Hot Air Treatment Research Articles

Contributions of Varna physicians in the field of thalassotherapy. Dr. Ivan Teodorov (1856-1934)

Dr Ivan Teodorov practiced in the state hospital in Varna until 1904. In 1907 he co-wrote with Dr. Iv. Farashov opened the first private physiotherapeutical hospital in Bulgaria with 20 beds for lying patients. A number of phaeoterapeutical methods of treatment are used: electrotherapy, mehano-therapy and massage, pneumotherapy, light therapy, inhalation treatment, hot air treatment, cold rays, seaside baths and hot baths with sea and freshwater all year round, sun and mud bathrooms. The main healing factor is the superb sea climate. Dr. Theodorov devotes a significant part of his creative work to sea treatment and sea prophylaxis, as a powerful factor for the preservation and restoration of human health.

Development of superhydrophobic coatings on AISI 304 austenitic stainless steel with different surface pretreatments

In the context of increasing industrial importance of superhydrophobic surfaces, three different pretreatments on an austenitic stainless steel surface have been tested to be coated with a silane-based solution containing SiO2 nanoparticles, in order to obtain superhydrophobic surfaces. The pretreatments are (i) an acetone degreaser, (ii) this one followed by a hot air treatment and acid pickling, and (iii) the previous one followed by an alkaline etching. Pretreated surfaces have been characterized by X-ray photoelectron spectroscopy, tapping-mode atomic force microscopy and contact angle measurements. After the three pretreatments, a solution of methyltrimethoxysilane and tetraethoxysilane in white spirit solvent and 1% of SiO2 (% by wt.) has been used to prepare a superhydrophobic coating on them. The hydrophobicity of the developed coatings has been studied using water contact angle measurements (static angles and advancing and receding angles). Besides, scanning electron microscope has been used to study the coatings. The results show that different tailored surfaces can be obtained in stainless steels using these pretreatments, obtaining surfaces that exhibit different physicochemical characteristics that may condition the formation of superhydrophobic coatings on them.

Effects of hot air treatment and chitosan coating on citric acid metabolism in ponkan fruit during cold storage.

In citrus fruit, citric acid is the predominant organic acid which influence fruit taste, flavor and quality. The effect of hot air treatment (HAT 40°C, 48 h) and 1.0% chitosan coating on the change of organic acids and the related gene expression of citric acid synthesis and degradation in ponkan (Citrus reticulata Blanco) fruit during cold storage have been studied. The results showed that citric acid was the main organic acid in fruit, the trend change of citric acid content was consistent with total organic acids and titratable acidity (TA) content, which decreased with the prolongation of storage time, hot air treatment significantly promoted but chitosan coating treatment significantly delayed citric acid degradation in Ponkan fruit. Hot air treatment could induced CitAco2/3, CitIDH2/3, CitGAD4, CitACLs, CitPEPCKs and CitFBPases expression during fruit storage period, but had no significant effect on CitGSs expression, The enhanced expression of degradation-related genes was closely related to the degradation of citric acid. The expressions of CitAco3, CitGAD4 CitACLα2/β, CitPEPCKs and CitFBPases were inhibited, which leading to the degradation rate of citric acid was slowed by chitosan coating during storage. These results showed that the degradation of citric acid in fruit was regulated by ATP citrate lyase (ACL) pathway and γ-aminobutyric acid (GABA) pathway.

Characteristic volatiles fingerprints and changes of volatile compounds in fresh and dried Tricholoma matsutake Singer by HS-GC-IMS and HS-SPME-GC–MS

The present study was to analyze the water dynamics of Tricholoma matsutake Singer during hot air drying by low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI), and to investigate the volatile compounds in the pileus, upper stipe and lower stipe of fresh and dried Tricholoma matsutake Singer by headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) and headspace solid-phase microextraction-gas chromatography–mass spectrometry (HS-SPME-GC–MS). Fresh samples were dried at 60 °C for 12 h. With the T2i relaxation times decreasing, the water migrated from the inner toward the periphery and then expelled during drying. The characteristic volatiles fingerprints of different parts of fresh and dried samples were established by HS-GC-IMS. The significant differences in volatile compounds were observed among different parts of the fresh sample and C8 compounds (70%–97%) were the principal components. After drying, the concentration of C8 compounds dramatically decreased and some volatile compounds (hexanal, heptanal, 2(5H)-furanone, acetophenone, nonanal, benzeneacetaldehyde) were formed. Thus, hot air treatment affected the volatile compounds in Tricholoma matsutake Singer.

