Dextran, a homologous polysaccharide with the main chain of glucose units composed by an α-1,6 glycosidic bond, is synthesized from dextrin by dextran-dextrinase (DDase), a transglucosidase, derived from acetic acid bacteria Gluconobacter oxydans and lactic acid bacteria (LAB). The effective culture conditions were examined for producing dextran via bio-conversion with acetic acid bacteria (AAB) demonstrating DDase activity in various medium compositions during 0 to 7 days with or without glycerol addition (2%, v/v) and different degrees of dextrin polymerization (D.E.) based on the addition level (1,5%, w/v). On day 7, the G. oxydans growth was almost tripled in presence of glycerol as observed via a cell growth curve (OD). After culturing for 7 days, the pH decreased from 6 to 3.1-3.5, and the acidity increased from 0.12% to 0.4-0.62%, depending on the dextrin D.E. and the addition level. The reducing sugar decreased continuously. The medium containing 5% dextrin showed shear-thinning characteristics. The apparent viscosity of the 5% dextrin DE4-7 culture solution was 5.6 mPa·s, which was similar to that of the 20% dextran aqueous solution. The analysis of constituent saccharides contained in the culture medium (HPAEC-PAD) showed a substance with a high degree of polymerization. 1H-NMR analysis showed that α-1,6 glycosidic bond existed as the intermolecular bond of this substance. Therefore, efficient production of dextran was possible by culturing in a medium containing 5% dextrin and glycerol during culture of AAB.

Dextran is an exopolysaccharide (EPS) with multifunctional applications in the food and pharmaceutical industries, primarily synthesized from Leuconostoc mesenteroides. Dextran can be produced from dextrin through Gluconobacter oxydans fermentation, utilizing its dextran dextrinase activity. This study examined how jar fermentor conditions impact the growth and enzyme activity of G. oxydans, with a focus on the effects of pH on dextran synthesis via bioconversion (without pH control, pH 4.5, and pH 5.0; Jp-UC, Jp-4.5, and Jp-5.0). After 72 h, the cell density (O.D. at 600 nm) was 7.2 for Jp-4.5, 6.5 for Jp-5.0, and 3.7 for Jp-UC. Flow property analysis, indicating dextran production, showed that Jp-4.5 had the highest viscosity (30.99 mPa·s). ¹H-NMR analysis confirmed the formation of α-1,6 glycosidic bonds in bioconversion products, with bond ratios ranging from ~1:0.17 to ~1:2.84. The distribution of molecular weights varied from 1.3 × 10³ Da to 5.1 × 10⁴ Da depending on pH. The hydrolysis rates to glucose differed with pH, with the slowest rate at pH 4.5 (53.96%). These results suggest that the production of dextran by G. oxydans is significantly influenced by the pH conditions. This dextran could function as a slowly digestible carbohydrate, aiding in postprandial glycemic regulation and mitigating chronic metabolic diseases like diabetes.

This study investigated the effects of relative humidity (RH) and storage period on the quality and metabolite profiles of perilla seed powder (PSP). PSP was stored for 12 weeks at RH levels ranging from 11% to 93%, and quality changes were monitored by assessing microbial growth, lipid oxidation, color, and metabolite profiles. Visual deterioration occurred rapidly above RH 69% due to microbial proliferation, becoming apparent after four weeks at RH 69% and after one week above RH 81%. In contrast, lipid oxidation, measured by acid and peroxide values, was significantly delayed at RH levels below 43%, whereas at 53% RH, the acid value increased 14.8-fold after 12 weeks compared to the initial level. Multivariate statistical analysis showed distinct metabolite patterns dependent on RH and storage period. Unsaturated fatty acids, such as linoleic and linolenic acids, decreased, whereas lysophosphatidylethanolamines (LPEs) and their oxidized derivatives, including hydroxylinolenic acid, increased by up to 167-fold at RH 53% after 12 weeks. Rosmarinic acid declined, whereas glycosylated phenolics, including rosmarinyl glucoside, increased. Multi-output regression models based on metabolite and quality traits effectively predicted RH and storage duration (R² > 0.87, RMSE < 5.37), demonstrating their potential utility in monitoring storage conditions. These findings suggest that PSP should be stored under RH below 43% for no longer than four weeks to minimize quality degradation. This study provides new insights into RH-dependent metabolic responses in seed-based powders and offers a scientific basis for RH-controlled storage strategies to maintain product stability.

In this study, we evaluated whether formulated depuration diets can modulate the nutritional quality, chemical safety, and volatile profile of Protaetia brevitarsis larvae. Late third-instar larvae were provided with glutinous rice powder (GRP) or one of three formulated diets (FD1-FD3) based on wheat bran, eggshell powder, and brewer’s spent grain for 48 h, followed by 48 h of fasting. Freeze-dried larval powders were analyzed for proximate composition, dietary fiber, fatty acids, minerals, and heavy metals, and volatile profiles were assessed using an electronic nose. Proximate composition, dietary fiber, and carbohydrate showed numerical treatment-dependent variation but no significant differences among groups by Tukey’s HSD test. Oleic acid was the predominant fatty acid, with FD3 forming the highest Tukey group. Calcium and iron were significantly higher in FD1-FD3. Pb was slightly but significantly higher in FD1-FD3 than in GRP, whereas Cd and As did not differ significantly; all measured heavy metals remained low and were below the Korean Food Code limits. Electronic-nose analysis revealed clear diet-dependent differences in volatile patterns: GRP was characterized mainly by butanal, 2,3-pentanedione, heptanal, and butane-2,3-dione, whereas FD2 was more closely associated with propyl propanoate, 2-heptanone, and anethole. These results indicate that diet formulation during depuration can serve as a practical pre-processing strategy to modulate selected nutritional and odor-related quality attributes of edible P. brevitarsis larvae without appreciable heavy-metal contamination.