Thermodynamic Stability of Thermolabile Longevity Compounds in High-Shear Processing

Thermodynamic Stability and Degradation Kinetics of Thermolabile Longevity Compounds Under High-Shear Manufacturing Stress

Abstract

Thermolabile longevity-associated compounds and polyphenolic bioactives frequently experience coupled thermal, oxidative, pH, and mechanical stresses during manufacturing (e.g., high-shear mixing, high-pressure homogenization, and spray drying), which can accelerate chemical degradation and reduce delivered potency. Quantitative, process-relevant stability parameters are therefore required to define manufacturable design spaces and to guide protective formulation strategies. [1–3]

Methods in the present synthesis focus on quantitative evidence extracted from studies reporting:

• Thermodynamic/thermal transitions assessed by DSC and TGA (melting, decomposition onset, glass transitions, and staged mass-loss behavior)
• Degradation kinetics (pseudo-first-order/first-order models, Arrhenius activation energies, pH dependencies, and time-to-fraction-decomposed measures) for NAD⁺ precursors (NR/NRH/NMN), stilbenoids (resveratrol-related systems), flavonoids (quercetin, fisetin, rutin/esters), and curcuminoids. [4–11]

Results indicate that several representative longevity compounds exhibit narrow thermal-processing windows in specific physical states. Nicotinamide riboside chloride (NRCl) exhibits an onset of melting at 120.7 ± 0.3 °C with rapid post-melt decomposition (e.g., 98% degradation at 130 °C by qNMR), while aqueous degradation follows pseudo-first-order kinetics with activation energies of 75.4–82.8 kJ·mol⁻¹ depending on pH. [4]

For trans-resveratrol, degradation kinetics are strongly pH- and temperature-dependent (e.g., half-life decreasing from 329 days at pH 1.2 to 3.3 minutes at pH 10), and accelerated-test extrapolation can be non-Arrhenius in tablet matrices. [7, 12]

High-shear unit operations can induce local heating and oxidative environments, as demonstrated by high-shear homogenization increasing outlet temperature with rotational speed and coinciding with 42.6% ascorbic-acid loss at 20,000 rpm, and by high-pressure homogenization mechanisms involving valve shear, cavitation, and turbulence at >100 MPa. [13, 14]

Conclusions emphasize integrating thermodynamic transition data (DSC/TGA/Tg) with kinetic models (Arrhenius, non-Arrhenius, and isoconversional methods) to produce time–temperature–shear maps and to rationally select mitigation strategies, including encapsulation, amorphous solid dispersions, cyclodextrin/nanosponge systems, oxygen control, and shear/temperature minimization. [15–18]

Keywords

thermolabile bioactives; degradation kinetics; Arrhenius; DSC; TGA; high-pressure homogenization; spray drying; NAD⁺ precursors

1. Introduction

Longevity-relevant compounds are increasingly formulated as nutraceuticals, functional foods, and advanced delivery systems, motivating manufacturing routes that expose actives to combined stressors including heating, oxygen contact, water activity, pH excursions, and intense mechanical energy input. [3, 5, 14, 19]

For NAD⁺ precursor chemistries, aqueous and solid-state stability are central because reactivity can occur via hydrolysis of glycosidic or phosphate-linked motifs, and because processing temperatures can cross solid-state transition thresholds that precede rapid decomposition. [4, 6]

For polyphenols and related botanical actives, stability constraints include autoxidation, epimerization, and enzymatic oxidation to quinones, which are sensitive to temperature, pH, metal ions, and oxygen availability during processing. [17]

A practical implication is that manufacturing design cannot rely solely on nominal bulk temperature; instead, it must integrate:

• Thermodynamic indicators such as glass transition, melting, and decomposition onset
• Kinetic models that capture the dependence of degradation on time, temperature, pH, oxygen, and (where measurable) mechanical energy input. [4, 9, 10, 14, 15]

This paper synthesizes quantitative evidence on representative longevity compounds and related bioactives for which the included sources provide explicit thermodynamic transitions and/or kinetic parameters, and it links those data to stress profiles of high-shear unit operations including high-shear mixing, high-pressure homogenization/microfluidization, mechanochemical milling, and spray drying. [1, 14, 15, 20]

2. Thermodynamic Framework

Thermodynamic stability in manufacturing contexts is operationally assessed using measurable thermal events (DSC/TGA) and state descriptors (e.g., amorphous vs crystalline; glass transition temperature) that indicate when a compound or formulation transitions into states with higher molecular mobility and therefore higher reaction rates or different mechanisms. [4, 9, 15]