Disinfestation of Chickpea and Green Gram from Callosobruchus maculatus Adults Through Hot-Air-Assisted Microwave Heating System

Pulse bruchid-infested samples of green gram (Vigna radiata) and chickpea (Cicer arietinum) having different moisture contents (7.5–9.5% wb) (1 cm bed depth) were exposed to microwave–hot air treatment for different exposure times (3 min 20 s to 6 min) and hot air temperatures (40–60 °C). Protein content, cooking time, textural kinetics, color and viability of the treated samples were analyzed, and techno-economic feasibility analysis was carried out for the process. Hundred percent mortality of adult insect (Callosobruchus maculatus) was achieved immediately, at an air temperature of 60 °C with microwave exposure period of 6 min at 2900 W power level. All the three processing parameters, i.e., moisture content, period of exposure and hot air temperature, were found to have significant effect on the mortality of pulse bruchids for both chickpea and green gram. Negligible differences were observed between the control and treated samples with respect to protein content for both chickpea and green gram. Cooking time, textural hardness, L value, greenness and viability of treated samples were lower than control sample. Cost of the treatment works out to be INR 6.28–7.07 per kg which is likely to come down with economics of scale.

Assessing the efficacy of controlled atmosphere temperature treatment system (CATTS) against codling moth inside harvested apples

The controlled atmosphere temperature treatment system (CATTS) was assessed as a disinfestation tool to control codling moth (CM; Cydia pomonella) larvae inside apples. Codling moth mortality and apple quality were assessed after exposure to one of 10 treatments, which were combinations of five variables, namely, O2 concentration (air 20.9%, 1, 2 or 3%); CO2 concentrations (air 0.04% or 15%); 12 or 24˚C/h ramp rate up to 46˚C; air speed 1.3 m/s; and either 2.5- or 3-h treatment time. CATTS treatments resulted in higher CM mortality than equivalent hot air treatments. The treatments involving 1 or 2% O2 combined with 15% CO2 and a ramp of 12˚C/h or 24˚C/h to 46˚C, with a total treatment time of 3 h or 2.5 h and a 1.3 m/s air speed resulted in 100% mortality of CM. However, all CATTS and hot air treatments compromised apple quality. High CM mortality can be achieved using CATTS, but refinement of the protocol is needed to improve fruit quality outcomes.

Microbial inactivation efficiency of supercritical CO2 drying process

ABSTRACTConventional drying of spices, as hot air treatment, often needs an additional downstream inactivation step to decrease the microbial load of the dried product and improve its microbial safety and microbial quality. In this regard, the present work explored the possibility to dry and decontaminate food in a single step using supercritical carbon dioxide (scCO2) as a drying agent. A case study was focused on the drying of herbs and the antimicrobial effects were evaluated on the naturally present microbiota. For this purpose, experiments were carried out on coriander leaves using a high pressure vessel at 10 MPa, at two different temperatures (40 and 50°C) with drying time of 0 and 150 min to establish the influence of each parameter on the microbial inactivation. Yeasts and molds appeared to be the least resistant to scCO2 as they could never be detected after the treatment (<2 log CFU/g). Mesophilic bacteria were also significantly reduced, up to 4 log CFU/g, but remained above the limit of quantification. The quality of the dried product was comparable with the quality of air-dried samples in terms of phenolic constituents. Overall, the results indicated that scCO2 drying was a promising green drying technique combining both drying and microbial inactivation in a single step with a relevant impact on safety and costs.

