Development of active packaging films based on quaternary ammonium chitosan, polyvinyl alcohol and litchi (Litchi chinensis Sonn.) pericarp extract

Litchi (Litchi chinensis Sonn.) pericarp contains abundant polyphenols that are suitable materials for developing active packaging films. In this study, 1 wt%, 3 wt% and 5 wt% of litchi pericarp extract (LPE) was added into qua-ternary ammonium chitosan (QAC) and polyvinyl alcohol (PVA) matrix to develop active packaging films. The structural, physical and functional properties of QAC-PVA (QP) films were compared with LPE (QP-LPE films) and without LPE (QP films). Results showed QP film had a heterogenous cross-section whereas QP-LPE films displayed rough and uneven cross-sections. After adding LPE, the N–H, O–H, C–H and C=O stretching bands of QP films shifted due to the formation of intermolecular interactions between LPE and film matrix. LPE made the colorless QP film turned brown. QP-LPE films presented lower ultraviolet–visible light transmittance than QP film. After adding LPE, film thickness increased from 0.091 to 0.103 mm, film water vapor permeability increased from 14.98 × 10−11 to 17.21 × 10−11 g m−1 s−1 Pa−1, film oxygen permeability increased from 0.16 to 0.22 cm3 mm m−2 day−1 atm−1, film tensile strength increased from 14.10 to 17.41 MPa, and film elongation at break decreased from 36.94% to 25.13%. QP-LPE films quickly released polyphenols in distilled water within 4 h and displayed potent antioxidant activity. The antimicrobial ratio of the film against Escherichia coli, Salmonella typhimurium, Staphylococcus aureus and Listeria monocytogenes was elevated from 50.40−68.04% to 58.93−91.38% after adding LPE. Results suggested QP-LPE films could be utilized as antioxidant and antimicrobial packaging materials in food industry.

Diabetes diminishes typical metabolite of litchi pericarp oligomeric procyanidins (LPOPC) in urine mediated by imbalanced gut microbiota

Animal studies and clinical trials have shown that dietary polyphenols and polyphenol-rich foods can reduce the risk of T2D and its complications, but how diabetes regulates the metabolism of polyphenol...

Selection and validation of reference genes for RT-qPCR analysis in Litchi chinensis Sonn. pericarp

Background: Quantitative real time PCR (qRT-PCR) is an important tool for gene expression analysis and function identification. Suitable reference genes are the basis of accurate and reliable qPCR results. Litchi ( Litchi chinensis Sonn.) is a commercially important tropical and subtropical fruit crop, rapid pericarp browning is the major negative impact on the industry. Reference gene validation would help screen for genes involved in the browning mechanism.Results: In this study, fifteen new candidate reference genes, identified with transcriptome data, were assessed to determine stable reference genes for qRT-PCR analysis of litchi pericarps from different varieties, with differing postharvest storage, and under pathogenic inoculation. Ct values, Genorm, Normfind, and Reffinder algorithms, were used to identify the most stable genes. The results showed that GAGA-25 was the most stable gene for comparing different varieties of fresh pericarp, HDAC9 was the most stable gene for postharvest pericarp, STAM was the most stable for inoculated pericarp. Among the candidate reference genes, GAGA-25 was the most stable reference gene across the complete sample set.Conclusion: This study evaluated reference gene stability for qRT-PCR with litchi pericarp. This work supplies a foundation for qPCR use in future gene function and molecular mechanism studies of litchi pericarp browning.

Effect of Storage Conditions on Phenolic Profiles and Antioxidant Activity of Litchi Pericarp

Changes of phenolic profiles and antioxidant activity of litchi pericarp during storage at 4 °C for seven days and at room temperature (RT) for 72 h were evaluated in this study. The contents of total phenolic and procyanidin decreased by 20.2% and 24.2% at 4 °C and by 37.8% and 47.8% at RT, respectively. Interestingly, the corresponding reductions of anthocyanins were 41.3% and 73%, respectively. Four phenolic compounds, including epicatechin, procyanidin A2, procyanidin B2, and quercetin-3-O-rutinoside-7-O-α-l-rhamnosidase were detected in litchi pericarp. Their contents after storage at 4 °C and at RT were decreased by 22.1–49.7% and 27.6–48.7%, respectively. The oxygen radical absorbance capacity (ORAC) and cellular antioxidant activity (CAA) of litchi pericarp decreased by 17.6% and 58.7% at 4 °C, and by 23.4% and 66.0% at RT, respectively. The results indicated that storage at 4 °C preserved more phenolics and retained higher antioxidant activity in litchi pericarp compared to storage at RT, suggesting that storage at 4 °C should be considered as a more effective method for slowing down the degradation of litchi pericarp phenolics.

Increasing Yield and Antioxidative Performance of Litchi Pericarp Procyanidins in Baked Food by Ultrasound-Assisted Extraction Coupled with Enzymatic Treatment

Extraction with organic solvents is a traditional method to isolate bioactive compounds, which is energy-wasting and time-consuming. Therefore, enzyme and ultrasound treatments were combined to assist the extraction of oligomeric procyanidins from litchi pericarp (LPOPC), as an innovative approach to replace conventional extraction methods. Under optimum conditions (enzyme concentration 0.12 mg/mL, ultrasonic power 300 W, ultrasonic time 80 min, and liquid/solid ratio 10 mL/g), the yield of LPOPC could be improved up to 13.5%. HPLC analysis indicated that the oligomeric procyanidins (OPC) content of LPOPC from proposed extraction was up to 89.6%, mainly including (−)-epicatechin, procyanidin A1, A2, and A-type procyanidin trimer. Moreover, LPOPC powder was added in baked food to inhibit the lipid peroxidation. It was found that 0.2% (w/w) of LPOPC could maintain the quality of cookies in the first 7 days, by decreasing the peroxide values. The procyanidin dimers and trimers in LPOPC played more important roles as antioxidants compared to monomers during storage. The results also showed that the combined extraction process can be considered as a useful and efficient method for the extraction of functional components from other plant sources.