Article Request Page ASABE Journal Article
Effect of Pretreatments on Quality of Jerusalem Artichoke (Helianthus tuberosus L.) Tuber Powder and Inulin Extraction
K. Khuenpet, W. Jittanit, S. Sirisansaneeyakul, W. Srichamnong
Published in Transactions of the ASABE 58(6): 1873-1884 (doi: 10.13031/trans.58.11036 ). Copyright 2015 American Society of Agricultural and Biological Engineers.
Submitted for review in October 2014 as manuscript number PRS 11036; approved for publication by the Processing Systems Community of ASABE in July 2015.
The authors are Krittiya Khuenpet, Doctoral Candidate, and Weerachet Jittanit, Lecturer, Department of Food Science and Technology, and Sarote Sirisansaneeyakul, Lecturer, Department of Biotechnology, Faculty of Agro-Industry, Kasetsart University, Bangkok, Thailand; Warangkana Srichamnong, Lecturer, Institute of Nutrition, Mahidol University, Salaya, Thailand. Corresponding author: Weerachet Jittanit, Department of Food Science and Technology, Kasetsart University, 50 Ngam Wong Wan Road, Chatuchak, Bangkok 10900, Thailand; phone: +66-2-562-5026; e-mail: firstname.lastname@example.org.
Abstract. In this study, Jerusalem artichoke tuber (JAT) samples were pretreated in four different ways including non-peeling/blanching, non-peeling/non-blanching, peeling/blanching, and peeling/non-blanching prior to hot air drying and milling into fine powder. The physical characteristics of Jerusalem artichoke tuber powder (JATP) specimens were determined in terms of color, moisture content, pH, microstructure, particle size, and solubility. Furthermore, JATP specimens were processed into inulin powder by applying extraction, evaporation, and spray drying procedures. Both JATP and inulin powder samples from four pretreatments were analyzed for their sugars, fructo-oligosaccharides (FOS), and inulin-type fructan contents. The aims of this research were to (1) determine the appropriate pretreatment condition for JAT in order to obtain superior-quality JATP and inulin powder products, (2) investigate the sugars, FOS, and inulin-type fructans in JATP and inulin powder, and (3) evaluate the yield of inulin powder production from JATP. The results indicated that non-peeling/blanching was the pretreatment that should be applied for JATP and inulin powder production because it provided JATP with the lowest sugars (10.00 ±1.59 g per 100 g dry mass) and high inulin-type fructans (39.09 ±0.87 g per 100 g dry mass) and provided spray-dried inulin powder with the lowest sugars (23.62 ±0.98 g per 100 g dry mass) and the maximum inulin-type fructans (56.29 ±0.58 g per 100 g dry mass). In addition, the benefit of blanching is to help preventing the browning reaction during inulin powder production. The extraction process could separate some impurities and increase the sugars, FOS, and inulin-type fructan contents in powder products. Additionally, the yields of inulin powder production ranged from 45.56% to 59.85% of the JATP dry weight.
Keywords.Blanching, Extraction, Inulin, Jerusalem artichoke tuber, Peeling.
Inulin is a linear polymer of fructose units joined by ß-(2?1)-D-fructosyl-fructose bonds and terminated with a glucose unit by a-D-glucopyranosoyl bond (Blecker et al., 2002; Ronkart et al., 2007). Ordinarily, the formation of inulin is GFn, where G is glucose, F is fructose, and n is the number of fructose molecules. The degree of polymerization (DP) of inulin ranges from 2 to 60 units (Van Loo et al., 1995; Judprasong et al., 2011) depending on species, harvesting maturity, storage time, and production conditions (Saengthongpinit and Sajjaanantakul, 2005; Stanley and Nottingham, 2007). Small molecules with DP < 10 are so-called fructo-oligosaccharides (FOS) (Sirisansaneeyakul et al., 2007). Inulin is generally applied in the food industry as a functional food ingredient, offering both nutritional properties (fiber enrichment, proven prebiotic, reduced calorie intake, etc.) and technical benefits (sugar/fat replacer, enhancing stability) (Vokov et al., 1993; Niness, 1999; Roberfroid, 2007).
Jerusalem artichoke (Helianthus tuberosus L.) is a tuberous plant belonging to the sunflower family. It is cultivated widely across the temperate zone; however, during the last few decades, many varieties of Jerusalem artichoke have been bred, developed, and successfully grown in Thailand, especially in the northeastern region (Vorasoot and Jogloy, 2006; Tanjor et al., 2012). At present, Jerusalem artichoke tuber (JAT) is a popular herbal food in Thailand due to its neutraceutical properties, especially for diabetics. According to Meijer and Mathijssen (1993) and Simonovska (2000), Jerusalem artichoke is rich in inulin; thus, it is one of the candidate crops for inulin production. The inulin content of JAT is 14% to 19%, while the crop that is commercially used for inulin production, namely chicory root, contains inulin between 15% and 20% (Van Loo et al., 1995). Referring to Judprasong et al. (2011), Jerusalem artichoke grown in Thailand is a potential source of inulin-type fructans, with an inulin content of 19.5 g per 100 g fresh weight.
The processing of JAT domestically grown in Thailand into either Jerusalem artichoke tuber powder (JATP) or inulin powder would be beneficial for both Jerusalem artichoke growers and food businesses in the region because it could help raising the demand and subsequently market value of JAT. In addition, JATP could be sold as a supplementary food due to its inulin and other nutrient contents, while inulin powder produced from JAT could replace the inulin powder imported from European companies.
