1. Introduction
Cakes are the highest consumed bakery products, despite being particular goods, but they are mostly used in festivals and happy celebrations [
1,
2,
3]. Cake is usually manufactured from soft wheat flour (WF), which is deficient in fibers and phytochemicals when processed at higher extraction [
4,
5]. In addition, the amino acids (AAs) profile of WF is deficient in some vital and essential amino acids (EAAs) such as lysine, threonine, and methionine [
6].
Adansonia digitata L. named also “Baobab”, belongs to the Malvaceae family and is a majestic tree revered for its medicinal and nutritional values [
7]. It is tolerant to high temperatures and long spans of drought and is grown for its sour fruit and leaves. Seeds, leaves, roots, flowers, fruit pulp, and bark of
A. digitata are edible and incorporated in various diets [
7,
8,
9]. The fruit consists of pulp and large seeds embedded in a dry acidic pulp, which is incorporated in food preparation and drinks [
10]. The fruit pulp has a very high vitamin C content, almost ten times that of oranges, and contains sugars but no starch. Moreover, the fruit pulp is rich in pectin [
9]. Several parts of this tree have gained much interest for their antioxidant and anti-inflammatory properties, which are frequently included in traditional medicine [
11]. Proximate composition and concentration of minerals in pulp and seed were determined [
12]. Considerable content of fiber, K, Ca, Mg, Na, P, Fe, and Zn was observed. Hyacinthe et al. [
13] confirmed that
A. digitata has valuable content of vitamin B
1, B
2, and minerals. Seeds are a good source of energy, protein, and fat. Amino acid analyses revealed high glutamic and aspartic acid content, with the sulfur-containing amino acids being the most limited amino acid [
9,
14]. The fatty acid profile showed that oleic and linoleic were the major unsaturated fatty acids, whereas palmitic was the major saturated acid [
9]. Hydroxycinnamic acid glycosides, iridoid glycosides, and phenylethanoid glycosides were found to be the main components in Baobab fruit pulp [
15]. HPLC analysis revealed that
A. digitata has appreciable levels of flavonoids and phenolic acids, including catechin, epicatechin, rutin, quercitrin, quercetin, kaempferol, luteolin, gallic, chlorogenic, caffeic, and ellagic acids [
16]. Recently, Sokeng et al. [
17] indicated that the profiling of primary and secondary metabolites of Baobab fruit and leaves addresses the limited knowledge of Baobab’s chemical composition and helps to support and clarify the increasing evidence of its nutritional and biological properties and to provide suggestions on the potential use of Baobab fruit and leaves in food, pharmaceutical, and cosmetic products. In fruit pulp, 46 phytochemicals belonging mainly to proanthocyanidins, phenolic acids, flavonols, and saponins were identified [
18]. The promising potential of Baobab fruit shells (BFSs) as a good source of phenolic compounds that can be used in food and pharmaceutical applications was demonstrated by Ismail et al. [
19].
Metabolic syndrome comprises a group of risk aspects for many pathological circumstances, including hyperglycemia, obesity, hyperlipidemia, and hypertension. The traditional information, taxonomic description, medicinal properties, and important nutritional value of
A. digitata were summarized [
7]. Fruit pulp and leaf extracts of
A. digitata improved the metabolism of carbohydrates and lipids [
16,
20,
21]. Its aqueous extract demonstrated antimetabolic syndrome potential, remarked as weight loss, anti-inflammatory, hypolipidemic, hypoglycaemic, renal, hepatic, and cardio-protective activities [
22,
23] as well as analgesic effect [
24]. Adeoye et al. [
25] confirmed that apigenin and quercetin as secondary metabolites of ethylacetate partitioned fraction of
A. digitata stem bark possess antimalarial activity, in silico. A positive effect of the use of Baobab to alleviate hunger, possibly having a positive effect on the maintenance of weight, was indicated [
26]. Hanafy et al. [
27] found a significant protective effect of
A. digitata extract against hepatotoxicity through amelioration of lipid peroxidation. In rats with predominantly normal myocardial structure and no inflammatory cell infiltration, Baobab pulp flour (as 200 mg per day of BPF) resulted in a cardioprotective effect against induced oxidative stress [
28].
