Effect of Pulsed Electric Field Pre-Treatment and the Freezing Methods on the Kinetics of the Freeze-Drying Process of Apple and Its Selected Physical Properties

Influence of pulsed electric field and glycerol pretreatments on freeze-thaw process and quality of white radish

This study focused on the effects of pulsed electric field (PEF) and glycerol (G) pretreatments on the quality of freeze-thawed white radishes. The optimal PEF strength, frequency, and treatment time were 800 V/cm, 5 Hz, and 0.1 s, respectively. The liquid-solid ratio of G impregnation pretreatment was 1:20 (w/w). The PEF, G, and PEF + G pretreatments accelerated the phase transition during the freeze-thaw process. Combination of PEF and G pretreatments decreased juice loss by 90.37 % and ascorbic acid loss by 59.3 % in thawed samples. Pretreatments also optimized the texture and color properties of the thawed samples. The low-field nuclear magnetic resonance results demonstrated that PEF pretreatment increased the water-holding capacity of the samples after thawing. The microstructure of the PEF + G-pretreated sample was the most homogeneous. These results revealed a potential method for preventing quality deterioration of freeze-thawed vegetables and fruits using PEF and G pretreatment.

Effect of cold plasma and ultrasonic pretreatment on drying characteristics and nutritional quality of vacuum freeze-dried kiwifruit crisps

The effect of ultrasound and plasma pretreatment on freeze-dried kiwifruit crisps was investigated in this study. Using unpretreated kiwifruit as a control group (CG), the effects of ultrasound (US), plasma-activated water (PAW), ultrasound combined with plasma-activated water (UPAW), plasma-jet (PJ), and ultrasound combined with plasma-jet (UPJ) on the quality of vacuum freeze-dried kiwifruit were investigated. The results showed that all the pretreatments could change the microstructure of the crisps. The microstructure of dried kiwifruit after pretreatment showed more porous structures with different number and size compared to the CG group. The largest pore structure was observed in the UPAW group which had the highest crispness. The activity of water (Aw) of all pretreatment samples was significantly lower than the CG group (P < 0.05). In addition, the UPAW group had the lowest moisture content (4.85 %) and the highest rehydration ratio (288.03 %), indicating the better drying characteristics. Furthermore, the UPAW pretreatment sample showed good appearance with the highest brightness and the lowest color difference (ΔE). The total sugars and total phenolics of the UPAW pretreatment sample were mostly retained, and its flavor was the closest to the CG group. The combination of US and PAW promoted the formation of a larger cavity structure and improved the drying characteristics and physicochemical properties of dried kiwifruit crips. However, all the pretreatments resulted in a decrease in antioxidant capacity, with the least decreasing of the US group and the most decreasing of the UPAW group. Correlation analysis showed that the chlorophyll and vitamin C were the major antioxidants in dried kiwifruit crips. The mechanism of decrease in antioxidant activity of pretreatment, especially UPAW, should be discussed and the effective measure to reduce the change in chlorophyll and vitamin C should be taken in future research.

Encapsulation of debittered pomelo juice using novel Moringa oleifera exudate for enrichment of yoghurt: A techno-functional approach

Debittering of pomelo juice was conducted using 3.7 g of activated resin, resulting in a 36.8% reduction in bitterness without affecting the bioactive properties of juice. The debittered juice was then encapsulated with Moringa oleifera exudate at various ratios (1-5%), yielding a powder with a slightly rough surface. Total phenol content (TPC) increased by 46-56% compared to the debittered juice. Functional yoghurt containing encapsulates at concentrations of 1% and 2% demonstrated that the 2% concentration led to longer storage duration, resulting in increased acidity and syneresis compared to the control. TPC of the yoghurt (161.89-198.22 μg Gallic acid equivalent (GAE)/g) remained significantly higher (p < 0.05) than that of the control (47.15 μg GAE/g) and acacia gum-based yoghurt (141.89-171.37 μg GAE/g), decreasing with storage duration. Addition of encapsulates significantly altered the yoghurt's texture, resulting in lower firmness (0.57 to 0.64 N) compared to the control, while adhesiveness values remained comparable (6.33 to 6.25 g.s). The highest values of G' and G" were observed in samples containing 2% encapsulates with moringa compared to those with acacia gum. This study suggests potential avenues for further exploration in functional foods with enhanced health benefits.

Novel Efficient Physical Technologies for Enhancing Freeze Drying of Fruits and Vegetables: A Review

Drying is the main technical means of fruit and vegetable processing and storage; freeze drying is one of the best dehydration processes for fruit and vegetables, and the quality of the final product obtained is the highest. The process is carried out under vacuum and at low temperatures, which inhibits enzymatic activity and the growth and multiplication of micro-organisms, and better preserves the nutrient content and flavor of the product. Despite its many advantages, freeze drying consumes approximately four to ten times more energy than hot-air drying, and is more costly, so freeze drying can be assisted by means of highly efficient physical fields. This paper reviews the definition, principles and steps of freeze drying, and introduces the application mechanisms of several efficient physical fields such as ultrasonic, microwave, infrared radiation and pulsed electric fields, as well as the application of efficient physical fields in the freeze drying of fruits and vegetables. The application of high efficiency physical fields with freeze drying can improve drying kinetics, increase drying rates and maintain maximum product quality, providing benefits in terms of energy, time and cost. Efficient physical field and freeze drying technologies can be well linked to sustainable deep processing of fruit and vegetables and have a wide range of development prospects.