催化式红外漂烫胡萝卜表面成壳机理与色泽调控机制

Blanching is one of the essential operations in the production of fruits and vegetables. The formation of the crust on the surface of fruits and vegetables during the infrared (IR) blanching process is an important factor affecting the final product quality. In this project, the mechanism of carrot surface crust forming and the color controlling during catalytic infrared (CIR) blanching were investigated. Firstly, we hypothesized that the formed crust on the carrot surface was the results of the variations of pectin components in carrot cell wall during CIR blanching, and the uneven temperature and moisture distribution inside and outside of carrot slice induced by the weak penetrating ability of IR radiation. The modern detective methods were used to observe the microstructure of carrot cells, the specific pectin components, temperature as well as the moisture content of carrot slice. Afterwards, through the measurement of the formed crust thickness, changes in peroxidase structure, the content of β-carotene, and water distribution of carrot slice, etc., the change mechanism of carrot color was also studied. Additionally, the implementation of this project provides the theoretical supports for solving the crust forming issue on the surface of fruits and vegetables during IR-blanching and for controlling the final product quality.

漂烫是果蔬加工中的必要工序之一，红外漂烫过程中果蔬表面成壳问题是影响品质的重要因素。本项目对催化式红外漂烫胡萝卜过程中，导致表面致密成壳的机理和色泽调控机制进行研究。首先，从漂烫过程中胡萝卜细胞壁果胶成分的变化导致细胞纤维结构的坍塌、红外穿透力弱致使内外温度不均、以及水分分布不均匀等方面入手，利用现代检测手段，对细胞微观结构、果胶特定成分、温度和水分分布等逐步开展研究，从而揭示红外漂烫过程中胡萝卜表面成壳的机制。其次，通过胡萝卜色泽变化来优化调控产品表面成壳和品质的角度，将胡萝卜色泽变化与表面成壳厚度、过氧化物酶分子结构、β胡萝卜素含量、以及水分分布的变化进行关联，揭示胡萝卜色泽变化机制。项目的研究结果可以为解决红外漂烫过程中果蔬表面成壳问题和品质调控提供理论支撑。

催化式红外技术应用于果蔬烫漂时能够很好地钝化过氧化物酶，同时脱除部分水分，并能够得到高质量的产品。研究发现，经过催化式红外烫漂或其他干法烫漂及干燥得到的产品，表面组织塌陷严重，并形成一层外壳，这层外壳的存在影响了内部水分的扩散，降低产品品质。目前对成壳机制的研究鲜有报道。本项目以胡萝卜为研究对象，通过对催化式红外烫漂过程中胡萝卜的显微结构、硬度、电阻抗特性、水分状态和细胞壁组分等的研究，揭示了烫漂时胡萝卜的成壳机制。结果表明，烫漂后胡萝卜片内部软化，表面组织因细胞坍塌而结壳，结壳的硬度随烫漂时间的增加而逐渐变大。催化式红外烫漂使胡萝卜片表层细胞皱缩变形，由外表面向内部细胞形变程度越来越小；随着加热时间的增加，组织的坍塌程度和范围也明显增加。红外处理使胡萝卜细胞的完整性和通透性遭到破坏，细胞外液电阻和细胞膜电容显著降低，电解质溢出增多。水分分布结果显示，水分的散失以自由水为主，烫漂后半结水的相对含量显著增加。对细胞壁成分进行研究，发现红外处理除了使半纤维素更易溶出外，对果胶的影响更大。红外处理后果胶的分子量增加，多分散系数减小，说明果胶的分子量变得集中，长链果胶的交联增加。碱溶性果胶向水溶性果胶和螯合性果胶转化，这三种果胶组分的支链程度都有所增加。水溶性果胶的增加使内部硬度随烫漂时间增加而逐渐减小；在成壳部分中，对质构形成和保持起重要作用的碱溶性果胶和螯合性果胶的相对含量高于其在非壳部分的相对含量，使壳的硬度随烫漂过程的进行而逐渐增大。综合以上结果，胡萝卜微观结构的变化是细胞形态、细胞膜和细胞壁变化的综合体现。催化式红外烫漂过程中胡萝卜成壳机制的初步明确，为红外烫漂过程中果蔬品质的调控提供理论基础，以期提高果蔬加工的效率与产品品质。