Key takeaways
- Vitamin C (L-ascorbic acid) is the most thermally labile micronutrient in dried fruit, making its retention the single most informative proxy for overall nutrient preservation during drying.
- Geothermal drying vitamin C preservation rates of 70–85 % are consistently documented at drying-air temperatures of 40–65 °C, compared with 28–55 % retention in conventional hot-air systems operating above 70 °C.
- Degradation follows first-order Arrhenius kinetics with published activation energies of 50–125 kJ/mol in fruit matrices. Every 10 °C increase in drying temperature roughly doubles the irreversible conversion rate of dehydroascorbic acid to 2,3-diketogulonic acid, the step that permanently destroys biological activity.
- Malatya-origin apricots dried geothermally in the Sindirgi basin retain 72–83 % of their fresh vitamin C content versus 31–48 % for gas-fired tunnel-dried equivalents from the same harvest lot.
- B2B buyers can leverage these retention figures for EU nutrient declaration labels, front-of-pack health claims under Regulation 1924/2006, and differentiated positioning in markets where consumers pay a premium for nutrient-dense ingredients.
Introduction
Geothermal drying vitamin C preservation is not a marketing claim. It is a measurable, repeatable outcome of physical chemistry. When a B2B procurement team evaluates dried fruit sourcing options, the vitamin C retention percentage in the finished product is the most informative single metric for assessing how much nutritional value survived the drying process. Vitamin C degrades faster and at lower temperatures than any other major micronutrient in fruit — faster than carotenoids, faster than polyphenols, faster than B-group vitamins. If a drying method preserves vitamin C well, it almost certainly preserves everything else.
This matters commercially. Nutrient declarations on packaging, health claim substantiation under EU Regulation 1924/2006, front-of-pack labelling schemes, and retailer-mandated nutritional specifications all depend on the actual vitamin content of the finished product, not the fresh fruit it came from. A dried apricot that has lost 60 % of its vitamin C during processing cannot support the same label claims as one that retained 80 %. For brands competing on nutritional superiority, the drying method is not a processing detail — it is a product design decision.
This article explains the chemistry of vitamin C degradation during thermal drying, presents the Arrhenius kinetics and time-temperature data that define the geothermal advantage, reviews apricot-specific lab data from Turkish geothermal facilities, and translates the science into actionable guidance for B2B procurement and product development teams. For a broader technology and sourcing overview, see the geothermal drying B2B guide.
Vitamin C — why it matters for dried fruit quality
L-ascorbic acid structure and instability
Vitamin C exists in two biologically active forms. L-ascorbic acid (AA), the reduced form, is a six-carbon lactone with an enediol group on carbons 2 and 3 that donates electrons readily. This electron-donating capacity is what makes vitamin C a potent antioxidant — and what makes it so vulnerable to degradation. The enediol moiety is oxidised easily by molecular oxygen, transition metal ions (Fe³⁺, Cu²⁺), and reactive oxygen species, even at room temperature.
The oxidised product, dehydroascorbic acid (DHAA), retains full biological vitamin C activity because mammalian cells reduce it back to AA via glutathione-dependent pathways. However, DHAA is unstable. Its lactone ring undergoes irreversible hydrolytic opening to form 2,3-diketogulonic acid (2,3-DKG), a compound with zero vitamin C activity that cannot be reconverted. This irreversible ring-opening step is the rate-limiting reaction in vitamin C destruction during drying, and its rate is strongly temperature-dependent.
The structural fragility of L-ascorbic acid explains why vitamin C functions as the canary in the coal mine for drying quality. No other abundant fruit micronutrient has a degradation rate constant this large at processing-relevant temperatures.
Why vitamin C is the benchmark for nutrient retention
Food scientists have long used vitamin C retention as the benchmark indicator of thermal processing severity. The rationale is straightforward: because ascorbic acid degrades faster than carotenoids, polyphenols, tocopherols, and B-group vitamins at any given temperature, a process that preserves vitamin C well will preserve all other heat-sensitive nutrients at equal or higher percentages. This principle has been validated across dozens of fruit and vegetable drying studies published in journals including the Journal of Food Engineering and Food Chemistry.
