High-humidity Hot Air Impingement Research Articles

High-humidity hot-air impingement blanching conditions for the inhibition of potato-browning enzymes and for quality retention.

Potato is an important non-cereal crop. It provides carbohydrates, a major source of energy in the human diet. Blanching during the processing of fresh fruits and vegetables is essential for their preservation. High-humidity hot-air impingement blanching (HHAIB) is a promising emerging technology for pretreating different food materials. This research aimed to identify the optimum HHAIB conditions for the inhibition of potato-browning enzymes, maintaining their nutritional and physical quality, and to compare this with conventional hot-water blanching (HWB). Polyphenol oxidase (PPO) inactivation, total phenol content (TPC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, color, textural attributes, thermal properties, microstructure, and particles crystallinity were evaluated. The relative humidity (RH), temperature, and duration of HHAIB required for PPO inactivation (2.59%) were 50%, 105 °C, and 4 min, respectively, which resulted in a complete gelatigination of potato starches, based on the thermal properties and the microstrcture of the blanched potatoes. These conditions led to improvements in TPC to 312.54 μg GAE.g-1 FP, DPPH scavenging to 1.99 μmol TE.g-1 FP, as well as enhancements in color and crystallinity. When HHAIB was conducted at lower temperatures (85 and 95 °C) there were negative effects on the blanched potatoes' color and crystallinity, along with a non-safe level of PPO activity. High-humidity hot-air impingement blanching was superior to HWB, inhibiting PPO, maintaining nutrients, and preserving physical properties, especially under the optimum conditions revealed by the principal component analysis. It provides an excellent technique for blanching and pretreating potatoes, preserving them, and maintaining their quality. © 2023 Society of Chemical Industry.

Peeling mechanism of tomato induced by HHAIB: Microscopic, ultrastructure, chemical, physical and mechanical properties perspectives

In order to better manage the peeling degree and avoid unnecessary losses, the current work aimed to explore the peeling mechanism of a novel peeling technology, high-humidity hot air impingement blanching (HHAIB). The relationships between HHAIB peeling performance and the changes in skin temperature, skin structure, water state, pectin fractions content, and skin mechanical properties of tomatoes were analyzed. Results showed, after HHAIB treatment, the epicuticular wax was disrupted, the skin exhibited more and longer random cracks, the degradation of inner skin tissue was observed by transmission electron microscopy, the free water percentage increased resulting in water loss in the whole tomato, the water-soluble pectin contents decreased in tomato fleshes, while the contents of chelate-soluble pectin and sodium-carbonate-soluble pectin increased. HHAIB heating reduced the elongation at break, and increased Young's Modulus of tomato peel. This study revealed the HHAIB peeling mechanism and provided new insights for developing HHAIB peeling technology.

Effects of high-humidity hot air impingement cooking on physicochemical properties and microstructure of Pacific white shrimp (Penaeus vannamei)

In this study, the potential of high-humidity hot air impingement cooking (HHAIC) was investigated as an alternative to other conventional cooking methods, including steaming, boiling, and roasting, by assessing the physicochemical properties, taste profile, and sensory evaluations of Pacific white shrimp (Penaeus vannamei). Compared to the steamed-, boiled-, and roasted-treated shrimp, HHAIC-treated samples demonstrated a lower cooking loss between 3.19% and 16.47%, which was possibly attributed to the decreasing muscle rupture. Moreover, HHAIC-treated samples exhibited improved textural properties, higher color retention, better water-holding capacity, and higher degree of polyphenol oxidase inactivation. By low-field nuclear magnetic resonance imaging, HHAIC-treated shrimp showed a pretty uniform water distribution. The main secondary structures of protein in fully-cooked P. vannamei shrimp were β-sheets and β-turns with no significant difference in free amino acid content among the four methods. Therefore, HHAIC could be considered a novel thermal technique for high-quality shrimp products as well as for other aquatic products.

