Impacts of high pressure assisted freezing on the denaturation of polyphenol oxidase

Instability of natural deep eutectic solvents (NADESs) induced by Amadori rearrangement and its effects on cryopreservation of yeast cells

Natural deep eutectic solvents (NADESs) showing higher cryoprotective effects are attracting concerns, because during the storage, system browning always occurs in aldose/amino acid-based NADESs, which generated brown substances remarkably weaken the cryoprotective effects. In this study, proline/glucose-based (PG) and proline/sorbitol-based (PS) NADESs were prepared, of which storage stability, browning profile, brown substance, and cryoprotective effects were investigated. Results showed that PG at molar ratios of 1:1, 2:1, and 3:1, as well as PS at 1:1, and 2:1 can form NADESs, among which only the PG-based ones could get browning after storage. The predominant brown substance was identified as 1-deoxy-1-L-proline-d-fructose (C11H19O7N, 278 m/z), which was subsequently verified to show cytotoxicity and decrease Saccharomyces cerevisiae cells viability after cryopreservation, suggesting that the brown substance could take a negative effect on cryopreservation. This study may help to attract more concerns to the storage and cryopreservation stabilities of the NADESs in food-related applications.

The effect of structural changes on the activity of peroxidase with different initial state under high-pressure freezing

The combined impact of initial state, pressure, and freezing on peroxidase denaturation during high-pressure freezing (HPF) processing of enzyme-containing foods remains unclear. This study investigated solid-liquid (initial low/high concentration) biphasic peroxidase using spectroscopic and computer simulation techniques to analyze structural changes affecting peroxidase (POD) activity under HPF. The results indicate that the primary factors determining POD activity during HPF treatment can be ranked as follows: concentration > physical state > pressure > freezing. Higher initial concentrations strengthen protein interactions, leading to a 1% increase in the molecular diameter and a 34% increase in molecular height of HL-POD, thereby increasing aggregation likelihood during crystallization and facilitating structural changes that activate enzymes by 6-17%. The amide I peak proves to be a reliable indicator for monitoring both POD activity and structural alterations. This study offers valuable insights for optimizing HPF technology in food processing.

In situ investigation of ice fractions and water states during partial freezing of pork loins and shrimps

Ice fractions and water states in partially frozen muscle foods greatly affect their quality. In the study, a variable temperature nuclear magnetic resonance (VT-NMR) with a liquid nitrogen temperature control system was employed to in situ investigate the relationship between ice fractions and temperatures and changes in water states during partial freezing and thawing of pork and shrimp. Results indicated that changes in ice fractions ranging from -2 ∼ -20 °C could be divided into 3 stages including slow increase, random leap and remarkable leap. More serious damages to the structures related to immobile water occurred in shrimp than in pork, and partial freezing also caused deterioration in muscle fibres related to free water. Additionally, -2 ∼ -3 °C and - 3.5 °C were the appropriate partial freezing temperatures for pork and shrimp, respectively. Therefore, the VT-NMR method possessed great potential for fundamental studies and applications of partial freezing of muscle foods.

Tunable thermoresponsive hydrogels for temperature regulation and warning in fruit and vegetables preservation

Fresh fruit and vegetables usually suffer from quality deterioration when exposed to inappropriate temperatures. Common energy-input temperature regulation is widely applied but there remain challenges of increasing energy consumption. Passive temperature management regulates the heat transfer without energy consumption, showing a sustainable strategy for food preservation. Here, thermoresponsive hydrogels were constructed by incorporating NaCl and sodium dodecyl sulfate (SDS) micelles into a poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAM-co-AM)) network. Due to the excellent mechanical properties and reversible thermochromism at 14 °C and 37 °C, Gel-8 wt%-NaCl could inhibit temperature rise and avoid sunburn damage to peppers under direct sunlight by blocking the input of solar energy and accelerating moisture evaporation. Additionally, hydrogels could act as a feasible sensor by providing real-time visual warnings for inappropriate temperatures during banana storage. Based on the self-adaptive thermoresponsive behaviour, the prepared hydrogels showed effective performance of temperature regulation and quality preservation of fruit and vegetables.

Effect of magnetic fields on the structure, properties, baking performance of frozen wheat dough at different frozen stage

As an emerging physical technology, magnetic fields have been used to improve the quality of frozen and refrigerated foods. This study compared the effect of applying a static magnetic field (2 mT) at different stages of freezing and storage on the quality of frozen dough. Results suggested that the magnetic field significantly impacted frozen dough quality. It not only prevented the formation of ice crystals during the pre-freezing stage but also inhibited ice crystal growth during the following frozen storage. This effect helped to maintain the integrity of gluten proteins and their adhesion to starch granules by preventing the breakage of disulfide bonds and the depolymerization of gluten macromolecules. It was also observed that yeast inactivation and glutathione release were reduced, resulting in improved air retention and air production capacity of the dough. This, in turn, led to a more appealing volume and texture quality of the finished bread.

