分葱采后不同干枯等级葱叶品质生理生化指标的变化

    Changes of Physiological and Biochemical Indexes of the Quality of Fistular Onion Leaves at Different Drying Grades After Harvest

    • 摘要: 探究分葱采后不同干枯等级中葱叶品质指标的变化情况,为分葱的贮藏运输提供理论依据。调查商品成熟期大叶分葱品种AF37和小叶分葱品种AF45的农艺性状,于采后常温(25±1)℃、相对湿度(70%±5%)条件下贮藏,依据葱叶干尖程度进行分级(0、1、5、9和10级),测定并比较两个分葱品种在各等级下的含水率、叶绿素、总蛋白、可溶性糖、维生素C和硝态氮含量。结果表明:两个分葱品种在农艺性状上存在差异,大叶分葱品种AF37株型较大,平均株高为57.51 cm、叶横径为1.02 cm;小叶分葱品种AF45株型较小,平均株高为42.52 cm、叶横径为0.53 cm,而单株叶数多达4叶·株-1。随着葱叶干枯等级增加,大叶分葱品种AF37和小叶分葱品种AF45葱叶含水率从0级的87.97%、90.29%降低至10级的7.28%、11.15%,干枯5级时分葱已丧失商品价值;叶绿素a、叶绿素b和总叶绿素含量随干枯等级增加均呈急速减少趋势,干枯5级之前下降均为极显著差异;总蛋白含量随着干枯程度的加深而缓慢降低,分别从0级的0.44、0.60 mg·g-1减少至10级的0.05、0.07 mg·g-1;葱叶可溶性糖含量分别从0级的30.83、40.02 mg·g-1减少至10级的2.86、3.81 mg·g-1;维生素C含量有较大幅度的下降,分别从0级的1.73、1.14 mg·g-1降至10级的0.03、0.04 mg·g-1,其中1级之前维生素C含量下降幅度较大之后慢慢降低;硝态氮含量也随着分葱的干枯而呈下降的趋势,大叶分葱AF37中硝态氮含量降低差异不显著(P>0.01),而小叶分葱AF45则差异显著(P<0.01)。相关性分析结果表明,葱采后干枯程度增加,伴随葱叶失水、失绿黄化及物质降解衰退过程,干枯等级数与分葱含水率、叶绿素、蛋白质、可溶性糖、维生素C及硝态氮含量等主要品质指标均呈显著或极显著相关性,其划分具有实际的意义。分葱在采后贮藏过程伴随葱叶失水、失绿黄化及物质降解衰退过程,各项品质的理化指标均向衰减或衰老方向发展,且分葱贮藏过程中品质衰减可能存在临界点(干枯等级5级),当干枯超过临界等级时分葱开始加速衰老。因此应在考虑减少贮运时间的同时在贮运前期着重于保水、保绿及防止蛋白质、可溶性糖等物质降解。

       

      Abstract: The changes of quality indexes of fistular onion leaves at different drying grades of shallot after harvest were studied, thus to provide theoretical basis for the storage and transportation of shallot. In order to investigate the agronomic characteristics of large-leaved variety AF37 and small-leaved variety AF45 in the mature period, they were stored at room temperature (25±1)℃ and relative humidity (70%±5%) after harvest. Then, the contents of moisture content, chlorophyll, total protein, soluble sugar, vitamin C and nitrate nitrogen of the two varieties of Allium fistulosum L.var.caespitosum Makino at different grades were determined and compared according to the drying degree of fistular onion leaves (which was graded to grades 0, 1, 5, 9 and 10). The results showed that there were differences in agronomic traits between the two varieties. The plant type of the large-leaved variety AF37 was larger, with an average plant height of 57.51 cm and leaf transverse diameter of 1.02 cm. The plant type of small-leaved variety AF45 was small, with an average plant height of 42.52 cm and leaf transverse diameter of 0.53 cm, and the number of leaves per plant was up to 4.With the increase of drying grades of fistular onion leaves, the moisture content of fistular onion leaves of the large-leaved variety AF37 and small-leaved variety AF45 decreased from 87.97% and 90.29% at grade 0 to 7.28% and 11.15% at grade 10, and the bunching onion has lost its commodity value when the drying grade was 5. The contents of chlorophyll a, chlorophyll b and total chlorophyll decreased rapidly with the increase of the drying grade, and the decrease was extremely significant before the drying grade was 5. The content of total protein decreased slowly with the deepening of the drying degree, from 0.44 and 0.60 mg·g-1 at grade 0 to 0.05 and 0.07 mg·g-1 at grade 10, respectively. The content of soluble sugar in fistular onion leaves decreased from 30.83 and 40.02 mg·g-1 at grade 0 to 2.86 and 3.81 mg·g-1 at grade 10, respectively. The content of vitamin C decreased significantly, from 1.73 and 1.14 mg·g-1 at grade 0 to 0.03 and 0.04 mg·g-1 at grade 10, respectively. Before grade 1, the content of vitamin C decreased significantly and then decreased gradually. The content of nitrate nitrogen also showed a decreasing trend with the drying of shallot. There was no significant difference in the reduction of nitrate nitrogen content in the large-leaved variety AF37 (P>0.01), while there was significant difference in the reduction of nitrate nitrogen content in the small-leaved variety AF45 (P<0.01). The correlation analysis results showed that the drying degree of green onion increased after harvest, accompanied by the process of water loss, chlorosis and degradation of the fistular onion leaves. There was a significant or extremely significant correlation between the dry grade and the main quality indexes of shallot, such as moisture content, chlorophyll, protein, soluble sugar, vitamin C and nitrate nitrogen content. So, its division has practical significance. During the storage process after harvest, the physical and chemical indexes of various qualities of shallot tended to decline or senescence with the process of water loss, chlorosis and degradation of the fistular onion leaves. In addition, there may be a critical point (at the drying grade 5) for quality degradation during the storage of shallot, and when the dry grade exceeded the critical level, the shallot began to accelerate senescence. Therefore, while considering the reduction of storage and transportation time, the emphasis should be placed on water retention, green preservation and the prevention of the degradation of storage reserves such as proteins and soluble sugars in the early stage of storage and transportation.

       

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