Effects of polyphenol enzymatic-oxidation on the oxidative stability of virgin olive oil

Oxidation of tea polyphenols promotes chlorophyll degradation during black tea fermentation

The color of black tea is directly affected by chlorophyll degradation during fermentation. In this study, the content of chlorophyll and its derivatives during fermentation was determined by HPLC, and chlorophyll a and b were shown to decrease significantly (44.23% and 24.24%). By analyzing the activity of chlorophyllase (CLH), magnesium dechelatase (MDcase) and pheophorbide a oxygenase (PAO), the key enzymes of chlorophyll degradation, as well as changes of tea polyphenols, tea pigments, pH, ROS and other physicochemical indexes, polyphenol oxidation rather than enzymatic catalysis was found to be the main cause of chlorophyll degradation. In vivo and in vitro verification tests showed that the chlorophyll structure was directly disrupted by the oxidation of polyphenols, and chlorophyll degradation was further promoted by ROS generated during oxidation, reduction of o-quinone, and pH decrease. This study provided a theoretical basis for improving the color quality of black tea.

Metabolomic insights into the browning of the peel of bagging 'Rui Xue' apple fruit

BACKGROUND

Bagging is one of the most important techniques for producting high-quality fruits. In the actual of cultivating, we found a new kind of browning in peel of apple fruit that occurs before harvest and worsen during storage period. There are many studies on metabonomic analysis of browning about storage fruits, but few studies on the mechanism of browning before harvest.

RESULTS

In this study, five-year-old trees of 'Rui Xue' (CNA20151469.1) were used as materials. Bagging fruits without browning (BFW) and bagging fruits with browning (BFB) were set as the experimental groups, non-bagging fruits (NBF) were set as control. After partial least squares discriminant analysis (PLS-DA), 50 kinds of metabolites were important with predictive VIP > 1 and p-value < 0.05. The most important differential metabolites include flavonoids and lipids molecules, 11 flavonoids and 6 lipids molecules were significantly decreased in the BFW compared with NBF. After browning, 11 flavonoids and 7 lipids were further decreased in BFB compared with BFW. Meanwhile, the significantly enriched metabolic pathways include galactose metabolism, ABC membrane transporter protein, flavonoid biosynthesis and linoleic acid metabolism pathways et al. Physiological indicators show that, compared with NBF, the content of malondialdehyde (MDA), hydrogen peroxide (H₂O₂)_, superoxide anion (O₂^-) in peel of BFW and BFB were significantly increased, and the difference of BFB was more significant. Meanwhile, the antioxidant enzyme activities of BFW and BFB were inhibited, which accelerated the destruction of cell structure. In addition, the metabolome and physiological data showed that the significantly decrease of flavonoid was positively correlated with peel browning. So, we analyzed the expression of flavonoid related genes and found that, compared with NBF, the flavonoid synthesis genes MdLAR and MdANR were significantly up-regulated in BFW and BFB, but, the downstream flavonoids-related polymeric genes MdLAC7 and MdLAC14 were also significantly expressed.

CONCLUSIONS

Our findings demonstrated that the microenvironment of fruit was changed by bagging, the destruction of cell structure, the decrease of flavonoids and the increase of triterpenoids were the main reasons for the browning of peel.

Insight of Polyphenol Oxidase Enzyme Inhibition and Total Polyphenol Recovery from Cocoa Beans

A full factorial design (ascorbic acid/l-cysteine inhibitors, temperature, and time as factors) study was conducted to enhance inhibition of polyphenol oxidase (PPO) activity without decreasing cocoa polyphenol concentrations. The data obtained were modelled through a new equation, represented by Γ, which correlates both high polyphenol content with reduced specific PPO activity. At optimized values (70 mM inhibitory solution at 96 °C for 6.4 min, Γ = 11.6), 93.3% PPO inhibition and total polyphenol of 94.9 mg GAE/g were obtained. In addition, microscopy images confirmed the cell morphological changes measured as the fractal dimension and explained the possible cell lysis and denaturation as a result of heat treatment and chemical inhibitors. Results also showed that PPO enzyme was most suitable (higher v_max/K_m ratio) for catechol, with a reduction in its affinity of 13.7-fold after the inhibition heat treatment. Overall, this work proposed a suitable and food-safe procedure for obtaining enriched polyphenol extract with low enzyme activity.

Ailanthus altissima (Miller) Swingle seed oil: chromatographic characterization by GC-FID and HS-SPME-GC-MS, physicochemical parameters, and pharmacological bioactivities

This study aimed to identify the physicochemical and the chemical properties of Ailanthus altissima (Miller) Swingle seed oil and to evaluate its in vitro antioxidant and antibacterial activities and in vivo analgesic and anti-inflammatory activities. The fatty acids' composition was determined using GC-FID. The oil was screened for antioxidant activity by DPPH test. The analgesic and anti-inflammatory activities were determined using the acetic acid writhing test in mice and the carrageenan-induced paw edema assay in rats, respectively. Volatile compounds were characterized by HS-SPME-GC-MS. A. altissima produces seeds which yielded 17.32% of oil. The seed oil was characterized by a saponification number of 192.6 mg KOH∙g of oil, a peroxide value of 11.4 meq O₂∙kg of oil, a K₂₃₂ of 4.04, a K₂₇₀ of 1.24, and a phosphorus content of 126.2 ppm. The main fatty acids identified were palmitic (3.06%), stearic (1.56%), oleic (38.35%), and linoleic acids ones (55.76%). The main aroma compounds sampled in the headspace were carbonyl derivatives. The oil presents an important antioxidant activity (IC₅₀ = 24.57 μg/mL) and a modest antimicrobial activity. The seed oil at 1 g/kg showed high analgesic (91.31%) and anti-inflammatory effects (85.17%). The presence of high levels of unsaturated fatty acids and the noteworthy antioxidant capacity of the seed oil can hypothesize its use as an analgesic and anti-inflammatory agent.

