Evaluation of high pressure pretreatment for enhancing the drying rates of carrot, apple, and green bean

Combined application of high pressure and ultrasound in fig paste: effect on bioactive and volatile compounds

The combined impact of high-hydrostatic pressure (HHP) and ultrasound (US) on the cyanidin-3-O-rutinoside (C3R), quercetin-3-O-rutinoside (Q3R), and volatile compounds from fig (Ficus carica) paste was investigated. The HHP increased the content of C3R and Q3R, from 70 to 133 mg/kg fw and 31 to 44 mg/kg fw, respectively. The combination of HHP and US further enhanced the extraction of these bioactive compounds. Specifically, processing fig paste with US for 5 min at 40 °C yielded approximately 250 mg of C3R/kg fw and 45 mg of Q3R/kg fw, after 20 min. More than 25 volatile compounds were identified, with benzaldehyde being the predominant compound, accounting > 75%. Trace amounts of hydroxymethylfurfural (< 0.36 mg/100 g fw) were detected in HHP-processed fig paste. The application of HHP at mild temperatures and short time, combined with US, effectively promotes the content of bioactive compounds present in fig paste without adversely affecting the fruit's volatile compounds.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01410-1.

Application of novel pretreatment technologies for intensification of drying performance and quality attributes of food commodities: a review

Drying is an energy-intensive process that can be reduced by the application of pretreatment prior to drying to enhance mass transfer and minimize energy consumption. This review summarizes the mechanistic aspects and applications of emerging pretreatment approaches, namely ohmic heating (OH), ultrasound (US), high pressure processing (HPP), and pulsed electric field (PEF), with emphasis on the enhancement of mass transfer and quality attributes of foods. Novel pretreatments significantly improved the drying efficiency by increasing mass transfer, cavitation, and microchannel formation within the cell structure. Various processing parameters have great influence on the drying performance and quality attributes of foods. Several studies have shown that novel pretreatments (individual and combined) can significantly save energy while improving the overall drying performance and retaining the quality attributes. This work would be useful for understanding the mechanisms of novel pretreatment technologies and their applications for future commercial research and development activities.

Advances in drying techniques for retention of antioxidants in agro produces

Antioxidants are compounds that are essential for the human body which prevents cell from disease causing free radicals. Antioxidants are present in a wide range of fruits, vegetables, and spices. However, a considerable amount of antioxidants is lost during the post-harvest drying operation of agro produces for their shelf-life enhancement. Hence, retention of antioxidants becomes utmost importance in preserving the nutritional aspects of fruits and vegetables. Compared to conventional hot air drying, methods like freeze drying, vacuum drying, and dehumidified drying helps in the retention of antioxidants. However, the drawbacks prevalent in current drying practices, such as high-power consumption and high capital cost, could be eliminated by adopting novel drying mechanisms. This review focuses on various pretreatment methods like ultra-sonication, high pressure processing, pulsed electric field and ethanol treatment prior to drying operation helps in enhancing the drying efficiency with maximum retention of antioxidants. In addition, hybrid drying technologies such as microwave assisted drying, IR-radiated drying and electro-magnetic assisted drying methods also could significantly improve the retention of antioxidants.HIGHLIGHTSDrying is the most commonly adopted unit operation for enhancing the shelf life of perishable agro produces.However, drying is accompanied by loss of bioactive, color, texture, and sensory attributes.Compared to conventional drying techniques like hot air drying, methods like freeze drying, vacuum drying and dehumidified drying helps in the retention of antioxidants present in agro/food produces.Pretreatment methods like Ozonation, ultra-sonication, and UV radiation prior to drying are also found to improve the drying performance with good retention of antioxidants.Recent developments like microwave-assisted and IR-assisted drying methods perform well in the retention of antioxidants with less energy consumption.