2.1 Gibbs Free Energy and Phase Stability

Several included sources explicitly compute Gibbs free energy changes for degradation processes or thermal destruction, providing a thermodynamic measure of feasibility under specific conditions. [8, 19]

• For NR borate, degradation spontaneity was evaluated via a Gibbs free energy calculation, with ΔG reported as 2.43 kcal·mol⁻¹. [19]
• For rutin and fatty-acid rutin esters under pyrolytic conditions, ΔG values were positive (84–245 kJ·mol⁻¹) alongside positive ΔH (60–242 kJ·mol⁻¹), indicating an endothermic and non-spontaneous pyrolysis profile in the reported analysis. [8]

In kinetic-formalism terms, several sources also apply transition-state and free-energy relations to interpret hydrolysis activation in systems such as the curcumin spiroborate complex. [21]

2.2 Glass Transition, Melting, and Decomposition Onset

DSC and TGA provide complementary markers of process risk: melting or softening events can sharply increase diffusion and enable rapid chemical conversion, and TGA mass-loss onset can indicate the beginning of irreversible decomposition even in the apparent solid state. [4, 9, 15]

• For NRCl, DSC indicates an onset of melting at 120.7 ± 0.3 °C and a melting peak at 125.2 ± 0.2 °C, followed by an immediate sharp exothermic event peaking at 130.8 ± 0.3 °C. [4]
• For NMN, decomposition begins at 160 °C and completes by 165 °C, with an endothermic DSC peak at 162 °C and enthalpy of decomposition 184 kJ·mol⁻¹. [6]
• For quercetin, an intense DSC endotherm (maximum at 303 °C) is often misattributed to melting, whereas TGA data indicate decomposition at 230 °C overlapping with mass loss. [9]
• For curcumin under nitrogen, a multi-stage decomposition is observed starting at 240 °C, with 37% residue remaining at 600 °C. [18]

2.3 Amorphous and Crystalline Stability

Amorphous formulations may improve solubility and bioavailability but can alter thermal behavior and stability by increasing molecular mobility relative to crystalline forms, making glass transition temperature (Tg) a critical stability parameter. [15, 16]

• Mechanochemically prepared fisetin amorphous solid dispersions (ASDs) show measurable Tg values in second heating scans and demonstrate compositional shifts in Tg consistent with miscibility. [15]
• For resveratrol and oxyresveratrol nanosponges, the melting endotherm of resveratrol disappears in the nanosponge formulations, attributed to encapsulation and amorphization. [16]
• For quercetin, combined DSC/TGA interpretation suggests decomposition and structural relaxation/softening in the 150–350 °C range. [9]

3. Degradation Kinetics Models and Parameters

Included sources employ various kinetic models (e.g., first-order, pseudo-first-order, sigmoidal) and temperature dependence treatments (e.g., Arrhenius behavior) to characterize degradation. [4, 7, 22]

3.1 Reaction-Order Models

A standard approach for solution-phase degradation uses the integrated first-order model. [4, 11, 12]

• For NRCl degradation in aqueous solutions, pseudo-first-order kinetics are reported. [4, 23]
• Spray-dried plant-extract markers demonstrate varying reaction orders, including zero-order and second-order models for specific compounds. [20]

3.2 Arrhenius and Eyring Treatments

Temperature dependencies of degradation are often modeled using Arrhenius-type expressions. [4, 10, 12]

• For NRCl, activation energies range from 75.4 to 82.8 kJ·mol⁻¹, with pH influencing these values. [4]
• Trans-resveratrol exhibits activation energy of 84.7 kJ·mol⁻¹ at pH 7.4. [12]
• Curcumin in varying media shows activation energies between 9.75–16.46 kcal·mol⁻¹. [11]

3.3 Isoconversional and Model-Free Methods

Isoconversional methods (e.g., KAS, FWO, Friedman) are used to identify multi-step decomposition and mechanism changes. [8, 18, 25]

• For rutin and fatty-acid rutin esters, activation energies vary with conversion degree. [8]
• Resveratrol–β-cyclodextrin clathrates show activation energy increases with transformation degree. [25]

3.4 Coupled Thermo-Mechanical and Oxidative Degradation

High-shear manufacturing processes couple mechanical stress with local heating and oxidation, promoting degradation pathways. [13, 14, 17]

• High-shear homogenization increases outlet temperatures significantly with rotational speed and causes severe ascorbic acid degradation due to elevated temperature and oxidation. [13]
• High-pressure homogenization mechanisms—such as valve shear, cavitation, and turbulence—induce oxidative and mechanical stress. [14]
• Oxidative coupling accelerates quercetin degradation in high-temperature, high-oxygen environments. [26]

