Study on the mechanism of volume expansion and texture formation of apple cube dried by instant controlled pressure drop drying (DIC)

Understanding the mechanism of saccharides type and concentration affecting texture of freeze-dried pectin-CMC cryogels through experiment and molecular dynamic simulation

Saccharides are the dominant factor shaping the texture of freeze-dried products. This study investigated the impact of various molecular-weight saccharides at different concentrations on the physical properties and intermolecular interactions of pectin-CMC cryogels by experiment and molecular dynamic (MD) simulations. Results showed that the increased shrinkage of cryogels and enhanced molecular interactions between saccharides and pectin-CMC were mechanisms that enhanced the hardness of cryogels. Notably, the cryogel with fructose exhibited significantly higher hardness compared to cryogels with other saccharides. The cryogel containing 16 % fructose had the lowest glass transition temperature (Tg), leading to the highest shrinkage (70 %). Moreover, the MD results revealed that fructose had the highest intermolecular interaction energy (coulombic short range) with pectin-CMC (-5316.78 kJ/mol). This study revealed that the intermolecular interactions between the added saccharide and the pectin-CMC, in addition to the density of the cryogel, are critical determinants of the hardness and crispness of cryogels.

Evaluation of Drying Characteristics and Quality Attributes for Microwave Vacuum Drying of Pork Skin Crisps

As an important by-product of pork, pork skin can be processed into meat-based leisure food products to improve its utilization. In this study, microwave vacuum drying (MVD) technology was used to investigate the effects of microwave powers (600, 700, and 800 W) and processing duration on the drying characteristics and quality attributes of pork skin crisps (PSC). Five classical drying models were used to non-linearly fit the experimental data, and the Midilli et al. model was suitable for characterizing the MVD process of PSC. Before reaching a constant rate of drying, increasing microwave power and time can improve the brittleness and expansion ratio of PSC. In the constant rate drying stage, most of the free water in PSC was removed, showing the best brittleness and a stable expansion ratio. High power and long processing time can lead to serious lipid oxidation and change the flavor of PSC. Overall, the desired quality of PSC is recommended as 700 W for 6 min. This study can provide a reference for MVD application of meat-based by-product leisure foods.

Textural formation of instant controlled pressure drop-dried peach chips: Investigation of the electrical, thermal, and textural properties of predried peach slices with osmotic dehydration pretreatment

In this study, the effect of osmotic dehydration (OD) pretreatment with various sugar (erythritol, glucose, and trehalose) on the quality of hot-air-predried peach slices was investigated, particularly focusing on electrical properties, texture, thermal stability, and cell wall strength. Furthermore, the correlation between the properties of predried peach slices and the texture of the instant controlled pressure drop (DIC) dried peach chips was explored. OD pretreatments improved the stability and integrity of the cell wall and cell membrane of pre-dried peach slices, which inhibited the excessive expansion of samples during DIC drying. Especially, peach chips with trehalose-OD exhibited the highest crispiness (1.05 mm), the highest hardness (101.34 N) was obtained in erythritol-OD samples. Overall, the type of osmotic agents affected the texture of DIC peach chips with OD pretreatments. It should be noted that trehalose is a promising osmotic agent for controlling and regulating the quality of DIC peach chips.

Pore development in viscoelastic foods during drying

In this paper, we present a numerical model that can describe the pore formation/cavitation in viscoelastic food materials during drying. The food material has been idealized as a spherical object, with a core/shell structure and a central gas-filled cavity. The shell represents a skin as present in fruits/vegetables, having a higher elastic modulus than the tissue, which we approximate as a hydrogel. The gas-filled pore is in equilibrium with the core hydrogel material, and it represents pores in food tissues as present in intercellular junctions. The presence of a rigid skin is a known prerequisite for cavitation (inflation of the pore) during drying. For modeling, we follow the framework of Suo and coworkers, describing the inhomogeneous large deformation of soft materials like hydrogels - where stresses couple back to moisture transport. In this paper, we have extended such models with energy transport and viscoelasticity, as foods are viscoelastic materials, which are commonly heated during their drying. To approach the realistic properties of food materials we have made viscoelastic relaxation times a function of Tg/T, the ratio of (moisture dependent) glass transition temperature and actual product temperature. We clearly show that pore inflation only occurs if the skin gets into a glassy state, as has been observed during the (spray) drying of droplets of soft materials like foods.

