Polyphenol oxidase browning in the formation of dark spots on fresh wet noodle sheets: How dark spots formed

Identification of novel natural anti-browning agents based on phenotypic and metabolites differences in potato cultivars

This study aimed to elucidate the changes of browning-related metabolite in fresh-cut potato and to identify anti-browning agents. Metabolomics and weighted correlation network analysis (WGCNA) were used to identify metabolites and correlate them with potato browning traits. A total of 79 browning trait-positive-related metabolites and 19 browning trait-negative-related metabolites were obtained from four key modules via WGCNA. The accumulation of metabolites with rich reducing groups and acidic groups were found to enhance anti-browning activity in potatoes. Among these metabolites, only L-pyroglutamic acid (L-PA) and ascorbic acid had variable importance for the projection (VIP) values greater than 1.5. In addition, it was found that L-PA inhibited polyphenol oxidase (PPO) activity by lowering pH and interacting with amino acid residues of PPO. L-PA also inhibited the growth of microorganisms in fresh-cut potato. Our results show that L-AP is an effective novel anti-browning agent with antibacterial activity.

Effect of surfactin on microbial content, appearance quality, and starch properties of fresh noodles during storage

Fresh noodles (FNs) are prone to quality deterioration during storage, negatively affecting their edibility. This study investigated the impacts of different surfactin concentrations on microbial content, appearance quality, and starch properties in FNs to enhance storage stability and shelf life. The addition of surfactin effectively controlled the microbial growth in FNs during storage, FNs containing 0.4 % surfactin maintained total aerobic plate count below 106 CFU/g for up to 72 h at 25 °C, which was at least 48 h longer than the control group. Furthermore, surfactin could inhibit yellowing and reduce the appearance of dark spots in FNs during storage. Results from Rapid Visco Analyzer, X-ray diffractometer, and Differential Scanning Calorimetry indicated that surfactin inhibited the decrease in starch viscosity, and the increase in relative crystallinity and enthalpy, and improved the storage stability of starch in FNs. This research provides a theoretical foundation for applying surfactin as an enhancer in FNs.

Effects of Peanut Shell Flavonoids on Composite Film Properties and Cherry Tomato Preservation

This study investigated the effects of varying concentrations of peanut shell flavonoids (PSFs) on the properties of peanut meal extract-tilapia skin protein composite films and their impact on cherry tomatoes preservation. Peanut meal alcohol extract (Pe) and tilapia skin protein (Co) were used as base materials, combined with PSFs to prepare composite films with excellent antioxidant properties. The results demonstrated that the optimized composite films exhibited superior mechanical properties, with a tensile strength of 9.83 MPa and an elongation at break of 204.04%. Increased flavonoid content enhanced the films' antioxidant capacity, achieving superoxide anion and DPPH radical scavenging rates of 15.08% and 21.37%, respectively. The microstructure, IR spectra, and circular dichroism spectra of the composite films are also significantly different with the change of flavonoid content. In the cherry tomato preservation experiment, the PeCo-0.5 composite film treatment group maintained a low weight loss rate (11.18%) and malondialdehyde content (13.33 μmol/g) after 15 days, delayed the peak respiration rate, and significantly reduced the peak respiration intensity (3.43 mgCO2∙ mg-1∙gh-1). At the same time, the activity of polyphenol oxidase in the tissue of Cherry Tomatoes was significantly inhibited, and the decrease rate of Vc content was also significantly decreased, which effectively preserving the bright color, smooth appearance, and good aroma of the cherry tomatoes. This study not only provides new insights into the comprehensive utilization of tilapia skin and peanut by-products but also opens new avenues for the development and application of fruit and vegetable preservation films.

Humidity-controlled heat treatment of fresh spinach noodles for color preservation and storage quality improvement

The high sensitivity to color browning during room-temperature storage was a significant factor in limiting the development of fresh spinach noodles (FSN). The practice of humidity-controlled heat treatment (HCHT) at varying temperatures, relative humidity, and time was carried out to limit enzyme activity and improve the quality of FSN. Results showed that HCHT could maximize the color preservation of fresh spinach noodle quality while effectively inactivating polyphenol oxidase and the yeasts, and mold count in FSN during storage was almost undetectable after mild conditions (80 °C). The hardness and chewiness of HCHT noodles were significantly increased, but the free sulfhydryl content was reduced. At 80 °C, 90 %, 5 min, protein structural aggregation was found in the microstructure of HCHT fresh spinach noodles. HCHT also caused partial gelatinization, as evidenced by the decrease in starch gelatinization enthalpy from 5.49 to 4.77 J/g, although the gelatinization degree of FSN was comparatively low.

