The effect of pressure on the kinetics of polyphenolics degradation – Implications to hyperbaric storage using Epigallocatechin-gallate as a model

Study of Brewer's Spent Grain Environmentally Friendly Processing Ways

BACKGROUND

This article is devoted to the study of the effect of electrochemically activated water (catholyte with pH 9.3) on organic compounds of the plant matrix of brewer's spent grain in order to extract various compounds from it.

METHODS

Brewer's spent grain was obtained from barley malt at a pilot plant by mashing the malt followed by filtration and washing of the grain in water and storing it at (0 ± 2) °C in craft bags. For the organic compound quantitative determination, instrumental methods of analysis (HPLC) were used, and the results were subjected to mathematical analysis.

RESULTS

The study results showed that at atmospheric pressure, the alkaline properties of the catholyte showed better results compared to aqueous extraction with respect to β-glucan, sugars, nitrogenous and phenolic compounds, and 120 min was the best period for extraction at 50 °C. The excess pressure conditions used (0.5 ÷ 1 atm) revealed an increase in the accumulation of non-starch polysaccharide and nitrogenous compounds, while the level of sugars, furan and phenolic compounds decreased with increasing treatment duration. The waste grain extract ultrasonic treatment used revealed the effectiveness of catholyte in relation to the extraction of β-glucan and nitrogenous fractions; however, sugars and phenolic compounds did not significantly accumulate. The correlation method made it possible to reveal the regularities in the formation of furan compounds under the conditions of extraction with the catholyte: Syringic acid had the greatest effect on the formation of 5-OH-methylfurfural at atmospheric pressure and 50 °C and vanillic acid under conditions of excess pressure. Regarding furfural and 5-methylfurfural, amino acids had a direct effect at excess pressure. It was shown that the content of all furan compounds depends on amino acids with thiol groups and gallic acid; the formation of 5-hydroxymethylfurfural and 5-methylfurfural is influenced by gallic and vanillic acids; the release of furfural and 5-methylfurfural is determined by amino acids and gallic acid; excess pressure conditions promote the formation of furan compounds under the action of gallic and lilac acids.

CONCLUSIONS

This study showed that a catholyte allows for efficient extraction of carbohydrate, nitrogenous and monophenolic compounds under pressure conditions, while flavonoids require a reduction in extraction time under pressure conditions.

The Effect of Storage and Pasteurization (Thermal and High-Pressure) Conditions on the Stability of Phycocyanobilin and Phycobiliproteins

The utilization of natural blue pigments in foods is difficult as they are usually unstable during processing and the commonly applied pH. The current study focuses on natural blue pigment, possessing antioxidant properties, found in Arthrospira platensis (spirulina), and phycobiliproteins (PBP). These pigments are a complex of conjugated protein and non-protein components, known as phycocyanobilin. PBP has low stability during pasteurization (high-pressure or heat treatments), resulting in protein denaturation and color deterioration that limits the application. The phycocyanobilin pigment might also be liable to oxidation during pasteurization and storage, resulting in color deterioration. Yet, the instability of the pigment phycocyanobilin during the pasteurization process and storage conditions was never studied before, limiting the comprehensive understanding of the reasons for PBP instability. In this study, the stability of phycocyanobilin under high-pressure and high-temperature conditions was compared to the stability of phycobiliproteins. We revealed that phycobiliproteins have a higher color deterioration rate at 70–80 °C than at high-pressure (300–600 MPa) whereas phycocyanobilin remained stable during high-pressure and heat processing. During storage at pH 7, phycocyanobilin was oxidized, and the oxidation rate increased with increasing pH, while at lower pH phycocyanobilin had low solubility and resulted in aggregation.

Shift of the reaction equilibrium at high pressure in the continuous synthesis of neuraminic acid

The importance of a compound that helps fight against influenza is, in times of a pandemic, self-evident. In order to produce these compounds in vast quantities, many researchers consider continuous flow reactors in chemical industry as next stepping stone for large scale production. For these reasons, the synthesis of N-acetylneuraminic acid (Neu5Ac) in a continuous fixed-bed reactor by an immobilized epimerase and aldolase was investigated in detail. The immobilized enzymes showed high stability, with half-life times > 173 days under storage conditions (6 °C in buffer) and reusability over 50 recycling steps, and were characterized regarding the reaction kinetics (initial rate) and scalability (different lab scales) in a batch reactor. The reaction kinetics were studied in a continuous flow reactor. A high-pressure circular reactor (up to 130 MPa) was applied for the investigation of changes in the position of the reaction equilibrium. By this, equilibrium conversion, selectivity, and yield were increased from 57.9% to 63.9%, 81.9% to 84.7%, and 47.5% to 54.1%, respectively. This indicates a reduction in molar volume from N-acetyl-ᴅ-glucosamine (GlcNAc) and pyruvate (Pyr) to Neu5Ac. In particular, the circular reactor showed great potential to study reactions at high pressure while allowing for easy sampling. Additionally, an increase in affinity of pyruvate towards both tested enzymes was observed when high pressure was applied, as evidenced by a decrease of K_I for the epimerase and K_M for the aldolase from 108 to 42 mM and 91 to 37 mM, respectively.

