Evaluation of drying technologies for retention of physical quality and antioxidants in asparagus (Asparagus officinalis, L.)

Effect of cyclic vacuum-steam blanching on the quality characteristics and functional properties of Malabar spinach (Basella alba) dried by non-water infrared refractance window drying

In the present work, an effluent-free novel method including cyclic vacuum steam pulsed blanching (VSPB) pretreatment and non-water infrared refractance window drying (non-water IR-RWD) was employed to explore its effect on enzyme inactivation, drying behavior, quality and functional properties of dried Malabar spinach. The highest inactivation of peroxidase (90.23 %) and polyphenol oxidase (94.58 %) was observed in the 4th cycle of the VSPB pretreatment. With the increase in VSPB cycles from 1 to 5, the drying time was significantly reduced by 27.27 % to 54.54 % compared to the untreated sample. The color change values (ΔE) of VSPB pretreated non-water IR-RWD samples varied from 7.37 to 8.03. The findings in the current work indicated that vacuum-steam pulsed blanching combined with a non-water IR-RWD process is a promising technique for Malabar spinach powder production.

Optimization of process parameters of refractance window drying for aonla slices and comparison with other drying techniques

BACKROUND

Aonla is as a good source of antioxidants due to its high ascorbic acid and polyphenol contents. However, because of its high acidity and astringent taste, aonla is rarely consumed in its fresh form. As the constituents in aonla are heat sensitive, it is essential to find a suitable drying method for preservation. Therefore, refractance window drying (RWD) of aonla slices was studied as it has the potential of retaining heat-sensitive compounds.

RESULTS

The effect of RWD process variables, namely water temperature (75, 82.5, 90 °C) and slice thickness (2, 4, 6 mm), on different quality parameters of dehydrated aonla was studied. Increasing water temperature resulted in significantly higher ascorbic acid content, titratable acidity and product temperature, while total phenolic content, free radical scavenging activity and moisture content decreased. With the exception of product temperature, higher slice thickness led to an increase in the values of all the parameters. At the optimized processing conditions of 83 °C water temperature and 4 mm slice thickness, the ascorbic acid content, total phenolic content, free radical scavenging activity, titratable acidity and moisture content values were found to be 269.03 mg (100 g)-1, 242.33 mg (100 g)-1, 87.11%, 3.62% and 4% respectively. The aonla slices subjected to RWD also possessed 4-6% higher phytochemical content than osmotically dried and hot-air-dried samples.

CONCLUSION

This research highlights the effectiveness of RWD in preserving heat-sensitive compounds in food like aonla. The RW-dried slices had a smoother and more uniform microstructure compared to osmotically dried and hot-air-dried samples. © 2024 Society of Chemical Industry.

Impact of Drying Process on Grindability and Physicochemical Properties of Celery

The objective of this study was to evaluate the impact of various drying methods: freeze drying, vacuum drying, convection drying, and convection-microwave drying at microwave powers of 50 W and 100 W, along with process temperatures (40 °C, 60 °C, and 80 °C), on the drying kinetics, selected physicochemical properties of dried celery stems, and their grindability. The Page model was employed to mathematically describe the drying kinetics across the entire measurement range. Convection-microwave drying significantly reduced the drying time compared to the other methods. The longest drying duration was observed with freeze drying at 40 °C. The product obtained through freeze drying at 40 °C exhibited the least alteration in color coordinates, the highest antioxidant capacity, and the greatest retention of chlorophylls and total carotenoids. At a specific temperature, the quality of the product obtained from vacuum drying was slightly lower compared to that from freeze drying. The most substantial changes in the physicochemical properties of the dried product were observed with convection-microwave drying at a microwave power of 100 W. The drying method selected had a significant impact on the energy consumption of grinding, average particle size, and the grinding energy index of the dried celery stems; these parameters worsened as the drying temperature increased. The product with the best quality characteristics and disintegration parameters was achieved using freeze drying at 40 °C.

