Effect of Thermal and Nonthermal Processing on Textural Quality of Plant Tissues

Recent Trends in the Pre-Drying, Drying, and Post-Drying Processes for Cassava Tuber: A Review

Cassava tuber is an essential staple crop in tropical regions with versatile applications in the food, feed, and industrial sectors. However, its high moisture content and perishable nature necessitate efficient preservation methods to extend its shelf life and enhance its value. Pre-drying, drying, and post-drying processes play pivotal roles in maintaining the quality and usability of cassava products. This review comprehensively examines the current status and future directions in the pre-drying, drying, and post-drying processes of cassava tuber. Various pre-drying or pretreatment methods and drying techniques are evaluated for their impacts on drying kinetics and product quality. Additionally, challenges and limitations in achieving high-quality processing of cassava flour are identified. Future directions in cassava drying methods emphasize the integration of combined pre-drying and drying techniques to optimize resource utilization and processing efficiency. Furthermore, the adoption of advanced online measurement and control technologies in drying equipment is highlighted for real-time monitoring and optimization of drying parameters. The importance of optimizing existing processes to establish a comprehensive cassava industrial chain and foster the development of the cassava deep-processing industry is emphasized. This review provides valuable insights into the current trends and future prospects in cassava drying technologies, aiming to facilitate sustainable and efficient utilization of cassava resources for various applications.

Ultrasound pretreatment enhances moisture migration and drying quality of mulberry via microstructure and cell-wall polysaccharides nanostructure modification

The effects of ultrasound pretreatment (20 kHz, 30 W/L) on mulberries' texture, microstructure, characteristics of cell-wall polysaccharides, moisture migration, and drying quality were investigated over exposure times ranging from 15 to 45 min. Ultrasound induced softening of mulberry tissue, accompanied by an increase in water-soluble pectin and a decrease in chelate-soluble pectin and Na2CO3-soluble pectin concentrations. Noticeable depolymerization of the pectin nanostructure was observed in the pretreated mulberries, along with a decrease in molecular weight, attributed to side-chain structure cleavage. Ultrasound loosened the cell wall structure, increased free water content and freedom, thereby reducing water diffusion resistance. Ultrasound pretreatment reduced drying time by 11.2 % to 23.3 % at various processing times compared to controls. Due to significantly enhanced drying efficiency, the optimal pretreatment time (30 min) yielded dried mulberries with higher levels of total phenolics and total anthocyanins, along with an increased antioxidant capacity. The results of this study provide insights into the mechanisms by which ultrasound pretreatment can effectively enhance the mulberry drying process.

Ultrasonic washing as an abiotic elicitor to increase the phenolic content in fruits and vegetables: A review

Ultrasonic washing has been widely applied to the postharvest storage of fruits and vegetables as a residue-free physical washing technology, which plays an important role in improving shelf-life, safety, and nutritional value. Phenolics are a large group of phytochemicals widespread in fruits and vegetables, and they have been considered potential protective factors against some diseases because of potent antioxidative properties. Previous studies have shown that ultrasonic washing can increase the phenolic content of fruits and vegetables immediately or during storage through the induction of plant stress responses, which is of great significance for improving the functional and nutritional value of fruits and vegetables. However, the mechanisms of ultrasound as an elicitor to improve the phenolic content remain controversial. Therefore, this review summarizes the applications of ultrasonic washing to increase the phenolic content in fruits and vegetables. Meanwhile, the corresponding physiological stress response mechanisms of the phenolic accumulation in terms of immediate stress responses (i.e., higher extractability of phenolics) and late stress responses (i.e., metabolism of phenolics) are expounded. Moreover, a hypothetical model is proposed to explain phenolic biosynthesis triggered by signaling molecules produced under ultrasound stress, including primary signal (i.e., extracellular adenosine triphosphate) and secondary signals (e.g., reactive oxygen species, Ca²⁺ , NO, jasmonates, and ethylene). Additionally, the techno-economic feasibility of ultrasonic washing technology is also discussed. Further, challenges and trends for further development of ultrasonic washing as an abiotic elicitor applied to the postharvest storage of fruits and vegetables are presented.

Textural Properties of Chinese Water Chestnut (Eleocharis dulcis) during Steam Heating Treatment

Chinese water chestnut (CWC) has become one of the most popular foods in China. The textural properties of food contribute considerably to consumer preferences. Fresh fruits and vegetables are normally softened after thermal treatment. However, CWC retains most of its crispness and hardness after steaming. To explore the relationship between thermal processes and sensory changes, a method for measuring the texture of CWC is warranted. This study aimed to examine the textural properties of CWC subjected to varying degrees of thermal treatments using instrumental and sensory methods. Instrumental tests included the shear force test and puncture test, while trained panelists assessed the sensory attributes. Two sensory attributes were selected for evaluation: crispness and hardness. The results indicated that with the extension of thermal treatment time, the crispness and hardness of CWC decreased slightly, while cells and starch grains were damaged. Sensory results showed a significant correlation with shear force index (slope of rising curve) (p < 0.05) and puncture index (slope of rising curve, slope of descending curve and compression work) (p < 0.05). Thereafter, the instrumental tests parameters could be used to establish regression models for predicting crispness and hardness and controlling the quality of CWC products.

Fresh Mushroom Preservation Techniques

The production and consumption of fresh mushrooms has experienced a significant increase in recent decades. This trend has been driven mainly by their nutritional value and by the presence of bioactive and nutraceutical components that are associated with health benefits, which has led some to consider them a functional food. Mushrooms represent an attractive food for vegetarian and vegan consumers due to their high contents of high-biological-value proteins and vitamin D. However, due to their high respiratory rate, high water content, and lack of a cuticular structure, mushrooms rapidly lose quality and have a short shelf life after harvest, which limits their commercialization in the fresh state. Several traditional preservation methods are used to maintain their quality and extend their shelf life. This article reviews some preservation methods that are commonly used to preserve fresh mushrooms and promising new preservation techniques, highlighting the use of new packaging systems and regulations aimed at the development of more sustainable packaging.

Modeling Softening Kinetics at Cellular Scale and Phytochemicals Extractability in Cauliflower under Different Cooking Treatments

The effects induced by heat on Depurple and Cheddar (Brassica oleracea L. var. botrytis) during boiling, steaming, and sous-vide were investigated to elucidate the role of the basic cellular elements in softening and extractability of sterols and tocopherols. With this aim, an elastoplastic mechanical model was conceptualized at a cell scale-size and validated under creep experiments. The total amount of the phytochemicals was used to validate multivariate regression models in forecasting. Boiling was the most effective method to enhance the softening mechanisms causing tissue decompartmentalization through cell wall loosening with respect to those causing cell separation, having no impact on the phytochemical extractability. Sous-vide showed the lowest impact on cell wall integrity, but the highest in terms of cell separation. Steaming showed an intermediate behavior. Tissue of the Depurple cauliflower was the most resistant to the heat, irrespectively to the heating technology. Local heterogeneity in the cell wall and cell membrane, expected as a plant variety-dependent functional property, was proposed as a possible explanation because sterol extractability under lower heat-transfer efficiency, i.e., steaming and sous-vide, decreased in Depurple and increased in Cheddar as well as because the extractability of sterols and tocopherols was greater in Cheddar.

Pea cell wall integrity controls the starch and protein digestion properties in the INFOGEST in vitro simulation

The cell wall microstructure has been recognized to modulate the digestibility and bioaccessibility of nutrients in whole pulse foods, while the role of cell wall integrity is unclarified in the hydrolysis of intracellular nutrients during human gastrointestinal transit. Intact pea cells were isolated to prepare a series of cell wall integrity subjected to cooking and followed by the in vitro hydrolysis of starch and protein properties using the INFOGEST 2.0 in vitro simulation. Thermal properties showed that cell samples either in raw or cooked form with different wall integrity exhibited similar and higher starch gelatinization temperatures compared to the isolated starch counterpart. It was found that intact pea cells showed the limited hydrolysis extent of the maltose (16.2%) and NH2 (6.7%) compared to the damaged cells. In addition, intact cells also withheld the cell wall integrity throughout gastrointestinal digestion with minor rupture, and presented the higher protein molecular weight (70 kDa) in the SDS-PAGE profiles. Results suggested that the in vitro starch and protein digestion properties are modulated by the cell wall integrity, which may lead to lower glycemic response and open up the possibilities of designing health food products.

Influence of high hydrostatic pressure pretreatment on properties of vacuum-freeze dried strawberry slices

Effects of high hydrostatic pressure (HHP) (50, 100, 150, 200 and 250 MPa) pretreatment on water mobility and distribution, drying duration, microstructure, color, cell wall fraction and tissue structure of strawberry slices were investigated. HHP significantly increased water mobility of the strawberry slices, resulting in the reduction of drying duration by 9-24%. As the pretreatment pressure was increased, redness value and anthocyanin content continuously increased, soluble pectin (SBP) content increased and then decreased, while the contents of protopectin (PTP) and cellulose decreased. After the HHP pretreatment, chromoplasts and moisture was distributed more uniformly in the strawberry slices. Microscopy images showed the formation of microscopic holes or channels in the matrix and the breakdown of tissue structure by HHP. Results suggested HHP pretreatment disrupted the integrity of the fresh strawberry which enhanced the drying efficiency and migration of the chromoplasts during the vacuum-freeze drying process.

Influence of ultrasound on the functional characteristics of indigenous varieties of mango (Mangifera indica L.)

The present study was conducted to evaluate the effect of ultrasonic (US) treatment on chemical characteristics and antioxidant potential of pulps obtained from eight mango varieties indigenous to Pakistan. There was a significant (p < 0.05) effect of varieties and US treatment on chemical characteristics i.e. pH, acidity, TSS, vitamin C contents, total sugars (%), reducing sugars (%) and non-reducing sugars (%). Microstructure evaluation of pulp from all mango varieties showed deshaped middle lamella and cell wall of cells after 8 min of US treatment. At 4 min of US treatment as per shaped cell wall and middle lamella, the chemical characteristics and antioxidant potential were higher. The total phenolics (TP), flavonoids (TF) and total antioxidant activity (TAA) of pulp from most varieties increased significantly (p < 0.05) after US treatment for 4 min but decreased successively after each treatment i.e. 8 and 12 min. The maximum value (314.17 μg AAE/mL pulp) of DPPH was shown by pulp from Dosehri and the minimum (158.67 μg AAE/mL pulp) was found in pulp from Langra before US treatment. The DPPH values of pulp from most of the varieties increased significantly (p < 0.05) after US treatment for 4 min but decreased successively after each treatment but pulp from Langra showed increasing trend after 8 min of US treatment which decreased after 12 min of treatment. The total anthocyanin (TA) values of pulp from Chaunsa, Dosehri, Sindhri, Gulab Khas and Langra increased abruptly after US treatment for 4 min but decreased successively after subsequent treatment. The pulp from Desi, Anwar Ratol, Gulab Khas and Langra showed an abrupt decrease in TA after 8 min of US treatment. An increasing trend of values of total carotenoids (TC) was shown by pulp from all mango varieties after 4 min of US treatment but decreasing trend was observed with subsequent increase in time of US treatment.

Application of non-thermal pretreatment techniques on agricultural products prior to drying: a review

BACKGROUND

Most agricultural crops contain high moisture content (80-95% wet basis (wb)) which makes them very susceptible to microbial damage leading to shorter shelf-life and high postharvest losses. The high perishability of these agricultural products requires preservation techniques to prolong their shelf-lives. Drying remains an important component of processing in this regard. Therefore, any pretreatment methods for drying agricultural product that decreases the moisture content and minimizes drying time by conserving the quality of the crop product is of prime significance. This article is a comprehensive review of recent developments of non-thermal pretreatment (NTP) methods. A summary of their significance, emerging and innovative methods of this technology together with its applications and limitations are discussed. This article further examines the environmental impact of NTP techniques.

RESULTS

NTP techniques, such as high pressure, ultrasound, pulsed electric field and osmotic dehydration methods are essential operations for pre-dehydration of agricultural products prior to drying. These techniques can avoid the deleterious effects of heat on nutritive value, colour and flavour of agricultural products compared to thermal pretreatments. They also enhance the inactivation of the enzymes, improve energy efficiency and mass transfer, reduce processing time, preserve bioactive compounds, improve drying kinetics and drying rate, minimize enzymatic browning, and enhance product quality.

CONCLUSION

These findings will provide a better understanding of different NTP methods and also make available more information for selecting pretreatment techniques for drying of agricultural products. © 2020 Society of Chemical Industry.

Texture Modification Technologies and Their Opportunities for the Production of Dysphagia Foods: A Review

Dysphagia or swallowing difficulty is a common morbidity experienced by those who have suffered a stroke or those undergone such treatments as head and neck surgeries. Dysphagic patients require special foods that are easier to swallow. Various technologies, including high-pressure processing, high-hydrodynamic pressure processing, pulsed electric field treatment, plasma processing, ultrasound-assisted processing, and irradiation have been applied to modify food texture to make it more suitable for such patients. This review surveys the applications of these technologies for food texture modification of products made of meat, rice, starch, and carbohydrates, as well as fruits and vegetables. The review also attempts to categorize, via the use of such key characteristics as hardness and viscosity, texture-modified foods into various dysphagia diet levels. Current and future trends of dysphagia food production, including the use of three-dimensional food printing to reduce the design and fabrication time, to enhance the sensory characteristics, as well as to create visually attractive foods, are also mentioned.

Innovative Nonthermal Technologies: Chlorophyllin and Visible Light Significantly Reduce Microbial Load on Basil

Due to the high amount of biologically active compounds, basil is one of the most popular herbs. However, several outbreaks have been reported in the world due to the consumption of basil contaminated with different food pathogens. The aim of this study is to apply nonthermal and ecologically friendly approach based on photosensitization for microbial control of basil which was naturally contaminated with mesophils and inoculated with thermoresistant food pathogen Listeria monocytogenes 56Ly. The obtained data indicate that soaking the basil in 1.5·10^-4 M chlorophyllin (Chl) for 15 min and illumination with light for 15 min at 405 nm significantly reduced total aerobic microorganisms on basil by 1.3 log CFU/g, and thermoresistant L. monocytogenes 56Ly from 6.1 log CFU/g in control to 4.5 log CFU/g in the treated samples. It is important to note that this treatment had no impact on enzymatic activity of polyphenol oxidase and pectinesterase. Results obtained in this study support the idea that photosensitization technique with its high selectivity, antimicrobial efficiency and nonthermal nature can serve in the future for the development of safe nonthermal and environmentally friendly preservation technology for different fruits and vegetables.

Evaluation of the impact of food matrix change on the in vitro bioaccessibility of carotenoids in pumpkin (Cucurbita moschata) slices during two drying processes

The variable bioaccessibility of carotenoids depended on changes of matrix driven by drying.