“Heat pump cold drying preserves heat-sensitive bioactive compounds such as carotenoids, betalains, and vitamins in vegetable powders better than conventional hot-air convection drying.”

Heat pump drying technology is used in high-value foods and biomaterials where low-temperature drying generally ranges from 45 to 70°C and well-controlled conditions are essential. Its ability to precisely control the operating temperature and relative humidity makes it ideal for drying functional foods, yielding minimal discoloration and ascorbic acid degradation. Well-controlled temperature profiles, making it highly suitable for heat-sensitive high-value products with better quality outcomes.

Mango has a high content of nutrients such as vitamins and antioxidants which are easily lost due to high temperatures during conventional drying, such as convection drying... Therefore, using the heat pump drying method instead of conventional drying methods at a high temperature helps improve product quality and increase economic value. Heat pump drying utilizes a system with a heat pump, auxiliary heater, and dehumidification system to precisely control drying temperature and humidity.

These studies demonstrate that single heat pump drying technologies are superior to hot air-drying systems regarding the rehydration ratio, nutrient retention, maintenance cost, and service life. Moreover, single heat pump drying systems dry fruits and vegetables at relatively low temperatures (typically 30–60 °C), mitigating issues related to excessive oxidation. For example, Sun et al. [59] demonstrated that dehumidification drying systems significantly reduce microbial activity through internal circulation dewatering and precise temperature control, extending the shelf life of dried carrot products by >1 year. By comparing six types of fruits and vegetables, the authors observed that vitamin C retention after dehumidification drying exceeded 90% of the fresh state, and the sensory scores, particularly for color and rehydration, were significantly better than those obtained with hot air drying.

However, the main challenge in drying biological materials is the loss of heat‐sensitive bioactive compounds. Studies have shown that prolonged exposure to elevated temperatures during drying can significantly reduce the content of vitamin C, phenolics, carotenoids, and flavonoids. Thus, drying wild edible plants at 60°C appears optimal for β‐carotene retention, and optimal temperatures for ascorbic acid retention in fruits and vegetables generally fall within the range of 40°C–60°C.

Freeze drying and shade drying had the best micronutrients retention effects across all the leafy vegetable samples while oven drying at varied temperatures of 40oC, 50oC and 60oC had gradual decrease in minerals and vitamins retention effects as the temperature increases. The order by which the various drying methods retained vitamins in the leafy vegetable samples were as follows: Freeze drying > shade drying > oven drying at 40oC > oven drying at 50oC > oven drying at 60oC.

Since betalains degrade at temperatures above 50°C, processing beetroot at freezing temperatures allows for greater preservation of these compounds. Compared with conventional oven drying, vacuum drying yielded powder with higher betalain content (3,478.33 mg/100 g) and stronger antioxidant activity.

The maximum total betalain content of 418 mg/L was recorded in sun-drying method and water for extraction, while the lowest total betalain content of 172 mg/L was obtained in hot air-drying (tray) method and ethanol 50% for extraction.

Among the investigated drying methods, hot-air drying at 80 °C and vacuum drying at 50 °C produced dried Gac peel that exhibited the highest retention of carotenoids and the strongest antioxidant capacity. In contrast, the dried Gac peel samples produced by drying with the heat pump dryer, which used low drying temperatures, and the freeze dryer, which used non-thermal conditions, retained the lowest carotenoid levels. The higher losses of total carotenoid content was observed in the drying methods using greater exposure time (11 to 20 hours) compared to the other methods (3-7 hours).

Heat-Pump Drying operates at a low temperature range (30-60°C) and recycles waste heat. Scientific studies have shown that Vitamin C and other heat-sensitive compounds are much better preserved at lower drying temperatures. In contrast, Electric Resistance Drying (Pure Heat) often uses very high temperatures (>70°C) which burns vegetables, causes shrinkage, destroys color, and eliminates almost all vitamins.

Heat pump drying provides energy efficiency but specific data on superior preservation of carotenoids or betalains in vegetable powders compared to hot air convection is not detailed; general improvements in quality are noted without quantitative comparison for these compounds.

The controlled environment of a heat pump dryer allows for better preservation of nutrients and flavors compared to traditional methods. The lower drying temperatures help maintain the integrity of vitamins and minerals in fruits and vegetables.

Peer-reviewed literature consistently shows heat pump drying, often operated at lower temperatures (30-50°C), preserves heat-sensitive bioactives like carotenoids, betalains, and vitamins better than hot-air convection drying (typically 60-80°C) in vegetables such as carrots, beets, and spinach powders, due to reduced thermal degradation.

Also known as heat pump drying, this energy efficient method operates at lower temperatures (typically +30°C to +45°C) within a closed air loop... dramatically reduces drying time without risking overheating or nutrient degradation.

Heat pump drying technology of the production technology about 38-52 ℃ lower than the conventional drying technology... heat pump drying process, stable product quality, good color, no SO2 and other dew residue.