Improvement of Antioxidant Activity and Sensory Properties of Functional Cookies by Fortification with Ultrasound-Assisted Hot-Air-Drying Blackberry Powders

In response to the global challenge of food wastage and high perishability of blackberries, this study evaluated the use of ultrasound-assisted hot air drying (US-HAD) to convert downgraded blackberries into powders, comparing it with traditional hot air drying (HAD). US-HAD reduced the drying time and achieved a final moisture content of 12%. Physicochemical analyses (colourimetry, total soluble solids, titratable acidity, and total phenolic content) were conducted on fresh fruit, powders, and fortified cookies. US-HAD cookies exhibited promising antioxidant activity, with ABTS values ranging from 8.049 to 8.536 mmol TEAC/100 g and DPPH values from 8.792 to 9.232 mmol TEAC/100 g, significantly higher than control cookies. The TPC was 13.033 mgGAE/g in HAD cookies and 13.882 mgGAE/g in US-HAD cookies. UHPLC-ESI-MS analysis showed an increase in phenolic compounds content in fortified cookies compared to the control. Sensory analysis highlighted a superior blackberry flavour and overall acceptability in US-HAD cookies, with statistical analysis confirming their superior nutritional and sensory qualities. Integrating US-HAD blackberry powder into cookies helps reduce food waste and enhances the nutritional profiles of baked goods, offering functional foods with health benefits. This work provides a scientific basis for developing enriched functional cookies, offering a healthy and sustainable alternative for utilising damaged fruits.

Development of an Apple Snack Enriched with Probiotic Lacticaseibacillus rhamnosus: Evaluation of the Refractance Window Drying Process on Cell Viability

The objective of this study was to develop a dried apple snack enriched with probiotics, evaluate its viability using Refractance Window (RWTM) drying, and compare it with conventional hot air drying (CD) and freeze-drying (FD). Apple slices were impregnated with Lacticaseibacillus rhamnosus and dried at 45 °C using RWTM and CD and FD. Total polyphenol content (TPC), color (∆E*), texture, and viable cell count were measured, and samples were stored for 28 days at 4 °C. Vacuum impregnation allowed for a probiotic inoculation of 8.53 log CFU/gdb. Retention values of 6.30, 6.67, and 7.20 log CFU/gdb were observed for CD, RWTM, and FD, respectively; the population in CD, RWTM remained while FD showed a decrease of one order of magnitude during storage. Comparing RWTM with FD, ∆E* was not significantly different (p < 0.05) and RWTM presented lower hardness values and higher crispness than FD, but the RWTM-dried apple slices had the highest TPC retention (41.3%). Microstructural analysis showed that RWTM produced a smoother surface, facilitating uniform moisture diffusion and lower mass transfer resistance. The effective moisture diffusion coefficient was higher in RWTM than in CD, resulting in shorter drying times. As a consequence, RWTM produced dried apple snacks enriched with probiotics, with color and TPC retention comparable to FD.

Effect of wall material on lipophilic functional compounds of high oleic palm oil emulsions encapsulated by Refractance Window drying

High-oleic palm oil is a food-grade oil with desirable properties, as it is characterised by having an oleic acid concentration above 50 % and a high vitamin E and provitamin A content. This study investigated the effect of different combinations of two wall materials (whey protein (WP) and Capsul®, a commercial octenyl succinic anhydride modified starch (OSA-MS)) on the concentration of provitamin A, vitamin E and oleic acid, and the physical properties of high oleic palm oil emulsions encapsulated by Refractance Window drying technology. Wall material composition significantly affected (p < 0.05) all response variables, and R2 values were above 0.75 for all responses. Phytonutrient preservation showed its highest at an OSA-MS: WP concentration ratio of 1: 3. Optimal results were achieved (minimum moisture content, water activity and hygroscopicity, and maximum encapsulation efficiency and phytonutrient preservation) at an OSA-MS concentration of 8.13 % and WP concentration of 91.87 %. Flakes were obtained as a solid structure that protects oil's phytonutrients with 94 %, 75 % and 87 % of preservation of oleic acid, vitamin E and carotenoids, respectively. It shows that the wall material combination and encapsulation technique are suitable for obtaining lipophilic functional compounds.

