Enzymatic impregnation by high hydrostatic pressure for preparing shape-retaining softened broccoli and carrot

Abstract

This study examined the feasibility of utilizing high-pressure processing (HPP) with enzymatic impregnation to soften vegetables. Freeze–thaw (FT) processing was used as a positive control to compare the hardness, physicochemical characteristics, and cell microstructure of vegetables. Carrot and broccoli samples were subjected to 200 MPa pressure for 15 min and then impregnated using a Viscozyme L enzyme solution. Compared with the hardness of fresh samples, the hardness of the carrot and broccoli samples that underwent HPP and enzymatic impregnation decreased by 84.6% and 95.5%, respectively, and the hardness of the carrot and broccoli samples that underwent FT processed decreased by 73.6% and 91.3%, respectively. In particular, HPP with enzymatic impregnation reduced the content of insoluble dietary fibers (18%), increased the content of soluble dietary fibers (3%), and considerably increased the concentration of carotene (1.9 times) and isothiocyanate (4.5 times) in carrots and broccoli, respectively. Scanning electron microscopy reveals that HPP physically damaged the intercellular compartments of the vegetables, thereby increasing the impregnation of enzymes. In addition, the level of HPP and the holding time increased, and the amount of vegetable residue and the degree of moisture retention substantially decreased, indicating a negative correlation between damage and hardness. Moreover, HPP pretreatment require a short processing time then FT, which promoted the penetration of enzymes and the internal microstructural biodegradation of vegetables, and it also helped these vegetables release more soluble nutrients. Overall, HPP can be used with enzymatic impregnation to obtain texture-modified vegetables for older consumers with mastication difficulties.