Effect of freezing and different thawing methods on the content of polyphenolic compounds of red grape skins

Cryoprotective role of vacuum infused inulin on the quality of artichoke: Interactive effects of freezing, thawing and storage period

Freezing of artichoke is a promising alternative to storing it in brine and canning. The perishable vegetable was vacuum infused with inulin to improve freezing tolerance. Artichokes with and without inulin were frozen by static, air blast and individual quick freezing (IQF) methods and thawed by microwave, 25 °C and 4 °C temperature levels at each month of 6-months storage. Process conditions were evaluated by multivariate analysis of variance (MANOVA) and were found significant on the quality parameters. Inulin infusion better conserved the aw, color, texture, ascorbic acid and overall integrity of artichokes during frozen storage. Inulin incorporation and IQF showed mutual positive effect on drip loss. Polyphenol oxidase (PPO) activity values fitted to 2nd order kinetic and the highest residuals were determined in static freezing. PPO showed alleviating effect on total phenolic content. Vacuum impregnation caused a color difference prior to freezing, but was found effective for maintaining color during storage. As a result, the use of quick freezing techniques together with the addition of cryoprotectant was effective in the preservation of artichoke quality attributes during frozen storage.

Revitalizing Unfermented Cabernet Sauvignon Pomace Using an Eco-Friendly, Two-Stage Countercurrent Process: Role of pH on the Extractability of Bioactive Phenolics

As the major byproduct of the winemaking industry, grape pomace remains an untapped source of valuable bioactive phenolic compounds. This study elucidated the optimal aqueous extraction parameters for maximizing phenolic extractability, while avoiding the use of harsh conventional solvents and limiting water usage, from Cabernet Sauvignon grape pomace in which the red grape was processed for white wine. In the single-stage aqueous extraction process (AEP), the concurrent impact of pH (2.64–9.36), solids-to-liquid ratio (SLR, g pomace/mL water) (1:50–1:5), and temperature (41.6–58.4 °C) on the total phenolic content (TPC) of Cabernet Sauvignon pomace was evaluated alongside a kinetic study (15–90 min). Optimal single-stage extraction conditions (pH 9.36, 1:50 SLR, 50 °C, 75 min) guided the development of a two-stage countercurrent extraction process (pH 9.36, 1:10 SLR, 50 °C, 75 min) to further reduce water consumption without compromising overall extractability. The countercurrent process reduced fresh water usage by 80%, increased the TPC of the extracts by 18%, and improved the in vitro antioxidant activities (ABTS and ORAC) of the extracts. Untargeted metabolomics enabled the identification of a diverse pool of phenolics, especially flavonol glycosides, associated with grape pomace, while further phenolic quantitation detected improvements in the release of commonly bound phenolics such as ferulic acid, p-coumaric acid, syringic acid, and protocatechuic acid in alkaline extracts compared to the ethanolic extract. This investigation provides an efficient, eco-friendly extraction strategy suitable for applications in functional food, beverage, nutraceutical, and cosmetic industries.

Effects of different thawing methods on the physicochemical changes, water migration and protein characteristic of frozen pompano (Trachinotus ovatus)

The effects of five thawing methods (ultrasonic thawing [UT], radiofrequency thawing [RFT], water immersion thawing [WIT], microwave thawing [MT], and cold storage thawing [CST]) on physicochemical properties, water migration, and protein characteristic of whole frozen pompano (Trachinotus ovatus) were investigated and compared with fresh samples (FS). The physicochemical changes of thawed pompano were analyzed based on pH, total volatile basic nitrogen (TVB-N), color difference. The protein aggregation, physicochemical properties and conformation of myofibrillar proteins (MPs) were evaluated by Sodium dodecyl sulfate polyacrylamide gel electrophoresis, differential scanning calorimetry, and Raman spectra, respectively. Water migration and MPs microstructure were measured by low-field nuclear magnetic resonance (LF-NMR) and scanning electron microscope (SEM), respectively. The results showed that different thawing methods could accelerate the protein denaturation and decrease of quality in pompano, especially MT treatment causing more seriously local overheating phenomena. Among the samples with different thawing treatments, the changes of pH, TVB-N values, and color difference in RFT and UT were closed to that from FS. The MT had the shortest thawing time, but could produce the damage of structural muscle. RFT had desirable thermal stability and made the protein secondary structure more stable, the myofibril bundles were also straight and smooth by SEM observation. The content of bound water and free water had no significant changes by LF-NMR. Therefore, compared with other thawing methods, RFT is a desirable thawing method for maintaining the quality of thawed pompano. PRACTICAL APPLICATIONS: Before further processing of frozen pompano, the thawing process is an important part, which is highly associated with the quality of products. The damage of conformation and properties in aquatic protein caused by freeze-thaw process is very obvious in food processing industry. Compared to microwave thawing, ultrasonic thawing, and traditional methods, the radiofrequency thawing (RFT) could reduce changes in structure and properties of protein, and have higher thawing efficiency. The temperature distribution on the pompano surface was uniform during the radiofrequency process with higher strong penetration and less local overheating. The RFT is a desirable thawing method to maintain the quality and extend the shelf life of frozen pompano for application in food industry.