High-humidity hot air impingement blanching (HHAIB) enhances drying behavior of red pepper via altering cellular structure, pectin profile and water state

In order to exploring a feasible pretreatment technology of red pepper, an emerging thermal pretreatment technology namely high-humidity hot air impingement blanching (HHAIB) was employed and its effect on drying behavior and related mechanisms were explored through analyzing the ultrastructure, the contents and composition of cell wall pectins, water state of red pepper during the blanching process under blanching temperature of 110 °C and relative humidity of 35%–40% for various exposure times ranging from 0 to 150 s. Results indicated HHAIB can extensively reduce the drying time from 11 h for the un-blanched samples to 8 h for the samples blanched for 90 s. In addition, HHAIB reduced the products' hardness by 8.19%–47.91% compared to the untreated samples. The cellular structure and water state experienced a significant alternation with the increasing blanching time. The content of water-soluble pectin (WSP) increased, while the contents of chelate-soluble pectin (CSP) and sodium‑carbonate-soluble pectin (NSP) decreased during the blanching process. Overall, HHAIB treatment is a promising blanching technology for red pepper as it can accelerate the drying process through softening tissue and altering the ultrastructure and moisture binding state. Industrial practiceDrying is one of the most frequently used methods for red pepper preservation as it can effectively reduce the moisture content so as to hinder the growth and reproduction of microorganisms and the moisture-mediated deteriorative reactions. While the existence of waxy hydrophobic layer covered the surface of red pepper results in long drying time and poor products' quality. In industrial practice chemical dipping is often used to remove the wax layer and enhance the drying rate of red pepper. However, the chemical residues can trigger food safety issues and how to deal with the highly corrosive chemical dipping solution is also a challenge. Therefore, it is very tempting for industry to explore innovative pretreatment for red pepper drying. The current work indicated that HHAIB is a promising alternative technology to replace the chemical dipping method as it extensively enhances the drying process of red pepper.

Application of blanching pretreatment in herbaceous peony (Paeonia lactiflora Pall.) flower processing: Improved drying efficiency, enriched volatile profile and increased phytochemical content

Although various techniques have been developed to dry herbaceous peony (Paeonia lactiflora Pall.) flowers, the dried products usually have a low retention level of bioactive compounds, which limits the valorization of peony-derived products. This work is the first to employ steam blanching (SB), high-humidity hot air impingement blanching (HHAIB), and vacuum-steam pulsed blanching (VSPB) before drying to improve the drying efficiency and quality of dried peony flowers. Results showed blanching pretreatment led to significant (p < 0.05) reductions in drying time by 7.02–40.35% and energy consumption by 6.86–39.96%, respectively. The final dried samples also exhibited reductions in browning degree by 30.93–62.89% and shrinkage ratio by 30.05–68.83%, respectively. Based on blanching pretreatment, the retention levels of bioactive compounds in dried samples were significantly (p < 0.05) improved. The dried samples blanched with VSPB possessed the highest contents of gallic acid (76.76 ± 1.75 mg/100 g DW), catechins (0.327 ± 0.010 mg/100 g DW), paeoniflorin (51.00 ± 1.41 mg/100 g DW), total phenolic (85.41 ± 1.81 mg GAE/100 g DW), flavonoid (11.00 ± 0.26 mg RE/100 g DW), and sugar (22.86 ± 0.13 g/100 g DW), thus causing superior antioxidant capacity. Furthermore, a total of 28 volatiles were identified, with alcohols (8.58–166.10 μg/g), alkanes (11.69–70.01 μg/g), and terpenes (5.89–47.93 μg/g) being the dominant contributors to the flavor of dried samples. This work provides insight for researchers to develop dried peony flowers with high added value using an energy-efficient strategy in the future.

The effect of high humidity hot air impingement blanching on the changes in cell wall polysaccharides and phytochemicals of okra pods.

