Caracterización de algunos compuestos de interés en los procesos de fermentación y tostado de dos especies de cacao Amazónico

Abstract

Theobroma bicolor y Theobroma grandiflorum cuyos nombres comunes son Maraco y Copoazú respectivamente, hacen parte de la agroforestería de la región Amazónica Colombiana, de sus semillas es posible fabricar un producto sucedáneo al chocolate después de aplicar procesos de beneficio y transformación similares a los del cacao como; fermentación, secado y tostado, además la fracción grasa de las semilla de T. bicolor y T. grandiflorum poseen mayor contenido de ácidos grasos insaturados con respecto al cacao, adicionalmente se ha reportado propiedades nutraceúticas a los extractos fenólicos. En la fermentación se forman los compuestos precursores de sabor como aminoácidos libres y azúcares reductores como glucosa y fructosa, además se reduce el contenido de polifenoles y metilxantinas contribuyendo a reducir la astringencia y amargor. En el proceso de tostado los compuestos precursores de sabor interactúan entre sí por medio de la reacción de Maillard y se generan grupos de compuesto volátiles heterocíclicos deseados para el aroma, de hecho, la condición de calidad del cacao está ligada al tipo y cantidad de compuestos volátiles que proporcionan un perfil sensorial determinado, uno de ellos son las pirazinas, un producto típico de la reacción de Maillard. Por lo tanto, para profundizar en el conocimiento de estas dos especies se realizó un estudio que consistió en determinar los compuestos fenólicos durante la fermentación y tostado de las dos especies, también se evaluó la formación de compuestos precursores de sabor y producción de pirazinas en la fermentación y en tostado infrarrojo a tres diferentes temperaturas (110, 140 y 170°C). Las mazorcas de las dos especies se cosecharon en zona rural del municipio de Puerto Asís (Putumayo), se retiró cerca del 30% de la pulpa y se realizó un proceso de fermentación por cinco días, en las primeras 48h se conservó un estado anaerobio, posteriormente se aireó la masa cada 24 horas por 3 min, cada día se recolectó muestras y se congelaron para posteriormente realizar el proceso de secado y los análisis de laboratorio. Las muestras para torrefacción se tomaron del último día de 6 Caracterización de algunos compuestos de interés en los procesos de fermentación y tostado de dos especies del género Theobroma. fermentación las cuales se secaron por radicación solar hasta alcanzar aproximadamente el 9% de humedad. Para el tostado se tomó nibs de muestras fermentadas y secas y se sometieron a un proceso de calentamiento usando un sistema Infrarrojo; el tostado inició a 20°C, con una tasa de calentamiento de 20°C.min-1 hasta alcanzar las temperaturas de 110, 140 y 170°C, cada temperatura se mantuvo por 15 min, proporcionando tiempos de tostado totales de 19,5, 21,0 y 22,5 minutos respectivamente. Se realizó una caracterización fisicoquímica, actividad antioxidante y fitoquímica, análisis de azucares por HPLC y composición volátil por micro extracción en fase sólida en modo de espacio de cabeza (HS-SPME) y cromatografía de gases acoplada a espectrometría de masas (GCMS). Los análisis mostraron que el factor especie, como los tratamientos de fermentación y tostado tienen un efecto significativo sobre el pH y acidez del cotiledón, compuestos fenólicos, actividad antioxidante, azúcares y aminoácidos libres (Tomado de la fuente)

