Effect of ultrasound and chemical pretreatment on drying characteristics and quality attributes of hot air dried pineapple slices

Effect of ultrasound combined with pineapple protease treatment on the tenderness of dried shrimp

BACKGROUND

In order to improve the tenderness of dried shrimp products as well as to reduce the hardness of the meat during the drying process, shrimp were treated with ultrasound combined with pineapple protease and the tenderization condition was optimized by measuring the texture and shear force of dried shrimp. In addition, the sulfhydryl content, myofibril fragmentation index (MFI) and microstructure were also examined to clarify the mechanisms of shrimp tenderization.

RESULTS

The results showed UB1 group with ultrasonic power of 100 W, heating temperature of 50 °C and pineapple protease concentration of 20 U mL-1 were the optimum tenderization conditions, where shrimp showed the lowest hardness (490.76 g) and shear force (2006.35 gf). Microstructure as well as sodium dodecyl sulfate-polyacrylamide gel electrophoresis results suggested that during the tenderization process the muscle segments of shrimps were broken, degradation of myofibrillar proteins occurred, and MFI values and total sulfhydryl content increased significantly (P < 0.05) (MFI value = 193.6 and total sulfhydryl content = 93.93 mmol mg-1 protein for UB 1 group).

CONCLUSION

Ultrasound combined with bromelain could be used as a simple and effective tenderization method for the production of tender dried shrimp. The best conditions were 100 W ultrasonic power, 50 °C ultrasonic temperature, and 20 U mL-1 bromelain. © 2024 Society of Chemical Industry.

Enzymatic treatment to improve permeability and quality of cherry tomatoes for production of dried products

BACKGROUND

Cherry tomatoes are nutritious and favored by consumers. Processing them into dried cherry tomatoes can prolong their storage life and improve their flavor. The pretreatment of tomato pericarp is crucial for the subsequent processing. However, the traditional physical and chemical treatments of tomato pericarp generally cause nutrient loss and environmental pollution.

RESULTS

In this study, a novel enzymatic method for cherry tomatoes was performed using mixed enzymes containing cutinase, cellulase and pectinase. Results showed that the pericarp permeability of cherry tomatoes was effectively improved due to enzymatic treatment. Changes in the microscopic structure and composition of the cuticle were revealed. After treatment with different concentrations of enzymes, cherry tomatoes exhibited higher pericarp permeability and sensory quality to varying degrees. The lycopene content and total polyphenol content significantly increased 2.4- and 1.45-fold, respectively. In addition, the satisfactory effect of the six-time reuse of enzymes on cherry tomatoes could still reach the same level as the initial effect, which effectively reduced the cost of production.

CONCLUSIONS

This study revealed for the first time that a mixed enzymatic treatment consisting of cutinase, pectinase and cellulase could effectively degrade the cuticle, enhance the pericarp permeability and improve the quality of cherry tomatoes, with the advantages of being mildly controllable and environmentally friendly, providing a new strategy for the processing of dried cherry tomatoes. © 2023 Society of Chemical Industry.

Influence of ultrasound pretreatment on drying characteristics of cocoyam (Xanthosoma sagittifolium) slices during convective hot air drying

BACKGROUND

Convective hot air drying of cocoyam is risk-free and inexpensive to a significant level. However, hot air drying causes negative changes to the color, texture, flavor and nutritional content of cocoyam as a result of the prolonged drying. Recently, the innovative technology of ultrasound pretreatment has been applied in food processing to reduce the processing time, conserve energy and preserve the quality of the food product. Thus, there is need to investigate the effect of ultrasound pretreatment with distilled water (UDW) and ultrasound with osmotic dehydration (UOD) for different ultrasonic times (10-30 min) on the drying kinetics of cocoyam slices during convective hot air drying. Ultrasound pretreatment was applied at a frequency of 20 kHz and an output power of 600 W for UDW and UOD. The ultrasound-pretreated samples were further dried in a convective hot-air drying oven at 70 °C.

RESULTS

UDW and UOD samples, respectively, had a 25% and 46% reduction in drying time compared to untreated samples. The UOD samples had the lowest activation energy (10.697 × 10 3 kJ), as well as the highest moisture diffusivity (3.782  × 10-10  m2  s-1 ) and mass transfer coefficient (2.006  × 10-8  m s-1 ), among the untreated and UDW samples. Wang and Singh, Page and Peleg models were found to be the most fitted models with respect to the drying characteristics of cocoyam for untreated, UDW and UOD samples, respectively.

CONCLUSION

Ultrasound pretreatment technology is a potential non-thermal process that can be incorporated as a pretreatment method in the convective drying of cocoyam to reduce processing time, conserve energy and enhance cocoyam product shelf life. © 2023 Society of Chemical Industry.

Optimum drying conditions for ginger (Zingiber officinale Roscoe) based on time, energy consumption and physicochemical quality

The effect of ultrasonic pre-treatment on moisture removal characteristics of ginger in a convective dryer was investigated. The slabs were dried by practicing sonication durations of 0, 15 and 30 min at different levels of the air temperature and velocity. Following increasing the sonication duration and air temperature, required time and energy to dehydrate the samples were decreased. The pre-treatment played important role in improving rehydration capability and surface color retention in the dried gingers. Content of the main volatile component (α-Zingiberene) was not influenced by the sonication. Mean values for the phenolic contents and antioxidant activity at sonication duration of 0, 15 and 30 min were determined to be 18.93, 18.15 and 17.49 GAE/g dry matter and 83.57, 78.33 and 74.58 %, respectively. The desired values for the temperature, velocity and sonication duration were revealed to be about 66 °C, 3 m/s and 20 min, respectively.

Individual and interactive effect of ultrasound pre-treatment on drying kinetics and biochemical qualities of food: A critical review

One of the earliest and most prevalent processing methods to increase the shelf-life of foods is drying. In recent years, there has been an increased demand to improve product quality while lowering processing times, expenses, and energy usage in the drying process. Pre-treatments are therefore effectively used before drying to enhance heat and mass transfer, increase drying efficiency, and lessen degradation of final product quality. When food is dried, changes are expected in its taste, color, texture, and physical, chemical, and microbial properties. This has led to the need for research and development into the creation of new and effective pre-treatment technologies including high-pressure processing, pulsed electric field, ultraviolet irradiation, and ultrasound. Sound waves that have a frequency >20 kHz, which is above the upper limit of the audible frequency range, are referred to as "ultrasound". Ultrasonication (US) is a non-thermal technology, that has mechanical, cavitational, and sponge effects on food materials. Ultrasound pre-treatment enhances the drying characteristics by producing microchannels in the food tissue, facilitating internal moisture diffusion in the finished product, and lowering the barrier to water migration. The goal of ultrasound pre-treatment is to save processing time, conserve energy, and enhance the quality, safety, and shelf-life of food products. This study presents a comprehensive overview of the fundamentals of ultrasound, its mechanism, and how the individual effects of ultrasonic pre-treatment and the interactive effects of ultrasound-assisted technologies affect the drying kinetics, bioactive components, color, textural, and sensory qualities of food. The difficulties that can arise when using ultrasound technology as a drying pretreatment approach, such as inadequate management of heat, the employment of ultrasound at a limited frequency, and the generation of free radicals, have also been explained.

Effect of drying methods on physico-chemical and bioactive compounds of mandarin (citrus reticulata) peel

Mandarin peel, an agro waste has an immense potential for bio utilization. The present study highlights the effect of drying on the physicochemical and biochemical properties of dried mandarin peel. Microwave drying and forced air drying accomplished at three different power levels (180, 360 and 540 W) and temperatures (30, 50 and 70 °C), respectively, while freeze drying was carried out at shelf temperature of –35 °C. The results revealed highest recovery of bioactive compounds from microwave drying at 540 W viz total phenolic (43.61 mg GAE/g), flavonoid (8.08 mg QE/g), tannin (8.73 mg GAE/g), saponin (159.91 mg EE/g−1), as well as, gallic acid antioxidant activity (3.58 mg GAEAC/g) and ferric reducing antioxidant power (50.61 mg TE/g−1). Furthermore, results from HPLC and UV–vis spectroscopy revealed presence of major polyphenols in dried peel. Microwave drying can be concluded as an industrial method for the bio utilization of mandarin peel.

Multi-frequency power ultrasound as a novel approach improves intermediate-wave infrared drying process and quality attributes of pineapple slices

This study evaluated the effect of mono-frequency ultrasound (MFU, 20 kHz), dual-frequency ultrasound (DFU, 20/40 kHz), and tri-frequency ultrasound (TFU, 20/40/60 kHz) on mass transfer, drying kinetics, and quality properties of infrared-dried pineapple slices. Pretreatments were conducted in distilled water (US), 35 °Brix sucrose solution (US-OD), and 75% (v/v) ethanol solution (US-ET). Results indicated that ultrasound pretreatments modified the microstructure of slices and shortened drying times. Compared to the control group, ultrasound application reduced drying time by 19.01-28.8% for US, 15.33-24.41% for US-OD, and 38.88-42.76% for US-ET. Tri-frequency ultrasound provoked the largest reductions, which exhibited time reductions of 6.36-11.20% and better product quality compared to MFU. Pretreatments increased color changes and loss of bioactive compounds compared to the control but improved the flavor profile and enzyme inactivation. Among pretreated sample groups, US-OD slices had lower browning and rehydration abilities, higher hardness values, and better retention of nutrients and bioactive compounds. Therefore, the combination of TFU and osmotic dehydration could simultaneously improve ultrasound efficacy, reduce drying time, and produce quality products.

Influence of Ultrasound Application in Fermented Pineapple Peel on Total Phenolic Content and Antioxidant Activity

Antioxidant phenolic compounds were extracted from fermented samples of Golden pineapple peels via an ultrasound method. The fermentation conditions to maximize the production of phenolic content and antioxidant activity were previously determined (pH: 5.5, T: 37.3 °C and 85% moisture content). A central composite design with 20 treatments was applied to evaluate the effect of the ethanol concentration, time, and temperature on the production of phenolic compounds and antioxidant activity of the extracts. The statistical analysis showed that the optimal conditions to produce extracts with high phenolic content and antioxidant activity were: 62 °C, 30 min and 58% ethanol. We obtained 866.26 mg gallic acid equivalents (GAE)/g d.m in total phenolic content and for antioxidant activity expressed as percentage inhibition, 80.06 ± 1.02% for ABTS and 63.53 ± 2.02% for DPPH, respectively. The bioactive compound profile in the extracts was identified and quantified using ultra-high performance liquid chromatography (UHPLC), this method showed the presence of rosmarinic acid, caffeic acid, vanillic acid, p-coumaric acid, ferulic acid, quercetin-3 glucoside, rutine, quercetin, kaempherol-3 glucoside and gallic acid, demonstrating the great potential of these by-products to obtain components that can benefit the consumer’s health.

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.

Osmo-air drying of banana slices: multivariate analysis, process optimization and product quality characterization

In the present work, osmotic dehydration (OD) was applied as a pretreatment to hot air drying of banana slices and the effect of OD parameters on mass transfer characteristics, color profile was analysed. Principal component analysis (PCA) of OD process revealed that solid gain, weight reduction, water loss and total soluble solids were positively correlated with each other but were found to be negatively correlated with moisture content (MC) of sample. Response surface methodology was used for optimizing the OD of banana slices and and the optimum conditions were 61.26°Brix sucrose concentration at 50 °C for 6 h, resulting in moisture reduction from 75 to 49.78%. PCA-biplot of osmo-air drying (OAD) process showed the association among response parameters, which further revealed a positive correlation of MC with bioactive components. Additionally, OAD samples were also studied for microstructure and Fourier Transform Infra-red analysis. Addition of calcium lactate to sucrose solution resulted in preserving the firmness and bioactive components during osmosis, in addition to fortifying the sample with calcium. The present study provides new possibilities for food industries in preserving the ripe banana and developing calcium fortified functional food products.

Developing ultrasound-assisted hot-air and infrared drying technology for sweet potatoes

The influence of ultrasound (US) pretreatments combined with infrared (IRD) and hot-air (HAD) drying on drying kinetics, mathematical modeling, bioactive compounds (antioxidant activities, Vitamin C, phenolics, and flavonoid contents), qualitative properties (β-carotene, total carotenoids, color indexes, textural profile), enzyme inactivation, and exergetic analysis of sweet potatoes. The US pretreatment at 40 kHz combined with IRD and HAD (70 °C) significantly lessened the drying time and water contents. Besides, it did not affect the sweet potato's bioactive components and other quality-related attributes. The samples' activation energy (E_a) ranged from 17.60 to 29.86 kJ/mol for both dryers, with R² (0.999-0.9809). Control samples had the highest specific energy consumption (SEC) due to the extended drying period, whereas ultrasound (40 kHz) treated samples had the lowest SEC during HAD and IRD at 80 °C. The thermodynamic parameters indicated that increasing the drying temperature lowers the enthalpy and Gibbs free energy, while entropy resulted in negative values. HAD had better textural qualities (hardness and resilience). The US pretreatments followed by HAD or IRD may lead to an energy-efficient method with acceptable quality maintenance.