Okra pods contain heat-sensitive substances, such as phenolic compounds and other phytochemicals that can be degraded when okra pods are subjected to heat treatment. The understanding of the impact of high humidity hot air impingement blanching (HHAIB) on the changes in physicochemical properties of polysaccharides and phytochemicals of okra pods is of great importance because over-blanching may result in cell membrane disruption and changes in biologically active compounds under prolonged exposure to the thermal treatment. Therefore, the present study aimed to investigate the effect of HHAIB on the changes in physicochemical properties of pectins and phytochemicals extracted from okra pods. Both the HHAIB time and method of extraction influenced their physicochemical characteristics and biological activity. Pectin fractions subjected to HHAIB were composed of polygalacturonic acid, rhamnogalacturonan, glucomannan, galactan, mannose, arabinose, rhamnose, calcium pectate and arabinogalactan. The contents of total phenolics, total flavonoids and antioxidant activity of extracts mostly increased during HHAIB (i.e. up to 19.0%, 13.2% and 35.3%, respectively). However, HHAIB reduced the chlorophyll-a (up to 55.7%) and lycopene (up to 52.6%) contents of okra pods. The acquired knowledge may be useful for better understanding and optimization of technologies based on HHAIB treatment. The HHAIB treated okra can be a promising natural alternative in different applications, including its use as a replacement of some ingredients in food or non-food systems as a result of richness in polysaccharides and polyphenols, as well as high antioxidant properties. © 2022 Society of Chemical Industry.

Effect of High-Humidity Hot Air Impingement Steaming on Cistanche deserticola Slices: Drying Characteristics, Weight Loss, Microstructure, Color, and Active Components.

Cistanche deserticola is one of the most precious herbal medicines and is widely used in the pharmaceutical and healthy food industries. Steaming is an important step prior to drying in the processing of C. deserticola. This research investigated the effects of high-humidity hot air impingement steaming (HHAIS) parameters such as temperature, time, and relative humidity (RH) on drying characteristics, weight loss, color, microstructure, and active components of C. deserticola slices. The results showed that the steaming process caused a weight loss in C. deserticola; however, increasing the RH reduced the weight loss. Starch gelatinization observed from the microstructure of the steamed samples explained their long drying time. The Page model can well fit the drying process with a high R2 (>0.956) under the drying conditions of 60°C and 6 m/s. Steaming increased the content of phenylethanoid glycosides, and the highest content was obtained at 95°C and 60% RH for 20 min, 75°C and 70% RH for 20 min, and 75°C and 60% RH for 30 min. The steamed samples appeared in an oil black color. When the color difference (ΔE) values were in the range of 16.79–20.12, the contents of echinacoside and acteoside reached the maximum. Steaming at 95°C and 60% RH for 20 min, 75°C and 70% RH for 20 min, and 75°C and 60% RH for 30 min are the optimum process conditions. The results from this work provide innovative steaming technology and suitable processing parameters for producing C. deserticola decoction pieces with a high quality, which will broaden its potential application in the functional health food industry.

High-humidity hot air impingement blanching (HHAIB): An emerging technology for tomato peeling

Peeling is an essential operation for tomato processing. A new peeling method, high-humidity hot air impingement blanching (HHAIB) heating technology, was developed as an alternative to the conventional lye and hot-water peeling to eliminate the use of chemicals and the discharge of wastewater. The current work explored the feasibility of HHAIB for tomato peeling. The effects of heating temperature (100–120 °C), relative humidity (20%–40%) and heating time (0–180 s) on the peeling performance were investigated. The optimum treatment was found to be 110 °C heating temperature in combination with 40% of relative humidity and 75 s treatment time, which resulted in lower peeling loss, firmness loss and color deterioration compared with other HHAIB conditions that achieved 100% peelability. The comparative study of optimized HHAIB peeling with conventional lye and hot-water peeling showed that HHAIB peeled tomato obtained lower peeling loss and firmness loss, and higher preservation of phytochemicals, antioxidant capacity and color. In addition, compared with fresh tomatoes, HHAIB processing increased the antioxidant activity, lycopene, and total phenolic content in peeled tomatoes by 16.01%, 10.46%, 12.80%, respectively. The laser scanning confocal microscopy image of fresh tomato skin surface and the scanning electron microscope images of peels and flesh showed that HHAIB caused cracking of the epidermis and melting of the cuticular membrane while reduced the serious damage of flesh. Industrial practicePeeling is a necessary step in tomato processing, which impacts subsequent processing efficiency and product quality. At present, the most common used peeling methods in the industry are hot water or/and alkali peeling, but it induces the loss of water-soluble nutrients, chemical residues and waste liquid treatment. Therefore, the industry urgently needs an alternative peeling technology. The current work shows that HHAIB is a very promising peeling technology as it not only has an excellent peeling performance, but also enhances the preservation of phytochemicals, antioxidant capacity and quality attributes compared to conventional lye and hot-water peeling.

An emerging pretreatment technology for reducing postharvest loss of vegetables-a case study of red pepper (Capsicum annuum L.) drying

Drying and pretreatment play key roles in reducing postharvest losses and improving food security. High humidity hot air impingement blanching (HHAIB) was employed in the present work to pretreat red peppers and its effects on natural micro flora, quality and drying characteristics of red pepper were evaluated. Results showed that the aerobic bacteria were decreased to1.72 log CFU/g; meanwhile, the mold and yeast populations were under the detection limit (<1.0 log CFU/g) after blanching for 30 s. Moreover, HHAIB treatment enhanced the drying rate, and the drying time was reduced by 14%-29% compared to the untreated samples. Weibull model precisely described the drying behavior of red pepper. HHAIB treatment (within 30 s) caused the decreases in ascorbic acid contents. At the same time, there was no significant (p > 0.05) effect on the surface color and natural pigment contents. The findings indicate that HHAIB pretreatment is a promising technique for increasing red pepper microbial safety and drying rate.

Pulsed Vacuum Drying of Pepper (Capsicum annuum L.): Effect of High-Humidity Hot Air Impingement Blanching Pretreatment on Drying Kinetics and Quality Attributes.

With a high moisture content, fresh peppers are perishable and rot easily. Drying is essential for shelf-life extension. The natural thin wax layer on the pepper surface hinders moisture transfer. Traditionally, chemical dipping or mechanical pricking is used to remove this wax layer. However, in chemical dipping, chemical residues can trigger food-safety issues, while the low efficiency of mechanical pricking hinders its industrial application. Feasible pretreatment methods are advantageous for industrial use. Here, an emerging pretreatment technique (high-humidity hot-air impingement blanching, HHAIB) was used for peppers before drying and its effects on drying characteristics, microstructure, and polyphenol oxidase (PPO) activity were explored. The impact of drying temperature on color parameters and red pigment content of pulsed-vacuum-dried peppers was also evaluated. PPO activity was reduced to less than 20% after blanching at 110 °C for 60 s. HHAIB reduced drying time and PPO activity and promoted chemical-substance release. Effective water diffusivity was highest (5.01 × 10−10 m2/s) after blanching at 110 °C for 90 s, and the brightness value and red pigment content were highest (9.94 g/kg) at 70 °C. HHAIB and pulsed vacuum drying are promising pretreatment and drying methods for enhancing the drying rate and quality of red peppers.

The effect of high humidity hot air impingement blanching on the changes in molecular and rheological characteristics of pectin fractions extracted from okra pods

