Stimulation of ACE inhibitory and improving α‐amylase and α‐glucosidase and antioxidant activities of semi‐prepared and dry soup by incorporating with date kernel powder

Abstract Date kernel as a functional food component has a special importance due to its rich nutritional profile, low price, and ease of access. For this, in this research, the sub‐product was used for formulation of semi‐prepared dry soup (SPDS); the effect of adding 0 (S1 = control), 2 (S2), and 4 (S3) %w/w date kernel powder (DKP) on physicochemical, nutritional, and organoleptic properties and beneficial effects of SPDS samples were evaluated. The results revealed that S2 and S3 samples were different from the control sample in some physicochemical properties so that viscosity increased 1.27 and 1.52 times and a* raised 5.6 and 8.5 times, respectively, while L* decreased 0.94 and 0.88 times and b* reduced 0.92 and 0.8 times, respectively. The nutritional properties of S2 and S3 samples compared with the control sample improved. Also, differences were observed in the beneficial effects of S2 and S3 compared with the control sample as total polyphenol content (TPC) increased 1.06 and 1.11 times, respectively (p < .05); antioxidant activities (AA) of S2 and S3 samples were 8.04 and 6.01 mg/ml and angiotensin‐converting enzyme (ACE) inhibitory activities were measured to be 8.2 and 7.86 mg/ml, respectively; also, α‐amylase and α‐glucosidase inhibitory activities of S2 and S3 samples were observed 4.48% and 5.70%, and 4.59% and 6.36%, respectively. From the organoleptic aspect, S3 had the highest acceptability. Generally, it is concluded that with the addition of DKP (maximally 4%w/w) to SPDS formulation, a functional soup could be produced considering the rich nutritional profile of DKP.

easiest way for receiving nutrients and with increasing workload and not having enough time for most people in the community to prepare this type of product in the food industry, ready-to-eat soups are produced in powder form, it is expected that by using a functional component as a value-added food ingredient, soups with high nutritional and healthful values are prepared and people can receive a major portion of nutrients and healthful components through the consumption of soup.
In recent years, with the introduction of functional foods and increasing consumer awareness of the relationship between health and food consumption, the demand for foods with significant healthgiving effects has increased. Currently, food factories are trying to generate a product with numerous health-giving effects. The healthgiving effects of functional foods are attributed to their healthful bioactive compounds, and date kernel, due to its nutritional and health-giving properties mentioned below, is among the compounds that can be used as a functional food ingredient.
Considering the available literature, most of the studies are devoted to the effect of DKP on bread quality and bakery products and except in one case , functional properties of prepared food products have not been discussed (Almana & Mahmoud, 1994;Bouaziz et al., 2010Bouaziz et al., , 2020Ghasemi et al., 2020;Najjar et al., 2022;Platat et al., 2014Platat et al., , 2015Vinita, 2016). Of course, some researchers evaluated physicochemical and organoleptic properties of non-bakery products rich in DKP or date kernel fiber (Amany et al., 2011;Asghari-pour et al., 2018;Bouaziz, 2020;El Sheikh et al., 2014;Fikry et al., 2019;Wedad & El-Khol, 2018). It should be noted that none of these studies have mentioned the adverse toxicological effects of date kernel powder; however, El Sheikh et al. (2014) have confirmed in vitro cytotoxic activity of roasted date kernels. Also, considering the available literature, no research on the evaluation of the effect of this valuable and cheap functional sub-product on the quality of dry soup has still been undertaken (Abdel-Haleem & Omran, 2014;Niththiya et al., 2014;Olubi et al., 2021;Upadhyay et al., 2017). On the other hand, based on the studies, the highest content of antioxidant compounds in dates is included in their kernels, which encompass phenolic compounds (Wahini, 2016). Also, date kernel has therapeutic effects and high level of dietary fibers which can be a good source for investigating α-amylase and α-glucosidase inhibitory activities. Nevertheless, a large amount of this functional sub-product is wasted in factories producing date by-products. For this reason, in this research, DKP is used as a health-giving food component in catering functional SPDS.
On this basis, the goal of this research was to formulate SPDS based on cereals and DKP and evaluation of its properties from different aspects.

| Preparation of semi-prepared dry soup samples
All required materials were approved by the quality control unit were weighed individually (according to Table 1) for the preparation of SPDS samples. Subsequently, all weighed materials were mixed in a special mixer and transferred to a particular silo for packaging in 75 g laminated bags (three layers of low-density polyethylene foil/ aluminum/low-density polyethylene). Random sampling was carried out from the produced soups, and the relevant tests were performed 7 days after production.
It should be mentioned that since the color of DKP had a great effect on the color of soups, first, the formulation was designed to prepare a control soup sample so that its color would not be substantially affected by the addition of low percentages of DKP.

