Colour kinetics and rheology of coriander leaf puree and storage characteristics of the paste Jasim Ahmed a, *, U.S. Shivhare b , P. Singh c a Department of Food Sciences, Faculty of Food Systems, United Arab Emirates University, Al Ain, PO Box 17555, United Arab Emirates b Department of Chemical Engineering & Technology, Panjab University, Chandigarh-160 014, India c Department of Food Science and Technology, G.N.D. University, Amritsar-143005, Punjab, India Received 21 January 2003; received in revised form 22 May 2003 Abstract Coriander leaves have been used as a food flavourant in various cuisines since ancient times. The colour degradation kinetics of coriander leaf puree was studied using a fraction conversion technique during thermal treatment at 50, 65, 80, 95 and 110  C for up to 60 min. Blanched, comminuted coriander leaf puree was subjected to heat treatment at selected temperatures in an oil bath with agitation. Treated samples were removed from the bath at selected time intervals (0–60 min after come-up period), cooled imme- diately and analyzed for colour using a Hunterlab colourimeter. The rheological characteristics of the puree were evaluated using a computer-controlled Haake rotational viscometer at 50, 60, 70 and 80  C and it was found that the Herschel–Bulkley model ade- quately represented shear stress-shear rate data. Temperature dependency of the consistency index and apparent viscosity at a shear rate of 100 s 1 followed the Arrhenius relationship and the flow activation energy ranged between 17.2 and 17.9 kJ/mol. Coriander puree was converted to paste by adding common salt (2%) and the required volume of citric acid to adjust the pH to 4.2. The paste was then filled into glass bottles and stored at selected temperatures (5, 25 and 37  C) for 6 months and was periodically evaluated for colour, total aerobic plate count and physicochemical properties. Coriander puree/paste colour was expressed in terms of tristimulus colour value a and combination (Lab). First order reaction kinetics adequately described the changes in colour values during both thermal treatment of puree and storage of paste. The process activation energies were 29.3 and 22.1 kJ/mol, respectively, for a and (Lab) during thermal treatment. The corresponding values during storage were 12.7 and 12.2 kJ/mol. The paste was microbiologically stable with no significant changes (P > 0.05) in physicochemical characteristics during storage. # 2003 Elsevier Ltd. All rights reserved. Keywords: Coriander leaves puree and paste; Kinetic model; Colour; Flow behavior; Storage; Activation energy 1. Introduction Coriander (Coriandrum sativum L.) is an umbellifer- ous annual plant of the parsley family, native to the east Mediterranean region and southern Europe. It is grown in Romania, Mexico, Argentina, Egypt, India, the Uni- ted States, China, Russia and many other countries. The herb is used as a valuable spice for its exotic flavour, stimulant and carminative properties while fluid-extract (and oil) is used medicinally as an antispasmodic, for rheumatism and as a tonic. The plant produces a slen- der, hollow stem 30–60 mm high with bipinnate leaves and small pink flowers. It is valued for the fruits, called coriander seeds and the fresh green leaves called cilan- tro. The delicate young leaves are widely used in Latin- American, Indian and Chinese dishes to impart flavour. The fresh coriander leaves contain 2-decenal and 2- dodecenal. Fresh coriander leaves are perishable in nature and require immediate processing or preservation. Drying is the major processing technology practised for coriander leaves so far. However, drying has a limitation on aro- matic herbs as it results in considerable losses of flavo- noid components and attractive colour pigments (Baranowski, 1985; Lee et al., 1992; Pezzutti & Crapiste, 1997). Therefore, there is a need for alternate processes for shelf-life extension and for developing other cor- iander leaf-based products. Puree and pastes are such 0308-8146/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0308-8146(03)00285-1 Food Chemistry 84 (2004) 605–611 www.elsevier.com/locate/foodchem * Corresponding author. E-mail addresses: jahmed@uaeu.ac.ae (J. Ahmed), usshiv@yahoo. com (U.S. Shivhare).