In practical terms, a dried apricot lot showing 80 % vitamin C retention can be expected to show at least 80 % retention of beta-carotene, at least 85 % retention of total polyphenols, and near-complete retention of minerals and dietary fibre. The vitamin C number is the floor, not the ceiling.
Consumer and regulatory significance
Consumer demand for nutrient-dense ingredients is accelerating across all major markets. In the EU, Regulation 1924/2006 governs nutrition and health claims. A "source of vitamin C" claim requires at least 15 % of the Nutrient Reference Value (NRV) per 100 g — equivalent to 12 mg of vitamin C per 100 g of solid food. A "high in vitamin C" claim requires 30 % NRV, or 24 mg per 100 g. Whether a dried fruit product meets these thresholds depends entirely on the drying temperature.
In the United States, the FDA's nutrient content claim regulations follow a parallel structure. In Japan, South Korea, and the GCC states, analogous frameworks exist. For brands selling internationally, the vitamin C content of a dried fruit ingredient determines which claims can appear on which markets — and the drying method determines the vitamin C content.
The science of vitamin C degradation during drying
Oxidation pathways (aerobic vs anaerobic)
Vitamin C degradation during drying proceeds through two mechanistically distinct pathways, both of which converge on the same irreversible endpoint.
Aerobic pathway. In the presence of molecular oxygen (the dominant scenario in convective drying), L-ascorbic acid is oxidised to DHAA, which then undergoes hydrolytic ring opening to 2,3-DKG. This pathway is catalysed by trace metal ions (particularly Cu²⁺ and Fe³⁺ naturally present in fruit tissue), by the enzyme ascorbate oxidase released during cell rupture at the onset of drying, and by free-radical chain reactions initiated when oxygen interacts with unsaturated lipids at elevated temperatures.
Anaerobic pathway. Even in the absence of oxygen, L-ascorbic acid undergoes acid-catalysed hydrolysis at low pH values typical of fruit (pH 3.0–4.5). This pathway is slower than aerobic oxidation but becomes significant during prolonged drying cycles, particularly in the interior of fruit pieces where oxygen penetration is limited by the drying front. The anaerobic pathway produces furfural and related compounds that contribute to non-enzymatic browning.
Both pathways are accelerated by temperature. The aerobic pathway is additionally accelerated by oxygen partial pressure, which is why enclosed drying chambers with controlled airflow (as used in geothermal systems) offer an inherent advantage over open-air tunnel dryers that circulate large volumes of ambient air across the product.
Temperature dependence — Arrhenius equation
The rate constant (k) for the irreversible conversion of DHAA to 2,3-DKG follows the Arrhenius equation:
k = A × exp(−Ea / RT)
Where A is the pre-exponential factor, Ea is the activation energy, R is the universal gas constant (8.314 J/mol·K), and T is the absolute temperature in Kelvin. Published activation energies for ascorbic acid degradation in fruit matrices range from 50 to 125 kJ/mol, with most studies on stone fruits reporting values in the 60–90 kJ/mol range (Demiray and Tulek, 2017, Journal of Food Engineering, 202, 44–51).
The practical implication of these Ea values is dramatic. With Ea = 75 kJ/mol (a representative mid-range value for apricot), increasing the drying temperature from 50 °C to 70 °C increases the degradation rate constant by a factor of approximately 3.8. At 80 °C, the factor rises to approximately 7.5 relative to 50 °C. This exponential scaling is the core physical principle underlying the geothermal advantage.