In-situ investigation of supercooling behaviour during high-pressure shift freezing of pure water and sucrose solution

Supercooling is a main controllable factor for the fundamental understanding the high-pressure shift freezing (HPSF). In the study, a self-developed device based on the diamond anvil cell (DAC) and confocal Raman microscopy was utilized to realize an in-situ investigation of supercooling behaviour during HPSF of the pure water and sucrose solution. The spectra were used to determine the freezing point which is shown as a spectral phase marker (SD). The hydrogen bond strengths of water and sucrose solution under supercooling states were estimated by peak position and peak area ratio of sub-peaks. The results showed that the OH stretching bands had redshift under supercooling states. Moreover, the addition of sucrose molecules could strengthen the hydrogen bonding strength of water molecules under supercooling states. Thus, the DAC combined with Raman spectroscopy could be considered a novel strategy for a deep understanding of the supercooling behaviour during HPSF.

Effect of tea polyphenols on the quality of Mackerel puree (Scomber scombrus) during refrigerated storage: Color, oxidative stability and microstructure

This study investigated the impact of adding tea polyphenols (TP) on the quality of mackerel puree during refrigerated storage. The study used whole mackerel fish and analyzed the sensory characteristics, physicochemical properties, and microstructure of the puree. As storage time increased, significant changes occurred in the puree, including increased levels of thiobarbituric acid value, protein carbonyl, and free radicals. The water holding capacity, whiteness, and pH value of the puree decreased. However, the addition of TP helped to preserve the quality of the mackerel puree, particularly in the later stages of storage. This was evidenced by reduced oxidation of lipids and proteins, minimal color change, and a more compact microstructure. The study also revealed that TP contributes to the development of a gel network within the mackerel puree, enhancing water retention and sensory qualities. These findings suggested that TP treatment has potential for preserving mackerel puree during refrigeration.

Deep eutectic solvents (DESs) films based on gelatin as active packaging for moisture regulation in fruit preservation

To develop a novel active packaging for fruit preservation, two different deep eutectic solvents (DESs) comprising choline chloride, betaine and glycerol [ChCl:Gly (1:2) and Be:Gly (1:2)] were prepared and the corresponding DESs-based films (DES@Gel) using gelatin as polymer matrix were fabricated. DES@Gel showed smoother morphologies and better optical and mechanical properties as compared with Gel. Moisture sorption isotherm curves, the enhancement of water vapour permeability (WVP) and the excellent moisture absorption-desorption cyclist performance illustrated the moisture regulation hypothesis mechanism of DES@Gel. Furthermore, cherry tomato preservation experiment was carried out and the groups treated with DES@Gel showed better performances. The moisture regulation property of DES@Gel could broaden new avenues for active packaging.

Comparative elucidation of bioactive and antioxidant properties of red dragon fruit peel as affected by electromagnetic and conventional drying approaches

The effects of near-infrared (NIRD), mid-infrared (MIRD), far-infrared (FIRD), microwave (MWD), and hot air drying (HAD) on drying kinetic, colour, phytochemical composition, and antioxidant activity of red dragon fruit peel (RDFP) was evaluated. Results indicated that drying methods induced varying microstructural and chemical changes on RDFP, significantly influencing moisture removal rates and phytochemical retention. The lowest drying time was observed for MWD, while MIRD presented the highest drying time. FIRD drying was more favourable for retaining TPC, TFC, betacyanin and betaxanthin, while the ascorbic acid content was better retained during MIRD and NIRD. Enhancements in ABTS, CUPRAC and reducing power were associated with FIRD, and NIRD and MIRD enhanced DPPH and HRSA. Overall, chemical modifications induced by drying improved the phytochemical and antioxidant properties but presented adversative effects on ascorbic acid and DPPH. The study presented an essential background for the optimal drying of RDFP.

