Effect of Combined Infrared and Hot Air Drying Strategies on the Quality of Chrysanthemum (Chrysanthemum morifolium Ramat.) Cakes: Drying Behavior, Aroma Profiles and Phenolic Compounds

Dynamic changes of drying behavior, physicochemical quality, and volatile oil of Exocarpium citri grandis under different drying temperatures

Drying is the primary processing step in Exocarpium citri grandis (ECG), yet its quality changes throughout the drying process have not been elucidated. Dynamic changes of drying behavior, structure, color, active components, antioxidant properties, and volatile oil in ECG under different drying temperatures (50, 60, 70, and 80°C) were investigated, and the quality change mechanism was revealed. Results showed that the moisture ratio decreased rapidly and that structural damage occurred as moisture content decreased from 1.0000 to 0.2175 g/g (on a dry basis, d.b.), which accelerated flavonoids, polysaccharides, volatile oil, and antioxidant activity degradation, whereas levels of naringin and rhoifolin were increased. The above quality change process was accelerated with the increasing temperature. Correlation analysis revealed that active components had a synergistic effect on antioxidant activity, and the total color difference (ΔE) value and that active components could be well fitted by a linear mathematical model with correlation coefficient (R2) of 0.7749-0.9781. Moreover, all the indicators were uniformly quantified using comprehensive evaluation method to obtain a comprehensive score, which was the highest (0.57) at 70°C, with high drying efficiency, well quality, and low energy consumption. The biosynthesis pathway verified that the species of volatile oil components increased, including newly terpenes, alcohols, aldehydes, esters, and others after 0.2175 g/g. This study revealed that the total content of active components in ECG decreased before 0.2175 g/g, and then the metabolite content and species increased during drying, as well as obtained the optimal drying temperature (70°C).

Edible flowers' flavor, safety and their utilization as functional ingredients: a review

Edible flowers have been a part of various traditional dishes around the world. The consumption of edible flowers has been rising due to their nutritional properties, minerals, antioxidants, phenolic and bioactive compounds, therapeutic properties, and also aesthetic appeal. Along with the nutrients, some antinutrients and other chemical, biological, microbial hazards may render flowers non-edible. The components responsible for flavor in edible flowers are different from species to species. Bioactive compounds play a major role in sensory attributes of edible flowers. Various functional food products such as bakery items, dairy products, beverages etc. can be developed by incorporating edible flowers. Understanding various properties of edible flowers, their safe consumption, and utilization as functional ingredients in the development of various food products is not only useful but also necessary to popularize edible flowers for novel applications. It is important for food safety experts to recognize and reduce the risks connected with edible flowers.

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Program temperature-controlled drying: An effective way to improve the quality of hot-air dried shiitake mushrooms

This study applied program temperature-controlled drying (PTCD) to optimize the hot-air drying process for shiitake mushrooms, adjusting the drying temperature based on activity changes of γ-glutamyl transpeptidase (γ-GTase) and cysteine sulfoxide lyase (C-S lyase). Compared with constant temperature drying, PTCD (ST_75 and ST_150) significantly enhanced the umami and aroma profiles and sulfur compounds, increasing the levels of key flavor compounds such as glutamic acid and 5'-GMP. Moreover, PTCD improved rehydration capacity (515.17%) and reduced shrinkage (12.43%) for ST_150 samples, achieving superior texture and color retention. Nutritional analysis indicated that PTCD better preserved nutrients such as ergothioneine, ergosterol, and purines, with ergosterol content reaching 9953.22 µg/g in the ST_150 group. This study provides theoretical support for improving the quality of hot-air-dried shiitake mushrooms in industrial applications. PRACTICAL APPLICATION: Although hot air drying is widely used for mushrooms, it is typically conducted using constant temperature methods. The application of PTCD and its effects on mushroom product quality have been scarcely studied. This study proved that compared with constant drying temperature, PTCD could significantly improve the flavor, texture, and nutrition retention of dried products. This may provide scientific foundation for the industrial application of hot air drying of shiitake mushrooms with improved quality.

