Functional Ingredients Based on Jerusalem Artichoke: Technological Properties, Antioxidant Activity, and Prebiotic Capacity ^†

Abstract

Functional ingredients from Jerusalem artichoke (JA) were produced using a 2² experimental design with two factors: “pretreatment” (W: water immersion; P: pressing with citric acid dip) and “drying method” (A: air-drying; F: freeze-drying). Four powders (JAPWA, JAPPA, JAPWF, and JAPPF) were analyzed for technological properties, inulin, phenolic, and flavonoid content, in vitro prebiotic activity score (PAS), and antioxidant capacity. Pretreatment influenced inulin content. JAPPF exhibited the highest PAS value (1.12 ± 0.08), whereas JAPWA presented the lowest (0.58 ± 0.04). These differences could be attributed to the influence of polyphenol content, as the freeze-dried powders retained more than twice the concentration due to the effect of low process temperatures, which usually protect phenolic compounds. Using a more cost-effective alternative, JAPPA exhibited better technological properties as well as higher inulin content and PAS than JAPWA.

1. Introduction

Tubers of Jerusalem artichoke (Helianthus tuberosus L.) are known to store fructans, primarily in the form of inulin, at levels similar to those of chicory roots (16–20% of the fresh tuber weight) [1]. Tanjor et al. [2] stated that Jerusalem artichoke grown in Thailand is a potential source of FOS and inulin-type fructans at a level of 5.81 and 19.5 g/100 g fresh weight, respectively. The differences in inulin content could be ascribed to the prevailing agricultural conditions, the cultivar, the harvesting maturity, and the storage conditions and duration [3,4]. Inulin is considered a prebiotic due to its ability to promote the growth and activity of beneficial microorganisms in the human gut, such as Bifidobacterium and Lactobacillus [5,6,7]. Its versatility has led to its incorporation into a wide range of commonly consumed foods. Applications in the food industry include its use as a low-calorie sweetener, fat replacer, fiber enhancer, and prebiotic ingredient in products such as yogurts, cereals, desserts, nutrition bars, beverages, and ice cream [8]. Specifically, research in recent years about health-oriented products has shown the use of inulin in obtaining low-energy healthy cookies, hypoglycemic bread with antioxidant potential for diabetics, cereal bars with prebiotic capacity, and as a healthy substitute for animal fat in meat products, among other applications [9,10,11]. While commercial inulin is typically derived from chicory root, Jerusalem artichoke tubers are also a promising source of inulin [12]. The comprehensive utilization of Jerusalem artichoke tubers for ingredient production, in addition to inulin, provides other nutritional compounds found in the tuber, such as phenolic compounds and minerals, among others [5]. This approach eliminates the need for an extractive process to recover inulin as a food additive, which typically requires higher energy consumption and generates effluents, resulting in a larger carbon footprint and high associated costs [11]. A typical process for inulin production includes three key stages: pretreatment, extraction, and purification. The extraction is typically performed using hot water. After separating the solid residues, the inulin and the water solution are further purified through processes such as bleaching, activated carbon adsorption, or ion-exchange methods. The water-purified inulin is then concentrated and dried to yield pure inulin powders [13]. The powders obtained using whole tubers of Jerusalem artichoke can be considered functional ingredients with high nutritional value and antioxidant potential for use in various food preparations, along with other benefits such as lower cost and environmental friendliness [10].

The objective of this work was to obtain powdered ingredients from Jerusalem artichoke tubers by applying combined pretreatments and dehydration methods, studying the functional potential in terms of antioxidant capacity and prebiotic activity, as well as their technological properties.

2. Materials and Methods

2.1. Materials

Jerusalem artichoke (JA) crops were cultivated organically on a farm located in north Patagonia, specifically in Villa Regina (Río Negro province, Argentina), at geolocation coordinates of 39°07′10″ S and 67°06′37″ W. The tubers were planted in October 2022 and harvested in June 2023.

Firstly, the tubers were washed and brushed, and then disinfected for 20 min in a sodium hypochlorite solution (280 ppm). Afterward, they were rinsed for 10 min with distilled water. Finally, excess water was removed by draining and surface drying with tissue paper, and tubers were stored in bags of low-density polyethylene at 0 ± 1 °C until use.

2.2. Process of Obtaining Jerusalem Artichoke Powder (JAP)

The experimental design included the combination of two factors: the “drying method” factor with two levels, convective drying (A) and freeze-drying (F), and the “treatment” factor with two levels, immersion in distilled water as control treatment (W) and application of three pressing cycles (5, 10, and 13 atm, for 1 min each) with 3 successive washes in a citric acid solution (pH 3.5 for 3 min) (P).

