高静压加工延缓绿芦笋木质化进程的作用机制研究

The texture degradation of vegetable shoot during processing and storage are a problem hard to be solved. For a long time, a lot of researches have been launched in order to solve this problem. High hydrostatic pressure (HHP) is one of the minimal processing technologies, which was also used for delaying the texture degradation of vegetable shoot. Some results showed that HHP treatment were benefit to the texture of vegetable shoot because that high pressure led to the death of plant cell and the stop of the lignification, however, those studies ignoring the fact that the vegetable was still alive during a certain period after HHP treatment. Although the physiological and biochemical metabolism of vegetable might be disordered due to the pressure treatment, the biochemical reaction was quite active in vivo. Based on those facts, the effects of HHP on the respiration intensity, chlorophyll fluorescence parameter of green asparagus (Asparagus officinalis L.) shoot, as well as the influence on the structure and function of related subcellular organelle such as membrane, Golgi apparatus, endoplasmic reticulum (ER) will be investigated. The changes of metabolic substances, including the endogenesis enzymes activity, lignin and its precursor substances will also be studied. The objects of this items is to explore the change law of lignin metabolic of green asparagus after HHP treatment, elucidate the mechanism of HHP on delaying lignification of green asparagus, and provide more scientific data for vegetable shoot processing by HHP.

木质化引起的质构劣变是嫩茎蔬菜贮藏中一直难以解决的问题。长期以来，众多学者针对这一难题展开了大量的研究，以期对其控制。高静压技术（HHP）是一种新兴的食品最少加工技术，也被研究用于控制该类蔬菜的质构劣变。研究表明，HHP技术能较好的保持嫩茎蔬菜的质构特性，该现象被认为是由于"HHP加工导致植物细胞死亡，木质素合成因此停止"，却忽略了HHP处理后植物在一段时间内仍是"活的有机体"，虽然其正常生理代谢可能紊乱，但胞内的生化反应却仍非常活跃。基于此，本项目以绿芦笋为材料，通过系统研究HHP处理对呼吸强度、叶绿素荧光参数等生理功能活性，对细胞膜、内囊体、高尔基体等亚细胞结构和功能的影响，以及深入探讨HHP处理对相关代谢基础物质包括内源酶、木质素及各阶段中间物质的影响，阐明HHP处理后绿芦笋木质素代谢的变化规律，揭示HHP延缓绿芦笋木质化进程的可能机制，为HHP技术应用于嫩茎蔬菜的加工提供理论依据。

本项目以绿芦笋为对象，系统研究了不同压力（10-600MPa）和不同保压时间（0.17-20min）高静压处理对绿芦笋呼吸速率的影响，在此基础上选取了7组代表性压力（10、20、50、100、200、400和600MPa）进一步探讨绿芦笋微观结构变化、细胞膜结构完整性、丙二醛含量及细胞膜渗透率的影响。确定了200MPa高静压处理可能是绿芦笋细胞死亡的一个临界压力，该压力以上处理的绿芦笋细胞均受到严重物理损伤甚至死亡，而100MPa以下高静压处理对绿芦笋细胞的破坏较小；研究了经20MPa、50MPa和100MPa处理的绿芦笋在4℃条件贮藏期间的生理活性，重点考察了贮藏期间定期测定绿芦笋的呼吸强度、丙二醛（MDA）含量、细胞膜渗透率、叶绿素含量、嫩茎硬度、总酚含量和失重率以及色泽的变化。明确了高静压处理可以有效降低贮藏期间绿芦笋呼吸强度，较好保持了绿芦笋的硬度和色泽；研究了高静压处理（20-100 MPa）对绿芦笋贮藏期间木质素含量、木质素代谢相关内源酶活性以及酚酸物质含量的影响。结果表明，与对照组相比，50MPa处理2min有效抑制了绿芦笋贮藏期间木质素含量的增加，降低了PPO酶的活性。50MPa处理有效抑制了咖啡酸和芥子酸含量的上升。综合分析，高静压导致的细胞壁、细胞膜等物理性损伤进而引发的生理代谢紊乱，以及高静压直接导致的木质素代谢有关酶活性的变化可能是高静压延缓木质素代谢的主要原因。本研究可为高静压保持果蔬质构品质的作用机制提供理论参考，推动高静压技术在果蔬贮藏和加工中的应用。