Effects of instant controlled pressure drop treatment combined with refractance window drying on infusion quality of made green tea

BACKGROUND

The study aimed to determine the effects of instant controlled decompression of steam pressure, termed as ICPD (instant controlled pressure drop) on fresh tea leaves, when combined with refractance window drying (RWD) of rolled green teas during green tea manufacturing. The ICPD steam treatment pressure (TP; 0.1-0.3 MPa), treatment time (TT; 10-20 s) and refractance window drying temperature (RWDT; 70-90 °C) were used as the processing parameters for manufacturing of green tea.

RESULT

Response surface methodology was employed to enumerate the effects of ICPD process conditions and temperature of RWD on total phenolic content (TPC), total flavonoid content (TFC) and DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity of the green tea infusion. An optimum condition for green tea processing was found at TP 0.2 MPa, TT 20 s with RWDT at 70 °C. In comparison to made green tea manufactured without ICPD treatment, the ICPD treated green tea showed enhanced TPC, TFC and DPPH radical scavenging activity along with better colour and sensory attributes. The microstructural study of ICPD treated green tea samples showed more deformed cell surface integrity, larger stomatal pore size and cracks at the leaf surface in comparison with non-treated green tea sample.

CONCLUSION

Present study reveals that an ICPD treatment at 0.2 MPa for 20 s can be used as an alternative to the traditional enzyme inactivation step of hot water treatment, for green tea leaves to improve the infusion quality in terms of increased levels of TPC and TFC and DPPH radical scavenging activity. © 2024 Society of Chemical Industry.

Improvement of phytochemical and quality characteristics of Dracocephalum kotschyi by drying methods

This experiment was conducted to evaluate the effects of different drying methods on drying parameters and qualitative characteristics of Dracocephalum kotschyi in a completely randomized design with three replications. Treatments included shade drying as control, sun drying, cabinet drying (CD at 50 and 60°C), refractance window drying (RWD), infrared drying (IRD) at 200 and 300 W, and combination of RWD+ IRD at 200 and 300 W. According to the results, IRD, RWD, and RWD+ IRD effectively maintained valuable secondary metabolites compared to the conventional drying methods. The maximum total phenol content (2.7 and 2.66 mg GAE/g dry weight), total flavonoid content (2.26 and 2.33 mg QE/g dry weight), antioxidant activity (79% and 78.33%), and essential oil content (0.65% and 0.76%) were obtained from plants dried by RWD and IRD. Samples dried by RWD, IRD, and RWD+ IRD had high color quality, acceptable green color, and less browning. Also, RWD and IRD methods effectively reduced microbial contamination of dried plants compared to the control and other methods. The minimum aerobic mesophiles, mold, yeast, and coliforms were observed at 3.11, 0, and 1.47 log CFU/g in IRD 300 W and 3.17, 1, and 1.30 log CFU/g in RWD. D. kotschyi dried at CD 50°C had the maximum microbial contamination. Generally, according to the obtained results, RWD and IRD methods are suggested for drying of D. kotschyi and similar herbs due to shortening the drying time, preserving and improving the quality properties of dried plants.

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 in the production of instant baker's yeast and its effect on the quality characteristics of bread

The study aimed to produce instant dried baker's yeast (BY) by conventional or infrared-assisted refractance window drying (RWD or InfraRWD, respectively) and compare their bakery performance with commercial BY. According to the findings of the study, the total yeast count was higher than 9.60 log cfu/g in all dried BY samples, and the lowest viability was obtained in BY dried by InfraRWD at 50°C. In general, BY produced by RWD increased the physical quality parameters of bread such as specific volume, total cell count, and the number of cell areas of bread crumbs. Moreover, bread leavened by BY dried by RWD slowed down the staling rate of bread, while infrared assistance accelerated the staling. Sensorial analysis showed that bread produced by refractance window dried BY was more acceptable than commercial BY. In a conclusion, RWD can be an effective alternative to the production of instant baker's yeast, but the most quality features of BY has negatively affected by infrared assistance. PRACTICAL APPLICATION: In the drying of baker's yeast, promising advantages can be obtained by refractance window drying. The higher specific volume and superior bread crumb with a retarded staling rate were determined when bread was produced by the refractance window. This is the first time that RWD and InfraRWD have been used for the production of instant baker's yeast and it has several practical applications for bread quality.

Process and product characteristics of refractance window dried Curcuma longa

This work addresses the optimality of hot water bath based refractance window drying (RWD) characteristics of 1 mm Curcuma longa (turmeric) slices. Mylar film thickness (125 to 350 µm) and water bath temperature (65 to 95 °C) have been considered as independent variables to evaluate drying kinetics and nutritional characteristics of the process product combination. Equilibrium drying time, moisture diffusivity, fitness of thin layer models, moisture content, total phenolic content, total flavonoids content, curcumin content, and antioxidant activity have been considered to evaluate the optimality of the RWD process parameters. It has been analyzed that while both parameters critically influence equilibrium drying time, only temperature had profound influence on nutritional characteristics. PRACTICAL APPLICATION: There is a need for a fast-drying method without significant loss in bioactive compounds. Refractance window drying (RWD) method is such a process. The study of RWD of turmeric slices will help in understanding the relations between different drying temperatures and mylar film thickness and its relation to nutritional characteristics of the product.

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.