Vitalis Flora, Muncan Jelena, Anantawittayanon Sukritta, Kovacs Zoltan, Tsenkova Roumiana
Department of Measurements and Process Control, Institute of Food Science and Technology, Hungarian University of Agriculture and Life Sciences, Somlói Street 14-16, H-1118 Budapest, Hungary.
Aquaphotomics Research Department, Graduate School of Agricultural Science, Kobe University, 1-1, Rokkodai, Nada, Kobe 657-8501, Japan.
Foods. 2023 Jan 6;12(2):258. doi: 10.3390/foods12020258.
Fresh-cut leafy vegetables are one of the most perishable products because they readily deteriorate in quality even during cold storage and have a relatively short shelf life. Since these products are in high demand, methods for rigorous quality control and estimation of freshness that are rapid and non-destructive would be highly desirable. The objective of the present research was to develop a rapid, non-destructive near-infrared spectroscopy (NIRS)-based method for the evaluation of changes during cold storage of lettuce using an aquaphotomics approach to monitor the water molecular structure in lettuce leaves. The reference measurements showed that after 6 days of dark, cold storage, the weight and water activity of lettuce leaves decreased and β-carotene decreased, while chlorophylls slightly increased. Aquaphotomics characterization showed large differences in the lettuce leaves' spectra depending on their growth zone. Difference spectra, principal component analysis (PCA) and linear discriminant analysis (LDA) confirmed the differences in the inner and outer leaves and revealed that spectra change as a function of storage time. Partial least squares regression (PLSR) allowed the prediction of the time spent in storage with a coefficient of determination of R = 0.80 and standard error of RMSE = 0.77 days for inner, and R = 0.86 and RMSE = 0.66 days for outer leaves, respectively. The following water absorbance bands were found to provide the most information in the spectra: 1348, 1360, 1373, 1385, 1391, 1410, 1416, 1422, 1441, 1447, 1453, 1466, 1472, 1490, 1503, 1515, 1521, 1534 and 1571 nm. They were further used as water matrix coordinates (WAMACs) to define the water spectral patterns (WASPs) of lettuce leaves. The WASPs of leaves served to succinctly describe the state of lettuces during storage. The changes in WASPs during storage reveled moisture loss, damage to cell walls and expulsion of intracellular water, as well as loss of free and weakly hydrogen-bonded water, all leading to a loss of juiciness. The WASPs also showed that damage stimulated the defense mechanisms and production of vitamin C. The leaves at the end of the storage period were characterized by water strongly bound to collapsed structural elements of leaf tissues, mainly cellulose, leading to a loss of firmness that was more pronounced in the outer leaves. All of this information was reflected in the changes of absorbance in the identified WAMACs, showing that the water molecular structure of lettuce leaves accurately reflects the state of the lettuce during storage and that WASPs can be used as a multidimensional biomarker to monitor changes during storage.
鲜切叶菜类是最易腐坏的产品之一，因为即便在冷藏期间它们的品质也很容易变差，且货架期相对较短。由于这些产品需求量很大，因此非常需要能够快速且无损地进行严格质量控制和新鲜度评估的方法。本研究的目的是开发一种基于近红外光谱（NIRS）的快速无损方法，利用水相光组学方法监测生菜叶片中的水分子结构，以评估生菜在冷藏期间的变化。参考测量结果显示，经过6天的黑暗冷藏后，生菜叶片的重量、水分活度和β-胡萝卜素含量下降，而叶绿素含量略有增加。水相光组学表征显示，生菜叶片的光谱因其生长部位不同而有很大差异。差示光谱、主成分分析（PCA）和线性判别分析（LDA）证实了内叶和外叶的差异，并揭示光谱随储存时间而变化。偏最小二乘回归（PLSR）能够预测储存时间，内叶的决定系数R = 0.80，均方根误差RMSE = 0.77天；外叶的决定系数R = 0.86，RMSE = 0.66天。发现以下吸水带在光谱中提供的信息最多：1348、1360、1373、1385、1391、1410、1416、1422、1441、1447、1453、1466、1472、1490、1503、1515、1521、1534和1571纳米。它们进一步被用作水基质坐标（WAMACs）来定义生菜叶片的水光谱模式（WASPs）。叶片的WASPs有助于简洁地描述生菜在储存期间的状态。储存期间WASPs的变化揭示了水分流失、细胞壁损伤和细胞内水分排出，以及游离水和弱氢键水的损失，所有这些都会导致多汁性丧失。WASPs还表明损伤刺激了防御机制和维生素C的产生。储存期结束时的叶片其特征是水与叶片组织塌陷的结构成分（主要是纤维素）紧密结合，导致外叶的硬度损失更为明显。所有这些信息都反映在已识别的WAMACs中吸光度的变化上，表明生菜叶片的水分子结构准确反映了生菜在储存期间的状态，且WASPs可作为多维生物标志物来监测储存期间的变化。