4. Compound-Class Review

The following synthesis emphasizes key kinetic and thermodynamic parameters relevant for manufacturing models, such as activation energies, rate constants, half-lives, decomposition onsets, and glass-transition or melting-related constraints. [4, 11, 12, 15, 24]

4.1 NAD⁺ Precursors

• NAD⁺ precursor stability is significantly affected by hydrolysis susceptibility, sensitivity to thermal transitions, and oxygen-driven oxidation. [4, 5]
• NRCl degradation kinetics exhibit pseudo-first-order behavior, with activation energies ranging from 75.4 to 82.8 kJ·mol⁻¹, strongly influenced by pH. [4]
• In solid-state, NRCl has a narrow thermal processing window, with rapid degradation occurring above its melting point of 120.7 ± 0.3 °C. [4]
• NRH shows rapid degradation under acidic conditions and in the presence of oxygen, highlighting its instability due to its N-glycosidic bond. [5]
• NMN decomposes at temperatures above 160 °C and exhibits pH and temperature-sensitive degradation patterns in aqueous solutions. [6, 27, 28]

NMN Degradation Pathway

The primary NMN degradation pathway is described as hydrolysis of the phosphodiester linkage yielding nicotinamide and ribose-5-phosphate, with pH dependencies described as acid-catalyzed hydrolysis below pH 4.5 and base-mediated cleavage above pH 7.5. [28]

Stilbenoids

Stilbenoids include resveratrol and related compounds that display strong pH- and oxygen-dependent degradation. Their stability in real formulations can deviate from Arrhenius extrapolation due to matrix effects and multiple pathways. [7, 12, 29]

In aqueous systems, trans-resveratrol is reported to be stable at acidic pH, but its degradation increases exponentially above pH 6.8. Half-life decreases from 329 days at pH 1.2 to 3.3 minutes at pH 10. [12]

At pH 7.4, trans-resveratrol degradation follows first-order kinetics across investigated temperatures, with an activation energy of 84.7 kJ·mol^-1. [12]

Degradation mechanisms vary with pH. In acidic conditions, hydroxyl groups are protected from radical oxidation by H₃O⁺, whereas in alkaline environments, phenate ions increase susceptibility to oxidation, promoting phenoxy radical formation. Additionally, oxygen in the medium accelerates radical reactions leading to degradation. [12]

Thermal stability experiments in aqueous solution (19 mg·L^-1) show no significant spectral changes after 30 minutes at temperatures up to 70 °C. However, elevated temperatures result in a decrease in absorbance at 304 nm and across the 270–350 nm range, indicating thermally induced degradation. [30]

Mechanistic interpretation of hydrothermal experiments proposes oxidative splitting of the double bond and formation of degradation products, including hydroxy aldehydes, alcohols, and hydroxy acids. FTIR analysis revealed bands consistent with aldehyde and carboxylic acid formation at 100–120 °C. [30]

In tablet matrices, resveratrol degradation follows first-order monoexponential kinetics with k values of 0.07140, 0.1937, and 0.231 months^-1 at 25, 30, and 40 °C, respectively. However, the ln(k) vs 1/T relationship is nonlinear and classified as super-Arrhenius, suggesting additional reactions, multiple pathways, or matrix effects at higher temperatures. [7]

Research indicates that accelerated testing may overestimate degradation, with authors recommending alternative methods for determining degradation kinetics. [7]

For stilbene-like phenolics in dry systems, thermal treatments such as steam sterilization at 121 °C for 20 minutes cause measurable losses (e.g., 20.98% decrease in pinosylvin by peak area), and oven drying at 105 °C for 24 hours leads to decreases of more than 50% for several phenolics. However, TGA indicates decomposition onset temperatures above ~200 °C for pinosylvin systems. [31]

Flavonoids

Flavonoids exhibit multi-pathway degradation that is sensitive to pH, temperature, oxygen, and formulation interactions such as protein binding. Their thermal behavior in DSC/TGA can involve overlapping decomposition and softening. [9, 22, 24]

Studies show that increasing medium pH from 6.0 to 7.5 accelerates degradation, with fisetin and quercetin experiencing 24-fold and 12-fold increases in respective degradation rate constants. Moreover, raising the temperature above 37 °C further increases the rate constants. [24]

• For fisetin: k increased from 8.30×10^-3 to 0.202 h^-1 as pH was raised, and to 0.490 h^-1 at 65 °C.
• For quercetin: k increased from 2.81×10^-2 to 0.375 h^-1 with pH and rose to 1.42 h^-1 at 65 °C. [24]

