Nutritional characterization and food value addition properties of dehydrated spinach powder

Abstract This study aimed at investigating the physicochemical and bread‐making features of dehydrated spinach. Physicochemical composition of spinach powder was compared with wheat flour and the effect of spinach powder supplementation on the nutritional composition, dough rheology, and quality attributes of chapatti were assessed. The results suggested spinach powder to be holding 8.2% crude fiber, 19.2% protein, 1,304 mg/100g calcium, and 40.4 mg/100g iron. Spinach powder indicated significantly increased values for hygroscopicity, swelling power, and water solubility index values, that is, 6.4%, 7.1 g/g, and 4.2%, respectively, when compared with wheat flour. Supplementation of spinach powder in wheat flour at 20% substitution level significantly reduced dough development properties including water absorption, dough stability, and peak dough development time. Color measurements of baked chapatti indicated a significant reduction in L*, a*, and chroma values with increasing the level of spinach powder supplementation; however, sensory profiling confirmed that supplementation of spinach powder at 7.5% had an optimum effect on the overall acceptability of the baked product. The results further suggested that replacing wheat flour with spinach powder (5%–7.5%, w/w) in baked products could be a viable dietary approach to enhance the optimum supply of micronutrients and to combat micronutrient deficiencies among various population segments.

also contain exceptionally higher amounts of phylloquinone that serves as a remedy to bleeding disorders (Edelman & Colt, 2016).
World Health Organization (WHO) estimated 190 million preschool children to be the victims of deficiency of one or more micronutrients including vitamin A and iron (Paul et al., 2017). Available information suggests increased production of food crops as a means to bridge up inherent nutritional inadequacies and losses. In addition to food fortification, dietary diversification serves as a sustainable approach to subside micronutrient malnutrition and related health challenges (Lindsay et al., 2006). Staple food crops and the products made thereof are recommended as potential means to mitigate micronutrient deficiencies in developing world (Khan et al., 2015).
Together with an array of bioactive compounds, spinach is regarded as a source of essential nutrients that may help in preventing a variety of nutritional disorders. Cereals based bakery products are the most common, viable, and acceptable consumable goods in various cultures. Sufficient literature demonstrates the application of vegetables as natural additives to improve nutritional and functional properties of baked goods, for example, carrot pomace-based bread and cakes (Kumar & Kumar, 2012), flaxseed powder-based muffins (Sudha et al., 2010), fenugreek flour-based biscuits (Hooda & Jood, 2005), and lotus seed flour-based cookies (Shahzad et al., 2020).  (Malik et al., 2016).

A significant upsurge in nutritional inadequacies and associated
health challenges necessitates the development of recipes and food formulations exploiting nonconventional functional ingredients. The present study aimed to investigate and evaluate the potential for supplementation of spinach powder in wheat flour and its effect on textural and sensory properties to chapattis made thereof. The study further highlights various functional properties and nutritional significance of the vegetable powder supplemented chapattis suggesting wheat flour value addition a viable approach to mitigating food and nutritional insecurity among regional folk.

| Raw materials and chemicals
Fresh whole spinach leaves (20 kg) and whole wheat flour (20 kg) were procured from the vegetable and grain markets of Multan, Pakistan, respectively. All the chemicals and reagents used in the physicochemical analysis were of analytical grade and procured from Merck and Sigma Chemical Co., Ltd. unless otherwise mentioned in this study.

| Preparation of spinach powder (SP)
Fresh leaves of spinach were subjected to preliminary operations such as sorting, grading, washing, and dirt removal. Leaves were dipped in 40 ppm sodium hypochlorite (NaOCl 3 ) solution for 30 min.
Residues of sodium hypochlorite were removed by subsequent washing of shredded spinach leaves with potable water. Drying of processed spinach leaves was carried out to 15%-17% moisture contents in a cabinet dryer (PAKFVS-40T) at 45 ± 2°C. Dehydrated leaves were ground to 72 mm mesh size in a heavy-duty grinder.
Spinach powder thus obtained was packed in airtight polyethylene bags and stored at 4-6 ± 2°C for further experimentation (Galla et al., 2017).

| Bulk density (BD)
Spinach powder and wheat flour samples were evaluated for bulk density by the method followed by Jan et al. (2015). Briefly, 100g of each sample was poured into the tarred graduated cylinders (500 ml). The cylinder was tapped twice to fill any of the remaining space for homogeneity. BD was estimated using the following formula:

| Rehydration Ratio (RR)
The rehydration ratio was determined by the method followed by Shaari et al. (2018). Five grams of each sample was soaked into 50 ml distilled water for 60 min at room temperature. Soaked samples were filtered using Whatman filter paper No. 41, and permeate was weighed. Samples' ability to absorb water or rehydrate upon soaking was measured using the following formula:

| Water absorption capacity (WAC)
The water absorption capacity of the samples was estimated following the method followed by Shafi et al. (2016). One gram of each sample was mixed in 10 ml of distilled water, and the mixture was subjected to incubation of 30 min. Thereafter, each sample was centrifuged (Hermle Z236K) at 2000 rpm for 10 min. The supernatant was decanted, and residues were inverted onto the filter paper to Bulk Density (g∕ml) = Sample weight (g) ∕ Volumeoccupied by sample (ml) .
Rehydration ratio = Weight of drained material (g) ÷ Weight of dried residues (g) . allow water to be released for 5 min. WAC was estimated by weighing the residues and represented as the percentage of water absorbed per gram of the sample.

