IntroductionGreen asparagus (Asparagus officinalis L.), belongingto the Asparagaceae family, is widely cultivated insubtropical and tropical regions around the world suchas China, Peru, Thailand, Mexico, etc. [1]. Asparagus iscommonly divided into two categories: green asparagusand white asparagus. The difference between them,however, is dependent on the growth of their spears.White stems are formed when growing below the soil,whereas green stems are developed when they aredirectly exposed to sunlight and become green viathe chlorophyll function [2]. Besides, another rarelyconsumed asparagus is purple asparagus which hasa higher anthocyanin content compared to green and642Nguyen Q.V. et al. Food Processing: Techniques and Technology. 2022;52(4):640–648white asparagus [3]. Asparagus is favorably consumedin many countries due to its high nutritional value andlow calorie content [1].Asparagus has a considerably higher protein contentthan many other vegetables, but it is low in carbohydratesand calories [4]. Besides, asparagus has been foundto be a rich source of such bioactive compounds asvitamin C, flavonoids, polyphenols, and tannins, whichlower cholesterol and have an anti-cancerous effect [4].Many antioxidants have been identified in green asparagusincluding rutin, tocopherol, ferulic acid, andglutathione [5]. The asparagus aqueous extract wasfound to have a 7-fold higher inhibitory effect againstα-glucosidase than that of acarbose used for a highfructosediet-induced metabolic syndrome in mice [6].Asparagus extracts were reported to have potential inimmunomodulatory activities [7]. The effectiveness ofantihyperglycemic treatment with an asparagus extract(500 mg/kg) on STZ-induced diabetic mice was foundto be the same as that of an anti-diabetic drug (glibenclamide,5 mg/kg) [8].On the other hand, asparagus is a highly perishableproduct due to its high respiration rate, limiting itsshelf-life [9]. Therefore, appropriate methods shouldbe applied to better maintain the quality of freshasparagus or to create innovative asparagus-basedproducts for long-term use. Asparagus stems are currentlycommercialized as fresh, frozen, or canned products [2].To date, many studies have aimed to develop innovativeproducts from green asparagus. White asparaguswas successfully employed to produce a spray-driedasparagus powder by Siccama et al. [10]. Asparaguspowder was used as an additive to improve the elasticityand rigidity of cheeses and ensure enhanced bioactivecompounds in the final cheese products [11]. MazaheriKalahrodi et al. showed a tendering effect of asparagusjuice on the textural characteristics of beefsteak [12].Adding asparagus powder into processed cheese wasfound to enhance the phenolic content, antioxidantactivity, and proteolysis of the processed cheeses,as well as to improve the textural characteristics ofprocessed cheese [11]. The term “herbal drink” is scarcelymentioned in the studies developing products from greenasparagus. Therefore, we, for the first time, developeda herbal drink from green asparagus which serves as ahealthy drink due to its nutritional value and bioactivecompounds. Besides, we selected an appropriate dryingmethod to ease the quality deterioration of fresh asparagusand prevent its harvest loss. Finally, we evaluated theprocess parameters for developing the asparagus herbaldrink to obtain a tea extract with a high solute yield.Study objects and methodsMaterials. Asparagus spears (edible part) of differentlength were collected from a local farm in Ea Kar, DakLak province. Anthrone (9,10-Dihydro-9-oxoanthracene),gallic acid, and vitamin C were purchased from Sigma-Aldrich (St. Louis, Missouri, USA). Other analyticalchemicals were purchased from standard commercialsuppliers.Preparation of asparagus herbal drink. Asparagusspears were washed with distilled water to removeimpurities and then sliced into specimens with varyinglengths (2, 5, 10, 15, and 20 mm). The samples (500 g)were blanched in hot water (90–100°C), dried at 55°C toobtain the moisture content of 12%, and roasted at 100°Cfor 3 min (SCR301, Barwell, China). The samples witha suitable length were then used for further experiments.To investigate the effect of heat pretreatment methodson the quality of the asparagus herbal drink, the selectedspecimens (500 g) were subjected to different heatpretreatments: without blanching (control sample), hotwater blanching at 70–80°C for 3 min, hot waterblanching at 90–100°C for 1.5 min, and microwaveheating (R-G302VN-S, Sharp Coporation, Osaka, Japan)for 30 s at 440 W. The pretreated samples were dried at55°C to the moisture content of 12% and then roasted at100°C for 3 min. An appropriate pretreatment method wasselected and the samples were prepared for subsequentevaluations.The pretreated asparagus samples (500 g) were thensubjected to different drying conditions (convectivedrying at 55°C, heat pump drying at 40°C, and microwavedrying) until obtaining the moisture content of 12%followed by roasting at 100°C for 3 min. A proper dryingmethod was selected for the herbal drink. Finally, thedried samples were ground into smaller pieces of differentsizes (< 0.5, 0.5–1.0, 1.0–1.5, 1.5–2.0, and > 2 mm).The dried asparagus samples (2 g) were packaged intoteabags made of filter paper. Analytical responses weredetermined to select the appropriate process parameters,including total soluble solids, total polyphenol content,total carbohydrate, vitamin C, and visual appearanceof asparagus samples.Total polyphenol determination. The total polyphenolcontent was determined according to a previousstudy by Nguyen et al. [13]. Each sample was extractedwith distilled water at the ratio of 1:10. An aliquot(1 mL) of the extract was mixed with 5 mL of 10%Folin-Ciocalteu reagent and 1 mL of 7.5% Na2CO3. Themixture was kept for 30 min in the dark before readingabsorbance values at 765 nm by using a 722-Visiblespectrophotometer (Yangzhou Wandong Medical Co.,China). Gallic acid served as a standard solution. Thetotal polyphend content was expressed as milligramsof gallic acid equivalent per gram of dry matter (mgGAE/g DM) by establishing a standard curve or varyingconcentrations of gallic acid (0.01–0.09 mg/mL) versusits absorbance.Vitamin C determination. The content of vitaminC was determined by using a high-performance liquidchromatography (HPLC) system (Waters Corp., Milford,MA, USA) equipped with a Bischoff prontosil column(AQ 4×125 mm×5 μm). A gradient of the mobile phase643Nguyen Q.V. [и др.] Техника и технология пищевых производств. 2022. Т. 52. № 4. С. 640–648consisting of methanol and 5 mmol/L KH2PO4 wasprogramed at 0.75 mL/min for 30 min at 30°C. Eachsample extract was injected to the column at the volumeof 20 μL and vitamin C was used as a standard solution.The detector recorded the absorbance at 254 nm [14].Total soluble solids and carbohydrate measurements.Total soluble solids were determined by usinga digital refractometer (PR-101α, 0–45°Brix, Atago Co.Ltd., Japan). The carbohydrate content was measuredfollowing the Anthrone method [15]. Each sample extract(2 mL) was mixed with 4 mL of an anthrone solutionand 5 mL of concentrated sulphuric acid. The mixturewas boiled in a water bath for 8 min and immediatelycooled to room temperature. The mixture was allowedto stand for 30 min in the dark before its absorbancewas taken at 585 nm.Sensory evaluation. The sensory evaluation ofthe asparagus herbal drink followed the Vietnamesestandard TCVN 3218:2012. Four sensory attributes(appearance, color, flavor, and taste) of the asparagusinfusion were evaluated according to a 5-point scale.For this, each teabag containing 2 g of dried asparaguswas placed in a glass cup with 100 mL of boiled waterand allowed to stand for 6 min. The sensory evaluationwas conducted by 20 panelists who were assigned toscore each attribute. The importance indexes were asfollows: 1 for appearance, 0.6 for color, 1.2 for flavor,and 1.2 for taste.Statistical analysis. Each experiment was conductedin triplicate and the data were presented as mean ±standard deviation. The results were analyzed by aone-way analysis of variance (ANOVA) with the SPSSsoftware (IBM Corp., Armonk, New York, USA). TheTukey HSD test was utilized to compare mean valuesat the significant level of 5% ( P < 0.05).Results and discussionEffect of asparagus size on the solute contentin the extract. Prior to heat pretreatment, greenasparagus needs to be reduced in size to facilitatefurther processes of blanching and drying. Table 1presents the effects of asparagus lengths on the solutecontent in the extract. We found that longer sampleshad ineffective extraction yields of total soluble solids,total polyphenol content, and total carbohydrates. Onthe other hand, the total soluble solids, total polyphenolcontent, and total carbohydrate values of a 2 mmasparagus extract were the highest, amounting to33.53 ± 0.21%, 0.74 ± 0.02 mg GAE/g