Selección de Nodos Capaces

As discussed in Section 1.3.2., potatoes are known to contain a number of bioactive phytochemicals. While many phytochemicals do not provide any nutritional value, they appear to contribute to improved health through their proposed roles in disease prevention through their antimutagenic, anticarcinogenic, antioxidant, antibacterial and immunity boosting functions (Liu, 2004; Liu, 2005; Rahal et al., 2014).

Being members of the Solanaceae family, potatoes are known to contain glycoalkaloids such as α-chaconine and α-solanine which can have adverse health effects if consumed in large quantities (Section 1.2.1.), or can impart bitter tastes that will affect consumer sensory acceptability (Friedman, 1997). Hence the aim of this experiment was to assess the relative phenolic and glycoalkaloid content as well as the potential antioxidant capacity of Taewa varieties compared to Nadine.

2.4.5.1. Phenolic, Flavonoid and Anthocyanin Content and Potential

Antioxidant Capacity of Taewa

All Taewa were found to have greater levels of phenolic, flavonoid and anthocyanin compounds compared to Nadine, in both the flesh and skin samples.

Potato Cultivar Harvest α-Solanine α-Chaconine Total Glycoalkaloids mg/100 g mg/100 g mg/100 g Potato Flesh Huakaroro 2004 0.9 1.1 2.2 Karuparera 2004 3.5 4.6 8.2 Moemoe 2004 1.8 1.9 3.8 Tūtaekuri 2004 3.9 3.5 7.5 Nadine 2004 0.7 0.9 1.6 Potato Skin Huakaroro 2004 21.9 37.3 60.4 Karuparera 2004 24.4 38.3 63.6 Moemoe 2004 15.0 21.4 36.5 Tūtaekuri 2004 23.4 32.2 56.7 Nadine 2004 7.2 19.2 26.4

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Tūtaekuri in particular had much greater total phenolic content (30-90 and 6-13 times greater in flesh and skin respectively); total flavonoid content (160-300 and 16-130 times greater in flesh and skin respectively); and total anthocyanin content (40-90 and 190-830 times greater in flesh and skin respectively) compared to Nadine. As expected due to the high phytochemical content, Tūtaekuri flesh and skin also had 4-10 fold greater antioxidant capacity than Nadine flesh or skin.

Similar to findings in this research, extractions from raw Taewa skin and flesh have been shown to exhibit variable degrees of phenolic, flavonoid and anthocyanin content and in vitro antioxidant activity. As found in this research, the purple-skinned, purple-fleshed variety Tūtaekuri / Urenika showed higher concentrations of phenolic compounds and greater antioxidative potential compared to white-skinned, white-fleshed varieties (Lewis et al., 1998; Gould et al., 2006; Philpott et al., 2009; Chong et al., 2013).

Lewis et al. (1998) provided information on the levels of phenolic compounds in tuber flesh and skin components over two consecutive harvest years from 26 potato varieties grown in New Zealand. Seven of these were Taewa varieties and included Urenika (varietal name for Tūtaekuri), Kowiniwini (varietal name for Karuparera) and Moemoe varieties. The content of total phenolics (TPC) found in this PhD research (20-523 mg and 158-970 mg per 100 g FW in Taewa flesh and skin) was higher than that reported by Lewis and colleagues (15-123 mg and 204-534 mg per 100 g FW in Taewa flesh and skin) for these three varieties. The TPC found in Tūtaekuri in this study is also likely to be greater than that determined in fifteen native Andean potato cultivars by Campos et al. (2006) (TPC ranged from 64 to 232 mg/100 g FW whole tuber), some of which were red and purple-fleshed cultivars (Campos et al., 2006).

Andre et al. (2007) investigated 74 genotypes from among the native Andean cultivars that represented the greatest range of genetic diversity available at the time. They found that TPC ranged from 112 to 1237 mg per 100 g dry weight (about 27 to 297 mg/100 g FW assuming a % dry weight of 24%). Thus Tūtaekuri are likely to align near the higher range reported in these cultivars based on its TPC flesh content.

Similar to findings in this PhD research, other researchers have found that varieties with deeper purple skin and flesh (such as Tūtaekuri) had greater TPC, and TPC were greater in tuber skin compared to tuber flesh (Lewis et al., 1998; Reyes et al., 2003; Brown, 2005; Campos et al., 2006; Albishi et al., 2013).

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Albishi et al. (2013) reviewed the phenolic content of four modern potato cultivars that included white, yellow or purple skinned and fleshed varieties and found that potato peel rather than potato flesh and purple-fleshed and skinned rather than white or yellow-fleshed and skinned varieties had much greater phenolic content and the highest antioxidant activity. In tuber skin, Lewis and colleagues (1998) found that the major phenolic acid was chlorogenic acid, followed by caffeic acid and lesser amounts of protocatechuic acid, vanillic acid, p- coumaric acid, ferulic acid, sinapic acid, salicylic acid and an unidentified phenolic acid. Lesser amounts of eriodictyol, naringenin, catechin, syringic acid and cinnamic acid were observed. In tuber flesh they found that again the major phenolic acid was chlorogenic acid, however, only small amounts of caffeic acid were present. Tuber flesh contained moderate amounts of protocatechuic acid, p-coumaric acid, ferulic acid plus traces of gallic acid, sinapic acid, catechin, epicatechin and eriodictyol (Lewis et al., 1998).