| Water solubility index (WSI)
The water solubility index was determined by following the method of Asaduzzaman et al. (2013). One gram of each sample was thoroughly mixed with 10 ml distilled water. The mixture was centrifuged (Hermle Z236K) for 30 min at 4,000 rpm. The supernatant thus obtained was oven-dried (Memmert) at 70 ± 5°C till the constant weight. Dried samples were cooled in the desiccator and weighed.
WSI was calculated by the following formula: W = Dried sample weight; W1 = Weight of petri dish and dried liquid; W2 = Weight of empty petri dish.

| Swelling power (S P )
Swelling power was determined by the method outlined by Shafi et al. (2016). Samples weighing 0.5 g each were dispersed in 50 ml distilled water. The mixture was heated for 30 min at 90°C.
Centrifugation of the homogenate was performed at 3,000 rpm for 15 min. Thereafter, the supernatant was decanted and oven-dried (Memmert) at 100 ± 5°C till constant weight. Results for S P were represented in g/g of the dried sample.

| Hygroscopicity assay
Hygroscopicity values of the samples were determined by the method of Jaya and Das (2004). Each sample (10 g) was added to a petri dish and shifted to a desiccator containing sodium sulfate (Na 2 SO 4 ) maintaining saturation level with approx. 81% relative humidity for one week. Results were calculated by determining differences in weight and expressed as g of moisture absorbed per 100g of the dry matter (g/100g) using the formula as mentioned below: Where ∆m shows the increase of powder's weight at equilibrium (g), m is the primary mass of the powder (g), where m 1 is the water-free moisture of powder before exposure to external air humidity (g/100 g).  , and carbohydrate contents of all samples were determined using the following formula: carbohydrates (%) = 100 -(moisture %+ ash% + protein%+ fat %+ fiber%) (Latimer, 2019). Mineral contents were estimated using atomic absorption spectrophotometer (Thermo Scientific iCE 3,000 series) and flame photometer (410, Sherwood Scientific Ltd-UK) (Latimer, 2019). Caloric contents of the samples were calculated by using the following formula:

| Preparation of chapattis premixes
Whole wheat flour chapattis premixes were prepared by supplementing with spinach powder at 0%-20% and were stored in airtight polyethylene bags until final preparation.

| Rheological measurements of chapattis premixes
Farinographic study was conducted and samples, that is, wheat flour and spinach powder supplemented premixes, were analyzed for water absorption, dough stability time, and dough development time by using the Brabender ® Farinograph (Brabender GmbH and Co. KG) (Mehfooz et al., 2018). AACC (2000) method 54-40 was followed to determine mixographic measurements, that is, peak height and the peak time of wheat flour-spinach powder preblends using Brabender ® Mixograph (National Mfg. Co).

| Preparation of chapattis
Wheat flour and spinach powder premixes were mixed in an optimum amount of water for developing composite chapattis. The dough was divided manually into dough balls each weighing 50 g. Dough balls were allowed to rest for 20 min and sheeted into 150 mm diameter chapattis with a roller pin. Chapattis were baked at 225 ± 5°C for 1.5-2.5 min (Kundu et al., 2019).
using a stainless steel scale following the method documented by Rao et al. (1986).

| Sensory evaluation of supplemented chapattis
Sensory evaluation of spinach powder supplemented chapattis was conducted by a panel of experts on the 9-Point Hedonic Scale using sensory acceptability scale from 1-dislike extremely, to 9-like extremely.
Chapattis prepared from flour without spinach powder (control) and spinach powder were evaluated for physical appearance, color, taste, texture, folding ability, and overall acceptability (Pathania et al., 2017).

| Statistical analysis
Each experiment was replicated twice, and means computed were presented as means ± S.D. Data collected from analyses of spinach powder, whole wheat flour, and spinach powder supplemented chapattis were statistically analyzed using the analysis of variance (ANOVA) technique on Statistics 8.1 (Tallahassee, FL). The level of significance among the means was analyzed by the least significance difference (LSD) at a 5% confidence interval (Steel et al., 1997).

| Functional properties of the dehydrated spinach and wheat flour
A comparison was made between the functional properties of wheat flour and spinach powder to elucidate spinach powder ability to be considered as a natural candidate for wheat flour enrichment. The results suggest significantly higher values for hygroscopicity (6.4%), swelling power (7.1 g/g), and water solubility index (4.2%) concerning spinach powder in comparison to the wheat flour (Table 1). Spinach powder holds higher swelling power and water solubility due to the presence of carbohydrates and higher amounts of dietary fibers. Earlier, a study by David et al. (2015) reported swelling power as an important functional property of starches and proteins from flours of various origins.
Increased swelling power and water solubility index (WSI) have also been attributed to higher starch contents (Shafi et al., 2016). Our results were similar for swelling power (7.95 g/g) for chestnut flour (Shafi et al., 2016). Spinach powder was found to carry 120% higher protein contents than wheat flour that might have anticipated improved hygroscopicity, SP, and WSI as compared with wheat flour.

