1. Introduction
In the Andean region, several crops have been improved by local farmers for centuries. However, they may yet be considered neglected and underutilized species (NUS). At present, they are subjected to a gradual loss of genetic variability or even verging extinction because of their reduced demand and the competition of readily marketable crops [
1]. Potentially, they may contribute to regional food security while providing a wide range of functional elements for healthy diets [
2,
3]. For a long time, these crops have been almost ignored. However, more recently, new interest appeared for being highly nutritious and sources of functional compounds [
4,
5,
6]. Furthermore, they constitute essential components of farm agrobiodiversity, playing a significant role by increasing food security and yield stability either by reducing pests’ impact [
7] or by providing nutrients to soils, e.g., N
2-fixing legumes [
8].
Among these NUS, the ahipa (Pachyrhizus ahipa [Wedd.] Parodi) is a legume with a tuberous root that has been used from the time of the Incas and is still cultivated locally in small areas in Southern Bolivia [
9]. The species provides valuable starch for food or industrial applications such as gluten-free bread or cookies and food additives [
10,
11,
12,
13,
14]. The available ahipa landraces have shown competitive yield figures for Mediterranean irrigation agriculture compared to traditional starch sources, e.g., potato (
Solanum tuberosum L.) and sugar-beet (
Beta vulgaris L. subsp.
vulgaris Cultivar group Altissima Group) [
15]. The ahipa roots might also provide essential amino acids, vitamins, sugars, minerals, and antioxidants with a low content of anti-nutrients (phytic acid, oxalate, tannins) [
15,
16]. In a previous study, Forsyth and Shewry [
10] did not find storage proteins in ahipa roots but proteins related to tuber metabolism and growth. Recently, root proteins have been characterized, and their possible food applications have been suggested because their chemical properties as highly digestible components for gluten-free foods or even as emulsifiers for dressings [
17].
Attempts to increase the crop dry matter yield have led to interspecific hybridization experiments involving the lowland South American species P. tuberosus (Lam.) Spreng., a related species complex holding higher dry matter contents in their roots [
18]. It should be stressed that the Chuin materials are the only cultivar group within the P. tuberosus complex known to possess this trait [
19]. Breeding could improve crop competitiveness even further by delivering cultivars with desirable agronomic traits, e.g., reduced flowering, shorter cycles, and mono-tuberous roots. At present, ahipa may be an attractive food to complement other traditional sources, which might be defective in some functional elements. In this report, we looked at the content of energy sources (starch, sugars, and organic acids), as well as macro- and micronutrients, and extended the analysis of structural compounds such as protein amino acids.
4. Discussion
The interspecific hybrid showed higher root weight and a superior dry matter content compared to the different ahipa accessions. Interestingly, its sugar content was lower than in the ahipa accessions, but starch accumulation did not show significant differences between genotypes.
The hybridization of ahipa with a Chuin genotype of
P. tuberosus proved to be a successful way of increasing root dry matter content in the ahipa species, as previously reported [
18]. Although root dry matter content in the hybrid was significantly higher than in the evaluated ahipa accessions, other reports found significantly greater dry matter values in progenies of interspecific crossings [
27]. In X207, root dry matter content was somewhat similar to the dry matter content of Chuin genotypes reported by Grüneberg et al. [
28]. Interestingly, some ahipa accessions and the hybrid produced a significant high root yield, despite not performing flower pruning. Starch contents in
P. ahipa and X207 were higher than reported values of 9.1% for the cultivated
Pachyrhizus relative,
P. erosus (L.) Urb., or Mexican yam bean [
29], species widely distributed and cultivated mainly in Central America and Southeast Asia [
9]. The amylose content in X207 was higher than the amylose content in ahipas, but still it was significantly lower than in jicama (
P. erosus) (approximately 24%) [
30] or other root crops such as cassava (
Manihot esculenta Crantz) [
31]. Thus, amylopectin, the main component of the stored starch in ahipas and X207, may provide interesting applications from the food to plastic industry [
13,
32].
Root sugars, which provide the characteristic sweet flavor of ahipa, were at a lower concentration in X207 (
Table 2). The most popular use of ahipa roots is either as a fruit [
33] or as fresh juice in urban markets consumed as a folk medicine [
34]. Roots may supply from 8.8 ± 2.6 (X207) to 10.6 ± 2.1 (mean among ahipa accessions) mg of ascorbate in 100 g fresh weight, a concentration in the range provided by yambean or potato [
29,
35]. Malate and citrate contents (
Table 3) reached values similar to other root or tuber crops [
3,
36].
Protein contents in the
Pachyrhizus roots (
Table 4) were significantly higher than in other roots crops used for human consumption as dietary energy sources [
37]. The protein content in roots was not remarkably high. However, it was among values found in other root and tuber crops cultivated in the Andean region such as potato, racacha (
Arracacia xanthorrhiza Bancr), yacón (
Smallanthus sonchifolius (Poepp.) H.Rob.), cassava, or achira (
Canna indica L.) [
2,
4,
10,
36]. For a human diet, the supply and composition of essential amino acids are deficient in sulfuric amino acids and tryptophan (
Table 4 and
Table 5). Hence, the necessary essential amino acids may be acquired from other plant or animal sources [
38]. In both ahipa and the X207 hybrid, the primary amino acid found in proteins was aspartate (
Table 4), as it was also reported in proteins isolated from market-purchased ahipa roots, which makes protein acidic and diverse from most plant proteins [
17]. The relatively high concentration of free amino acids provided by fresh roots (
Table 8), where the amide asparagine was predominant, followed by the amino acids glutamate and arginine (
Table 6), deserve to studied for their nutritional and functional values. The role of non-essential amino acids in humans is a matter of interest for improving health, such as arginine as immuno-stimulant [
39] or asparagine and its role in avoiding apoptosis when cellular glutamine deficiency is induced by human tumors [
40].
Mineral contents in roots are good sources for macro- and micronutrients (
Table 7), comparable to potato or other Andean root and tuber crops [
3,
36]. However, whereas most mineral contents are similar to those found in potato [
36], ahipas (and especially the hybrid) might provide a significantly higher amount of Mn, which might be required in diets based on processed foods [
41].
From an agronomic perspective, the interspecific hybrid X207 and a few of the ahipa accessions assessed in this study may indeed provide economic root yields if cultivated extensively without requiring the labor-intensive field operation of flower pruning [
42]. In addition, the dry matter yield obtained from X207 roots is similar to that of potatoes, and it may approach the DM content of other root and tuber crops, cassava, and sweet potato (
Ipomoea batatas (L.) Lam.) [
43], after selection and appropriate management [
15].
The tuberous roots of this genus provide a valuable food source to compensate for nutritional imbalances in the diet in different regions of the world [
34,
44]. They are also an alternative source of fresh products for the development of new food products, e.g., gluten-free bread, cookies, and food additives [
12,
14], or even industrial uses such as biodegradable films [
13,
32].