High-humidity hot air impingement blanching (HHAIB) enhances drying behavior of red pepper via altering cellular structure, pectin profile and water state

Abstract

In order to exploring a feasible pretreatment technology of red pepper, an emerging thermal pretreatment technology namely high-humidity hot air impingement blanching (HHAIB) was employed and its effect on drying behavior and related mechanisms were explored through analyzing the ultrastructure, the contents and composition of cell wall pectins, water state of red pepper during the blanching process under blanching temperature of 110 °C and relative humidity of 35%–40% for various exposure times ranging from 0 to 150 s. Results indicated HHAIB can extensively reduce the drying time from 11 h for the un-blanched samples to 8 h for the samples blanched for 90 s. In addition, HHAIB reduced the products' hardness by 8.19%–47.91% compared to the untreated samples. The cellular structure and water state experienced a significant alternation with the increasing blanching time. The content of water-soluble pectin (WSP) increased, while the contents of chelate-soluble pectin (CSP) and sodium‑carbonate-soluble pectin (NSP) decreased during the blanching process. Overall, HHAIB treatment is a promising blanching technology for red pepper as it can accelerate the drying process through softening tissue and altering the ultrastructure and moisture binding state. Industrial practiceDrying is one of the most frequently used methods for red pepper preservation as it can effectively reduce the moisture content so as to hinder the growth and reproduction of microorganisms and the moisture-mediated deteriorative reactions. While the existence of waxy hydrophobic layer covered the surface of red pepper results in long drying time and poor products' quality. In industrial practice chemical dipping is often used to remove the wax layer and enhance the drying rate of red pepper. However, the chemical residues can trigger food safety issues and how to deal with the highly corrosive chemical dipping solution is also a challenge. Therefore, it is very tempting for industry to explore innovative pretreatment for red pepper drying. The current work indicated that HHAIB is a promising alternative technology to replace the chemical dipping method as it extensively enhances the drying process of red pepper.