Aqueous Extraction of Curcuminoids from Curcuma longa: Effect of Cell Disintegration Pre-treatment and Extraction Condition

Cell structure modification techniques have the potential to improve curcuminoid recovery in Curcuma longa. In this study, different pre-treatments such as high hydrostatic pressure (HPP, high pressure processing), ultrasound (US), pulsed electric field (PEF), and ohmic heating (OH) were used on dried C. longa before aqueous extraction at pH 2.0, 5.0, and 8.0. The released curcuminoids, cell disintegration index (Zp), particle size distribution (PSD), and color (CIE L*, a*, b*) were used to evaluate the different pre-treatment impacts on plant structure and extract properties. In untreated turmeric, the highest amount of released curcuminoids (3.89 mg/g dry matter) was obtained after extraction for 30 min at 95° in the aqueous phase. After pre-treatments, the acidic conditions showed a considerable improvement in curcuminoid recovery; PEF, HPP, and OH improved the curcuminoid recovery by 3.39-, 3.13-, and 1.24-fold, respectively; while US did not lead to an increased release of curcuminoids compared to the untreated material. The highest curcuminoid recovery (with PEF and extraction at pH 5.0) was 6.6% w/w of the total curcuminoids. The non-thermal pre-treatments have less impact on the extract’s color compared to the extraction pH, with alkaline conditions reducing the lightness of the extract.

Effect of Osmotic Pretreatment Combined with Vacuum Impregnation or High Pressure on the Water Diffusion Coefficients of Convection Drying: Case Study on Apples

The paper presents water diffusion coefficients as providing a significant contribution to the creation of a comprehensive database and knowledge of weight variation during the drying process of raw plant materials that is used for modelling the technological process and designing innovative products. Dehydration is one of the most widely used methods for improving the stability and durability of fruit and vegetables because it reduces water activity and microbial activity, and minimises the physical and chemical changes during storage. The considerable impact of pressure on heat exchange and weight during the convection drying process of osmotically pretreated apples is demonstrated. The course of the drying curves and the drying rate is determined by the use of pressures of 0.02 and 500 MPa. Varied pressure applied during osmotic impregnation significantly influences the value of the diffusion coefficient: the average determined for the entire course of the drying curve and the average determined in the intervals of the reduced water content. The lowest values of the average water diffusion coefficient are obtained for apples preboiled under overpressure conditions and, at the same time, the determined diffusion coefficients in the water content are characterised on the drying curve by a clearly decreasing course until the reduced water content reaches approximately 0.2.

Selected Quality Parameters of Air-Dried Apples Pretreated by High Pressure, Ultrasounds and Pulsed Electric Field-A Comparison Study

The aim of this work was to compare selected physicochemical properties of air dried ‘Golden Delicious’ apples, pretreated either by high-pressure processing (HPP), ultrasound (US) or pulsed electric field (PEF). Following parameters of pretreatment were used: HPP–400 MPa for 15 min, US–21 kHz, 180 W for 45 min, PEF–1 kV/cm, 3.5 kJ/kg. The quality of materials was evaluated by their rehydration properties, hygroscopicity, color and total phenolic content. To compare the effectiveness of the utilized methods, determined properties were expressed as relative comparison values against the reference sample obtained without any pretreatment in the same conditions. The performed research demonstrated that properties can be shaped by the application of proper pretreatment methods. For instance, PEF was shown to be the best method for improving water uptake during rehydration, whereas HPP was the most effective in decreasing hygroscopic properties in comparison with untreated dried apples. Among the investigated methods, HPP resulted in the deepest browning and thus total color difference, while the effects of US and PEF were comparable. For all pretreated dried apples, the total phenolic content was lower when compared with reference material, though the smallest drop was found in sonicated samples.

Effect of Selected Drying Methods and Emerging Drying Intensification Technologies on the Quality of Dried Fruit: A Review

Drying is one of the oldest methods for food preservation that removes the water from fruit and makes it available for consumption throughout the year. Dried fruits can be produced by small- and large-scale processors, which makes them a very popular food among consumers and food manufacturers. The most frequent uses of drying technology include osmotic dehydration, vacuum drying, freeze-drying and different combinations of other drying technologies. However, drying may provoke undesirable changes with respect to physiochemical, sensory, nutritional and microbiological quality. Drying process energy efficiency and the quality of dried fruits are crucial factors in fruit drying. Recently, innovative technologies such as ultrasound, pulsed electric field and high pressure may be used as a pretreatment or in combination with traditional drying technologies for process intensification. This could result in quality improvements of dried fruits and enhanced efficiency and capacity of the production process, with a positive impact on environmental and economic benefits.