Minimizing polyphenols and enzymes degradation using hydrogel packaging with combined evaporative and daytime radiative cooling functions during ambient transportation

Polyphenols and enzymes usually suffer from degradation during transportation due to the lack of a cold chain system in developing countries and regions. In this study, anthocyanin and trypsin were selected as examples of polyphenols and enzymes and investigated for minimizing their degradation during ambient transportation using hydrogel packaging with combined evaporative and daytime radiative cooling functions. A polyacrylamide/polyvinyl alcohol contained with nanoparticles (NPs@PAAm/PVA) hydrogel packaging was thus developed. The NPs@PAAm/PVA packaging exhibited desirable swelling behaviour, high solar reflectance, and strong atmospheric emissivity to synergistically achieve evaporative and daytime radiative cooling. The indoor experiments indicated that the vial with NPs@PAAm/PVA packaging realised sub-ambient temperatures under different working temperatures and humidities, and the field tests indicated that the vial with NPs@PAAm/PVA packaging could effectively preserve the anthocyanin and trypsin without degradation caused by strong sunlight and high temperature. Consequently, the NPs@PAAm/PVA packaging with evaporative and daytime radiative cooling effects has promising prospects for anthocyanin and trypsin transportation in an energy-saving and sustainable manner.

Natural deep eutectic solvent: A promising eco-friendly food bio-inspired antifreezing

Bio-antifreezing is a green and highly effective strategy to inhibit ice nucleation. Bio-inspired antifreezing faces the severe challenges of significant toxicity and complex manufacturing procedures. Bio-inspired antifreezing natural deep eutectic solvent (Ba-NADES) could be an efficient and low or no-toxicity approach for the frozen food industry. Ba-NADES form a strong hydrogen bond network system under cold conditions, capably reducing the melting point of the system below the freezing point and effectively inhibiting ice growth. It has efficaciously alleviated freeze injury by Ba-NADES. The review highlights the current strategies of bio-inspired antifreezing, cold resistance behavior in organisms, and the existing applications of Ba-NADES. It updated information concerning their mechanisms for antifreezing. It emphasizes that the role of water on the antifreezing quality of NADES is worthy of further investigation for more extensive food applications. This work will provide a comprehensive overview of NADES antifreezing.

Insight into the microorganisms, quality, and protein structure of golden pompano (Trachinotus ovatus) treated with cold plasma at different voltages

Cold plasma (CP) is a non-thermal novel technology for the processing of heat-sensitive food products, but there is concern regarding its impact on food quality. Voltage is one of the most direct factors affecting the bacteriostatic effect of CP. Golden pompano (Trachinotus ovatus) was treated with CP at different voltages (10, 20, and 30 kV). The total viable count decreased as the CP voltage increased, reaching a maximum reduction of 1.54 lg CFU/g on golden pompano treated at 30 kV. No effects on water-holding capacity, pH, total volatile base nitrogen, and T_2b relaxation time were observed, indicating that all CP treatments retained the freshness and bound water of the samples. However, as the CP voltage increased, peroxide value and thiobarbituric acid-reactive substances of golden pompano gradually increased, the protein tertiary structure unfolded, and α-helices converted to β-sheets, indicating inevitable lipid and protein oxidation caused by excessive CP voltage. Therefore, a suitable voltage of CP should be selected to inhibits the growth of microorganisms, which avoids deterioration of sea-foods quality.

Effects of high pressure synergistic enzymatic physical state and concentration on the denaturation of polyphenol oxidase

The synergistic effect of the initial state of the enzyme and pressure level on the denaturation of PPO has not been clear yet, but it significantly affects the application of high hydrostatic pressure (HHP) in the enzyme-containing food processing. Solid (S-) and low/high concentration liquid (LL-/HL-) polyphenol oxidase (PPO) was used as the study object, and the microscopic conformation, molecular morphology and macroscopic activity of PPO under HHP treatments (100-400 MPa, 25 °C/30 min) were investigated by spectroscopic techniques. The results show that the initial state has a significant effect on the activity, structure, active force and substrate channel of PPO under pressure. The effec can be ranked as follows: physical state > concentration > pressure, S-PPO > LL-PPO > HL-PPO. High concentration has a weakening effect on the pressure denaturation of the PPO solution. Under high pressure, the α-helix and concentration factors play a crucial role in stabilizing the structure.

