Changes in aroma of 'Darselect' strawberry during development and characterization of the key aroma components

Abstract：【Objective】Because of its advantages of high yield, less disease, fruit clean sanitation, hydroponic strawberry cultivation has been increasingly used. Strawberry flavor is determined by the soluble sugars, organic acids and aroma compounds. Aroma plays an important role in flavor formation and is an important subject in fruit quality related research. The aim of this study is to clarify the composition and content of aroma in'Darselect'strawberry and to reveal the dynamic change during fruit development.【Methods】Fruit were sampled at every stage, cut into pieces, grinded into powder in liquid nitrogen and stored under-80 ℃. 5 g of the freeze dried powder was transferred into 20 mL bottles, to which 5 mL saturated sodium chloride solution and 10 μL diluted standard of cyclohexanone (18.956 g·L-1) were added. After sealing, blending and headspace extraction for 30 min, 1 μL of the extract was injected into a GC-MS spectrometer (Agilent 6890 N-5973, the United States) . Each sample had 3 replicates. For HSSPME, fiber head used was 50/30 μm DVB/CAR/PDMS. The furnace temperature was set at 45 ℃and the extraction lasted 30 min with a desorption period of 4 min. The carrier gas was He, and the flow rate 1.0 mL · min-1. The temperature program was 34 ℃ for 2 min followed by temperature increase at 3 ℃ per minute to 80 ℃, and then at 6 ℃ per minute to 180 ℃, and finally at 10 ℃ per minute to 250 ℃, which was maintained for 2 min. Carrier gas was He with a flow rate of 1.3 mL · min-1 with no shunt. The inlet temperature was 250 ℃. The mass spectra of the detected compounds were matched with NIST Library and also subjected to artificial qualitative analysis based on literatures.【Results】Totally, 70 aroma compounds were identified from samples at five stages. Among them, the maincomponents were aldehydes, ketones, esters and terpenes. 27 esters, 11 terpenes, 9 aldehydes, 9 alkanes, 8 alcohols, 4 acids, 2 ketones and 1 other substance were indentified. The green fruit period and white fruit period were dominated by aldehydes and alkanes. A small amount of esters was found at veraison, and aldehydes were the most abundant at this stage. The contents of aldehydes and alkanes at the pink fruit stage had increased and became much higher at full red stage. After the full red stage, the strawberry had a different aromatic type. Hexenal and (E) -2-hexenal were the most abundant aldehydes. During the development of fruit, the contents of hexenal and (E) -2-hexenal increased first and then decreased, and then increased to a maximum value of 2.82 μg · g-1 and 35.45 μg · g-1, respectively, at veraison. Terpenes were mainly concentrated at pink fruit and full red stages. D-limonene, β-acacia, trans-α-limonene and β-bisabolene were relatively heavy terpenes, and D-limonene only appeared at pink fruit stage and was not detected at the full red stage. Methyl hexanoate, (2 E) -2-hexenyl acetate, ethyl hexanoate, hexyl hexanoate, butyl butyrate, octyl isovalerate and octyl hexanoate were the dominant esters.At full red stage, methyl hexanoate reached 1.19 μg · g-1, (2 E) -2-hexenylacetate 2.31 μg · g-1, ethyl hexanoate 1.28 μg · g-1, and octyl octanoate 1.61 μg · g-1. Among the alcoholic substances detected, linalol and trans-nerolido were the main substances. Linalol appeared from the veraison, and the trans-nerolido appeared from the pink fruit period. Acidic substances mainly appeared at the full red stage, and hexanoic acid reached 2.5 μg · g-1. Two ketones were detected, namely γ-decalactone and DMMF (2, 5-dimethyl-4-methoxy-3 (2 H) -furanone) .【Conclusion】The results showed that aldehydes and alkanes were the main types of aroma during the green fruit and white fruit periods, when the strawberry takes fragrant type. A small amount of esters appeared at veraison, and aldehydes were the most abundant. Aldehydes and alkanes reduced and esters increased during the pink fruit period. In comparison, the content of esters was more abundant during the full red period, when strawberry was fully mature and became aromatic. The characteristic aroma components of'Darselect'were hexanal, (E) -2-hexenal, nonanal, octanal, cis-3-hexenol, linalool, trans-nerolidol, γ-decalactone, 2, 5-dimethyl-4-methoxy-3 (2 H) -furanone, methyl butyrate, ethyl hexanoate, octyl butyrate, ethyl octoate, D-limonene, β-farnesene and so on.