FTIR determination of the degree of molar substitution for hydroxypropyl chitosan.

We developed and validated a novel Fourier transform infrared (FTIR) method to determine the degree of molar substitution (MS) for hydroxypropyl chitosan (HPCS) using nuclear magnetic resonance (1H NMR) as a reference, and investigated the factors influencing the MS assay. Through extensive screening of integration methods for candidate bands in the FTIR spectrum of HPCS using 20 HPCS samples with degrees of acetylation (DA) ranging from 0.003 to 0.139, we found that when using band area at 2970 cm-1 as a probe integral, the MS values obtained via the 1H NMR method exhibited linear correlations (R2 > 0.98) with at least 16 integral ratios derived from their FTIR spectra. The optimal reference bands with high reliability are located at 3440 cm-1 and 1415 cm-1, with R2 exceeding 0.99 and a MS range of 0.17-1.92. The band at 2875 cm-1 is less affected by the trace moisture present in HPCS samples than the others. The results of the method validation demonstrated a mean recovery of 98.9 ± 2.8 % and an RSD below 10 %, suggesting a simple, robust, and highly accurate and precise method. This method could be extendable for the determination of the MS of insoluble HPCS derivatives and other hydroxypropylated polysaccharides.

Enhancing grasshopper optimization algorithm (GOA) with levy flight for engineering applications.

The grasshopper optimization algorithm (GOA) is a meta-heuristic algorithm proposed in 2017 mimics the biological behavior of grasshopper swarms seeking food sources in nature for solving optimization problems. Nonetheless, some shortcomings exist in the origin GOA, and GOA global search ability is more or less insufficient and precision also needs to be further improved. Although there are many different GOA variants in the literature, the problem of inefficient and rough precision has still emerged in GOA variants. Aiming at these deficiencies, this paper develops an improved version of GOA with Levy Flight mechanism called LFGOA to alleviate the shortcomings of the origin GOA. The LFGOA algorithm achieved a more suitable balance between exploitation and exploration during searching for the most promising region. The performance of LFGOA is tested using 23 mathematical benchmark functions in comparison with the eight well-known meta-heuristic algorithms and seven real-world engineering problems. The statistical analysis and experimental results show the efficiency of LFGOA. According to obtained results, it is possible to say that the LFGOA algorithm can be a potential alternative in the solution of meta-heuristic optimization problems as it has high exploration and exploitation capabilities.

Bacterial community diversity and its potential contributions to the flavor components of traditional smoked horsemeat sausage in Xinjiang, China.

Smoked horsemeat sausage is a famous fermented traditional food in Xinjiang, China. However, the microbial diversity and its potential contributions to the flavor components of smoked horsemeat sausage are unclear. In this study, the microbial community and flavor components of smoked horsemeat sausage from six regions of Xinjiang were measured by using amplicon sequencing and headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS) technology, respectively. Relations among microbial communities, flavor components and environmental factors were subsequently predicted based on redundancy analysis (RDA) and Monte Carlo permutation tests. Although smoked horsemeat sausage samples from different regions possessed distinct microbial communities, lactic acid bacteria (LAB) were identified as the dominant consortium in smoked horsemeat sausage. Lactobacillus, Vagococcus, Lactococcus, and Carnobacterium were detected at high abundance in different sausages. The moisture content, nitrite content, and pH of the sausage might be important factors influencing the dominant bacterial community, according to the RDA. Among the dominant consortia, the eight core bacterial genera showed considerable correlations with the formation of sixteen volatile compounds in smoked horsemeat sausage based on multivariate statistical analysis. For example, the levels of Leuconostoc and Lactobacillus were positively correlated with those of 1-hexadecanol, hexyl acetate, 2-methyl-phenol, 1-pentanol, d-limonene, and 2-heptanone, and the levels of Leuconostoc, Lactobacillus, and Weissella were negatively correlated with those of 1-octanol, acetic acid, octanal, heptanal, and 1-hexanol. This study will provide a theoretical basis for understanding the microbial metabolic modes of Xinjiang smoked horsemeat sausages.

The Effect of the Ratio of Gamma Aminobutyric Acid-Producing Saccharomyces cerevisiae DL6-20 and Kluyveromyces marxianus B13-5 Addition on Cheese Quality.