Dehydration study of apple slices by a non-thermal process

This study investigated the impacts of a drying process under low temperature and reduced pressure (non-thermal drying) on the final dehydrated products characteristics. This process is based on the retention of water on molecular sieves with a good selectivity against these molecules. In this study, drying experiments of 7mm thick apple slices (AS) were performed and compared to apple slices pretreated by freezing. It was concluded that the dehydrated apple slices were depleted of the maximum amount of water after 12 hours of drying, with a final water content equal to 12 ± 1.75%, whereas after freezing pretreatment, a decrease in drying time to 7 hours was observed, as well as a decrease in water content to 10 ± 0.5%. This explains the effect of freezing pretreatment on accelerating water transfer. In addition, a convective drying was performed on the apple slices at 60°C, which allows comparison with the slices dried by our non-thermal drying process. In order to characterize the obtained fruits, characteristic analyses such as water activity (Aw), color, texture (hardness), and dimensions (diameter and thickness) were performed before and after each drying experiment. Thus, continuous measurements of temperature, humidity, and pressure, within the enclosure, were determined during the experiments using a wireless sensor system controlled by a programming Arduino. Finally, mathematical modeling by various models (Newton, Page, Midilli, etc.) was performed to determine the most suitable model describing the non-thermal and convective drying of apple slices.

Freezing pre-treatment improves radio frequency explosion puffing (RFEP) quality by altering the cellular structure of purple sweet potato [Ipomoea batatas (L) Lam.]

Radio frequency explosion puffing (RFEP) is a novel oil-free puffing technique used to produce crispy textured and nutritious puffed snacks. This study aimed to investigate the effects of freezing at different temperatures (-20 °C, -40 °C, -80 °C) for14 h and freezing times (1 and 2 times) on the cellular structure of purple sweet potato and the quality of RFEP chips. The analysis of cell microstructure, conductivity, and rheology revealed that higher freezing temperatures and more freezing times resulted in increased damage to the cellular structure, leading to greater cell membrane permeability and decreased cell wall stiffness. However, excessive damage to cellular structure caused tissue structure to collapse. Compared with the control group (4 °C), the RFEP sample pre-frozen once at -40 °C had a 47.13 % increase in puffing ratio and a 61.93 % increase in crispness, while hardness decreased by 23.44 % (p < 0.05). There was no significant change in anthocyanin retention or color difference. X-ray microtomography demonstrated that the RFEP sample pre-frozen once at -40 °C exhibited a more homogeneous morphology and uniform pore distribution, resulting in the highest overall acceptability. In conclusion, freezing pre-treatment before RFEP can significantly enhance the puffing quality, making this an effective method for preparing oil-free puffing products for fruits and vegetables.

Effects of inoculation with a binary mixture of Lactobacillus plantarum and Leuconostoc citreum on cell wall components of Chinese Dongbei suancai

This study aimed to investigate the effects of inoculation with a starter culture consisting of Lactobacillus plantarum LNJ002 and Leuconostoc citreum BNCC 194779 on microbial community, cell wall polysaccharide characteristics, cell wall degrading enzymes, and microstructure during Chinese Dongbei suancai fermentation. The results showed that Lactobacillus (98.75%) was the dominant genus during fermentation of Dongbei suancai. The principal coordinates analysis (PCoA) suggested that inoculation with Lactobacillus promoted the stability of microbial community structure during Chinese Dongbei suancai fermentation. Besides, the lower content in cellulose (80.28 ± 2.61 ug/mg) and pectin (53.56 ± 2.67 ug/mg) observed in the inoculated fermented suancai. Simultaneously, the inoculated fermented suancai had the most decreases in SR 1 (70.35%) and SR 3 (72.06%) and the most increase in SR 2 (950%), which suggested that inoculation intensified the decrease of the linearity and the RG-1 branching degree of pectin. The contents of polygalacturonase (PG) and pectin methylesterase (PME) in inoculated fermented suancai were 21.06% and 21.86% higher than those in naturally fermented suancai. In addition, the surface of suancai leaves gradually changed from smooth to rough during fermentation, which was accelerated by inoculation. Moreover, Lactobacillus, Aspergillus, Wallemia and Mucor were all negatively correlated with cellulose and GalA. These results revealed that inoculation promoted the formation of dominant genus structure during suancai fermentation, changed the effects of enzymes on the degradation of cell wall components, thereby accelerated the formation of Chinese Dongbei suancai texture.

