© E.E. Martinez-Soberanes et al., Published by EDP Sciences, 2025

1 Introduction

Although extracting oil from canola is a standard food application, isolating protein from canola meal at industrial scales remains challenging. The fibre-rich canola seed hull contributes little nutrient value and limits its use as feed. Therefore, producing canola meal with a high protein content requires removing the hull from the seed. Processes that separate hull from embryo are known as dehulling. Hull-free canola seed meal has 70.0% less total seed Neutral Detergent Fibre (NDF) than seed meal with hulls. Dehulled seed meal has improved digestibility and protein content (Kracht et al., 2004). Theoretically, defatted canola meal derived from hull-free winter rapeseed could reach a protein content of 43.1%, assuming a moisture level of 11% and a residual oil content of 2% (Carré et al., 2014). Canola seed content includes 38.0–43.0% oil, 27.0–30.0% protein, and 16.5–18.7% hull (Shahidi, 1990).

Dehulling is a common practice in seed processing. However, the physical properties of canola present some challenges to hull removal. Unlike sunflower, canola seed does not have gaps between the embryo and hull. In canola, mature cotyledons are in contact with the inner face of the hull, creating a tight connection with the endosperm. Furthermore, the canola hull is between 20.0–50.0 μm in thickness, and the average seed size is approximately 2 mm in diameter (Borisjuk et al., 2013; Hajnos et al., 2015). In all, these characteristics demand specific methods to achieve clean separation of hull from embryo.

Dehulling is not typically a one-step process, but rather a series of operations that can include cleaning, sorting, preconditioning, dehulling, and fraction-separation (Fig. 1). Although there is extensive research for each of these subprocesses, in this work, we focus our attention on preconditioning.

Seed preconditioning has been reported using hydrothermal treatments, which consist of adding or removing moisture and heat to or from the seed. Induced changes in moisture content can lead to differential swelling and shrinkage of seed tissues, creating stresses (Thakor, 1993). Seed tissues are composite materials that include different phases. The internal stresses in the seed occur as these phases contract and expand at different rates. The objective of conditioning, within the context of dehulling, is to promote the separation of the hull from the embryo, regardless of the treatment used.

Our literature review identified that several preconditioning treatments have been proposed to improve hull removal from canola, including moistening, drying, and freezing. Moistening and drying treatments can change the seed’s physical and mechanical properties, and freezing the seeds prevents oil losses during dehulling (Davison et al., 1975; Cenkowski et al., 1992; Izli et al., 2009; Reaney, 2016; Martinez-Soberanes et al., 2022). Yet, among the different possible treatments, drying may be the one that has the greatest likelihood of causing the larger effects that make dehulling canola seed easier. Dehulling studies that used drying in the precondition stage obtained better separation of hull and embryos after dehulling (McCurdy, 1992; Thakor et al., 1995; Ikebudu et al., 2000; Kracht et al., 2004; Carré et al., 2016; Ethana, n.d.). Drying methods include fast-drying techniques such as fluidized beds, infrared, and microwaves, and slow-drying techniques such as air blowing, ovens, and drums (Thakor et al., 1995; McCurdy, 1992). While other studies (McCurdy, 1992; Thakor et al., 1995; Ikebudu et al., 2000) have reported indirect indices based on dehulling yield to compare the efficacy of preconditioning treatments in canola seed, to the best of our knowledge, no study has attempted to analyse and measure the changes created on the seed that improve the removal of the hull after preconditioning. Thakor et al. (1995) visually evaluated the effects of moistening and drying, but they did not provide quantitative data of the observed effects in the seed.

To better understand the physical changes in canola seed that enhance its suitability for hull removal, this study employs a non-destructive imaging approach to directly assess and quantify the effects of three thermal treatments on seed structure. Additionally, bulk seed samples were prepared using each preconditioning method to evaluate dehulling yield through dehulling testing. This research builds on previous work aimed at developing a more efficient oilseed dehulling technique to overcome existing challenges and produce low-fibre meals. The primary objective is to analyse, compare, and measure the effects of preconditioning treatments on canola seed, gaining insight into their impact and identifying the most effective method for optimizing dehulling performance.

