Morpho-structural description of epidermal tissues related to pungency of Capsicum species L. Sánchez-Segura a , D.I. Téllez-Medina a , S. Evangelista-Lozano b , E. García-Armenta a , L. Alamilla-Beltrán a , H. Hernández-Sánchez a , A.R. Jiménez-Aparicio b , G.F. Gutiérrez-López a,⇑ a Departamento de Graduados e Investigación en Alimentos, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Carpio y Plan de Ayala S/N, Col. Santo Tomás, C.P. 11340 D.F. México, Mexico b Centro de Desarrollo de Productos Bióticos, Instituto Politécnico Nacional, Carretera Yautepec-Jojutla, Km. 6, Calle Ceprobi No. 8, Col. San Isidro, Apartado Postal 24, Yautepec, Morelos, México C.P. 62731, Mexico article info Article history: Received 13 May 2014 Received in revised form 15 October 2014 Accepted 27 November 2014 Available online 4 December 2014 Keywords: Capsicum Fractal dimension Lacunarity Capsaicin Morphological changes Ripening abstract Chili peppers (Capsicum spp.) production is important worldwide due to its capsaicin contents. This work aimed to evaluate morphometrics of chili pepper tissues and in the formation of ampullas (structures related to pungency) by digital image analysis (DIA). Structural changes of epidermis in pungent chili peppers ‘‘habanero’’ and ‘‘jalapeno’’ were evident at 15 and 31 dpa (days post-anthesis), respectively, while in ‘‘bell pepper’’ (no pungent), only minor changes were observed during 82 dpa. Fractal dimension (Fd) and lacunarity (K) values of cropped tissue images were useful to distinguishing between pungent on one side and intermediate and non-pungent varieties on the other. Correlations between fractal areas of evaluated tissues were high for ‘‘jalapeno’’ and ‘‘bell pepper’’ while for ‘‘habanero’’ no correlation was found. Linear regressions and significant correlations between Fd and K indicated that DIA morphology characteristics are related to ripening stages, thus indicating commercialisation and processing possibilities. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Chili peppers (Capsicum spp.) are one of the most important crops worldwide (Wang and Bosland, 2006). Economic value of this crop has gained attention since the world production in 2012 reached 31,171,567 ton/year (FAO, 2014) being the main producer countries, China with 51.32% of the whole worldwide production followed by Mexico with 7.6% (FAO, 2014). In the food field, Capsi- cum species are important due to the presence of compounds such as b-carotene, phenols, and ascorbic acid among others (Antonious et al., 2009). The main pungent Capsicum species are Capsicum chinense Jacq., ‘‘habanero’’ and Capsicum annuum L., ‘‘jalapeno’’, on the other hand, C. annuum L., ‘‘bell pepper’’ is the main non- pungent chili pepper consumed in the world (Frank et al., 2001). Pungency depends mainly on the presence of capsaicin and dihy- drocapsaicin (Kosuge and Furuta, 1969; Perucka and Oleszek, 2000). Iwai et al. (1979) and Fujiwake et al. (1982a) found that capsaicinoids become detached from placenta causing morpholog- ical changes in the epidermal cells of this tissue (Suzuki et al., 1980). Stewart et al. (2007) reported that the main morphological change in pungent species was the formation of cell structures with capsaicinoid-producing properties which were called glands or ampullas so describing a swelling of the epidermis produced by the filling of the subcuticular cavities throughout the interlocu- lar septum of pungent species of Capsicum. These ampullas have been associated with the production of capsaicin and have been described by Zamski et al. (1987) and Stewart et al. (2007), who found that capsaicinoids are secreted into the spaces between the cell wall and the cuticle so that greater intercellular spaces are associated with the accumulation of capsaicinoids. Further- more, it has been reported that capsaicinoids are compartmenta- lised into vesicles 0.15–1.0 lm in diameter having ‘‘small droplet’’ morphology, dark in colour and osmiophilics, which were found in fragments of thickened endoplasmic reticulum. During ripening, these vesicles move through the cytoplasm and fusion with the plasmalem which has been reported to play an important role on the excretion of capsaicinoids towards the external part of the cell wall (Suzuki et al., 1980; Zamski et al., 1987). Morpholog- ical changes of whole fruits and tissues have been associated to the ripening process of various fruits. Platt-Aloia et al. (1980) found that during the ripening of avocado, the cell walls of the paren- chyma presented ultrastructural changes which were correlated to wall-hydrolytic enzyme activity, thus favouring fruit softness. This process was monitored by using transmission (TEM), scanning (SEM) and freeze fracture (FFEM) electron microscopy techniques. http://dx.doi.org/10.1016/j.jfoodeng.2014.11.022 0260-8774/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: gusfgl@gmail.com (G.F. Gutiérrez-López). Journal of Food Engineering 152 (2015) 95–104 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng