Bitter gourd, a vegetable with various health benefits, suffers from limited consumption due to its strong bitterness. Traditional Chinese medicine uses it to treat various ailments, and modern research confirms its blood sugar-lowering, anti-inflammatory, and antioxidant properties. Its richness in carbohydrates, proteins, fibers, vitamins, and bioactive compounds like saponins, polysaccharides, polyphenols, and flavonoids further highlights its nutritional value. However, triterpenoid saponins contribute to its unpleasant taste, limiting its consumption. Various bitter gourd products have been developed to improve palatability and extend shelf life, but consumer acceptance remains low due to persistent bitterness. Spray drying, a common food industry technique, is used to encapsulate substances and improve product properties. This research systematically compares the bitterness-masking abilities and effects on physicochemical properties of different wall materials on spray-dried bitter gourd powders to identify the most suitable ones for producing high-quality, consumer-acceptable products. The aim is to establish spray-drying encapsulation technology that minimizes bitterness while retaining active substances.

Several studies have explored the use of different wall materials in spray drying to enhance the properties of various food products. Whey protein isolate, maltodextrin, and their combinations have been shown to protect active compounds during storage in spray-dried paprika and cinnamon. Maltodextrin has been reported to reduce hygroscopicity and maintain acceptable color in spray-dried amla juice powder. Whey protein concentrate has been used to reduce bitterness and hygroscopicity in whey protein hydrolysate. Gum arabic has proven effective in attenuating the bitter taste of hydrolyzed casein. Maltodextrin and gum arabic have also shown effectiveness in encapsulating aqueous bitter melon extract and protecting bioactive compounds during spray drying. However, systematic research comparing the bitterness-masking abilities and retention of functional components using various wall materials for bitter gourd is lacking.

Fresh bitter gourd ('Lvbaoshi' variety) was processed into a slurry. Five wall materials (soybean protein isolate, gum arabic, maltodextrin, resistant starch, and a soybean lecithin calcium caseinate mixture) were mixed with the slurry at a 1:1 ratio (based on solid content), adjusting the total solid content to 9%. The mixture was homogenized. Spray drying was performed at an inlet air temperature of 130 °C, atomisation speed of 100 rpm, and feeding speed of 2 rpm. Various analyses were conducted on the resulting spray-dried bitter gourd powders (SD-BGP): moisture content (oven drying at 105 °C), water activity (Novasina LabSwift-aw), water-soluble index (WSI), dispersion time, color (UltraScan VIS colorimeter), bitterness (taste dilution analysis (TDA) and electronic tongue), total polyphenol content (Folin-Ciocalteu method), total flavonoid content (aluminum chloride colorimetric method), total saponin content (vanillin-perchloric acid method), vitamin C content (fluorometric method), oxygen radical absorbance capacity (ORAC) index, and α-glucosidase inhibitory activity. Statistical analysis (one-way ANOVA with Duncan's test) was performed using SPSS 18.0 software.

All five wall materials significantly reduced moisture content and water activity compared to non-encapsulated spray-dried bitter gourd powder (NE SD-BGP). Maltodextrin was most effective at reducing water activity, while soybean protein isolate best maintained color. Soybean lecithin calcium caseinate mixture exhibited the best hygroscopicity reduction and bitterness masking. All wall materials enhanced the retention of flavonoids, saponins, and vitamin C, with soybean protein isolate showing the highest total flavonoid retention and soybean lecithin calcium caseinate mixture showing the best retention of total saponins and vitamin C. Soybean protein isolate resulted in the spray-dried powder with the highest antioxidant activity (ORAC) and α-glucosidase inhibitory activity. Particle size analysis revealed differences among the wall materials, with soybean protein isolate showing the largest particles and maltodextrin and gum arabic producing smaller, more uniform particles. Taste dilution analysis and electronic tongue analysis confirmed the superior bitterness-masking ability of the soybean lecithin calcium caseinate mixture, followed by soybean protein isolate and resistant starch.

The findings demonstrate that the choice of wall material significantly impacts the physicochemical properties of spray-dried bitter gourd powder. The reduced moisture content and water activity contribute to improved shelf life. The enhanced solubility with maltodextrin and gum arabic is advantageous for applications requiring easy reconstitution. The superior color retention with soybean protein isolate is crucial for maintaining product appeal. The effective bitterness masking, particularly by the soybean lecithin calcium caseinate mixture, addresses the major consumer limitation of bitter gourd. The protective effects of all wall materials on bioactive compounds like flavonoids, saponins, and vitamin C are important for maintaining the health benefits of the product. The improved antioxidant and α-glucosidase inhibitory activities further demonstrate the potential of this encapsulation approach for developing functional foods.

This study provides comprehensive insights into the influence of various wall materials on the properties of spray-dried bitter gourd powder. Soybean lecithin calcium caseinate mixture demonstrated superior bitterness-masking and hygroscopicity reduction, while soybean protein isolate offered the best protection for bioactive compounds and enhanced functional properties. The findings offer valuable guidance for optimizing bitter gourd processing to create high-quality, consumer-friendly products. Future research could focus on optimizing spray-drying parameters and exploring other wall materials to further enhance the functional properties and shelf life of spray-dried bitter gourd powder.

The study focused on a single bitter gourd variety. The findings may not be directly generalizable to other varieties with differing physicochemical properties. The sensory evaluation of bitterness was limited to taste dilution analysis and electronic tongue measurements; a comprehensive sensory panel evaluation involving human assessors could provide further insights. Long-term storage stability studies are warranted to fully assess the impact of wall materials on product shelf life.