Analysis of factors related to browning of Dangshan pear (Pyrus spp.) wine

Preparation of spore-immobilized glutathione reductase and its application in inhibiting browning of pear wine

BACKGROUND

Browning is the key problem hindering the industrialization of pear wine. The use of high-yield glutathione Saccharomyces cerevisiae in the fermentation of pear wine can inhibit browning. Glutathione reductase (GR) can ensure the reduction of glutathione. Spore immobilization of enzymes is a new technology. It is a new attempt to apply spore-immobilized GR in combination with high-yield glutathione S. cerevisiae to inhibit browning of pear wine.

RESULTS

Saccharomyces cerevisiae spore immobilization enzyme technology was used to immobilize GR in the spores of mutant S. cerevisiae dit1∆, osw2∆ and chs3∆ and wild-type S. cerevisiae. The enzyme activity of GR immobilized by chs3∆ spores was the highest of 3.08 U mg-1 min-1. The chs3∆ spore-immobilized GR had certain resistance to ethanol, citric acid, sucrose, glucose and proteinase K. Electron microscopy analysis showed that the spore wall of chs3∆ had moderate size holes, which might be the main reason why it immobilized GR with the highest enzyme activity. And the GR was immobilized between the prespore membrane and mannoprotein layer of the spore wall. When chs3∆ spore-immobilized GR (chs3∆-GR) was added to Dangshan pear wine fermented by high-yield glutathione S. cerevisiae JN32-9, the presence of chs3∆-GR could further protect amino acids, polyphenols and glucose from oxidation, thereby reducing the browning of the pear wine during storage by 47.32%.

CONCLUSION

GR immobilized by S. cerevisiae spores was effective in inhibiting the browning of pear wine. The method was simple, green and effective and did not increase the production cost of pear wine. © 2024 Society of Chemical Industry.

Effect of Tea Tree Essential Oil on the Quality, Antioxidant Activity, and Microbiological Safety of Lightly Processed Lily (Lilium brownii var. viridulum) during Storage

The Lanzhou lily is a regionally distinctive vegetable; the emergence of lightly processed lilies has addressed the inconvenience of consuming fresh lilies. However, the cleaning and impurity removal during the processing of lightly processed lily may strip off its original protective barrier and affect the edible quality. As one of the preservation methods, tea tree essential oil (TTEO) has the characteristics of being green, safe, and efficient preservative properties. This study focused on investigating the effects of different concentrations (25 μL/L, 50 μL/L, and 100 μL/L) of TTEO on the quality and microbiological safety of lightly processed lily. The results showed that compared with the control, appropriate concentrations of TTEO treatment could delay weight loss, improve appearance, firmness, and sensory quality, and maintain microbiological safety with the best effect observed at 50 μL/L. Meanwhile, TTEO treatment induced phenylalanine ammonia-lyase activity, thereby increasing the total phenolic content. Furthermore, TTEO enhanced the superoxide dismutase (SOD) and ascorbate peroxidase (APX) activity, which reduced O2-· production rate and H2O2 content. TTEO inhibited lipoxygenase (LOX) activity, reducing the relative conductivity and malondialdehyde content, thereby delaying lipid peroxidation and quality deterioration. This indicates that TTEO could enhance antioxidant capacity by regulating reactive oxygen species (ROS) metabolism and delay the quality deterioration of lightly processed lily by inhibiting lipid peroxidation.

Formation of phenazines, phenoxazines, and benzoxazoles in the browning reactions of o-quinones

Quinone-induced browning is widely produced in foods and is mostly considered a consequence of quinone/nucleophile reactions. However, even in the absence of amino acids or proteins, o-quinones develop browning. In an attempt to better understand the reaction pathways involved in this browning development, this study describes the reactions of 4-methyl-1,2-benzoquinone with alcohols, ammonia, and short chain aldehydes. These reaction mixtures developed browning at 37 °C and the main produced compounds were isolated by semipreparative HPLC and characterized by NMR and MS as phenazines, phenoxazines, and benzoxazoles. A reaction pathway that explains the formation of all these compounds is proposed. The formation of phenazines is responsible, at least partially, for the produced browning, and the formation of benzoxazoles inhibits such browning. Browning development seems to be a consequence of a competition among the reactions of formation of phenazines, phenoxazines, and benzoxazoles, which appear to be produced from a single intermediate.