| Experiments on date kernel powder and soup samples
For preparation of soups, 75 g SPDS was mixed with 1 L cold water and boiled for 20 min at mild temperature. Then, the prepared and cooled soup was poured in a mixer, and the mixed sample (with ambient temperature) was tested.

| Physicochemical properties
Titratable acidity was calculated by titrating the samples with 0.1 N NaOH (Niththiya et al., 2014) and pH was measured by a pH meter (Schott GERATE;Fikry et al., 2019).
Moisture content was evaluated using dry air oven (Fikry et al., 2019).  For calculation of rehydration, 2 g of functional semi-prepared dry soup was mixed with 20 ml distilled water at a fixed speed (100 rpm) and rehydrated in a water bath at a given temperature (45°C) for 10 min; then, samples were filtered, weighed and the relevant factor was calculated (Abdel-Haleem & Omran, 2014).

| Beneficial effects
The total polyphenol content (TPC) was calculated through the Folin-Ciocalteu method and reported in terms of mg gallic acid per 100 g of sample (Fikry et al., 2019). According to the Folin-Ciocalteu procedure, the sample and Folin-Ciocalteu reagent were thoroughly mixed in a volumetric flask. After 3 min, 5 ml of 10% Na2CO3 solution was added, and the mixture was left for 1 h. The absorbance of the mixture was determined at 760 nm by using a spectrophotometer (UV2100). The total concentration of phenolic compounds was determined by comparison with the absorbance of chlorogenic acid as standard.
Antioxidant activity (AA) was measured through the evaluation of free radical scavenging capacity of 2,2-diphenyl−1-picrylhydrazyl (DPPH) and reported in terms of IC 50 (Bouhlali et al., 2015). IC 50 is inhibitory concentration (mg/ml) required for the reduction of DPPH radicals to 50% of its original content and able to inhibit 50% of its activity. The lower IC 50 , the higher antioxidant capacity. The sample was mixed with 0.4 mmol/LDPPH radical in ethanol. The mixture was vigorously shaken and left for 10 min. The absorbance of the mixture was determined at 525 nm with a spectrophotometer (UV2100). The radical scavenging activity was calculated using Equation (2) as follows: (1) Total energy (calories) = (Total fats per 100 g) × 9 + (Total carbohydrates per 100 g) × 4 + (Total proteins per 100 g) × 4.
(2) Inhibition ( % ) = 1 − abs sample ∕ abs control × 100. To measure ACE inhibition, first, 75 g of sachet content was mixed in individual containers with 1 L cold water and boiled gradually by thermal energy for 20 min while stirring; after cooling down to room temperature, it was filtered through Whatman filter paper and the fil- The enzyme inhibition rate expressed as a percentage of inhibition was calculated using Equation (4).

TA B L E 1 Introduction of treatments used in research
C: absorbance of the control (100% enzyme activity). S: absorbance of the tested sample.

| Organoleptic properties
Organoleptic properties of DKP were measured through evaluation of its color, flavor, taste, and odor.
Organoleptic properties such as flavor, odor, oral and non-oral texture (mouthful, pouring, stirring, and spoon able), color, and overall acceptability of soup samples were measured by a 5-point hedonic system. Evaluation levels included (from 1 to 5): 1 = inconsumable or very weak, 2 = unacceptable or weak, 3 = acceptable or average, 4 = satisfactory or good, 5 = very satisfactory or very good

| Statistical analysis
A completely randomized design was used to analyze and evaluate the data obtained from the different experiments. Analysis of variance and comparison of means (three replicates for each experiment) were carried out through SPSS software version 16.0 (Duncan's multiple range test and confidence level of 95%).  (3)
promoted viscosity (p < .05); viscosity of S2 and S3 was 1.27 and 1.52 times higher than control sample, and, in fact, S3 had the highest viscosity.
Reduced moisture content is ascribed to the availability of insoluble cellulose fibers, hemi-cellulose, and lignin in DKP, which, owing to the lack of ability to absorb and hold water, caused the decrease in moisture content of DKP (Al-Farsi & Lee, 2008). Also, hydration (swelling and water retention capacity) characteristics of date kernel dietary fiber have been reported to be lower than fibrex (Shokrollahi & Taghizadeh, 2016). The dwindled moisture content of soup samples enriched with DKP is due to the replacement of DKP with wheat (7% moisture) and barley (5% moisture) as these ingredients possess higher moisture content than DKP (3% moisture).
The viscosity of final product is dependent on the type of raw/ initial material. Abdel-Haleem and Omran (2014) (Elleuch et al., 2011;Figuerola et al., 2005). The ability to absorb water in DKP might be attributed to soluble dietary fiber and protein. Water-soluble polysaccharides of date kernel also own the ability to absorb water and increase viscosity. Because of hydroxyl groups and ability to interact with water molecules through hydrogen bonds and, as a result, increased ability of water holding, the fiber of DKP causes increased viscosity and moisture of enriched product (Bouaziz et al., 2010Najjar et al., 2022).
The results of researches related to the effect of moisture are different based on the formulation of products enriched with DKP.  reported that the increase in DKP leads to the increase in moisture content in muffin samples. Ghasemi et al. (2020) and Platat et al. (2015) expressed no significant change in moisture content of sponge cake and pita bread after elevating the percentage of DKP. However, Asghari-pour et al. (2018) and Vinita (2016)

