Chemical and physical pretreatments of fruits and vegetables: Effects on drying characteristics and quality attributes – a comprehensive review

Abstract

Pretreatment is widely used before drying of agro-products to inactivate enzymes, enhance drying process and improve quality of dried products. In current work, the influence of various pretreatments on drying characteristics and quality attributes of fruits and vegetables is summarized. They include chemical solution (hyperosmotic, alkali, sulfite and acid, etc.) and gas (sulfur dioxide, carbon dioxide and ozone) treatments, thermal blanching (hot water, steam, super heated steam impingement, ohmic and microwave heating, etc), and non-thermal process (ultrasound, freezing, pulsed electric field, and high hydrostatic pressure, etc). Chemical pretreatments effectively enhance drying kinetics, meanwhile, it causes soluble nutrients losing, trigger food safety issues by chemical residual. Conventional hot water blanching has significant effect on inactivating various undesirable enzymatic reactions, destroying microorganisms, and softening the texture, as well as facilitating drying rate. However, it induces undesirable quality of products, e.g., loss of texture, soluble nutrients, pigment and aroma. Novel blanching treatments, such as high-humidity hot air impingement blanching, microwave and ohmic heat blanching can reduce the nutrition loss and are more efficient. Non-thermal technologies can be a better alternative to thermal blanching to overcome these drawbacks, and more fundamental researches are needed for better design and scale up.

Effects of ultrasound, osmotic dehydration, and osmosonication pretreatments on bioactive compounds, chemical characterization, enzyme inactivation, color, and antioxidant activity of dried ginger slices

“…Lemos, Oliveira, and Saraiva () stated that osmosonication inactivation of POD occurs by dissociation and degradation of the active enzyme system. For example, agricultural products such as tomato, apple, dried lemon, and coconut water have been inactivated intensely by the combined action of ultrasound and osmotic dehydration as well as other treatment (masonication and thermosonication) (Abid et al, ; Deepika & Sutar, ; Deng et al, ).…”

Thermal kinetics of enzyme inactivation, color changes, and allicin degradation of garlic under blanching treatments

“…The main purpose of blanching is to inactivate quality‐changing enzymes responsible for deterioration reactions that contribute to undesirable color and off‐flavors. Other objectives of blanching are to reduce the microbial load of products to improve its conservation, to eliminate air in the intracellular space to prevent oxidation, to dissociate the wax on the tissues, to form superficial micro‐crack on the product, and to soften tissues for special texture (Deng et al, ; Wang et al, ; Xiao et al, ; Xiao, Bai, Sun, & Gao, ; Xiao, Law, Sun, & Gao, ). Hot water blanching is the most popular and commercially adopted blanching method.…”

Comparison of non-contact blanching and traditional blanching pretreatment in improving the product quality, bioactive compounds, and antioxidant capacity of vacuum-dehydrated apricot

“…Fante and Norena () found that SB showed a slower efficiency of PPO and POD inactivation than that by water blanching and could also reduce the quality of processed fruits. Moreover, other inevitable disadvantages of SB are its non‐uniform blanching and lower heat transfer, which increase its inefficiency (Deng et al, ; Gibert, Baxerres, & Kim, 1980; Mukherjee & Chattopadhyay, ; Xiao, Bai, Sun, & Gao, ). Consistent with this, in our study, every result with SB showed a greater standard error than that of the other groups.…”

“…Similar to bioactive compounds, we found that all blanching pretreatments could retain the antioxidant capacity, with NB being the most effective method. Some studies reported that blanching could mainly prevent the discoloration caused by oxidative and enzymatic browning during fruit processing without loss of antioxidants as the oxygen was expelled from the processing environment (Araújo et al, ; Deng et al, ; Volden et al, ). Except for FRAP, the antioxidant capacities measured by the other three assays between VD‐NB and VD‐SB were not significantly different.…”

“…Hence, there are some problems regularly encountered such as browning and loss of nutrients (Christian et al, ). In contrast, a combined blanching with dehydration treatment appears advantageous (Deng et al, ). The purpose and effect of blanching is to inactivate enzymes responsible for deterioration reactions, which contribute to off‐flavor, odor, and undesirable color and texture, and to preserve nutrients of dehydrated products (Bahc¸ Serpen, Gökmen, & Acar, ; Neves, Vieira, & Silva, ; Xiao et al, ).…”