The role of fructose at a range of concentration on the texture and microstructure of freeze-dried pectin-cellulose matrix cryogel

Freeze-dried (FD) fruit and vegetable materials with a large amount of sugar are unstable. With the aim to understand the structure formation of FD products, the effects of fructose content on the texture and microstructure of FD matrix were investigated by using pectin-cellulose cryogel model. Cryogels containing fructose of 0-40% were produced using freeze-drying at three different primary drying temperatures of -40, -20, and 20°C. The resultant cryogels were characterized by texture profile analyzer, scanning electron microscope, and μCT. Results indicated that at drying temperature of -40°C, increasing fructose concentration promoted the hardness of the cryogels, and cryogels of 16% fructose obtained maximum hardness. Excessive fructose (≥20%) weakened the described hardness, while exhibiting stronger springiness and resilience. The microstructure showed that dense pores and increased wall thickness due to fructose aggregation were critical factors responsible for increased hardness. The porous structure as well as relatively large pore size were necessary for crispness, in addition, rigid pore wall with certain strength were also required. At the drying temperature of 20°C, large hetero-cavities dominated the microstructure of cryogels with 30% and 40% fructose, caused by melting inside during FD process. In this situation, lower Tm (-15.48 and -20.37°C) were responsible for cryogels' melting In conclusion, if possible, regulating fructose content and state may enable the precision texture design of FD fruit and vegetable foods.

Instant controlled pressure drop drying: A review on preservation of quality characteristics in fresh produce

This review describes the efficient Instant controlled pressure drop drying technology. The Détente Instantanée Contôlée (DIC), French for Instant Controlled Pressure-Drop drying, has prodigious potential to cause least variations in the quality characteristics of the final dried product. This review article spotlights the principle of DIC with its effect on vitamins (ascorbic acid), bioactive compounds (carotenoids, polyphenols), physicochemical properties (moisture, rehydration capacity, water holding capacity, color, microstructure texture) and sensory properties of fresh produce. DIC is a thermo-mechanical technique accomplished by treating the fresh produce to saturated steam for less time period, which is carried out by an immediate pressure drop to achieve vacuum. This technique also provides reduced drying time, better volume expansion with larger porosity in the final dried product. It leads to a swift vaporization of the water within fresh produce cells. DIC-treated fresh produce are quickly rehydrated and retains sensory and nutrient quality.

Effect of osmotic dehydration with different osmosis agents on water status, texture properties, sugars, and total carotenoid of dehydrated yellow peach slices

The water status, texture properties, sugars, and total carotenoid of dehydrated yellow peach slices pretreated with or without osmotic dehydration (OD) combined with heat pump drying were studied. In this study, different osmotic agents were used, namely, sucrose and isomaltooligosaccharide (IMO) with 30 °Brix for 1, 3, and 5 h. Results showed that the dehydrated samples pretreated by sucrose-OD with the best shape and cell structure showed lower hardness compared to the dehydrated yellow peach slices with IMO-OD pretreatment and without OD pretreatment. Notably, the highest total carotenoid content was found in dehydrated yellow peach slices pretreated by IMO-OD, followed by samples without OD, and samples with sucrose-OD pretreatment. In addition, the lowest a_W (0.517) was obtained in samples with IMO-OD for 5 h, which was beneficial for storage. The assessment of water status and total carotenoid content of dehydrated yellow peach slices showed that IMO-OD pretreatment could better improve the quality of dehydrated fruits. Moreover, the use of IMO in OD treatment was a good alternative to sucrose.

An Overview on Food Applications of the Instant Controlled Pressure-Drop Technology, an Innovative High Pressure-Short Time Process

Food processing systematically aims at meeting the needs of consumers who are looking for total high quality and perfect food safety. As the various thermal and non-thermal food preservation technologies often affect the natural properties in terms of sensation, flavor, texture, etc., instant controlled pressure drop (DIC) has been conceived as a relevant, innovative process in this field. DIC uses high saturated steam pressure and short duration to provide a new way to expand biological matrices, improve drying, decontaminate, and extract biologically active compounds, among other attributes. Therefore, this review focuses on describing the applications of DIC technology on a wide range of products such as foods and by-products that have been processed both in the laboratory and on an industrial scale. The application of DIC has shown the possibility of a significant leap in quality improvement and cost reduction in the food industry. DIC reduces the drying time of fruits and vegetables, and improves the extraction of essential oils, vegetable oils, and antioxidant components. It also provides strong decontamination, eliminates vegetative microorganisms and spores, and reduces non-nutritional and allergenic components. Over the past 33 years, this technology has continued to expand its food applications and improve its characteristics on an industrial scale. But there are still many food unit operations that can be taken to the next level with DIC.