Influence of high hydrostatic pressure pretreatment on properties of vacuum-freeze dried strawberry slices

Effects of high hydrostatic pressure (HHP) (50, 100, 150, 200 and 250 MPa) pretreatment on water mobility and distribution, drying duration, microstructure, color, cell wall fraction and tissue structure of strawberry slices were investigated. HHP significantly increased water mobility of the strawberry slices, resulting in the reduction of drying duration by 9-24%. As the pretreatment pressure was increased, redness value and anthocyanin content continuously increased, soluble pectin (SBP) content increased and then decreased, while the contents of protopectin (PTP) and cellulose decreased. After the HHP pretreatment, chromoplasts and moisture was distributed more uniformly in the strawberry slices. Microscopy images showed the formation of microscopic holes or channels in the matrix and the breakdown of tissue structure by HHP. Results suggested HHP pretreatment disrupted the integrity of the fresh strawberry which enhanced the drying efficiency and migration of the chromoplasts during the vacuum-freeze drying process.

Unconventional Methods of Preserving Meat Products and Their Impact on Health and the Environment

A dual objective of food storage is to retain nutritional value and safe consumption over time. As supply chains have globalized, food protection and preservation methods have advanced. However, increasing demands to cater for larger volumes and for more effective food storage call for new technologies. This paper examines promising meat preservation methods, including high pressure process, ultrasounds, pulsating electric and magnetic field, pulsed light and cold plasma. These methods not only make it possible to obtain meat and meat products with a longer shelf life, safer for health and without preservatives, but also are more environment-friendly in comparison with traditional methods. With the use of alternative methods, it is possible to obtain meat products that are microbiologically safer, whilst also high quality and free from chemical additives. Moreover, these new technologies are also more ecological, do not require large quantities of energy or water, and generate less waste.

The drying process of Sarcocornia perennis: impact on nutritional and physico-chemical properties

The Sarcocornia genus is an extreme salt-tolerant plant that can be cultivated in saline habitats almost worldwide. To preserve Sarcocornia perennis, convective drying experiments were conducted and their effects on the physico-chemical properties and phenolic content of the plant were studied using conventional and vibrational spectroscopy techniques. The drying process of Sarcocornia perennis at temperatures of 40 °C, 50 °C, 60 °C and 70 °C revealed three periods of convective drying process with drying times ranging between 4.5 and 24.9 h, respectively to higher and lower temperatures. The heating-up period can be neglected as compared with the drying process, and the duration of constant rate period, as a percentage of the total drying time, ranged between 34 and 20% respectively at 40 °C and 70 °C. The Modified Page model was proposed to describe the drying process at the different temperatures. From a nutritional point of view, this halophyte plant may be considered as a good source of fibres, phenolic compounds and natural minerals, such as sodium, potassium, calcium and magnesium. The convective drying, in the temperature range currently used, was found to preserve the colour, nutritional characteristics and phytochemical value of Sarcocornia perennis. These results were confirmed by FTIR-ATR and highlight the potential use of the dried plant in novel food products.

High pressure-assisted vacuum-freeze drying: A novel, efficient way to accelerate moisture migration in shrimp processing