Fig. 1 Flow diagram of the typical processing of seed from cereal, pulse, and oilseed crops (Martinez-Soberanes et al., 2020).

2 Materials and methods

2.1 Canola seed

The canola seed used in this study was InVigor hybrid canola seed (B. napus) harvested in 2017 near Kelliher SK (51°15’49.19" N 103°44’18.12" W). The seed was kindly provided by Mr. Zenneth Faye of Foam Lake, SK. Experiments were conducted in 2020. Seed was stored at 21° C in a low moisture storage room to avoid spoilage, and initial moisture content was 4.2% wet mass basis (w.b.). For the experiments, three samples of 100 g each were obtained from the main batch and stored in resealable plastic bags before preconditioning studies. Moisture content was measured in triplicate using the air oven method for unground seed described in the ASAE Standard S352.2 (ASAE, 1998).

2.2 Preconditioning thermal treatments

Three thermal treatments were proposed to compare their individual effects in canola seed,

• moistening plus conventional oven drying,

• moistening plus microwave oven drying, and

• moistening plus fluidized bed drying.

2.2.1 Treatment (i): Oven Drying

Seed samples were first moistened by submerging them in distilled water at 75°C for 30 min, resulting in a moisture content of 39.4% (w.b.). They were then dried in a conventional oven at 130°C for 45 min until reaching a final moisture content of 5.5% (w.b.).

2.2.2 Treatment (ii): Microwave Drying

Following the same moistening procedure, seeds were dried in a typical household microwave oven (Panasonic NN-ST975S) at 1200W for a total of 125 s. Drying was performed in five cycles of 25 s, each followed by 60 s of cooling at room temperature to improve control. After drying, the seeds reached a moisture content of 8.9% (w.b.), with a maximum registered temperature of 82.8°C measured using an infrared thermometer. Measures to reduce the heterogeneity of the electromagnetic field within the microwave to improve heating uniformity were not considered.

2.2.3 Treatment (iii): Fluidized Bed Drying (FBD)

After moistening, seeds were dried using a lab-designed fluidized bed dryer with a measured air flow of 0.0245 m³/s and a maximum air temperature of 90 °C. Drying was conducted in four cycles of 15 s, each followed by 180 s of cooling at room temperature. The maximum temperature recorded during the final cycle was 61.6°C, and the final moisture content was 4.9% (w.b.).

For the dehulling study, seed samples were prepared in 20g batches. For the micro-CT analysis, individual seeds were used, with five seeds examined per treatment. Moreover, for all three treatments, the target final moisture content was approximately 5% (w.b.), as lower moisture levels in canola seeds have been shown to reduce deformation under mechanical stress. According to Martinez-Soberanes et al. (2022), seeds with reduced moisture exhibit greater structural integrity during mechanical processing, which may enhance the efficiency of dehulling operations.

2.3 Canola dehulling after preconditioning

Dehulling tests were conducted to explore the influence of each thermal treatment on dehulling effectiveness (η’). Given the limited sample size, our aim was to identify qualitative trends and assess practical implications. This experiment also served to contextualize the micro-computed tomography findings by linking observed structural changes at the seed level to functional performance during dehulling. For this purpose, three batches of 20g of canola seeds were prepared according to the tempering treatments described in Section 2.2.

Dehulling experiments were conducted in a completely randomized design using three replicates. Each replicate run consisted of 20 seeds with a diameter of 2 mm, randomly selected from the treated batches. Seeds were processed one by one in the dehulling device, collected, and visually analysed with a magnifying glass to calculate η’ as per equation (1).