Hot air convective drying of hog plum fruit (Spondias mombin): effects of physical and edible-oil-aided chemical pretreatments on drying and quality characteristics

This aim of this study was to evaluate the effects of pretreatments and temperature on the hot air drying characteristics of hog plum fruits. Hog plum fruits were pretreated with olive oil/K₂CO₃ or sunflower oil/K₂CO₃ at 28 °C and olive oil/NaOH cum blanching at 96 °C for 15s, hot water at 96 °C for 15s, and dried in a hot air drier at 50, 60, and 70 °C. Mathematical models were used to fit the data of drying and rehydration kinetics. Results showed that increase in temperature reduced drying time, increased effective diffusivity and shrinkage. Sunflower oil aided chemical pretreated sample had the shortest drying time (780 min) and highest effective diffusivity (6.3 × 10⁻⁸ m²/s) at 60 °C, faster rehydration ability at 60 °C, highest retention rate for ascorbic acid (15 %), phenolic content (29 %), and antioxidant activity (12.3 %), while olive oil aided chemical (K₂CO₃) pretreated sample had the shortest drying time at 50 °C (990 min) and 70 °C (600 min), lowest shrinkage (48.5 %), slower rehydration capacity at 40 °C, and lowest colour change (ΔE = 11.5). Modified Henderson and Pabis and Vega-Gálvez were superior to other fitting models in predicting the drying and rehydration kinetics. Sunflower oil/K₂CO₃ pretreatment could help improve the drying and quality characteristics of hog plum.

Application of immersion pre-treatments and drying temperatures to improve the comprehensive quality of pineapple (Ananas comosus) slices

Drying of pineapple slices combined with different pre-treatments was done to reduce various adverse changes by adding satisfactory value. Process optimization was done by dipping the pineapple slices in four different solutions (1% trehalose, 2% NaCl, 10% sucrose, and 10% fructose) before drying. The effects of different pre-treatments and drying temperatures of 50, 55, and 60 °C with a constant 30% relative humidity (RH) were optimized based on the quality attributes, drying time and microbial load of dried pineapple slices. The optimal drying temperature was 55 °C using 1% trehalose pre-treatments based on the physical and biochemical properties. The reconstituted dried pineapples implied at this condition, contributed to the better structure preservation as indicated by the lower shrinkage (0.21) and the higher Coefficient of Rehydration (0.941), and rehydration ratio (6.840). On the other hand, the retention of color, vitamin C, B vitamins, and antioxidant activity of the samples were decreased by increasing drying time and temperatures. The highest Total Phenolic Content (121.02 mg GAE/100g), Total Flavonoid Content (8.72 mg QE/100g), and DPPH radical scavenging activity (7.22 EC50 g/100g) were found at 60 °C drying temperature with 10% fructose pretreatment's samples. The lowest drying time required was 7.64 h using 2% NaCl pre-treatment at 60 °C, considering the time required to reach 20% moisture content in the dried product at 30% RH. Based on the reported results, it is concluded that 1% trehalose at 50 °C can be used to develop high quality pineapple snacks, which maintained the maximum desired physicochemical and nutritious properties. This study could play an essential role in meeting the emerging demand of developing good quality nutritious dried pineapple snacks.

Modelling of moisture migration during convective drying of pineapple slice considering non-isotropic shrinkage and variable transport properties

The present work aims to develop a 3-dimensional finite element (FE) model to analyze moisture migration during drying of pineapple ring considering moisture dependent diffusion coefficient (D) and mass transfer coefficient (h_m) along with radial and longitudinal shrinkage. Pineapple rings were dried at 70 °C temperature and 0.6 m/s air velocity to study the moisture loss and shrinkage kinetics during drying. Thickness, outer radius and inner radius of hollow cylindrical pineapple slices were reduced by 79.3%, 32.2%, and 51.2%, respectively due to the occurrence of shrinkage during drying. Non-linear regression analysis showed the quadratic model to best fitted to the experimental moisture ratio data for explaining the shrinkage phenomenon in pineapple slice during drying. Shrinkage was accommodated into FE modelling using the arbitrary lagrange-eulerian method. Consideration of variable D showed better agreement with the experimental data than consideration of constant D, however constant and variable h_m predicted similar results. Incorporation of shrinkage phenomena during modelling led to prediction of more accurate result showing 0.06% deviation from experimental curve, but neglecting the shrinkage resulted in a 17% deviation. Hence, model developed with consideration of shrinkage along with variable D and h_m presented best fit with experimental drying curve. Developed model allowed the visualization of spatial moisture profile within the sample during drying, which would be useful for estimating the correct drying time, optimizing and designing of drying process.