In order to comprehensively understand the genetic background of Paenarthrobacter ilicis CR5301 and dissect the key enzymes of CR5301 for transforming rebaudioside C (RC), the whole genome of CR5301 was sequenced using nextgeneration Illumina HiSeq and third-generation Nanopore-based DNA sequencing, and the key enzymes for RC convertion were predicted. The results showed that CR5301’s genome was a closed circular chromosomal DNA molecule without plasmids. The genome sequence was 4748281 bp in length, with a GC content of 62.92%. The genome encoded a total of 4458 genes, including 4 gene islands, 1 prophage and 14 CRISPR-Cas coding sequences. CR5301 is the first strain of P. ilicis whose genome has been completely determined, and it is also the strain with the largest known genome of the genus Paenarthrobacter. P. ilicis CR5301 was more closely related to P. aurescens, but more distantly related to P. ureafaciens, according to genome collinearity and 16S rRNA gene-based phylogenetic tree analysis. Comprehensive annotation analysis against seven protein databases showed that P. ilicis CR5301’s genome contained 523 carbohydrate active enzyme genes, of which 18 glycosidase genes may be the key enzyme genes for the transformation of RC by CR5301. Finally, the physicochemical properties and secondary structures of the 18 glycosidases were predicted by the bioinformatics software ProtParam and SOPMA. These results provide clear and complete genetic information for understanding the mechanism of RC transformation by CR5301, and provide a complete and reliable reference genome sequence for extensive biological studies on P. ilicis.

In this paper, selenized mung bean resistant starch (MB-RS4·Se (Ⅳ)) was prepared from mung bean resistant starch (MB-RS4) by the nitric acid-sodium selenite method. Scanning electron microscopy (SEM) revealed that the starch granules were completely collapsed and fragmented after selenization. The structural characteristics of MB-RS4 and MB-RS4·Se (Ⅳ) were analyzed by ultraviolet (UV) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), gel permeation chromatography (GPC), and nuclear magnetic resonance (NMR). The results showed that selenization resulted in a red shift of the UV peak and a hyperchromic effect. Additionally, the characteristic peaks of Se=O, C-C (Se)₂ and Se-O-C appeared at wavenumbers of 787.88, 730.88 and 654.75 cm^-1, respectively, and the crystal structure was destroyed. The molecular mass dropped significantly, and MB-RS4·Se (Ⅳ)’s configuration was reversed and the C6 position was substituted compared with MB-RS4. MB-RS4·Se (Ⅳ) had a significantly enhanced inhibitory effect on α-glucosidase and α-amylase. The results of the enzymatic reaction kinetics showed that the inhibition of α-glucosidase was competitive type, and the inhibition of α-amylase was mixed anticompetitive type.

In order to clarify the influence of microwave drying on the protein and starch quality of sorghum, non-glutinous sorghum grains (cv. Longza 10) were intermittently dried in a microwave dryer. The protein content of sorghum was tested before and after drying, as well as its starch quality characteristics, such as starch content, microscopic morphology, functional groups, aging properties and gelatinization properties. The changes in differential protein expression, functional classification and metabolic pathways were also analyzed. The results showed that under the experimental conditions of this study, the total protein content of sorghum was not significantly changed after microwave drying (by up to 0.4%). In total, 85 significantly differential expressed proteins were identified, 51 of which were up-regulated while the rest were down-regulated. The differentially expressed proteins were involved in metabolic pathways, such as carbon metabolism, glycolysis/gluconeogenesis, carbon fixation in photosynthetic organisms, biosynthesis of amino acids, amino sugar and nucleotide sugar metabolism, and the tricarboxylic acid cycle (P < 0.01). The contents of total starch and amylose increased by up to 2.55% and 1.06%, respectively with increasing time of single microwave cycle. Microwave drying did not result in the formation of new functional groups in the starch but it altered the microscopic morphology of starch granules. In addition, the maximum increase in retrogradation value was 267 mPa·s, suggesting that the starch was easier to retrogradate. The phase transition temperature of the starch was not obviously changed, while the gelatinization enthalpy dropped significantly. These results will provide theoretical and data support for the industrial application of sorghum microwave drying and for the deep processing of sorghum.