Application of physical field-assisted freezing and thawing to mitigate damage to frozen food

Freezing is an effective technique to prolong the storage life of food. However, the freeze-thaw process also brings challenges to the quality of food, such as mechanical damage and freeze cracks. Increasingly, physical fields have been preferred as a means of assisting the freezing and thawing (F/T) processes to improve the quality of frozen food because of their high efficiency and simplicity of application. This article systematically reviews the application of high-efficiency physical field techniques in the F/T of food. These include ultrasound, microwave, radio frequency, electric fields, magnetic fields, and high pressure. The mechanisms, application effects, advantages and disadvantages of these physical fields are discussed. To better understand the role of various physical fields, the damage to food caused by the F/T process and traditional freezing is discussed. The evidence shows that the physical fields of ultrasound, electric field and high pressure have positive effects on the F/T of food. Proper application can control the size and distribution of ice crystals effectively, shorten the freezing time, and maintain the quality of food. Microwave and radio frequency exhibit positive effects on the thawing of food. Dipole rotation and ion oscillation caused by electromagnetic waves can generate heat inside the product and accelerate thawing. The effects of magnetic field on F/T are controversial. Although some physical field techniques are effective in assisting F/T of food, negative phenomena such as uneven temperature distribution and local overheating often occur at the same time. The generation of hotspots during thawing can damage the product and limit application of these techniques in industry. © 2022 Society of Chemical Industry.

Ca2+ATPase enzyme activities and lipid and protein oxidations of grass carp (Ctenopharyngodon idellus) stored at 4 °C for 30 min under electromagnetic fields

This work studied the effects of electromagnetic fields (EMF) with frequencies between 100 and 400 Hz and a fixed strength of 12 mT on cold storage of grass carp at 4 °C for 30 min, and Ca²⁺ATPase enzyme activities, and lipid and protein oxidations in samples were measured to assess changes in intracellular Ca²⁺ concentration and oxidative stability. Results showed higher Ca²⁺ATPase activities in samples treated with EMF frequencies. Significant (p < 0.05) decreases occurred in protein oxidation for samples treated between 100 and 300 Hz, but an increase was observed for treatment with 400 Hz. However, the lipid oxidation increased for samples treated up to 200 Hz and decreased with further increase in frequency to 300 and 400 Hz. Nuclear magnetic resonance analysis showed that exposure to different frequencies of EMF could reduce the association of water molecules with protein for both bound and immobilized water. Overall, treatments of EMF between 100 and 400 Hz could improve grass carp quality during cold storage.

Comparative freezing study of broccoli and cauliflower: Effects of electrostatic field and static magnetic field

The effects of 1, 3, 5 kV/cm electrostatic field (EF) and 2, 5, 8 mT static magnetic field (MF) on the quality of frozen broccoli and cauliflower (B and C) were studied. The freezing parameters were significantly improved by 3, 5 kV/cm EF or 8 mT MF treatment (P < 0.05), a maximum reduction of nucleation time and phase transition time by 20.14 % and 32.09 % was found in 5 kV/cm EF treated cauliflower. EF or MF treatment improved sample quality to some extent, the overall effect of 3 kV/cm EF was the best, which led to a maximum drip loss reduction of 64.3 % in cauliflower, accompanied by lower relative conductivity, higher ascorbic acid and less cell rupture. EF or MF did not significantly reduce the damage of the flavor. MF was less effective than EF in improving the quality of frozen B and C.

Development of natural deep eutectic solvents (NADESs) as anti-freezing agents for the frozen food industry: Water-tailoring effects, anti-freezing mechanisms and applications

Nature-inspired natural deep eutectic solvents (NADESs) as anti-freezing agents including Pro:Glc (5:3), Pro:Glc (1:1), Pro:Sor (1:1), and Urea:Glc:CaCl₂ (3:6:1) were prepared. Viscosity (η), conductivity (σ), activation energy of viscous flow (E_η) and conduction (E_ᴧ), transverse relaxation time (T₂), thermal behaviours, and anti-freezing capacities of the NADESs were investigated. A critical T₂ of 24.60 ms for η changes was obtained, and the relationship between η and T₂ was determined as lnη = -1.398lnT₂ + 10.688. Differentialscanningcalorimetry and low-field nuclear magnetic resonance analyses indicated NADESs could hinder the molecular motion as temperature decreased through enhancing the hydrogen-bonding strength, endowing them with excellent anti-freezing capacity. NADESs showed varied E_η (41.58 ∼ 45.72 kJ mol^-1) and E_ᴧ (48.31 ∼ 63.08 kJ mol^-1), of which Pro:Sor (1:1) possessed the greatest ones, showing its greatest temperature sensitivity and best anti-frosting capacity. Applications in frozen chicken breast further announced the potentials of NADESs as anti-freezing agents for the industry.

