31(1–2) - Sodininkystė ir daržininkystė - Sodininkystės ir ...

Object, methods and conditions. Green onion cv. ‘Parade’ was grown in thePūre Horticultural Research Center.In this study modified atmosphere was created passively through product respiration.For this purpose green onions were stored in hermetically closed glass containers,which were placed in the Besseling controlled atmosphere chambers (Besseling CAsystems BV, Zwaag, The Netherlands).Respiration rate of green onions was measured with gas analyzer EASI-1 (Absoger,Les Barthes, France).The extracts for the total phenolics assay were obtained by extracting 5 g of homogenizedgreen onions with 25 ml of methanol at ambient temperature for 1 h underconstant shaking. The solution was filtered and the residue was repeatedly extractedwith 25 mL of methanol for 1 h. The extracts were combined and diluted up to 50 mLwith methanol.Total phenolics in the methanolic extracts were determined with Folin-Ciocalteureagent according to the method of Slinkard and Singleton (1977). The absorbance ofthe samples was measured at 765 nm using the Genesys-10UV/Vis spectrophotometer(Thermo Spectronic, Rochester, USA). Results were expressed in mg of gallic acidequivalents (GAE) per 100 g of fresh weight.The extracts for the radical scavenging activity assay were obtained by extracting5 g of homogenized green onions with 25 ml of methanol at ambient temperaturefor 2 h under constant shaking. The radical scavenging activity of extracts againststable 2,2-diphenyl-1-picrylhydrazyl hydrate DPPH• (Sigma-Aldrich, Germany) wasdetermined by a slightly modified spectrophotometric method of Brand-Williams etal. (1995). DPPH• methanolic solution (2 mL, 6 × 10 -5 M) was mixed with 20 µLof prepared extract. The decreasing absorbance at 515 nm due to the scavenging ofDPPH • was measured with a spectrometer Genesys-10 UV/Vis. Simultaneously theabsorption of blank sample containing the same amount of methanol and DPPH •solution was measured.Antiradical activity of the samples was expressed as Trolox equivalent antioxidantcapacity TEAC. For this purpose calibration curve of Trolox was made in DPPHassay (r 2 = 0.999).Ascorbic acid was determined by the titrimetric method using 2,6-dichlorphenolindophenolsodium salt solution (AOAC, 1990).Soluble solids content was measured using a refractometer (ATAGO pR-32, AtagoCo., Ltd., Tokyo, Japan).Nitrate concentration was measured by a potentiometric method using the nitrateion selective electrode (ECNO30301B) (Metodiniai nurodymai..., 1990).The surface color of green onions was measured with a portable spectrophotometerMiniScan XE Plus (Hunter Associates Laboratory, Inc., Reston, USA). CIEL*a*b*colorparameters were recorded as L* (lightness), a* (+ redness/- greenness), b*(+ yellowness/-blueness). The chroma (C*) and hue angle (h°) were also calculated (McGuiere,1992).Experiment data were processed using Microsoft Office Excel (Microsof, USA).42