Elsevier

Food Research International

Volume 96, June 2017, Pages 113-120
Food Research International

Key odor and physicochemical characteristics of raw and roasted jicaro seeds (Crescentia alata K.H.B.)

https://doi.org/10.1016/j.foodres.2017.03.009Get rights and content

Highlights

  • Twenty-seven volatile compounds were identified in raw and roasted jicaro seeds.

  • Mild roasting enhanced the release of ethyl-2-methylbutyrate and pyrazines.

  • Ethyl-2-methylbutyrate was identified as the key odor compound of jicaro seed.

  • Roasting lead to the coalescence of oil bodies and denaturation of protein bodies.

  • SAFE, GC/MS and SPME/ODP were used to characterize volatile compounds of the seeds.

Abstract

Jicaro seeds (Crescentia alata) are widely consumed in Central America, primarily as a popular tasty and nutritious beverage called “horchata”. Seeds are roasted to develop a specific aroma through a process that has never been explored. Volatile compounds, extracted from raw and roasted jicaro seeds (140 °C for 140 s) by SAFE (Solvent Assisted Flavor Evaporation), were analyzed by Gas Chromatography/Mass Spectrometry (GC/MS). Twenty-seven volatile compounds were isolated, among which, ethyl-2-methylbutyrate was designated by olfactometry as providing the characteristic jicaro note (0.16 and 0.47 mg/kg dry basis (d.b.) in raw and roasted seeds, respectively). The release of volatile compounds from the Maillard reaction, such as pyrazines, and the increase of ethyl-2-methylbutyrate after roasting, exhausted the pleasant jicaro aroma.

This mild roasting process had a slight impact on polyphenol, fructose and free amino acid contents, in agreement with the Maillard reaction. Confocal microscopy showed the coalescence of lipids in roasted jicaro seeds, which might explain the higher extracted fat content.

Introduction

Jicaro (Crescentia alata), a species of the Bignoniaceae family, is a small tree native to Mexico and Central America and is widespread in dry regions of Central and South America (Bass, 2004) as well as India (Madhukar, Srivastava, & Dubey, 2013). The jicaro fruit has a lignified pericarp with many seeds embedded in a sweet pulp. The jicaro seed structure consists of a white cotyledon surrounded by a dark brown coat. It has been reported that jicaro cotyledon is rich in protein (43 g/100 g dry basis) and fat (38 g/100 dry basis) content. In addition, the seeds do not contain anti-nutritional factors (Corrales et al., 2017).

Jicaro seeds are used in the preparation of one of the most consumed traditional beverages in Central America (mainly Nicaragua, Honduras and Salvador). This beverage presents pleasant sensory properties with high caloric value and has been part of school nutrition programs in Central America (Gutiérrez, 2012). During homemade preparation of the beverage, the seeds are roasted in mild conditions (90–110 °C during < 5 min) (personal information) to develop a specific flavor, which is a key step. It is well known that roasting induces changes in chemical and physical properties that are more or less intense depending on both roasting time and temperature. High temperature and long roasting times decrease the content of unsaturated fatty acids (Yen, 1990) and the solubility of proteins (Davis, Dean, Price, & Sanders, 2010). In addition, roasting induces changes in the internal microstructure and texture of the roasted product (Young & Schadel, 1993). Additionally, the characteristic and pleasant flavor of roasted products results from the formation of numerous volatile compounds (aldehydes, ketones, alcohols and pyrazines) (Xiao et al., 2014). Qualitative and quantitative determination of volatile compounds in foods requires high resolving power methods (Esteban, Martinez-Castro, Morales, Fabrellas, & Sanz, 1996). Solvent assisted flavor evaporation (SAFE) (Engel, Bahr, & Schieberle, 1999) and headspace solid-phase micro extraction (HS-SPME) (Pawliszyn, 1997) are among the common methods adopted for the analysis of volatile compounds. Another effective tool for the discrimination of odor components from a complex mixture is the combination of olfactometry and gas chromatography (GC-O) (D'Acampora Zellner, Dugo, Dugo, & Mondello, 2008). Odor compounds were studied using SAFE along with SPME-GC–O for the discrimination of key odorants.

In the case of jicaro seeds, traditional roasting is relatively mild and atypical, both in temperature and time compared to other seeds which can exceed 200 °C and take > 40–45 min. Coffee roasting is usually conducted at higher temperature and longer time (180–250 °C during 12–60 min for light-dark roast) (Franca et al., 2005, Moon and Shibamoto, 2009) to get the particular roasted color and flavor required. In the same way, nuts and seeds such as hazelnuts and sesame, are roasted between 150 and 200 °C for times ranging from 15 up to 100 min (Amaral et al., 2006, Kaya and Kahyaoglu, 2006). Although the composition of the raw seed has been published recently (Corrales et al., 2017), no information exists about the impact of mild roasting on the seed. Additionally, volatile compounds naturally present in jicaro seed have not been explored neither before nor and after roasting. The aim of this work was to characterize the profile of the volatile compounds of raw and roasted jicaro seeds obtained in mild conditions (140 °C for 140 s). The effect of this roasting on some physicochemical characteristics of the seeds and on the evolution of their aroma were also studied. In addition, the existence of Maillard reactions in our mild conditions was considered.

Section snippets

Raw materials

Jicaro seeds (Crescentia alata, H.B.K.) were collected in the Pacific region of Nicaragua during the harvesting season in November 2013. The seeds were obtained traditionally as follows: breakage of the calabash, fermentation of the pulp, separation of seeds from the pulp, washing and sun drying. A total of 100 kg of dried seeds were collected from the northwestern region of Nicaragua (latitude: 12.66°N, longitude: 86.44°W, altitude: 115.7 m). Upon reception at the University of Leon, Nicaragua,

Effect of roasting on physicochemical properties of jicaro seeds

Mild roasting at 140 °C and 140 s caused changes in jicaro seeds. Jicaro seeds lost approximately 11.4% of their weight due to loss of water during roasting. Roasting resulted also in a quasi-total dehydration of jicaro seeds, with a moisture content decreasing from 15 to 2%. Simultaneously, seed density was reduced from 1.31 g/mL to 0.64 g/mL due to a gain in seed volume. The prominent characteristic of dehulled raw seeds was their high protein and lipid contents, (Corrales et al., 2017) which is

Acknowledgments

The authors wish to thank each panelist for their contribution to the olfactometry analysis. The present study was supported by PRESANCA II/CSUCA grant no. C-15-2012, the French Cooperation in Central America (Institut Français pour l'Amérique Centrale-IFAC) and the Europea Union Latin America Academic Links grant no. EULA1401013.

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