According to Angus et al. (2005), the production of inulin powder from plant tissue is similar to sucrose production from sugar beets because inulin is soluble in hot water. Inulin production involves three general steps comprising hot water extraction, purification of the inulin extract, and then drying of the purified solution to inulin powder. Although global inulin production is estimated at approximately 100,000 tonnes per year, almost all of it is manufactured from chicory root. Moreover, the production technology for inulin has not been disclosed by the key producers. Lingyun et al. (2007) pointed out that, so far, most JAT are not processed into inulin powder because the purification technology is not well developed. Several methods for inulin extraction from JAT have been proposed. Laurenzo et al. (1999) ground JAT and then applied boiling water extraction for 10 to 15 min. Wei et al. (2002) applied microwave heating to assist inulin extraction from JAT. In addition to hot water extraction, Sangthongpinit and Sajjaanantakul (2005) applied a process of inulin coagulation by alcohol prior to drying. However, Lingyun et al. (2007) pointed out that the precipitation of inulin by alcohol is uneconomical and inappropriate for industrial-scale production. Furthermore, they claimed that the important factors influencing the effectiveness of inulin extraction from JAT include pH, duration, temperature, and proportion of solvent to raw material. It was concluded that the optimal conditions for maximizing inulin extraction yield (83.6%) in conventional processes were natural pH at 76.7°C for 20 min and a solvent:solids ratio of 10.56:1 (v/w). Franck (2002) stated that, for industrial production, inulin must be extracted by hot water, followed by refining using exchanger technology, and then concentrated using evaporation and spray drying. In past decades, thermal extraction, multistage extraction, and countercurrent extraction have been conducted using only hot water; however, an ultrasound technique has recently been applied by some researchers to assist inulin extraction from JAT (Li et al., 2012).
JAT has light brown peel that is thin and edible. A high content of phenolic compounds was found in the peel, but not in the flesh of the tubers; therefore, JAT should be consumed unpeeled in order to obtain more nutrients (Seljåsen and Slimestad, 2007). In addition, Yildiz (2006) found that the yield values of sweetening syrups produced from Jerusalem artichoke were 17 g and 13 g, and DP values were 7 and 7.9, for extracts obtained from whole and peeled tubers, respectively. Nearly 31% increase in yield and 13% decrease in DP were obtained with whole tubers. Therefore, for the production of functional syrups, JAT should not be peeled. According to Milala et al. (2009), the inulin-type fructan contents in extracts of chicory root and of chicory root peel were 61.8% and 47.7%, respectively, indicating that chicory root should not be peeled for inulin production. This finding could be also a guideline for inulin production from JAT. Although it is clear that the use of whole JAT would result in a higher production yield of JATP and inulin powder, the effect of peeling on powder quality should be investigated.
Blanching is a common pretreatment step for the processing of many food products. The benefits of blanching are to inactivate enzymes (mainly in fruits and vegetables), reduce the initial load of microorganisms, and remove impurities in raw materials. For JAT, inulinase and polyphenol oxidase (PPO) are deemed vital enzymes that can affect JAT quality. Inulin is usually degraded to shorter DP by an internal enzyme (inulinase) during storage. PPO is related to the occurrence of undesirable browning and off-flavors. Usually, JAT develops off-flavors and blackening of the tubers as a result of oxidation during processing. Therefore, a thermal treatment such as hot water blanching is generally required to inactivate inulinase and PPO, which influence the degradation of inulin, color changes, and off-flavors (Modler et al., 1993; Ziyan and Pekyardimci, 2003; Takeuchi and Nagashima, 2011). It appeared that inulinase could be inactivated by a lower-temperature treatment than PPO. Heat treatment at 60°C could inactivate inulinase (Marx et al., 1997; Takeuchi and Nagashima, 2011), whereas 50% of PPO activity remained after hot water blanching at 100°C for 2 min (Takeuchi and Nagashima, 2011). Takeuchi and Nagashima (2011) pointed out that blanching for 2 min did not completely inactivate PPO, but it was enough to maintain a pale color of the JAT samples. Moreover, blanching for longer than 60 s resulted in inulin loss from JAT samples, whereas one-third of the total soluble saccharides were lost after blanching JAT for 2 min. Even though blanching provides some benefits for JAT samples as previously stated, the effects of blanching on JAT powder quality and on inulin extraction should be clarified.