Wild Asparagus Shoots Constitute a Healthy Source of Bioactive Compounds

Wild Asparagus shoots are consumed worldwide, although most species remain understudied. In this work, a total of four wild Asparagus species were collected from different locations and analyzed compared with farmed A. officinalis. Shoots were screened for (i) phenolic compounds by HPLC-DAD and LC-MS; (ii) total phenolic acids and total flavonoid content by the Folin-Ciocalteu and aluminum chloride methods; (iii) vitamin C by HPLC-DAD; (iv) antioxidant activity by the DPPH and ABTS•+ methods; and (v) the in vitro antiproliferative activities against HT-29 colorectal cancer cells by the MTT assay. Phenolics ranged from 107.5 (A. aphyllus) to 605.4 mg/100 g dry weight (dw) (A. horridus). Vitamin C ranged from 15.8 (A. acutifolius) to 22.7 mg/100 g fresh weight (fw) (A. officinalis). The antioxidant activity was similar in all species, standing out in A. officinalis with 5.94 (DPPH) and 4.64 (ABTS) mmol TE/100 g dw. Among phenolics, rutin reached the highest values (574 mg/100 g dw in A. officinalis), followed by quercetin, nicotiflorin, asterin, and narcissin. The MTT assay revealed the inhibitory effects of ethanol extracts against HT-29 cancer cells, highlighting the cell growth inhibition exercised by A. albus (300 µg/mL after 72 h exposure to cells). This work improves knowledge on the phytochemicals and bioactivities of the shoots of wild Asparagus species and confirms their suitability for use as functional foods.

Comparison of Different Drying Methods for Asparagus [Asparagus cochinchinensis (Lour.) Merr.] Root Volatile Compounds as Revealed Using Gas Chromatography Ion Mobility Spectrometry

Asparagus [Asparagus cochinchinensis (Lour.) Merr.] is a traditional herbal medicine plant commonly used to nourish yin, moisten dryness, and clear fire cough symptoms. Drying is an excellent option to conserve food materials, i.e., grains, fruits, vegetables, and herbs, reducing the raw materials volume and weight. This study aims to evaluate different drying approaches that could increase the value of asparagus, particularly as an ingredient in fast foods or as nutraceutical byproducts. The volatile components of asparagus roots were analyzed by using headspace-gas chromatography-ion mobility spectroscopy under different drying conditions, i.e., natural drying (ND) at ambient air temperature in the dark, well-ventilated room, temperature range 28-32°C, blast or oven drying at 50°C, heat pump or hot-air drying at temperature 50°C and air velocity at 1.5 ms-1 and vacuum freeze-drying at the temperature of -45°C and vacuum pressure of 10-30 Pa for 24 h. The findings revealed that the various drying processes had multiple effects on the color, odor index, and volatile compounds of the asparagus roots. As a result of the investigations, multiple characteristics of components, therefore, exploitation and comparison of various flavors; a total of 22 compounds were identified, such as alcohols, ketones, aldehydes, acids, esters, heterocyclic, and terpene. The present findings may help understand the flavor of the processed asparagus roots and find a better option for drying and processing.

Optimization of drying conditions for Jackfruit pulp using Refractance Window Drying technology

Refractance window drying is a novel technology with high operational efficiency and high product quality retention compared with conventional drying methods. This study assessed the effect of refractance window dryer water temperature and pulp thickness on nutrient content and the antioxidant activity of jackfruit. Response surface methodology (RSM) was used to optimize the drying temperature and fruit pulp thickness. Optimal drying temperature and pulp thickness were found to be 93.4°C and 2.56 mm, respectively. The respective values for the response variables drying time (min), ascorbic acid (mg/100 g), antioxidant activity (mg/100 g AA equiv) and total carotenoid content (μg/g) were 60.47, 17.97, 82.34, and 13.34, respectively. Models for prediction of these values had R 2 values of .964, .980, .994, and .994, respectively, and nonsignificant lack of fit (p < .05). This indicates the suitability of the model in predicting the RWD operating conditions to produce quality dried jackfruit.

Hygroscopic Properties of Sweet Cherry Powder: Thermodynamic Properties and Microstructural Changes

Understanding sorption isotherms is crucial in food science for optimizing the drying processes, enhancing the shelf-life of food, and maintaining food quality during storage. This study investigated the isotherms of sweet cherry powder (SCP) using the static gravimetric method. The experimental water sorption curves of lyophilized sweet cherry powder were determined at 30°C, 40°C, and 50°C. The curves were then fitted to six isotherm models: Modified GAB, Halsey, Smith, Oswin, Caurie, and Kühn models. To define the energy associated with the sorption process, the isosteric sorption heat, differential entropy, and spreading pressure were derived from the isotherms. Among the six models, the Smith model is the most reliable in predicting the sorption of the cherry powder with a determination coefficient (R2) of 0.9978 and a mean relative error (MRE) ≤1.61. The values of the net isosteric heat and differential entropy for the cherry increased exponentially as the moisture content decreased. The net isosteric heat values varied from 10.63 to 90.97 kJ mol−1, while the differential entropy values varied from 27.94 to 273.39 J. mol−1K−1. Overall, the enthalpy-entropy compensation theory showed that enthalpy-controlled mechanisms could be used to regulate water adsorption in cherry powders.

