Effects of radiofrequency blanching on lipoxygenase inactivation, physicochemical properties of sweet corn (Zea mays L.), and its correlation with cell morphology

Effects of innovative dry-blanching on moisture, cell wall structure, physicochemical properties and volatile compounds of microwave infrared coupled dried ginger (Zingiber officinale roscoe)

In this study, various innovative dry-blanching methods (infrared, microwave, hot air, microwave-infrared, and microwave-hot air) were employed to process ginger prior to microwave-infrared coupled drying. The effects of dry-blanching on drying kinetics, moisture characteristics, ultrastructure, cell wall components, physicochemical properties, volatile compounds, and antioxidant activity of ginger were investigated. The study found that dry-blanching led to the destruction of the cellular structure and promoted moisture migration and evaporation. Concurrently, the process induced the release of phenolic compounds, thereby enhancing antioxidant activity. Dry-blanching accelerated the drying process. Furthermore, enzyme activity was inactivated, and the browning value was reduced by 0.29-10.87 % following dry-blanching. Infrared dry-blanching increased volatile compounds by 30.31 %, resulting in the highest levels of terpenes and the best preservation of flavor components. This research can serve as a reference for developing new pretreatment methods in drying.

Lipoxygenases (LOXs): Will turning off this genetic switch help safeguard the flavor and nutritional quality of stored lipid-rich staple foods?

Beyond storage capacity, long-term grain storage faces significant challenges due to the activity of lipoxygenases (LOXs). These enzymes catalyze the production of volatiles from free fatty acids, leading to stale odors and off-flavors. These changes degrade the quality of stored grains, even under regulated conditions, affecting the profitability of stored products to the farmers and the assurance of high-quality food for consumers. While LOXs are essential for various biological functions, their impact on storage highlights the need for targeted research to mitigate their negative effects. Optimizing LOX activity could enhance grain storability, reduce spoilage, and improve nutrient retention. This review explores recent advancements in understanding the roles of LOXs, focusing on how they can be tailored to enhance nutritional quality and shelf life. By modulating LOX activity, it is possible to address quality deterioration, support more sustainable food systems, and contribute to better nutritional security for consumers.

The exploration of pasteurization processes and mechanisms of inactivation of Bacillus cereus ATCC 14579 using radio frequency energy

Radio frequency (RF) heating has been utilized to investigate sterilization techniques, but the mechanism of sterilization via RF heating, particularly on Bacillus cereus (B. cereus), has not been thoroughly examined. In this paper, sterilization processes and potential bactericidal mechanisms of B. cereus using RF were investigated. The best heating and sterilization efficiency was achieved at (Electrode gap 130 mm, conductivity of bacterial suspension 0.1 S/m, volume of bacterial suspension 40 mL). Heating a suspension of B. cereus to 90 °C in 80 s using RF reduced the number of viable bacteria by 4.87 logarithms. At the cellular level, there was a significant leakage of nucleic acids and proteins from the bacterial cells. Additionally, the integrity of the cell membrane was severely damaged, with a decrease in ATP concentration of 2.08 mM, Na, K-ATPase activity to 10.7 (U/109 cells), and Ca, Mg-ATPase activity to 11.6 (U/109 cells). At the molecular level, transcriptomics analysis showed that RF heating of B. cereus to 65 °C produced 650 more differentially expressed genes (DEGs) compared with RF heating to 45 °C. The GO annotation analysis indicated that the majority of differentially expressed genes (DEGs) were predominantly associated with cellular components. KEGG metabolic analysis showed enrichment in microbial metabolism in diverse environments, etc. This study investigated the potential bactericidal mechanism of B. cereus using RF, and provided some theoretical basis for the research of the sterilization of B. cereus.

Study on the effects of radio frequency blanching on polyphenol oxidase activity, physicochemical properties, and microstructure of iron yam

The effects of radio frequency (RF) and hot water blanching on polyphenol oxidase (PPO) activity, physicochemical properties, and microstructure of iron yams were investigated. The heating rate of RF was the largest, and the heating uniformity was the best at the electrode gap of 160 mm and the material height of 90 mm. The residual activity of PPO was significantly reduced from 49.95% to 4.21%, whereas the RF heating temperature (65-85°C) increased (p < 0.05). The color and texture of yams treated with RF blanching were better preserved compared with those of hot water blanching at a similar degree of enzyme inactivation. The microstructure showed that these changes in physicochemical properties were caused by cellular damage. The surface cells of yams were more severely damaged than the center cells after hot water blanching at 95°C for 3 min. Moreover, the surface cells after hot water blanching also showed more damage than the cells after RF blanching. Thus, RF blanching is a technique with development potential in the food industry.