Preparation of fat replacer utilizing gluten and barley β-glucan and the interaction between them

BACKGROUND

Fat replacers prepared from polysaccharides and proteins possess functional properties of both polysaccharides and proteins. In this study, an aqueous system of barley β-glucan (BBG) and gluten was prepared. The interactions between BBG and gluten (with/without extrusion modification) were studied. Triple analysis methods, including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and low-field nuclear magnetic resonance (LF-NMR), were utilized to analyze the freezing-thawing and thermal evaporation process, as well as the distribution state of water. Meanwhile, fluorescence microscopic analysis, dynamic rheological analysis and electrophoresis analysis were used to study the structure and rheological properties of the system.

RESULTS

The results showed that BBG significantly increased the water-holding capacity of gluten, regardless of extrusion treatment, with the water absorption reaching about 4.8 to 6.4 times of its weight, which was 1 to 2.5 times higher than that without BBG. The triple analysis results suggested that BBG increased the binding capacity of the system to weakly bound water, hindered the aggregation of gluten and reduced the thermal decomposition temperature of the BBG and gluten composite system. After the gluten was extruded and homogenized with the BBG solution, the appearance of the composite system was more uniform and delicate.

CONCLUSIONS

In conclusion, BBG increased the water-holding capacity of the BBG and gluten composite system. With these changes, the composite system presented great potential for the preparation of polysaccharide-gluten fat replacer. © 2023 Society of Chemical Industry.

Inhibitory mechanism of sodium hexametaphosphate on enzymatic browning in yellow alkaline noodles

The effect and mechanism of sodium hexametaphosphate (SHMP) on polyphenol oxidase (PPO) enzymatic browning in yellow alkaline noodles (YAN) were investigated. The browning degree and PPO activity in YAN or PPO solutions decreased with the SHMP concentrations increased. Variations in pH values (pH 7-8.5) adjusted by HCl or acetic acid slightly affected the PPO activity, but SHMP inhibited PPO activity more pronounced. The inhibition of SHMP on PPO activity was irreversible. SHMP formed coordinate covalent bonds with Cu²⁺ to make PPO inactive. HPLC analysis revealed that SHMP reduced the browning products and led to the color of PPO-catechol systems being lightened. Furthermore, SHMP inhibited browning by hampering the auto-oxidization of intermediate products due to the change in pH value. Besides, the HPLC chromatogram, UV-vis spectrum, and mass spectrometry revealed that SHMP could convert melanin (m/z 248.97, 723.5, and 836.58) to light-colored substances (m/z 137.11).

Substrate specificity of polyphenol oxidase and its selectivity towards polyphenols: Unlocking the browning mechanism of fresh lotus root (Nelumbo nucifera Gaertn.)

Polyphenol oxidase (PPO) causes the browning of lotus roots (LR), negatively affecting their nutrition and shelf-life. This study aimed to explore the specific selectivity of PPO toward polyphenol substrates, thus unlocking the browning mechanism of fresh LR. Results showed that two highly homologous PPOs were identified in LR and exhibited the highest catalytic activity at 35 ℃ and pH 6.5. Furthermore, the substrate specificity study revealed (-)-epigallocatechin had the lowest Km among the polyphenols identified in LR, while (+)-catechin showed the highest Vmax. The molecular docking further clarified that (-)-epigallocatechin exhibited lower docking energy and formed more hydrogen bonds and Pi-Alkyl interactions with LR PPO than (+)-catechin, while (+)-catechin entered the active cavity of PPO more quickly due to its smaller structure, both of which enhance their affinity to PPO. Thus, (+)-catechin and (-)-epigallocatechin are the most specific substrates responsible for the browning mechanism of fresh LR.