Chrysanthemum morifolium Ramat. as a traditional tea material: Unraveling the influence of kill-green process on drying characteristics, phytochemical compounds, and volatile profile

The dried capitulum of chrysanthemums is a traditional material in scented tea, and the kill-green process is a critical step in determining their quality. However, the changes in the physicochemical properties during kill-green and the mechanisms by which these changes affect drying characteristics, metabolic components, and aroma profiles remain unclear. Therefore, this study investigated the changes in water status, polyphenol oxidase and peroxidase activities, and microstructure during high-humidity air impingement kill-green (HHAIK) and steam kill-green (SK), and their effects on drying behavior, color, phytochemicals, and volatile profile of dried chrysanthemums. Results showed that the kill-green process increased the freedom degree of immobile water, reduced the relative content of free water, and induced microstructure alterations, thus enhancing the water diffusion and shortening the subsequent drying time by up to 46.15 %. Compared to SK, HHAIK more rapidly inactivated PPO and POD, causing an improved color profile of dried samples. Dried samples treated with HHAIK for 60 s exhibited higher retention of 9 individual phenolics, total sugar, amino acids, and volatile compounds, thus resulting in higher sensorial acceptance than those treated with SK for 60 s. This study offers theoretical insights and technical support for the future development of high-quality chrysanthemum products.

Effects of combined drying techniques and cellulase hydrolysis on the nutritional value and sensory properties of shiitake mushrooms (Lentinus edodes)

Dried shiitake mushrooms offer rich nutritional value and unique sensory properties, prompting further investigation. The effects of different drying techniques (hot air drying (HAD), infrared hot air drying (IRHAD), pulsed vacuum drying (PVD), vacuum freeze drying (VFD), and natural drying (ND)) combined with enzymatic hydrolysis on the release of flavor compounds and nutrients from shiitake mushrooms were explored. The combination of HAD with cellulase hydrolysis yielded notably high levels of umami amino acids (5.4723 ± 0.1501 mg/g) and 5'-nucleotides (4.0536 ± 0.0062 mg/g), and superior volatile flavors. Combined with cellulase hydrolysis, IRHAD achieved the highest level of total sugars (6.57 ± 0.34 mg/mL), VFD resulted in the greatest soluble protein content (153.21 ± 0.23 μg/mL), PVD yielded the highest total phenolics content (93.20 ± 0.41 μg GAE/mL), and ND produced the maximum reducing sugar content (5.79 ± 0.13 mg/mL). This study addresses crucial gap in the post-drying processing of shiitake mushrooms, offering valuable insights for further product development of shiitake mushrooms.

Advancement and Innovations in Drying of Biopharmaceuticals, Nutraceuticals, and Functional Foods

Drying is a crucial unit operation within the functional foods and biopharmaceutical industries, acting as a fundamental preservation technique and a mechanism to maintain these products' bioactive components and nutritional values. The heat-sensitive bioactive components, which carry critical quality attributes, necessitate a meticulous selection of drying methods and conditions backed by robust research. In this review, we investigate challenges associated with drying these heat-sensitive materials and examine the impact of various drying methods. Our thorough research extensively covers ten notable drying methods: heat pump drying, freeze-drying, spray drying, vacuum drying, fluidized bed drying, superheated steam drying, infrared drying, microwave drying, osmotic drying, vacuum drying, and supercritical fluid drying. Each method is tailored to address the requirements of specific functional foods and biopharmaceuticals and provides a comprehensive account of each technique's inherent advantages and potential limitations. Further, the review ventures into the exploration of combined hybrid drying techniques and smart drying technologies with industry 4.0 tools such as automation, AI, machine learning, IoT, and cyber-physical systems. These innovative methods are designed to enhance product performance and elevate the quality of the final product in the drying of functional foods and biopharmaceuticals. Through a thorough survey of the drying landscape, this review illuminates the intricacies of these operations and underscores their pivotal role in functional foods and biopharmaceutical production.

Revealing the mechanism of post-harvest processing on rose quality based on dynamic changes in water content, enzyme activity, volatile and non-volatile metabolites

Existing studies on post-harvest processing of edible roses have mainly focused on processing techniques and physicochemical properties of the final dried products, with limited studies on how changes in metabolites during processing affect the quality of these products. This study investigated changes in water content and status, enzyme activity, phenolic compounds, and volatile and non-volatile compounds during processing and revealed the mechanisms by which post-harvest processing (drying without blanching (WBD) and drying with blanching (BD)) affects the quality of dried roses by establishing their correlations. Results showed that the blanching reduced the relative content of free water and water activity, thus reducing the subsequent drying time and enzyme activity. The BD method caused higher levels of phenolic compounds than the WBD method in terms of gallic acid, ellagic acid, epicatechin, and quercetin. The OPLS-DA analysis identified 6 differential volatiles out of 72 detected volatiles, contributing to the unique aroma of dried roses by activating olfactory receptors through hydrogen bonding and hydrophobic interactions. 58 differential metabolites were screened from 964 non-volatile metabolites. KEGG pathway analysis revealed that the changes in volatile and non-volatile metabolites induced by different processing methods were due to the effect of blanching on glutathione and fatty acid metabolism. These findings provide a comprehensive understanding of how post-harvest processing affects the quality of dried roses.

Characterization of the Aroma Profile of Ginger Powder Produced by a Split-Stream Spray-Drying Process

Freeze-dried ginger (Zingiber officinale) is renowned for its high quality, but it is expensive. As an alternative, spray drying can be explored for producing ginger powder. However, sugar rich feed solutions can lead to stickiness development during the process. Adding carrier materials increases costs and labeling. Accordingly, a split-stream spray-drying process was developed, where ginger fibers in their natural composition were reintroduced as a carrier material into the spray-drying process. The inlet and outlet temperatures were set at 220 and 80 °C, respectively, for optimal aroma retention. Using a stir bar sorptive extraction-gas chromatography-mass spectrometry-olfactometry, the results revealed that reintegrating ginger fibers significantly increased the concentration of eight key odorants. Although freeze-dried ginger retains more aroma, the total concentration of twenty-seven odorants in the developed spray-dried ginger was 1.9 times higher compared to frozen ginger.

Drying kinetic, thermodynamic and quality analyses of infrared drying of truffle slices

Kinetic and thermodynamic parameters are the most important part for making a suitable tool for drying agricultural products. Moreover, calculation of the energy required for the drying of product, the properties of the rehydration ratio, the food appearance changes, and the evaluation of the microstructure of food are crucial. Since the thermodynamic properties of truffle slices have not yet been reported, this study aims to establish a mathematical model to describe drying process of agriculture product, evaluate the effective moisture diffusion coefficient (Deff), determining the activation energy (Ea) to elucidate the thermodynamic characteristics, measure color characteristics, and rehydration ratio (RR) during the drying process of truffle slices. Truffle slices were dried in an infrared (IR) dryer at four temperatures of 50-80°C and two thicknesses of 0.5 and 1 cm. The best model to describe the drying process of truffle slices was Midilli et al.'s model. The value of Deff, SEC, and RR were in the range of 3.06 × 10-8 to 2.48 × 10-7 m2/s, 79.68-191.271 kWh/kg, and 5.99-7.49, respectively. The Deff of truffle slices increased with the above-mentioned parameters of the samples. The Ea obtained was 26.62-27.43 kJ/mol. The results indicated that enthalpy and entropy decreased with increasing drying temperature, while Gibbs free energy improved. The enthalpy, entropy, and Gibbs free energy values changed between 24.48-25.28 kJ/mol, -130.47 to -122.63 J/mol °K, and 63.97-70.17 kJ/mol, respectively. In addition, the results of color attributes decreased with increasing temperature, while chroma oppositely increased.

Effect of constant and variable temperature drying processes on drying characteristics, quality, and volatile profile of rose petals in infrared-assisted spouted bed drying

The edible rose (Rosa Crimson Glory) petals were dried using infrared-assisted spouted bed drying technology. The effects of different drying temperature conditions (30, 35, 40, 45, and 50°C, as well as stepped heating drying [SHD] and stepped cooling drying) on the drying characteristics, physicochemical properties, antioxidant capacity, and changes in volatile flavor compounds of the rose petals were investigated. The results showed that the drying time was shortened with increasing drying temperature. Both variable temperature drying processes gave the shortest drying times. Optimal color retention of rose petals was achieved at a constant temperature of 40°C and SHD. Increased drying temperature resulted in higher water-soluble polysaccharide content in the dried rose petals, whereas lower temperatures facilitated anthocyanin preservation. The variable temperature drying processes favored the retention of water-soluble polysaccharides in rose petals, but not anthocyanins. Regarding antioxidant capacity, the samples dried at 40°C and those subjected to the two variable temperature drying processes performed better. This study also analyzed the differences in volatile flavor compounds of rose petals dried under different drying conditions. It was found that the majority of volatile flavor compounds in the rose petals dried by SHD exhibited higher content levels than the other drying conditions. Therefore, considering a thorough evaluation of all relevant factors, it was clear that utilizing the SHD process was the most efficient method for obtaining the best quality rose petals overall.

The effectiveness of hot-air, infrared and hybrid drying techniques for lemongrass: appearance acceptability, essential oil yield, and volatile compound preservation

Lemongrass is a fragrant herb with lengthy, thin leaves that contains myrcene (an aromatic compound) as well as citral and geraniol (antimicrobial compounds). Therefore, identifying an appropriate drying method for this plant is crucial for maintaining aromatic and antimicrobial compounds and enhancing the shelf life of the product. This investigation seeks to assess the influence of various drying tactics involving hot air at temperatures of 40, 50, and 60 °C, infrared radiation at intensities of 0.5, 0.6, and 0.8 [Formula: see text], sequential hot-air/infrared, as well as simultaneous hot air-infrared, on the drying mechanism, color, appearance, yield, and essential oil constituents of lemongrass leaves, with the objective of enhancing the marketability of the product. The essential oils of lemongrass were extracted through the process of hydro-distillation, and subsequently, the volatile compounds present were analyzed using Gas Chromatography-Mass Spectrometry (GC-MS). The findings indicated: (a) The most appropriate technique for preserving optimal color quality of lemongrass leaves was through the application of hot air drying solely at a temperature of 60 °C; (b) To optimize the retention and amplification of the essential oil content in lemongrass, our study recommends the employment of a simultaneous hybrid drying technique involving hot air drying at a temperature of 50 °C in conjunction with infrared drying set at a radiation intensity level of 0.6 [Formula: see text]; and (c) The data analysis demonstrated that in order to achieve elevated levels of volatile compounds, specifically neral and geranial, infrared drying with a radiation intensity of 0.6 and 0.8 [Formula: see text], respectively, was found to be optimal.

Effect of Combined Infrared Hot Air Drying on Yam Slices: Drying Kinetics, Energy Consumption, Microstructure, and Nutrient Composition

Using hot air drying (HAD) and combined infrared hot air drying (IR-HAD) test devices, the drying kinetics, unit energy consumption, color difference values, rehydration rate, microstructure, and changes in polysaccharide and allantoin contents of yam slices were examined at various temperatures (50 °C, 55 °C, 60 °C, 65 °C, and 70 °C). The findings demonstrated that each of the aforementioned parameters was significantly impacted by the drying temperature. IR-HAD dries quicker and takes less time to dry than HAD. The Deff of IR-HAD is higher than that of HAD at the same temperature and increases with the increase in temperature. The activation energy required for IR-HAD (26.35 kJ/mol) is lower than that required for HAD (32.53 kJ/mol). HAD uses more energy per unit than IR-HAD by a factor of greater than 1.3. Yam slices treated with IR-HAD had higher microscopic porosity, better rehydration, lower color difference values, and higher polysaccharide and allantoin levels than HAD-treated yam slices. The IR-HAD at 60 °C had the greatest comprehensive rating after a thorough analysis of the dried yam slices using the coefficient of variation method. Three statistical indicators were used to evaluate six thin-layer drying models, and the Weibull model was most applicable to describe the variation of drying characteristics of yam slices.

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.

Response Surface Methodology Approach for Predicting Convective/Infrared Drying, Quality, Bioactive and Vitamin C Characteristics of Pumpkin Slices

In this research, a convective/infrared (CV/IR) dryer was used to dry pumpkin slices. For optimization of the drying conditions, the influence of three levels of independent variables including air temperature (40, 55, and 70 °C), air velocity (0.5, 1, and 1.5 m/s), and IR power (250, 500, and 750 W) were assessed by response surface method (RSM) through a face-centered central composite design. Analysis of variance (non-fitting factor and R² value) was employed to determine the desirability of the model. Response surfaces and diagrams were also utilized to show the interactive influence of the independent variables with the response variables (drying time, energy consumption, shrinkage, total color variation, rehydration ratio, total phenol, antioxidant, and vitamin C contents). According to the results, optimal drying conditions involved a temperature of 70 °C, air velocity of 0.69 m/s, and IR power of 750 W. At the mentioned conditions, response variables of drying time, energy consumption, shrinkage, color, rehydration ratio, total phenol, antioxidant, and vitamin C contents were 72.53 min, 24.52 MJ/kg, 23%, 14.74, 4.97, 617.97 mg GA/100 g dw, 81.57%, and 4.02 mg/g dw, with a confidence level of 0.948, respectively.