Hot-air-assisted radio frequency blanching of broccoli: heating uniformity, physicochemical parameters, bioactive compounds, and microstructure

BACKGROUND

Vegetables are often blanched before drying. The hot-water blanching (HWB) of broccoli reduces quality and is environmentally harmful. In this work, hot-air-assisted radio frequency heating blanching (HA-RFB) of broccoli was developed for use before further drying processes. Blanching sufficiency, heating uniformity, and heating rate during HA-RFB were investigated to improve the product's physicochemical properties and texture. Suitable heating conditions were achieved when HA-RFB was applied with hot air at 70 °C, with an electrode gap of 10.7 cm, using a cylindrical container for the broccoli.

RESULTS

Under these conditions, the relative peroxidase activity in broccoli decreased to 3.26% within 117 s, with 13.45% of weight loss. In comparison with HWB broccoli, the products blanched by HA-RFB preserved their texture, bioactive compounds, and microstructure better. The ascorbic acid, sulforaphane, and total glucosinolate content in HA-RFB products were 251.1%, 131.9% and 36.7% higher than those in HWB broccoli, and HA-RFB treatment led to a greater weight loss (13.45 ± 0.50%) than HWB (8.70 ± 1.70%), which is very helpful for the subsequent drying process.

CONCLUSION

This study demonstrated that HA-RFB could be a promising substitute for HWB to blanch broccoli and other flower vegetables, especially as a pretreatment in the drying process. © 2023 Society of Chemical Industry.

Sensory Evaluation and Model Prediction of Vacuum-Packed Fresh Corn during Long-Term Storage

The postharvest shelf life of fresh corn largely depends on the packaging method and storage temperature. This study investigated the effect of vacuum packaging (VP) with high-barrier (HB) or ordinary (OR) nylon/nylon/polypropylene (PP) composite films and the impact of storage temperature (4, 25, and 38 °C) on the shelf life of fresh corn. The sensory quality and color changes of the corn were evaluated, indicating a significant improvement in the glossiness (GL), sourness (SO), and color changes compared to corn packaged using OR films. The results showed that the HB films preserved corn freshness under refrigerated and normal temperature storage conditions, delaying color changes and SO development. A shelf-life model was established based on the Arrhenius equation. The predicted values of the corn at different temperatures were compared with the experimental data, indicating that the model could accurately predict the shelf life. The shelf life observed via sensory evaluation was more than 50% shorter than the results obtained by instrumental measurements. Therefore, sensory evaluation could be applied to determine shelf life and avoid food waste.

Developing radio frequency (RF) heating protocol in packed tofu processing by computer simulation

Packed tofu was produced by reheating the mixture of preheated soymilk and coagulant in a sealed container. This study aimed to replace the conventional heating method with RF heating during the reheating of soymilk for packed tofu production. In this study, dielectric properties (DPs), thermal properties (TPs), and rheological properties of soymilk were determined. A mathematical model was developed to simulate the RF heating process of soymilk to determine the appropriate packaging geometry. Water holding capacity (WHC), texture analysis, color measurement, and microstructure observation were performed to evaluate the quality of RF-heated packed tofu. Results showed that soymilk added with Glucono-Delta-Lactone (GDL) coagulated at the temperature above 60 °C, and the loss factor (ε″) was slightly reduced when soymilk was converted to tofu at coagulation temperature. Based on the simulation results, the cylindrical vessel (φ50 mm × 100 mm) was chosen as the soymilk container for desired heating rate (5.9 °C/min) and uniformity (λ = 0.0065, 0.0069, 0.0016 for top, middle, and bottom layers). The texture analysis revealed that the hardness and chewiness of packed tofu prepared by RF heating were enhanced (maximum 1.36 times and 1.21 times) compared with commercial packed tofu, while the springiness were not significantly changed. Furthermore, the denser network structure was observed inside RF-heated packed tofu by SEM. These results indicated that packed tofu prepared by RF heating was of higher gel strength and sensory quality. RF heating has the potential to be applied in packed tofu production.

Sterilizing Ready-to-Eat Poached Spicy Pork Slices Using a New Device: Combined Radio Frequency Energy and Superheated Water

In this study, a new device was used to inactivate G. stearothermophilus spores in ready-to-eat (RTE) poached spicy pork slices (PSPS) applying radio frequency (RF) energy (27.12 MHz, 6 kW) and superheated water (SW) simultaneously. The cold spot in the PSPS sample was determined. The effects of electrode gap and SW temperature on heating rate, spore inactivation, physiochemical properties (water loss, texture, and oxidation), sensory properties, and SEM of samples were investigated. The cold spot lies in the geometric center of the soup. The heating rate increased with increasing electrode gap and hit a peak under 190 mm. Radio frequency combined superheated water (RFSW) sterilization greatly decreased the come-up time (CUT) compared with SW sterilization, and a 5 log reduction in G. stearothermophilus spores was achieved. RFSW sterilization under 170 mm electrode gap reduced the water loss, thermal damage of texture, oxidation, and tissues and cells of the sample, and kept a better sensory evaluation. RFSW sterilization has great potential in solid or semisolid food processing engineering.