Caleb Nindo

Refractance Window Dehydration Technology: A Novel Contact Drying Method

Refractance Window® (RW) system is a novel drying method for converting liquid foods and other related biomaterials into powders, flakes, or sheets with added value. In this system, purees or juices prepared from fruits, vegetables, or herbs dry in short times, typically 3–5 min, resulting in products with excellent color, vitamin, and antioxidant retention. The RW drying systems are simple and relatively inexpensive when compared with freeze drying, which usually needs large installations to be economical. In RW drying systems thermal energy is transferred from hot water to a film of puree or juice spread thinly on a plastic conveyor belt. These drying systems operate at atmospheric pressure and are used for commercial production of scrambled egg mix, avocado powder, high carotenoid-containing algae, herbal extracts and human nutrition supplements, and food ingredients, as well as dried fruits and vegetables. This article presents the principle of Refractance Window® drying and highlights some results that show its potential and how it compares with other dryers for processing fruits, vegetables, and other heat-sensitive products.

Effect of ultrasound frequency on antioxidant activity, total phenolic and anthocyanin content of red raspberry puree

Ultrasound in the 20-1000 kHz range show unique propagation characteristics in fluid media and possess energy that can break down fruit matrices to facilitate the extraction of valuable bioactive compounds. Red raspberries carry significant amounts of specific antioxidants, including ellagitannins and anthocyanins that are important for human health. The objective of this study was to investigate the effects of ultrasound frequencies associated with cavitation (20 kHz) and microstreaming (490 and 986 kHz) on total antioxidant activity (AOA), total phenolics content (TPC), and total monomeric anthocyanin content (ACY) of red raspberry puree prepared from crushed berries. The pureed fruit was subjected to high-intensity (20 kHz) and higher frequency-low intensity (490 and 986 kHz) ultrasound for 30 min. The temperature of treated purees increased to a maximum of 56 °C with 986 kHz. Sonication at 20 and 490 kHz significantly (p<0.05) affected the AOA, ACY, and TPC of red raspberry puree, while 986 kHz had no significant effect on ACY and AOA (p<0.05). In all cases, ultrasound treatment had significant and positive effect on at least one of the measured parameters up to 30 min. Sonication beyond 10 min (and up to 30 min) using 20 kHz either produced no change or caused a drop in AOA and ACY. However, for 986 and 20 kHz, TPC, increased by 10% and 9.5%, respectively after 30 min (p<0.05) compared to the control. At 20 kHz, AOA and ACY increased by 17.3% and 12.6% after 10 min. It was demonstrated that 20 kHz ultrasound treatment, when limited to 10 min, was the most effective for extraction of bioactive compounds in red raspberry compared to 490 and 986 kHz although the effect could be similar at the higher frequencies if different amplitudes are used.

Water Sorption, Glass Transition, and Microstructures of Refractance Window– and Freeze-Dried Mango (Philippine “Carabao” Var.) Powder

Water sorption isotherms, glass transition, and microstructures of Refractance Window (RW)– and freeze-dried Philippine “Carabao” mango powders were investigated. Water sorption isotherms were developed by the isopiestic method, while thermal transition of the powders, at various water activities (a w = 0.11–0.86), was determined using differential scanning calorimetry (DSC). The sorption isotherms of RW- and freeze-dried (FD) mango powders exhibited a type III sigmoidal curve, showing higher and lower adsorption capacities above and below 0.5 a w , respectively. A significant difference (p < 0.05) in water content of RW- and freeze-dried mango powders for equivalent water activities was obtained above 0.5 a w . The onset glass transition temperature (T gi ) of RW- and freeze-dried mango powder solids decreased as the water content increased. There were no significant differences (p ≥ 0.05) in T gi of RW- and freeze-dried mango powder solids at constant water activities, except for a w = 0.86. Microscopic examination of mango powders indicated that freeze-dried mango powders exhibited greater surface area and porosity in comparison to RW-dried mango powders.

Thermal properties of aloe vera powder and rheology of reconstituted gels.

Aloe vera (Aloe barbadensis L.) is a plant from the lily family that possesses therapeutic and antioxidant properties. Extracts from aloe vera leaves are widely used in skin care products, and recently in health drinks and supplements. Substandard aloe products arising from poor processing methods or adulteration with other compounds is a major problem for the aloe industry. Functional properties of aloe vera may be affected by processing procedures that involve heat or shearing action. In this study, aloe vera extract was dried using spray drying (SD), freeze drying (FD), and Refractance Window (RW) drying methods to investigate the effect of those methods on glass transition temperature (Tg), total carbohydrates, reducing groups, particle size distribution, and viscosity of solutions formed after reconstitution with deionized water. The Tg of SD aloe was in the range of 65°C ±3.2°C compared to 70°C to 78°C for the latter two drying methods. Addition of corn maltodextrin contributed to shifts in Tg of aloe powder. Solutions prepared from spray-dried aloe had the lowest viscosity, while freeze-dried and RW-dried counterparts had higher and nearly equal consistency. The activation energy for network formation of solutions reconstituted from SD powder was 23.9 ±0.1 kJ mol-1, which was slightly lower than the 24.6 ±0.3 and 24.7 ±0.4 kJ mol-1 obtained with FD and RW drying, respectively.

