Pulsed Vacuum Drying of Pepper (Capsicum annuum L.): Effect of High-Humidity Hot Air Impingement Blanching Pretreatment on Drying Kinetics and Quality Attributes

Abstract

With a high moisture content, fresh peppers are perishable and rot easily. Drying is essential for shelf-life extension. The natural thin wax layer on the pepper surface hinders moisture transfer. Traditionally, chemical dipping or mechanical pricking is used to remove this wax layer. However, in chemical dipping, chemical residues can trigger food-safety issues, while the low efficiency of mechanical pricking hinders its industrial application. Feasible pretreatment methods are advantageous for industrial use. Here, an emerging pretreatment technique (high-humidity hot-air impingement blanching, HHAIB) was used for peppers before drying and its effects on drying characteristics, microstructure, and polyphenol oxidase (PPO) activity were explored. The impact of drying temperature on color parameters and red pigment content of pulsed-vacuum-dried peppers was also evaluated. PPO activity was reduced to less than 20% after blanching at 110 °C for 60 s. HHAIB reduced drying time and PPO activity and promoted chemical-substance release. Effective water diffusivity was highest (5.01 × 10−10 m2/s) after blanching at 110 °C for 90 s, and the brightness value and red pigment content were highest (9.94 g/kg) at 70 °C. HHAIB and pulsed vacuum drying are promising pretreatment and drying methods for enhancing the drying rate and quality of red peppers.

Prediction of Apple Slices Drying Kinetic during Infrared-Assisted-Hot Air Drying by Deep Neural Networks

“…However, the highest , , and values occur at 60 °C with v = 2 m/s and d = 14 cm, 70 °C with v = 3 m/s and d = 14 cm, and 60 °C with v = 1 m/s and d = 14 cm, respectively. This discrepancy in color may be explained by a combination of factors such as enzymatic browning, vitamin C oxidation, and Maillard reactions [ 46 , 47 ].…”

Hot-Air Flow Rolling Dry-Blanching Pretreatment Improves the Drying Quality of Acanthopanax sessiliflorus by Increasing the Drying Rate and Inactivating Enzymes

“…Particularly, hot water blanching is the most popular and widely used method in the food industry due to low cost and simple operation [ 10 ]. However, hot water blanching may cause a loss in soluble nutrients (vitamins and bioactive compounds) via dissolution into the water and may generate wastewater that pollutes the environment [ 11 ]. Steam blanching can effectively reduce the loss of nutrients but its efficiency is low due to low heat transfer efficiency and uneven heating [ 11 ].…”

“…However, hot water blanching may cause a loss in soluble nutrients (vitamins and bioactive compounds) via dissolution into the water and may generate wastewater that pollutes the environment [ 11 ]. Steam blanching can effectively reduce the loss of nutrients but its efficiency is low due to low heat transfer efficiency and uneven heating [ 11 ]. There is a need to develop an efficient blanching technology that increases quality and improves the processing efficiency of A. sessiliflorus .…”

Application of Two-Stage Variable Temperature Drying in Hot Air-Drying of Paddy Rice

“…A spectrophotometer (UltraScan VIS, HunterLab, Reston, VA, USA) was used to measure the color difference of the dried paddy rice. The L value (lightness), b value (yellow/blue), and a value (green/red) of the dried paddy rice were measured by using the spectrophotometer [ 17 , 18 ]. The dried samples were shelled into brown rice, which was then crushed and passed through a 100-mesh sieve to measure the color difference.…”