Several methods have been proposed in the literature for determining the inulin content of samples. Lingyun et al. (2007) determined the inulin content of samples by calculating the difference between total carbohydrates and reducing sugars. The total carbohydrates were determined by the phenol-sulfuric acid method, while the reducing sugars were determined by the dinitrosalicylic acid method using D(-)-fructose as the standard. Moreover, Lingyun et al. (2007) applied high-performance anion exchange chromatography (HPAEC) with pulsed amperometric detection (PAD) to determine the oligofructan pattern in more detail. The major drawback of HPAEC-PAD is that quantifying high-DP compounds is very difficult due to the lack of appropriate standards and the reduced sensitivity of the PAD detector for high-DP polymers. A high-temperature capillary gas chromatographic method has been developed for quantitative determination of inulin-type oligosaccharides with DP < 10 (Joye and Hoebregs, 2000). Sample preparation involves oxime formation and silylation of the extracted sugars. The oxime-trimethylsilyl derivatives are analyzed on an apolar capillary Al-clad column with temperature programming up to 440°C and detection by flame ionization. The method is accurate and specific. Moreover, ß-(2-6) oligosaccharides (levan) can be clearly distinguished from ß-(2-1) compounds (inulin), and GFn molecules can be distinguished from Fn molecules. Bach et al. (2012) calculated the inulin content of JAT extract from the difference in the concentrations of glucose and fructose before and after hydrolysis, applying the method of Kocsis et al. (2007). They analyzed the content of free sugars by HPAEC according to the method of Kaack et al. (2004). They found low total sugar contents in three varieties of JAT, ranging from 1.55 to 2.15 g per 100 g of fresh weight. Sucrose appeared to be the main part of the total sugars. Baldini et al. (2004) determined inulin content by analyzing the free sugars, i.e., sucrose (fs), glucose (fg), and fructose (ff), in inulin extract and then investigated the total fructose (F) and glucose (G) content in acid-hydrolyzed inulin extract by HPLC. Judprasong et al. (2011) applied a method similar to that of Baldini et al. (2004) for evaluating inulin content, but they used enzyme hydrolysis instead of acid hydrolysis. Chabbert et al. (1985, 1993) claimed that the DP of inulin depended on the cultivar and age of Jerusalem artichoke. Saengthongpinit and Sajjaanantakul (2005) stated that a decrease in the more polymerized fractions (DP > 10) with an increase in fructose and sucrose composition was observed for late-harvested (20 weeks) JAT.
In this study, JAT samples were pretreated with four different conditions comprising non-peeling/blanching, non-peeling/non-blanching, peeling/blanching, and peeling/non-blanching prior to hot air drying and milling to fine powder. The physical characteristics of the JATP specimens were determined, including color, moisture content, pH, microstructure, particle size, and solubility. JATP samples were also processed into inulin powder by applying extraction, evaporation, and spray drying. JATP and inulin powder samples from the four pretreatments were analyzed for their sugars, FOS, and inulin-type fructan contents by applying high-temperature gas chromatography. The main objectives were to (1) determine the appropriate pretreatment conditions for JAT in order to obtain superior-quality JATP and inulin powder products, (2) investigate the sugars (fructose, glucose, and sucrose), FOS, and inulin-type fructans in JATP and inulin powder, and (3) evaluate the yield of inulin powder production from JATP. The outcome of this research would be beneficial to entrepreneurs who intend to pursue manufacturing processes for JATP or inulin.
Materials and Methods
Pretreatments and JATP Production
Fresh JAT (variety JA102) was supplied by the Agro-Ecological System Research and Development Institute of Kasetsart University (Petchaboon Research Station), Thailand. Raw JAT samples were exposed to the preparation procedures from washing to milling, as shown in figure 1. JAT samples were washed to remove soil and other impurities and then kept at 2°C in a coldroom before use. JAT samples taken from the coldroom were left at room temperature prior to the four different pretreatments, including non-peeling/blanching, non-peeling/non-blanching, peeling/blanching, and peeling/non-blanching. A vegetable cutter was used for slicing JAT into 2 mm thicknesses. Immersion of the samples in 0.5% w/v citric acid solution for 5 min was done to prevent enzymatic browning. For the
blanching step, the sliced samples were immersed in boiling water for 2 min (Takeuchi and Nagashima, 2011), and then tap water at room temperature was applied for cooling. Each pretreated sample was drained and then laid on filter fabric before tray drying at 65°C. This drying temperature was chosen based on a previous study because it provided a short drying time and acceptable product quality. Dried JAT chips were ground into JAT powder in two milling steps with a Fitz mill (model M5, The Fitzpatrick Co., Elmhurst, Ill.) and an Alpine Augsburg Pin mill (model 160Z, Alpine American Corp., Natick, Mass.). The JAT powder was screened through a 60 mesh sieve after the first milling with the Fitz mill and through an 80 mesh sieve after the second milling with the Pin mill. Four samples were obtained from the preparation procedure, namely JATP1, JATP2, JATP3, and JATP4, as shown in figure 1. All four samples were processed into inulin powder by applying extraction, evaporation, and spray drying procedures.
Inulin Powder Production
The procedure for inulin powder production and quality determinations for the samples collected in each step are shown in figure 2. The JATP1, JATP2, JATP3, and JATP4 samples were used as the raw materials for inulin powder production. Inulin was extracted from the JATP using hot water at 85°C for 30 min with a powder:water ratio of 1:35 (w/w). The extract was then cooled at ambient conditions, and the sediment was separated using a basket centrifuge at 1500 rpm with a polypropylene-fabric multifilament bag (model F254-3, Cannew International Trading Co., Ltd., Thailand). The inulin extract was evaporated to a concentration of 30 °Brix by boiling on a hot plate with stirring. The concentrated solution was processed into powder with a small-scale spray dryer (Mobile Minor 2000, GEA Process Engineering, Inc., Columbia, Md.) with inlet and outlet drying at 150°C and 90°C, respectively. This spray drying condition was applied because in preliminary tests it provided high powder recovery, acceptable powder appearance, and sufficiently low moisture content of the powder product. Quality determinations for JATP, sediment, inulin extract, concentrated inulin extract, and inulin powder were carried out based on various characteristics, as shown in figure 2.
