3.3. Physicochemical Characterization of Umami-Rich Seasoning Powder
The umami-rich seasoning powder samples from the 15 groups of conditions obtained from the RSM analysis were analyzed in terms of physicochemical properties including salinity (g/100 g), saccharinity (%), pH, moisture content (%), AW, chromatic (
Table 1), free amino acids (
Table 2), WSI (%), bulk density tapped density (
Table 3), appearance (
Figure A3), microstructure (
Figure 1), and FTIR (
Figure 2). To avoid caking the powder in cases without other food additives, the quality index of the umami-rich seasoning powder was the moisture content. Therefore, among the 15 groups of conditions obtained from the RSM calculation, runs 6, 10, and 14 showed relatively low water contents of 3.68, 3.84, and 3.81%, respectively (
Table 1), compared to other runs with significant differences (
p < 0.05). This also implies that the operating conditions used in the present study were efficient for evaporative water drying, which was consistent with the results of Ferreira et al. [
33]. In addition, the moisture content of foods under 6% have high stability and shelf life [
34]. Interestingly, the AW (0.28–0.40) for all conditions was below the microbial growth level (<0.6) [
33]. In terms of salinity, saccharinity, and pH, there were significant differences among each run (
p < 0.05), though these were not considered quality indicators. However, maltodextrin is a hygroscopic material that results in a lower moisture content of the powders and with higher hygroscopicity [
31,
33]. The chromatic analysis (
L*,
a*,
b*, and ΔE) of the run powders were statistically significantly different (
p < 0.05); however, the variation was difficult to detect through visual observation (
Figure A3).
Regarding the determination of free amino acids, there were no significant differences between the umami-rich seasoning powders in all the runs. However, glutamic acid (0.12–0.29 mg/100 g), glycine (0.06–0.12 mg/100 g), aspartic acid (0.06–0.14 mg/100 g), and lysine (0.06–0.11 mg/100 g) were found in higher contents than other amino acids in this study (
Table 2), thus providing a richer umami flavor. These results were similar to those of the umami amino acids identified in porcine bone soup [
35]. Yin et al. [
36] reported that free amino acids in tilapia fillets contain five sweet amino acids (Gly, Ala, Arg, Thr, and Lys), with glycine being the most abundant. However, the amino acid contents in this study were lower than those mentioned above, which could be attributed to the fact that the samples in this study were sourced from offcuts from the fish-flavored soy sauce process.
In addition, umami-rich seasoning powder contains several amino acids, which can be used as natural seasoning agents to replace commercially available food additives such as high-flavor monosodium glutamate (MSG; L-glutamate) and seasoned chicken/mushroom essence, whose sodium content has been considered to be excessive [
37]. However, each culinary culture has a unique flavor combination of seasonings and ingredients, which is why local consumer preferences are referred to as flavor principles [
38,
39,
40]. It is worth mentioning that regardless of which culinary culture is inseparable from the umami flavor, including free amino acids (aspartic acid), 5′-nucleotides, short peptides, organic acids (such as lactic and succinic acid), and some Maillard reaction derivatives, which are widely distributed in food to enhance the overall flavor of food, for example, adjusting sweetness, enhancing salty taste, suppressing acidity, and bitterness, MSG is a classic seasoning type [
37,
39,
41,
42,
43,
44]. All tastes are related to each other, especially umami’s enhancement of salty taste [
45], which has no adverse effects on the human body in appropriate amounts, unlike MSG [
43,
46]. It has a significantly stronger effect on saltiness enhancement than an MSG-free solution with 0.3% NaCl [
42]. Thus, a suitable amount of umami seasoning is available to replace salt while preserving consumer acceptance of food [
47]. Despite the encouraging potential, it has also been reported that excessive intake of MSG combined with a high-lipid diet may lead to systemic damage through metabolic modulation of different signaling pathways, such as dyslipidemia due to the leptin/adiponectin ratio and inflammation due to oxygen species due to altered redox homeostasis, with severe cases of apoptosis [
48]. K.-C. Hsu, E.C.Y. Li-Chan, and C.-L. Jao [
49] showed that small-molecule amino acid sequences from tuna hydrolysis had an inhibitory effect on the proliferation of MCF-7 cells. The bitter taste of protein hydrolysates (due to alkaline protein hydrolysis enzymes releasing specific peptides) has previously limited their application but has been partially solved by substances such as glutamate, polyphosphate, activated carbon, gelatin, or glycine [
50,
51,
52].
In terms of powder properties, the WSI of the umami-rich seasoning powder obtained for each run condition ranged from 98.46–99.89% (
Table 3), with significant differences between the runs (
p < 0.05). In addition, the umami-rich seasoning based on maltodextrin showed a relatively better performance than the commercially available seasoning powder (bonito soup stock) (WSI 89.7). In addition, these values were significantly different from those of all the runs in this study (
p < 0.05). Other properties of the powders, such as bulk and tapped densities, were significantly different (
p < 0.05) as measured for the umami-rich seasoning powders obtained for each run condition, ranging from 0.40–0.63 (g/cm
3) and 0.43–0.69 (g/mL), respectively (
Table 3). Additionally, the inlet temperature rises, and the water evaporates rapidly, which forms the shell on the particle’s surface instantly, whereby the water vapor inside the particle will be released from the pores due to high pressure, which will lead to decreased bulk density [
29,
31,
53]. Unfortunately, it was impossible to compare the differences in powder densities owing to the different drying methods used in this study and the commercially available products mentioned above.
