Texture and Key Components of Frozen Cabbage Leaves as Affected by Maturity Type

The objectives of this study were to (i) evaluate the impact of maturity types on the texture and microstructure of frozen cabbage leaves and (ii) elucidate the relationships between variables (alcohol-insoluble solid (AIS), pectin, insoluble dietary fiber (IDF), total soluble solid (TSS), and pH) and the firmness of frozen cabbage leaves. Fourteen cabbage cultivars of four maturity types grown in three regions of Japan for 3 years were used as samples. Higher firmness and less drip loss in frozen cabbage leaves were obtained in the late maturing cultivars, followed by the medium-late, medium, and early maturing cultivars. Scanning electron microscopy showed severe cell wall damage in frozen leaves of the early maturing cabbage, while well-defined individual cells could be observed in the late maturing cabbage. Positive linear correlations between the firmness of frozen cabbage leaves and the amount of cell wall components (AIS (R2 = 0.818), pectin (R2 = 0.670), IDF (R2 = 0.841)) and the concentration of solutes (TSS (R2 = 0.799)) were detected. On the other hand, there was no relationship between pH values and the firmness of frozen cabbage leaves (R2 < 0.1). Thus, we proposed the combination of two phenomena (i.e., greater cell wall rigidity and smaller ice crystals due to the higher solute concentration) regulating the firmness of frozen cabbage leaves. These results highlight the importance of cultivar selection, especially with respect to maturity type, for the manufacture of frozen cut cabbage.