Characterization of some compounds of interest in the fermentation and roasting processes of two species of Amazonian cocoa. Theobroma bicolor (TB) and Theobroma grandiflorum (TG), commonly known as Maraco and Copoazú respectively, are part of the agroforestry of the Colombian Amazon region, from their seeds it is possible to obtain a product similar to chocolate after applying processes of transformation similar to cocoa beans such as; fermentation, drying and roasting, in addition the fat fraction of the TB and TG seeds have a higher content of unsaturated fatty acids with respect to cocoa, additionally nutraceutical properties have been reported to phenolic extracts. During fermentation, flavor precursor compounds are formed such as free amino acids and reducing sugars as glucose and fructose, the content of polyphenols is reduced allowing less acidity and bitterness, on the other hand in the roasting process the flavor precursor compounds interact with each other In the Maillard reaction generating desired heterocyclic volatile compounds for the aroma, in fact the quality condition of the cocoa is linked to the type and quantity of volatile compounds that provide a specific sensory profile, one of them is pyrazines, a typical product of the Maillard reaction.Therefore, to broad the chemical knowledge of these two species, the content of phenolic compounds during fermentation and roasting of the two species was studied, the formation of flavor precursor compounds and pyrazine formation before and after fermentation was also evaluated in roasting at three different temperatures (110, 140 and 170 °C). The pods of T. bicolor and T. grandiflorum were harvested in the rural area of the municipality of Puerto Asís (Putumayo, Colombia), about 30% of the pulp was removed and a fermentation process was carried out for five days, in the first 48 hours it was preserved an anaerobic state, subsequently the product was aerated every 24 hours for 3 minutes, samples were collected every day and frozen to later carry out the drying process and laboratory analysis. The samples for roasting were taken from the last day of fermentation which they were dried by solar radiation until reaching a moisture content close to 9% w.b. For roasting, nibs were obtained from fermented and dry samples and they were subjected to a heating process using an Infrared system; Roasting started at 20°C, with a heating rate of 20°C. min-1 until reaching temperatures of 110, 140 and 170°C, each temperature was maintained for 15 min, providing total roasting times of 19.5, 21.0 and 22.5 minutes respectively. A physicochemical characterization, antioxidant capacity and secondary metabolites and sugars quantification by HPLC were performed, in addition a volatile composition analyzes was achieved by micro-extraction in solid phase in headspace mode (HS-SPME) and gas chromatography coupled to mass spectrometry (GC-MS). The results showed that the type of specie, and fermentation and roasting treatments have a significant effect on the pH and acidity of the cotyledon, phenolic compounds, antioxidant activity, sugars and free amino acids (p <0.05). Total polyphenols content (TPC) and antioxidant activity for the radical ABTS in unfermented beens of Theobroma bicolor (TB) and Theobroma grandiflorum (TG) were 60.50 GAE mg.g.DW-1, 42.21 µmol.g.DW-1 and 193.34 GAE mg.g.DW-1, 1783.48 µmol.g.DW-1 respectively. After fermentation, the TPC value and the antioxidant activity for the radical ABTS were reduced in the following proportions 37.10 %, 34.34% and 32.24%, 28.64% for TB and TG respectively, probably due to the diffusion processes and oxidation during fermentation.TPC was also decreased by the increase in the roasting temperature at 110, 140 and 170 ° C in the proportions of 25.58%%, 47.39, 66.83% for TB and 21.51%, 38.60%, 56.12% for TG. Although, the antioxidant activity decreased with temperature, it was found that the differences were not statistically significant between some of the roasting treatments, which probably suggests the formation of compounds with antioxidant activity in the heat treatment, such as melanoidins.Regarding the formation of flavor precursor compounds during the fermentation of T. bicolor (TB) and T. grandiflorum (TG) beans, the unfermented TB seeds presented a higher protein content with respect to TG, which probably it influenced the formation of a greater amount of free amino acids in fermentation due to the activity of endogenous proteolytic enzymes of the beens.The variation of the content of glucose, fructose and free amino acids at the beginning and end of the fermentation were: for TB of 2.33 - 6.32 mg.gDW-1, 3.32-16.64 mg.gDW-1, 3.01-11.43 mg.gDW-1 and for TG of 1.35 - 5.53 mg.gDW-1, 2.38 -12.53 mg.gDW-1and 1.27- 6.08 mg.gDW-1.The formation of reducing sugars and free amino acids during fermentation is important for the development of aromatic compounds during roasting, since they are key reactive compounds in the Maillard reaction that occurs in roasting, this phenomenon was corroborated by studying the glucose content, fructose, free amino acids and the formation of pyrazines in roasting at 110, 140 and 170 ° C. It was found that there is a negative relationship between reducing sugars (glucose and fructose), free amino acids and the total content of pyrazines with roasting temperature, at a higher roasting temperature there is a decrease in reducing sugars and free amino acids and the total content of pyrazines, therefore, the highest content of pyrazines was recorded for roasting at 170°C showing values of 173.45 µg.gDW-1 and 48.86 µg.gDW-1 in TB and TG respectively. No all pyrazines have a positive effect on aroma; a pyrazine frequently reported with a high impact on the characteristic cocoa aroma is Tetramethylpyrazine TMP, which was detected in the dry and roasted fermented TB and TG samples, the roasting temperature where the highest TMP content was reached was 140 ° C for the two species. (Tomado de la fuente)