed strong activity in DPPH scavenging and protect linoleic acid from oxidation where the antioxidative effectiveness is correlated with polyphenol concentration Nebesny et al., 2003. Furthermore, chlorogenic acid and caffeine were contributed to high antioxidant activity 0.10mM FeIIg SCG of spent coffee ground extracts Mussatto et al., 2011. Figure 3 Antioxidant mechanisms of phenols 7

F. ANTIMICROBIAL ACTIVITY