High pressure processing (HPP), as nonthermal processing technology, has the potential to increase the drying rate due to its improvement of heat and mass exchange in different processes. In this study, the moisture migration in shrimps during HPP-vacuum-freeze drying (HPP-VFD) processes has been monitored by using low-field nuclear magnetic resonance and magnetic resonance image (MRI) in comparison with hot air-drying and VFD. Based on the T₂ relaxation spectra, three water fractions corresponding to bound water (hydrogen-bonded water), immobile water (water trapped by organization structure or cell member), and free water were observed. For group B, with increasing drying time (4 to 22 hr), the transverse relaxation times of T₂₁ , T₂₂ , and T₂₃ were significantly decreased (76.79%, 57.78%, and 40.9%) (P < 0.05). The content of immobile water (A₂₂ ) and free water (A₂₃ ) decreased (81.55% and 89.07%), whereas the bound water (A₂₁ ) increased (7.26%). In comparison with group B, the T₂₁ , T₂₂ , and T₂₃ of group C showed greater decrease (83.12%, 87.12%, and 89.57% for group C) so that HPP pretreatment could shorten the relaxation time. MRI analysis further proved that HPP-VFD drying has improved drying efficiency, and moisture migration was from the exterior to the interior part with increasing drying time. SEM analysis demonstrated that no significant damage of muscle fibers with narrower gaps was observed for groups B and C. Overall, HPP, as a pretreatment technology, could accelerate the moisture migration and improve the drying efficiency of VFD process for shrimp. PRACTICAL APPLICATION: High pressure processing (HPP) is now well known as a nonthermal processing technology and becoming increasingly acknowledged. However, there is limited information about its application in shrimp-drying process and the moisture dynamic of shrimp subjected to high pressure processing-assisted vacuum-freeze drying. This study could provide valuable information regarding the moisture status and migration in HPP-VFD shrimp monitored by LF-NMR and MRI methods. The results showed that HPP processing at 550 MPa for 10 min can be used as an interesting method for drying pretreatment, increasing its drying rate and consequently reducing its process time, and it demonstrated that the methods used in this study had good correlation coefficient with physicochemical properties of shrimp, which may be real-time and nondestructive monitoring methods for shrimp-drying process.

Application of non-thermal pretreatment techniques on agricultural products prior to drying: a review

BACKGROUND

Most agricultural crops contain high moisture content (80-95% wet basis (wb)) which makes them very susceptible to microbial damage leading to shorter shelf-life and high postharvest losses. The high perishability of these agricultural products requires preservation techniques to prolong their shelf-lives. Drying remains an important component of processing in this regard. Therefore, any pretreatment methods for drying agricultural product that decreases the moisture content and minimizes drying time by conserving the quality of the crop product is of prime significance. This article is a comprehensive review of recent developments of non-thermal pretreatment (NTP) methods. A summary of their significance, emerging and innovative methods of this technology together with its applications and limitations are discussed. This article further examines the environmental impact of NTP techniques.

RESULTS

NTP techniques, such as high pressure, ultrasound, pulsed electric field and osmotic dehydration methods are essential operations for pre-dehydration of agricultural products prior to drying. These techniques can avoid the deleterious effects of heat on nutritive value, colour and flavour of agricultural products compared to thermal pretreatments. They also enhance the inactivation of the enzymes, improve energy efficiency and mass transfer, reduce processing time, preserve bioactive compounds, improve drying kinetics and drying rate, minimize enzymatic browning, and enhance product quality.

CONCLUSION

These findings will provide a better understanding of different NTP methods and also make available more information for selecting pretreatment techniques for drying of agricultural products. © 2020 Society of Chemical Industry.

Effects of ultrahigh pressure and ultrasound pretreatments on properties of strawberry chips prepared by vacuum-freeze drying

The present work investigated the influences of ultrahigh pressure (UHP), ultrasound (US) and their combination (UHP-US) as pretreatments on properties of vacuum-freeze dried strawberry slices. During vacuum-freeze drying, drying duration and total energy consumption of UHP sample, US sample and UHP-US sample was decreased. After the UHP or US pretreatments, a* value (redness), antioxidative substances (total anthocyanin content, total flavonoid content, total phenolic content, diphenyl picrylhydrazyl (DPPH), hydroxyl (-OH) radical-scavenging assay), hardness and cross-section areas of matrix in the dried slices were significantly (P < 0.05) increased. Transverse relaxation times and peak area corresponding to free water in the pretreated samples were obviously decreased, indicating lower mobility in the pretreated samples. As compared with UHP or US individually, UHP in combination with US increased those parameters more pronouncedly. Therefore, UHP and US are promising techniques for the vacuum-freeze drying processing of strawberry products.

