Water sorption behavior and thermal analysis of freeze-dried, Refractance Window-dried and hot-air dried açaí (Euterpe oleracea Martius) juice

Evaluation of the Survival of Lactobacillus fermentum K73 during the Production of High-Oleic Palm Oil Macroemulsion Powders Using Rotor-Stator Homogenizer and Spray-Drying Technique

This study aimed to evaluate the survival of the probiotic Lactobacillus fermentum when it is encapsulated in powdered macroemulsions to develop a probiotic product with low water activity. For this purpose, the effect of the rotational speed of the rotor-stator and the spray-drying process was assessed on the microorganism survival and physical properties of probiotic high-oleic palm oil (HOPO) emulsions and powders. Two Box-Behnken experimental designs were carried out: in the first one, for the effect of the macro emulsification process, the numerical factors were the amount of HOPO, the velocity of the rotor-stator, and time, while the factors for the second one, the drying process, were the amount of HOPO, inoculum, and the inlet temperature. It was found that the droplet size (ADS) and polydispersity index (PdI) were influenced by HOPO concentration and time, ζ-potential by HOPO concentration and velocity, and creaming index (CI) by speed and time of homogenization. Additionally, HOPO concentration affected bacterial survival; the viability was between 78-99% after emulsion preparation and 83-107% after seven days. The spray-drying process showed a similar viable cell count before and after the drying process, a reduction between 0.04 and 0.8 Log10 CFUg^-1; the moisture varied between 2.4% and 3.7%, values highly acceptable for probiotic products. We concluded that encapsulation of L. fermentum in powdered macroemulsions at the conditions studied is effective in obtaining a functional food from HOPO with optimal physical and probiotic properties according to national legislation (>10⁶ CFU mL^-1 or g^-1).

Use of Refractance Window Drying as an Alternative Method for Processing the Microalga Spirulina platensis

Microalgae such as Spirulina platensis have recently attracted the interest of the pharmaceutical, nutritional and food industries due to their high levels of proteins and bioactive compounds. In this study, we investigated the use of refractance window (RW) drying as an alternative technology for processing the microalga Spirulina biomass aiming at its dehydration. In addition, we also analyzed the effects of operating variables (i.e., time and temperature) on the quality of the final product, expressed by the content of bioactive compounds (i.e., total phenolics, total flavonoids, and phycocyanin). The results showed that RW drying can generate a dehydrated product with a moisture content lower than 10.0%, minimal visual changes, and reduced process time. The content of bioactive compounds after RW drying was found to be satisfactory, with some of them close to those observed in the fresh microalga. The best results for total phenolic (TPC) and total flavonoids (TFC) content were obtained at temperatures of around 70 °C and processing times around 4.5 h. The phycocyanin content was negatively influenced by higher temperatures (higher than 80 °C) and high exposing drying times (higher than 4.5 h) due to its thermosensibility properties. The use of refractance window drying proved to be an interesting methodology for the processing and conservation of Spirulina platensis, as well as an important alternative to the industrial processing of this biomass.

Refractance window drying of food and biological materials: Status on mechanisms, diffusion modelling and hybrid drying approach

Refractance window (RW) dryer has an immense advantage in terms of final product quality (textural and color attributes, nutrient retention), energy consumption, and drying time over other conventional dryers. RW is a thin film drying system and a technologically evolving drying process. RW drying is an energy-efficient (re-circulation of water) short drying process as the drying of food materials occurs due to a combined mode of heat transfer conduction, radiation, and convection (hot air circulates over film). The high-quality dried product is obtained because the product temperature remains below 80 °C. RW dryer application is not only limited to drying food products, but it can also be further used for improving the gelling and emulsion properties, formation of leather and edible film, and can be used for handling high protein products, drying leafy vegetables or marine foods as this process does not change any functional properties. Due to these advantages over other drying techniques, RW drying has gained academic and industrial interest in recent years. The industrial application of this technology at large scale is becoming difficult due because of large surface area requirement for mass production. Researchers are trying to scale-up by combing this technology with others technology (Infrared, ultrasound, solar energy, and osmotic dehydration). RW dryer is now extending from the food sector to other sectors like pharmaceutical, cosmetic, pigment, edible film formation, and encapsulation. Majority of the reviews on RW drying focuses on the product quality aspects. This review paper aims to comprehend the RW drying system more mechanistically to understand better the principles, diffusion models explaining the transfer processes, and emerging novel hybrid drying approaches.

