Xanthan gum as an alternative to replace the fat for coating and flavoring the extruded snacks

Abstract

Food industries adapt their products and processes to the needs and desires of consumers. Extruded snacks include 10–20% fat sprinkled to fix flavors, seasonings, and salt. Considering the need to flavor snacks and simultaneously reduce the intake of calories, a polysaccharide is proposed in this study as a fat replacer. Impact of aqueous xanthan gum (Xg) solutions (0.25, 0.5, 1.0%) under two pH conditions (3.5 and 7.0) on structural and sensory characteristics of extruded snacks was analyzed. Rheological features of the coating solutions, as flow behaviour and viscoelastic profile (storage and loss moduli), were assessed. Texture analysis, to evaluate the snacks firmness and moisture content, water activity, retraction, and agglomeration index of the coated snacks, were also evaluated. Results for the aqueous Xg coatings were very encouraging showing good coating properties, not damaging the texture of the extrudates or causing agglomeration. Sensory analysis reflected a good overall acceptability of these snacks, as compared to oil-coated snacks. Therefore, xanthan gum should be used by the industry, to replace fat, on extruded snacks flavor coating solutions.

Introduction

The manufacture of salty snacks consists of corn gritz extrusion to obtain a product with almost no taste and aroma. To make the product more sensorially attractive, flavoring is performed by spraying 10 to 20% (w/w) fat on the extrudates followed by the addition of flavorings, seasonings, and salt (Monteiro et al. 2016). Fat plays an important role in this process, as is responsible for the adherence of flavorings and salt to the snacks.

The food industry has been under pressure from regulators and consumers to develop healthier products, to control obesity and prevent the onset of several serious chronic diseases (Salgado et al. 2017). The extruded snack foods present a high caloric value since the carbohydrates and fat are the major components (Korkerd et al. 2016). Food industries are looking for new healthier alternatives aligned with the food market trends.

Xanthan gum (Xg) is a polysaccharide produced by the microorganism Xanthomonas campestris fermentation activity (El-Sayed et al. 2002). It is approved for food use and can be used as a fat replacer (Lii et al. 2002). Furthermore, Xg acts as a soluble fiber in human body, since it is not absorbed in the small gut but is fermented in the large intestine by bacteria microbioma, adding nutritional arguments to its use instead of starch (Gularte and Rosell 2011). In addition, Xg presents a high number of tecnhologycal properties that justified their extensive: solubility, rapid hydration, water binding, thermal pH and salt stability. In terms of rheology properties, presents shear-thining flow behaviour and shows slight variation in viscosity with changing temperature and pH (Gyawali and Ibrahim 2016).

Considering the need for flavoring snacks and simultaneously reducing the calorie’s intake, Xg can be an alternative to replace the fat fraction on coating solutions (Busch et al. 2018 and Tunnarut and Pongsawatmanit 2018).

This work aimed to evaluate the effect of aqueous Xg solutions, at different concentrations (0.25 up to 1.0%) and two pH conditions (pH 7.0 and 3.5), that impact shelflife and sensory perception, as fat replacers, to coat and flavor the salty extrudates. Rheology properties of Xg solutions, based on flow behaviour and viscoelasticity (storage and loss moduli) and firmness of coated snacks by texture analysis were assessed. Other quality attributes, such as moisture, water activity, retraction, agglomeration index and sensory characteristics, were also evaluated.

Materials and methods

Raw materials

Snacks prepared at pilot scale using only maize grits (KOWALSKI S.A., Rio Verde, Brazil), with 1515 of granulometry. Xanham gum (SOSA INGREDIENTS S.A., Barcelona, Espanha) was used to coat the snacks and soybean oil as control (SADIA, S.A., Joacaba, Brazil). Citric acid (MERCK Group, Darmstadt, Germany) to adjust pH.

A mixture of dried herbs and salt: 25% Parsley, 15% oregano, 10% basil, and 50% sodium chloride, was used as flavoring.

Snacks extrusion

Snacks were produced in a single screw (50 mm in diameter and 200 mm longer) extruder (Inbramaq, IB-50) with a die plate with two 3 mm diameter holes. A single batch was prepared. Snacks were dried in a rotating drum at 65ºC for 30 min, left to cool down, and conditioned in polypropylene bags.