Role of oxygen, light, and moisture
Temperature is the dominant variable, but three co-factors modulate vitamin C loss during drying:
- Oxygen partial pressure. The aerobic oxidation pathway requires dissolved or surface-adsorbed O₂. Conventional tunnel dryers circulate 3–6 m/s ambient air at atmospheric oxygen levels (≈21 % O₂), maximising oxygen flux across the product surface. Geothermal dryers with enclosed chambers and lower airflow velocities (0.5–2.0 m/s) reduce oxygen exposure, slowing the aerobic pathway.
- Light exposure. Ultraviolet radiation cleaves the ascorbic acid lactone ring directly via photolysis, bypassing the DHAA intermediate entirely. This explains why open sun drying achieves poor vitamin C retention (20–45 %) despite low temperatures: UV degradation operates in parallel with thermal pathways. Enclosed geothermal chambers exclude all UV radiation.
- Moisture content. The rate of ascorbic acid oxidation is highest at intermediate water activity (aw 0.3–0.7), which is precisely the range that fruit passes through during drying. Below aw 0.3, molecular mobility is restricted and reaction rates slow. Above aw 0.7, the dilution effect reduces reactant concentration. The speed at which a drying process moves the product through this critical aw zone affects total vitamin C loss.
Time-temperature integral concept
Total vitamin C loss during drying is not determined by temperature alone or by time alone, but by the integral of the degradation rate over the entire drying cycle. This time-temperature integral accounts for the fact that geothermal drying takes longer (12–24 hours versus 6–14 hours for conventional methods) but operates at a lower rate constant throughout.
The mathematics are unambiguous. For apricot halves with Ea = 75 kJ/mol, a 20-hour drying cycle at 55 °C produces approximately 18 % total vitamin C degradation. A 10-hour cycle at 75 °C produces approximately 52 % degradation — nearly three times more, despite half the duration. The lower rate constant at geothermal temperatures more than compensates for the longer exposure. This is the quantitative basis for the 70–85 % retention figures consistently observed in geothermal-dried fruit.
Geothermal drying: how low temperature protects vitamin C
Temperature profile: 40–65 °C vs conventional 70–80 °C
The 40–65 °C operating window of geothermal dryers is defined by two physical constraints, not by arbitrary convention.
The lower bound (40 °C) is set by food safety and economic throughput. Below 40 °C, drying rates become uneconomically slow, water activity decreases too gradually, and the extended wet period creates microbial proliferation risk. Codex Alimentarius and EFSA guidance consistently recommends reducing water activity below 0.65 within 24–36 hours for fruit products.
The upper bound (65 °C) is set by degradation kinetics. Above 65 °C, the Arrhenius-predicted rate constant for ascorbic acid degradation shifts into a regime where shorter drying times no longer compensate for the faster reaction rate. Maillard browning between reducing sugars and amino acids becomes visually significant in high-sugar fruits (apricots, figs, dates), creating a secondary degradation pathway that oxidises ascorbic acid through reactive carbonyl intermediates. Volatile aromatic compounds — esters, aldehydes, and terpenes — begin evaporating at rates that measurably reduce sensory quality.
Geothermal heat sources in the Turkish Aegean basin deliver water at 60–95 °C at the wellhead, which after heat-exchange losses translates to drying-air temperatures of 45–65 °C — a natural match for this optimum window.
Quantified retention rates
The following table synthesises published literature and facility-level analytical data for vitamin C retention across drying temperatures, using stone fruit (apricot, peach, cherry) as the reference matrix.
| Drying air temperature (°C) | Typical drying time (hours) | Vitamin C retention (%) | Rate constant relative to 50 °C | Primary degradation driver | |---|---|---|---|---| | 40–45 | 20–28 | 82–90 | 0.5–0.7× | Minimal — slow aerobic oxidation only | | 45–55 | 14–22 | 75–85 | 0.7–1.0× | Low-rate thermal oxidation | | 55–65 | 10–18 | 68–78 | 1.0–2.0× | Moderate thermal + early Maillard | | 65–75 | 8–14 | 45–62 | 2.0–3.8× | Thermal oxidation + Maillard browning | | 75–85 | 6–10 | 28–48 | 3.8–7.5× | Aggressive thermal + Maillard + aroma loss | | 85–95 | 4–8 | 15–30 | 7.5–15× | Severe degradation across all nutrients |
The geothermal operating range (rows 1–3) consistently delivers 68–90 % retention. Conventional hot-air drying (rows 4–5) delivers 28–62 %. The gap is not marginal — it represents a 20–40 percentage point difference in the nutrient that matters most for label claims and product positioning.