Colorant and antioxidant properties of freeze-dried extracts from wild berries: use of ultrasound-assisted extraction method and drivers of liking of colored yogurts

This work aimed at developing powders rich in antioxidants and pigments from two wild berries: maqui (Aristotelia chilensis) and murra (Rubus ulmifolius). Fruits were subjected to successive ultrasound-assisted extractions (UAE) and then freeze-dried. Physical properties, anthocyanin stability of powders, and their performance as natural colorants in yogurts were evaluated. The optimum extraction methods were: UAE for 10 min in murra, and without UAE (control) in maqui, with juice extraction yields ranging between 80 and 82%. Maqui powder exhibited ≈ 2.8 times more polyphenol and anthocyanin content than murra. However, murra powder showed better stability characteristics as powder colorant since it exhibited greater protection of anthocyanins by means of copigmentation phenomena. Regarding consumer's perception of colored yogurt, samples with 4% and 8% maqui powder could be considered as future prototypes to be launched into the market. The obtained powders may be used in different industrial food applications.

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.

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.

Effect of conductive hydro-drying on physiochemical and functional properties of two pulse protein extracts: Green gram (Vigna radiata) and black gram (Vigna mungo)

In this study, the effect of two drying methods (conductive hydro-drying - CHD and freeze-drying - FD) on the physical and functional properties of green gram (GG) and black gram (BG) protein powders was investigated. CHD dried protein powder showed excellent powder characteristics with moisture contents ranging from 3 to 6%, water activity of ~0.4 and Carr index ≤10. The CHD samples were dried in 210 min; with higher drying rates, CHD samples showed no significant changes in powder characteristics, color value, and water and oil absorption indices. The solubility of both proteins were found to be lower at pH 4 to 7 and higher at pH 1, 2, 8, 9 and 10; at certain pH, the solubility of CHD protein was higher than that of the FD counterparts. No significant differences were observed in the oil absorption capacity, surface hydrophobicity, protein gel formation, pasting and thermal properties. XRD and FTIR analyses were used to explain changes in protein structure and the presence of both α-helix and β-sheet was observed, with higher β-sheet levels in both pulses dried using CHD. Results confirmed that CHD, a variant of the refractance window drying (RWD) offered protein quality in par with FD.

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.

Comportamento higroscópico da polpa de graviola em pó obtida por secagem em spray dryer

Resumo Produtos em pó são caracterizados por sua praticidade e longa vida útil, no entanto as polpas de fruta em pó apresentam alta higroscopicidade e tendência à aglomeração devido à sua natureza hidrofílica. Sua estabilidade pode ser estudada por meio das isotermas de equilíbrio higroscópico. A polpa de graviola, por sua vez, apresenta grande potencial econômico e industrial e destaca-se em relação às outras polpas devido a seus excelentes atributos sensoriais. O presente trabalho teve como objetivo a caracterização físico-química e higroscópica da polpa de graviola em pó e avaliou seu comportamento higroscópico através da análise de isotermas de adsorção, obtidas por ajuste dos dados experimentais através dos modelos matemáticos de GAB, BET, Henderson e Oswin nas temperaturas de 25 °C, 30 °C, 35 °C e 40 °C. Os resultados demonstraram que a polpa de graviola em pó é uma boa fonte de ácido ascórbico, ligeiramente higroscópica e abundante em formação de caking. O modelo GAB foi o que melhor representou as isotermas de adsorção, com coeficientes de determinação (R2) maiores que 0,99 e erros médios (E) menores que 5%, apresentando comportamento do tipo III, característico dos alimentos ricos em açúcar e mostrando que é necessário ter cuidado no armazenamento desse produto em ambientes com umidade relativa acima de 60%.