The effect of process variables on the physical properties and microstructure of HOPO nanoemulsion flakes obtained by refractance window

Refractance window (RW) drying is considered an emerging technique in the food field due to its scalability, energy efficiency, cost and end-product quality. It can be used for obtaining flakes from high-oleic palm oil (HOPO) nanoemulsions containing a high concentration of temperature-sensitive active compounds. This work was thus aimed at studying the effect of temperature, thickness of the film drying, nanoemulsion process conditions, and emulsion formulation on the flakes’ physical properties and microstructure. The results showed that HOPO flakes had good physical characteristics: 1.4% to 5.6% moisture content and 0.26 to 0.58 a_w. Regarding microstructure, lower fractal dimension (FDt) was obtained when RW drying temperature increased, which is related to more regular surfaces. The results indicated that flakes with optimal physical properties can be obtained by RW drying of HOPO nanoemulsions.

Nutricosmetic effects of Asparagus officinalis: a potent matrix metalloproteinase-1 inhibitor

This study aimed to investigate the nutricosmetic effect of Asparagus officinalis extracts. The tip and spear of A. officinalis were successively extracted with 95% ethanol. The rutin, phenolic, and flavonoid contents of A. officinalis extracts were investigated. The antioxidant activities were determined by 2,2-azinobis (3-ethylbenzothiazoline-6-sulphonic acid) and a ferric reducing antioxidant power assay. Matrix metalloproteinase-1 (MMP-1), elastase, and hyaluronidase inhibition were determined by in vitro enzyme reaction assay. The cytotoxicity was analyzed on peripheral blood mononuclear cellss. Findings revealed that drying temperature and drying duration had significant effects on the chemical composition and biological activity of A. officinalis extract. A. officinalis tips dried at 50 °C for 24 h contained the (significantly) highest flavonoid and rutin content. The most potent extract was from A. officinalis spears since it possessed the (significantly) highest MMP-1, elastase, and hyaluronidase inhibition rates of 83.4 ± 1.5%, 70.4 ± 4.1%, and 75.2 ± 1.0%, respectively. Interestingly, at the same concentration, the A. officinalis spear extract was more potent in MMP-1 inhibition than oleanolic acid and epigallocatechin gallate, the well-known natural MMP-1 inhibitors. The results show that A. officinalis extract is an attractive source of natural anti-skin-wrinkle ingredients.

Pharmacological properties of edible Asparagus acutifolius and Asparagus officinalis collected from North Iraq and Turkey (Hatay)

In this study, antioxidant, oxidant, antimicrobial, and antiproliferative activities of Asparagus acutifolius L. and Asparagus officinalis L., known for their nutritional properties, were determined. In this context, methanol (MeOH) and dichloromethane (DCM) extracts of plants were obtained. Total antioxidant status (TAS), total oxidant status (TOS), and oxidative stress index (OSI) were determined using Rel Assay kits. Antimicrobial activities of plant extracts were determined against the test microorganisms using the agar dilution method. Antiproliferative activity was tested on the lung cancer cell line A549. As a result of the studies, it has been determined that the plant species have high antioxidant potential. In addition, it was observed that the antifungal potentials of plant extracts are high. Antiproliferative activity was determined to be at high level in both plant species. As a result, it has been determined that A. acutifolius and A. officinalis have medical potential and can be used as natural agents in pharmacological designs.

Handling wine pomace: The importance of drying to preserve phenolic profile and antioxidant capacity for product valorization

Four different wine grape pomaces (GP) (Vitis vinifera) varieties, Auxerrois, Pinot Blanc, Gamay and Pinot Noir, and obtained from white, rosé or red wine vinification, were considered for possible valorization in food supplement industry. Stabilization of GP by drying is paramount prior to further processing in the valorization chain, as GP might suffer spoilage over time. The objectives of this work were therefore to: evaluate the effect of microbiological spoilage and drying on the polyphenol profile and antioxidant capacity of GP; define a drying procedure by comparing kinetics of freeze-drying (FD) and vacuum oven (VO) (at 60 °C and 40 °C). Microbiological spoilage led to significant losses (P < 0.01) of antioxidant capacity (40% to 87%) and total phenolic content (70% to 90%), while drying had no significant effect. FD and VO at 60 °C drying kinetics exhibited similar drying curves, and a dry weight (DW) plateau was reached by 48 hr. In contrast VO at 40 °C required 170 hr to reach similar DW values, pointing out the importance of temperature when opting for VO technology. Antioxidant capacity of GP extracts did not differ between drying methods. Interestingly, GPs from white and rosé wines (AUX, PB, and GAM) had up to 3.5 times higher content (P < 0.001) of total polyphenols compared to PN, obtained from red wine. These results reinforce the importance of drying of GP as a pretreatment, which otherwise could result in significant product degradation. Additionally, we propose white and rosé GP as more interesting sources for valorization, with higher phenolic content, compared to red wine GP.