Protein co-ingredients can mitigate degradation, as indicated by decreased k values in their presence. For example, fisetin k decreased from 3.58×10^-2 to 1.76×10^-2 h^-1, and quercetin k decreased from 7.99×10^-2 to 3.80×10^-2 h^-1. Stabilization is attributed to hydrophobic interactions and hydrogen bonding, with SDS causing destabilization. Further studies are needed to quantify hydrogen-bond contributions. [24]

For quercetin at 90 °C near neutrality, strong pH effects are observed. The degradation rate constant increases approximately five-fold from pH 6.5 to 7.5, yielding intermediate oxidation products such as quercetin quinone, with protocatechuic acid (PCA) and phloroglucinol carboxylic acid (PGCA) as end products. [22]

High-temperature systems (150 °C) accelerate degradation, with rate constants reported as 0.253 h^-1 under nitrogen, 0.868 h^-1 in oxygen, and 7.17 h^-1 in oxygen with cholesterol. Quercetin loss increases from 7.9% at 10 minutes in nitrogen to 20.4% in oxygen, and decreases further to 10.9% remaining with cholesterol plus oxygen. [26]

Thermal analysis shows that quercetin has a small endothermic peak at 90–135 °C (associated with minor mass loss) and starts to decompose at 230 °C. A prominent DSC endotherm at 303 °C overlaps with decomposition, with hydrogen bonding both constraining melting-like behavior and facilitating decomposition. [9]

For rutin (a quercetin glycoside) and its fatty acid esters, TGA indicates that rutin is thermally stable up to 240 °C, whereas esters exhibit lower initial degradation temperatures and higher mass loss during major degradation stages. Activation energies range from 65 to 246 kJ·mol^-1 depending on the degree of conversion. [8]

Cyclodextrin-Derived Carrier Systems

Cyclodextrin-derived carrier systems provide another strategy: resveratrol–β-cyclodextrin clathrates show thermal events including water release near 50 °C and higher-temperature degradation events, and binding free energies (e.g., −86 kJ·mol⁻¹ by MM/PBSA) quantify strong inclusion interactions. [25]

Nanosponge Encapsulation

Nanosponge encapsulation of resveratrol eliminates its DSC melting endotherm and provides photoprotection: free resveratrol shows 59.7% degradation within 15 min under UV exposure, while resveratrol nanosponges provide approximately two-fold protection, consistent with encapsulation preventing direct UV exposure. [16]

Amorphous Solid Dispersions

Amorphous solid dispersions can be engineered via mechanochemical milling, and hydrogen bonding between fisetin and Eudragit® ester groups is explicitly identified, providing a mechanistic basis for miscibility and altered Tg that can stabilize against crystallization-dependent changes in dissolution behavior. [15]

Excipient and Carrier Selection

Excipient selection can alter kinetic mechanisms and stability outcomes, as reported in spray-dried plant-extract systems where reaction order and decomposed-fraction times differ by excipient mixtures, indicating excipient-dependent degradation kinetics. [20]

Protein co-ingredients can stabilize flavonoids via hydrophobic interactions, lowering k values for fisetin and quercetin, and SDS disruption of these interactions supports the interpretation that hydrophobic binding is a key stabilizing mechanism. [24]

Process Engineering Controls

Process controls that reduce thermal exposure and oxygen contact are directly supported by multiple datasets. [5, 18]

For NRCl, DSC/qNMR evidence indicates that exceeding the melting onset region (~120–130 °C) can produce extremely rapid degradation, supporting hard upper bounds on temperature and residence time in heated solid-state operations. [4]

For NRH, the difference between air and N₂ half-life at 25 °C implies that inerting and oxygen exclusion can be material, and the authors report that samples under an N₂ blanket at 4 °C show no detectable degradation after 60 days while samples at 4 °C in air show ~10% degradation. [5]

For high-shear homogenization, the direct observation that increasing rpm increases outlet temperature and is associated with higher loss of oxidation-sensitive ascorbic acid supports engineering measures that limit shear-driven heating (e.g., cooling jackets, shorter mixing times, staged addition). [13]

For spray drying, the assertion that oxygen and heat exposure decrease (poly)phenols and that high temperatures may be detrimental to thermolabile phenolics supports choices such as lowering outlet temperature when feasible and using encapsulation to reduce oxidation and heat sensitivity. [3]

Antioxidants and Oxygen Management

Antioxidant and oxygen-management strategies are mechanistically supported across polyphenol datasets. [12, 22]