Coating and flavoring of the extruded snacks

Coating solutions were prepared by dispersing Xg in destiled water at two pH conditions: pH 7.0 and at pH 3.5, and three different concentrations: 0.25, 0.50 and 1.00%, under 10 min constant stirring, and left for 7 h, before use. Coating with soybean oil (10%), was the control.

Rheology characterization of the coating solutions

The Xg coating solutions were tested in a controlled-stress rheometer (Haake Mars III – Thermo Scientific, Germany) coupled to a UTC-Peltier system for temperature control. The effect of different levels of Xg addition on coating solutions, based in two fundamental rheology measurements, was evaluated: steady shear flow behaviour, using a 2°cone and plate sensor system (CP35), ranging the shear rate from 1.0 × 10^–1 to 1.0 × 10³ s⁻¹.

Experimental data of apparent viscosity (η_ap—Pa s) versus shear rate (γ^.- s⁻¹), was fitted to the Power-Law model, according to Eq. 1:

$${\mathrm{\eta }}_{\text{ap}}=\mathrm{K}{\left({\mathrm{\gamma }}^{.}\right)}^{\text{n}-1}$$ 1

where η_ap the apparent viscosity (Pa s), K the consistency index (Pa sⁿ), γ^. the shear rate (s⁻¹) and “n” the flow index, a dimensionless parameter.

Frequency sweep, expressed in terms of storage (G′) and loss (G″) moduli changes, ranging the frequency from 0.001 Hz to 10.0 Hz, was assessed. Viscoelastic functions were determined within the linear viscoelastic region of each sample, respectively at: 0.25%Xg—1 Pa; 0.5%Xg—5 Pa; 1.0%Xg—10 Pa previously determined (at 1 Hz) by a stress sweep.

All assays were performed at 20 °C and repeated at least three times.

Texture characterization of coated snacks

The impact of Xg coating solutions, at different concentrations, on snacks firmness values, was compared to the control, using a texturometer TA-XTplus (Stable MicroSystems, UK), in compression mode. An acrylic cylindrical probe with 25 mm of diameter (P/25L) at 1 mm s⁻¹ of test speed with a load cell of 5 kg, was applied.

Moisture, water activity, rectraction (RI) and agglomeration index (AI)

Moisture was gravimetrically determined (AACC 44–15.02). The Hygrolab (Rotronic, UK) determined the a_w of the snacks, at (20.0 ± 0.2 °C).

The retraction index (RI) was calculated based on specific volume (SV) decrease, by measuring the diameter of the spheric coated snacks before and after the coating procedure.

The agglomeration index was carried out after Nakagawa et al. (2019) by measuring how each coating type can affect the snacks adhesion during flavouring mixing. Randomized samples of 100 g snack were weighted after flavouring and drying, and the formation of agglomerates was counted for each type of cover used.

Sensory analysis

Tasting of flavored coated snacks was performed in a sensory evaluation room with individual cabinets, by a panel of 112 untrained panelists (20–35 years), who were regular snack consumers.

Samples were randomly coded, in white cups. Experimental protocol was approved by the Research Ethics Committee of the Maringá State University (protocol CAAE 18,718,013.3.0000.0104). Flavored coated snacks were sensory analised 24 h after preparation, based on their sensory acceptance, scoring with the descriptors: aroma/ taste, appearance and overall acceptability on a nine-point hedonic scale.

Statistical analysis

Triplicates, except for hardness-20 replicates, were performed. Results are expressed as average values and standard deviations and analyzed by the ANOVA with post-hoc Tukey test at 95% confidence.

Results and discussion

Coating rheology

Flow behaviour

Results of flow measurements to evaluate the effect of concentration on aqueous coating solutions with different levels of Xg addition, are presented on Fig. 1. Impact of pH conditions was checked, although significant variations were not expected. As it can be observed, the apparent viscosity of the aqueous solutions increased significantly (p < 0.05) with increasing concentration of Xg, and for each concentration, the viscosity of the Xg solutions decreased with shear rate increasing, revealing the typical shear-thinning behaviour.

Fig. 1.

