Biochemical, anatomical, and histochemical characterization of cachichín (Oecopetalum mexicanum Greenm. & C.H. Thomps: Metteniusaceae) seeds exposed to different thermal treatments

Abstract

Background Cachichín (Oecopetalum mexicanum Greenm. & C.H. Thomps: Metteniusaceae) is an arboreal species native to the Misantla mountain range, Veracruz, Mexico, whose fruit contains an edible seed with potential nutraceutical properties. Basic biochemical analyses have been performed, though the effects of thermal treatments on the concentration of vital molecules, the seed structure and the histochemistry have yet to be elicited. Herewith we determined the effect of different thermal treatments on the concentrations of total sugars; glucose and fructose; proteins; and amino acids; as well as the impact of such treatments on the anatomy and histochemistry of seeds. Methods Biochemical, anatomical, and histochemical characterizations of the cachichín seed were carried out in raw form (T1) and under three thermal treatments: boiled (T2), commercial toasting (T3), and controlled toasting (T4). The biochemical variables evaluated were total and reducing sugars, total proteins, and total amino acids. Observations of the seed structure were performed by scanning electron microscopy (SEM), while histochemical staining was carried out to identify starch, lipids, tannins, polysaccharides and proteins under compound light microscopy. Results Concentration of total sugars was reduced in boiled (T2) and commercial toasting (T3) seeds as compared to raw (T1) and controlled toasting (T4) seeds; boiled seeds (T3) displayed the lowest concentration of total sugars. An increase in the concentrations of glucose and fructose was observed in T4. As compared to T1, all other treatments did not change protein concentrations in the seed; the only significant difference observed was between T2 and T3, with commercial toasting displaying the highest mean for this variable. Amino acid concentrations decreased in T3 and T4 compared to T1, while in T2 the concentration of these molecules increased. The anatomic analysis of (T1) revealed a well-organized structure, compared to applied thermal treatments, where degradation of anatomical structures was observed. In general, the thermal treatments tested modified the concentrations and distribution of starch, lipids, tannins, polysaccharides and proteins as compared to raw seeds. The raw cachichín seed has a well-defined anatomical and cellular compartmental organization, while the application of the thermal treatments caused a loss of its structural organization and degradation of vital biomolecules. Conclusion The cachichín seed can be considered a good source of proteins and lipids. Thermal treatments can improve its organoleptic properties, though they negatively impact its nutritional value and anatomical structure. Among thermal treatments tested, the controlled toasting can maintain or even improve some nutraceutical properties with a few structural and biochemical modifications.