DM, and13.36 ± 0.32%, respectively. This was because smallerasparagus samples facilitated the diffusionof the blanching water to soften the plant tissues,increasing the extraction efficiency of solutes ingreen asparagus [16]. Our results were consistentwith many previous reports that found smaller particlesizes to achieve higher extraction efficacy [16–18].According to our analysis, there was no difference inthe total soluble solids, total polyphenol content, andtotal carbohydrate values between the 2 and 5 mmsamples. The content of vitamin C, however, showedan increasing trend at larger sample sizes. Vitamin Cis highly susceptible to environmental conditionssuch as light, temperature, and oxygen [19]. Thelowest content (83.57 ± 2.43 mg/100 g) of vitamin Cwas found in the 2 mm sample. This was because thesmall size contributed to a larger surface exposure tothe hot blanching temperature, causing vitamin C todecay faster. Moreover, the loss in vitamin C couldpossibly be ascribed to the leakage to the blanchingmedium [20].The visual appearance of asparagus specimens atdifferent sizes is presented in Fig. 1a. As we can see,the 2 mm asparagus samples had a soft structure afterblanching, with a dark brown color in some of thespecimens. Meanwhile, the other samples showed harderstructures with a greenish color, which were suitablefor further processing. We found that the 5 mm samplecould be suitable for further processing to develop anasparagus herbal drink.Table 1. Effect of asparagus lengths on total soluble solids, polyphenol, carbohydrates, and vitamin C in the asparagusextractТаблица 1. Зависимость общего содержания растворимых сухих веще ств, полифенолов, углеводов и витамина С в экстрактеот длины нарезанных образцов спаржиSample length,mmTotal soluble solids,%Total polyphenol content,mg GAE/g DMTotal carbohydrate,%Vitamin C,mg/100 g2 33.53 ± 0.21c 0.74 ± 0.02bc 13.36 ± 0.32d 83.57 ± 1.43a5 32.77 ± 0.59c 0.72 ± 0.03b 11.39 ± 1.67cd 85.43 ± 1.21ab10 28.57 ± 0.34b 0.67 ± 0.04ab 10.56 ± 0.65bc 86.33 ± 1.05b15 26.64 ± 0.82a 0.63 ± 0.03a 9.51 ± 0.34b 88.53 ± 0.67b20 25.56 ± 0.48a 0.61 ± 0.03a 8.33 ± 0.24a 90.78 ± 0.77cValues are expressed as mean ± SD. Different letters (a, b, c, d) show significant differences within the same column ( P < 0.05).Данные представлены как среднее значение ± стандартное отклонение. Буквами a, b, c, d обозначены значительные различияв пределах одного и того же столбца ( P < 0,05).644Nguyen Q.V. et al. Food Processing: Techniques and Technology. 2022;52(4):640–648Effect of blanching methods on the quality ofasparagus herbal drink. Heat pretreatment of theasparagus samples aims to inactivate the browningenzymes such as polyphenol oxidase and peroxidase,as well as to inhibit microbial growth on the materialsurfaces. It can also shorten the drying time as itsoftens the structure of the material, leading to ahigher water evaporation rate [21]. According toour results, all the methods of heat pretreatmentshowed an increment in total soluble solids and totalpolyphenol content but a decline in vitamin C andtotal carbohydrates, compared to the control sample(without blanching). As previously discussed, hightemperature might degrade vitamin C molecules. Thedecrease in total carbohydrates could be ascribedto the leakage to the blanching water, which waspreviously mentioned by Xanthakis et al. [20]. HighTemperature Short Time (HTST). Heat treatment canincrease the content of solutes and polyphenols bycausing structural changes in plant cells. In particular,it can disrupt cell membranes and weaken hemicellulaseand cellulase bonds, thus enhancing theextraction efficacy [22]. In our study, the microwavetreatment showed the best extraction efficiency inthe total soluble solids (32.67 ± 0.43%) and totalpolyphenol content (0.80 ± 0.05 mg GAE/g DM) ofasparagus, while having a lesser effect on the vitamin Ccontent and total carbohydrates in the extract. Itwas noted that the microwave treatment promoteda thermal gradient between the extracting mediumand plant cells, facilitating the liberation of phenoliccompounds [23]. A similar finding was reported inthe study by Severini et al., where the microwaveblanching showed an increase in phenolic compoundsand impaired the degradation of vitamin C in thesample, compared to hot water blanching and steamblanching [24].As seen in Fig. 1b, the blanching processes causednoticeable impacts on the color of the driedasparagus samples. Hot