Comparison of pulsed vacuum and ultrasound osmotic dehydration on drying of Chinese ginger (Zingiber officinale Roscoe): Drying characteristics, antioxidant capacity, and volatile profiles

The effects of pulsed vacuum osmotic dehydration (PVOD) and ultrasound osmotic dehydration (USOD) on drying characteristics and quality attributes of ginger were investigated. PVOD was subjected to pulsed vacuum at 13 kPa for 30 min, and USOD was subjected to ultrasound with the frequency of 40 kHz for 30 min. After PVOD and USOD treatments, the samples were then dried at intermittent microwave & air-drying oven with an output of 700 W and temperature of 60°C to the final moisture content of 0.12 g water/g d.w. The results showed PVOD and USOD treatments could improve the total phenolic contents by -1.8% to 16.4%, total flavonoid content by 7.7%-18.7%, DPPH radical scavenging by 9.5%-12.2%, and ABTS+ antioxidant activity by 17.8%-27.4%, although they prolonged the later stages drying of ginger. Besides, the PVOD- and USOD-pretreated dried samples had less brownings than the untreated-dried samples which could be attributed to the inactivation of polyphenol oxidase (PPO) and peroxidase (POD). The PPO activity was significantly reduced in the PVOD and USOD ginger, whereas POD activity was decreased in USOD ginger but increased in PVOD ginger. Moreover, PVOD pretreatment also led to a better preservation of volatile profiles and cell structure than USOD treatment. Therefore, both PVOD and USOD are effective pretreatments for drying of ginger.

Effects of High Hydrostatic Pressure on Water Absorption of Adzuki Beans

The effect of high hydrostatic pressure (HHP) treatment on dried soybean, adzuki bean, and kintoki kidney bean, which are low-moisture-content cellular biological materials, was investigated from the viewpoint of water absorption. The samples were vacuum-packed with distilled water and pressurized at 200 MPa and 25 °C for 10 min. After the HHP treatment, time courses of the moisture contents of the samples were measured, and the dimensionless moisture contents were estimated. Water absorption in the case of soybean could be fitted well by a simple water diffusion model. High pressures were found to have negligible effects on water absorption into the cotyledon of soybean and kintoki kidney bean. A non-linear least square method based on the Weibull equation was applied for the adzuki beans, and the effective water diffusion coefficient was found to increase significantly from 8.6 × 10^-13 to 6.7 × 10^-10 m²/s after HHP treatment. Approximately 30% of the testa of the adzuki bean was damaged upon HHP treatment, which was comparable to the surface area of the testa in the partially peeled adzuki bean sample. Thus, HHP was confirmed to promote mass transfer to the cotyledon of legumes with a tight testa.

Influence of drying by convective air dryer or power ultrasound on the vitamin C and β-carotene content of carrots

Convective air drying and power ultrasound effects on vitamin C and β-carotene contents in carrots were studied. For convective air drying, a central composite face-centered design fitting temperature between 40 and 65 °C and air flow rate between 2 and 6 × 10(-1) m/s were used; previously, carrots were blanched. Likewise, ultrasound drying was performed on both unblanched and blanched carrots at 20, 40, and 60 °C for 120, 90, and 75 min, respectively. Blanching had a sharp effect on vitamin C and β-carotene degradation (80-92% retentions, respectively), and convective air drying led to further losses (32-50% and 73-90% retentions, respectively). According to the response surface model, a combination of 40 °C and 6 × 10(-1) m/s will maximize vitamin C retention in dried carrots, whereas 40 °C and 3.3 × 10(-1) m/s will ensure the highest β-carotene content. Ultrasound drying caused higher vitamin C and β-carotene retention (82-92% and 96-98%, respectively) than convective air drying. Blanched carrots dehydrated by ultrasound showed retentions of 55% and 88% of vitamin C and β-carotene, respectively. Ultrasound drying at 20 °C for 120 min caused the maximum vitamin C and β-carotene contents. Therefore, power ultrasound may be considered a valuable tool to obtain high nutritive dehydrated carrots.