The 10 °C rule — why small differences matter exponentially
A useful heuristic from food science is the Q₁₀ rule: for many chemical and enzymatic reactions, the rate approximately doubles for each 10 °C increase in temperature. For ascorbic acid degradation in fruit, published Q₁₀ values range from 1.8 to 2.5, meaning the 10 °C rule slightly underestimates the true sensitivity.
This exponential relationship means that seemingly small temperature differences produce large retention differences. Drying at 55 °C instead of 65 °C does not improve retention by a linear 15 %. It reduces the integrated degradation by 35–45 % because the rate constant is exponentially lower. This is why precision temperature control — a natural feature of geothermal systems with their stable heat source — matters far more than operators of gas-fired dryers typically realise, where temperature fluctuations of ±10 °C are common during batch cycles.
Humidity control in geothermal chambers
Temperature is the primary variable, but humidity control is the secondary mechanism through which geothermal drying protects vitamin C. Geothermal dryers typically operate as enclosed systems with programmable humidity extraction and low airflow velocities (0.5–2.0 m/s versus 3–6 m/s in tunnel dryers). This design delivers three distinct benefits:
- Prevention of case hardening. Controlled humidity gradients prevent the premature surface crust that traps interior moisture and creates micro-anaerobic zones prone to fermentation and off-flavour development.
- Reduced oxygen flux. Lower airflow velocity means less atmospheric oxygen sweeping across the product surface per unit time, directly slowing the aerobic ascorbic acid oxidation pathway.
- UV exclusion. Fully enclosed chambers eliminate photolytic degradation — the mechanism responsible for poor vitamin C retention in open sun drying despite its low temperatures.
Head-to-head: drying methods and vitamin C retention
Comparison table
The following table consolidates data from published literature, USDA FoodData Central baselines, and facility-level analytics to compare the five principal commercial drying methods across nutritional, operational, and economic parameters.
| Parameter | Open sun drying | Conventional hot-air (tunnel) | Geothermal drying | Freeze-drying (lyophilisation) | Microwave-vacuum | |---|---|---|---|---|---| | Temperature range (°C) | 25–45 (variable) | 70–90 | 40–65 | −40 to +50 (vacuum) | 40–60 (vacuum) | | Drying time (hours) | 48–120 | 6–14 | 12–24 | 24–48 | 1–4 | | Vitamin C retention (%) | 20–45 | 28–55 | 70–85 | 90–97 | 75–90 | | Beta-carotene retention (%) | 30–55 | 40–60 | 75–88 | 88–95 | 80–90 | | Polyphenol retention (%) | 35–60 | 50–65 | 75–90 | 85–95 | 78–88 | | Colour retention (L* value) | Poor (browning + bleaching) | Poor to moderate | Good to excellent | Excellent | Good to excellent | | Energy cost per kg dried | ≈ USD 0 (solar) | USD 0.08–0.15 | USD 0.01–0.03 | USD 0.25–0.50 | USD 0.15–0.30 | | Capital cost | Very low | Moderate | Moderate (site-dependent) | Very high | High | | CO₂e per ton dried product | 30–80 | 850–1,200 | 35–110 | 600–900 | 300–500 | | Food safety risk | High (insects, dust, microbes) | Low | Low | Very low | Low |
For a detailed cost-benefit analysis between geothermal and freeze-dried options specifically, see the freeze-dried vs geothermal-dried fruit comparison.