Dehulling effectivity was assessed based on a modified version of the dehulling effectiveness index (η) proposed by Ikebudu et al. (2000). Here, the dehulling effectivity (η’) summarizes in a single variable the observed dehulling outcomes. The outcomes observed during dehulling tests included seeds with:

• intact hulls (no cracks or visual damage),

• cracked hulls,

• partially removed hulls,

• completely removed hulls with a sound embryo, or

• removed hulls with a broken embryo.

These five outcomes are combined in the modified dehulling effectiveness index as,

$$\eta \text{'}=\frac{\left(H_R+H_{PR}\right)-\left(S_I+S_B+S_C\right)}{S},$$(1)

where:

• H_R = sound embryo with hull completely removed,

• H_PR = sound embryo with hull partially removed,

• S_I = seeds with intact hull,

• S_B = broken embryo,

• S_C = cracked hull, and

• S = total number of seeds.

The variable (η’) can take values from −1 to +1, being +1 the maximum, indicating that all the seeds were dehulled without damaging the embryo.

The dehuller used is depicted in Figure 2, and it encompasses two step motors with 1.8° step angle (85BYGH450C-012B) that can drive the rollers independently. Each motor has a half-inch shaft, easily accessible, on which rollers of different sizes can be mounted. The position of one of the motors is fixed, while the other can be positioned at any point along a sliding riel, that allows the adjustment of the gap between the rollers with a 0.02 mm resolution. The rollers used had a diameter of 50.0 mm and were coated with rubber (Plasti Dip ® Aerosol Spray) to increase the friction between interacting surfaces. Rubber coat thickness was of approximately 0.38 ± 0.02 mm on the front roller and 0.42 ± 0.02 mm on the rear roller. The thickness difference is the results of manually applying the rubber coat.

Preliminary dehulling tests (data not shown) were conducted to determine the operational parameters and settings for the dehulling machine. Thus, dehulling was conducted with the rollers spinning in the same direction with the rear roller running at 140.0 rpm and the front one at 95.0 rpm. The spacing between the rollers was set to 1.60 mm, this is 0.40 mm smaller than the average seed size used of 2.00 mm.

Fig. 2 Experimental roll-dehuller. The gap between the rollers can be easily adjusted to process seeds of different sizes, and both motors can run in both directions with tunable speed.

2.4 Micro-computed tomography imaging (Micro-CT)

Following the dehulling study, it was crucial for this work to identify the factors that would be responsible for the results obtained in the dehulling test and that would explain the difference in the dehulling performance observed among the four samples tested, including the control sample. In order to examine any physical changes in the seed structure following the preconditioning treatments, a non-destructive and non-invasive imaging approach called micro-computed tomography imaging (micro-CT) was selected.

For this study, it was paramount to keep track of the seeds to be able to compare the scans of the same seed before undergoing any treatment and after being thermally treated. To afford one-to-one comparisons (control vs treatment), single seeds were isolated inside labelled porous sealed “tea” bags as depicted in Figure 3. Such an approach permitted tracking the seeds during tempering treatments and micro-CT scanning.

In order to create the control scans, fifteen untreated seeds that made up the sample for this experiment were randomly divided into three groups of five seeds. Following the completion of the control scans, each seed was isolated in a "tea" bag and preconditioned in accordance with Section 2.2, i.e., five seeds for each of the three preconditioning treatments under investigation. The preconditioned seeds were then scanned, resulting in a total of 30 scan files: 15 for control seeds, 5 for oven-dried seeds, 5 for microwave-dried seeds, and 5 for fluidized-bed dried seeds.

Micro-CT scans were done one at a time on individual seeds using an X-ray microtomography system (Bruker SkyScan 1172) at a source voltage of 40 kV and current of 250 μA. Images were captured at a voxel resolution of 10 μm, an exposure time of 160 ms, a frame averaging of 4, and a rotation step of 0.2 °. These settings generated serial cross-sectional 1000 × 1000 pixel images with a voxel size of 9.59 μm, which were later analysed using open-source software Image J. The software Amira (version 2020) by Thermo Fisher Scientific was used for 3D rendering.

Fig. 3 Single seeds were placed inside small porous sealed bags to identify them easily during the experiments. Trackability was paramount for the experiment.