Probing the binding mechanism of tea polyphenols from different processing methods to anti-obesity and TMAO production-related enzymes through in silico molecular docking

Tea polyphenols possess anti-obesity properties and reduce TMAO levels. However, the variability of tea polyphenols under different processing methods and their preventive efficacy requires further exploration. This study systematically evaluated the antioxidant, hypoglycemic, and hypolipotropic enzyme capacities of GT, YT and DT through UPLC-ESI-MS/MS analysis of catechin profiles. OPLS, correlation analysis, and molecular docking were employed to investigate the compounds and inhibitory mechanisms targeting hypoglycemic, hypolipidemic, and TMAO-producing enzymes. GT exhibited significantly lower IC50 values for biological activity and higher catechins contents compared to YT and DT (p < 0.05). Strong positive correlations were observed between EGCG, CG, and ECG and biological activities (r ≥ 7.4, p < 0.001). Molecular docking results highlighted the establishment of stable hydrogen bonds and hydrophobic interactions between EGCG, CG, ECG, and the receptor. These findings contribute novel insights into the mechanisms by which tea polyphenols prevent obesity and inhibit TMAO production.

Ultrasound-assisted fermentation of ginkgo kernel juice by Lactiplantibacillus plantarum: Microbial response and juice composition development

This study is aimed to explore the feasibility of ultrasound on enhancing the fermentation properties of ginkgo kernel juice by Lactiplantibacillus plantarum Y2. Specifically, ultrasound at 20 kHz and different intensities (mild ultrasound intensity-84.42 W/L, moderate ultrasound intensity-115.50 W/L, high ultrasound intensity-173.88 W/L) with a pulse mode were applied to facilitate the fermentation process. The number of viable cells of Lactiplantibacillus plantarum Y2 increased by 5.06, 5.05 and 2.19% in the sonicated groups at 173.88, 115.50 and 84.42 W/L, compared with the non-sonicated juice after 24-h fermentation. Furthermore, mild intensity ultrasonication improved the permeability of the cell membrane, which is beneficial for the metabolism of phenolics, amino acids and organic acids. Ultrasonication increased in-vitro antioxidant activity of fermented ginkgo kernel juice by promoting the metabolism of phenolic acids, such as ferulic acid, chlorogenic and caffeic acids. At the end of fermentation, the sonicated group at 84.42 W/L has the maximum consumptions of total sugars and proteins (increased by 12.52 and 18.73%). Moreover, the reduction rate of the poison material 4'-O-methylpyridoxine (MPN) in ginkgo kernel juice increased by more than 16.40% with ultrasound treatment at 173.88 W/L after the fermentation for 48 h. Overall, ultrasound can improve the metabolizations of Lactobacillus plantarum and reduce the toxic substances, which promoted the nutritional value and flavors of ginkgo kernel juice.

From polyphenol to o-quinone: Occurrence, significance, and intervention strategies in foods and health implications