Apricot-specific data
Facility-level analytical data from Arovela's geothermal drying operations in the Sindirgi basin (Balikesir province) and conventional tunnel drying operations in Malatya, using apricots from the same harvest year and comparable cultivar mix (primarily Hacihaliloglu and Kabaasi), shows the following:
| Parameter | Geothermal dried (Sindirgi) | Conventional tunnel dried (Malatya) | Delta | |---|---|---|---| | Drying temperature | 48–58 °C | 72–85 °C | 24–27 °C lower | | Drying time | 16–22 hours | 8–14 hours | 8–10 hours longer | | Vitamin C retention | 72–83 % | 31–48 % | +34–35 pp | | Beta-carotene retention | 78–88 % | 42–58 % | +30–36 pp | | Total polyphenol retention | 80–90 % | 55–68 % | +22–25 pp | | Colour (L* lightness) | 58–64 | 38–46 | Significantly lighter | | SO₂ treatment required | No | Typically yes (1,000–2,000 ppm) | Clean-label advantage | | Water activity (aw) | 0.58–0.64 | 0.60–0.68 | Comparable or tighter |
The 34–35 percentage point vitamin C retention gap is consistent with the predictions of Arrhenius modelling at these temperature differentials and aligns with published data in the food science literature. Santos and Silva (2008) reported similar magnitude differences between low-temperature and conventional convective drying of apricot halves in the Journal of Food Engineering, attributing the gap to the exponential temperature dependence of ascorbic acid degradation kinetics.
Fig and grape data for comparison
Vitamin C retention varies by fruit type due to differences in sugar content, pH, tissue density, and initial ascorbic acid concentration. High-sugar fruits show wider retention gaps between geothermal and conventional drying because Maillard browning — a temperature-sensitive secondary degradation pathway — is more aggressive in sugar-rich matrices.
| Fruit | Fresh vitamin C (mg/100 g) | Geothermal retention (%) | Conventional retention (%) | Gap (pp) | Key factor | |---|---|---|---|---|---| | Apricot | 8–12 | 72–83 | 31–48 | 34–35 | High sugar amplifies Maillard above 65 °C | | Fig | 2–3 | 65–78 | 25–40 | 38–40 | Very high sugar, extreme Maillard sensitivity | | Grape (sultana) | 3–4 | 60–75 | 20–35 | 40 | Traditional sun-drying is worst case | | Mulberry | 36–40 | 74–86 | 38–52 | 34–36 | High initial AA amplifies absolute mg loss | | Sour cherry | 10–15 | 70–82 | 35–50 | 32–35 | Low pH partially stabilises AA | | Rosehip | 400–500 | 68–80 | 22–38 | 42–46 | Massive absolute loss at high temperature |
Rosehip deserves special attention. With fresh vitamin C content of 400–500 mg per 100 g, even geothermal-dried rosehip retains 270–400 mg per 100 g — among the most vitamin-C-dense dried botanical ingredients commercially available. Conventional drying reduces this to 88–190 mg per 100 g, a loss that translates to USD 2–5 per kg in ingredient value for formulations priced on vitamin C content. For more on these product categories, explore the geothermal-dried fruit range.
Polyphenol co-retention
Vitamin C and polyphenols share a protective synergy during drying. Ascorbic acid acts as a sacrificial antioxidant, scavenging free radicals that would otherwise oxidise polyphenolic compounds (chlorogenic acid, catechins, rutin, quercetin glycosides). In a low-temperature drying environment where more vitamin C survives the initial processing, more polyphenol protection is maintained throughout the cycle.
This co-retention effect means that geothermal-dried fruit typically retains 75–90 % of total polyphenolic content, compared with 50–65 % in conventionally dried equivalents. The practical significance for B2B buyers: antioxidant capacity (ORAC, FRAP, or DPPH assay values) in geothermal-dried product runs 30–50 % higher than in conventional product from the same origin. These figures support marketing claims centred on antioxidant richness that are increasingly valued in functional food, nutraceutical, and premium snack categories.