| Effect of spinach powder supplementation on rheological properties of chapattis premixes
Rheological properties of composite flour were evaluated to assess the impact of spinach powder supplementation on functional properties of dough. A significant decrease (p < .05) in water absorption, that is, from 63% to 55% and dough stability from 13.21 min to 10.67 min was noticed at 0% -20% spinach powder supplementation level. However, a significant increase in peak height was recorded, that is, from 48.59BU to 66.39BU at 20% supplementation of spinach powder (Table 2)

| Nutritional composition of dehydrated spinach and value-added product
Spinach powder dried to moisture contents at ~8% was shown to carry a considerable amount of fiber (8.2%), ash (2.9%), and protein (19.2%).
A relatively lower amount of fiber, ash, and protein contents, that is, 2.4%, 0.2%, and 8.6%, respectively, were recorded for wheat flour (Table 3). Increased variability was recorded for protein (21%-32%) and   (Table 3). The results suggested significant improvement in protein, ash, and fiber contents of composite chapattis with values ranging from 8.0% to 9.3%, 0.3 to 0.9%, and 2.4 to 4.1%, respectively. A significant increase (p < .05) in protein, ash, and fiber contents of wheat-spinach composite chapattis might be ascribed to spinach powder supplementation which had itself delivered higher amounts of these constituents (Table 3). A notable decrease in moisture contents of spinach powder supplemented chapattis was also noted which hinted at the lower water holding capacity of the spinach powder to be the reason as com- crops like beans to anticipate comparatively higher levels of fiber, ash, and protein in supplemented chapattis, that is, 9.2%-10.2%, 1.6%-2.1%, and 0.4%-0.8%, respectively, while relatively lower values of the aforesaid nutrients were recorded for sorghum supplemented chapattis, that is, 9.0%-9.3%, 1.6%-1.7%, and 0.4%-0.5%.
A significant increase (p < .05) in levels of micro-and macrominerals in composite flour chapattis was observed indicating spinach powder supplementation to be directly associated with improved minerals profile of the final product (Table 4). Wheat flour enrichment with spinach powder (20%) increased K, Ca, and Fe contents of chapattis from 448 to 494 mg/100g, 40 to 301 mg/100g, and 3.3 to 11.6 mg/100g, respectively, and such an elevation in minerals concentration of chapattis is attributed to a better micronutrients profile of spinach powder (

| Effect of spinach powder supplementation on textural properties of chapattis
Color measurements of dried spinach substituted chapattis are presented in Table 5 (Galla et al., 2017;Singh et al., 2015).
Similarly, other studies reported similar findings for b* values in chapattis made with jering seeds flour (Cheng & Bhat, 2015).
Hardness and chewiness of spinach powder supplemented chapattis significantly increased (p < .05) from 22 to 90 g and 67 to 138 g, respectively, with increasing spinach powder supplementation level (Table 5). A study by Singh et al. (2015) re- with jering seed at 0 to 100% substitution level significantly increased hardness in chapattis, that is, 332.4 g to 1627.5 g (Cheng & Bhat, 2015).
Puffing of chapattis is a desirable quality attribute that significantly influences consumers' preference (Wani et al., 2016). Textural profiling of spinach powder supplemented chapattis revealed a significant decline in puffing quality of the baked good and puffing height score declined from 5.45 to 4.03 cm at 0 to 20% supplementation (Table 5). Reduction in chapattis puffing height might be attributed to higher amounts of the dietary fibers and nongluten proteins of spinach powder.
Another study by Khan et al. (2015) reported an organoleptically acceptable sensory score for chapattis developed at 5%spinach powder supplementation.

| CON CLUS IONS
Growing micronutrient deficiencies especially in lower-middleincome countries are a leading cause of increased disease burden. Novel intervention strategies to confront the challenges associated with malnutrition and food insecurities are imperative.
Archetypical consumption of vegetables is now transitioning to novel approaches to foster their enhanced intake. The application of dehydrated vegetables is being widely practiced in a variety of recipes and food preparations. Spinach powder is considered a valuable source of dietary fibers, micronutrients, and bioactive compounds that can ameliorate several nutritional and health disorders. The present investigation confirmed the addition of spinach powder in wheat flour-based baked goods at ~ 10% level of supplementation not to contribute undesirable sensory attributes to unleavened bread, that is, chapattis. Our findings conclude that spinach powder supplementation at 7.5% could be a viable and practical approach to develop value-added baked goods. The results further indicate that the utilization of green leafy vegetables as powder formulae or premixes could help abridge nutritional inadequacies and food insecurities cost-effectively among vulnerable population groups.

ACK N OWLED G M ENT
The authors are very grateful to Pakistan Agricultural Research Council (PARC), Islamabad for financial assistance under Agriculture Linkage Program (ALP)-Project no. AE-037.

CO N FLI C T O F I NTE R E S T
Authors declare to not have any conflict of interest.