Influence of Two Different Cryoextraction Procedures on the Quality of Wine Produced from Muscat Grapes

Freezing grapes is a winemaking technique known as cryoextraction that intends to modify the composition of the final wines. The changes that take place in the frozen grapes facilitate the transfer of certain compounds from the grape skins into the musts because of the grape's unstructured tissues. For this study, the white grape variety Muscat of Alexandria was selected. Two different cryoextraction procedures have been analyzed as follows: (i) Ultrafast freezing, and (ii) liquid nitrogen freezing. The wines obtained using liquid nitrogen freezing exhibited higher levels of terpenoids, as well as higher levels of hydroxylic compounds and fatty acids than both the wines obtained through traditional methods and ultrafast freezing wines. In any case, both freezing techniques produced wines of a more intense aroma compared with those wines obtained by traditional methods. In fact, liquid nitrogen freezing produced the wines with the most intense aroma and were the best valued by the tasting panel.

Effect of fuzzy-controlled slow freezing on pumpkin (Cucurbita Moschata Duch) cell disintegration and phenolics

Freezing has been widely used to preserve vegetables including seasonal pumpkins. This work aimed to investigate the effects of freezing on pumpkin cell disintegration and phenolics. A fuzzy logic control (FLC) system was built to obtain better temperature control of the freezing system. Changes in cellular disintegration, electrical conductivity and phenolics content were evaluated. The angle measure technique and principal component analysis were used to delineate the surface texture changes of the frozen pumpkin cells. The results showed that FLC offered reliable temperature control performance. Freezing at -18 °C for 7 h caused the highest cell degradation of 0.467 on the disintegration scale. Decomposition was also indicated by an almost double increase in electrical conductivity. The changes in texture were accurately reflected in the mean angle spectra and 81.3% and 7.4% of the variability due to treatments could be explained by two principal components respectively. Freezing pumpkin at -18 °C for 6 h correlated to the maximum increase in total phenolics of 70.44%. The increased phenolics were dominated by caffeic acid, chlorogenic acid and p-coumaric acid. In conclusion, as the freezing system exhibits positive effects on the phenolics content of pumpkin, it may be employed to process seasonal pumpkin to obtain higher value from the produce.

Advantages of Liquid Nitrogen Quick Freezing Combine Gradient Slow Thawing for Quality Preserving of Blueberry

Berries are perishable fruits with high nutritional value. Freezing is an effective way for food preservation. Freezing and thawing methods play key roles in preserving edible values and commodity values of food. This study investigated the effects of spray liquid nitrogen quick freezing (NF−20~−100 °C) and gradient thawing on the physical and functional characteristics of blueberries by using immersion and refrigerator freezing and microwave, ultrasonic, room- and low-temperature, and static-water thawing as comparisons. The results show that NF−80 °C freezing combined with −20~−5~4 °C. gradient thawing can retain more than 95% of polyphenols and other nutritional compounds (including pectin, soluble sugar, and vitamin C) in thawed blueberries compared with fresh blueberries. Besides, this method shows the best results in preserving the hardness, cell structure, and water distribution of blueberries. It is also revealed that the ultralow temperature (−100 °C) freezing does not bring a significant advantage in preserving blueberries. Rapid thawing methods such as microwave and ultrasound thawing are not suitable for blueberries, which might be due to their small size and thin skin. The results suggested that the combination of NF−80 °C freezing and −20~−5~4 °C gradient thawing is the optimal process for blueberry preservation. The outcomes of this study will serve as theoretical guidance for improving the industrial process for freezing and thawing blueberries.