Beyond vitamin C — other heat-sensitive nutrients
Beta-carotene (provitamin A)
Beta-carotene is the principal carotenoid in apricots, responsible for their characteristic orange colour and providing provitamin A activity. Carotenoids are more thermally stable than ascorbic acid but degrade through isomerisation (trans-to-cis conversion) and oxidative cleavage at temperatures above 60–70 °C. Published data from Food Chemistry (Igual et al., 2012, Food Chemistry, 132, 1585–1591) shows that beta-carotene retention in apricots dried at 50 °C averages 82 %, declining to 54 % at 70 °C and 38 % at 80 °C. Geothermal drying temperatures sit squarely in the high-retention zone.
The colour implication is direct: beta-carotene degradation produces the dull brown appearance of conventionally dried apricots. Geothermal-dried product retains the vibrant orange hue of fresh fruit, which is a visual quality cue that buyers and consumers recognise immediately. CIELAB L* (lightness) and b* (yellow-blue) colour measurements consistently score 15–25 % higher in geothermal-dried product.
Polyphenols and antioxidant capacity
As discussed above, polyphenol retention in geothermal-dried fruit ranges from 75 to 90 %, driven by lower thermal stress and the co-protective effect of retained vitamin C. Key polyphenolic compounds in Turkish dried fruit — chlorogenic acid in apricot, rutin in mulberry, gallic acid in fig — are each individually more thermally stable than vitamin C but collectively suffer significant losses above 70 °C due to enzymatic and non-enzymatic oxidation.
Total antioxidant capacity, measured by ORAC or FRAP assays, is the composite metric that captures the combined contribution of vitamin C, polyphenols, and carotenoids. Geothermal-dried apricots typically show ORAC values of 1,200–1,800 micromoles Trolox equivalents per 100 g, versus 700–1,100 for conventional product.
Enzyme activity preservation
Certain endogenous fruit enzymes — notably pectinmethylesterase and polygalacturonase — contribute to the desirable soft, chewy texture of dried fruit by maintaining controlled cell-wall modification during rehydration. Above 70 °C, these enzymes are rapidly and irreversibly denatured. Geothermal drying at 45–60 °C preserves partial enzyme activity, which contributes to the superior mouthfeel that sensory panels consistently attribute to geothermal-dried product.
Colour retention as a quality proxy
Colour is the most immediately visible quality indicator in dried fruit, and it correlates strongly with nutrient retention. The Maillard reaction and carotenoid degradation that cause browning above 65 °C are the same reactions that destroy vitamin C and reduce antioxidant capacity. CIELAB colour analysis provides a rapid, non-destructive quality screen: a dried apricot with an L* value above 55 and a b* value above 30 almost certainly has vitamin C retention above 65 %. These colour metrics are increasingly included in B2B quality specifications alongside traditional parameters (moisture, aw, SO₂, microbial counts).
What this means for B2B buyers
Label claims and marketing advantages
The vitamin C retention difference between geothermal and conventional drying has direct consequences for regulatory compliance and competitive positioning. Under EU Regulation 1169/2011 (Food Information to Consumers), nutrient declarations must reflect the product as sold, based on analytical testing of the dried product rather than calculated from fresh-fruit data.
For a Malatya apricot with fresh vitamin C content of 10 mg per 100 g:
- Geothermal dried: 7.2–8.3 mg per 100 g retained — equivalent to 9–10 % of the NRV. Close to the 15 % NRV threshold for a "source of vitamin C" claim, and achievable in blended products (apricot + rosehip, apricot + sea buckthorn).
- Conventional dried: 3.1–4.8 mg per 100 g retained — equivalent to 4–6 % of the NRV. Too low for any vitamin C claim under any regulatory framework.
For brands that blend geothermal-dried apricot with high-vitamin-C ingredients in trail mix, granola, or functional snack formulations, the combined product can reach the "source of vitamin C" threshold — enabling front-of-pack claims that are structurally unavailable to formulations built on conventionally dried inputs.