Flow curves obtained for xanthan gum solutions, at different levels (0.25, 0.50, 1.0%, w/w), under two pH conditions (7.0 and 3.5)

These typical results of hydrocolloids in terms of flow behavior are in agreement with those obtained by other authors (Tunnarut and Pongsawatmanit 2018), from a study designed to improve the consistency of the syrup seasoning, using Xg as a coating solution. No significant differences on apparent viscosity were registered at the different pH conditions (pH 7.0 and 3.5) tested, as expected.

The experimental data was fitted to a Power Law model (Eq. 1), to describe the flow behavior of the aqueous solutions with different Xg additions, and a good correlation was registered (R² > 0.9990). Results of fitted rheology parameters (data not shown) showed that the consistency coefficient (K) values of coating solutions increased as the Xg content increased (p < 0.05), varying from around 2.50 Pa sⁿ for lower concentration of Xg (0.25%Xg) to 27.00 Pa.sⁿ for the higher level tested (1.0%Xg). The addition of Xg also changed the flow behaviour index (n) from around 0.30 (0.25%Xg) to around 0.15 (1.0%Xg). Lower flow index value (n) characterizes good mouth feel food properties (Ahmed and Ramaswamy 2004). These findings suggested that Xg can be used to enhance the viscosity of the coating solutions and to modify the flow index, increasing the shear-thinning behaviour. From industrial point of view, these rheology features can constitute an advantage to flavor coating increasing the adherence of the flavoring mixtures to snacks. Results showed that both pH conditions tested (pH 7.0 and 3.5) had no significant impact on flow rheology properties, as expected, since Xg is known to be stable in flow at temperature, pH and salt variations (Gyawali and Ibrahim 2016). Therefore, one can say that pH 3.5 is most favorable in aqueous coatings, better in terms of snacks preservation and taste.

Coating solutions viscoelastic profile

The impact of different Xg concentrations on viscoelastic functions of the coating aqueous solutions, based on storage (G′) and loss (G″) moduli changes, by frequency sweep measurements, was assessed.

From Fig. 2a–c, it is evident that the Xg concentration promoted a significant impact on viscoelastic behaviour of coating solutions. Lower values of Xg (0.25%) (Fig. 2a) resulted in a coating solution with a viscoelastic fluid behaviour (Picout and Ross-Murphy 2003), expressing values of G″ higher than G′, in almost whole range of frequency applied. This behaviour was more pronounced at pH 7. These results are in line with those obtained by Busch et al. (2018), by rheology characterization of a galactomannan extracted from Prosopis ruscifolia seeds. However, increasing the levels of Xg on aqueous solutions, a typical weak gel behaviour (Picout and Ross-Murphy 2003) can be observed (Fig. 2b), by the dominance of the G′ values over the G″, with a slight frequency dependence (Razmkhah et al. 2017). A remarkable effect on coating structuration was obtained for higher level of Xg tested (1.0%Xg), and no significant impact of the pH conditions tested was registered at this concentration (Fig. 2c).

Fig. 2.

Viscoelastic profile, expressed in storage (G′) and loss (G″) moduli (Pa), of the aqueous solutions produced with different levels of Xg addition (0.25, 0.5 and 1.0%), at two pH conditions (pH 7.0 and 3.5)

Charaterization of the flavored coated snacks

The effect of the coating solution, with different Xg content, at two pH conditions (pH 7.0 and 3.5), was evaluated based on snacks quality parameters: texture profile in terms of firmness, water activity (aw), retraction and agglomeration indexes. Results of snacks quality attributes was compared to control, i.e., snacks coated by soybean oil (10%).

Figure 3 shows the impact of the flavoring coating solutions, at different levels of Xg and pH conditions, on snacks firmness values, ranging from 50.48 N for control snacks (coated by soybean oil) to 49.52 N (pH 7.0) and to 53.41 N (pH 3.5) for higher level of Xg used as coating (1.0%Xg). As it can be seen (Fig. 3), significant differences were only observed at snacks coated with 0.25% of Xg under both pH conditions, and for coating solutions obtained with 0.5% of Xg at pH 7.0.

Fig. 3.