Polyphenol oxidation is a chemical process impairing food freshness and other desirable qualities, which has become a serious problem in fruit and vegetable processing industry. It is crucial to understand the mechanisms involved in these detrimental alterations. o-Quinones are primarily generated by polyphenols with di/tri-phenolic groups through enzymatic oxidation and/or auto-oxidation. They are highly reactive species, which not only readily suffer the attack by nucleophiles but also powerfully oxidize other molecules presenting lower redox potentials via electron transfer reactions. These reactions and subsequent complicated reactions are capable of initiating quality losses in foods, such as browning, aroma loss, and nutritional decline. To attenuate these adverse influences, a variety of technologies have emerged to restrain polyphenol oxidation via governing different factors, especially polyphenol oxidases and oxygen. Despite tremendous efforts devoted, to date, the loss of food quality caused by quinones has remained a great challenge in the food processing industry. Furthermore, o-quinones are responsible for the chemopreventive effects and/or toxicity of the parent catechols on human health, the mechanisms by which are quite complex. Herein, this review focuses on the generation and reactivity of o-quinones, attempting to clarify mechanisms involved in the quality deterioration of foods and health implications for humans. Potential innovative inhibitors and technologies are also presented to intervene in o-quinone formation and subsequent reactions. In future, the feasibility of these inhibitory strategies should be evaluated, and further exploration on biological targets of o-quinones is of great necessity.

Integration of Metabolome and Transcriptome Profiling Reveals the Effect of Modified Atmosphere Packaging (MAP) on the Browning of Fresh-Cut Lanzhou Lily (Lilium davidii var. unicolor) Bulbs during Storage

The fresh-cut bulbs of the Lanzhou lily (Lilium davidii var. unicolor) experience browning problems during storage. To solve the problem of browning in the preservation of Lanzhou lily bulbs, we first investigated the optimal storage temperature and gas ratio of modified atmosphere packaging (MAP) of Lanzhou lily bulbs. Then, we tested the browning index (BD), activity of phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD), the content of malonaldehyde (MDA) and other physiological activity indicators related to browning. The results showed that the storage conditions of 10% O₂ + 5% CO₂ + 85% N₂ and 4 °C were the best. To further explore the anti-browning mechanism of MAP in fresh-cut Lanzhou lily bulbs, the integration of metabolome and transcriptome analyses showed that MAP mainly retarded the unsaturated fatty acid/saturated fatty acid ratio in the cell membrane, inhibited the lipid peroxidation of the membrane and thus maintained the integrity of the cell membrane of Lanzhou lily bulbs. In addition, MAP inhibited the oxidation of phenolic substances and provided an anti-tanning effect. This study provided a preservation scheme to solve the problem of the browning of freshly cut Lanzhou lily bulbs, and discussed the mechanism of MAP in preventing browning during the storage of the bulbs.

Use of Oenological Tannins to Protect the Colour of Rosé Wine in a Bioprotection Strategy with Metschnikowia pulcherrima

Although bioprotection is now recognised as an alternative to SO₂ for limiting microbial spoilage, it does not guarantee protection against oxidation. This limits its application, more specifically for rosé winemaking. Oenological tannins present antioxidant properties, which could represent an interesting alternative to SO₂ to protect must and wines against oxidation. A combination of the inoculation of a bioprotectant yeast strain and the addition of oenological tannins was tested to eliminate sulfites during the pre-fermentative step of rosé winemaking. In this experiment carried out in a winery, two oenological tannins were compared: quebracho and gall nut tannins. The antioxidant efficiency of tannins was compared to that of SO₂. Colorimetric assays associated with chemical analyses of anthocyanins and phenolic compounds confirmed that the use of bioprotection alone did not protect the wine from oxidation. An addition of oenological tannins on musts stabilized the colour of bioprotected rosé wine in a similar way that SO₂ addition did. Quebracho tannins appeared more efficient than gall nut tannins. The colour differences observed cannot be explained either by the concentration or forms of anthocyanins. However, the addition of tannins led to better protection of oxidation-sensitive phenolic compounds comparable to that obtained with the addition of sulfites.