Optimization of Microencapsulation of Human Milk Fat Substitute by Response Surface Methodology

Human milk fat substitutes (HMFS) are rich in polyunsaturated fatty acids which upon microencapsulation, can be used as a source of high quality lipids in infant formula. The response surface methodology (RSM) was employed to optimize the microencapsulation condition of HMFS as a functional product. The microencapsulation efficiency (MEE) of microencapsulated HMFS was investigated with respect to four variables including concentration of soy lecithin (A), ratio of demineralized whey powder to malt dextrin (B), HFMS concentration (C), and homogenizing pressure (D). The optimum conditions for efficient microencapsulation of HMFS by the spray drying technique were determined as follows: the amount of soybean lecithin-0.96%, ratio of desalted whey powder to malt dextrin-2.04:1, oil content-17.37% and homogeneous pressure-0.46MPa. Under these conditions, the MEE was 84.72%, and the basic indices of the microcapsules were good. The structure of the microcapsules, as observed by scanning electron microscopy (SEM), revealed spherical, smooth-surfaced capsules with diameters ranging between 10-50 μm. Compared with HFMS, the peroxide value (POV) and acid value (AV) of the microcapsule were significantly lower during storage indicating that the microencapsulation process increases stability and shelf life. Infrared spectroscopic analyses indicated that HFMS had the same characteristic functional groups as the oil extracted from microcapsules. Simulated in vitro digestion revealed that the microcapsules were digested completely within 2h with maximum lipid absorption rate of 64%. Furthermore, these results advocate the embedding process of HFMS by RSM due to its efficacy.

E-nose, e-tongue and e-eye for edible olive oil characterization and shelf life assessment: A powerful data fusion approach

The aim of this work was to investigate the applicability of e-senses (electronic nose, electronic tongue and electronic eye) for the characterization of edible olive oils (extra virgin, olive and pomace) and for the assessment of extra virgin olive oil and olive oil quality decay during storage at different temperatures. In order to obtain a complete description of oil samples, physico-chemical analyses on quality and nutritional parameters were also performed. Data were processed by PCA and a targeted data processing flow-sheet has been applied to physico-chemical and e-senses dataset starting from data pre-processing introducing an innovative normalization method, called t0 centering. On e-senses data a powerful mid-level data fusion approach has been employed to extract relevant information from different analytical sources combining their individual contributions. On physico-chemical data, an alternative approach for grouping extra virgin olive oil and olive oil samples on the basis of their freshness was applied and two classes were identified: fresh and oxidized. A k-NN classification rule was developed to test the performance of e-senses to classify samples in the two classes of freshness and the average value of correctly classified samples was 94%. Results demonstrated that the combined application of e-senses and the innovative data processing strategy allows to characterize edible olive oils of different categories on the basis of their sensorial properties and also to follow the evolution during storage of extra-virgin olive oil and olive oil sensorial properties thus assessing the quality decay of oils.

Characterization of laccase from apple fruit during postharvest storage and its response to diphenylamine and 1-methylcyclopropene treatments

To gain better understanding on laccase in apples and reveal its role in browning color formation during storage, laccases in apples were investigated. The full-length complementary DNAs encoding laccase genes were obtained from different tissues of apple including flowers, calyx, leaves and fruit peel of 'Red Delicious' and 'Cortland'. The apple laccases were compared to those in other plant species and found to have up to 99% homology to Arabidopsis and litchi. qRT-PCR analysis revealed changes in transcript abundance of LAC genes (2, 7, 9, 12, 14, 15 and 16) during storage and in response to DPA and 1-MCP treatments. Enzyme activity of laccase protein in apple peel increased with storage in control fruit, while decreased significantly with DPA or 1-MCP. Changes in phenolic compounds in pericarp tissues decreased generally during storage, but no significant effect of DPA and 1-MCP treatments on the phenolic compounds was found.

Evidence of oleuropein degradation by olive leaf protein extract

The enzymatic activity of raw protein olive leaf extract has been investigated in vivo, on olive leaf homogenate and, in vitro with pure oleuropein and other phenolic substrates. At least two types of enzymes were found to be involved in the degradation of endogenous oleuropein in olive leaves. As for the in vitro experiments, the presence of active polyphenoloxidase and β-glucosidase was determined by HPLC and UV-Visible spectroscopy. Interestingly, both the enzymatic activities were found to change during the storage of olive leaves. Specifically, the protein extracts obtained from fresh leaves showed the presence of both the enzymatic activities, because oleuropein depletion occurred simultaneously with the formation of the oleuropein aglycon, 3,4-DHPEA-EA. In comparison leaves subjected to the drying process showed a polyphenoloxidase activity leading exclusively to the formation of oxidation products responsible for the typical brown coloration of the reaction solution.