CoA specifications for vitamin C content
Claimed retention percentages are only as credible as the analytical data behind them. B2B buyers should insist on lot-specific Certificates of Analysis from ISO 17025-accredited laboratories showing vitamin C content measured by HPLC (AOAC 967.21 or equivalent), expressed as mg per 100 g of dried product. Titrimetric methods (DCPIP titration) overestimate vitamin C in the presence of reducing sugars and SO₂ — both common in dried fruit. The CoA reading guide for botanical ingredients provides a detailed framework for evaluating analytical documentation across all quality parameters.
Premium pricing justification
The 8–18 % price premium of geothermal-dried over conventionally dried product is supported by measurable quality differences: 70–85 % versus 28–55 % vitamin C retention, 75–90 % versus 50–65 % polyphenol retention, superior colour scores, clean-label status (no SO₂), and documentable Scope 3 emission reductions. For brands selling into health-conscious, sustainability-aware retail channels, the premium is typically recovered within the first margin tier. For sourcing economics and MOQ structures, see the wholesale dried fruit Turkey sourcing guide.
Scope 3 and sustainability co-benefits
The same geothermal infrastructure that preserves vitamin C delivers an 88–96 % reduction in processing-step carbon emissions relative to fossil-fuel drying. This dual benefit — improved nutrition and reduced carbon footprint — is a rare alignment that simplifies ESG storytelling and CDP/CSRD reporting. B2B buyers can document both nutritional and environmental advantages from a single sourcing decision. The Scope 3 carbon reduction guide provides the detailed life-cycle arithmetic.
Arovela's geothermal facility — Sindirgi, Balikesir
Geothermal well specifications
Arovela's drying operations are located in the Sindirgi district of Balikesir province, western Turkey, directly on one of the country's most productive geothermal fields. The Sindirgi geothermal resource delivers:
- Wellhead temperature: 65–85 °C year-round, with seasonal variation of ±3 °C.
- Flow rate: Sufficient thermal energy to support continuous drying operations across multiple enclosed chambers.
- Drying-air temperature after heat exchange: 45–62 °C, falling within the optimum vitamin C preservation window.
- Availability: 24/7/365 — unlike solar drying, there is no interruption for nightfall, cloud cover, or seasonal weather changes.
The geothermal resource eliminates fossil-fuel input for the drying step entirely. Electricity consumption for pumps, fans, and controls constitutes the only non-renewable energy input, resulting in a carbon footprint of 35–110 kg CO₂e per metric ton of dried product — compared with 850–1,200 kg CO₂e for natural gas tunnel dryers.
Processing capacity
The facility operates multiple enclosed drying chambers with mesh tray configurations, designed for controlled humidity extraction and low-velocity airflow. Batch capacity supports commercial-scale orders at B2B volumes, with MOQ starting at sample quantities (1–5 kg with full CoA) and scaling to full container loads (20 ft container at approximately 18 MT net).
Processing protocols are standardised per fruit type, with documented temperature profiles, humidity curves, and endpoint water activity targets. Each batch is logged with time-temperature data that can be provided to buyers for traceability and Scope 3 reporting purposes.
Third-party lab verification
All vitamin C retention claims are substantiated by independent analytical testing from ISO 17025-accredited laboratories. Test protocols follow AOAC 967.21 (HPLC quantification of L-ascorbic acid and DHAA). Lot-specific CoA packages are provided with every commercial shipment and are available with sample orders upon request.
Retention figures reported in this article (72–83 % for apricot, 65–78 % for fig, 74–86 % for mulberry) are based on multi-lot averages from the 2024 and 2025 harvest seasons, tested by accredited third-party laboratories in Turkey, with comparative conventional-dried samples tested in parallel using identical analytical protocols.
FAQ
Does geothermal drying preserve more vitamin C than conventional hot-air drying?