A. digitata is rich in flavonoids with superior antioxidant activity [
29], which may not ultimately limit the bioavailability of carotenoids [
30]. Present minerals and phytochemicals in Baobab root tubers suggest their nutritional and medicinal potential [
31]. The fruit pulp of
A. digitata is rich in procyanidins and flavonol glycosides, with tiliroside as the major constituent which provides a promising source of health-promoting substances [
32]. Adding Baobab seed extract (BSE) to beef patties improved the lipid stability and keeping quality as a result of increasing the antioxidant and antimicrobial activities which extended the shelf-life [
33]. Mixing Baobab milk and fermented Baobab/acha (African grain) flour provided more nutrients than the Baobab or the acha flour alone, which can be incorporated as a nutritious and economic ingredient into diets of the lower-income group [
34].
Due to its current use as emergency food during food shortages and the relatively healthy and stable rejuvenating populations, a recent study showed great potential for Baobab to become an important part of the diet [
35]. Moreover, BPF flour could potentially become an interesting improver and structuring agent for gluten-free products [
36]. However, despite the literature showing great potentialities related to the use of BPF flours, the effects of BPF flour substitutions on dough rheology and cake characteristics need to be carefully examined. Particular attention needs to be paid to the milling process (both for wheat and for BPF) [
37], dough rheology [
4,
5], and final cake characteristics [
4,
5]. Moreover, to the best of the authors’ knowledge, the literature review mainly highlighted the substitution of WF with interesting alternative flours like insects [
38,
39], legumes [
40], and other by-products [
41], but only a few studies considered substitutions with BPF flours, which need further investigation, thus motivating this work. Therefore, this study aimed to investigate the effects of WF substitution with 5%, 10%, and 15% of BPF on the chemical composition, minerals, and amino acids content, total phenolic content (TPC), and antioxidant activity (AOA); rheological parameters of different substituted flour and sensory evaluation of baked cakes were performed as well.
4. Discussion
The cake is considered one of the most widely consumed bakery products in the world, with an estimated global cake market size of USD 42.94 billion in 2019, which is expected to rise at a compound annual growth rate of 3.3% from 2020 to 2027 [
58]. It is well known that cakes are based mainly on WF in manufacturing with various food ingredients.
Interestingly, cakes are essential for celebrating various types of occasions, favored for children, serving consumers with wide age-grouping, used as a snack between diets, or as desserts post meals during dine-out. However, to help customers fulfill their nutritional requirements, food fortification is a helpful and valuable technique [
38,
39,
40,
59]. Fortification is not materializing as one single issue to that purpose, but also coexists for dietary diversification and supplementation approaches. It also provides a relatively easy solution to enrich micronutrient intakes in traditional dietary patterns and ensured that food diversification can be maintained [
60,
61]. Consequently, substitution levels were proposed in this experiment to provide a substantial amount of EAAs, minerals, and even fiber to complement the intake of some deficient nutrients in the cake.
In the current study, incorporating BPF in WF to be used in cake manufacturing increased the macro- and microelements [
12,
30,
62]. Compaoré et al. [
62] confirmed that BPF has a good potential in macro and micronutrient content and valorizing it can effectively be used to fortify staple food, particularly for children, and contribute to eradicate malnutrition due to micronutrients deficiencies. Our results remarked that substituting 5–15% of WF with BPF significantly increased total ash [
63] and fiber content without significant changes in crude protein, available carbohydrates contents, and energy values of prepared flour mixtures. This may be due to the BPF containing considerable amounts of minerals [
63] and fiber [
12,
13,
62], and being a good source of EAAs [
9] and carbohydrates [
63]. Current results in
Table 2 are very close to those of Nour et al. [
64], Osman [
9], and are additionally confirmed by Fagbohun et al. [
63], who indicated that BPF contains 10.2, 7.67, 0.4, 5.7, 12.16, 73.87% and 307.6 kcal g
−1 for moisture, ash, fat, crude fiber, crude protein, carbohydrate, and metabolizable energy.
