Morphometric Analysis of Storage and Transport Structures in Zingiber officinale

Ginger rhizomes (Zingiber officinale Roscoe) represent a valuable agro-industrial crop due to its bioactive profile and starch reserves [1]. Despite its broad utility, scientific literature still lacks specific quantitative data regarding its microstructure, which is crucial for understanding and optimizing processes such as dehydration, comminution, and quality control [2]. To address this, the present work aimed to morphometrically analyze storage and transport tissues employing optical and scanning electron microscopy (SEM), providing precise data for its industrial valorization. Histological and ultrastructural characterization of ginger rhizomes were prepared as presented in Figure 1. The histological preparation was performed following the methodology described by Vicente-Flores et al [3]. Fresh rhizomes were first thoroughly washed with distilled water and subsequently cut into small cubic blocks (1 cm2) without removing the periderm. Samples previously embedded in paraffin (KD-BM II, Kedee, China), were sectioned transversely at 16 µm using a rotary microtome (RM 2235, Leica, Germany). Following sectioning, deparaffinization was carried out by incubating the sections at 58°C for 48 h, followed by immersion in xylene to ensure total paraffin removal. Subsequently, tissues were rehydrated through a graded ethanol series (96%, 70%, and 25%). To enhance the visualization of cell wall architecture, tissues were stained with 1% safranin. Lastly, sections were mounted with synthetic resin for analysis via optical microscopy (Eclipse Ti-U, Nikon, Japan). Ultrastructural characterization was performed according to Polat and İzli [4]. Washed rhizome fragments (1 cm2) were prepared without removing the periderm and fixed in a modified Karnovsky solution (4% glutaraldehyde, 2.5% formaldehyde in PBS) for 72 h. After fixation, the samples were dehydrated in a graded ethanol series (30–100%) and subjected to critical point drying (K850, Quorum, UK). The specimens were mounted on conductive carbon tape and sputter-coated with carbon (SPI Supplies, USA). Samples were examined in a field emission scanning electron microscope (JSM-7800F, JEOL, Japan) operated at 20 kV, using a backscattered electron detector. Morphometric analysis was performed using ImageJ v1.53 software [5]. The area, circularity, and Feret diameter of storage parenchyma cells, starch granules, and xylem vessels were quantified by recording 50 random measurements per structure (n=50). The combined microscopy analysis enabled a comprehensive assessment of the cellular architecture of the Z. officinale rhizome. Figure 2 presents a comparison between the ultrastructure observed by SEM (Figure 2a-c), depicting the spatial distribution of starch granules within the storage parenchyma, and the optical histology (Figure 2d-f), which delineates the lignification of vascular elements through safranin staining. Microstructural analysis revealed that the architecture of the Z. officinale rhizome corresponds to the typical anatomy of monocotyledons, organized to fulfill vital storage and transport functions [6]. The predominant tissue, the parenchyma, acts as an energy reservoir comprising voluminous cells densely packed with starch granules [6]. The recorded dimensions of these granules and other morphometric parameters derived from the image analysis for these tissues are synthesized in Table 1. Notably, their morphology, visibly elliptical and flattened in SEM (Fig. 2b), suggests low circularity (defined on a scale of 0 to 1, where 1 is a perfect sphere), a characteristic that biologically facilitates spatial packing within the cell cytoplasm. From an industrial perspective, these non-spherical shapes directly influence specific swelling and gelatinization kinetics, which are critical parameters for the formulation of flours and thickening agents [7]. Furthermore, xylem elements were clearly identified via safranin staining (Fig. 1f). These xylems elements performed a physiological function that involves water transport and mechanical support for the rhizome. The lignification of their secondary walls and their arrangement in an atactostele ensures the rigidity of the underground organ [8]. The average diameter of these vessels is a determining factor not only for water conduction but also for the fibrous texture of the final product. From a processing perspective, a high density of these support structures increases mechanical resistance, thereby affecting the efficiency of dry crushing and milling [9]. The integration of multimodal microscopy and digital image analysis establishes a precise morphometric profile of the Zingiber officinale rhizome. It was determined that the microstructure is predominantly composed of a storage parenchyma containing abundant elliptical starch granules of specific micrometric dimensions and a lignified vascular system that mechanically reinforces the tissue matrix. These quantitative parameters shown in Table 1, validate the botanical identity of the species and constitute key technical indicators for predicting material behavior critical agro-industrial processes such as milling, drying, and the extraction of bioactive compounds. Multiscale morphological and ultrastructural characterization of ginger (Zingiber officinale) rhizome using optical and scanning electron microscopy. SEM (a-c) and Optical Microscopy (d-f) of Zingiber officinale rhizome tissues. Arrows indicate specific anatomical structures as cortical cells (S), parenchyma cells (L), starch (N), and xylem vessels (V). Morphometric parameters of storage and transport tissues in the Zingiber officinale rhizome. Values are expressed as mean ± standard deviation.