The Effect of Freeze-Drying on the Properties of Polish Vegetable Soups

The aim of this study was to investigate selected physical and biochemical properties of four vegetable freeze-dried soups. The water content, water activity, pH, color parameters, antioxidant activity (EC50), total polyphenolic content of fresh tomato, pumpkin, beetroot, and cucumber, and freeze-dried soups were measured. Sensory analysis was applied to compare sensory attributes of fresh and rehydrated soups. The sorption isotherms of freeze-dried soups were obtained with the application of the static and dynamic vapor sorption (DVS) method. The application of the freeze-drying method enabled the obtaining of dry soups with a low water content of 2–3%. The drying caused a significant change of color of all soups. The redness of soups decreased after drying for the beetroot soups from +39.64 to +21.91. The lower chroma value of 25.98 and the highest total color change ΔE*ab = 36.74 were noted for freeze-dried beetroot soup. The antioxidation activity and total polyphenolic content were reduced after drying, especially for the cucumber and tomato soups. The Peleg model was selected to describe the sorption isotherms of dried soups. The sorption isotherm of freeze-dried cucumber and beetroot soups had a sigmoidal shape of type II. The shape of the moisture sorption isotherm for freeze-dried tomato and pumpkin soups corresponded more with type III isotherms. The DVS method can be used to characterize the moisture sorption isotherms of freeze-dried products.

Synthesis, Characterization, and Application of Carboxymethyl Cellulose from Asparagus Stalk End

Cellulose from Asparagus officinalis stalk end was extracted and synthesized to carboxymethyl cellulose (CMC_as) using monochloroacetic acid (MCA) via carboxymethylation reaction with various sodium hydroxide (NaOH) concentrations starting from 20% to 60%. The cellulose and CMC_as were characterized by the physical properties, Fourier Transform Infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC), Scanning electron microscopy (SEM) and X-ray diffraction (XRD). In addition, mechanical properties of CMC_as films were also investigated. The optimum condition for producing CMC_as was found to be 30% of NaOH concentration for the carboxymethylation reaction, which provided the highest percent yield of CMC_as at 44.04% with the highest degree of substitution (DS) at 0.98. The melting point of CMC_as decreased with increasing NaOH concentrations. Crystallinity of CMC_as was significantly deformed (p < 0.05) after synthesis at a high concentration. The L* value of the CMC_as was significantly lower at a high NaOH concentration compared to the cellulose. The highest tensile strength (44.59 MPa) was found in CMC_as film synthesized with 40% of NaOH concentration and the highest percent elongation at break (24.99%) was obtained in CMC_as film treated with 30% of NaOH concentration. The applications of asparagus stalk end are as biomaterials in drug delivery system, tissue engineering, coating, and food packaging.

Comparison of Traditional and Novel Drying Techniques and Its Effect on Quality of Fruits, Vegetables and Aromatic Herbs

Drying is known as the best method to preserve fruits, vegetables, and herbs, decreasing not only the raw material volume but also its weight. This results in cheaper transportation and increments the product shelf life, limiting the food waste. Drying involves the application of energy in order to vaporize and mobilize the moisture content within the porous products. During this process, the heat and mass transfer occurs simultaneously. The quality of dehydrated fruits, vegetables, and aromatic herbs is a key problem closely related to the development and optimization of novel drying techniques. This review reports the weaknesses of common drying methods applied for fruits, vegetables, and aromatic herbs and the possible options to improve the quality of dried products using different drying techniques or their combination. The quality parameters under study include color, bulk density, porosity, shrinkage, phytochemicals, antioxidant capacity, sugars, proteins, volatile compounds, and sensory attributes. In general, drying leads to reduction in all studied parameters. However, the behavior of each plant material is different. On the whole, the optimal drying technique is different for each of the materials studied and specific conditions must be recommended after a proper evaluation of the drying protocols. However, a novel or combined technique must assure a high quality of dried products. Furthermore, the term quality must englobe the energy efficiency and the environmental impact leading to production of sustainable dried products.

