Polysaccharides are biological macromolecules that are difficult to absorb into intestinal epithelial cells for exerting activities, whereas the interaction between polysaccharides and gut microbiota might be an alternative method. This study aimed to explore the in vitro digestion of hawthorn polysaccharides (HPS) and their interaction with the gut microbiota. Results showed that the content of reducing sugars increased slightly during gastric digestion. However, no free monosaccharide was detected during the whole simulated digestion process, indicating that HPS was indigestible. The total carbohydrate residue decreased during in vitro fermentation. This result was due to the utilization by the gut microbiota. Meanwhile, short-chain fatty acids were produced due to the utilization of HPS. Notably, HPS could significantly modulate the composition of human gut microbiota; in particular, the relative abundances of Megasphaera, Acidaminococcus and Mitsuokella increased, whereas the relative abundances of Escherichia Shigella and Fusobacterium decreased. It was suggested that HPS could decrease the abundances of harmful intestinal microbiota and regulate the proportion of beneficial bacteria in the intestinal tract. Overall, the beneficial effects of HPS were believed to be related to the gut microbiota and could be used as a potential dietary supplement.

The interaction between polyphenols and polysaccharides plays an important role in increasing the turbidity stability of fruit juice and improving unpleasant sensory experiences. The binding adsorption behavior between hawthorn pectin (HP) and polyphenols (epicatechin and chlorogenic acid) accorded with the monolayer adsorption behavior driven by chemical action and were better fitted by pseudo-second order dynamic equation and Langmuir model. The HP binding sites (Q_m) and adsorption capacity (Q_e) to epicatechin were estimated at 75.188 and 293.627 μg/mg HP, respectively, which was about nine and twelve times higher than that of chlorogenic acid. The interaction between HP and polyphenols exhibited higher turbidity characteristics, particle size and lower zeta potential than epicatechin and chlorogenic acid alone. Meanwhile, according to Fourier Transform Infrared Spectroscopy (FT-IR) analysis, it could be speculated that the interaction between HP and polyphenols resulted in chemical combination. Moreover, ΔH < 0 and TΔS < 0, which indicated that the interaction between HP and polyphenols was mainly driven by hydrogen bonds and van der Waals forces.

The global production of quinoa has been increasing in recent years. In plant-based foods, ultrasound stress has received increasing attention, owing to its ability to enhance the production of primary and secondary metabolites. We studied the effects of ultrasonic stress at the pre-germination stage on the γ-aminobutyric acid (GABA) accumulation and characteristics of nutrition and function in quinoa. The results showed that ultrasonic conditions of 100 W for 4 min promoted an increase in GABA content by 9.15-fold, to 162.47 ± 6.69 mg/100 g·DW, compared to that of untreated quinoa, through promoting a 10.2% and 71.9% increase in the water absorption and glutamate decarboxylase activity of quinoa, respectively. Meanwhile, compared to untreated quinoa, ultrasonic stress at the pre-germination stage enhanced the total phenolic, total flavonoid, and total saponin contents of quinoa by 10.2%, 33.6%, and 90.7%, to 3.29 mg GA/g·DW, 104.0 mg RE/100 g·DW, and 7.13 mg/g, respectively, without decreasing its basic nutritional quality. Ultrasonic stress caused fissures on the surface of quinoa starch particles. Additionally, germination under ultrasonic stress increased the n3 polyunsaturated fatty acids by 14.4%. Furthermore, ultrasonic stress at the pre-germination stage promoted the scavenging of 2,2-diphenyl1-picrylhydrazyl radicals and inhibitions of α-amylase, α-glucosidase, and pancreatic lipase by 14.4%, 14.9%, 24.6%, and 20.0% in vitro, compared to untreated quinoa. The results indicated that the quinoa sprouted via ultrasonic stress could represent a promising method through which to develop nutritionally balanced whole grains rich in GABA, with hypoglycemic and hypolipidemic activities, which could provide theoretical support for the development of functional whole-grain foods based on quinoa.

Gamma-aminobutyric acid (GABA) is a nonprotein amino acid, which confers stress resistance to plants. Precise mechanisms underlying GABA accumulation in quinoa (Chenopodium quinoa) subjected to dark and ultrasonic stresses have not been elucidated. We conducted transcriptome and metabolome analyses of quinoa samples exposed to various stress treatments to reveal molecular pathways leading to GABA accumulation. Through the comprehensive integration of metabolome and transcriptome data, an association was revealed between GABA accumulation, 9 differentially expressed metabolites, and 27 differentially expressed genes. Two pathways responsible for GABA synthesis were identified, involving glutamate decarboxylase and aldehyde dehydrogenases, respectively. These enzymes regulate the enrichment of GABA in quinoa under dark and ultrasonic stress conditions. We demonstrated that under ultrasonic stress, proline and alanine increased, whereas glutamate and arginine declined. Phenolic acid, flavonoids, and alkaloid metabolites increased. These findings provide novel insights into the mechanism by which darkness and ultrasound stress enhance GABA, supporting the development of targeted synthetic biology techniques.