Classification of the hot air heat treatment degree of larch wood using a multivariate analysis of near-infrared spectroscopy

In this study, hot air heat treatments of larch (Larix kaempferi) wood specimens were conducted at various temperatures (160–220 °C) and times (1–12 h) to classify the degree of hot air heat treatment using near-infrared (NIR) spectroscopy. NIR reflectance spectra were acquired from specimen cross-sections and were then preprocessed using the standard normal variate. Hierarchical clustering analysis (HCA) using the complete linkage and squared Euclidean distance was conducted to classify the three degrees of heat treatment. A principal component score plot of the NIR spectra was well grouped by the HCA grouping result, and the first component reflected the cluster analysis grouping well. A partial least squares discriminant analysis was performed to develop the discriminant regression model of the three heat treatment degrees. The R2 and root mean square error of validation were 0.959 and 0.191, respectively. NIR is considered to be a good candidate to routinely measure the degree of hot air treatment for larch wood.

Effects of Pichia guilliermondii and Hot Air Treatment on the Postharvest Preservation of Red Fuji Apple Quality Attributes

The effects of individual and combined Pichia guilliermondii (at 1 × 108 CFU mL-1) and hot air (at 38°C for 96 h) treatments on the three major postharvest diseases Botrytis cinerea, Penicillium expansum, and Colletotrichum gloeosporioides, as well as the quality and antioxidant content of Red Fuji ( Malus pumila var. domestica) apple fruit, were investigated in this work. Results suggested that the combined hot air and antagonistic yeast ( P. guilliermondii) treatment effectively and completely inhibited the infection of apple fruit wounds by the three major postharvest diseases. Furthermore, apple fruit treated with antagonistic yeast or heat alone maintained better quality, which included mass loss, firmness, solid/acid ratio, and ascorbic acid content, than the control. The combination of the two treatments yielded the optimum apple quality. Moreover, the combined hot air and P. guilliermondii treatment also maintained or enhanced the antioxidative enzyme activities and total phenolic content of apple fruit. All results demonstrated that the combined antagonistic yeast and hot air treatment maintained the postharvest freshness of apple fruit.

Superheated steam treatment on wheat bran: Enzymes inactivation and nutritional attributes retention

Superheated steam (SS) was used to inactivate peroxidase and lipolytic enzymes of wheat bran (WB) in this study. Meanwhile, the effects of SS on nutritional attributes of WB were also evaluated. Compared with conventional hot air (HA) treatment (16 min), SS processing could inactivate enzymes of WB within a much shorter time (7 min). SS processing did not cause the loss of non-starch nutrients (lipid, protein, ash and dietary fiber) or promote the oxidation of lipids in WB. Superheated steam-stabilized wheat bran (SS-WB) also showed comparable antioxidant activities to that of native WB. However, compared with hot air-stabilized wheat bran (HA-WB), SS-WB exhibited a brighter color (L* value, 69.96 and 64.65, respectivly), higher extractable phenolic compounds contents (3736.7 and 2952.1 μg GAE/g WB d.b., respectivly) and stronger antioxidant activities (13.76 and 11.95 μmol Trolox equivalent/g WB d.b., respectivly) as well as lower peroxide value (1.27 and 1.81 meq O2/kg d.b., respectivly), higher unsaturated fatty acid contents (64.05% and 58.11%, respectivly) and sensory evaluation scores. Therefore, SS treatment should be a new efficient technology that could stabilize WB while maintain its nutritional attributes at the same time. The resultant SS-WB may be a potential alternative to native WB and HA-WB.

