Abstract
Mung bean (Vigna radiata (L.) Wilczek) seed coat (MBSC) is an underutilized by-product rich in vitexin and isovitexin, but its potential as a source of spray-dried functional powders has not been systematically evaluated. This study investigated the spray drying of MBSC extract using three structurally distinct polysaccharide-based carriers—maltodextrin, trehalose, and inulin—to compare their effects on process yield, powder quality, and the content of phenolic compounds, flavonoids, and antioxidant activity. Response surface methodology (RSM) with a Box–Behnken design was employed to examine the influence of inlet temperature (130–160 °C) and carrier concentration. Maltodextrin provided the highest process yield (84.85%), while trehalose and inulin formulations exhibited stronger antioxidant activity, with the lowest DPPH IC50 values of 0.096 mg/mL and 0.100 mg/mL, respectively (expressed per mg of spray-dried powder). Trehalose yielded the highest total phenolic content (TPC = 28.12 mg GAE/g extract) and acceptable flowability (Carr’s index = 20.72%). Inulin gave the highest total flavonoid content (TFC = 126.8 mg QE/g extract) but showed greater variability, attributed to its polymeric network and higher hygroscopicity. The RSM models showed high predictive accuracy for TPC (R2 > 0.98) and DPPH antioxidant activity (R2 ≈ 1.00). These findings offer a multi-objective optimization framework that links carrier structure to powder performance, providing practical guidance for selecting polysaccharide carriers in the development of spray-dried nutraceutical and functional food ingredients. However, direct measurement of encapsulation efficiency, particle morphology, and storage stability was beyond the scope of this study and warrants further investigation.
Introduction
The increasing consumer demand for natural bioactive ingredients in functional foods, nutraceuticals, and cosmetics has intensified interest in converting agricultural by-products into value-added sources of phytochemicals [1]. Vigna radiata (L.) Wilczek (mung bean) seed coat (MBSC), a major residue from milling, is an abundant and inexpensive candidate. Far from being simple waste, the seed coat concentrates bioactive phenolic compounds, notably the flavone C-glycosides vitexin and isovitexin [2]. These molecules exhibit potent antioxidant, anti-inflammatory, anti-diabetic, and cardioprotective activities, largely mediated through free-radical scavenging and the modulation of cellular signaling pathways [3,4,5]. Exploiting this waste stream would therefore simultaneously reduce environmental burden and create functional ingredients for health-promoting products. However, direct application of crude plant extracts is hindered by the inherent instability of polyphenols. Vitexin and isovitexin are readily degraded by light, oxygen, heat, and pH changes, leading to a rapid loss of bioactivity and short shelf-life [6]. Additionally, the extracts often possess unpleasant sensory attributes (e.g., astringency, bitterness) and poor handling properties (high hygroscopicity, low flowability), which complicate their incorporation into acceptable formulations [7]. An effective stabilization and delivery technology is therefore essential to convert these promising bioactives into robust commercial ingredients.
Spray drying is the most industrially scalable technique for overcoming such limitations [8]. The process transforms a liquid feed into a dry powder by atomizing it into a hot convective medium; the carrier material simultaneously isolates the sensitive core from environmental stressors, masks off-flavors, and improves powder flow and dosage precision. The quality of the resulting powder—process yield, stability, and bioactive content—depends critically on the interplay between formulation variables (carrier type and concentration) and process parameters (inlet temperature, feed solid content) [9]. The selection of an appropriate carrier material is therefore paramount. Three polysaccharide-based carriers with distinct physico-chemical profiles were investigated. Maltodextrin (MD) is an economical, widely used starch-hydrolysis product that provides high solubility and good oxygen-barrier properties, but its relatively low glass transition temperature (Tg) can lead to stickiness during drying and caking upon storage [10]. Trehalose (TH) is a non-reducing disaccharide with an exceptionally high anhydrous Tg (~110 °C) and a unique ability to replace water molecules via hydrogen bonding, thereby preserving the native structure of biomolecules during thermal and oxidative stress [11,12,13]. Inulin (IN) is a prebiotic dietary fiber that forms a highly rigid, amorphous glassy matrix upon rapid drying; this drastically reduces molecular mobility and affords superior oxidative protection, while also adding functional value as a prebiotic [14,15,16,17]. Despite the recognized potential of MBSC extract, systematic comparisons of these carriers for spray-dried MBSC extract have not been reported and the simultaneous optimization of drying temperature and carrier concentration to balance yield, powder flowability, and bioactive content remains unexplored.