Regrading to mineral analysis, the results in
Table 3 demonstrate that K and Fe were the most abundant macro- and microelements in BPF when compared with WF, respectively. Na presented low content in BPF and high content in WF. These observations are in accordance with previous studies of Osman [
9], Compaoré et al. [
62], and Adubiaro et al. [
65]. The obtained results demonstrated that BPF-enriched WF in the range of 5–15% could represent modified macro- and microelements profiles with significant increases in Ca, K, P, Mg, Zn, Fe, and Cu content and a significant decrease in Na content to improve the nutritional profile and desired health attributes [
31]. Recently, Debelo et al. [
30] recommended that the incorporation of BPF in the range of 5–15% in composite pearl millet porridges modified the bioaccessibility of carotenoids and produced rich mineral products.
Interestingly, a remarkable incremental trend in TPC and AOA in BPF-enriched WF was observed (
Table 4). This may be due to the rich content of bioactive compounds and phytochemicals in BPF, which was increased with increasing BPF levels. The substitution of WF with BPF into cake flour formulas improved the AOA by more than 50 and 60%, assessed by DPPH and ABTS scavenging assays, respectively. The antioxidant capacity was probably due to the presence of phenolic compounds and ascorbic acid [
16,
18,
32,
63]. The AOA could improve the bakery products’ shelf-life stability and delay oil oxidation, particularly in cake products. These results agree with [
47,
66,
67]. Recently, Debelo et al. [
30] recommended that the incorporation of BPF in the range of 5–15% in composite pearl millet porridges modified the bioaccessibility of carotenoids and produced rich minerals products.
Concerning the amino acid composition, our results showed that the addition of BPF verified a change in the amino acid composition in the prepared composite flour, in particular for EAAs (
Table 5 and
Table 6). Amino acid profile in BPF demonstrated rich EAA and NEAA content, surpassing the WF profile, which made it useful in raising the AA content, as expected according to various studies that confirmed valuable AA content of BPF [
9,
14,
17]. The analyzed AA profile in our study was closely associated that of with Osman [
9], who stated that the sulfur-containing amino acids were present in low content, while the predominant EAAs in
A. digitata were leucine and phenylalanine and predominant NEAAs were glutamic acid and tyrosine in seed and fruit pulp, respectively. Our results noticed that the predominant EAA in
A. digitata pulp flour was leucine and the predominant NEAA was glutamic acid. Similarly, Busson et al. [
14] observed that
A. digitata fruit pulp had the highest glutamic acid content, with lower content of the sulfur-containing amino acids. In the same context, the amino acid content of
A. digitata revealed glutamic acid was the most abundant amino acid, followed by aspartic acid, lysine, leucine, proline, alanine, and valine [
17,
28,
68]. Remarkably, lysine, as the most deficient EAA in WF, was compensated by 5.9, 11.4, and 16.7% when BPF was incorporated at 5%, 10%, and 15%, respectively, as a result of high lysine content in BPF, as previously confirmed [
9,
17,
28].
Interestingly, our results showed that the addition of BPF determined a considerable change in the biological efficiency, EAAI, PER, and requirement index of different age groups, as presented in
Table 6. BCAAs are a group of three essential amino acids: leucine, isoleucine, and valine, which commonly booste muscle building, enhance exercise performance, and reduce fatigue [
69]. The incorporation of BPF increased the BCAA content in a dose-dependent manner, and increasing the substitution level could increase the BCAAs, resulting in a cake with high nutritious and biological value. The best enrichment was noticed in BAA content, such as that of lysine, arginine, and histidine, which associatively increased up to 5.58%, 10.93%, and 15.88% with increasing BPF level. The basic amino acids are highly associated with increasing protein bioactivity [
70] and possess antioxidant and antimicrobial activities [
71].