Mathematical Modelling of Convective Drying of Orange By-Product and Its Influence on Phenolic Compounds and Ascorbic Acid Content, and Its Antioxidant Activity

Orange peel is one of the main by-products from juice processing, and is considered as a promising source of phenolic compounds with anti-carcinogenic, anti-inflammatory, anti-microbial and antioxidant properties. The drying is an essential step to ensure the storage of this by-product at an industrial level, in order to use it as a functional ingredient or as a nutraceutical. Thus, this research focuses on the evaluation of the effect of the convective air-drying process in orange by-products at three different temperatures (40, 60 and 80 °C) and air flows (0, 0.8 and 1.6 m/s) on the phenolic content (measured by HPLC-MS), the antioxidant activity (measured by DPPH, ABTS and FRAP), and the vitamin C content (measured by HPLC-UV/VIS). Moreover, the mathematical modelling of its drying kinetics was carried out to examine the orange by-product behavior. Among the tested mathematical models, the Page model reported the highest fit and the best drying conditions, which showed the lowest reductions were at 60 °C with an air flow of 1.6 m/s and taking 315 min.

Multi-Response Optimization of Pyrrolizidine Alkaloids Removal from Chrysanthemum morifolium by High-Pressure Extraction

As an ingredient in various foods, Chrysanthemum morifolium flower is popular due to its multiple health benefits. Pyrrolizidine alkaloids (PAs) are hepatotoxic secondary metabolites in Chrysanthemum family. Effects of high-pressure extraction (HPE) on PAs removal efficiency, as well as the retention efficiency of functional components, including chlorogenic acid, luteolin-7-β-D-glucopyranoside, 3,5-dicaffeyl quinic acid and total flavonoids, were investigated and optimized using response surface methodology (RSM). Pressure (0.1-200 MPa), numbers of cycles (1-5) and acetic acid concentration (0-10%) were chosen as the independent variables. The results indicated that the pressure was the most significant factors affecting all responses. The optimum HPE for removing Pas and retaining functional components were set at 124 MPa, with one cycle and with an acetic acid concentration of 10%. After comparing the experimental optimum values and predicted optimum values, the validity of RSM model was proved.

Prediction of Apple Slices Drying Kinetic during Infrared-Assisted-Hot Air Drying by Deep Neural Networks

The effects of temperature, air velocity, and infrared radiation distances on the drying characteristics and quality of apple slices were investigated using infrared-assisted-hot air drying (IRAHAD). Drying temperature and air velocity had remarkable effects on the drying kinetics, color, total phenol content, total flavonoid content, and vitamin C content (VCC) of apple slices. Infrared radiation distance demonstrated similar results, other than for VCC and color. The shortest drying time was obtained at 70 °C, air velocity of 3 m/s and infrared radiation distance of 10 cm. A deep neural network (DNN) was developed, based on 4526 groups of apple slice drying data, and was applied to predict changes in moisture ratio (MR) and dry basis moisture content (DBMC) of apple slices during drying. DNN predicted that the coefficient of determination (R2) was 0.9975 and 1.0000, and the mean absolute error (MAE) was 0.001100 and 0.000127, for MR and DBMC, respectively. Furthermore, DNN obtained the highest R2 and lowest MAE values when compared with multilayer perceptron (MLP) and support vector regression (SVR). Therefore, DNN can provide new ideas for the rapid detection of apple moisture and guide apple processing in order to improve quality and intelligent control in the drying process.

Hot-Air Flow Rolling Dry-Blanching Pretreatment Improves the Drying Quality of Acanthopanax sessiliflorus by Increasing the Drying Rate and Inactivating Enzymes

The processing of Acanthopanax sessiliflorus has attracted interest due to its health benefits. In this work, an emerging blanching technology, called hot-air flow rolling dry-blanching (HMRDB), was employed to treat A. sessiliflorus before drying. The effects of varied blanching times (2–8 min) on enzyme inactivation, drying characteristics, bioactive compound retention, and microstructure were examined. The results demonstrated that blanching for 8 min rendered polyphenol oxidase and peroxidase nearly inactive. The blanching process reduced the drying time of samples by up to 57.89% compared to an unblanched sample. The Logarithmic model showed good fitting performance for the drying curves. The total phenolic and flavonoid content of the dried product increased as blanching time increased. The total anthocyanin content of the samples blanched for 6 min was 3.9 times higher than that of the unblanched samples, and 8 min of blanching produced the greatest DPPH• and ABTS• scavenging capabilities. The retention of active compounds in a dried product is a result of the inactivation of enzymes and a reduced drying period. Changes in the porous structure of the blanched samples would be responsible for the accelerated drying rate, according to microstructural analysis. These results indicate that HMRDB enhances the drying process and improves drying quality when applied to A. sessiliflorus before drying.