Optimization of total phenol and anthocyanin extraction from the peels of eggplant (Solanum melongena L.) and biological activity of the extracts

Metabolite concentrations and the expression profiles of the corresponding metabolic pathway genes in eggplant (Solanum melongena L.) fruits of contrasting colors

Eggplant (Solanum melongena L.) ranks fifth in importance among vegetable crops of the Solanaceae family, in part due to the high antioxidant properties and polyphenol content of the fruit. Along with the popular purple-fruited varieties of S. melongena, there are cultivars, the fruits of which are rich in phenolic compounds, but are white-colored due to the lack of anthocyanin biosynthesis. Determination of the amount of anthocyanins and other phenolic compounds, as well as carotenoids and sugars, is included in the assessment of the quality of eggplant fruits of commercial (technical) ripeness. In addition to antioxidant and taste properties, these metabolites are associated with fruit resistance to various stress factors. In this study, a comparative analysis of the content of anthocyanins, carotenoids and soluble sugars (sucrose, glucose, fructose) in the peel and pulp of the fruit of both technical and biological ripeness was carried out in purple-fruited (cv. Vlas) and white-fruited (cv. Snezhny) eggplant accessions of domestic selection. The peel and pulp of biologically ripe fruits of the cvs Vlas and Snezhny were used for comparative transcriptomic analysis. The key genes of the flavonoid and carotenoid metabolism, sucrose hydrolysis, and soluble sugar transport were shown to be differentially expressed between fruit tissues, both within each cultivar and between them. It has been confirmed that the purple color of the peel of the cv. Vlas fruit is due to substantial amounts of anthocyanins. Flavonoid biosynthesis genes showed a significantly lower expression level in the ripe fruit of the cv. Vlas in comparison with the cv. Snezhny. However, in both cultivars, transcripts of anthocyanin biosynthesis genes (DFR, ANS, UFGT) were not detected. Additionally, the purple fruit of the cv. Vlas accumulated more carotenoids and sucrose and less glucose and fructose than the white fruit of the cv. Snezhny. Biochemical data corresponded to the differential expression pattern of the key genes encoding the structural proteins of metabolism and transport of the compounds analyzed.

Fine Mapping of Candidate Gene Controlling Anthocyanin Biosynthesis for Purple Peel in Solanum melongena L

Fruit color is an intuitive quality of horticultural crops that can be used as an evaluation criterion for fruit ripening and is an important factor affecting consumers' purchase choices. In this study, a genetic population from the cross of green peel 'Qidong' and purple peel '8 guo' revealed that the purple to green color of eggplant peel is dominant and controlled by a pair of alleles. Bulked segregant analysis (BSA), SNP haplotyping, and fine genetic mapping delimited candidate genes to a 350 kb region of eggplant chromosome 10 flanked by markers KA2381 and CA8828. One ANS gene (EGP22363) was predicted to be a candidate gene based on gene annotation and sequence alignment of the 350-kb region. Sequence analysis revealed that a single base mutation of 'T' to 'C' on the exon green peel, which caused hydrophobicity to become hydrophilic serine, led to a change in the three-level spatial structure. Additionally, EGP22363 was more highly expressed in purple peels than in green peels. Collectively, EGP22363 is a strong candidate gene for anthocyanin biosynthesis in purple eggplant peels. These results provide important information for molecular marker-assisted selection in eggplants, and a basis for analyzing the regulatory pathways responsible for anthocyanin biosynthesis in eggplants.

Ultrasonic Extraction of Phenolic Compounds from Eggplant Peel and Formulation of Eggplant Peel Extract-Enriched Ice-Cream

In this study, ultrasound-assisted extraction (UAE) was used for the extraction of bioactive compounds from eggplant peels (EPP) and conditions were optimized by using response surface methodology (RSM). Methanol concentrations (60%, 70%, and 80%), time (30 min, 45 min, and 60 min), and temperature (30°C, 45°C, and 60°C) were selected as independent extraction parameters, whereas total anthocyanin content (TAC), DPPH inhibition, and total phenolic content (TPC) were response variables. The optimal extraction was at 45°C for 45 min of extraction time with 70% solvent which corresponded to TAC, TPC, and DPPH inhibition values of 7.94 mg/g, 7.03 mg GAE/g, and 94.8%, respectively. The optimized EPP extract was chemically characterized by a Fourier-transform infrared spectrometer (FTIR), high-performance liquid chromatography (HPLC), and a gas chromatography mass spectrometer (GCMS). The optimized extract was further evaluated for antioxidant and anticancer potential. For antioxidant and anticancer potential, the corresponding IC50 values of the EPP extract were 243.2 μg/ml and 1.52–1.99 mg/ml, respectively. Furthermore, the EPP extract significantly inhibited the migratory ability of cancer cells in a dose-dependent manner. Major components identified in the EPP extract were chlorogenic acid (261.76 mg/kg), benzoic acid (184.41 mg/kg), syringic acid (78.48 mg/kg), p-coumaric acid (49.59 mg/kg), cinnamic acid (32.17 mg/kg), quercetin (5.24 mg/kg), sinapic acid (5.14 mg/kg), and gallic acid (4.34 mg/kg). The EPP extract-enriched ice-cream showed high antioxidant potential and consumer acceptability than the blank ice-cream formulation. The EPP extract, due to its antioxidant and anticancer potential, can be used in the formulation of functional food products.