Similarly, total uncharged polar AAs (glycine, serine, threonine, tyrosine, and cysteine) have shown an increase in a dose-dependent manner. Singh and Sogi [
72] stated that increasing uncharged polar AAs might be responsible for increasing protein solubility. PER is the easiest method of assessing the quality of proteins [
73]. The calculated PER indicated major improvement during adding BPF to WF in a dose-dependent manner, which could improve the biological availability of presented protein content in cakes [
7,
17]. Similarly, incorporating BPF with WF exuded noticeable increases in calculated biological and EAAI values, which may be due to the rich content of EAAs in BPF [
9]. According to WHO, 2007 amino acid requirements, incorporating BPF in cake formulas improved the nutritious value and gradually increased the efficacy of prepared WF + BPF composite mixtures to cover the protein requirements of different age groups.
The Mixolab analysis is a globally standardized test primarily intended to measure the rheological properties of the dough and thereby ensure a smooth manufacturing process and the quality of finished bakery products. The quality of a cereal-based product is appreciated not only through its characteristics of taste and nutrition but also through its physical characteristics. These physical characteristics depend largely on the quantity and functionality of the protein, starch, and enzymes that make up flour [
74]. To measure the combined effect of WF and BPF, the behavior during kneading of WF + BPF dough was subjected to a Mixolab analysis to check the quality and regularity of the flours in a single test [
57]. The incorporation of BPF increased the water absorption capacity, which indicates the quantity of product that can be produced from a given quantity of flour, which is an important economic factor. A gradual increase in water absorption, which was up to 10% in WF + 15% BPF, was possibly due to the rich content of pectin, minerals, fiber, and polysaccharides in BPF [
9,
62,
68]. According to sundry previous publications, the water absorption rate directly affects the amount of profit, the shelf-life of the product, and the smoothness of technological processes during the manufacturing process [
75,
76]. The behavior of dough during kneading helps to ensure that the raw material is compatible with industrial processing. Remarkably, increasing BPF level reduced the stability of dough in dose-dependent manner during kneading. However, the major factors to decrease gluten stability are sugars and pectin in BPF, which cause weaknesses in the gluten network [
74]. Sometimes this change is seen as undesirable, but in our study, this change is somewhat desirable to give the appropriate texture and the ability of the cake to retain gases to reach the appropriate shape and volume [
75]. In our study, WF containing BPF showed curved increases in dough viscosity associated with rising α-amylase activity when BPF was added up to 10%. Subsequently, adding 15% of BPF dramatically affected the α-amylase activity, possibly due to the presence of thermostable proteinaceous α-amylase inhibitors [
77]. The changing in the viscosity of the dough as its temperature increases gives indications about the internal structure of the finished product. Interestingly, the viscosity and stability at 90 °C provide information about the amylase activity, which has an impact on the color of the finished product. Finally, the cooling phase indicates the rate of starch retrogradation, which is a direct relationship with the shelf-life. Concerning viscosity index and retrogradation index, with the highest addition (15%) of BPF, a significant recede was observed in retrogradation index, which relates closely with product properties after production and determines the shelf-life of the product. Indeed, to the best of our knowledge, no work about the thermo-mechanical and rheological parameters of WF substituted with BPF was found, and the most important findings were agreed by Kahraman et al. [
57]. Regardless of changes in gluten index, which modifies the flour mixture for satisfying cake making, the addition of BPF at 5% and 10% to cake product kept all characteristics close to those of the WF cake sample.
Sensory evaluation indicated significant differences between WF cake and WF + BPF cakes in all organoleptic characteristics as a result of substituting with a high level of BPF with distinguished taste. However, no significant changes in all organoleptic parameters could be observed, even a positive improvement in taste using 5% BPF was recorded, and it is encouraging that adding BPF at a low level can enhance some of the organoleptic properties [
33]. Conclusively, 5–10% of BPF did not drastically affect the organoleptic characteristics of WF + BPF cake, even adding 15% was still acceptable, but using high substituting levels will not only affect the organoleptic characteristics slightly but will also influence the rheological properties [
42,
77]. On the contrary, Mounjouenpou et al. [
78] stated that the incorporation of BPF at 20% improved the sensory and nutritional qualities of rice cookies.