Effects of onion peel extract on bioactive components, textural and sensory characteristics of chickpea‐based fried snack

Onion peel waste is generated in huge amount during processing. This waste is a huge source of antioxidants specially quercetin. Therefore, it can be utilized to increase the phenolic and flavonoid content of food products. The present study proposed the use of different onion peel extracts (OPE) in a South Asian snack called “sew.” Sew is a cold‐extruded rod‐shaped snack made from chickpea flour and spices. After extrusion, it is deep fried till appearance of golden‐brown color. The polyphenols from onion peels were extracted in (a) EWE (ethanol and water‐based) medium, (b) EAAE (ethanol and acetic acid‐based) medium, and (c) WE (water extract). These three OPEs were separately sprayed over chickpea grits before making flours, which were then used for making sew. Antioxidant activity of EWE, EAAE, and WE extracts were found to be 59.06%, 36.85%, and 28.07%, respectively, and both gram‐positive and gram‐negative bacteria were inhibited by these three extracts. Addition of OPE led to a significant increase in antioxidant activity of snack (sew), and panelists were unable to perceive any statistical difference in control and extract added snacks in terms of sensory attributes. Interestingly, marked improvement was observed in textural characteristics (measured objectively) of snacks containing extracts and the percent decline in hardness as observed in EAAE, EWE, and WE containing fried snacks were found to be 56.83%, 37.95%, and 34.55%, respectively, after 60 day's storage, whereas 71.28% decline was recorded for control snack. Thus, incorporation of OPE proved to be an innovative method to improve the nutraceutical profile of chickpea‐based fried snack.

served as a functional food after being fortified with nutritive ingredients. Several attempts have been made in order to enhance the functional and nutritional characteristics of snacks by partial or complete incorporation of bioactive components (Ainsworth et al., 2007;Ajila et al., 2008). Fortification with natural antioxidants is gaining special attention in improving food functionality (Keskin et al., 2022). Ever since, many scientific evidences indicated the important role of antioxidant against coronary and degenerative diseases. Li et al. (2020) studied the antioxidant and anti-neuroinflammatory capacities of onion phenols and found these ideal for developing functional foods.
Natural polyphenols possess strong antioxidant properties that aid in the prevention of various degenerative chronic diseases like cancer, cardiovascular disorder, and neurodegenerative disorder (Koch, 2019;Potì et al., 2019;Scalbert et al., 2007). Moreover, plant derived polyphenols have also served the role of natural food preservatives (Valenzuela et al., 1991) and are also found to have wide applications as food colorants. Agricultural wastes are rich sources of bioactive components. Waste utilization plays a vital role in minimizing ecological burden. Namir et al. (2017) reported the polyphenol extraction and its incorporation for the development of functional foods. Kumar et al. (2015) and Topkaya and Isik (2019)  Onion is one of the main horticulture crops as well as the main exportable horticulture commodity of Pakistan (Akhtar et al., 2013).
Pakistan is the sixth largest producer of onion accounting 1.8 million tons production per annum (Khokhar, 2014). Currently, the onion waste is difficult to handle, and it cannot be used even in fodder due to its objectionable aroma. Fortunately, onion waste is rich in some of the dietary ingredients such as fiber (principally the nonsoluble type) and phenolic compounds such as quercetin and other flavonoids (Ali et al., 2020;Segundo et al., 2022).
The aim of the present study was to utilize bio waste, that is, onion peels, and prepare extracts in different solvents followed by evaluation of its nutraceutical and antibacterial property. The extract prepared was then added into a deep fried product (snack), popularly known as "sew" in the Indian subcontinent. Sew is basically a savory food made from chickpea flour added with spices and seasonings.
Water is added to flour to turn it into a thick batter. This batter was then cold extruded using manual extruder and deep fried in hot oil.
Fried sew appears cylindrical in shape with crispy texture.

| MATERIALS AND METHODS
Onion peels of Sariab variety were collected from local market of Karachi in March 2020, Pakistan. All chemicals used in the present study were reagent grade. Chickpea, red chili, salt, and fresh lemons were purchased from the local market.

| Preparation of onion peels
Onion peels were washed with tap water followed by drying in oven at 45 C. The dried peels were then ground in waring spice grinder.

| Isolation and optimization of polyphenols from dried onion peels
Two hundred grams (200 g) of onion peels were added to 1000-ml beaker containing different mediums/solvents described below for half an hour on shaking water bath at 25 C followed by filtration.