The aim of study was to evaluate the changes in molecular and rheological characteristics of pectin fractions extracted from okra pods subjected to high-humidity hot air impingement blanching (HHAIB). HHAIB had pronounced impact on the pectin solubility of okra pods, their structure and rheology. For example, short HHAIB, i.e. 15 and 30 s, resulted in some microcracks on the surface of okra pods, while the longer ones, i.e. 60, 90 and 120 s, resulted in higher stress and teared the outer skin of okra pods. HHAIB for 15 and 30 s prevented extractability of pectins from okra pods and resulted in a decrease in yield. HHAIB for 60 s facilitated pectin extraction providing higher yields, while HHAIB for 90 and 120 s led to the extraction of non-pectin cell wall components as well. Molecules of pectins of okra pods have been characterized by different molecular size, shape, and branching that depended on both solvent used for extraction and the time of HHAIB treatment. Degradation, aggregation and transformation of molecules to more easy soluble fractions was observed during blanching treatment. A pick of consistency index and viscosity was observed for pectins extracted from okra pods subjected to HHAIB treatment for 30–60 s. HHAIB was found to be one of the heat treatment methods that may be suitable support for improving pectin extraction and useful in tailoring pectin properties for further applications.

Quantitative characterization and effective inactivation of biological hazards in struvite recovered from digested poultry slurry

Struvite formed from digested poultry slurries can serve as an alternative to chemical fertilizers; however, the biological safety of such products is questionable. Therefore, quantification and inactivation of foodborne pathogens existing in struvite are important. Herein, the dynamics of foodborne pathogens' (Streptococcus faecalis, S. typhimurium, Clostridium perfringens, and Escherichia coli) living status, whether culturable and viable but non-culturable (VBNC) in struvite, were quantified for the first time. Meanwhile, inactivation technologies, namely high-humidity hot air impingement blanching (HHAIB), cold plasma, and hot air treatment, were evaluated and compared for their potential to inactivate/kill foodborne pathogens in struvite. An increase in precipitation pH from 9.0 to 11.0 decreased the culturable count of pathogens in the struvite from 75 to 86% to 7–20%, while the VBNC pathogen counts increased from 16 to 24% to 35–55%. Among the tested inactivation technologies, the HHAIB treatment at 130 °C for 120 s killed approximately 68–79% of foodborne pathogens in struvite precipitated at pH 9.0. VBNC pathogens increased from 16 to 24% to 57–68% after HHAIB treatment at 130 °C for 120 s. Struvite treatment with different inactivation technologies did not change its crystalline structure; however, it reduced functional group abundance. Therefore, further research on inactivation technologies is required to achieve better pathogen reduction efficiency in struvite to make it a biologically safe fertilizer for crop production.

Effects of high-humidity hot air impingement steaming on Gastrodia elata: steaming degree, weight loss, texture, drying kinetics, microstructure and active components

Steaming is a key process affecting quality of herbal medicine Gastrodia elata (G. elata). This research investigated the effects of high-humidity hot air impingement steaming (HHAIS) on weight loss, texture, drying characteristics, microstructure, and active ingredients of G. elata, as well as the judgement of steaming degree. It was demonstrated that G. elata steaming degree was correlated to starch gelatinization and could be quantified by monitoring central temperatures of the cross section with the maximum diameter. While just well-steamed, the G. elata central temperature was around 62.8–67.2 ℃, near to gelatinization temperature. Steaming led to decreased weight and shear hardness, while increased adhesion force and prolonged drying time. Hydrolysis of polysaccharide and gelatinization of starch granules were observed from microstructure of steamed G. elata, which confirmed changes in weight, texture and drying rate. Furthermore, steaming increased gastrodin content and decreased p-hydroxybenzyl alcohol content.

Effect of high-humidity hot air impingement blanching and pulsed vacuum drying on phytochemicals content, antioxidant capacity, rehydration kinetics and ultrastructure of Thompson seedless grape

