An improved vacuum-steam pulsed blanching machine design and garlic scape blanching verified experiment

Vacuum-steam pulsed blanching (VSPB) is an emerging blanching method resulting in high efficiency and product quality. However, inconvenient loading, small loading capacity, uneven rinsing and imprecise control hinder its application in food industry. Therefore, the current work aimed to design a VSPB machine, including selection of components, building a control system and designing a steam nozzle in order to increase the load capacity and improve device control. For this purpose, a horizontal blanching chamber with internal nozzle was designed and optimized using CFD method. The vacuum chamber design required a more evenly distributed steam inlet. A water-sealing vacuum pump, a cooling device and a hardware system were developed. The distribution of steam released from the nozzle in the chamber was numerically investigated by solving the three-dimensional Reynolds-averaged Navier-Stokes equations, with a velocity uniformity index value of 0.448. The validation blanching test was conducted using garlic scape as the test material. The steam holding time and the number of cycles significantly affected (p < 0.05) the color of the garlic scapes. Peroxidase (POD) activity decreased with the increase of blanching cycles until the enzymes were completely inactivated. VSPB significantly decreased (p < 0.05) the lignin content of the garlic scapes. The findings indicate that the best results were obtained after 2 cycles of VSPB and steam holding time of 30 s.

Industrial relevance

Hot water and steam thermal blanching are the two most frequently used blanching methods in food processing. Generally, they are used as a pretreatment before drying, freezing or canning of different fruits and vegetables. In current work, an improved vacuum-steam pulsed blanching machine was designed and the validation blanching test with garlic scape as the material indicated that VSPB operation was effective in preventing the synthesis of lignification in garlic scapes. By considering enzyme inactivation, lignification, color, and other quality attributes, 2 cycles of VSPB and steam holding for 30 s were proposed as the optimal VSPB conditions.