Extraction of phenolics and anthocyanins from purple eggplant peels by multi-frequency ultrasound: Effects of different extraction factors and optimization using uniform design

In this work, multi-frequency ultrasound (working modes for the single-, dual- and tri-frequency in simultaneous ways) was applied to extract bioactive compounds from purple eggplant peels. The single-factor experiments were performed by varying six independent variables. A six-level-five-factor uniform design (UD) was further employed to evaluate the interaction effects between different factors. It was found that extraction temperature and extraction time significantly affected the total phenolic content (TPC), whereas the total monomeric anthocyanins (TMA) was mainly influenced by ethanol concentration, extraction temperature and solid-liquid ratio. Based on partial least-squares (PLS) regression analysis, the optimal conditions for TPC extraction were: 53.6 % ethanol concentration, 0.336 mm particle size, 44.5 °C extraction temperature, 35.2 min extraction time, 1:43 g/mL solid-liquid ratio, and similar optimal conditions were also obtained for TMA. Furthermore, the TPC and TMA extraction were investigated by ultrasound in different frequencies and power levels. Compared with single-frequency (40 kHz) and dual-frequency ultrasound (25 + 40 kHz), the extraction yield of TPC and TMA with tri-frequency ultrasound (25 + 40 + 70 kHz) increased by 23.65 % and 18.76 % respectively, which suggested the use of multi-frequency ultrasound, especially tri-frequency ultrasound, is an efficient strategy to improve the TPC and TMA extracts in purple eggplant peels.

Role of phenylalanine/tyrosine ammonia lyase and anthocyanidin synthase enzymes for anthocyanin biosynthesis in developing Solanum melongena L. genotypes

Solanum melongena is a widely consumed vegetable crop comprising health-benefiting phenolic compounds. It has a complex network of biosynthetic enzymes involved in synthesizing nutraceuticals, including anthocyanins. The present study was conducted to investigate the activities of key enzymes involved in biosynthesis and accumulation of anthocyanins in developing genotypes, such as phenylalanine ammonia lyase (PAL), tyrosine ammonia lyase (TAL), and anthocyanidin synthase (ANS). As inadequate information is available in this context, fruit and leaf tissues were analyzed for enzyme activities and anthocyanin accumulation. The study included characterization of extracted anthocyanin followed by expression studies for gateway enzyme (ANS) involved in anthocyanin biosynthesis. Delphinidin was a major anthocyanidin present in fruit tissues (1.46-110.49 mg/100 g) of S. melongena. Anthocyanin accumulation is backed up by the correlation between biochemical analysis and expression studies. The study has shown variation for PAL, TAL and ANS enzymes in different tissues at developmental stages. Enzyme activities had a strong positive correlation with anthocyanin biosynthesis.

SmMYB113 Is a Key Transcription Factor Responsible for Compositional Variation of Anthocyanin and Color Diversity Among Eggplant Peels

To understand the color formation mechanism in eggplant (Solanum melongena L.) peel, a metabolomic analysis was performed in six cultivars with different peel colors. A total of 167 flavonoids, including 16 anthocyanins, were identified based on a UPLC-MS/MS approach. Further analysis revealed that the delphinidins/flavonoids ratio was consistent with the purple coloration of eggplant peels, and SmF3'5'H expression level was consistent with the delphinidin 3-O-glucoside and delphinidin 3-O-rutinoside contents, the main anthocyanins in the purple-peels eggplant cultivars identified in this study. SmMYB113 overexpression promoted anthocyanins accumulation in eggplant peels and pulps. Metabolomic analysis revealed that delphinidins were still the main anthocyanins class in the peels and pulps of SmMYB113-OE4, but most anthocyanins were glycosylated at the 5-position of the B-ring. Our results provide new insights into the anthocyanin composition of eggplant peels and demonstrate the importance of SmMYB113 in stimulating anthocyanin biosynthesis in eggplant fruits.