water blanching at 70°Ccaused a browning effect, while blanching at 90°Cand microwave heating gave the dried asparagus ayellow-greenish color. This could be explained by thefact that blanching at 90°C and microwave heatingshowed better efficiency in inactivating polyphenoloxidase compared to blanching at 70°C [13, 20]. HighTemperature Short Time. Thus, microwave blanchingcould be a suitable option to develop a yellow-greenishcolor for asparagus tea, as well as to achieve highertotal soluble solids, total polyphenol content, andvitamin C contents in the extract.Effect of drying conditions on the quality ofasparagus herbal drink. The effects of different dryingconditions on the extraction yield of the asparagusherbal drink are presented in Table 3. Microwavedrying had the shortest drying time of 29 min.However, it considerably reduced the contents ofvitamin C, carbohydrates, and total soluble solids inthe asparagus drink. Meanwhile, convective dryingand heat pump drying resulted in higher total solublesolids and vitamin C content in the extract. The rapiddegradation of vitamin C by microwave heatingwas due to excessive heat generated in the internalmolecular structures of asparagus. As shown in Fig. 1c,Figure 1. Visual appearance of asparagus samples: a) different lengths; b) blanching methods; c) drying methods;d) asparagus tea at different particle sizesРисунок 1. Внешний вид образцов спаржи: а) нарезки длины; б) ме тоды бланширования; в) методы сушки; г) напиток из спаржипри разной величине помола2 mm 5 mm 10 mm 15 mm 20 mmMicrowave drying Converctive drying Heat pump dryingHot water (70°C) Hot water (90°C) Microwaver Controla bc d< 0.5 mm 0.5 mm–1.0 mm 0.0 mm–1.5 mm 1.5 mm–2.0 mm > 2.0 mm645Nguyen Q.V. [и др.] Техника и технология пищевых производств. 2022. Т. 52. № 4. С. 640–648convective drying and heat pump drying gave driedasparagus a yellow-greenish color, whereas microwavedrying induced a brown-yellowish color, reducing thesensorial attributes of the asparagus herbal drink. Thelower total polyphenol content caused by convectivedrying and heat pump drying, as compared to themicrowave-dried asparagus, could be attributed to thedegradation of phenolic compounds when exposed toan extended drying time (17–22 h). The decrease inthe total polyphenol content could also be due to theenzymatic processes that occurred during drying [25].Although the heat generated by microwave dryingwas considerably higher than that in the other dryingmethods, the microwave drying time was not sufficientto cause a significant impact on phenolic compounds.As for sensorial properties, the asparagus samplesTable 2. Effect of blanching methods on total soluble solids, polyphenol, carbohydrates, and vitamin C in the asparagusextractТаблица 2. Зависимость общего содержания растворимых сухих веще ств, полифенолов, углеводов и витамина С в экстрактеспаржи от методов бланшированияBlanching method Total soluble solids, % Total polyphenol content,mg GAE/g DMTotal carbohydrate,%Vitamin C,mg/100 gControl sample (withoutblanching)27.56 ± 0.32a 0.60 ± 0.03a 12.78 ± 0.54b 72.10 ± 1.51cHot water (70°C) 28.31 ± 0.21b 0.68 ± 0.02b 10.40 ± 0.43a 63.52 ± 2.43aHot water (90°C) 30.63 ± 0.18c 0.74 ± 0.01c 9.92 ± 0.67a 65.29 ± 2.67aMicrowave 32.67 ± 0.43d 0.80 ± 0.02d 11.56 ± 0.81ab 68.61 ± 1.43abValues are expressed as mean ± SD. Different superscripts (a, b, c, d) indicate significant differences within the same column (P < 0.05).Данные представлены как среднее значение ± стандартное отклонение. Буквами a, b, c, d обозначены значительные различияв пределах одного и того же столбца ( P < 0,05).Table 3. Effect of drying methods on total soluble solids, polyphenol, carbohydrates, and vitamin C in the asparagus extractТаблица 3. Зависимость общего содержания растворимых сухих веще ств, полифенолов, углеводов и витамина Св экстракте спаржи от методов сушкиDrying method Total soluble solids, % Total polyphenol content,mg GAE/g DMTotal carbohydrate, % Vitamin C,mg/100 gDrying timeMicrowave 26.93 ± 1.44a 0.75 ± 0.04b 11.53 ± 0.54a 52.69 ± 2.54a 29 minConvection 30.46 ± 1.20b 0.61 ± 0.02a 13.58 ± 0.32b 68.36 ± 2.45b 17 hHeat pump 29.62 ± 2.12b 0.59 ± 0.03a 12.47 ± 0.67b 70.33 ± 3.12b 22 hData are expressed as mean ± SD. Different superscripts (a, b, c, d) indicate significant differences within the same column ( P < 0.05).