For quercetin at 90 °C, antioxidants such as cysteine reduce k, with 200 μmol·L⁻¹ cysteine producing a k reduction of ~43% compared to control, and mechanistic interpretation considers stabilization of quercetin quinone and radical quenching effects. [22]

For trans-resveratrol, oxygen is explicitly reported to promote radical reactions leading to degradation, supporting inert processing atmospheres or oxygen barriers where feasible for alkaline/neutral aqueous processing. [12]

In liposomal systems, resveratrol is reported to limit stigmasterol oxidation by neutralizing free radicals and to integrate into lipid bilayers increasing rigidity, reducing permeability to oxygen and oxidizing agents, thereby enhancing thermal and oxidative stability of the system. [35]

Discussion

Across the evidence base synthesized here, the strongest quantitative pattern is that chemical microenvironment (pH, oxygen, water presence) can dominate stability outcomes even at modest temperatures, and that several bioactives exhibit sharp stability discontinuities at specific thermal-transition thresholds. [4, 5, 12]

For NAD⁺ precursors, the NRCl dataset highlights a dual regime: in aqueous solution, pseudo-first-order hydrolysis can be modeled with Arrhenius activation energies and a roughly twofold rate increase per 10 °C, while in the solid state a narrow region around 120–130 °C corresponds to melting followed immediately by rapid decomposition. [4]

For resveratrol, a dominant process risk emerges from pH sensitivity: half-life collapses from long durations at acidic pH to minutes at high pH, while oxygen promotes radical reactions, indicating that high-shear operations that increase oxygen transfer and local alkalinity could be disproportionately damaging even if bulk temperature remains moderate. [12]

For flavonoids, oxidation via quinone intermediates and pH-dependent deprotonation mechanisms (quercetin) combine with high-temperature oxidation and radical-chain coupling (e.g., oxygen plus cholesterol), suggesting that lipid-containing formulations and oxygen exposure can strongly amplify oxidative loss pathways. [22, 26]

For curcumin, there is a mechanistic tension between hydrolysis-driven narratives (in some GI-buffer work) and autoxidation-driven narratives (in micelle-focused work), but both converge on a strong pH effect and on the protective role of hydrophobic microenvironments and oxygen limitation. [11, 32]

At the unit-operation level, high-shear processes can act primarily as indirect accelerants by generating heat and increasing oxidative susceptibility; this is directly demonstrated in high-shear homogenization where rotational speed increases outlet temperature and coincides with oxidative loss of ascorbic acid. [13]

HPH/UHPH introduce additional complexity because the valve region imposes extreme shear, cavitation, and turbulence, and may generate high local temperatures, although residence times can be very short (e.g., <0.2 s in UHPH descriptions), implying that chemical outcomes may depend on whether degradation is controlled by fast radical processes, diffusion-limited steps, or slower thermal activation steps. [14, 34]

Finally, several sources highlight that stability modeling must be mechanistically validated in the relevant matrix: resveratrol tablet data show non-Arrhenius behavior and matrix effects that limit general Arrhenius extrapolation from accelerated tests, and spray-dried plant-extract markers show excipient-dependent kinetic orders and fraction-decomposed times. [7, 20]

Conclusions

Quantitative thermodynamic transition markers (DSC/TGA) and degradation kinetics (k, t_1/2, E_a, conversion-dependent activation energies) provide a process-relevant basis for designing manufacturing conditions that preserve potency of thermolabile longevity compounds and related bioactives. [4, 8, 9]

For NAD⁺ precursors, NRCl exhibits a narrow thermal-processing window near melting followed by rapid decomposition, while aqueous kinetics show pH-dependent pseudo-first-order behavior with activation energies of 75–83 kJ·mol⁻¹ that can parameterize thermal exposure models. [4]

For resveratrol, pH and oxygen are dominant variables, with half-life collapsing from hundreds of days at acidic pH to minutes at high pH, and formulation matrices can produce non-Arrhenius behavior that complicates accelerated-testing extrapolation. [7, 12]

For flavonoids and curcuminoids, oxidation pathways (quinone intermediates for quercetin; autoxidation for curcumin) motivate oxygen control and hydrophobic encapsulation strategies, which are quantitatively shown to extend half-life by orders of magnitude in micellar systems and materially in Pickering emulsions produced under high-shear mixing. [1, 10, 22, 32]

For high-shear unit operations, available evidence shows that shear can elevate temperature and promote oxidation (high-shear mixing) and that valve-based high-pressure processes generate extreme shear and cavitation with pressure, pass count, and inlet temperature as key stress variables; these insights support implementing time–temperature–shear mapping and PAT using stability-indicating analytics. [12–14]

Conflict of Interest

The authors declare no conflict of interest. [20]