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.
Highlights
Peppers (Capsicum annuum L.) are annuals or limited perennials belonging to the nightshade family [1] and are popular for their bright color and pungent taste
The objectives of the current study were to (1) explore the effect of humidity hot-air impingement blanching (HHAIB) on pulsed vacuum drying (PVD) kinetics and quality attributes, including red pigment content and color parameters of peppers; (2) investigate ultrastructural changes in peppers under different blanching conditions and elucidate the mechanisms underlying the changes in macroscopic properties; and (3) identify a suitable kinetic model for drying peppers, which is necessary for selecting suitable pretreatment and drying technology for red pepper drying
polyphenol oxidase (PPO) promotes biochemical reactions, and its activity is closely related to changes in product quality; PPO activity is often used as an indicator of the effects of blanching [53]
Summary
Peppers (Capsicum annuum L.) are annuals or limited perennials belonging to the nightshade family [1] and are popular for their bright color and pungent taste. Peppers naturally form a waxy layer on their skin during growth, which provides protection from external microbial infection and UV damage [3] This layer prevents moisture diffusion during the drying process, leading to difficulties in drying: prolonged drying time; increased energy consumption and biochemical reactions, oxidative degradation, and physical changes in the function of pepper enzymes; and serious quality deterioration [5]. The equipment for hot-water blanching requires low investment and is easy to operate This method involves processing at high temperatures for a long period and may result in considerable loss of heat-sensitive material. Hot-air drying, low cost and applicable to shortening the drying time, involves prolonged exposure to a high-temperature environment and causes oxidative degradation of heat-sensitive components, reducing the quality and active ingredient extraction rate of chili peppers [19]. The objectives of the current study were to (1) explore the effect of HHAIB on PVD kinetics and quality attributes, including red pigment content and color parameters of peppers; (2) investigate ultrastructural changes in peppers under different blanching conditions and elucidate the mechanisms underlying the changes in macroscopic properties; and (3) identify a suitable kinetic model for drying peppers, which is necessary for selecting suitable pretreatment and drying technology for red pepper drying
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