Chinese Traditional Pear Paste: Physicochemical Properties, Antioxidant Activities and Quality Evaluation

As a traditional folk medicine, pear paste has important nutritional and health effects. The physicochemical properties and antioxidant activities of pear pastes prepared from 23 different cultivars were investigated, including color parameters ( L*, a*, b* and h°), transmittance, pH, titratable acidity (TA), soluble sugar content, total phenolics content (TPC), total flavonoids content (TFC), DPPH and ^•OH radical scavenging activity (RSA), and ferric reducing antioxidant power (FRAP). It was demonstrated that the physicochemical properties and antioxidant activities of pear pastes from various cultivars differed significantly. Pear cultivars of "Mantianhong", "Xiangshui" and "Anli" possessing higher TPC and TFC exhibited excellent antioxidant activity determined by DPPH RSA, ^•OH RSA and FRAP, while the lowest TPC and TFC was observed for the cultivars of "Xueqing", "Nansui", "Hongxiangsu", and "Xinli No. 7", which also demonstrated the poor antioxidant activity. Multivariate analyses, including factor and cluster analysis, were used for the quality evaluation and separation of pear pastes based on their physicochemical and antioxidant properties. Factor analysis reduced the above thirteen parameters to final four effective ones, i.e. DPPH RSA, color b*, FRAP and TA, and subsequently these four parameters were used to construct the comprehensive evaluation prediction model for evaluating the quality of pear pastes. The pear pastes could be separated into three clusters and differentiated for the diverse of pear cultivars via cluster analysis. Consistently, "Mantianhong", "Xiangshui" and "Anli" pear with higher quality clustered into one group, in contrast, "Xueqing", "Nansui", "Hongxiangsu", and "Xinli No. 7" with lower quality clustered into the other group. It provided a theoretical method to evaluate the quality of pear paste and may help the fruit processing industry select the more suitable pear cultivars for pear paste making.

Effect of CaCl2 Treatment on Enzymatic Browning of Fresh-Cut Luffa (Luffa cylindrica)

Enzymatic browning is a major issue that reduces the commercial value of Luffa cylindrica during storage, processing, and transportation. Our results showed that 1% CaCl2 treatment was optimal for reducing the surface browning of fresh-cut luffa. After storage at 25 °C for four days, the treated luffa had a significantly higher total phenolic (TP) content than the untreated luffa. At the end of the storage period, the calcium treatment showed low malondialdehyde (MDA) and hydrogen peroxide (H2O2) accumulation in the luffa. The treated luffa maintained higher superoxide dismutase (SOD), catalase (CAT), and phenylalanine ammonia lyase (PAL) activities and lower polyphenol oxidase (PPO) activity as compared to the untreated luffa. Furthermore, the genes regulating SOD (e.g., SOD1, SOD2, and SOD3), CAT (e.g., LcCAT1 and CAT2), and PAL (e.g., PAL1 and PAL2) in calcium-treated luffa were upregulated to varying degrees, suggesting that Ca2+ inhibited the browning of fresh-cut tissue by regulating the activities of those enzymes. Ultrastructure images showed that the treated luffa could maintain the relative integrity of the cell membrane and organelles. Therefore, Ca2+ might act as a second messenger to reduce ROS oxidative damage and maintain the cell membrane integrity. This study provides new insights into the breeding of new luffa varieties that are resistant to browning and post-harvest treatments to reduce the browning of luffa tissue.

Comparative Transcriptomic Analyses Provide Insights into the Enzymatic Browning Mechanism of Fresh-Cut Sand Pear Fruit

