Effect of multiple-frequency ultrasound-assisted transglutaminase dual modification on the structural, functional characteristics and application of Qingke protein.

Qingke protein rich in restricted amino acids such as lysine, while the uncoordination of ratio of glutenin and gliadin in Qingke protein has a negative impact on its processing properties. In this study, the effect of multiple-frequency ultrasound combined with transglutaminase treatment on the functional and structural properties of Qingke protein and its application in noodle manufacture were investigated. The results showed that compared with the control, ultrasound-assisted transglutaminase dual modification significantly increased the water and oil holding capacity, apparent viscosity, foaming ability, and emulsifying activity index of Qingke protein, which exhibited a higher storage modulus G' (P < 0.05). Meanwhile, ultrasound combined with transglutaminase treatment enhanced the cross-linking degree of Qingke protein (P < 0.05), as shown by decreased free amino group and free sulfhydryl group contents, and increased disulfide bond content. Moreover, after the ultrasound-assisted transglutaminase dual modification treatment, the fluorescence intensity, the contents of α-helix and random coil in the secondary structure of Qingke protein significantly decreased, while the ß-sheet content increased (P < 0.05) compared with control. SDS-PAGE results showed that the bands of Qingke protein treated by ultrasound combined with transglutaminase became unclear. Furthermore, the quality of Qingke noodles made with Qingke powder (140 g/kg dual modified Qingke protein mixed with 860 g/kg extracted Qingke starch) and wheat gluten 60-70 g/kg was similar to that of wheat noodles. In summary, multiple-frequency ultrasound combined with transglutaminase dual modification can significantly improve the physicochemical properties of Qingke protein and the modified Qingke proteins can be used as novel ingredients for Qingke noodles.

Structural and physicochemical properties of the different ultrasound frequency modified Qingke protein.

There is a burgeoning demand for modified plant-based proteins with desirable physicochemical and functional properties. The cereal Qingke is a promising alternative protein source, but its use has been limited by its imperfect functional characteristics. To investigate the effect of ultrasound treatment on Qingke protein, we applied single- (40 kHz), dual- (28/40 kHz), and tri- (28/40/50 kHz) frequency ultrasound on the isolated protein and measured subsequent physicochemical and structural changes. The results showed that the physicochemical properties of proteins were modified following ultrasound treatment, and many of these changes significantly increased with increasing frequency. Compared with the native Qingke protein (control), the solubility, foaming activity, stability, and water or oil holding capacity of tri-frequency ultrasound modified Qingke protein increased by 43.54%, 20.83%, 20.51%, 28.9%, and 45.2%, respectively. Furthermore, ultrasound treatment altered the secondary and tertiary structures of the protein resulting in more exposed chromophoric groups and inner hydrophobic groups, as well as reduced ß-sheets and increasedrandom coils, relative to the control. Rheological and texture characterization indicated that the values of G' and G'', hardness, gumminess, and chewiness decreased after ultrasound treatment. This study could provide a theoretical basis for the application of multi-frequency ultrasonic technology for modification of Qingke protein to expand its potential use as an alternative protein source.

Characterization of sonicated gluten protein and subsequent rheological properties of model dough and noodles.

BACKGROUND: The present study aimed to investigate the effects of the thermo-mechanical and rheological properties of a wheat gluten-sonicated model dough and noodles, as well as the effects of ultrasonic frequency (20, 28, 40, 68 and 80 kHz) on the functional properties and structural features of gluten. RESULTS: Water absorption, stability and developmental time, and viscoelastic behavior of gluten-sonicated model dough were all found to be improved. Water absorption, tensile resistance and stretching distance of noodles increased markedly, whereas cooking loss decreased. Ultrasonication at different frequencies also significantly affected gluten structure, including its surface hydrophobicity, micro-network structure, and secondary and tertiary structures. These alterations then caused changes in its functional characteristics. Compared to untreated gluten, sonicated gluten exhibited significantly increased oil and water capacities (8.75-15.26% and 100.65-127.71% higher than the untreated gluten, respectively), foaming and emulsifying properties, and increased solubility (63.46-98.83% higher than control). In addition, these findings indicated that 40 kHz was the likely resonance frequency of the cavitation bubble in the gluten solution. However, sodium dodecyl sulfate-polyacrylamide gel electrophoresis electropherograms revealed that such treatments did not affect the molecular weight of gluten, which was also consistent with its unchanged disulfide bond content. CONCLUSION: The present study clarified the impact of frequency on the properties of gluten and model dough. The best frequency for modification of gluten was 40 kHz. Collectively, these findings suggest that ultrasonic technology has the potential for use in modifying wheat gluten and commercial noodle processing. © 2022 Society of Chemical Industry.