TA B L E 3
Physicochemical properties of semi-prepared dry soup samples* (mean ± standard deviation) and Taghizadeh (2016) reported an increase in firmness of bread fortified with higher than 2.5% of DKP.

| Soluble, insoluble, and total fibers
In line with our results, the higher fiber content of foods enriched with date kernel powder has been reported (Almana & Mahmoud, 1994;Asghari-pour et al., 2018;Ghasemi et al., 2020;Platat et al., 2015;Vinita, 2016). with the control soup sample shows their calcium content was 1.01 and 1.03 times, the iron content was 1.05 and 1.11 times, the zinc content was 3.2 and 5.2 times and selenium content was 1.16 and 1.28 times higher than those of the control sample, respectively; S3 allocated the highest minerals contents to itself. The sodium content of soup samples dwindled as a consequence of the increase in percentage of DKP (p < .05), while no significant change was observed in potassium and magnesium content (p > .05).

| Minerals
The reason for the increase in calcium, magnesium, iron, zinc, copper, and selenium content in enriched soup samples is the presence of DKP; as it is observed in the compounds of DKP (Table 2), DKP is rich in these minerals, and the availability of these minerals is in this order: copper > selenium > iron > potassium > magnesium > calcium > zinc > sodium. Since the iron level is high in date kernel, the importance of this sub-product in the enrichment of food products feels great. The reason for the low sodium content of enriched soup samples is the reduced level of this mineral in DKP. It should be noted that selenium owns antioxidant capacity and is regarded as an anticancer ingredient; the amount of which depends on the cultivation environment of date (Hamada et al., 2002). Martinez-Ballesta et al. (2010) reported that among minerals of date kernel, potassium, and iron are available in higher amounts. Ghasemi et al. (2020) observed an increase in sodium, zinc, calcium, iron, and potassium content of the sponge cake sample with the increase in the percentage of DKP.

| Antioxidant activity and total polyphenol content
The changes in AA and TPC of soup samples are inserted in Table 5.
AA and TPC of functional soup samples increased through increasing the percentage of DKP (p < .05). By comparing TPC of enriched soup samples (S2 and S3) with the control soup sample, it is observed that their TPC was 1.06 and 1.11 times higher, respectively, and S3 had the highest TPC. AA (IC 50 ) of S2 and S3 was measured to be 8.04 and 6.01 mg/ml, respectively.
One of the reasons for the application of DKP as a functional food ingredient is its great phenolic compounds (Al-Farsi & Lee, 2008); the AA of DKP has been reported to be quite high due to its high phenolic content (Ghnimi et al., 2017;Shams Ardekani et al., 2010).

TA B L E 5 Functional properties of semi-prepared dry soup samples* (mean ± standard deviation)
Characteristics treatment AA (mg/ml) (IC 50 ) TPC (mg GAE/g)
In fact, TPC is the most effective factor in AA. Antioxidant compounds with two or more electron donor groups have higher AA (Simić et al., 2007). There is a strong correlation between AA and TPC as well as flavonoids (Bouhlali et al., 2015). Flavonoids of date kernel include luteolin, quercetin, kaempferol, apigenin, and isorhamnetin (Hinkaew et al., 2021). The presence of carotenoids with AA in date kernel has been reported (Alharbi et al., 2021). It should be mentioned that TPC and AA capacity of date kernel are higher than date paste, and is comparable to that of tea and grape seed (Platat et al., 2014). Some compounds such as gallic acid, vanillic acid, ferulic acid, caffeic acid, p-coumaric acid, syringic acid (Amany et al., 2011;Hinkaew et al., 2021), protocatechuic acid and p-hydroxybenzoic acid (Amany et al., 2011) have been found in the kernel of date varieties. Radfar et al. (2019) detected and measured seven phenolic compounds including chlorogenic acid, caffeic acid, vanillic acid, gallic acid, cinnamic acid, 3,5-DHB, and 2,5-DHB in four varieties of date kernel while they reported cinnamic acid as the most frequent phenolic compound in date kernel extract. Besides, polysaccharides Jiao et al., 2011;Luo et al., 2010) and plant fibers (Hamada et al., 2002) have AAs as well. Ansari and Kumar (2012) reported that soups could be functional enriched foods through replacement of its common ingredients with healthful ingredients; for example, the presence of onion (rich of quercetin) in the formulation of soup samples increases their AA.
Substantial amount of phenolic compounds, mainly flavan-3-ols as well as flavonoids, in the bread having DKP has been reported (Platat et al., 2015). The intensification of AA caused by the increase in TPC of food products enriched with DKP has been reported before (Amany et al., 2011;Asghari-pour et al., 2018;Ghasemi et al., 2020;Platat et al., 2015).

