Abstract
X-ray diffractograms, optic and electronic microscopy were used to study the structural changes on extruded orange pulp using a Brabender® laboratory single-screw extruder (GNF 1014/2, 20:1, L/D). The results showed that most of the cellulose would be in the amorphous state, with small crystalline areas in the angular region of 2θ = 14.5°. The evaluated extrusion conditions did not affect the crystallinity of the raw cellulose, maintaining the size of the crystalline regions in the angular region of 2θ = 22.5°. Neutral detergent solubilized the crystalline areas of potassium citrate and cellulose, formed during the extrusion process. However, these conditions did not affect the crystallinity of the raw cellulose. In addition, no change was observed in the crystallinity of pectin. The electron microphotographs allowed for the estimation of the heterogeneity of orange pulp and assessment of the difference of resistance between the walls of the buds and juice vesicles. Thus, it was demonstrated that during the extrusion process most of the porosity and the cellular structure of the endocarp remained unaltered.
Highlights
The production of oranges in Brazil reached more than 17 million metric tons in 2019, an increase of around 2.3 percent in comparison to the previous year [1]
The analysis demonstrated that dehydrated orange pulp conserved its porous structure and that; the extrusion process conserved the structure of the vegetal tissue and promotes discrete fragmentation
Extrusion process did not diminish the size of the crystalline areas of the cellulose orange pulp
Summary
The production of oranges in Brazil reached more than 17 million metric tons in 2019, an increase of around 2.3 percent in comparison to the previous year [1]. Orange pulp is the main by-product during the processing of citrus fruits, and a latent load to environment without further treatment [2]. In the inward of each segment are located the juice vesicles, which are linked to the capillary membrane for fine coats or trichomes, that gradually accumulate juice during the fruit maturation. In orange can be found up to six staple fiber sources, located in the vesicles of juice, core, albedo, flavedo membranes and seeds [3]. The pulp is composed of pieces of membrane materials from the ruptured juice sacs and segment walls, contributing to the texture and mouthfeel of citrus juice. A manual dissection of the components of mature orange (Pineapple orange) showed the following distribution in weight: flavedo and albedo (37%); juice vesicles (10%); membranes (19%); seeds (8%) and juice (26%) [5]
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