2.5 Statistical analysis

Statistical analysis of the developed volume after preconditioning treatments was evaluated using a one-way analysis of variance, ANOVA. The collected data was transformed, in advance, using a logarithmic transformation to account for the variations observed from a normal distribution. A significance of p < 0.05 was used for comparison of means after conducting Fisher’s protected least significant difference test at p = 0.05. Statistic analyses were conducted using the open-source software R (R Core Team, 2020).

3 Results and discussion

3.1 Dehulling

As a reminder, the dehulling effectivity index (η′) ranges from −1 to +1, with +1 representing the optimal outcome, complete dehulling without any damage to the embryo. Figure 4 presents a box plot of the η′ values obtained for each thermal treatment following seed processing through the dehulling device. These values were calculated using equation (1), as described in the methodology. The FBD treatment resulted in the highest number of fully dehulled and undamaged embryos, indicating its effectiveness in facilitating the removal of the hull during the mechanical dehulling process. In contrast, the dehulling effectivity values obtained with the other treatments (oven and microwave) did not show a considerable improvement in dehulling effectiveness when compared to the values obtained with the untreated seeds. In fact, the dehulling effectivity value for FBD was very close to the maximum possible of +1, which would mean that all seeds were dehulled without breaking a single embryo.

The dehulling effectivity index (η′), while useful as a performance metric, does not provide insight into the underlying structural changes induced by the fluidized bed drying (FBD) treatment that may facilitate hull removal without damaging the embryo. To investigate whether the thermal treatments produced observable modifications in the seed structure that could explain the dehulling outcomes presented in Figure 4, micro-computed tomography (micro-CT) imaging was employed. The results of such analysis are discussed in Section 3.2.

Fig. 4  Box plot of the average dehulling effectivity index (η’) of each preconditioning treatment.

3.2 Micro-CT scans analysis

The seeds experienced some noticeable changes after the treatments, especially those that were dried using the FBD method, as can be seen in the 2D pictures shown in Figure 5. The development of a gap between the embryo and the hull, which was not previously present in the seed, can be seen on the FBD scan (Fig. 5 C-3). In contrast, every control scan reveals a close association between the seed shell and the embryo. One of the biggest difficulties with dehulling operations is this. The capacity to manoeuvre the hull out of the way without exerting any stress on the embryo is constrained by the close connection between the seed parts. Thus, even when the hull gets broken it remain firmly attached to the embryo. Thereby, the air gap seen in the scans of the FBD-treated seeds (Fig. 5 C-3) suggests that this space enables the hull to break while shielding the embryo from the forces applied during the dehulling, and when the hull is broken, the embryo is released because it had already been partially detached from the hull during the preconditioning step. These results are in line with observations of interior spaces on seeds dried in a fluidized bed dryer made by Thakor et al. (1995), even though they did not offer any quantitative descriptions and utilized an invasive technique that might have altered the seed structure.

Table 1 presents the measured air volume values between the hull and embryo of the 15 analysed seeds. All three treatments resulted in an increase in air volume between hull and embryo, with the fluidized bed drying (FBD) technique producing the largest volume. For example, the air volume of sample S1 went from 0.001 mm³ to 0.244 mm³ after treatment, representing a volume increase of 200 folds.

It is important to note that the space measured for this analysis corresponds to the volume developed between the embryo and the hull, specifically around the embryo. The space inside the embryo, between the cotyledons, was not considered. However, cotyledon separation was observed, which could affect the dehulling yield as larger internal gaps might promote complete detachment of cotyledons, resulting in the production of embryo fines and oil losses during mechanical dehulling (Martinez-Soberanes et al., 2022; Thakor et al., 1995).

