Evaluation of the effect of ripening on the sensory quality and properties of tamarillo (Cyphomandra betaceae) fruits Gikuru Mwithiga a, * , Michael Inzoberi Mukolwe b , Douglas Shitanda b , Paul Nyota Karanja c a Department of Agricultural Engineering and land Planning, Botswana College of Agriculture, Private Bag 0027, Gaborone, Botswana b Department of Biomechanical and Environmental Engineering, Jomo Kenyatta University of Agriculture and Technology, P.O. Box 62000, Nairobi, Kenya c Department of Food Science and Post-harvest Technology, Jomo Kenyatta University of Agriculture and Technology, P.O. Box 62000, Nairobi, Kenya Received 17 June 2005; accepted 16 January 2006 Available online 6 March 2006 Abstract Tamarillo (Cyphomandra betaceae) fruits were sourced from a single farmer from the Central province of Kenya soon after harvest- ing. The fruits were then cleaned and sorted in order to remove all immature and damaged fruits. The resulting fruits were by visual inspection divided into eleven groups or ripeness scales depending on the degree of ripening and then subjected to a sensory evaluation for taste and colour using an untrained panel of 10 people. Objective measurements of firmness, colour, juice yield, pH and total soluble solids were also done for all the eleven ripeness groups. The sensory score for both taste and colour increased with the degree of ripeness to reach a maximum at the ripeness scale of between 7 and 9, respectively, and thereafter decreased with further ripening. There was a remarkable change in the fruit pulp colour with L * and b * decreasing with increase in ripeness from 64.6 to 36.1 and 40.8 to 13.2, respectively, while a * values increased from 4.3 to 8.5. Changes in fruit surface colour were well pronounced and decreased from 46.3 to 22.1 and 28.3 to 4.9 for L * and b * , respectively, while a * increased from 4.9 to 28.3. There was progressive increase in juice yield (10.6–26.0%), total soluble solids (9.4–10.9) and pH (3.35– 3.85) with increase in degree of ripeness. However, the firmness decreased from 115.5 to 71.6 N with increase in degree of ripeness. There was a linear relationship between the colour lightness coordinates for peel and pulp with an R 2 value of 0.989 indicating that fruit surface L * values are good indicators of internal quality. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Tamarillo fruits; Ripening; Sensory quality; Objective measurement; Fruit properties 1. Introduction The tamarillo (Cyphomandra betaceae) fruits, also known as tree tomatoes are smooth skinned, oval shaped berries capped with a calyx and stem (Verheij & Coronel, 1992) and are usually 5–10 cm long and 4–5 cm wide (Fig. 1). Popeone et al. (1989) identified three main fresh market types based on the peel and pulp colour, which is either red, dark red or yellow depending on the variety. The fruit is native to Peru in South America but is grown in small quantities in many other parts of the world (Popeone et al., 1989). This interesting and unusual botan- ical relative of potatoes and tomatoes has commercial promise for many regions (Verheij & Coronel, 1992) and is an attractive option for processing into juice and wine as is already done in South America (Popeone et al., 1989). As a practice, fruits should be harvested at the correct physiological maturity and state of ripeness (Harman & Patterson, 1984). Fruits that will be used for juice extrac- tion should be processed at the degree of ripeness that 0260-8774/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2006.01.035 * Corresponding author. Tel.: +267 7247 2087; fax: +267 3928 75. E-mail address: gikurum@yahoo.com (G. Mwithiga). www.elsevier.com/locate/jfoodeng Journal of Food Engineering 79 (2007) 117–123