Four dry ingredients (JAPWA, JAPWF, JAPPA, and JAPPF) were produced as shown in Figure 1 through the following processing steps (n = 3): fileted (2 mm thick), application of the corresponding treatment (W and P), hot air-drying or freeze-drying, milling, sieved (No. 70 ASTM), and packaging in an airtight polypropylene bag.

Convective drying was performed in a convection oven at 60 ± 1 °C and 5% relative humidity (RH) for 6 h. Freeze-drying was carried out under a condenser temperature of −84 °C and a chamber pressure of 0.22 mbar for 48 h. As the final water activity of the powders in both cases was below 0.3 (a_w = 0.22 for A samples, and 0.25 for F samples), and the moisture content ranged from 3.7% to 5.8% (wet basis), it can be assumed that all JAP are suitable for long-term storage without risk of microbial growth and with minimal oxidative degradation reactions [14].

2.3. Analytical Methods

Regarding hydration and oil absorption properties, water holding capacity (WHC) and water binding capacity (WBC) were determined according to AACC methods [15]. Swelling capacity (SC) was measured by placing 1 g of dry ingredient in a graduated cylinder, adding 50 mL of distilled water, and measuring the total volume reached after 18 h at 25 °C. Oil absorption capacity (OAC) was determined according to Rocha Parra et al. [16]. All determinations were performed in triplicate.

Total phenolic content (TPC) was determined using the Folin–Ciocalteu reagent according to Gomez Mattson et al. [17].

Total flavonoids (TF) were determined by the AlCl₃ complex formation method according to Zhishen et al. [18]. The results were expressed as mg quercetin (Qu) equivalent per 100 g of ingredient (db).

Antioxidant capacity was measured by two methods: the ferric reducing antioxidant power (FRAP) following the technique described by Sette et al. [19] and the bleaching of 2, 2-azinobis-[3-ethylbenzothiazoline-6-sulfonic acid] radical cations (ABTS⁺˙) according to Gomez Mattson et al. [17]. Gallic acid was used as standard for the calibration curve, and the results were expressed as mg gallic acid equivalent (GAE) per 100 g of ingredient (db) for the three determinations (TPC, FRAP, and ABTS⁺).

The extracts to measure TPC, TF, and antioxidant capacity were obtained starting from 1 g of JAP ingredient and performing two successive extractions in distilled water (65 °C, 500 rpm, 30 min). The extract was filtered and brought to a final volume of 25 mL.

Inulin content was determined by an anion-exchange HPLC method. Chromatography equipment included Agilent 1260 HPLC (Agilent Technologies, Santa Clara, CA, USA) equipped with an automatic injector (5 μL) and IR detector. Separation was achieved using a HIPLEX H column (300 mm × 7.7 mm, 8 µm particle size, Agilent Technologies, Santa Clara, CA, USA) at 348 K. The mobile phase was composed of 0.001 M H₂SO₄ at a flow rate of 0.4 mL/min. Inulin extraction of samples was performed according to Zuleta and Sambucetti [20].

2.4. PAS Determination

The commercial strains Lacticaseibacillus casei ATCC 393 and Escherichia coli ATCC 25922 purchased from the American Type Culture Collection (ATCC) were used. The initial suspensions (10⁷–10⁸ CFU/mL) were prepared from an overnight culture of L. casei grown in De Man, Rogosa, and Sharpe (MRS, Biokar Diagnostics, Beauvais, France) broth and E. coli in TSB (Tryptic Soy Broth, Difco, Detroit, MI, USA), both centrifuged at 6000× g for 10 min at 4 °C, and the cell pellets were washed twice with a phosphate-buffered saline solution (PBS) before use.