Данные представлены как среднее значение ± стандартное отклонение. Буквами a, b, c, d обозначены значительные различияв пределах одного и того же столбца ( P < 0,05).Table 4. Dried asparagus in the teabag and sensorial properties of asparagus infusion at different particle sizesТаблица 4. Высушенная спаржа в пакетиках и органолептические св ойства настоя спаржи при разной величине помолаParticle size,mmAppearance of driedasparagus in the teabagColor Flavor Taste Sensory score< 0.05 Fine powder Light yellowish color,presence of many fineparticlesVery light characteristicflavor of asparagusVery light sweet 7.40 ± 0.320.5–1.0 Homogenous form Presence of particles,light yellowish colorLight characteristic flavorof asparagusLight sweet 9.00 ± 0.231.0–1.5 Homogenous form Yellowish color Intense characteristicflavor of asparagusRelative sweet 15.40 ± 0.241.5–2.0 Homogenous form Yellowish color Intense characteristicflavor of asparagusRelative sweet 16.00 ± 0.35> 2.0 Inhomogeneous form Light yellowish color Very light characteristicflavor of asparagusVery light sweet 9.60 ± 0.32646Nguyen Q.V. et al. Food Processing: Techniques and Technology. 2022;52(4):640–648acquired a yellow-greenish color from convectivedrying and heat pump drying and a dark brown colorfrom microwave drying, which significantly affectedtheir appearance. Both convective drying and heatpump drying produced the drinks with the same valuesof total soluble solids, total polyphenol content, totalcarbohydrate, and vitamin C. However, convectivedrying required a shorter time (17 h) to achieve thedesired moisture content (12%) in the asparagus tea.Therefore, this method proved the most suitable fordeveloping the asparagus herbal drink.Effect of asparagus particle sizes on total solublesolids in the asparagus infusion. After drying, theasparagus samples were ground to different particlesizes and packaged into teabags. The effect of particlesizes on total soluble solids in the tea extract isillustrated in Fig. 2. We found that the grinding sizefrom 1 to 2 mm produced the highest total solublesolids (> 26%), while very fine powder (< 0.5 mm)produced the lowest total soluble solids (13.37%) inthe asparagus infusion. This agreed with many previousstudies where the small particle size facilitated theextraction of solute in the solvent medium. However,very fine particles tended to agglomerate and depositat the bottom of the teabag, preventing the diffusionof solute to the extracting medium sieving and selectingthe optimal granulometry (0.15–0.74 mm) [16].Table 4 shows a sensorial description of asparagustea, while Fig. 1d features the appearance of driedasparagus at different particle sizes. According to thesensory evaluation, dried asparagus with 1.5–2 mmparticles produced an asparagus infusion with thehighest score (16) for color, intense taste, andcharacteristic flavor. Therefore, this size proved themost suitable for developing the asparagus herbaldrink since it produced the highest soluble solidsand good sensorial properties.ConclusionIn this study, we developed an innovative asparagusherbal drink. The asparagus length of 5 mm was foundto facilitate subsequent steps. Microwave blanchingcaused the dried asparagus to acquire a yellow-greenishcolor. Unlike hot water blanching, this method producedhigher values of total soluble solids, total polyphenol,and total carbohydrate, while having a lesser effect on thecontent of vitamin C. Of all drying methods, convectivedrying proved suitable for higher total soluble solids andtotal carbohydrate, as well as better visual appearance ofasparagus tea. Finally, the grinding size of asparagus wasselected at 1.5–2.0 mm to obtain the highest total solublesolids in the asparagus infusion and the highest sensoryscore. The asparagus herbal drink had a yellowish color, anintense characteristic flavor of asparagus, and a relativelysweet taste. In addition, we selected the process parametersfor the asparagus teabag to maintain a high content of totalpolyphenol and vitamin C in the asparagus herbal drinkto enhance its nutritional value. Further investigationscan be carried out to produce an asparagus herbal drinkwith a higher polyphenol content in the infusion. Besides,a pilot-scale study should be conducted to enhance thefeasibility of the asparagus herbal drink as a commercialproduct.ContributionThe authors were equally involved in writing themanuscript and are equally responsible for plagiarism.Conflict of interestThe authors declare that there is no conflict of interestregarding the publication of this article.