In this study, the quality of the samples was determined in terms of color, moisture content, pH, particle size, microstructure, and the contents of sugars, FOS, and inulin-type fructans depending on the production step. Furthermore, the solubility of JATP, the powder recovery in spray drying, and the production yield of inulin powder were calculated using the experimental data. The determinations of color, moisture content, pH, and contents of sugars, FOS, and inulin-type fructans were done in three replicates. The software package SPSS (ver. 12.0) was used for statistical analysis.
Figure 1. JATP production procedure. Figure 2. Inulin powder production process and quality determinations for each step.
The color of samples was measured with a colorimeter (MiniScan XE, HunterLab, Reston, Va.) using the L*, a*, b* scale, where L* represents lightness (0 = L = 100), while a*(+), a*(-), b*(+) and b*(-) represent redness, greenness, yellowness, and blueness, respectively. The colorimeter was calibrated with a standard white tile using illuminant D65 and the 10° standard observer (Sootjarit et al., 2011a, 2011b).
The moisture contents were determined by the oven method using 2 g of sample and 105°C drying air temperature until constant weight (AOAC, 2005).
Prior to pH measurement, 2 g of the powder samples were dissolved in 75 mL of distilled water. The pH values of the solutions were measured with a pH meter (model PH-207, Lutron, Taipei, Taiwan).
To analyze particle sizes of JATP, a set of sieves was used with a mechanical sieve shaker. Sieves with mesh sizes of 125, 149, 177, and 250 µm were used. They were assembled in ascending order, with mesh size increasing from bottom to top, while the pan was installed below. A 20 to 30 g sample of JATP was placed on the top sieve and shaken for 10 min with an amplitude of 1.5 mm. The powders on each sieve were weighed. The weight was divided by the total weight to calculate the percentage of powder retained on each sieve.
The physical structures of JATP and JAT inulin powders were observed by scanning electron microscopy (SEM). Powder samples were sprinkled onto double-sided tape on SEM stubs. The samples were then sputtered with gold (model SCD 040, Balzers, Liechtenstein) prior to microstructure observation with a scanning electron microscope (model JSM-6610LV, Seal Laboratories, El Segundo, Cal.). Magnifications of 200× to 1000× and accelerating voltage of 15 kV were applied using the signals of secondary and backscattered electrons (Totosaus and Perez-Chabela, 2009).
Sugars, FOS, and Inulin-Type Fructan Contents
The sugars, FOS, and inulin-type fructan contents in JAT powder and inulin powder were analyzed following AOAC Method 997.08 (AOAC, 2005). First, total sugars, FOS, and inulin-type fructans were extracted from powder samples (2 to 3 g), which contained about 1 g of inulin-type fructans, by applying hot water at 85°C ±2°C for 15 min in a shaking water bath. FOS and inulin-type fructans in a portion of the extract were hydrolyzed by inulinase. Both hot water extract samples and enzyme-hydrolyzed fractions were derivatized by oxymation and silylation reactions. Individual sugars that contained native fructose, glucose, sucrose, and FOS, i.e., 1-kestose (GF2), nystose (GF3), and 1F-ß-fructofuranosyl nystose (GF4), were then defined by high-temperature gas chromatography. For sugars in the
solution of inulinase-hydrolyzed extract that contained native sugars, sugar fractions from inulin and FOS (fructose and glucose) were determined using another gas chromatography (Joye and Hoebregs, 2000; Judprasong et al., 2011). The amount of inulin-type fructans was calculated from the difference of the amounts of each sugar (fructose, glucose, and sucrose) before and after enzyme hydrolysis as given in AOAC Method 997.08 (AOAC, 2005) (Judprasong et al., 2011).
Solubility of JATP
The loss of dry solids contained in JATP during hot water extraction and basket centrifugation could be realized if the solubility percentage was calculated using equation 1:
A higher solubility percentage implied that a lower loss of dry solids occurred. For the inulin extraction experiment, 300 g of JATP were used as raw material. After hot water extraction and basket centrifugation, the sediments were weighed, and the moisture contents of the JATP and sediments were determined. The moisture content values were used for calculating the dry solids contents in the JATP and sediments.
Powder Recovery in Spray Drying
The production yield of the spray drying process could be represented by the powder recovery value. The total soluble solids (°Brix) in the concentrated inulin extract after the evaporation step was measured with a digital refractometer (model HI96801, Hanna Instruments, Inc., Ann Arbor, Mich.). The weight of total solids in the concentrated inulin extract that was fed into the spray dryer for each experimental run was calculated. In addition, the weight of inulin powder collected from each spray drying experiment was recorded. The powder recovery value was then determined using equation 2:
Production Yield of Inulin Powder
The production yield of inulin powder was calculated from the total solids weight in inulin powder collected from the spray dryer and the dry mass of JATP used as the raw material in the extraction process, as shown in equation 3:
The software package SPSS (ver. 12.0) was used for the analysis of variance (ANOVA) and Duncan’s multiple range test in the statistical analysis.
Results and Discussion
After the production of JATP applying four different pretreatments, the JATP samples were used as raw materials for inulin powder production. The quality of the samples was determined in terms of color, moisture content, pH, particle size, microstructure, and the contents of sugars, FOS, and inulin-type fructans at various production steps.