Application of MAP and ethylene–vinyl alcohol copolymer (EVOH) to extend the shelf-life of green and white asparagus (Asparagus officinalis L.) spears

In this study, ethylene vinyl alcohol copolymer (EVOH) and polypropylene/polyethylene (PP/PE) films combined with MAP packaging were developed to enhance the shelf-life of green and white asparagus spears. The scope of the research included measurements of weight loss, pH, acidity, color, texture, and sensory analysis as indicators of green and white asparagus spear quality for up to 17 days of storage at 2 and 10 °C. The application of modified atmosphere packaging combined with EVOH-based packaging material and refrigeration at 2 °C promoted a reduction in asparagus weight loss, preventing changes in color and texture as well as sensory quality, thereby extending the shelf-life of the asparagus. According to the obtained results, it was possible to maintain good quality of green and white asparagus for up to 17 and 10 days, respectively, when packed in MAP using EVOH-based packaging stored at 2 °C. Asparagus stored in packaging with PP/PE film showed lower quality during storage at 2 and 10 °C. These results suggest that EVOH films are potential candidates for advanced packaging materials for the asparagus packaging application.

Modelling and kinetic study of microwave assisted drying of ginger and onion with simultaneous extraction of bioactive compounds

Onion and ginger are rich sources of bioactive compounds which are lost during conventional drying process. The present study was designed to optimize the novel Microwave Assisted Drying and Extraction technique (MADE) for simultaneous drying and extraction/recovery of bioactive compounds from model food products. The time required for drying of samples was 11 (onion) and 16 (ginger) minutes with recovery yield of 87% (onion) and 85% (ginger). The drying time was reduced to 100 times compared to hot air drying and moisture ratio of dried samples was best described by Midilli model. The diffusivities of onion and ginger slices were 1.27 e^-11 and 1.43 e^-11 m²/s, respectively. Moreover, microwave-based extraction was compared with conventional one. The results of antioxidant activity and total phenolic contents of condensates obtained through MADE were higher compared to conventional method. In short, MADE exhibited better yield of extraction and drying properties compared to conventional methods.

Reuse of Food Waste and Wastewater as a Source of Polyphenolic Compounds to Use as Food Additives

The problem of waste and byproducts generated from agro-industrial activities worldwide is an increasing concern in terms of environmental sustainability. In this ambit, the quantity of food wastes—produced in all steps of the whole food chain—is enormous, and it may be forecasted that food waste could amount to more than 120 billion tonnes by 2020. The reuse of food waste and wastewater as source of polyphenolic compounds could be an interesting discussion in this ambit. In fact, polyphenols obtained in this way might be used for food and non-food purposes by means of new, improved, and safe extraction methods. In light of the opportunity represented by the treatment of agro-industrial waste, different systems concerning the winemaking and olive oil production industries have also been discussed as describing approaches applicable to other sectors. More research is needed before considering recovery of phenolic compounds from wastewater as an economically convenient choice for the food sector.

Effects of Infrared-Assisted Refractance Window™ Drying on the Drying Kinetics, Microstructure, and Color of Physalis Fruit Purée

The objective of this work was to study the influence of the drying temperature, infrared (IR) radiation assistance, and the Mylar™ film thickness during Physalis fruit purée drying by the Refractance Window™ (RW™) method. For this, a RW™ dryer layout with a regulated bath at working temperatures of 60, 75, and 90 °C, Mylar™ thicknesses of 0.19, 0.25, 0.30 mm and IR radiation of 250 W for assisting RW™ drying process was used. Experimental curves data were expressed in moisture ratio (MR) in order to obtain moisture effective diffusivities (non-assisted RW™: D_eff = 2.7-10.1 × 10^-10 m²/s and IR-assisted RW™: D_eff = 4.2-13.4 × 10^-10 m²/s) and further drying curves modeling (Page, Henderson-Pabis, Modified Henderson-Pabis, Two-Term, and Midilli-Kucuk models). The Midilli-Kucuk model obtained the best-fit quality on experimental curves regarding statistical tests applied (Coefficient of Determination (R²), Chi-Square (χ²) and Root Mean Square Error (RMSE). Microscopical observations were carried out to study the RW™ drying conditions effect on microstructural changes of Physalis fruit purée. The main findings of this work indicated that the use of IR-assisted RW™ drying effectively accelerates the drying process, which achieved a decrease drying time around 60%. Thus, this combined RW™ process is strongly influenced by the working temperature and IR-power applied, and slightly by Mylar™ thickness.

