Green alternative methods for pretreatment of whole jujube before the drying process

Abstract

BACKGROUND: Jujube contains a waxy cuticle that acts as a barrier against fungal pathogens, prevents nutrition damage and leakage due to mechanical damage, and maintains water content. Chemical treatment before drying is the most commonly used method for whole jujube. Although chemical pretreatment can effectively enhance drying kinetics, it can lead to the loss of soluble nutrients and cause food safety issues due to chemical residues. Therefore, this study aimed to explore the effect of various pretreatments (cold plasma, cold plasma activated water, ultrasonics, thermosonication, and blanching) on the drying process and quality properties of whole jujube so as to find effective green alternatives to chemical pretreatment. RESULTS:The application of chemical, cold plasma, and thermosonication significantly altered the surface morphology of jujube by etching larger cracks and holes, which can facilitate the transfer of moisture, thereby improving the drying rate and the effective diffusivity. Chemical, cold plasma, and thermosonication pretreatment reduced drying time by 18%, 12%, and 7% respectively, thereby increasing the content of total phenolics by 13%, 12%, and 6% respectively, and enhancing antioxidant capacity (ferric reducing antioxidant power) by 13%, 11%, and 3% respectively. In addition, chemical and cold plasma pretreatment reduced the generation of 5-hydroxymethylfurfural by 25% and 15% respectively. CONCLUSION: Cold plasma is a promising green alternative method to chemical pretreatment for drying processes of whole jujube.

Effects of cold plasma, high hydrostatic pressure, ultrasound, and high-pressure carbon dioxide pretreatments on the quality characteristics of vacuum freeze-dried jujube slices

“…None of the pretreatments significantly ( p > 0.05) affected the FRAP and ABTS assays of freeze-dried jujube slices compared to the control ( Table 3 ). These results are in accordance with previous reports that the antioxidant activity of fresh and dried walnuts [ 83 ] and dried jujube [ 45 ] did not change significantly after CP, US, and BC pretreatment. In terms of DPPH scavenging capacity, the HHP, US, HPCD, and control samples revealed significantly ( p < 0.05) higher DPPH free radical scavenging capacities than the samples pretreated with CP and BC.…”

“…The increased porosity of US samples may be due to the inertial flow and sponge effect induced by ultrasonic cavitation, which triggers the formation of intercellular micropores [ 44 ]. These results are consistent with the microstructural changes in whole jujubes subjected to different pretreatments before hot air drying [ 45 ].

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Ultrasound‐assisted ascorbic acid solution pretreated hot‐air drying improves drying characteristics and quality of jujube slices

“…5‐Hydroxymethylfurfural is considered to be one of the specific indicators for monitoring the Maillard reaction, which is a food toxicant produced by the heating or drying of food products 28 . Our study found that content of HMF in dried jujubes slices varied with variation in the pretreatment.…”

“…These HMF results were associated with browning index data, whereas decreased production of HMF could be an outcome of the inhibition of enzymatic browning phenomena 39 . The UVC pretreatment group also exhibited reduced HMF content in comparison with VC pretreatment groups, which could be due to the ultrasound‐assisted shortened drying time and less heat exposure of the product 28 …”

“…The browning index of dried jujube slices was measured according to previously published work 28 with some modifications. Briefly, 1 g of powder from dried jujube slices was mixed with 20 mL distilled water for 2 h followed by centrifugation at 12 000× g for 10 min.…”