The in vitro prebiotic activity score (PAS) was determined following the methodology proposed by Sousa et al. [21] and Tarifa et al. [22] with some modifications. PAS was determined using Equation (1):

$$\mathrm{A}\mathrm{p}\mathrm{r}\mathrm{e}\mathrm{b}={\displaystyle \frac{{\left(\mathrm{L}\mathrm{o}\mathrm{g}{\mathrm{P}}_{24}-\mathrm{L}\mathrm{o}\mathrm{g}{\mathrm{P}}_0\right)}_{\mathrm{p}\mathrm{r}\mathrm{e}\mathrm{b}\mathrm{i}\mathrm{o}\mathrm{t}\mathrm{i}\mathrm{c}}}{{\left(\mathrm{L}\mathrm{o}\mathrm{g}{\mathrm{P}}_{24}-\mathrm{L}\mathrm{o}\mathrm{g}{\mathrm{P}}_0\right)}_{\mathrm{g}\mathrm{l}\mathrm{u}\mathrm{c}\mathrm{o}\mathrm{s}\mathrm{e}}}}-{\displaystyle \frac{{\left(\mathrm{L}\mathrm{o}\mathrm{g}{\mathrm{E}}_{24}-\mathrm{L}\mathrm{o}\mathrm{g}{\mathrm{E}}_0\right)}_{\mathrm{p}\mathrm{r}\mathrm{e}\mathrm{b}\mathrm{i}\mathrm{o}\mathrm{t}\mathrm{i}\mathrm{c}}}{{\left(\mathrm{L}\mathrm{o}\mathrm{g}{\mathrm{E}}_{24}-\mathrm{L}\mathrm{o}\mathrm{g}{\mathrm{E}}_0\right)}_{\mathrm{g}\mathrm{l}\mathrm{u}\mathrm{c}\mathrm{o}\mathrm{s}\mathrm{e}}}}$$

(1)

where P is the growth (Colony-Forming Units [CFU]/mL) of the probiotic bacteria at t 24 h and t 0 h, E is the growth (CFU/mL) of E. coli at t 24 h and t 0 h, the indicated subscript corresponds to the prebiotic ingredient under study (JAPWA, JAPWF, JAPPA, or JAPPF) or glucose as a positive control, all added at 1% (w/v). Briefly, to assess the prebiotic activity, an MRS carbohydrate-free basal medium was used for L. casei while an M9 medium was used as the basal medium for E. coli. After 24 h of incubation at 37 °C, counts were conducted on the MRS agar for the probiotic and on Tryptic Soy Agar (Tryptic Soy Agar, Difco, Detroit, MI, USA) for E. coli.

2.5. Statistical Analysis

All determinations were performed in triplicate, except inulin (n = 2), and results were expressed as the mean and standard deviation. A multifactorial analysis of variance (ANOVA) was conducted, considering two factors in the model: “drying method” (D) and “pretreatment” (T). Additionally, a multiple comparison test (Tukey’s test) was conducted with a significance level of 5%. All results were analyzed using InfoStat statistical software version 2020.

3. Results and Discussion

In

Table 1. Hydration properties of JA powders.

Ingredients	Factors		WHC	WBC	OAC	SC
	Pretreatment (T)	Drying Method (D)	g Water/g dm	g Water/g dm	g Oil/g dm	mL/g dm
JAPWA	W	A	6.0 ± 0.1 A,b	2.7 ± 0.1 A,b	1.6 ± 0 A,a	6.1 ± 0.2 A,b
JAPPA	P	A	6.8 ± 0.5 A,b	3.1 ± 0.3 B,b	1.6 ± 0 B,a	7.5 ± 0.2 A,b
JAPWF	W	F	4.7 ± 0.1 A,a	2.0 ± 0.1 A,a	2.0 ± 0.1 A,b	4.9 ± 0.3 A,a
JAPPF	P	F	3.9 ± 0.3 A,a	2.0 ± 0.1 B,a	2.1 ± 0.1 B,b	4.1 ± 0.1 A,a
Interaction T × D			N. sig	N. sig	N. sig	N. sig

Interaction between factors: Sig. (significant); N. Sig. (not significant). Means with the same superscript do not show significant differences (p > 0.05). Uppercase and lowercase letters represent the main effects of the “Pretreatment” and “Drying method” factors, respectively.

, the hydration properties of the different ingredients are presented. No significant interaction was observed between the studied factors; therefore, the main effects of these factors can be noted. The air-dried ingredients showed significantly higher WHC, WBC, and SC compared to the freeze-dried ones (p < 0.05), while the pressing treatment significantly affected the WBC and OHC, increasing them.

Among the different processing methods applied to obtain powdered ingredients, grinding can alter the physical properties of the fiber, thereby affecting its hydration properties. Hydration properties are important in food formulation, affecting the absorption of water by dry ingredients [16]. Low water retention capacity can result in liquid loss during processing, potentially altering the texture of the final products. Our findings fall within the range of those obtained by other authors when producing JAP using different drying methods, including convective drying, solar drying, freeze-drying, and microwave drying [3,23]. The results for JAPWA and JAPPA powders suggest that they could be used as an alternative to other substances characterized by their water-holding capacity, such as potato starch, soybean fiber, wheat, and maize hulls, for which WHC values ≈4 g water/g dry matter have been reported by Afoakwah et al. [3] and Inchuen et al. [23].