| Determination of TPC
The concentration of total phenols in onion extract (OPE) was analyzed by using micro Folin-Ciocalteu (FC) method (Waterhouse, 2005) using standard curve of Gallic acid. Total phenolic concentration was expressed as Gallic acid equivalent in mg per gram of onion peel (dry basis). All assays were carried out in triplicate.
2.3.2 | Determination of total flavonoid content (TFC) TF content was evaluated by a colorimetric technique used earlier by Özkök et al. (2010). The outcomes were communicated as milligrams of Quercetin equivalent per gram of onion peel (dry basis).

| DPPH radical scavenging activity
The DPPH radical scavenging activity was measured according to the method of Marinova and Batchvarov (2011) with some modifications.
Aliquots of 4 ml of 0.6-mM DPPH ethanolic solution was mixed with 1 ml of the extract. The mixture was vigorously shaken and left to stand for 30 min under subdued light. The absorbance was measured at 517 nm. The DPPH radical scavenging activity (%) was calculated by the following equation: where A sample is the absorbance in the presence of sample and A control is the absorbance in the absence of sample. were incubated at 37 C until turbidity of 0.5 (1.5 Â 10 8 CFU/ml)

| Determination of antibacterial activity
Mcfarland index was achieved. After incubation, the tubes were checked for bacterial growth in terms of bacterial turbidity.

| Polyphenol rich chickpea flour preparation
The chickpea were coarsely ground into grits. Chickpea grits (2500 g) were mixed with 375 ml of WE, EWE, and EAAE, separately. Then the grits were sun dried followed by oven drying using convection oven (Model 9010-0078, Binder GmbH, Germany) at 40 C for 24 h to evaporate the solvents and the bioactive components mainly polyphenols get adsorbed into the grits. After complete removal of solvents, the grits were converted into fine flour by using Perten laboratory mill (Model 3100, Perten Instruments, Sweden). The fine chickpea flour was then used to prepare sew by using cold extrusion technique.

| Sew (snack) preparation
Chickpea flour (200 g) was mixed with 5.5-g red chili powder, 5-g iodized sodium chloride, 6-ml fresh lemon juice, and 105-ml water to form a thick batter followed by cold extrusion. The extruded ropes (3 mm) diameter of flour were deep fried in hot oil at 180 C. It was then cooled to room temperature and packed to a laminated pouch followed by heat sealing. The laminated pouch was composed of three layers. The inner and outer layers were made of PE whereas the middle layer was composed of aluminum, so as to provide a hermetic seal.

| Sew extract (SE) preparation for chemical analysis
Sew were dried at 40 C for 24 h followed by grinding to a fine powder using commercial waring spice grinder (WSG60, Waring Commercial, USA).
whereas R0 is the reading taken at zero day and R60 was taken on extract made from snacks stored for 60 days at room temperature in a laminated pouch.

| Textural analysis of sew
Texture was determined using the method of Kumar et al. (2015) with some modifications. Sew were placed in 3.5 cm inside diameter plastic cum, and hardness of sew was measured using 5-mm diameter cylindrical probe at a preloaded speed of 10 mm/min using Universal Testing Machine (Zwick/Roell, GmbH and Co, D-89079 Ulm). The post penetration speed was changed to 5 mm/s. The F max required to break the rope was measured for different samples of sew at 0, 7, 30, and 60 days of storage to monitor reduction in hardness (shelf life). For 0 day analysis, fresh samples were prepared and presented before each panelist in a random order. Plain water was given to the panelists for mouth rinsing between the samples testing. The snack was scored in terms of color, texture, appearance, taste, smell, and overall liking of deep fried snack.

| Statistical analysis
All experiments were performed in triplicate. The obtained results were analyzed through ANOVA, t test, and Duncan's multiple range test at significance level of p < 0.05 using SPSS Software (Version 17.0. Inc., Chicago, USA).

| Phenolic content in onion extracts
In the present study, the extracts of OPE were evaluated for TPC.

| TFC
The OPE were also used for analyzing TFC and for comparing the most effective medium for extraction (Table 1). The TFC was found within the range of 9.10 to 12.53 mg/g. The maximum yield of flavonoids were observed in aqueous ethanolic extracts EWE (12.53 mg/g) and were statistically different from EAAE (9.26 mg/g) and WE  Note: All values are mean of triplicate determinations. Means within a column with different superscripts are significantly different at p < 0.05. WE: Water extract prepared from distilled water and onion peels. EWE: Ethanol and water based extract prepared from 70% ethanol and distilled water in 9:1 ratio and onion peels. EAAE: Ethanol and acetic acid based extract prepared from 70% ethanol and 0.1-N acetic acid in 9:1 ratio and onion peels.
findings that onion peels are rich in quercetin, which is known to have excellent antioxidant activity.