Yes. Published literature and facility-level HPLC analytics consistently show 70–85 % vitamin C retention in geothermal-dried fruit processed at 40–65 °C, versus 28–55 % retention in conventional hot-air-dried fruit processed above 70 °C. The difference is driven by the exponential temperature dependence of ascorbic acid degradation: the Arrhenius equation predicts that the irreversible conversion of DHAA to 2,3-DKG approximately doubles in rate for every 10 °C temperature increase. The geothermal temperature window keeps this reaction rate low enough that even longer drying cycles (12–24 hours) produce less total vitamin C destruction than shorter conventional cycles at higher temperatures.
Can I make a vitamin C health claim on geothermal-dried fruit packaging?
Under EU Regulation 1924/2006, a "source of vitamin C" claim requires at least 15 % of the NRV per 100 g (12 mg). A "high in vitamin C" claim requires 30 % NRV (24 mg per 100 g). Geothermal-dried rosehip, mulberry, and fruit blends incorporating high-vitamin-C ingredients can meet these thresholds based on analytical data. Geothermal-dried apricots alone typically fall just below the "source of" threshold for standalone product but can reach it in blended formulations. All claims must be substantiated by lot-specific HPLC analysis of the product as sold, not estimated from fresh-fruit composition data.
How should I verify a supplier's vitamin C retention claims?
Request a lot-specific Certificate of Analysis from an ISO 17025-accredited laboratory showing vitamin C content measured by HPLC (AOAC 967.21 or equivalent). The result should be expressed as mg per 100 g of dried product. Compare this against published fresh-fruit baseline values (USDA FoodData Central is the standard reference database) to calculate retention percentage. Be cautious of suppliers who provide only "typical analysis" sheets without lot traceability, who express vitamin C as "fresh equivalent" rather than dried-product content, or who rely solely on titrimetric methods that overestimate values in the presence of reducing sugars and sulphite residues.
Does vitamin C continue to degrade during storage after drying?
Yes, but at a much slower rate. In properly dried product with water activity below 0.65, stored at 15–25 °C in moisture-barrier packaging with low oxygen permeability, vitamin C degrades at approximately 1–3 % per month. A product with 80 % retention at production will show roughly 68–75 % retention after six months of ambient storage. Accelerated shelf-life testing (40 °C, 75 % RH) should be part of any supplier's quality management system. CoA test dates within 30–60 days of the production date provide the most accurate representation of as-shipped nutritional values.
What is the Arrhenius activation energy for vitamin C degradation in dried apricot?
Published activation energy (Ea) values for ascorbic acid degradation in apricot matrices range from 60 to 95 kJ/mol, with the variation depending on cultivar, pre-treatment method, moisture content range, and whether the measurement captures the aerobic pathway alone or the combined aerobic-plus-anaerobic pathway. A representative mid-range value of 75 kJ/mol is widely used in predictive modelling. This Ea implies a Q₁₀ (rate increase per 10 °C) of approximately 2.0–2.3 across the 40–80 °C range relevant to commercial drying. Demiray and Tulek (2017) provide one of the most comprehensive kinetic datasets for Turkish apricot cultivars, with rate constants measured at 50, 60, and 70 °C intervals.
Verify for yourself — request samples
The data in this article is not theoretical. It is measured, batch-documented, and available for independent verification. If nutrient density is part of your product specification, sourcing strategy, or brand positioning, the drying method determines whether the ingredient can deliver.
Geothermal-dried fruit from Turkey's Sindirgi basin offers 70–85 % vitamin C retention, 75–90 % polyphenol retention, clean-label compatibility without SO₂ treatment, and Scope 3 carbon advantages — all documented with lot-specific HPLC analytics and ISO 17025-accredited CoA packages.
Browse Arovela's geothermal-dried fruit range, review the wholesale dried fruit sourcing guide for logistics and pricing, or request a quote with your target product, volume, and vitamin C specification.