Study on dry fruit flavor of Huizao and Junzao jujubes from different habitats

Abstract:【Objective】Fruit flavor substances are divided into flavor and aroma substances. The former is perceived through taste. The research focus on flavor is sugar and acid, which determine the two most important flavors of fruit: sweet and acid. Acid is perceived by olfactory sense, and fruits contain a lot of volatile aromatic substances. At present, comprehensive flavor analysis has been carried out on many fruits such as grapes, cherries and so on. For jujube fruit, the research focus is limited to the sugars and acids that affect the taste and aroma substances, thus affecting the sense of smell. Substance analysis lacks comprehensive flavor analysis and systematic research. The fruits of Huizao and Junzao during mature period were studied in this experiment. The sugar, acid and aroma compounds that affected the flavor of jujube fruit were comprehensively analyzed, and their sources (Xinzheng, Henan; Jiaocheng, Shanxi) and four introduced places in Xinjiang (Kashi, Hetian, Ertuan and Wensu) were studied in order to provide a theoretical basis for the flavor evaluation of dried jujube fruit and a reference for the intro- duction and fine application of desired jujube varieties【. Methods】Determine the total sugar and total ac- id by spectrophotometry and acid-base titration, respectively; weigh 0.2 g of the dried sample and put into a 10 mL centrifuge tube, add 7.5 mL of 80% ethanol, shake in a water bath at 70 °C for 30 min, cen- trifuge at 8000 r·min-1 10 min, take the supernatant in a 25 mL glass test tube, repeat 3 times, dilute the volume (80% ethanol) to 25 mL and shake well. Take 10 mL (8 mL) into a 50 mL centrifuge tube, dry at 55 °C, add 10 mL (8 mL) redistilled water to dissolve, filter with 0.45 um filter, it was the test solu- tion. The soluble sugar was determined by high performance liquid chromatography, using COSMOSIL Packed Column 5NH2-MS column (4.6ID×150 nm), the detector was RI Detector L-2490 differential detector, and the mobile phase was acetonitrile: water (80:20), the standard products were sucrose, fructose and glucose; the organic acid was determined by ultra-high performance liquid chromatography, the acid was determined with a C18 column and a UV detector, the mobile phase was a potassium dihy- drogen phosphate solution with pH=2.4, and the standard product was malic acid, citric acid, succinic acid and quinic acid. Determination of aroma substances was performed by the gas chromatography-tan- dem mass spectrometry, and the chromatographic mass spectrometry acquisition conditions were as fol- lows: Chromatographic column: HP-5MS (30 m×0.25 mm×0.25 mm); carrier gas: helium (0.83 mL·mL-1); sample inlet temperature: 250 °C; solution delay: 3 min; program temperature rise: hold at 60 °C for 1 min, increase to 250 °C at a rate of 10 °C·min-1 and hold for 1 min, then increase to 280 °C at a rate of 20°C·min-1 and hold for 1 min, and finally increase at a rate of 10°C·min-1 to 315°Cand keep for 4 min; split mode: 10:1; mass spectrometry conditions: transmission line temperature 280 °C, electron energy 70 eV, ion source temperature 250 °C, quadrupole temperature 150 °C, acquisition mode MRM. SPME sampling parameters: aging temperature 250 °C, aging time 5 min, heating temperature 60 °C, heating time 10 min, adsorption time 20 min, desorption time 5 min, aging time 5 min after sample in- jection.【Results】The soluble sugar contents of Huizao and Junzao dried fruits from different origins were the highest (accounting for 42.09%-65.33% of total sugar), followed by fructose, and glucose content was the lowest; organic acid had the highest content of malic acid (accounting for 36.02%- 56.94%), followed by citric acid and succinic acid, with the lowest content of quinic acid; the high sugar and low acid characteristics of the 4 kinds of jujube fruits in Xinjiang, which led to a higher sugar-acid ratio than the original place, making them a better taste. A total of 68 aroma substances were detected in Huizao jujube and jujubes from different origins. The main aroma substances that affected the aroma of dried jujube fruits were acids, ketones, alcohols and hydrocarbons. The comprehensive evaluation of aroma quality by principal component analysis showed that the flavor from the original producing area was better than that of the four introducing areas. The flavor difference in dried jujube from different areas may be closely related to environmental factors such as sunshine, temperature, precipitation and soil characteristics. The results can provide reference for the introduction and fine application of desired jujube varieties in Xinjiang.【Conclusion】(1) The contents of soluble sugar and organic acid in dried jujube fruits from different areas were different. Sucrose was the main soluble sugar and malic acid was the main organic acid. Planting land can result in the jujube dried fruit flavor being better than the original place. (2) The main aroma components affecting the aroma quality of dried jujube were acids, ketones, alcohols and hydrocarbons; the content of aroma components changed greatly, mainly for acids and ketones. The comprehensive aroma scores of jujube and sour jujubes from different producing areas were higher than those from the introduction areas. (3) The flavor differences in dried jujube from dif- ferent producing areas may be closely related to environmental factors such as sunshine, temperature, precipitation and soil characteristics. Further study on the key environmental factors affecting the aroma of dried jujube is of great significance to improve the aroma of dried jujube in cultivation area.