Color, Moisture Content, and pH
Color is one of the main attributes that influence the consumer preference in JATP and inulin powder. Usually, a less intense color is preferred. The results of color measurement are presented in table 1. The blanched samples (JATP1 and JATP3) were significantly darker than the non-blanched samples (JATP2 and JATP4). Among all JATP, the powder prepared using non-peeling and blanching pretreatment (JATP1) was found to be the darkest due to its lowest L* and highest a* and b* values. This may have been caused by non-enzymatic browning, such as the Maillard reaction, during blanching. Bach et al. (2013) claimed that JAT slices turned brown after peeling and drying due to an enzymatic browning reaction. Moreover, if the JAT slices were heated in boiling water, their colors would be darker as a result of a non-enzymatic darkening reaction between iron and phenolic acids, forming a complex of Fe2+ and o-diphenolic acid. When exposed to air, this complex was oxidized to a bluish-grey Fe3+-o-diphenolic acid complex (Hughes et al., 1962). In this study, JATP1 was significantly darker than JATP3 because JATP1 contained JAT peel. According to Takeuchi and Nagashima (2011), JAT peel contained more polyphenolics than JAT flesh; therefore, a more intense of non-enzymatic darkening reaction occurred in JATP1.
All JATP specimens were used as the raw materials for inulin extraction, as previously mentioned. The sediments and inulin extracts were collected after basket centrifugation. The colors of the sediments and extracts for non-blanched samples were darker than those of blanched samples. This phenomenon could be due to two main reasons. First, blanching could inactivate PPO, which is considered the main cause of undesirable browning in JAT during storage (Modler et al., 1993; Ziyan and Pekyardimci, 2003; Takeuchi and Nagashima, 2011). Takeuchi and Nagashima (2011) pointed out that blanching JAT in boiling water for 2 min could not completely inactivate PPO, but it was enough to maintain a pale color of JAT samples. Secondly, during blanching, some soluble compounds such as sugars and peptides that are substrates for the Maillard reaction were eluted from the JAT to the hot water (Takeuchi and Nagashima, 2011). As a consequence, when the blanched samples were heated during the extraction process, the development of brown color due to the Maillard reaction in both sediments and extracts was less than in non-blanched samples. Considering the color values of the concentrate and inulin powder samples, it appears that the tendency was similar to that for the sediments and inulin extracts. The reasons for this phenomenon would be identical to those for the sediments and inulin extracts, as previously explained. The color measurements showed that a blanching pretreatment should be applied to prevent browning during storage and during the inulin powder production process. In addition, the samples containing JAT peel (JATP1 and JATP2) and their subsequent products had more intense color when compared with samples without JAT peel. This was because polyphenolics normally occur in JAT peel to a greater extent than in JAT flesh, leading to more intense non-enzymatic darkening during heating, as previously described (Takeuchi and Nagashima, 2011). Although the use of JATP that included JAT peel produced darker color in the resulting inulin powder, it could also increase the production yield of inulin powder due to the high content of inulin-type fructans in the peel (Yildiz, 2006).
Table 1. Color values of samples collected from each production step.[a] Sample Color Lightness (L*) Redness (a*) Yellowness (b*) Jerusalem artichoke tuber powder JATP1 (non-peeling/blanching) 72.38 d ±0.24 0.27 a ±0.05 13.56 a ±0.17 JATP2 (non-peeling/non-blanching) 84.07 b ±0.06 -0.14 b ±0.03 11.44 c ±0.03 JATP3 (peeling/blanching) 83.70 c ±0.08 -0.82 c ±0.01 12.22 b ±0.04 JATP4 (peeling/non-blanching) 86.89 a ±0.18 -0.93 d ±0.02 10.84 d ±0.05 Sediment Sediment 1 49.86 c ±0.56 1.99 b ±0.02 18.46 a ±0.17 Sediment 2 39.15 d ±0.05 3.30 a ±0.19 18.39 a ±0.17 Sediment 3 61.01 a ±0.05 -0.44 d ±0.04 16.68 c ±0.05 Sediment 4 54.69 b ±0.12 0.70 c ±0.06 17.22 b ±0.09 Inulin extract Extract 1 53.01 c ±0.90 -1.79 c ±0.16 12.68 b ±0.18 Extract 2 50.63 d ±0.31 -0.08 a ±0.06 20.81 a ±0.13 Extract 3 57.31 b ±0.73 -1.29 b ±0.01 4.32 d ±0.09 Extract 4 61.63 a ±0.66 -1.72 c ±0.01 5.19 c ±0.08 Concentrated inulin extract Concentrate 1 13.83 b ±0.24 2.04 b ±0.17 10.90 b ±0.40 Concentrate 2 7.85 d ±0.11 2.31 b ±0.09 7.70 c ±0.19 Concentrate 3 20.94 a ±0.28 2.17 b ±0.24 11.76 a ±0.08 Concentrate 4 9.73 c ±0.39 5.98 a ±0.01 11.79 a ±0.48 Spray-dried powder Inulin powder 1 77.43 b ±0.09 0.45 b ±0.03 14.39 c ±0.06 Inulin powder 2 71.59 d ±0.03 1.64 a ±0.02 17.02 b ±0.06 Inulin powder 3 84.08 a ±0.14 -0.44 c ±0.02 11.08 d ±0.10 Inulin powder 4 75.07 c ±0.17 1.70 a ±0.06 19.88 a ±0.01
[a] Values in the same column within the same sample group followed by different letters are significantly different (p < 0.05).