A new pretreatment method using high humidity hot air impingement blanching (HHAIB) followed by pulsed vacuum drying (PVD) was employed for Thompson seedless drying. The effect of this dehydration technique on phytochemicals content (ascorbic acid, total phenols and chlorophyll), antioxidant capacity (tetraethylammonium chloride, TEAC, ferric ion-reducing antioxidant power, FRAP and 2,2-diphenyl-1-picrylhydracyl, DPPH) and rehydration kinetics of Thompson seedless grape was explored. Results revealed that both HHAIB and PVD had a significant influence on phytochemicals composition and antioxidant capacity. After blanching for 150 s, the ascorbic acid and total chlorophyll content reduced by about 33% and 51%, respectively, while the total phenols and antioxidant capacity increased significantly (p ＜ 0.05). Ultrastructure observations explained why the total phenols and antioxidant capacity increased even as the ascorbic acid and total chlorophyll decreased. The findings indicate that HHAIB can enhance the total phenols content and antioxidant capacity of seedless grapes during blanching process and after drying. This information could be useful to change the general believed hypothesis that thermal processes lower the nutritional value of fruits and vegetables.

High-humidity hot air impingement blanching (HHAIB) efficiently inactivates enzymes, enhances extraction of phytochemicals and mitigates brown actions of chili pepper

In current work, high-humidity hot air impingement blanching (HHAIB) was employed to inactivate peroxidase enzymes (POD) of chili pepper under three independent variables, namely blanching temperature (105, 110, and 115 °C), relative humidity (20%, 30%, and 40%), and blanching time (30, 60, and 90 s). Response surface methodology (RSM) was used to optimize the blanching conditions based on product POD residual activity and browning index. Results indicated that blanching temperature of 110 °C, relative humidity of 40% and blanching time of 38 s were the optimum blanching conditions, which resulted in the minimum POD residual activity (0.52%) and browning index difference (7.09). Validation test showed that the predicted data had good agreement with the experimental data. Results also indicated that compared with the non-blanched samples, the extraction content of ascorbic acid and red pigment from blanched pepper under optimal blanching conditions increased by 42.85% and 8.20%, respectively. Ultrastructural observations explained why moderate blanching can promote the extraction of phytochemicals. The findings in current work indicate that HHAIB can efficiently inactivate enzymes, enhance extraction of phytochemicals and at the meantime mitigate brown actions under optimal conditions.

Experimental and simulation studies of heat transfer in high-humidity hot air impingement blanching (HHAIB) of carrot

A mathematical model was presented to characterise heat transfer in high-humidity hot air impingement blanching (HHAIB) of cuboid carrots. The model accounts for condensation heat transfer and predicts the sample’s core temperature evolution with time. The simulation was performed at different relative humidity of 20%, 40%, 60%, 80% with constant temperature of 383K. Results showed that the heat transfer process of HHAIB is divided into two stages based on vapor–liquid phase transition, namely a condensing heat transfer segment and a non-condensing heat transfer segment. In the initial stage of HHAIB, a comprehensive and intense condensation occurred on the sample surface leading to high heat transfer coefficient and greatly enhancing heat transfer, but at the same time creating a huge temperature gradient in the sample. The relative humidity of 40%–60% at 383K could not only enhance the heat transfer rate but also improve the homogeneity of temperature distribution in the sample. Simulated core temperatures were compared with experimental measurements, showing good agreement with a coefficient of determination R2 of 0.991. The findings of current work provide theoretical basis to better design and control of the process conditions of HHAIB as it elucidates the heat transfer characteristic taking account condensation phenomenon and illustrates the temperature distribution and evolution profiles.

Effect of high-humidity hot air impingement blanching (HHAIB) and drying parameters on drying characteristics and quality of broccoli florets

In current work, the influences of high-humidity hot air impingement blanching (HHAIB) time (60, 90, 120, and 150 s), drying temperature (60, 65, 70, and 75 °C), and air velocity (6, 9, and 12 m/s) on drying characteristics and quality attributes of broccoli florets were explored. Extreme learning machine (ELM) was employed to describe the drying behavior of broccoli florets. Results showed that proper HHAIB pretreatment can extensively increase drying rate compared to the control group (unblanched samples). The entire drying process of broccoli florets occurred in the falling period. Besides, proper HHAIB pretreatment can enhance vitamin C preservation, the color quality, and the rehydration capacity of dried broccoli florets. Based on error analysis results, the prediction accuracy of the optimal ELM model with 4-50-1 topology is found to be satisfied for the moisture ratio prediction of broccoli florets during air impingement drying process, with the R2, , and MSE reached to 0.9993, 8.04e−5, and 2.01e−4, respectively.