Only two seeds, sample S5 and sample S2 from the oven treatment and the microwave treatment, respectively, exhibited a decrease or shrinkage in air volume after treatment. This behaviour is attributed to possible over-drying, and the environment created within an oven. In an oven, seeds sit steadily on a hard bed without any external airflow which might lead to compression effects due to the seed weight and lack of air. Seeds dried below 5% (w.b.) showed concave regions on the hull surface, which might have been produced due to the collapse of air pockets previously present between the hull and the embryo.

The impact of the different thermal treatments on the internal space development between the hull and the embryo of canola seeds was analysed, and the results are presented in Table 2. The FBD treatment was the only treatment that induced a significant effect (p < 0.05) on the development of internal space. The large standard deviation (SD) values calculated were consistent with the large data dispersion observed in the recorded values for each treatment (Tab. 1). Nevertheless, the lower SD for the FBD treatment suggests that this treatment may not only be more effective in producing larger gaps but also more consistent in producing similar outcomes in all the treated seed. This could be due to the behaviour of the seeds in the different drying methods used. For example, in a fluidized bed dryer, seeds are continuously in motion due to the air flow input, leading to a more homogenous distribution of heat among the seed than in a microwave or conventional oven, where seeds are still and tend to form clusters. On the other hand, ovens consist of enclosed chambers without external airflow creating steaming conditions that might reduce their drying capacity.

Figure 6 provides a visual representation of the air volume between the hull and the embryo, before and after thermal treatment. Also, the depicted 3D images provide a visual comparison of the generated volume by each treatment. These 3D images were produced from the original micro-CT scans. As per the quantitative results summarized on Table 1, Figure 6F shows that the FBD method produced the largest gap between the hull and the embryo. Moreover, these images show the location where the gap was developed, and it is evident that the disconnection is all around the seed for the FBD dried seeds.

The results suggest that differences in the mechanical properties of the tissues in the hull and in the embryo are responsible for the observed effects when thermally treated. As previously stated, the expansion and contraction rates for the hull and embryo might be different, resulting in the separation of hull tissue from the embryo (Thakor, 1993). Additionally, the speed at which expansion and contraction occur might contribute to the magnitude of the observed effects. The moistening step of the treatments achieved a larger moisture content in a shorter time than reported by Thakor et al. (1995), 39.4% (w.b.) in 30 min vs 37% (w.b.) in 140 min. The main difference in the process was moistening the seed with water at 75° C. Raising the temperature promotes water diffusion within the seed structure at a faster rate, resulting in larger stress gradients (Zhao, 2016). Higher temperatures were avoided to reduce the risk of negatively impacting seed oil and protein properties.

In general, drying is a complex thermal process that is hard to describe with precision as it involves a continuous exchange of mass and heat that is governed by material thermal properties such as specific heat, thermal conductivity, thermal diffusivity, and emissivity. In addition, when electromagnetic heating methods, such as microwaves, are involved, the dielectric properties of the materials must also be considered. For canola seed, these material characteristics have already been identified, and they depend on temperature and moisture content, adding complexity to the drying phenomenon (Yu et al., 2015a, Yu et al., 2015b). An educated explanation is nevertheless provided even if further research would be required to pinpoint the physical principles underlying the emergence of the gap observed in canola seeds after drying.

When considering drying rate, microwave and fluidized bed drying were very similar in terms of how fast both methods brought the seed samples to similar moisture contents (Fig. 7). Therefore, we do not believe that faster drying necessarily explains the separation of the hull and embryo in canola. Instead, the effects seen in the treated seed could be attributed to differences in heat distribution and heat transfer among the seed layers with different biological characteristics and the drying method used. In comparison to a microwave or traditional oven, a fluidized bed dryer distributes heat among the seeds more evenly. This is largely because of the constant fast air flow that moves the particle samples. Additionally, compared to other materials, canola seed was discovered to have a reasonably high emissivity (0.93 to 0.99), which indicates that it can absorb or emit more thermal radiation from its surroundings (Yu et al., 2015a). A thermal characteristic that might account for the advantages of giving each seed a consistent environment through the motion created by a fluidized bed drier and preventing the creation of seed clusters seen in convection and microwave ovens. In microwave drying, non-uniformity heating is a well-known problem where sample geometry and motion have a significant impact. For instance, the sphere-like shape of a canola seed causes the waves in a microwave oven to concentrate on the seed’s centre, overheating it (Feng et al., 2012). If bulk samples are used, the electromagnetic heating drying performance would be impacted by the container’s shape and absence of motion.