Cross-processing herring and salmon co-products with agricultural and marine side-streams or seaweeds produces protein isolates more stable towards lipid oxidation

Herring and salmon filleting co-products were pH-shift processed together with seven antioxidant-containing raw materials ("helpers") including lingonberry-, apple-, oat-, barley- and shrimp-co-products, and two seaweeds (Saccharina latissima, Ulva fenestrata) to produce protein isolates stable towards lipid oxidation. Malondialdehyde (MDA) and 4-hydroxy-(E)-2-hexenal (HHE) levels revealed that all helpers, except shrimp shells, to different extents retarded lipid oxidation both during pH-shift-processing and ice storage. The three helpers performing best were: lingonberry press-cake > apple pomace ∼ Ulva. Color of protein isolates was affected by helper-derived pigments (e.g., anthocyanins, carotenoids, chlorophyll) and lipid oxidation-induced changes (e.g., metHb-formation, pigment-bleaching). In conclusion, combining fish co-products with other food side-streams or seaweeds during pH-shift processing appears a promising new tool to minimize lipid oxidation of protein isolates, both during their production and subsequent storage. Lingonberry press-cake was the most efficient helper but provided dark color which may narrow product development possibilities, something which requires further attention.

Recent developments in cold plasma-based enzyme activity (browning, cell wall degradation, and antioxidant) in fruits and vegetables

According to the Food and Agriculture Organization of United Nations reports, approximately half of the total harvested fruits and vegetables vanish before they reach the end consumer due to their perishable nature. Enzymatic browning is one of the most common problems faced by fruit and vegetable processing. The perishability of fruits and vegetables is contributed by the various browning enzymes (polyphenol oxidase, peroxidase, and phenylalanine ammonia-lyase) and ripening or cell wall degrading enzyme (pectin methyl-esterase). In contrast, antioxidant enzymes (superoxide dismutase and catalase) assist in reversing the damage caused by reactive oxygen species or free radicals. The cold plasma technique has emerged as a novel, economic, and environmentally friendly approach that reduces the expression of ripening and browning enzymes while increasing the activity of antioxidant enzymes; microorganisms are significantly inhibited, therefore improving the shelf life of fruits and vegetables. This review narrates the mechanism and principle involved in the use of cold plasma technique as a nonthermal agent and its application in impeding the activity of browning and ripening enzymes and increasing the expression of antioxidant enzymes for improving the shelf life and quality of fresh fruits and vegetables and preventing spoilage and pathogenic germs from growing. An overview of hurdles and sustainability advantages of cold plasma technology is presented.

Inhibition of L-Cysteine on the Browning of Fresh Wet Noodles

This research explored the effect of L-cysteine on the browning of fresh wet noodles (FWN). With the increasing addition of L-cysteine (0.02–0.1%), the ΔL* decreased and Δa*, Δb* increased. The L-cysteine could reduce the pH value and polyphenol oxidase (PPO) activity and increase the retention rate of polyphenol of FWN. It suggested that L-cysteine could inhibit the browning of FWN by decreasing pH value, PPO activity, and the oxidation of polyphenols. In the in vitro PPO solution, the inhibitory effect of L-cysteine on PPO activity was related to the decrease in pH and the ability of chelating Cu²⁺. According to UPLC-TOF-MS analysis, L-cysteine could reduce the generation of browning products, which suggested that L-cysteine could react with the browning intermediate product (quinone) and generate a light-colored substance (-C₉H₁₀NO₄S). L-cysteine effectively inhibited the browning of FWN and had the potential to be used in noodle industry.

The Influence of Supercritical Carbon Dioxide on Graham Flour Enzyme Polyphenol Oxidase Activity

Graham flour is a form of whole wheat flour made by grinding the endosperm and is thus also the most nutritious. Generally, the enzyme polyphenol oxidase (PPO) catalyzes two different reactions in the presence of molecular oxygen: the hydroxylation of monophenols to ortho-diphenol and the oxidation of o-diphenol to o-quinone. The purpose of the work was to inactivate PPO activity to extend the shelf life of graham flour and at the same time preserve all the of its high-quality properties. The influence of supercritical CO₂ (scCO₂) treatment on PPO activity in graham flour was investigated. First, graham flour was exposed to scCO₂ conditions, then the proteins were extracted, and in the last step the concentration of total proteins and the specific activity of the PPO enzyme were determined by spectrophotometric assay. PPO activity decreased with an increase in treatment pressure. Furthermore, the flour quality characteristics that meet all needs for wheat end-use products after scCO₂ treatment have been preserved. No major changes in the structure of the granulate or shape of the flour particles were observed. A slightly reduced value of the moisture content in scCO₂-treated graham flour also implies an extension of the shelf life.