High-humidity hot air impingement blanching (HHAIB) enhances drying quality of apricots by inactivating the enzymes, reducing drying time and altering cellular structure

Effects of high-humidity hot air impingement blanching (HHAIB) on peroxidase (POD) and polyphenol oxidase (PPO) activities, ultrastructure, water distribution, drying time, and key quality attributes of apricots were investigated under air temperature of 110 °C and relative humidity of 35%–40% for various exposure times ranging from 30 to 150 s. HHAIB inactivated POD and PPO fully within 120 s, induced alteration of cellular structure and resulted in redistribution of water among the cell compartments. Compared to the untreated sample, HHAIB reduced the drying time by 19.36%–36.40%. Optimal pretreatment (120 s) resulted in dried apricots with higher total phenolics (TP) and total carotenoids (TC) along with enhanced antioxidant capacity, as well as better color. The TP, TC and antioxidant capacity were observed to be significantly correlated to POD and PPO activities, water distribution and drying time. Over-blanching (150 s) prolonged drying time, induced higher degradation of TP, TC, antioxidant capacity and color compared to dried products pre-blanched for 120 s. Hence, proper HHAIB pretreatment enhances drying process and improves the quality attributes of dried apricots.

High humidity hot air impingement blanching (HHAIB) enhances drying rate and softens texture of apricot via cell wall pectin polysaccharides degradation and ultrastructure modification

The effects of high humidity hot air impingement blanching (HHAIB) over a range of application times (30, 60, 90, and 120 s) on drying characteristics, hardness, cell wall pectin fractions contents and nanostructure, as well ultrastructure of apricot were investigated. Results showed that HHAIB reduced drying time and decreased the hardness of apricot by 20.7%–34.5% and 46.57%–71.89%, respectively. The water-soluble pectin (WSP) contents increased after blanching, while the contents of chelate-soluble pectin (CSP) and sodium-carbonate-soluble pectin (NSP) decreased significantly (P < 0.05). The hardness and drying time were found to correlate inversely with the WSP content, but positively with CSP and NSP contents. Atomic force microscopy (AFM) detection showed the decomposition and degradation of pectin fractions during blanching. Additionally, transmission electron microscopy (TEM) observation indicated that the cell wall structure was degraded and middle lamella integrity was destroyed by blanching.

High-humidity hot air impingement blanching alters texture, cell-wall polysaccharides, water status and distribution of seedless grape

Blanching pretreatment plays an essential role in fruits and vegetables processing to obtain excellent final products. The purpose of current work was to characterise the texture, cell-wall polysaccharides and water distribution of grapes pre- and post- high-humidity hot air impingement blanching (HHAIB). The cell-wall pectins nanostructure, water status and distribution of samples were determined by atomic force microscopy (AFM), low field nuclear magnetic resonance (LF-NMR) and magnetic resonance image (MRI), respectively. Results revealed that blanching caused significant berry tissue softening which was accompanied by an increase of water-soluble pectin (WSP, from 39.57 to 57.44 g/100 g fresh weight) and a decrease of chelate-soluble pectin (CSP, from 79.34 to 53.78 g/100 g fresh weight) and sodium-carbonate-soluble pectin (NSP, from 364.23 to 187.64 g/100 g fresh weight) concentration. Obvious depolymerization and degradation was observed in cell-wall polysaccharides nanostructure in blanched berries. The length frequencies of WSP chains are mainly distributed in the range of 0.51–2.00 μm, while it was 1.01–2.00 μm for the CSP chains of blanched samples. LF-NMR transverse relaxation time and MRI analysis indicated that HHAIB treatment resulted in a water loss and migration from berry interior to surface tissue. The findings in present study provide a deeper understanding in tissue softening and moisture variation of blanched berries.