Phytochemical and physical properties of blueberries, tart cherries, strawberries, and cranberries as affected by different drying methods

The effects of hot-air drying (AD), freeze drying (FD) and Refractance Window drying (RWD) on the retention of anthocyanins, phenolics, flavonoids, vitamin C and B, and antioxidant capacity (ORAC) in blueberries, tart cherries, strawberries, and cranberries, as well as organic acids and proanthocyanins in cranberries and chlorogenic acid and catchins in blueberries were evaluated. Changes in color, glass transition, specific heat, and surface morphology of the dried fruits were also evaluated. The quality retention in the dried fruits was found to be product and drying method specific. The FD products exhibited a better retention of vitamin C, ORAC, anthocyanins, and phenolics than the AD and RWD fruits. The RWD produced samples with a less effective ORAC, anthocyanins, and phenolics retention, but a higher total vitamin B retention compared to the FD products. The AD-dried fruits displayed significantly lesser quality retention in most of the quality indexes measured in the study.

Functional properties of chickpea protein isolates dried by refractance window drying

In the present study, the effect of Refractance Window (RW) drying on the functional properties of chickpea protein isolates was investigated and compared to freeze drying at different pH levels. The functional properties investigated were protein solubility, water and oil holding capacity, emulsifying properties, foaming properties, flocculation and coalescence indices and textural properties. The solubility, oil holding capacity and foam stability of the freeze dried protein isolates were determined to be higher than the RW dried samples. On the other hand, the RW dried samples had better water holding capacity and emulsion stability compared to the freeze dried protein isolates. The emulsion activity index, flocculation and coalescence indices of the chickpea protein isolates prepared by different drying techniques showed different tendencies depending on the pH level. Freeze dried protein isolates exhibited higher gelation ability than RW dried samples according to the texture profile analysis. This study clearly showed that the drying technique used in the preparation of protein isolates can affect their functional properties.

The Influence of Refractance Window Drying on Qualitative Properties of Kiwifruit Slices

In this research, effect of Refractance Window (RW) drying on the quality properties of the kiwifruit samples was investigated. Drying temperatures of 80–100 °C, slice thickness of 0.8–2.4 mm and Mylar thickness of 100–300 µm were the independent variables and different qualitative attributes including drying duration, textural hardness, colour, rehydration ratio and organoleptic properties were responses monitored in each situation. Drying temperature was the most important factor contributed to quality features of RW dried kiwifruits with significant effects on all properties. Similarly, slice thickness influenced nearly all quality traits except textural hardness and some colour indices. However, Mylar membrane thickness failed to affect about every qualitative property of kiwifruit samples significantly. The majority of organoleptic properties of RW dried kiwifruits, including flavour, colour, texture, shrinkage and overall acceptance, were judged to be in the range of medium to good quality (scores of 3–4) by panellists.

Refractance Window™ drying of haskap berry--preliminary results on anthocyanin retention and physicochemical properties

The goal of this work was to determine the anthocyanin retention and physicochemical properties of haskap powder prepared by Refractance Window™ (RW) drying. In general, the RW-dried powder particles had a smooth surface with similar thickness, consistent with the preparation method, and had a solubility of 75.63% in water. The RW-dried powder (consisting of 98% haskap berries) retained approximately 93.8% of anthocyanins from the original frozen fruits, as assessed by the pH-differential method. This result is in good agreement with HPLC analysis that indicated 92.9% retention. Three anthocyanins were identified in frozen berries and RW-dried powder: cyanidin 3-glucoside, cyanidin 3-rutinoside, and peonidin 3-glucoside. Surprisingly, cyanidin 3-rutinoside exhibited the lowest retention.