Case hardening, which refers to the result of the outermost layers in a sample becoming tougher and drier than the internal layers, is another phenomenon that may explain the formation of air pockets in canola seed during drying. This effect, however, might be advantageous for the gap’s creation in the FBD. The hull will hold its shape and size as it dries, whereas the embryo will continue to contract as it loses moisture. In contrast, as demonstrated in earlier investigations (Ni et al., 1999), microwave drying does not cause case hardening. Actually, microwave drying removes moisture from the innermost layers of samples and dries them from the inside out. If this is the case, the hull of the canola seed will continue to stay moist while the embryo shrinks, allowing it to contract alongside the embryo without ever separating from it.

Although the gap created between embryo and hull is relatively small, its creation is crucial for achieving an effective separation of fractions during dehulling, as demonstrated by the dehulling experiment. Breaking the connection between the embryo and the hull is crucial not only for protecting the embryo from damage but also to achieve easy separation among dehulling fractions once the hull is broken.

While this study did not explicitly evaluate the feasibility of fluidized bed drying (FBD) and dehulling at industrial scale, the findings provide a foundational understanding that supports future scale-up efforts. Industrial adoption of the proposed process will require further investigation, particularly regarding throughput, energy efficiency, and integration with existing seed processing infrastructure—areas that were beyond the scope of this study. Nonetheless, the demonstrated effectiveness of the dehulling mechanism and embryo-hull separation validates the core working principle, which serves as a stepping stone toward large-scale implementation. Our ongoing research aims to develop a mechanical system capable of dehulling preconditioned canola seeds in bulk, while optimizing the FBD method to reduce resource consumption. Notably, FBD is already employed in large-scale food processing due to its high energy efficiency and gentle handling of particulate materials, making it well-suited for seed treatment applications (ANDRITZ Separation, n.d.). Combined with the widespread use of roller mills in seed processing, these parallels suggest that the proposed approach has strong potential for industrial scalability, both in terms of technical feasibility and operational compatibility.

Fig. 5 2D micro-CT scans of three different canola seeds, each preconditioned with a different treatment. The 2D scans depicted on the tempered column were taken from the same seed depicted on the control column. The only difference between both columns is that control scans were taken before treatment and tempered after preconditioning. A-1 and A-2 correspond to a seed tempered using the oven method; B-1 and B-2 correspond to a seed tempered using the microwave method; and C-1 and C-3 correspond to a seed tempered using the FBD method. C-3 is the same image as C-2 but enlarged to better visualize the gap between the hull and the embryo.

Fig. 6 Diagram of the development of the internal hull-embryo gap in canola seed after the fluidized bed drying (FBD) treatment. (A) A single 2D micro-CT image of a canola seed before treatment, sh − seed hull and em − embryo. (B) A single 2D micro-CT image of the seed depicted in A after treatment, sh − seed hull, ag − airgap and em − embryo. (C) 3D render of the seed depicted in A. (D) 3D render of the seed depicted in A after treatment, where the developed airgap is highlighted in red. (E) 3D render with the hull set as transparent and showing in red the developed air volume in between the hull and the embryo. (F) 3D renders of each treatment showing in red the developed air volume produced by each preconditioning treatment. While the microwave and heat oven treatments produced air pockets only in a few locations, the FBD produced an airgap all around the seed.

Fig. 7 Reduction of seed moisture content with drying time of both drying methods, fluidized bed drying and microwave drying.

4 Conclusions

Mechanical dehulling of canola seeds often risks damaging the embryo due to its tight attachment to the hull. While hull removal is possible, it typically generates fine debris that complicates separation. This study explored three hydrothermal preconditioning treatments to facilitate dehulling, with particular focus on structural changes induced by drying methods.