The moisture contents and pH values of JATP and inulin powder samples are presented in table 2. The moisture contents of JATP and inulin powder were in the range of 5.7% to 6.8% wet basis (w.b.) and 5.7% to 7.6% w.b., respectively. These moisture contents are low enough for long-term storage. Lingyun et al. (2007) dried fresh JAT to a moisture content of about 5.61% w.b. to prevent brown rot. The effect of pretreatment on the moisture content of JATP is not obvious. However, pretreatment should not directly influence the moisture content of inulin powder because the samples are exposed to more heat and moisture during hot water extraction for inulin production than during blanching. For pH determination, 2 g of sample were dissolved in 75 mL of distilled water. The pH values were 5.52 to 5.91 and 5.67 to 6.65 for JATP and inulin powder samples, respectively, indicating that these specimens were acidic. It is noticeable that the pH values were significantly higher for blanched JATP samples than for non-blanched samples. Blanching the sliced JAT samples in hot water for 2 min resulted in an increase of pH due to leaching of acidic substances from the sample to the water. However, blanching is not the key factor that influences the pH of inulin powder because the samples are exposed to hot water extraction for a long time in the inulin production process. Soaking of the sliced JAT samples in citric acid solution should be a cause of the rather low pH values of JATP and inulin powder. This pH information would be useful for food industries that use these powders as an ingredient in products such as health drinks.
Table 2. Moisture content (MC, % w.b.) and pH of JATP and inulin powder samples.[a] Sample MC pH Jerusalem artichoke tuber powder JATP1 (non-peeling/blanching) 6.75 a ±0.07 5.88 b ±0.00 JATP2 (non-peeling/non-blanching) 5.68 d ±0.02 5.54 c ±0.00 JATP3 (peeling/blanching) 6.09 c ±0.01 5.91 a ±0.01 JATP4 (peeling/non-blanching) 6.39 b ±0.03 5.52 d ±0.02 Inulin powder produced from JATP Inulin powder 1 (from JATP1) 5.77 bc ±0.08 5.75 c ±0.00 Inulin powder 2 (from JATP2) 7.56 a ±0.04 5.67 d ±0.03 Inulin powder 3 (from JATP3) 5.72 c ±0.16 5.90 b ±0.02 Inulin powder 4 (from JATP4) 5.95 b ±0.08 6.65 a ±0.01
[a] Values in the same column within same sample group followed by different letters are significantly different (p < 0.05).
Particle Size and Solubility of JATP
The particle size distribution of JATP samples was determined using a mechanical sieve shaker, as previously described. The results are shown in figure 3. It is clear that particles smaller than 125 microns constituted the majority of the JATP samples in all cases, with a proportion between 51.43% and 81.11% of total weight. This was likely due to the application of two-stage milling using the Fitz mill and Pin mill. Furthermore, the blanched samples (JATP1 and JATP3) contained higher proportions of larger particles than the non-blanched specimens (JATP2 and JATP4). In other words, the powders of non-blanched JAT were finer than those of JAT exposed to blanching. This result indicates that the blanching pretreatment affected the grinding and size-reduction of dried JAT to fine powder. According to Rubel et al. (2014), JAT consists of protein (9.78% w/w dry mass), ash (6.14% w/w dry mass), lipids (1.16% w/w dry mass), cellulose (2.73% w/w dry mass), hemicellulose (2.22% w/w dry mass), and lignin (0.52% w/w dry mass), while inulin is the greatest part with a content of 78.1% w/w dry mass. During hot water blanching, protein denaturation occurred in the JAT slices, leading to a tougher texture. Moreover, blanching pretreatment might cause cooking and subsequent structural changes of cellulose and hemicellulose, resulting in larger particle sizes of JATP after milling. The effect of peeling on the particle sizes of JATP samples was not obvious because the particle size profile of JATP1 was similar to that of JATP3. Moreover, there were no clear differences in particle size distributions between JATP2 and JATP4. This may be because the main components of JAT flesh and JAT peel are alike (Yildiz, 2006; Milala et al., 2009).
Figure 3. Particle size distribution of JATP samples.
All JATP samples were used as raw materials for inulin powder production. The experimental data, which were needed for calculating solubility percentage values, obtained from extraction and basket centrifugation are shown in table 3. The solubility values were calculated to indicate the loss of dry solids contained in JATP during hot water extraction and basket centrifugation. A greater solubility percentage implies a lower loss of dry solids. Obviously, higher amounts of sediments were separated by basket centrifugation when using blanched samples (JATP1 and JATP3) as raw materials, leading to greater dry solids loss, less soluble solids in the extract, and subsequently lower solubility. This could be explained by the particle sizes of the JATP samples. As previously discussed, the blanched samples (JATP1 and JATP3) contained higher amounts of powder with larger particle sizes than the non-blanched samples (JATP2 and JATP4). Hence, after extraction, the particle size of the remaining insoluble solids would be larger than in non-blanched samples and could not pass through the filter bag of the basket centrifuge. Furthermore, the specific surface areas of non-blanched samples were considerably larger than those of blanched samples, resulting in higher soluble solids extraction capability. In addition, the blanched samples, which had larger particle sizes, would trap more soluble solids, especially inulin, in their structure, causing lower soluble solids in the extract. When comparing samples with peel (JATP1 and JATP2) and without peel (JATP3 and JATP4), it appears that the solubility of samples without peel was slightly higher. This is because JAT peel contains more insoluble solids compounds, such as cellulose, hemicellulose, and lignin, than JAT flesh.
Table 3. Experimental data obtained from extraction and basket centrifugation processes.[a] JATP1 JATP2 JATP3 JATP4
300 300 300 300
Moisture content of JATP (% w.b.)