Evaluation of cultivars diversity and lipid composition properties of Idesia polycarpa var. vestita Diels.

Idesia polycarpa var. vestita Diels is a perennial deciduous tree widely distributed throughout China. Four I. polycarpa fruit of different cultivars with different fruit issues during the growth process were compared, which were on the basis of morphological characteristics and chemical compositions. The influencing factors of oil accumulation in I. polycarpa fruit and the correlation between different components were investigated, and the results revealed a negative correlation between oil content and total sugar (r = -0.930), ash (r = -0.606), and crude fiber (r = -0.952). Except for oil, none of the chemical components changed substantially during the growing phase, and most cultivars showed higher oil content in the pulp portion (14.14-43.99 g/100 g). Linoleic acid was the most abundant fatty acid in I. polycarpa oil (IPO), with values ranging from 52.18% to 66.65% (fruit), 55.44% to 65.15% (pulp), and 68.99% to 78.76% (seed). Principal component analysis revealed that Hubei varieties are more advantageous. Besides, the lipid composition of IPO was identified by ultrahigh-performance liquid chromatography coupled with electrospray ionization Q-Exactive Focus mass spectrometry. The glyceride components of IPO were mostly composed of 22 triacylglycerols, 30 diacylglycerols, and 8 monoacyglycerols. Meanwhile, linoleic acid was mainly distributed in sn-2 and sn-3 positions. PRACTICAL APPLICATION: Morphologic characteristics, chemical compositions, oil fatty acid profiles, and oil correlation factors of I. polycarpa were analyzed. The comprehensive score of oil quality by PCA in Hb fruit was the highest. The glyceride components of I. polycarpa oil were mainly composed of 22 triacylglycerols, 30 diacylglycerols, and eight monoacyglycerols.

Evaluation of bitter compounds in Zanthoxylum schinifolium Sieb. et Zucc. by instrumental and sensory analyses.

As a common food seasoning in China, Zanthoxylum schinifolium Sieb. et Zucc. is desired by consumers for its special aroma; however, its bitter taste has a negative economic impact on the food industry. In this study, untargeted metabolomics was used to perform full-coverage detection of metabolites in Z. schinifolium Sieb. et Zucc. A total of 53 potential bitter metabolites were screened. Additionally, key bitter compounds were concentrated using sensory-guided fractionation technique and subsequently characterized by UPLC-Q-TOF-MS, and a total of 13 bitter compounds were obtained. Then, dose over threshold values (DOT) of these 13 compounds were calculated, showing that 11 compounds significantly contribute to the bitterness of Z. schinifolium Sieb. et Zucc., with quercetin, isorhamnetin and kaempferol have particularly low thresholds and high contents. This study is the first to comprehensively define the bitter substances in Z. schinifolium Sieb. et Zucc., providing a reliable theoretical basis for future research on bitterness mechanisms.

Distribution and natural variation of free, esterified, glycosylated, and insoluble-bound phenolic compounds in brocade orange (Citrus sinensis L. Osbeck) peel.

Brocade orange (Citrus sinensis L. Osbeck) peel, a by-product which is usually discarded in large amounts, is rich in a broad spectrum of phenols. Accordingly, this study investigated the distribution and natural variation of free, esterified, glycosylated and insoluble-bound phenols (FPs, EBPs, GBPs, and IBPs) in the peels. Regardless of phenolic fraction or peel position, the total phenol and flavonoid contents, and most tested phenolic compound contents were generally abundant during the immature and semi-mature stages but existed at lower levels during the commercial mature period. The flavedo was much richer than the albedo in a few phenolic acids, flavonols, flavones, and especially polymethoxyflavonoids, which was particularly true for EBPs. Flavanones, particularly in GBP form, were generally present in equal or even much higher levels in the albedo. The four phenolic forms exhibited distinct trends in terms of abundance. In the flavedo (except the young fruit stage) followed the order: EBPs > GBPs ≈ FPs ≫ IBPs, and in the albedo: GBPs ≫ FPs ≈ EBPs ≫ IBPs. Generally, the phenols examined for this study were highly abundant in the citrus peels, endowing this agricultural waste with great potential to be an excellent natural source of functional ingredients.