Simultaneous Extraction and Depolymerization of Condensed Tannins from Chinese Bayberry Leaves for Improved Bioavailability and Antioxidant Activity

Biorefineries of polyphenols from plant leaves maximize their commercial value for developing biomedicines and nutrients. However, condensed tannins (CTs) constitute extensive polyphenols from plant leaves, which hinders the maximization due to extremely low bioavailability. Therefore, a simple, and sustainable one-step method was established to simultaneously extract polyphenols and depolymerize CTs with only endogenous flavan-3-ols from Chinese bayberry leaves via acid catalysis, which markedly improved the bioavailability of total polyphenols. Afterward, purification of polyphenols from depolymerized extract was studied with specific polymeric resins. Silica C18 showed the highest absorption efficiency of total polyphenols, while Amberlite XAD-7 and XAD-2 presented high selectivity toward polyphenols with high and low molecular weight, respectively. Combined depolymerization of CTs and purification with Amberlite XAD-2 showed the highest bioavailability and cellular free-radical scavenging activity of total polyphenols, which proved to be an ideal methodology for improving the bioavailability and activity of polyphenols from plant leaves.

Reactivity of flavanols: Their fate in physical food processing and recent advances in their analysis by depolymerization

Flavanols, a subgroup of polyphenols, are secondary metabolites with antioxidant properties naturally produced in various plants (e.g., green tea, cocoa, grapes, and apples); they are a major polyphenol class in human foods and beverages, and have recognized effect on maintaining human health. Therefore, it is necessary to evaluate their changes (i.e., oxidation, polymerization, degradation, and epimerization) during various physical processing (i.e., heating, drying, mechanical shearing, high-pressure, ultrasound, and radiation) to improve the nutritional value of food products. However, the roles of flavanols, in particular for their polymerized forms, are often underestimated, for a large part because of analytical challenges: they are difficult to extract quantitatively, and their quantification demands chemical reactions. This review examines the existing data on the effects of different physical processing techniques on the content of flavanols and highlights the changes in epimerization and degree of polymerization, as well as some of the latest acidolysis methods for proanthocyanidin characterization and quantification. More and more evidence show that physical processing can affect content but also modify the structure of flavanols by promoting a series of internal reactions. The most important reactivity of flavanols in processing includes oxidative coupling and rearrangements, chain cleavage, structural rearrangements (e.g., polymerization, degradation, and epimerization), and addition to other macromolecules, that is, proteins and polysaccharides. Some acidolysis methods for the analysis of polymeric proanthocyanidins have been updated, which has contributed to complete analysis of proanthocyanidin structures in particular regarding their proportion of A-type proanthocyanidins and their degree of polymerization in various plants. However, future research is also needed to better extract and characterize high-polymer proanthocyanidins, whether in their native or modified forms.

Comparison of Thermal and High-Pressure Gelation of Potato Protein Isolates

Potato protein isolate (PPI), a commercial by-product of the starch industry, is a promising novel protein for food applications with limited information regarding its techno-functionality. This research focused on the formation of both thermal and high-pressure gels at acidic and neutral pH levels. Our results reveal that physical gels are formed after 30 min by heat at pH 7 and pH 3, while pressure (300-500 MPa) allows the formation of physical gels only at pH 3, and only when the system crosses 30 °C by adiabatic heating during pressurization. Texture profile analysis (TPA) revealed that gel hardness increased with both gelation temperature and pressure, while water-holding capacity was lower for the pressure-induced gels. The proteins released in the water-holding test suggested only partial involvement of patatin in the gel formation. Vitamin C as a model for a thermally liable compound verified the expected better conservation of such compounds in a pressure-induced gel compared to a thermal one of similar textural properties, presenting a possible advantage for pressure-induced gelation.

The Link between Polyphenol Structure, Antioxidant Capacity and Shelf-Life Stability in the Presence of Fructose and Ascorbic Acid

Polyphenols play an important role in the sensorial and health-promoting properties of fruits and vegetables and display varying structure-dependent stability during processing and shelf-life. The current work aimed to increase the fundamental understanding of the link between the stability of polyphenols as a function of their structure, presence of ascorbic acid and fructose and total antioxidant capacity (TAC), using a multi-component model system. Polyphenol extract, used as the multi-component model system, was obtained from freeze-dried, high polyphenol content strawberry (Fragaria × ananassa ‘Nerina’) and twenty-one compounds were identified using high-performance liquid chromatography-mass spectrometry (HPLC-MS). The TAC and the first-order degradation kinetics were obtained, linking the polyphenol stability to its chemical structure, with and without the presence of fructose and ascorbic acid. The TAC (measured by oxygen radical absorption capacity (ORAC) and ferric reducing antioxidant potential (FRAP) assays) was not dramatically affected by storage temperatures and formulation, while polyphenol stability was significantly and structure dependently affected by temperature and the presence of ascorbic acid and fructose. Anthocyanins and phenolic acids were more unstable in the presence of ascorbic acid, while flavonol stability was enhanced by its presence. Shelf life study performed at 37 °C revealed significantly higher stability of purified polyphenols vs. the stability of the same polyphenols in the strawberry extract (multi-component system).