Dry solids in JATP (g)
279.75 282.96 281.73 280.83
Weight of sediment separated by basket centrifugation after extraction (g)
967 661 1017 442
Moisture content of sediment (% w.b.)
Dry solids in sediments (g)
114.56 78.74 104.88 55.50
Soluble solids in extract (g)
165.19 204.22 176.85 225.33
59.05 72.17 62.77 80.24
[a] Values in the same row followed by different letters are significantly different (p < 0.05).
(a) (b) (c) (d)
Figure 4. Scanning electron micrographs of JATP samples: (a) JATP1 (non-peeling/blanching), (b) JATP2 (non-peeling/non-blanching), (c) JATP3 (peeling/blanching), and (d) JATP4 (peeling/non-blanching) (1000×).
Microstructure of JATP and Inulin Powder
SEM micrographs of all four JATP samples and of inulin powders produced from the JATP samples are shown in figures 4 and 5, respectively. Blanching apparently influenced the microstructure of the powders. The microstructure of the blanched samples (JATP1 and JATP3) appears flattened and more porous than that of the non-blanched samples due to the collapse of cells and pores during hot water blanching. The flattened and porous microstructures due to blanching could help increase the drying rate of JAT slices in later processing. Furthermore, some spherical shapes were seen on the surfaces of non-blanched samples. These round granules were likely water-soluble compounds, such as sugars, FOS, inulin, and protein. These components would be dissolved in hot water if blanching pretreatment was applied.
The SEM micrographs of inulin powders in figure 5 show that the particles of blanched samples (inulin powders 1 and 3) were smaller than those of non-blanched samples (inulin powders 2 and 4). The larger particle size of inulin powders 2 and 4 may have been caused by the thermoplasticity and hygroscopicity of these powders due to their higher contents of low-molecular-weight sugars, which have low glass transition temperatures (Bhandari et al., 1997). The high thermoplasticity and hygroscopicity resulted in powder agglomeration and powder swelling, as shown in figures 5b and 5d. The non-blanched samples had higher contents of low-molecular-weight sugars because these components could be easily leached into the hot water during blanching.
(a) (b) (c) (d) Figure 5. Scanning electron micrographs of inulin powder produced from different JATP samples: (a) inulin powder 1 (JATP1), (b) inulin powder 2 (JATP2), (c) inulin powder 3 (JATP3), and (d) inulin powder 4 (JATP4) (200×).
According to the particle size distributions of JATP1 and JATP3, as shown in figure 3, and the particle sizes of inulin powders 1 and 3, as shown in figure 5, the average particle size of JATP1 is larger than that of JATP3, but the particle size of inulin powder 1 is smaller than that of inulin powder 3. A possible reason is that inulin powder 3 contained a much higher content of low-molecular-weight sugars and FOS than inulin powder 1. These low-molecular-weight sugars and FOS have high thermoplasticity and hygroscopicity, resulting in more agglomeration and swelling, and subsequently greater particle size for inulin powder 3 than for inulin powder 1. Dissimilarly, although JATP3 had higher contents of low-molecular-weight sugars and FOS than JATP1, the other compounds, such as proteins and insoluble fiber, might help protect these sugars and FOS from agglomeration and swelling by trapping these sugars and FOS in their structures.
Contents of Sugars, FOS, and Inulin-Type Fructans in JATP and Inulin Powder
The content of sugars, FOS, and inulin-type fructans in JATP and inulin powders is presented in table 4. The results show that the contents of fructose and glucose in all JATP samples were low, with values ranging from 0.01 to 0.08 g per 100 g dry mass and from 0.02 to 0.05 g per 100 g dry mass, respectively, except for JATP3, which showed higher levels of fructose and glucose. The sucrose contents in all JATP samples were much higher than the fructose and glucose contents. This tendency agrees with the findings of Saengthongpinit and Sajjaanantakul (2005), who stated that the glucose, fructose, and sucrose contents of fresh 20-week maturity JAT were 0.26, 3.00, and 8.76 g per 100 g dry mass, respectively. Moreover, they found that sucrose content increased significantly with storage time at 5°C. Significantly higher levels of inulin-type fructans (DP = 2 to 60) were found in JATP samples containing peel. This result implies that JAT peel has a higher content of inulin-type fructans than JAT flesh. Lower contents of sugars and inulin-type fructans were found in blanched JATP samples than in non-blanched samples, which could be due to leaching of sugars and inulin-type fructans from JAT during blanching. Takeuchi and Nagashima (2011) reported that 20% to 30% of inulin was lost during blanching.
Although blanching resulted in lower contents of sugars, FOS, and inulin-type fructans in blanched JATP samples, a different result was found for inulin powder. Inulin powder produced from blanched JATP had higher contents of inulin-type fructans than inulin powder produced from non-blanched JATP. The collapse of cells and pores during hot water blanching caused better inulin extraction from blanched JATP samples. Furthermore, figure 3 shows that the average particle size of blanched JATP was larger than that of non-blanched JATP. Consequently, when using non-blanched JATP samples for inulin powder production, more impurities, such as protein and insoluble fiber, would be able to pass through the multifilament bag during separation of sediment from inulin extract in basket centrifugation. More impurities in the inulin extract resulted in a lower proportion of inulin-type fructans in the inulin powder. Among all JATP samples, JATP1 contained the lowest level of total sugars (fructose, glucose, and sucrose) and FOS content but almost the highest level of inulin-type fructans. This characteristic is preferable if the powder is consumed as a food supplement, especially for diabetics. The inulin-type fructan contents in the JATP samples in this study were lower than in the samples investigated by Saengthongpinit and Sajjaanantakul (2005), who reported 88 g per 100 g dry mass in fresh JAT at 20-week maturity. De Leenheer and Hoebregs (1994), Coussement (1999), and Saengthongpinit and Sajjaanantakul (2005) pointed out that the sugars, FOS, and inulin-type fructans in JAT depend on various factors, such as JAT variety, climate and growing conditions, harvesting maturity, storage time, and temperature after harvest. In this study, the fresh JAT samples were stored at 2°C for many weeks, leading to degradation of inulin-type fructans.