An extensive survey of phenolic compounds was not the goal of this PhD research; however, chlorogenic acid was identified as a major phenolic compound in both tuber skin and flesh, as was procyanidin and also caffeic acid in the skin components. Other phenolics identified included epicatechin, phloridzin xyloside, phloridzin, quercetin and quercetin derivatives (Tables 2.11 and 2.12). Lewis et al. (1998) were also able to determine the major anthocyanins in seven Taewa varieties, which had varying degrees of purple pigmentation in the tuber skin or flesh. The major anthocyanin compounds identified included petunidin-3-(p-coumaroyl- rutinoside)-5-glucoside (Pt-crg) and malvidin-3-(p-coumaroyl-rutinoside)-5-glucoside (Mlv-crg). Of the seven varieties, only Tūtaekuri /Urenika and Karuparera/Kowiniwini contained Mlv-crg. In this PhD research, malvidin and cyanidin glycosides were detected in Tūtaekuri flesh and skin as well as Karuparera and Moemoe skin, however, other major anthocyanin constituents (Pt-crg) were not identified as these standards were not included, but were likely included within the Total Anthocyanin content. Like other yellow or white fleshed and skinned potato varieties, a much lower content of anthocyanins were detected in Huakaroro and Nadine compared to the purple fleshed or skinned varieties. Cyanidin galactosides were only detected in Huakaroro, Moemoe and Nadine skin samples (Table 2.13). Compared to white-fleshed, white-skinned potato varieties, those with coloured skin and flesh (particularly red-fleshed and dark purple-fleshed varieties), have been found to contain greater amounts of antioxidative phytochemicals (and thus greater overall potential antioxidant activity and greater potential health benefits), (Lewis et al., 1998; Hamouz et al., 2011; Navarre et al., 2011; Lachman et al., 2012; Hu et al., 2012; Albishi, 2013; Kulen, 2013).

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This was also found to be the case in this PhD research when comparing the relative antioxidant capacity of Nadine and Huakaroro (yellow or white fleshed and skinned potato varieties) to Moemoe and Karuparera (white-fleshed, light to dark purple skinned) or Tūtaekuri (dark purple skin and flesh). Tūtaekuri had 4 to 8 times greater antioxidant capacity compared to Huakaroro, Moemoe and Karuparera and 5 to 10 times greater antioxidant capacity compared to Nadine (as measured by ORAC and FRAP) (Table 2.14).

Thus with regards to nutritional or health value, substituting consumption of Taewa varieties such as Tūtaekuri for Nadine is likely to provide greater antioxidant benefit. Since the skin of potatoes generally have a greater phenolic content relative to the flesh, it would be advisable to eat the whole potato rather than peeling them. However, as potatoes are not eaten in their raw state, it is of importance to know the effect of cooking treatments on the phenolic and anthocyanin content in potatoes. This will be assessed in Chapter 5 of this research.

2.4.5.2. Glycoalkaloids

As part of the screening process prior to introducing new potato cultivars to the market, anti- nutrient components are measured. This research found that the total glycoalkaloid content of the four Taewa varieties ranged from 2.2-8.2 mg/100 g FW in Taewa flesh and 36.5 – 63.6 mg/100 g FW in Taewa skin, which is 2-8 times greater than Nadine flesh and 1.5-2 times greater than Nadine skin (Table 2.15).

As shown by a number of researchers (Hellenas et al., 1995a; Friedman et al., 2003; Savage et al., 2000), glycoalkaloid content appears to vary significantly both between and within varieties. An analysis of 8 modern cultivars grown in the United States (Atlantic, Dark Red Norland, Ranger Russet, Red Lasoda, Russet Burbank, Russet Norkota, Shepody, and Snowden) found a 0.7 – 18.7 mg difference in total glycoalkaloid content per 100 g of fresh, whole potato between these varieties (Friedman et al., 2003). Levels of α-chaconine and α-solanine in the whole, fresh weight tubers ranged from 0.5 and 0.3 mg/100 g FW respectively in Russet Norkota, to 11.9 and 6.8 mg/100 g FW respectively in Snowden (Friedman et al., 2003). Hellenas and colleagues (1995a) found a total glycoalkaloid range of 5.1 – 22.1 mg/100 g FW in nine Swedish cultivars , then later found a 10 fold variation (6.1–66.5 mg/100 g FW) in total glycoalkaloid content within 300 commercial batches of the same Swedish potato cultivar (Magnum Bolum) grown in the same season (Hellanas et al., 1995b).

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In a study of 10 Taewa cultivars grown in New Zealand, Savage et al., (2000) found that glycoalkaloid content ranged from 3.9 to 14.3 mg/100 g FW whole potato between Taewa cultivars, with the higher glycoalkaloid content found in cultivars that had purple flesh and skin (most likely Tūtaekuri). Although the glycoalkaloid content of whole Taewa tubers were not analysed in this research, 2.2-8.2 mg/100 g FW of glycoalkaloids were found in Taewa flesh and 36.5 – 63.6 mg/100 g FW in Taewa skin. These levels are likely to be similar to the amounts found by Savage et al., (2000) due to the low glycoalkaloid flesh content found in this research and the minor contribution of the skin to the whole tuber.

Potato varieties with a total glycoalkaloid content of less than 20 mg/100 g FW are considered appropriate for the general market, as this level limits both adverse health effects and unacceptability with regards to perception of bitterness (Shakya and Navarre, 2006). Based on these criteria, the results from this PhD research and from Savage and colleagues (2000), it is likely that the glycoalkaloid content of these Taewa falls within acceptable levels, although varieties such as Tūtaekuri, Huakaroro and Karuparera may be more likely to impart a bitter taste compared to Moemoe and Nadine due to their higher glycoalkaloid content in the tuber flesh or skin as mentioned above. A taste test conducted by Savage et al. (2010) on 10 Taewa varieties found that the Taewa were generally well accepted although some (including a variety likely to be Tūtaekuri) were noted to have a slightly bitter after-taste (Savage et al., 2010). Thus it is advisable that future Taewa product development involves a sensory trial to assist in the assessment of consumer acceptability of varieties that may be perceived as bitter (carried out in Chapter 6).