Study of physiological and quality parameters during development and ripening of pepino Solanum muricatum Aiton) fruit

Carolina Contreras1, Wilfried Schwab2, Mechthild Mayershofer2, Ignacio Morales3, Mauricio Gonzalez-Agüero3, and Bruno G. Defilippi3*
Pepino (Solanum muricatum Aiton) fruit served as an important crop in Pre-Columbian Andean cultures. Despite the fact that pepino has been known for centuries, information about maturity indices and physiological quality parameters of its fruit is scarce. The objective was to increase our knowledge of pepino fruit physiology and maturity to improve fruit handling and storage. Pepino fruit were studied during 2015 and 2016 seasons. During 2015, developmental and maturity studies were carried out, whereas in 2016 the developmental study was repeated. Twenty-five fruit were analyzed during six developmental stages ranging from immature (stage 1) to senescent fruit (stage 6). Fruit were analyzed for soluble solid content (SSC), titratable acidity (TA), color, respiration and ethylene production, soluble sugars, organic acids, and aroma. For the maturity assay, nonsignificant differences were found between green background color (M1) and white background color (M2) in the different quality parameters, with the exception of firmness. Pepino is a non-climacteric fruit with a low ethylene production rate. Unlike foreign cultivars, Chilean pepinos have low amounts of citric acid, being the predominant acids: malic and quinic. Out of 22 volatile compounds identified in this study, the predominant aroma volatiles are 3-methyl-3-butenyl acetate and 3-methyl-2-butenyl acetate from the terpenoid pathway, and trans-2-hexenal from the lipoxygenase pathway. The quality parameters changing in a ripening-dependent manner were firmness, SSC, aroma and color. Other parameters such as TA and organic acids stayed constant throughout development. In addition to color and SSC, this study also suggests aroma as a harvest index.
Keywords: Aroma, firmness, fruit ripening, harvest index, maturity, sucrose.
1Pontificia Universidad Católica de Chile, Facultad de Agronomía e Ingeniería Forestal, Departamento de Fruticultura y Enología, Vicuña Mackenna 4860, PO Box 7820436, Santiago, Chile.2Technical University of Munich, Center of Life and Food Science Weihenstephan, Biotechnology of Natural Products, Liesel-Beckmann-Str. 1, 85354 Freising, Germany.3Instituto de Investigaciones Agropecuarias, INIA La Platina, Santa Rosa 11610, Santiago, Chile. *Corresponding author (bdefilip@inia.cl).