Comparison of the firmness values of flavored coated snacks, with a aqueous xanthan gum solution, at different levels (0.25, 0.5, 1.0%) and pH conditions (pH 7.0 and 3.5) and control snacks flavor coated by soybean oil (10%)

These results showed to be consistent with those obtained by rheology characterization, since the coating solutions obtained from 0.25% and 0.5% of Xg under pH 7.00 showed certain rheology instability, that can negatively influence the texture of snacks after coating. From these results we can say that Xg solutions obtained with 0.5% and 1.0%, at acid conditions, can be a potential fat replacer to produce a coating solution to flavour the snacks, since the firmness values of these snacks presented no significant differences, comparing to control (with soybean oil).

Moisture values of the snacks coated with aqueous Xg solutions showed no significant differences, comparing to control snack values, varying from 4.98% for control to 5.05% (pH 7.0) and to 5.18% (pH 3.5) for 1.0%Xg solution. The same trend was also observed on water activity (a_w) values, ranging from 0.183 for control to 0.186 (pH 7.0) and 0.182 (pH 3.5) for 1.0%Xg. Water activity is a parameter highly related to food stability, based on chemical rections and microbial growth (Tunnarut and Pongsawatmanit 2018), since it is directly related to the immobilization of the system, with molecules “freezed” inside the structure at low values of a_w (free water), unable to react or to feed microorganisms. In addition, no significant differences (p > 0.05) between the different treatments applied, on moisture and a_w values were obtained, compared to control snacks. These obtained results can be attributed to the water binding and holding capacity of Xg (Gyawali and Ibrahim 2016). Similar findings were registered by other authors (Busch et al. 2018), by rheology characterization of vinal gum, with different pH and ionic strength conditions.

Retraction index (RI) is another quality parameter widely used to physical characterization of the coated snacks, where no significant differences (p > 0.05) between control and coated snacks by Xg aqueous solutions were found. These findings are in line with those obtained by Monteiro et al. (2016) and Marques et al. (2017), studing the potential of fat replacement by an aqueous solution of cassava starch, to coat the snacks.

Regarding the agglomeration index, the results obtained suggested that the Xg solution showed to be an efficient coating to flavour the snacks and can be successfully used in industrial scale-up as a coating, since no agglomeration effects were observed. This result is better than that found by Nakagawa et al. (2019), using guar gum and starches as coating solutions, where a considerable number of agglomerated snacks was obtained, suggesting that these coating solutions may not be suitable to these snacks manufacturing.

Sensorial analysis

Sensory analysis results (not shown), obtained for Xg at pH3.5 coated and flavored snacks, showed no significant differences detected in appearance, flavor/aroma with high scores around 7 to 8, compared to control soybean oil coated snacks. The overall acceptability scored very high as well, around 8.3.

Therefore, results for sensory characteristics indicated that a replacement of fat by Xg can be a potential industrial procedure to produce coating solutions, with no significant impact on consumer acceptability, and a considerable reduction on calories.

Conclusion

From this study, the potential of Xg as fat replacer in flavor coating solutions of extruded snacks was evaluated, focused on rheology properties of the Xg solutions and quality parameters of the coated extrudates.

Results based on coating rheology properties, showed that 0.5 and 1.0% of Xg at acid pH (3.5) condition, can be used to produce coating solutions with desirable rheology features in terms of viscoelastic and shear thinning behaviour, expressing a weak gel-like structure for concentrations higher than 0.5%, better at pH 3.5.

Based on snacks quality attributes, these Xg coating solutions compared well with the oil-based coatings, for texture profile, water activity, retraction, and agglomeration index.

Sensory analysis scores reflected a good overall acceptability of these snacks with none significantly different from control snacks.

In conclusion, it can be stated that it is possible to replace the fat portion by an aqueous solution of Xg to flavor the snacks, and obtain a good quality final product, with lower scores on calories and a better impact on health.

Author contributions

A. Monteiro conceived and planned the experiments and supervised the research work; C. Graça, contributed to the acquisition of rheology data, data analysis, interpretation of the results and wrote the manuscript; D. Marques performed all samples preparation and performed the analysis, I. Sousa supervised the rheology work, data analysis, and interpretation of the results and revised the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by CAPES, and Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil (CNPq) for the grants, and by the Portuguese Foundation for Science and Technology (FCT) through the research unit UID/AGR/04129/2013 (LEAF- Research Center Linking Landscape, Environment, Agriculture, and Food).

Compliance with ethical standard

Conflict of interest

The authors declare no conflicts of interest.