| DPPH radical scavenging activity
DPPH radical scavenging activity was measured and presented in

| Effect of onion extract addition on TPC, flavonoid content, and DPPH radical scavenging activity of SEs
Total phenolic and flavonoid contents of sew are shown in Table 3. In the present study, the SEs were analyzed for TPC and it ranged from 7.95 to 12.67 GAE (mg/g). The highest phenolic content was obtained in SE-EWE and the lowest value was observed for the control sample.
TFC in control and sew enriched with three different OPE were found within the range of (8.02 and 15.61) mg/g. The maximum yield of flavonoid content was observed in sew enriched with SE-EWE (15.61 mg/g) and the lowest was found in the controlled sew sample (8.02 mg/g). Control snack sample also exhibited TP and TF content but lower than the enriched sample. The reason behind this is the use of chickpea flour that is also reported to have phenol and flavonoid content (Han & Baik, 2008;Li et al., 2008). The results derived for pure extracts showed elevated level of TP (35.5 mg/g), TF (12.53 mg/g), and DPPH (59.06%) activity in EWE sample. It is evident that the SE-EWE containing snack sample also showed increased content of total polyphenols (TP = 12.67 mg/g) and total flavonoids (15.61 mg/g) in snacks as well.
The DPPH activity and % drop in DPPH activity over prolonged storage of snacks (60 days) at room temperature was analyzed in this study (

| Texture analysis
The texture analysis of sew snacks enriched with onion peel polyphenols (OPP) was analyzed for hardness upon 2 months' storage at room temperature and the obtained results are presented in Table 4. Results showed that at zero day, the highest force required to break the snacks was observed in WE sample (1058.3 g) and then for EWE containing snack (971.3 g). The lowest hardness value was recorded for CE snack (702.7 g). In comparison with the CE sample (702.7 g), the enriched snacks showed the higher values for hardness. Sew snacks enriched with OPP displayed higher hardness values. It might be due to polyphenol and protein interactions that reinforced the structure of snack, thereby increasing the firmness values. It has been reported earlier that significant increase in hardness values were also observed when noodles and cheddar cheese were fortified with polyphenols (Cutrim & Cortez, 2018;Han et al., 2020). The sew samples were also observed for hardness upon storage. It was observed that WE snack sample showed no significant difference in hardness until 1 month, but a significant drop in the hardness after 2 months was observed.
Similarly, the results of EWE sample showed that hardness decreased on seventh day as compared with the zero day but no significant difference was found between the 1 month and 2 months' stored sam-  (Amoako & Awika, 2016). Polyphenols interact with amylose through hydrophobic interactions and also via hydrogen bonding (Ou et al., 2019). These bondings/interactions reduce hydrophilic sites availability on starch and protein for water uptake and that is why a decline in percent hardness was found to be less for polyphenol enriched snack samples as compared with control ones which were devoid of polyphenols.

| Sensory evaluation
Sensory analysis was carried out at 0 day for different enriched sew snacks and the obtained results are presented in Table 5 Note: All values are mean of triplicate determinations. Means within a row with different superscripts are significantly different at p < 0.05. CE-Snack: Control snack sample did not contain onion peel extract. WE-Snack: Snack added with water based onion peel extract prepared from distilled water. EWE-Snack: Snack added with ethanol and water based onion peel extract prepared from 70% ethanol, and distilled water in 9:1 ratio. EAAE-Snack: Snack added with ethanol and acetic acid based onion peel extract prepared from 70% ethanol and 0.1-N acetic acid in 9:1.
T A B L E 5 Sensory evaluation of fresh and stored sew samples The results obtained in the present study indicate that significant changes could be made by the addition of antioxidant rich onion extract to the traditional snack and could be successfully commercialized, although more studies are required to commercialize this product. The above study suggested that onion extract rich snacks may serve as a good alternative for currently existing snack foods in markets as it contains significantly higher amount of polyphenols and antioxidants. The OPE could also be added in other food products to confer health benefits in an economical way and is also an efficient method of waste utilization.

CONFLICT OF INTEREST
There is no conflict of interest between the authors

AUTHOR CONTRIBUTIONS
Nabia Siddiqui conducted lab work in addition to write up of the manuscript. Tahira Mohsin Ali designed the whole study and reviewed the manuscript. Natasha Abbas Butt helped in writing up of the manuscript. Dr. Abid Hasnain supervised the study and helped in acquiring funding for this project.

DATA AVAILABILITY STATEMENT
None.