TPC and TF content are shown in Figure 2, where the main effects of the studied factors in both variables were observed. Freeze-drying retained approximately twice the TPC and three times the TF content, which would indicate that some of these bioactive compounds are thermolabile. Afoakwah et al. [3] recorded a slightly higher TPC in freeze-dried JAP (444 mg/100 g dm) compared to air-dried ones (426 mg/100 g dm). On the other hand, Inchuen et al. [23] reported values ranging from 251 to 640 mg/100 g dm depending on the dehydration method applied (microwave, hot air, or open-air sun shade drying).

Regarding the treatment, the control allowed for greater retention of TPC and TF, in contrast to the pressing treatment, which caused the greatest losses in both variables. The pressure applied during pressing may lead to the rupture of cell vacuoles and the loss of some water-soluble compounds, such as phenolic compounds.

As shown in Figure 3, the antioxidant capacity measured by ABTS⁺˙ showed a significant interaction between the studied factors, while the FRAP method evidenced main effects of the same factors. The JAPWF ingredient demonstrated remarkable antioxidant potential, as indicated by its ability to trap and stabilize free radicals using the ABTS+˙ method (356 ± 4.5) and its ferric ion reduction capacity in the FRAP assay (44 ± 1), both expressed in mg AGE/100 g dm.

These results are consistent with the levels of bioactive compounds present in JAPWF, which showed the highest value of TPC (416 ± 5 mg AGE/100 g dm) and TF (1054 ± 8 mg Qu/100 g dm).

According to data shown in

Table 2. Inulin content and PAS of JA powders.

Ingredients	Factors		Inulin Content	PAS
	Pretreatment (T)	Drying Method (D)	(g/100 g dm)
JAPWA	W	A	56 ± 0.2 A,a	0.58 ± 0.05 A,a
JAPPA	P	A	61 ± 3 B,a	0.82 ± 0.05 B,a
JAPWF	W	F	54 ± 1.5 A,a	0.93 ± 0.15 A,b
JAPPF	P	F	60 ± 1 B,a	1.12 ± 0.08 B,b
Interaction T × D			N. sig	N. sig

Interaction between factors: Sig. (significant); N. Sig. (not significant). Means with the same superscript do not show significant differences (p > 0.05). Uppercase and lowercase letters represent the main effects of the “Pretreatment” and “Drying method” factors, respectively.

, the pressing pretreatment favored inulin retention (61 ± 3 g/100 g dm in JAPPA and 60 ± 1 g/100 g dm in JAPPF), while the drying method showed no significant differences (p < 0.05), which indicates good preservation of this nutrient against temperature. Similar values of inulin (ranging from 51.60% to 57.45% on a dry basis) were reported by Burnete et al. [10] in JAP obtained from six different varieties of Jerusalem artichoke air-dried at 50 °C.

On the other hand, the studied factors had main effects on PAS, with pressing and freeze-drying resulting in ingredients with higher PAS, while control and convective drying produced ingredients with lower PAS. Differences in prebiotic activity could be attributed firstly to a higher inulin content in P powders and secondly to polyphenols’ influence, since freeze-dried powders presented almost double the polyphenol content of air-dried powders (416 ± 5 vs. 223 ± 3 mg AGE/100 g dm). The results obtained are superior to those found by Rubel et al. [24] where the highest PAS for carbohydrates extracted from JA freeze-dried powders was 0.3.

The JAP with PAS values close to or greater than 1 could indicate the effectiveness of prebiotic components in promoting probiotic growth and simultaneously preventing the colonization of pathogenic microorganisms.

4. Conclusions

All the ingredients obtained in the present study demonstrated functional potential.

Although the freeze-dried ingredients retained a higher amount of bioactive compounds, with greater antioxidant capacity and higher PAS, the cost of freeze-drying makes it a more expensive way for the development of functional powders, which could be used in nutraceutical applications.

The ingredients obtained through convective drying exhibited the best technological properties, with JAPPA showing higher inulin content and prebiotic capacity than JAPWA, making it a cost-effective alternative for producing functional JAP with possible applicability in food matrices.

In particular, the inulin content could be beneficial for gut health and also suitable for incorporation into products intended for individuals with diabetes.