Trout-skin gelatin-based edible films containing phenolic antioxidants: effect on physical properties and oxidative stability of cod-liver oil model food.

UNLABELLED Trout-skin (Oncorhynchus mykiss) gelatin-based films containing antioxidants (epigallocatechin gallate (EGCG), 50 and 250 ppm w/w) and green tea powder (1% and 20% w/w of gelatin) were tested for tensile strength, elastic modulus, and elongation, and oxygen and water vapor transmission rates, in vitro antioxidant activity using the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay and effect on stabilizing cod-liver oil held under mild thermal abuse conditions. Cod-liver oil overlaid with films was stored at 40 °C for 20 d and analyzed for peroxide value (PV) and thiobarbituric acid reactive substances (TBARS). Antioxidant activity was retained in films containing green tea powder, but was reduced (P < 0.05) in EGCG films (20 d, 23 °C). Water vapor transmission rate of the films incorporated with antioxidants did not change significantly (P > 0.05), but the oxygen transmission rate for films with 50 ppm EGCG and 20% green tea powder was significant (P < 0.05). Other physical properties varied with antioxidant incorporation. The TBARS and PV of control oil increased from 0.05 ± 0.01 to 4.71 ± 0.30 g MDA/kg oil and from 3.6 ± 0.2 to 178.3 ± 24.5 millieq peroxides/kg oil, respectively, after 20 d. For cod-liver oil covered with control or antioxidant-containing films, TBARS remained below 0.37 g MDA/kg oil and PV below 7 millieq peroxides/kg oil. Incorporation of antioxidants to the films did not reduce oil oxidation (P > 0.05) at the levels tested and this was confirmed by activation energy calculations. The rate of oil oxidation was more dependent upon the inherent oxygen barrier property of the films than the presence of antioxidants. PRACTICAL APPLICATION This research has the potential to enhance the utilization of fish skins, a valuable food processing by-product, as edible films with natural antioxidants to extend the shelf life of foods. The film physical properties and barrier to oxygen and water are investigated.

Glass Transition and Rheological Properties of Aloe Vera (Aloe Barbadensis, L.) Dried by Different Methods

Aloe vera (Aloe barbadensis L.) is a plant from the lily family that possesses therapeutic and antioxidant properties. Extracts or gels from aloe vera leaves are widely used in skin care products, and lately, as health supplement. Substandard products arising from poor processing methods are a problem for the aloe market. Aloe vera possesses bioactive properties that may be lost when subjected to processing procedures that involve heat or shearing action. The suitability of emerging techniques such as Refractance Window (RW) method for drying heat sensitive herbal products such as aloe vera was investigated and comparisons made with freeze and spray drying. The dried materials were examined for changes in glass transition temperature and rheological behavior after reconstitution. Addition of corn maltodextrin contributed to shifts in glass-liquid transition of aloe powder. Variously dried aloe powder had different viscosities after reconstitution. Both the RW and freeze-dried aloe vera had a light cream color compared to the whiter (higher lightness value) spray dried powder. During 7 weeks of storage at 35°C, yellowness and redness of both RW and freeze-dried aloe increased slightly and in proportion to the overall hue was from 4 to 6.

Energy Consumption during Refractance Window™ Evaporation of Selected Berry Juices

The Refractance Window™ evaporator is a patented technology that uses hot water at atmospheric pressure to evaporate water from liquid foods. Energy from the circulating hot water is transmitted through a plastic sheet interface to evaporate water from a liquid product flowing concurrently on the top surface of the plastic. The objectives are to study this evaporator’s heat transfer characteristics, determine its energy consumption, and capacity at different tilt angles and specified flow rates. Using water, raspberry and blueberry juices/purees as feed, temperature and flow rates of both heated water and feed were recorded to determine the evaporator performance. The steam economy ranged from 0.64 and 0.84, while the average evaporation capacity and product temperature were 24.5 kg/hr.m² and 65°C, respectively. The highest evaporation rate was 31.8 kg/hr.m². The average specific energy consumption was 2492~2719 kJ/kg of water evaporated. These results are expected to improve after the airflow and heat exchange optimization is completed.