In situ investigation of cellular water transport and morphological changes during vacuum cooling of steamed breads

Dynamic investigation of the effects of vacuum cooling on cellular water transport and structural changes of steamed bread was carried out using transverse relaxation times (T₂) and proton density-weighted images in a nuclear magnetic resonance (NMR)/magnetic resonance imaging (MRI) analyser, respectively. Initially, both steamed bread at room temperature of 25 °C and freshly steamed bread at 85 °C had three peaks of T₂₁, T₂₂, and T₂₃, respectively representing the tightly bound water, loosely bound water, and free water, while an additional peak T₂₄, was observed in freshly steamed bread at 85 °C. After vacuum cooling, freshly steamed bread at 85 °C had a higher mass loss of 10.29% due to its high initial temperature, and both samples were clearly discriminated with PCA of 88.2%, indicating that the initial food condition affected the vacuum cooling process. Lastly, the NMR/MRI technique and correlations were accurate (R²> 0.98), thus suitable for model validation at microscale and macroscale.

Processing, chemical signature and food industry applications of Camellia sinensis teas: An overview

The plant Camellia sinensis is the source of different teas (white, green, yellow, oolong, black, and pu-ehr) consumed worldwide, which are classified by the oxidation degree of their bioactive compounds. The sensory (taste, aroma, and body of the drink) and functional properties of teas are affected by the amount of methylxanthines (caffeine and theobromine), amino acids (l-theanine) and reducing sugars in their composition. Additionally, flavan-3-ols, mainly characterized by epicatechins, catechins, and their derivatives, represent on average, 60% of the bioactive compounds in teas. These secondary metabolites from teas are widely recognized for their antioxidant, anti-cancer, and anti-inflammatory properties. Thus, Camellia sinensis extracts and their isolated compounds have been increasingly used by the food industry. However, bioactive compounds are very susceptible to the oxidation caused by processing and degradation under physiological conditions of gastrointestinal digestion. In this context, new approaches/technologies have been developed for the preservation of these compounds. This review presents the main stages involved in production of Camellia sinensis teas following a description of their main bioactive compounds, biological properties, stability and bioaccessibility. Besides, and updated view of Camellia sinensis teas in the field of food science and technology was provided by focusing on novel findings and innovations published in scientific literature over the last five years.

High-Pressure Processing for Sustainable Food Supply

Sustainable food supply has gained considerable consumer concern due to the high percentage of spoilage microorganisms. Food industries need to expand advanced technologies that can maintain the nutritive content of foods, enhance the bio-availability of bioactive compounds, provide environmental and economic sustainability, and fulfill consumers’ requirements of sensory characteristics. Heat treatment negatively affects food samples’ nutritional and sensory properties as bioactives are sensitive to high-temperature processing. The need arises for non-thermal processes to reduce food losses, and sustainable developments in preservation, nutritional security, and food safety are crucial parameters for the upcoming era. Non-thermal processes have been successfully approved because they increase food quality, reduce water utilization, decrease emissions, improve energy efficiency, assure clean labeling, and utilize by-products from waste food. These processes include pulsed electric field (PEF), sonication, high-pressure processing (HPP), cold plasma, and pulsed light. This review describes the use of HPP in various processes for sustainable food processing. The influence of this technique on microbial, physicochemical, and nutritional properties of foods for sustainable food supply is discussed. This approach also emphasizes the limitations of this emerging technique. HPP has been successfully analyzed to meet the global requirements. A limited global food source must have a balanced approach to the raw content, water, energy, and nutrient content. HPP showed positive results in reducing microbial spoilage and, at the same time, retains the nutritional value. HPP technology meets the essential requirements for sustainable and clean labeled food production. It requires limited resources to produce nutritionally suitable foods for consumers’ health.

Pressure-related cooling and freezing techniques for the food industry: fundamentals and applications

Cooling and freezing are two widely used methods for food preservation. Conventional cooling and freezing techniques are usually with low efficiency and prone to damage foodstuffs. In order to increase cooling and freezing efficiencies and ensure better food quality, many efforts have been performed. As effective solutions, pressure-related techniques such as vacuum cooling (VC), vacuum film cooling (VFC), vacuum spray cooling (VSC), pressure shift freezing (PSF) and isochoric freezing (ICF) have attracted a lot of interests. The current review intends to provide an overview of pressure-related cooling and freezing techniques for the food industry. In the review, the fundamentals including principles, experimental systems, thermodynamic and kinetic mechanisms and their relevant mathematical models are presented, latest applications of these techniques in the food industry are summarized, and future trends concerning technological development and industrialization are highlighted. Pressure plays an important role in improving the cooling and freezing processes and ensuring food qualities, and mathematical modeling is an effective tool for understanding the thermodynamic and kinetic mechanisms of these processes. However, the latest researches showed that despite many merits of these pressure-related processes, limitations still exist in applying some of the techniques in the food industry. For achieving technological development and industrialization of the pressure-related processes, further researches should focus on improving model performance, integrating multiple technologies, and cost control.