Although the individual attributes of maltodextrin, trehalose, and inulin as encapsulating agents are well documented, their comparative performance in the spray drying of polyphenol-rich plant extracts has received limited critical attention. Prior spray-drying studies involving botanical extracts have predominantly relied on maltodextrin or gum arabic as single-carrier systems—for example, in the processing of grape pomace phenolics [18], pomegranate peel extract [19] and various berry by-products [20]. Tolun et al. (2016) compared maltodextrin and gum arabic for grape polyphenol microencapsulation and reported carrier-dependent differences in phenolic retention and antioxidant activity; however, the study did not extend to disaccharide- or fructan-based carriers that may have offered distinct stabilization mechanisms [18]. Kuck and Noreña (2015) evaluated gum arabic, polydextrose, and partially hydrolyzed guar gum for grape skin phenolics, yet trehalose and inulin—both of which possess fundamentally different physico-chemical properties—were outside the scope of their comparison [21]. Trehalose, with its exceptionally high anhydrous glass transition temperature (~110 °C) and capacity to replace water through hydrogen bonding [12,13], has been investigated principally as a protein stabilizer and cryoprotectant rather than as a primary wall material for polyphenol-rich plant extracts. Inulin, despite its demonstrated efficacy in probiotic and lipid encapsulation [14,15,17], has only sporadically been applied to plant polyphenol systems, and its performance relative to conventional polysaccharide carriers in a head-to-head comparison remains largely uncharacterized. Importantly, no previous study has systematically compared a starch hydrolysate (maltodextrin), a non-reducing disaccharide (trehalose), and a polydisperse fructan (inulin) within a single experimental framework for any legume by-product extract. Furthermore, the combined use of such a comparative carrier evaluation with response surface methodology to simultaneously optimize process parameters and multiple powder quality responses—including yield, flowability, phenolic content, flavonoid content, and antioxidant activity—has not been reported for MBSC or related systems. This integrated approach is particularly warranted for MBSC, as its predominant flavonoids, vitexin and isovitexin [2,3], are flavone C-glycosides that differ markedly in structure and stability from the anthocyanins, catechins, and ellagitannins that have been the primary focus of most plant extract encapsulation research [6,7].
Therefore, the objective of the present study was to investigate the spray drying of MBSC extract using maltodextrin, trehalose, and inulin as carrier materials and to apply response surface methodology (RSM) with a Box–Behnken design to examine the effects of inlet air temperature and carrier concentration on process yield, moisture content, flowability (Carr’s index), total phenolic content (TPC), total flavonoid content (TFC), and DPPH radical scavenging activity. The work focuses on immediate post-drying powder properties and bioactive compound content, and does not include the measurement of encapsulation efficiency, surface phenolic content, particle size distribution, powder morphology, water activity, hygroscopicity, solubility, reconstitution behavior, or storage stability. Consequently, the findings should be viewed as an initial screening and process optimization study, providing a basis for carrier selection and further in-depth characterization in future work.
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Materials
Maltodextrin (MD, DE−10 Neo-Maldex NM−10, Neotech Food Co., Ltd., Ratchaburi, Thailand), trehalose (TH, Chemipan Corporation Co., Ltd., Bangkok, Thailand), inulin (IN, Chemipan Corporation Co., Ltd., Bangkok, Thailand). Acetonitrile (HPLC grade) was obtained from Thermo Fisher Scientific (Waltham, MA, USA), while ethanol (analytical grade) and methanol (HPLC grade) were sourced from RCL (Labscan Ltd., Bangkok, Thailand). Vitexin and isovitexin were obtained from Sigma Aldrich, St. Louis, MO, USA. All other chemicals were of analytical grade and obtained from reputable suppliers.
Areemit, J.; Saoha, C.; Kanpipit, N.; Mattariganont, S.; Thapphasaraphong, S. Spray-Dried Powder of Vigna radiata Seed Coat Extract: Response Surface Optimization of Carrier and Process Parameters for Powder Quality and Bioactive Content. Polysaccharides 2026, 7, 73. https://doi.org/10.3390/polysaccharides7020073
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