Investigation of the effects of mechanical treatments on cellular structure integrity and vitamin C extractability of broccoli (Brassica oleracea L. var. italica) by LF-NMR.

Extraction of nutrients from plants is an important unit operation in the food and biological industries. The target nutrient is usually spatially distributed throughout the plant tissue. The intact cell wall and adhering membranes are the main resistances to molecular diffusion. Therefore, disintegration of the intact structure, which in turn increases the permeability of adhering membranes, can significantly improve the nutrient extraction yield and efficiency. In this study, different physical treatments (homogenization, high pressure homogenization, and ball mill grinding) were applied to investigate their effects on the tissue microstructure and the release of vitamin C. The changes in the microstructure were reflected by LF-NMR based on T2 distribution, particle size distribution, and microscopy images. The extraction yield of vitamin C obtained by high-pressure homogenization was increased by 75.69% for floret and 28.84% for stalk, respectively, as compared to that obtained by mechanical homogenization. The degradation of vitamin C was significant due to prolonged operation of the ball mill grinding method although the integrity of the tissues was similar to that of the high-pressure homogenization-treated tissues. This study confirms that the degree of tissue disintegration has a positive correlation with the release of the nutrient (vitamin C) within a limited operating time. LF-NMR has been proven to be an effective method to study the impact of different physical treatments on the cellular structure integrity of plant-originated food materials.