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Plants & People: The Intersection of Botany and Human Experience

Pouteria lucuma: An exploration of historical and modern medical uses of the Andean lucuma fruit

Pouteria lucuma is a fruit tree of the family Sapotaceae of the order Ericales native to the Andean Valley of South America. The fruit is commonly used in Peruvian desserts, especially icecream, for its unique flavor, often described as resembling maple, butterscotch, or sweet potato. It was used as a subsistence crop by the native peoples of coastal Chile and Peru as early as 700 BC. The fruit was an important part of fertility rituals of these peoples, as its consumption was thought to promote lactation in new mothers. No studies have been done to that effect, however there has been significant research into other medicinal properties of the fruit. The oil extracted from the seeds and skins of the fruit, which are typically discarded as industrial waste, has high phenolic content and has been shown to aid in wound closure and skin regeneration. These properties have made the fruit of special interest to the skin care industry. By Jasmine White, Quinn Schwabauer, Jin Zhu #lucuma

Nomenclatural History

Pouteria lucuma is a fruit with an ever-changing nomenclatural history. Though commonly known as lucuma, there are many regional names for this fruit. It is known as logma in the Bolívar region of Ecuador, lohma or louma in the Cotopaxi region of Ecuador, lucma or lucmo throughout Ecuador, lucumo in the Lima region of Peru, maco or rucma in Colombia, and mamón in Costa Rica (Pennington, 1990, pp. 381-385; Thulin et al., 2021). The current common name, lucuma, is a derivative of these indigenous names. First appearing in scientific literature as a genus, Lucuma fell within Icosandria Digynia according to the Linnean sexual system, as described by Juan Ignacio Molina’s “Saggio”. Since then, Lucuma has been used by multiple authors to describe a genus of Sapotaceae beyond the Andean region, including Asia, Australia, and Africa. This genus is currently synonymous with Pouteria, based on work published by T.D. Pennington (Thulin et al., 2021). The lucuma fruit, now known as Pouteria lucuma (Ruiz and Pavón) Kuntze was initially known as Lucuma bifera Molina, with other historic binomial names including Achras lucuma Ruiz and Pavón, Lucuma obovata Kunth, and Pouteria insignis Baehni (Pennington, 1990, pp. 381-385; Thulin et al., 2021).

Evolutionary History

Pouteria lucuma belongs to the family Sapotaceae within the order Ericales (Ericales, n.d.). The number of genera in the Sapotaceae family has fluctuated, from Aubréville’s historic 122 to Pennington’s current 53, all based on morphological characteristics (de Faria et al., 2017; Swenson & Anderberg, 2005). Because of Pennington's wide generic concepts, the genus Pouteria includes 304 species with pantropical distributions (Swenson & Anderberg, 2005). Phylogenetic reconstructions have demonstrated that Pouteria is polyphyletic, meaning that the type species from the New World should be placed in their own clade separate from other tropical Pouteria species (de Faria et al., 2017; Swenson & Anderberg, 2005; Thulin et al., 2021). This large genus shows homoplasy instead of synapomorphies, because of the previous reliance on morphological classifications instead of genetic analysis (de Faria et al., 2017; Swenson & Anderberg, 2005). New molecular evidence suggests that there is a strongly supported clade that includes P. lucuma that should be separated from Pouteria and reinstated under the genus Lucuma (Thulin et al., 2021).

Although the molecular phylogeny of P. lucuma specifically has not been published yet, there is morphological evidence of relation to Pouteria campechiana, a member of the former Lucuma genus, supported by geographical evidence (Pennington, 1990, pp. 381-385; Thulin et al., 2021). By looking at the molecular phylogeny of the Pouteria genus and focusing on P. campechiana, we can gain insight into P. lucuma’s evolutionary history (de Faria et al., 2017).

Ecology and Life History

Lucuma grows on a subtropical fruit tree that originated in the Ecuadorian and Peruvian Andes mountains (Duarte & Paull, 2015, pp. 117–123). Its current distribution is from Andean Colombia heading southward to Northern Chile, growing in wet montane and cloud forest, usually between 1500 and 3000 m altitude, but can rarely be seen as low as 700 m (Pennington, 1990, pp. 381-385). The lucuma tree is most suited to sandy or sandy loam soils with high contents of organic matter and good drainage. It is able to moderately tolerate salinity and alkalinity, but the ideal pH is around 6.5-7.5. The tree is adapted to fairly dry conditions but needs rainfall of about 800-1,000 mm per year to give higher yields. The ideal temperature for fruit production is between 18 °C and 24 °C, and the tree is killed by temperatures lower than -5 °C. It is able to grow in full sunlight and flowers and fruits year-round in ideal conditions (Duarte & Paull, 2015, pp. 117–123).