Optimization study for refractance window drying process of Langra variety mango

Refractance window (RW) drying of mango pulp has shown good quality retention compared to conventional drying methods. Different pulp thickness (2, 3 and 4 mm) and drying temperature (85, 90 and 95 °C) were optimized for RW drying of mango pulp for responses as drying time, ascorbic acid, total phenolics content (TPC) and hardness of mango leather. Face-centered central composite design was performed for optimization using Design-Expert software. RW drying of 2 mm thick mango pulp took the shortest drying time, however lower ascorbic acid and TPC were determined as compared to 3 mm and 4 mm thick pulp mango leather. Hardness of RW dried mango leather was determined to be in the chewable range as 3.62-5.33 N. The optimum solution generated for RW drying temperature and pulp thickness was 95 °C and 2.49 mm, respectively. The drying time was 22.5 min with high quality retention in terms of ascorbic acid, TPC and hardness as 62.33 mg/100 g DW, 7.72 mg GAE/g DW and 4.60 N respectively of dried product with desirability function obtained was 0.969. More nutrients were preserved in mango leather as well as microstructure of mango powder was observed as smooth and flaky with uniform thickness of powder particles with RW drying process when compared with tray and oven drying at 95 °C drying temperature and 2.50 mm mango pulp thickness.

Physicochemical Properties of Guava Snacks as Affected by Drying Technology

Guava is widely consumed because of its agro-industrial use, and its antioxidant properties attributed to vitamin C and carotenoids content. However, it has a short shelf life. Guava has been dried by atomization, fluidized bed, lyophilization (FD) and convective drying (CD). CD requires long operation times and the product characteristics are not desirable. In contrast, FD produces high quality products, but requires long processing times, high energy consumption and high operation costs. As an alternative, the Refractance Window® (RW) drying is relatively simple and cheap technique. The objective of this study was to compare the effect of CD, FD and RW techniques, on the moisture content, water activity, color, porosity, volume change, vitamin C and carotenoids content in guava samples. The samples dried by RW required less time to reduce the moisture content and exhibited smaller changes in color than CD or FD. There were greater losses of carotenoids and vitamin C when drying by CD whereas RW had similar losses than FD. Lyophilized products exhibited minor change in volume and greater porosity. RW results in better retention of properties, compared with other drying techniques. Based on this, RW is a promising technique for the development of guava snacks.

Freeze-Drying of Plant-Based Foods

Vacuum freeze-drying of biological materials is one of the best methods of water removal, with final products of highest quality. The solid state of water during freeze-drying protects the primary structure and the shape of the products with minimal volume reduction. In addition, the lower temperatures in the process allow maximal nutrient and bioactive compound retention. This technique has been successfully applied to diverse biological materials, such as meats, coffee, juices, dairy products, cells, and bacteria, and is standard practice for penicillin, hormones, blood plasma, vitamin preparations, etc. Despite its many advantages, having four to ten times more energy requirements than regular hot air drying, freeze-drying has always been recognized as the most expensive process for manufacturing a dehydrated product. The application of the freeze-drying process to plant-based foods has been traditionally dedicated to the production of space shuttle goods, military or extreme-sport foodstuffs, and specialty foods such as coffee or spices. Recently, the market for 'natural' and 'organic' products is, however, strongly growing as well as the consumer's demand for foods with minimal processing and high quality. From this perspective, the market for freeze-dried plant-based foods is not only increasing but also diversifying. Freeze-dried fruits and vegetables chunks, pieces, or slices are nowadays majorly used in a wide range of food products such as confectionaries, morning cereals, soups, bakeries, meal boxes, etc. Instant drinks are prepared out of freeze-dried tea, coffee, or even from maple syrup enriched with polyphenol concentrated extracts from trees. The possibilities are endless. In this review, the application of freeze-drying to transform plant-based foods was analyzed, based on the recent research publications on the subject and personal unpublished data. The review is structured around the following related topics: latest applications of freeze-drying to plant-based foods, specific technological problems that could be found when freeze-drying such products (i.e., presence of cuticle; high sugar or lipid concentration), pretreatments and intensification technologies employed in freeze-drying of plant-based foods, and quality issues of these freeze-dried products.