The most effective treatment involved moistening seeds in distilled water at 75°C for 30 min, resting for 24 h, and drying with a fluidized bed dryer. This approach produced the largest structural gap between the embryo and hull, significantly improving dehulling performance. Seeds treated with this method achieved higher dehulling effectivity and yielded cleaner output fractions—primarily whole embryos and halved hulls—simplifying post-processing separation.

However, increased separation between the cotyledon and radicle in treated seeds may introduce structural fragility, potentially leading to embryo breakage during dehulling. Despite this, the results support the inclusion of fluidized bed preconditioning in mechanical dehulling systems. By promoting embryo-hull disconnection, this method should reduce bruising and enhances fractionation efficiency in front-end dehulling technology.

Acknowledgments

The authors wish to acknowledge the support of the Saskatchewan Agricultural Development Fund ADF20180255, and Mitacs IT16156. We wish to thank Z. Faye for research materials.

Funding

Saskatchewan Agricultural Development Fund ADF20180255, and Mitacs IT16156.

Note: Neither of the funding institutions was involved in the research work here presented, including experiments and manuscripts.

Conflicts of interest

The authors declare no conflicts of interest in regards to this article.

Author contribution statement

Edgar E. Martinez-Soberanes: Conceptualization, Methodology, Formal analysis, Investigation, Writing − Original draft. David Cooper: Writing − Review & Editing, Supervision, Validation. Martin JT Reaney: Conceptualization, Resources, Writing − Review & Editing, Supervision, Funding Acquisition. W.J. Zhang: Conceptualization, Resources, Supervision.

Ethics approval

During the preparation of this work, the authors used Microsoft Copilot to check and improve grammar, spelling and punctuation. After using this tool, the authors reviewed and edited the content as needed and took full responsibility for the publication’s content.

References

All Tables

All Figures

	Fig. 1 Flow diagram of the typical processing of seed from cereal, pulse, and oilseed crops (Martinez-Soberanes et al., 2020).
In the text

	Fig. 2 Experimental roll-dehuller. The gap between the rollers can be easily adjusted to process seeds of different sizes, and both motors can run in both directions with tunable speed.
In the text

	Fig. 3 Single seeds were placed inside small porous sealed bags to identify them easily during the experiments. Trackability was paramount for the experiment.
In the text

	Fig. 4  Box plot of the average dehulling effectivity index (η’) of each preconditioning treatment.
In the text

Fig. 5 2D micro-CT scans of three different canola seeds, each preconditioned with a different treatment. The 2D scans depicted on the tempered column were taken from the same seed depicted on the control column. The only difference between both columns is that control scans were taken before treatment and tempered after preconditioning. A-1 and A-2 correspond to a seed tempered using the oven method; B-1 and B-2 correspond to a seed tempered using the microwave method; and C-1 and C-3 correspond to a seed tempered using the FBD method. C-3 is the same image as C-2 but enlarged to better visualize the gap between the hull and the embryo.

In the text

Fig. 6 Diagram of the development of the internal hull-embryo gap in canola seed after the fluidized bed drying (FBD) treatment. (A) A single 2D micro-CT image of a canola seed before treatment, sh − seed hull and em − embryo. (B) A single 2D micro-CT image of the seed depicted in A after treatment, sh − seed hull, ag − airgap and em − embryo. (C) 3D render of the seed depicted in A. (D) 3D render of the seed depicted in A after treatment, where the developed airgap is highlighted in red. (E) 3D render with the hull set as transparent and showing in red the developed air volume in between the hull and the embryo. (F) 3D renders of each treatment showing in red the developed air volume produced by each preconditioning treatment. While the microwave and heat oven treatments produced air pockets only in a few locations, the FBD produced an airgap all around the seed.

In the text

	Fig. 7 Reduction of seed moisture content with drying time of both drying methods, fluidized bed drying and microwave drying.
In the text