Coffee is a rich source of bioactive metabolites such as caffeine, trigonelline, chlorogenic acid, arabinogalactans, melanoidins along with ash, organic acids, and caffeic acid etc and their profile in beans is important and helpful to know the quality of coffee brew (Sridevi & Giridhar, 2008). Among these caffeine, CGAs and trigonelline are major compounds which imparts bitterness in coffee, apart from their diverse physiological functions in humans (Clifford & Wilson, 1985). Intake of such bioactive compounds from coffee drink may be associated with either health benefits or risks. Coffee consumption has been correlated to reduced risk of colon rectal cancer (Lee, Inouem, Otani, Iwasaki, Sasazuki & Tsugane, 2007), Type 2 diabetes (Campos & Baylin, 2007) and Alzheimer’s disease (Barranco, Allam, Serrano Del Castillo & Fernandez, 2007). Recent studies demonstrated caffeine’s positive effects such as pshychoactive response and neurological condition such as Parkinson disease infant hyperactivity, and metabolic disorder like diabetic gallstones and liver function (Dorea & da Costa, 2005). Similarly, coffee bean contains trigonelline (N-methylnicotinic acid or N-methylbetaine of pyridine-3-carboxylic acid) as the second abundant alkaloid compound and it thermally converted to nicotinic acid (antipellagra factor) and some flavour compounds during roasting (Taguchi, 1988). In addition it is considered important for taste and nutrition (Adrian & Fragne, 1991).
Trigonelline content in green coffee beans is in the range of 0.88 to 1.77% in Arabica, 0.75 to 1.24% in Robusta coffee (Ky, Doulbeau, Guyot, Chareir, Hamon, Louarn & Noirot, 2000a), 1.02% in C. pseudozangaeboriae and 0.57% of DMB in C. liberica var Deweveri (Ky, Guyot, Louran, Hamon, & Noirot, 2000b) respectively. Several health promoting properties such as hypoglycaemic, hypocholesterolemic, antitumor, antimigraine, or antiseptic effects have been attributed to triogonelline as cited in Allred, Yackley, Vanamala and Allred (2009). As a biomarker, trigonelline contains inherent measurable biological activity and is a unique compound with many diverse properties. Several studies have attributed the anticancer properties of coffee to metabolites other than caffeine (Hirose, Niwa, Wakai, Matsio, Nakanishi & Tajma, 2007) and the same was further strengthened by a recent study which showed phytoestrogenic nature of trigonelline from coffee beans (Allred et al., 2009).
Trigonellline is synthesized by the methylation of nicotinic acid by S-adenosyl-L-Methionine (SAM) dependent nicotinate N-Methyltransferase (EC 188.8.131.52) which has been found in crude extracts of pea (Joshi & Handler, 1960) and in coffee leaves (Taguchi, Yamaki Sakaguchi & Shimabayashi, 1987). Trigonelline and its synthetic ability from nicotinic acid are distributed in all parts of coffee seedlings (Zheng & Ashihara, 2004; Mazzafera, 1991). However the levels of nicotinic acid are quite less compared to trigonelline as most of the nicotinic acid is converted to trigonelline. In raw coffee beans NA is in the range of 16-44 μg/g (Hughes & Smith, 1946; Carvalho,1962; Casal, Olivera, & Ferreira, 2000). During roasting trigonelline partially degrades to produce pyridines and nicotinic acid and other minor compounds which impart flavour and aroma, hence essential from organoleptic features point of view. Various studies indicate that trigonelline demethylating enzyme activity leads to nicotinic acid production (Taguchi & Shimabayashi, 1983) and also by pyrolysis of trigonelline (Viani & Horman, 1974). The demand for high quality coffee is rapidly increased over the last few years and is still expected to increase. Though arabica coffee brewed from beans of C. arabica is preferred as filter coffee, robusta coffee from C. canephora too is having importance in global market as it is used as soluble coffee (instant coffee).
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(Author: Sridevi V., Giridhar Parvatam