The combined effects of tea tree oil and hot air treatment on the quality and sensory characteristics and decay of strawberry

In this study, the antifungal activities of tea tree oil (TTO) combined with hot air (HA) treatment against Botrytis cinerea, the causal agent of strawberry gray mold, was tested in vitro and in vivo. Results showed that both TTO and HA treatment inhibit mycelial growth and destroy the hyphal ultrastructure of B. cinerea. The combined treatment (TTO+HA) results in a significantly synergistic effects in in vitro tests. Compared with control fruit, each treatment (TTO, HA, TTO+HA) reduced the gray mold in strawberry fruit inoculated with B. cinerea, the combined treatment resulted in lowest decay incidence and lesion diameter. The combined treatment also induced higher activities of chitinase (CHI) and β-1, 3-glucanase (GLU) and these strawberries subjected to this combined treatment maintained a better commercial quality as measured by firmness, TSS, a* value and sensory evolution, than those treated with TTO or HA alone. It was concluded that combined TTO and HA treatment of strawberry fruit is more effective at controlling decay and maintaining fruit quality than single treatment, that may be a potential strategy for commercial application in strawberries.

Effects of hot air treatment on the quality attributes of semidry-milled Indica rice

To investigate the effects of hot air treatment (HAT) on the quality attributes of Indica rice semidry-milling, HAT was applied at various temperatures (45–120 °C) and processing times (0–240 min). The changes in grain-surface cracking, moisture absorption rate, damaged starch, rheological properties, microbial decontamination, and texture qualities were evaluated. HAT induced many cracks in the rice grains, shortening the soaking time to reach maximum water content (28%) to 8 min. However, at high temperatures, extending the HAT time slowed the water absorption rate. Under the optimum HAT conditions and soaking time, the total viable counts in the rice flour were similar to those of dry-milled rice flour (102–103 cfu/g), with no coliforms and few yeasts and molds. The damaged starch content, rheological and texture properties were similar to those of wet-milling. Therefore, an appropriate HAT can shorten the soaking time of the rice and clean it during the milling process.

Forced hot-air treatment against Bactrocera papayae (Diptera: Tephritidae) in papaya

The Asian papaya fruit fly, Bactrocera papayae Drew and Hancock, was treated with hot-water immersion and forced hot air to develop a phytosanitary heat treatment schedule. Hot-water immersion tests were conducted with 12- and 24-h-old eggs and with first and third instar larvae to compare the relative thermotolerances of this fruit fly among these life stages. The 24-h-old eggs, the most thermotolerant among the four life stages tested, were subjected to time and temperature tests using cage-infested papaya fruits in a forced hot-air chamber. Heating the papayas to a minimum core temperature of 47.7 °C (95% confidence interval 47.2–48.3 °C) was estimated to induce probit-nine mortality based on a probit analysis of the data. Confirmatory tests in which papayas infested with 24-h-old eggs were heated to a minimum fruit core temperature of 47.2 °C that was maintained for 0–30 min followed by hydrocooling to a fruit core temperature of ≈25 °C resulted in the complete mortality of an estimated treated population of 43,425 eggs aged 24 h (99.9931% mortality at the 95% confidence level). Therefore, heating the papaya fruits to a core temperature of 47.2 °C for a minimum dwell time of 30 min, which was the longest dwell time in the confirmatory tests, may serve as a phytosanitary heat treatment schedule for the control of B. papayae in papaya fruits.

High-Temperature Hot Air/Silane Coupling Modification of Wood Fiber and Its Effect on Properties of Wood Fiber/HDPE Composites

The surfaces of poplar wood fibers were modified using high-temperature hot air (HTHA) treatment and silane coupling agent. The single factor test was then used to investigate the performances (e.g., the change of functional groups, polarity, cellulose crystallinity, and thermal stability) of modified poplar wood fibers (mPWF) through Fourier transform infrared spectrometry, X-ray diffraction and thermo-gravimetric analysis for the subsequent preparation of wood-plastic composites (WPCs). The effect of HTHA treatment conditions—such as temperature, inlet air velocity, and feed rate—on the performances of WPCs was also investigated by scanning electron microscopy and dynamic mechanical analysis. The main findings indicated that HTHA treatment could promote the hydration of mPWF and improve the mechanical properties of WPCs. Treatment temperature strongly affected the mechanical properties and moisture adsorption characteristics of the prepared composites. With the increase of treated temperature and feed rate, the number of hydroxyl groups, holocellulose content, and the pH of mPWF decreased. The degree of crystallinity and thermal stability and the storage modulus of the prepared composites of mPWF increased. However, dimensional stability and water absorption of WPCs significantly reduced. The best mechanical properties enhancement was observed with treatment temperature at 220 °C. This study demonstrated the feasibility for the application of an HTHA treatment in the WPC production industry.