For the inulin powders, it was clear that all samples (inulin powders 1 to 4) contained more FOS and inulin-type fructans than their JATP counterparts, showing that the extraction process applied in this study could remove some impurities. The amounts of sugars and FOS also increased when compared with those of JATP. The non-peeling and blanching pretreatment resulted in the highest level of inulin-type fructans but the lowest level of total sugars and FOS, as shown in the results for inulin powder 1. Moreover, the inulin-type fructan content of inulin powder 1 was comparable to the values reported by Bekers et al. (2008). According to Bekers et al. (2008), JAT chips were extracted in water at 50°C for 4 h with stirring. The JAT extract was then concentrated by boiling at 100°C for 2 h. After evaporation, an inulin content of 55.87% dry mass was found in the Jerusalem artichoke syrup. According to the results of this study, it can be stated that the pretreatment applied for JATP1 was suitable because it provided a product with low sugars, reasonable FOS, and high inulin-type fructans.
Table 4. Sugars, FOS, and inulin-type fructans in JATP and inulin powder.[a] Sample
(g per 100 g dry mass)
(g per 100 g dry mass)
(g per 100 g
Fructose Glucose Sucrose GF2 GF3 GF4 Jerusalem artichoke tuber powder JATP1 (non-peeling/blanching) 0.01 e
JATP2 (non-peeling/non-blanching) 0.08 e
JATP3 (peeling/blanching) 1.29 c
JATP4 (peeling/non-blanching) 0.01 e
Spray-dried inulin powder Inulin powder 1 2.27 b
Inulin powder 2 3.49 a
Inulin powder 3 0.70 d
Inulin powder 4 3.45 a
[a] Values in the same column followed by different letters are significantly different (p < 0.05).
The experimental data obtained from the inulin production process, the powder recovery percentage in the spray drying process, and the production yields of inulin powder are presented in table 5. Total solids in the feeds (concentrated extract) prepared from blanched samples (JATP1 and JATP3) were lower than those of non-blanched samples (JATP2 and JATP4). These results agree with the percentage of solubility, as previously discussed. The values of powder recovery ranged from 76.15% to 86.12%, indicating that the inulin extracts prepared from all JATP samples could be spray dried without difficulty. Therefore, it was unnecessary to add any drying adjuncts to the feed. When considering the production yields of inulin powder, it appears that producing inulin powder from non-blanched samples resulted in higher yields. The key reason was the higher solubility of non-blanched samples and subsequently higher total solids in the feeds. Furthermore, the mass of inulin-type fructans in the collected inulin powders produced from 300 g of JATP can be estimated by multiplying the values of (1) the production yields of inulin powder calculated in this part with (2) the amount of JATP used for each inulin powder production experiment (300 g), (3) the dry solids content (% w.b.) in JATP [(100 - moisture content of JATP in table 3) ÷ 100], and (4) the inulin-type fructan contents in table 4. It appears that the inulin-type fructans were 71.74, 71.31, 57.12, and 57.59 g when using JATP1, JATP2, JATP3, and JATP4, respectively, as the raw material. Therefore, the pretreatment applied for JATP1 sample preparation was deemed suitable because it provided the highest inulin-type fructan content in the collected inulin powders produced from a specific amount of JATP.
Table 5. Experimental data obtained from inulin production processes and calculated production yields.[a] JATP 1 JATP2 JATP3 JATP4
300 300 300 300
Moisture content of JATP (% w.b.)
Dry solids in JATP (g)
279.75 282.96 281.73 280.83
°Brix of concentrated extract
29.3 30.3 30.5 30.5
Weight of concentrated extract (g)
520 680 540 715
Total solids in the feed (g)
152.36 206.04 164.70 218.07
Powder collected from spray drying (g)
135.25 183.21 150.45 176.56
Moisture content of spray-dried powder (% w.b.)
Total solids in collected spray-dried powder (g)
127.45 169.36 141.84 166.05
Powder recovery in spray drying (%)
83.65 82.20 86.12 76.15
Production yield of inulin powder (%)
45.56 59.85 50.35 59.13
[a] Values in the same row followed by different letters are significantly different (p < 0.05).
The JATP1 sample prepared using non-peeling and blanching pretreatment had the darkest color due to a non-enzymatic browning reaction that occurred during blanching. However, blanching should be applied to prevent the browning reaction during storage of JATP and inulin powder production. The blanched samples (JATP1 and JATP3) contained higher proportions of larger particles than the non-blanched samples (JATP2 and JATP4). The pretreatment applied for JATP1 preparation was the most suitable pretreatment because it resulted in the lowest sugar content and the highest inulin-type fructan content, together with the maximum inulin-type fructan content in the collected inulin powder produced from a specific amount of JATP.
This research was jointly funded by Kasetsart University and the Thailand Research Fund.
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