Kazakh cheese is a traditional dairy product in Xinjiang, China. The function and potential probiotic characteristics of Saccharomyces cerevisiae DL6-20 and Kluyveromyces marxianus B13-5 in Kazakh cheese and its contribution to cheese fermentation was studied. In this study, the effect of the addition ratio of gamma aminobutyric acid (GABA)-producing S. cerevisiae DL6-20 and K. marxianus B13-5 on cheese quality was investigated. Cheeses were prepared by fermentations with a total of six treatments: comercial culture alone as control (CS), a combination with one yeast, either; K. marxianus B13-5 (CSM); S. cerevisiae DL6-20 (CSS); and three different proportions of this two yeasts (CSM:CSS 1:1, 1:2, 2:1). We measured the GABA content of cheese, as well as basic physical and chemical indicators, microbial content, free amino acid (FAA) content, texture, and flavor compound content. The total FAA content of mixed bacteria fermentation was higher than that of the single bacteria alone. The GABA content CSM:CSS 1:2 GABA content was 0.114 g/100 g, CSM:CSS 2:1 GABA content was 0.12 g/100 g, CSM:CSS1:1 content of GABA produced in the late ripening period of cheese was the highest, reaching 0.189 g/100 g and the number of LAB and yeasts in CSM:CSS 1:1 was higher than that of other cheeses. The mixed-strain fermentation generally produced cheeses with a higher protein content than that of the single-strain fermentation in the late stage of the maturation process, especially the protein content of CSM:CSS 1:1 during the ripening period, when the protein content was highest at day 50. CSM:CSS 1:1 had a low moisture content, making it easy to store. With the exception of water and protein content, there is no significant difference in other physical and chemical indicators. CSM:CSS 1:1 contributed to the formation of cheese texture. In addition, multivariate statistical analysis indicated that mixed-strain fermentation was beneficial to the production of cheese aroma, with the aroma production performance of CSM:CSS 1:2 and CSM:CSS 2:1 found to be better than that of CSM: CSS 1:1.

Development and validation of an improved 3-methyl-2-benzothiazolinone hydrazone method for quantitative determination of reducing sugar ends in chitooligosaccharides.

An accurate and sensitive analytical method for detecting and quantifying reducing sugar ends (RSE) in chitooligosaccharides (COSs) is the key quality parameter for evaluating their structure-function relationship and potential applications. In this work, we develop and validate a novel colorimetric assay with high accuracy and precision for determining RSE content using 3-methyl-2-benzothiazolinone hydrazone (MBTH). Under optimal conditions, the stoichiometry is verified using mono-, di-, and tri- glucosamine hydrochlorides, and the dilution ratio does not interfere with the RSE content measured at 590 nm. The regression equation of glucosamine reveal a good linear relationship (R2 = 0.9999). The detection limit, quantification limit, mean relative standard deviation (RSD), and recovery are 2.28 µM, 9.11 µM, 1.90%, and 98.0%, respectively. The newly developed method is potentially useful for monitoring COS hydrolysis, number average molecular weight, and chitosanase activity.

Simultaneous determination of molar degree of substitution and its distribution fraction, degree of acetylation in hydroxypropyl chitosan by 1H NMR spectroscopy.

Under the assistance of 13C NMR and 1H-13C HSQC, we develop a novel 1H NMR assay for the substitution sites and degrees in hydroxypropyl chitosan (HPCS) by optimizing sample preparation and measurement method. We find that the chemical shift of HOD peak increases linearly with the increase of DCl concentration but declines with the rise of measurement temperature. According to the regression line, the HOD peak could be moved to a desired position of non-interference with other peaks by changing DCl concentration. Other DCl-responsive peaks are found and elucidated. Accordingly, the substitution fraction (NH2-substitution and OH-substitution) and the degree of acetylation are well discriminated and determined. The total molar degree of substitution (MS) obtained is basically consistent with those of elemental analysis and the existing NMR methods. This structural analysis is extendable to other amino-containing saccharides. The 1H NMR method could be used widely in acid-soluble polysaccharides and their derivatives.

Ultrastructural observations of human epidermal melanocytes cultured on polyethylene terephthalate film.

OBJECTIVE: To assess the application of polyethylene terephthalate film as a supporting material of cultured human epidermal melanocytes and to observe the ultrastructure of human epidermal melanocytes in vitro. METHODS: Human epidermal melanocytes were isolated from 7- to 14-years old children foreskins and were cultured in M254 culture medium containing human melanocyte growth supplement. Cultured melanocytes were purified via a differential trypsinization method. Purified melanocytes were cultured on a film and prepared for transmission electron microscopy. RESULTS: In comparing with the cellular supporting materials polyvinylidene chloride and cellophane, human epidermal melanocytes only attached and grew on polyethylene terephthalate film. Melanocytes grown on polyethylene terephthalate film maintained an intact shape, and retained special ultrastructures characteristic of melanocytes such as dendrites. CONCLUSIONS: Polyethylene terephthalate film proved to be an ideal cellular supporting material for the cultivation of human epidermal melanocytes. Ultrastructure of melanocytes showed melanosomes are transferred both from the tip and middle section of dendrites.