Influence of hormetic heat treatment on quality and phytochemical compounds of broccoli florets during storage

The effect of moist hot air treatment applied to broccoli florets was studied in order to maintain quality and phytochemical compounds during postharvest storage at 4°C. Exposure to hormetic heat doses of 41°C for 180min (low temperature, LT) and 47°C for 12min (high temperature, HT) delayed yellowing for 21 d compared with non-heated florets that yellowed after 14 d. Chlorophyll content was also higher in florets treated with both the LT and HT heat treatments. The respiration rate of heat-treated broccoli was significantly higher immediately after heat treatments, being 10-times greater in LT-treated and 15-times greater in HT-treated florets on day 0 when compared with the control florets. However, after 7 d of storage differences were not significant, even though respiration rates were lower in treated broccoli after 21 d of storage compared with non-heated florets. Off-odors were also detected in HT-treated broccoli. Titers of indole-type glucosinolates were significantly enhanced by both heat treatments, while the glucoraphanin content of florets only increased with the HT treatment. A similar pattern was observed with gene expression, where overexpression of tryptophan N-hydroxylase (CYP79B3) was greater than the expression of dihomomethionine N-hydroxylase (CYP79F1) in heat-treated broccoli florets. Titers of hydroxy-cinnamic acids of florets were increased by both heat treatments. The total antioxidant capacity was significantly enhanced by the HT treatment. Similarly, overexpression of coumarate ligase (CoL), chalcone synthase (CHS) and phenylalanine N-hydroxylase (CYP79A2) was triggered by the HT treatment. The results indicate hormetic heat treatments can enhance the content of phytochemicals in broccoli florets during storage. However, the application of heat at 41°C (LT) was superior to the HT treatment in maintaining quality, although the enhancement of phytochemicals was less.

Effect of hybrid post treatments on the structural property and water flux of polysulfone hollow fiber membrane

The application of post treatments in preparation of high flux membranes is expanding rapidly. In this work, several hybrid post treatments have been introduced and used for change in the water flux of polysulfone (PSf) hollow fiber membranes. Dry wet spinning method was employed for fabrication of PSf hollow fiber membrane from spinning dope in mass ratio of 15:5:80 of PSf/PVP-K90/NMP. The simultaneous effects of single and hybrid post treatments containing traditional hypochlorite; high pressure injection technique (HPI) of hypochlorite, hot air and hot water treatments on the morphology and water flux of fabricated hollow fibers has been investigated. AFM analysis and image processing of SEM microphotographs of hollow fibers were used for structural studies. The mechanical properties of hollow fibers as well as strain at break and strength also were studied. It was found that the pores size and surface roughness parameter of hollow fiber membranes have been increased after traditional hypochlorite, HPI technique and hot water treatments while decreased when heat treated in air. In general all the employed hybrid post treatments caused to increase in the pores size of hollow fibers although the pores size increase rate in the membranes treated by the hybrid post treatments involving hot air was much lower than the others. The mechanical properties of hollow fibers have been decreased after hybrid and single post treatments containing traditional hypochlorite, HPI technique and hot water treatment while slightly increased after post treatments containing hot air. It was stated that the fabricated PSf hollow fibers were considerably affected by the employed hybrid post treatments. This can be attributed to the combine effects of used post treatments.

