Targeted Inhibition of Enzymatic Browning in Wheat Pastry Dough

Effects of Different Drying Methods on Drying Characteristics, Microstructure, Quality, and Energy Consumption of Apricot Slices

An appropriate drying method is crucial for producing high-quality dried apricots. In this study, the effects of four drying methods, hot air drying (HAD), infrared drying (IRD), pulse vacuum drying (PVD), and vacuum freeze-drying (VFD), on the drying kinetics and physical and nutritional characteristics of apricot slices were evaluated. PVD required the shortest time (16.25 h), followed by IRD (17.54 h), HAD (21.39 h), and VFD (34.64 h). VFD resulted in the best quality of apricot slices, with the smallest color difference (ΔE = 13.64), lowest water activity (0.312 ± 0.015) and browning degree (0.35), highest color saturation (62.84), lowest hardness (8.35 ± 0.47 N) and shrinkage (9.13 ± 0.65%), strongest rehydration ability (3.58 ± 0.11 g/g), a good microstructure, and high nutrient-retention rates (ascorbic acid content: 53.31 ± 0.58 mg/100 g, total phenolic content: 12.64 ± 0.50 mg GAE/g, and carotenoid content: 24.23 ± 0.58 mg/100 g) and antioxidant activity (DPPH: 21.10 ± 0.99 mmol Trolox/g and FRAP: 34.10 ± 0.81 mmol Trolox/g). The quality of PVD-treated apricot slices was second-best, and the quality of HAD-treated apricot slices was the worst. However, the energy consumption required for VFD was relatively high, while that required for PVD was lower. The results of this study provide a scientific basis for the large-scale industrial production of dried apricots.

Multi-target genome editing reduces polyphenol oxidase activity in wheat (Triticum aestivum L.) grains

Introduction

Polyphenol oxidases (PPO) are dual activity metalloenzymes that catalyse the production of quinones. In plants, PPO activity may contribute to biotic stress resistance and secondary metabolism but is undesirable for food producers because it causes the discolouration and changes in flavour profiles of products during post-harvest processing. In wheat (Triticum aestivum L.), PPO released from the aleurone layer of the grain during milling results in the discolouration of flour, dough, and end-use products, reducing their value. Loss-of-function mutations in the PPO1 and PPO2 paralogous genes on homoeologous group 2 chromosomes confer reduced PPO activity in the wheat grain. However, limited natural variation and the proximity of these genes complicates the selection of extremely low-PPO wheat varieties by recombination. The goal of the current study was to edit all copies of PPO1 and PPO2 to drive extreme reductions in PPO grain activity in elite wheat varieties.

Results

A CRISPR/Cas9 construct with one single guide RNA (sgRNA) targeting a conserved copper binding domain was used to edit all seven PPO1 and PPO2 genes in the spring wheat cultivar 'Fielder'. Five of the seven edited T1 lines exhibited significant reductions in PPO activity, and T2 lines had PPO activity up to 86.7% lower than wild-type. The same construct was transformed into the elite winter wheat cultivars 'Guardian' and 'Steamboat', which have five PPO1 and PPO2 genes. In these varieties PPO activity was reduced by >90% in both T1 and T2 lines. In all three varieties, dough samples from edited lines exhibited reduced browning.

Discussion

This study demonstrates that multi-target editing at late stages of variety development could complement selection for beneficial alleles in crop breeding programs by inducing novel variation in loci inaccessible to recombination.

Tea film formation in artificial tap water

On the surface of tea infusions, the formation of a transparent, shiny film which cracks upon disturbance can often be observed. This study aims to determine how water composition, tea varieties, and tea additives impact the formation and properties of tea film, often also called tea scum. The strength of the surface film, composed of polyphenols complexed with various ions from tap water, was investigated by interfacial rheology. Microscopy and ellipsometry were used to investigate structure and thickness of the adsorption layer, respectively. We find that green tea forms more visible layers than black tea in soft and moderate artificial tap water, but in these same waters, black tea demonstrated greater surface strength. In hard artificial tap water, green tea demonstrated greater surface strength than black. No visible layer nor surface strengthening was observed on rooibos tea. Brews in hard artificial tap water formed brittle films for green tea, fracturing at strains one order of magnitude lower than in soft or moderate. Despite large variations in film strength, black tea at all water hardness levels tested formed a film with 20 nm thickness. In black tea an increased resilience to deformation was found when adding β-casein, a protein found in milk.

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.

