Data on free and bound volatile compounds in six Ribes nigrum L. blackcurrant cultivars

The data investigated 198 volatile compounds of six currant cultivars grown in China which is analyzed by SPME–GC–MS. Volatile compounds in these currant samples were identified by two methods, comparing retention indices with reference standards and matching mass spectrum in the NST11 library. A synthetic currant matrix prepared according to the currant juice condition were extracted and analyzed using the same extraction procedure as the currant samples. The standard curve was generated for quantification of volatile compounds. For the volatiles without the available standard, the data provided consulting standards that had the same carbon atom or the similar functional structure for quantification. Further interpretation and discussion can be seen in article entitled “Characterization of Free and Bound Volatile Compounds in Six Ribes nigrum L. Blackcurrant Cultivars” (Liu et al., 2018) [1].


a b s t r a c t
The data investigated 198 volatile compounds of six currant cultivars grown in China which is analyzed by SPME-GC-MS. Volatile compounds in these currant samples were identified by two methods, comparing retention indices with reference standards and matching mass spectrum in the NST11 library. A synthetic currant matrix prepared according to the currant juice condition were extracted and analyzed using the same extraction procedure as the currant samples. The standard curve was generated for quantification of volatile compounds. For the volatiles without the available standard, the data provided consulting standards that had the same carbon atom or the similar functional structure for quantification. Further interpretation and discussion can be seen in article entitled "Characterization of Free and Bound Volatile Compounds in Six Ribes nigrum L. Blackcurrant Cultivars" (Liu et al., 2018) [1].
& Each currant cultivar was mashed and centrifuge to obtain currant juice. The currant juice was mixed with NaCl and 4-methyl-2-pentanol (internal standard). The bound volatile extraction was released by AR2000 enzyme solution.

Experimental features
The free and bound volatile extraction was analyzed by HS-SPME followed by GC-MS using a 60 m × 0.25 mm, 0.25 µm thickness HP-INNOWAX capillary column.

Data source location
The horticultural experimental station at the Northeast Agricultural University in China (latitude 44°04′ and longitude 125°42′ )Data accessibility Data is provided with this article.

Value of the data
This data provided physicochemical parameters of six currant cultivars for further studies of currant quality control.
Total 198 Volatile compounds were identified in six currant cultivars by GC-MS. The standard curve of some volatile compounds was generated for quantification of volatile compounds by GC-MS. The data can be used for reference of volatiles quantification.
The data calculated the retention indices of volatiles compounds that can be used for qualitative analysis by GC-MS.

Chemicals and reagents
Glucose, sodium hydroxide, sodium chloride, citric acid, and sodium dihydrogen phosphate were obtained from Beijing Chemical Works (Beijing, China). HPLC grade dichloromethane, ethanol, and methanol were purchased from Honeywell (Morris Township, NJ, USA). Pure water was obtained from Milli-Q purification system (Millipore, Bedford, MA, USA). The volatile standards used for identification were purchased from Sigma-Aldrich (St. Louis, MO, USA) with a purity above 98%. Other reagents were of analytical grade unless specifically noted.

Volatile extraction
Each currant cultivar was mashed and centrifuged to yield currant juice. The currant juice (5 mL) was mixed with NaCl (1.00 g) and 1.0018 g/L 4-methyl-2-pentanol (10 µL, internal standard) in a 15-mL glass vial containing a magnetic stirrer with a PTFE-silicon septum. The mixture was equilibrated on a heating and agitation platform at 40°C for 30 min. The free volatile compounds in the sample were concentrated with headspace SPME regarding our previous report [2]. Each currant cultivar was conducted in three independent extractions.
The bound volatiles were released using AR2000 enzyme solution according to our published methods [2]. Afterwards, the bound volatile compounds were extracted and analyzed using the same SPME as the free volatile compounds.

GC-MS analysis
The volatile compounds analysis on GC followed our previous method [3]. An Agilent 7890 gas chromatography equipped with an Agilent 5975 mass spectrometer (Agilent Technologies, Santa Clara, CA, USA) was used to analyze volatile compounds. A 60 m × 0.25 mm, 0.25 µm thickness HP-INNOWAX capillary column (J&W Scientific, Folsom, CA, USA) was used to separate the volatile compounds using the carrier gas (helium) at 1 mL/min flow rate. The over temperature was programmed as follows: 50°C held for 1 min, then increased from 50°C to 220°C at a rate of 3°C /min and held at 220°C for 5 min, and then increased to 250°C at 5°C /min and held at 250°C for 5 min. The temperature of MS transfer line was set at 280 o C. Mass spectrum was recorded at 70 eV with 130°C in the electron impact (EI) mode. All scan mass from m/z 25 to 300 was recorded. C 6 -C 24 alkane series (Supelco, Bellefonte, PA, USA) was analyzed under the same chromatographic conditions for calculation of retention indices of volatiles. The volatiles in currant were identified by comparing their retention indices and mass spectrum with reference standard. The volatiles without the available standard were tentatively identified by comparing their retention indices and mass spectrum with the NIST11 library (Table 3).

Standards analysis
A synthetic currant matrix was prepared regarding the physicochemical index of the currant juice. The synthetic currant matrix consisted of 170 g/L sugar and 3.5 g/L citric acid with its pH adjusted 4.0 using 5 M NaOH solution. Each external volatile standard was dissolved in HPLC-grade ethanol to generate the stock standard solution. These stock standard solutions were then combined using the synthetic matrix to form standard working solution. Afterwards, the standards working solution was diluted using the synthetic matrix to 18 successive levels. The standards were analyzed using the same extraction procedure as the currant samples, and analyzed under the same GC method. The standard curve was integrated using the peak area ratio of external volatile standard to internal standard versus the concentration of external standard (Table 2).