Postharvest hot air and hot water treatments affect the antioxidant system in peach fruit during refrigerated storage

Peach fruit are susceptible to chilling injury (CI) during low temperature storage. In this study, the effect of hot air (HA, 38°C for 3h) and hot water (HW, 48°C for 10min) treatments on CI, fruit quality, reactive oxygen species (ROS) and antioxidants in peach fruit during storage at 4°C was investigated. The results indicated that HA or HW treatments maintained fruit quality, decreased Reactive oxygen species (ROS) and enhanced antioxidants activity of fruit. However, HW was more effective than HA in alleviating internal browning (IB) symptoms in fruit. HW treatment may be easier to affect the antioxidant system in peach fruit due to the higher heat transmission in water. HA treatment had no effect on either AsA metabolism or GSH metabolism. However, HW enhanced the AsA metabolism in the early stage of storage and the GSH metabolism in the late stage of storage. Enhanced AsA-GSH metabolism and up-regulated expressions of PpaSOD5, PpaCAT1 and PpaAPX2 in the HW treated fruit might play an important role in maintaining the lower ROS level and IB index during refrigerated storage.

Hot air treatment activates defense responses and induces resistance against Botrytis cinerea in strawberry fruit

The effect of hot air (HA, 45°C, 3.5 h) treatment on reducing gray mold caused by Botrytis cinerea in strawberry fruit and the possible mechanisms were investigated. The results showed that HA treatment significantly reduced lesion diameter and enhanced activities of chitinase (CHI), β-1,3-glucanase and phenylalanine ammonia-lyase (PAL) in strawberry fruit. Total phenolic contents were also increased by HA treatment. The activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) were higher in HA treated strawberry fruit than those in control. Expression of three defense related genes such as CAT, CCR-1 allele and PLA6 was greatly induced in HA treated strawberry fruit with or without inoculation by B. cinerea. In addition, the in vitro experiment showed that HA treatment inhibited spore germination and tube growth of B. cinerea. These results suggested that HA treatment directly activated disease resistance against B. cinerea in strawberry fruit without priming response and directly inhibiting growth of B. cinerea.

Influence of Cold Plasma Treatment on Textural and Color Characteristics of Two Tomato Varieties

New technologies had been developed to prolong postharves sustainability of horticultural crops. Technologies as hot air treatment or iridation with UV-C spectral emissions are among them. Al of them have positive and negative effects on quality of horticultural crops. Increasingly under research for decontamination of foods is cold plasma technology, especially fresh fruits and vegetables. Possibility of creating cold plasma under atmosferic presures (ACP) offers new preservation tool to reduce microbial infections of vegetable crops. Effects of atmosferic cold plasma on food quality, however, remains under researched.. In this study, tomato is treated with air ACP generated with an dielectric barrier discharge reactor (DBD). Changes in textural and color characteristics of two tomato fruit varieties after cold plasma treatment were analysed by performing TPA test and color measurements. The effect of air ACP on tomato texture and color was insignificant.

Physical treatments to control postharvest diseases of fresh fruits and vegetables

Physical treatments have gained great interest in recent years to control many postharvest diseases in fruits and vegetables because the total absence of residues in the treated product and minimal environmental impact. The present review shows the extensive research work conducted during many years and increased in the last 10years, developing physical means for consistent disease control. The review include the use of cold storage as the main physical method for delaying or reducing biotic and abiotic diseases. Physical treatments, like heat, including hot water and hot air treatments, radio frequency and microwave, hypobaric and hyperbaric pressure and far ultraviolet radiation (UV-C light), are treated as promising control means, and controlled and modified atmospheres as complementary physical tools essential to reduce or delay the development of postharvest pathogens. A particular emphasis is given to the mode of action, which involve direct effect to the pathogen (lethal or sub-lethal) of spore germination and mycelial growth of fungi and the resistance induction in the host which is not well known but nowadays, with the new tools available in molecular biology will be easy to highlight other physiological and biochemical pathways on which the phenomenon are based. Besides benefits of treatment in different commodities, also limitations of use, including low persistence, risk of adverse effects and technological problems for commercial application are discussed.