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

The role of polyphenol oxidase (PPO) in the browning of fresh wet noodle sheets (FWNS) was discussed. To release the chemical formation mechanism of the dark spots formed on FWNS, the reconstituted FWNS and PPO-catechol reaction systems were prepared. Different from the overall color change of FWNS, almost all the melanins in dark spots were indirect products of PPO catalysis. The PPO catalytic dehydrogenation was an essential step for the formation of dark spots, but once the phenol dehydrogenation products were formed, the dark spots could still form through a further polymerization process, even though the PPO was completely deactivated. The optimum pH for the phenolic dehydrogenation in FWNS was about 7, and the alkaline condition was advantageous to the progress of the polymerization. Comprehensively, the maximum amount of dark spots was formed at about pH 9.

Inhibition of hexose oxidase on the dark spots in fresh wet noodle sheets: A feasible prevention of dark spots

Hexose oxidase was a feasible prevention for the dark spots in the fresh wet noodle sheets (FWNS). The chemical mechanism that hexose oxidase recucing the melanins of dark spots was discussed basis on the UPLC-TOF-MS analysis of the polyphenol oxidase (PPO)-catechol system. In the process of PPO browning, hexose oxidase catalyzed the oxidation of o-benzoquinone derivatives and their oligomers, hindering the formation of melanins. Hexose oxidase was efficient in FWNS with low ash content when water addition was 24%~44% or pH range was 4 ~ 7.5. Hexose oxidase could inhubit dark spots in the presence of 10 metal ions. The recommended addition amount was 40 ~ 60 ppm, by which the dark spots could be compolitely inhibited. Hexose oxidase was also suitable for wholewheat and oat FWNS, ΔL_6d of wholewheat and oat FWNS were reduced by 4 and 7.98, respectively.

Inhibitory Effect of Azamacrocyclic Ligands on Polyphenol Oxidase in Model and Food Systems

Enzymatic browning is one of the main problems faced by the food industry due to the enzyme polyphenol oxidase (PPO) provoking an undesirable color change in the presence of oxygen. Here, we report the evaluation of 10 different azamacrocyclic compounds with diverse morphologies as potential inhibitors against the activity of PPO, both in model and real systems. An initial screening of 10 ligands shows that all azamacrocyclic compounds inhibit to some extent the enzymatic browning, but the molecular structure plays a crucial role on the power of inhibition. Kinetic studies of the most active ligand (L2) reveal a S-parabolic I-parabolic noncompetitive inhibition mechanism and a remarkable inhibition at micromolar concentration (IC₅₀ = 10 μM). Furthermore, L2 action has been proven on apple juice to significantly reduce the enzymatic browning.

Recent Trends in Controlling the Enzymatic Browning of Fruit and Vegetable Products

Enzymatic browning because of polyphenol oxidases (PPOs) contributes to the color quality of fruit and vegetable (FV) products. Physical and chemical methods have been developed to inhibit the activity of PPOs, and several synthetic chemical compounds are commonly being used as PPO inhibitors in FV products. Recently, there has been an emphasis on consumer-oriented innovations in the food industry. Consumers tend to urge the use of natural and environment-friendly PPO inhibitors. The purpose of this review is to summarize the mechanisms underlying the anti-browning action of chemical PPO inhibitors and current trends in the research on these inhibitors. Based on their mechanisms of action, chemical inhibitors can be categorized as antioxidants, reducing agents, chelating agents, acidulants, and/or mixed-type PPO inhibitors. Here, we focused on the food ingredients, dietary components, food by-products, and waste associated with anti-browning activity.

Study on the shelf life and quality characteristics of highland barley fresh noodles as affected by microwave treatment and food preservatives

In this work, the effect of microwave (MW), ε-poly-L-lysine (ε-PL), calcium propionate (CP), and their combinations on the shelf life and quality characteristics of highland barley fresh noodle (HBFN) was studied. Firstly, the mixed flour was treated by MW (800 W) for different time. Subsequently, HBFN was prepared by mixing flour and sterilized water with addition of 0.04% ε-PL combined with different concentrations of CP (0.025%, 0.020%, 0.015%) and stored at 25 ± 1°C. Changes of total plate count (TPC), moisture content, water state, textural properties, color, and pH in HBFN were monitored during storage. The results indicated that microwave treatment (40 s) provided 30% reduction of initial TPC of the flour without decline of noodle quality. Shelf life of HBFN treated with MW + ε-PL (0.04%) + CP (0.02%/0.025%) reached 80 and 88 hr, respectively, and had good edible qualities during storage.