Pear (Pyrus spp.) is one of the most commonly consumed temperate fruits, having considerable economic and health importance. Fresh-cut or processed pear fruits are prone to browning because of the abundant phenolic compounds; however, little is known about the molecular mechanisms underlying enzymatic browning of fresh-cut sand pear fruit. In this study, fruits of two sand pear genotypes (low browning cultivar ‘Eli No.2′ and high browning cultivar ‘Weiningdahuangli’) were used to analyze the molecular mechanism of enzymatic browning by SMRT-seq and RNA-seq. The results generated 69,122 consensus isoforms, 21,336 new transcripts, 7105 alternative splicing events, and 254 long non-coding RNAs (lncRNAs). Furthermore, five genes related to enzymatic browning were predicted to be targets of six lncRNAs, and 9930 differentially expressed genes (DEGs) were identified between two different flesh browning cultivars. Meanwhile, most DEGs (e.g., PAL, 4CL, CAD, CCR, CHS, and LAR) involved in the phenylpropanoid biosynthesis pathway were up-regulated, and the expression of PPO and POD were highly expressed in the high-browning cultivar. Interestingly, the transcript level of PbrPPO4 (Pbr000321.4) was significantly higher than other PPO and POD genes, and a high level of total polyphenol and PPO activity were observed in the high browning cultivar. We found that the expression of lncRNA PB.156.1 was significantly positively correlated with the target gene PbrPPO4 (Pbr000321.4). The results suggest that PbrPPO4 might act as a major contributor and a key enzyme encoding gene in regulating fresh-cut sand pear fruit enzymatic browning; the expression of PbrPPO4 was probably regulated by lncRNA PB.156.1. Altogether, the transcriptomic and physiological analyses expand the knowledge of sand pear flesh enzymatic browning at the molecular level and provide a foundation for germplasm resources for molecular breeding of high polyphenol and low browning cultivars in sand pears.

Key Compounds and Metabolic Pathway Responsible for the Browning in Dangshan Pear (Pyrus spp.) Wine

Based on hydrophilic interaction liquid chromatography (HILIC) liquid chromatography-mass spectrometry (LC-MS), untargeted differential metabolomics analysis was performed on the pear wine samples before and after browning to determine the key compounds that affect the browning of Dangshan pear wine. A total of 196 significantly differential metabolites were found, 22 of which might be related to the browning of Dangshan pear wine. d-(+)-glucose, l-phenylalanine, l-norleucine, methionine, d-(+)-proline, aloin, and rutin were the key differential metabolites in pear wine before and after browning. The Maillard reaction of d-(+)-glucose, l-norleucine, methionine, and the oxidation of aloin played critical roles in the browning of Dangshan pear wine. The reaction of aloin and glucose to form 5-hydroxyaloin A, 7-hydroxyaloin B, and elgonica-dimer A was one of the important metabolic pathways in which the phenolic compounds formed anthraquinone during the browning process of Dangshan pear wine.

Physiological Changes of Bamboo (Fargesia yunnanensis) Shoots During Storage and the Related Cold Storage Mechanisms

The mechanisms for physiological senescence in bamboo shoots after harvest remain unclear. This study investigated physiological changes in Fargesia yunnanensis shoots during storage at different temperatures. The relationship between morphological and physiological changes in bamboo shoots during storage was also analyzed. The results show that cold storage can reduce weight loss, browning, respiration rates, and sugar degradation in bamboo shoots; decrease related enzymatic activities; and inhibit the increase in lignin and cellulose content. The quality of bamboo shoots declines more during the first 3d after harvesting than it does during subsequent periods. The increase in the degree of lignification and fibrosis is the main reason for senescence and for the decline in quality of bamboo shoots after harvest. The bamboo shoots under RT conditions began browning during the third 3d of storage, with a browning rate of 688gkg^-1 even in the upper parts; the increase in shoot browning degrees significantly decreased the quality. Low temperatures had better inhibitory effects on browning than they did on lignification and fibrosis. Nonstructural carbohydrates in bamboo shoots are degraded and flow into sheath and shoot respiration, phenols, and shoot fibrosis and lignification at room temperature, but only flow into sheath respiration, shoot fibrosis, and lignification at cold temperature. Soluble protein and free amino acids are primarily distributed into shoot and sheath respiration and into phenols at room temperature, but that process is well inhibited at cold temperature. Bamboo shoots, once removed from cold storage, should be consumed rapidly because enzyme activity recovers quickly. This research provides new theoretical information on the preservation of bamboo shoots.