| ACE inhibitory activity
Hypertension is an important factor in cardiovascular diseases and   (Iwaniak et al., 2014); Ferulic acid is a weak ACE inhibitor (Al Shukor et al., 2013). Karakaya, El, Simsek, and Buyukkestelli (2015) confirmed the ACE inhibitory activity in plant product containing seeds and sprouts of lentil, pea, and caseinomacropeptide extracted from whey, and ACE inhibitory activity (37%) of salad dressing containing this plant product was attributed to peptides resulting from hydrolysis of storage proteins by endopeptidases as a result of germination, bioactive peptide glycomacropeptide as well as polyphenol content of dietary plants .  reported that the addition of 5% DKP to muffin did not show any ACE inhibition but the level of 2.5% DKP hydrolysate displayed ACE inhibitory activity (app. 13%, IC 50 = 66 mg/ml); ACE inhibitory activity of the control muffin sample was significantly (app. 36%, IC 50 = 28 mg/ml) higher than samples containing DKP. Patten et al. (2012) found that ACE inhibitory activity was directly related to TPC and that the processed form of dietary plants showed a wider capacity to regulate the renin-angiotensin system in vitro. Godos et al. (2017) confirmed ACE inhibitory activity by phenolic acids. Hung et al. (2020) reported the highest ACE inhibitory activity in the extracts of different types of bitter watermelon to be 15.8 mg/ml and concluded that with increasing TPC and peptides and triterpenoids in bitter watermelon extract, ACE inhibitory activity intensified.  confirmed that protein hydrolysates of date kernel can be used to inhibit ACE activity; IC 50 values of these hydrolysates were much higher than captopril (a synthetic drug that inhibits ACE).   Fratianni et al. (2021) did not find any correlation between the content of total polyphenols and the α-glycosidase inhibition in honey.

| α-
Also, the inhibitory effect of flavonoids on key enzymes linked to type 2 diabetes, α-amylase, and α-glucosidase has been demonstrated (Kim et al., 2000;Laoufi et al., 2017;Ng et al., 2015;Tadera et al., 2006;Williams, 2013). In general, the weak inhibitory activity of α-amylase and α-glucosidase in the soups could be attributed to their low polyphenolic content. α-amylase and α-glucosidase inhibitory activities were measured 34.57% and 19.9% for DKP, respectively (Table 1). Table 6 shows the changes in the scores of organoleptic properties of soup samples. The scores of organoleptic properties (except color) of soup samples increased through increasing the percentage of DKP (p < .05). While the highest scores of organoleptic properties (except color) allocated to S3 sample, the highest score of color property belonged to S2 and the lowest score of color property to S3. Date kernel could be used as a food component to improve the sensory properties of food products, and the decrease in water activity affects product stability (Bouaziz et al., 2010). In this re- well; It should be noted that the color darkness caused by DKP may be desirable or undesirable depending on the product type (Almana & Mahmoud, 1994;Amany et al., 2011;Ghasemi et al., 2020;Halaby et al., 2014;Shokrollahi & Taghizadeh, 2016;Vinita, 2016). Finally, the results of this study hint that DKP can be used as a cheap natural source for the production of functional foods such as SPDS based on cereals due to their valuable and functional compounds. For this purpose, the utmost amount of DKP for functional soup production is suggested to be 4% as the color change in products with higher than this threshold amount of DKP is unpleasant;

| CON CLUS IONS
besides, a high level of incorporation causes astringent taste and flavor. It is proposed that dark food products such as meat products, confectionery, chocolates, bakery products, cream-filled of cakes and biscuits especially biscuits with cocoa and coffee flavors are the best choices for fortification with DKP.

ACK N OWLED G EM ENTS
There is no person or organization to thank for doing the present research.

FU N D I N G I N FO R M ATI O N
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

CO N FLI C T O F I NTE R E S T
The authors declare that there is no conflict of interest.

TA B L E 6
Organoleptic properties of semi-prepared dry soup samples* (mean ± standard deviation)

DATA AVA I L A B I L I T Y S TAT E M E N T
The authors declare that data supporting the findings of this study are available within the article.

PA RTI C I PA NT S
The manuscript does not contain experiments using animals or human studies.