Effects of microwave blanching conditions on the quality of green asparagus (Asparagus officinalis L.) butt segment

Blanching is a pretreatment method that is often applied in fruit and vegetable processing to inhibit enzyme activity and reduce loss of food quality. It was recently discovered that well-controlled microwave volumetric heating could improve the blanching efficiency and retain nutritional and sensorial values of product. This study was conducted to investigate effects of microwave blanching conditions on the quality of green asparagus (Asparagus officinalis L.) butt segments, a rich source of fiber and antioxidants but are often discarded during processing. The experiments were designed by one-factor-at-a-time method with two varying factors including blanching time (2, 4, 6, and 8 min) and microwave power output (150, 300, 450, and 600 W). Quality of product was evaluated by sensory, retention of phenolics, and free-radical scavenging activity retention. The results showed that longer blanching time or higher microwave power was associated with reduced quality of green asparagus butt segment. Besides, the appropriate parameters for microwave blanching of the green asparagus butt segment was found at 300 W for 4 min.

Encapsulation of Lactobacillus fermentum K73 by Refractance Window drying

The purpose of this work was to model the survival of the microorganism and the kinetics of drying during the encapsulation of Lactobacillus fermentum K73 by Refractance Window drying. A whey culture medium with and without addition of maltodextrin were used as encapsulation matrices. The microorganism with the encapsulation matrices was dried at three water temperatures (333, 343 and 353 K) until reaching balanced moisture. Microorganism survival and thin layer drying kinetics were studied by using mathematical models. Results showed that modified Gompertz model and Midilli model described the survival of the microorganism and the drying kinetics, respectively. The most favorable process conditions found with the mathematical modelling were a drying time of 2460 s, at a temperature of 353 K. At these conditions, a product with 9.1 Log CFU/g and a final humidity of 10% [wet basis] using the culture medium as encapsulation matrix was obtained. The result shows that Refractance Window can be applied to encapsulate the microorganism probiotic with a proper survival of the microorganism.

Development of dehydrated products from peach palm-tucupi blends with edible film characteristics using refractive window

This study aimed to obtain a dehydrated product with film characteristics with superior functional and technological quality, prepared from different varieties of peach palm (Bactris gasipaes) using the refractance window drying (RW) process. The experiments were carried out at 70 °C and drying was fully performed at an increasing rate. The physicochemical characteristics and mechanical, technological, and morphological properties were determined and the moisture and water activity curves of the different peach palm varieties were assessed. The dehydrated product by refractance window have good visual appearance and bright yellowish color due to the carotenoid content found in the samples used as raw material. All dehydrated products had non-homogenous microstructure, however, the products had low tensile strength, percent elongation, hygroscopicity, and water absorption and solubility, desired properties to obtain a food product. The presence of components such as proteins, lipids, and fibers had important effects on the mechanical properties of the products because the mechanical resistance of the biopolymers is influenced by the cohesion of the constituents of the polymer matrix. The production of a dehydrated product with film characteristics through the RW technique presented some advantages over conventional casting drying as such as short drying times, lower costs and without addition of plasticizers or non-food grade components. In general, the products dehydrated by RW are promising and can be consumed immediately after production as snacks or in the substitution of other ingredients, such as algae in sushi.

Refractance window drying of fruits and vegetables: a review

Fruit and vegetable drying to make leather, pestil or powder products is a challenging task. Traditional drying adversely affects the taste, colour, nutritional qualities and preservation of bioactive compounds due to high-temperature exposure of the product. The substitute for traditional drying processes is consequently necessary to impart superior quality and preserve greater nutritional value in processed foods. Refractance window (RW) drying is a thin film drying system having high heat and mass transfer rates that speeds up the rate of drying. Polyester (Mylar), an infrared transparent plastic sheet transmits radiative heat to food during the RW drying process with higher drying rate, more retention of nutrients and low aroma and flavour loss. RW drying is reported to be affected by the thickness of puree or slices and temperature of drying, as thick samples need longer drying time, generate higher water activity, bring changes in colour parameters, experience higher effective diffusion coefficient (D_eff ) and result in lower solubility of powder. RW drying was compared with different drying processes and was observed to have more retention of nutrients and be more economical. RW dried samples were better in terms of colour and textural quality when compared with other traditional drying methods. © 2018 Society of Chemical Industry.