FTIR was primarily measured by determining the difference in the spectroscopic spectra of the functional groups, which quickly and directly identified the sample’s chemical composition [
22], allowing the measurement and evaluation of the effects of different processes on the sample. The images (
Figure A3) of the umami-rich seasoning powders showed no significant difference in appearance between the various run conditions. These results were in agreement with those of the color analysis, albeit with significant differences in the results of the precision instrumentation, where such differences were not discerned visually. In addition, the microstructure images were taken by dynamic optical microscopy (confocal), and the microstructure profile of the umami-rich seasoning powder emerged more clearly. The results demonstrated that the microstructures of runs 1, 2, 4, 5, 6, 7, and 8 were not round, indicating that the umami-rich seasoning powder formation was not unsatisfactory (
Figure 1). However, the other run conditions (3, 9, 10, 11, 12, 13, and 15) exhibited a rounded morphological structure, which failed the quality index (moisture content). However, all the samples in this study were observed to be single spherical particles agglomerated with smooth crystalline surfaces. According to Saavedra-Leos et al. [
25], the inlet temperature affects the microstructure and morphology of particles. Hence, the variation in particle size and morphology may be attributed to the different processing conditions used in the spray-drying process. In contrast, run 14 had bright-yellow powder pellets and a round microstructure. Consequently, this serves as the optimum bulk production condition for umami-rich seasoning powder in this study.
The FTIR measurements of 15 run conditions of umami-rich seasoning powders showed no significant difference in the functional chemical composition of the powders obtained under each condition (
Figure 2). The initial vibrational regions of all samples were observed in the 3600–3000 cm
−1 from the FTIR spectra. These were attributed to the characteristic stretching vibrations of the -OH group of carbohydrates, water, and organic acids. The results of this study agree with those of Matwijczuk et al. [
22] and L. Svečnjak, D. Bubalo, G. Baranović, and H. Novosel [
54]. Łopusiewicz et al. [
53] and Matwijczuk et al. [
22] also reported that the vibration at 3300–3200 cm
−1, which belongs to the irregular absorption of carboxylic acid (with a wide -OH band) while enhancing the stretching vibration of the C-H group and the wide band of vibration, is due to the strong hydrogen bonding of carboxylic acid dimer [
55]. The regions of 3000–2800 cm
−1 were characterized by stretching vibrations of the C-H groups. From 1500–1200 cm
−1, the bands were dominated by the deformation vibrations of the O-CH and C-C-H groups in the carbohydrate structure and by the deformation vibrations belonging to the δ-OH group in the C-OH structure [
33]. The range from 1200–800 cm
−1 contains the stretching vibrations of the C-H group or (C-O) in the carbohydrate structure, while there are also C-O stretching vibrations of the C-OH group or C-C stretching vibrations in the carbohydrate structure [
22,
56]. Additionally, the spectral region 900–700 cm
−1 represents anomalous regional vibrations or C-H and C-C deformations of carbohydrates, which implies relative changes in sugar bonding [
57]. Thus, FTIR technology serves as a structural profiling of the chemical functional groups of samples to determine the variation [
22,
33].
3.4. Sensory Evaluation
Sensory evaluation includes the assessment of the odor, flavor, taste, texture, and appearance of food [
58]. The samples for the sensory evaluation were umami-rich seasoning powder and two commercially available products, which were evaluated and analyzed statistically (
Table 4). The appearance (color) score was the highest for commercially available product 2 (8.07), followed by the umami-rich seasoning powder (7.67), and then the lowest for commercially available product 1 (7.07), which was significantly different (
p < 0.05). Flavor (odor) showed no significant difference, with umami-rich seasoning powder (7.33) being the highest, followed by commercially available products 2 (7.20), and with 1 (7.13) being the lowest. The highest score for umami was obtained for commercially available product 2 (7.80), followed by umami-rich seasoning powder (7.53) and product 1 (7.00), with no significant difference. The sweetness scores were highest for umami-rich seasoning powder (7.40), followed by commercially available product 2 (7.07), and then lowest for product 1 (6.87), with a significant difference (
p < 0.05). Therefore, the results were attributed to the use of maltodextrin as the powder carrier in this study, which provided significant sweetness. The highest score for saltiness was umami-rich seasoning powder (7.60), followed by commercially available product 2 (7.53) and product 1 (6.73), with no significant difference. However, the source of sodium in all samples was associated with fish soup stocks. In the case of mouthfeel, commercially available product 2 (7.53) was the highest, followed by umami-rich seasoning powder (7.47), and with product 1 (6.40) being the lowest, with no significant difference. The overall acceptance ratings were highest for umami-rich seasoning powder (7.53), followed by commercially available product 2 (7.47), and then lowest for product 1 (6.73), with no significant difference. Altogether, the sensory evaluation showed that the umami-rich seasoning powder was sufficient to raise interest in consuming natural ingredients. It also confirmed the excellent commercial value of tilapia offcut soup stock and pelletizing by spray drying, which minimizes the cost of raw materials while providing additional economic benefits, especially in large-scale production. Recently, a few studies have shown that consumers prefer more “natural” foods with ingredients whose “chemical-sounding names” (as described above for umami flavor) may lead to less recognition of the naturalness of the umami-rich seasoning powder in the study [
59,
60]. However, compared to popular enzymatic hydrolysis processes, in this study, the raw material had more natural attributes (no bitterness masking), which provides the potential to be part of the flavoring in the human diet.