To elucidate the effects of cultivar and harvest month on the phenolic content and antioxidant activity of mulberry leaves, four major phenolics, including chlorogenic acid (ChA), benzoic acid (BeA), rutin (Rut) and astragalin (Ast), were quantified using an HPLC-UV method. Leaves from six mulberry cultivars, collected from April to October, were analyzed. The antioxidant activity of mulberry leaves was assessed by ferric reducing antioxidant power (FRAP), hydroxyl radical scavenging activity (HSA) and superoxide radical scavenging activity (SSA) assays. The results showed that the total values of the four phenolic compounds ranged from 2.3 dry weight (DW) to 4.2 mg/g DW, with ChA being the major compound. The mean total phenol (TP) content of the six cultivars ranged from 30.4 equivalents (GAE) mg/g DW to 44.7 GAE mg/g DW. Mulberry leaves harvested in May had the highest TP content. Moreover, the antioxidant activities of mulberry leaves harvested from April to October differed noticeably. In general, Kq 10 and May were considered to be a better cultivar and harvest month concerning phenolic content and antioxidant activity, respectively.

Morusin is a prenylated flavonoid found in mulberry that shows antimicrobial activity against foodborne pathogens. The MIC values of morusin toward S. aureus ATCC 6538 and S. aureus ATCC 25923 were both 14.9 μmol L⁻¹. This study further investigated the antimicrobial mechanism of morusin in inhibiting the growth of Staphylococcus aureus ATCC 6538. Scanning electron microscopy and transmission electron microscopy revealed that morusin disrupted the integrity of the bacterial cell membrane. Morusin may also affect the phospholipid-repair system of bacteria, which repairs membrane structures. To test this hypothesis, quantitative real-time PCR was used to examine the effect of morusin treatment of S. aureus on the regulation of genes associated with the cell phosphatidic acid biosynthesis pathway. Gas chromatography–mass spectrometry was used to investigate the fatty acid components, which are used to synthesize bacterial phosphatidic acids. In summary, the results revealed that morusin showed a potent antibacterial effect by disrupting the cell membrane architecture and inhibiting the phosphatidic acid biosynthesis pathway of S. aureus.

The liver is the primary organ regulating glucose metabolism. In our recent study, cinnamon improved liver function in diabetic mice. However, it is not clear whether cinnamon can reduce the glycemia of diabetic animals by regulating liver glucose metabolism. The purpose of this study was to investigate the hypoglycemic mechanism of cinnamon powder (CP) from the perspective of regulating liver glucose metabolism. To achieve this, different doses of CP (200, 400, or 800 mg/kg body weight) were given to diabetic mice by gavage once per day for 8 weeks. These mice were compared with healthy controls, untreated diabetic mice, and diabetic mice treated with metformin (the main first-line drug for type 2 diabetes). CP treatment effectively reduced fasting blood glucose levels and food intake, improved glucose tolerance and fasting serum insulin levels, and decreased glycated serum protein levels in diabetic mice. Furthermore, treatment with CP increased liver glycogen content and reduced the level of the gluconeogenesis precursor pyruvate in the liver. Data obtained by qPCR and western blotting suggested that CP improved glucose metabolism disorders by regulating AMPKα/PGC1α-mediated hepatic gluconeogenesis and PI3K/AKT-mediated hepatic glycogen synthesis. CP exhibits good hypoglycemic effects by improving hepatic glycogen synthesis and controlling hepatic gluconeogenesis. Therefore, CP may be applied as a functional food to decrease blood glucose.

The effects of natural and synthetic galactooligosaccharides (GOS) on inflammation were explored by investigating the structure-activity relationship between the degree of GOS polymerization and in vitro anti-inflammatory activity, together with the potential underlying mechanism of their anti-inflammatory effects. The results demonstrated that GOS had strong anti-inflammatory effects in lipopolysaccharide (LPS)-induced RAW264.7 macrophages, including the inhibition of nitric oxide production and the reduced expression of pro-inflammatory mediators (interleukin-1β, interleukin-6, and tumor necrosis factor α), induced nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2), and proteins related to the Toll-like receptor 4 (TLR4)/nuclear factor (NF)-κB signaling pathway. GOS4, which has the highest degree of polymerization, exerted the strongest anti-inflammatory activity among the GOS examined. More importantly, our findings confirmed the anti-inflammatory effects of GOS on RAW264.7 macrophages via the TLR4/NF-κB pathway. Our experimental results could provide further support for the exploration of GOS in human nutrition and health.

Prenylated flavonoids show antibacterial activity towards Staphylococcus aureus (S. aureus). Previous studies have suggested that the prenyl side-chain is an important active group for antimicrobial activity. However, prenylated flavonoids also often contain a pyran ring isopentene group. Few studies have explored the contribution of the pyran ring isopentene group to antibacterial activity. In this study, the antibacterial activities of structurally related flavonoid compounds from mulberry root bark were studied by detecting the minimum inhibitory concentration (MIC) and colony counting. These flavonoid compounds all exhibited antibacterial activities against S. aureus ATCC6538, S. aureus ATCC25923 and methicillin-resistant S. aureus (MRSA) ATCC43300 with MIC values of 7.3–248.2 μmol/L, 7.3–330.9 μmol/L, and 7.3–330.9 μmol/L, respectively. Structure-activity relationship analyses demonstrated that the pyran ring isopentene group plays an important role in antibacterial activity. Thus, the pyran ring isopentene group is an overlooked antimicrobial active group in prenylated flavonoids. Graphical Abstract