Vegetative and Reproductive Morphology

The lucuma tree is an evergreen that grows to heights of 8-15 m and has a dense crown with branches that produce white latex (Yahia, 2011). The leaves are clustered and spirally arranged in groups of 6-30 and 3.1-15 cm in size. They are oblanceolate to elliptic. The leaf apex is usually obtuse and rounded or slightly emarginate. The midrib is flat or slightly raised on the upper surface with 9-15 pairs of straight, parallel secondary veins. The petiole is 1.3-2 cm long and not channeled (Pennington, 1990).
Lucuma flowers are bisexual with 5 sepals. The pedicel is 0.8-2.1 cm long. The corolla is cylindrical at 1-1.8 cm long with 5 lobes 4-8mm long. There are 5 stamens fixed at the top of the corolla tube with filaments 1.5-2 mm long. The ovary is oblong to ovoid. The style is 0.8-1.5 cm long, exserted or equalling the corolla with a simple style-head (Pennington, 1990).
The fruit is 6-12 cm long and ovoid or elliptical shaped with a pointed or depressed apex. The epicarp is greenish-yellow when ripe and the mesocarp is dry and orange/yellow. It often has 2 seeds, but 1 to 5 are possible. The seeds are round/oval and are dark brown with a glossy appearance (Yahia, 2011).

Historical Reports of Lucma

The first written report of Lucuma occurred in 1531 in the Chinchasuyu region of Ecuador (Morton, 1987). A myth recorded in the Huarochiri manuscript in the late 1600s includes lucuma as part of a creation myth (Columbus,1998). However, there is a clear legacy of the fruit’s importance to the native Peruvian and Ecuadorian people long before that. Plant remains have been found in native settlements in Chile dating back to 2500 AD. The quantity of remains suggests lucuma was once a staple in local diets (Cohen, 1978). Lucuma served as more than just food to these groups. Lucuma pottery was often buried with the ancient indigenous people of coastal Peru, the Nazca (600-200 BC) and Moche (100-700 AD) (Morton, 1987). These double spouted bottles made from four lucuma fruits represented fertility, both human and agricultural. The lucuma forms were tied to lactation, and the linked structure of four fruits is likely a reference to the different growing seasons (Elder, 2015).

Domestication History

Little is known about the domestication history of P. lucuma. There is some evidence it was actively cultivated by the Moche empire around 200 AD, who irrigated large numbers of trees for harvest (Pozorski, 1979). However, it is unclear if the tree was ever formally domesticated, as there are no obvious differences between ancient and modern P. lucuma specimens (Cohen, 1978). There do exist various cultivars today, which does suggest some selection, whether natural or artificial, for different traits in different geographic ranges. Many of the cultivars native to the Andes outside of Chile, Peru, and Ecuador are larger, drier, and less sweet than the more commercial cultivars. They are not suitable for desserts, although they are still utilized as chicken feed (National Research Council, 1989).

Cultivation Practices

Cultivation of lucuma is concentrated in the Andean highland, but it is still cultivated in several other places, like Auckland in New Zealand and Arizona in the US, though often without much successful production of fruits. Lucuma requires higher elevation in tropical climates with medium rainfall and lower elevation in subtropics. It does not do well in hot tropical lowland areas. Since some non-native cultivated places lack water, such as Arizona, irrigation is required for the trees to grow well.
Lucuma's success rate of seed germination is low and slow, taking between about 25 and 40 days. Seedlings' juvenile period can take 7-15 years. When young, weed control is important, as growth in the first 2 years is slow. Pruning begins when young to form 3-4 well-spaced main scaffold branches that will open up the canopy. Thereafter branches longer than 30-40cm can be tipped to promote further branching. Pollination is by bees. Fruit takes 8-9 months to mature from pollination. Lucuma trees start producing fruit after 4 or 5 years, and tree flowers and fruits throughout the whole year. Ten-year-old trees can produce 200-300 fruit per year (Prolucuma, 2010). After mature fruit falls from the tree, they need several days to ripen before they are consumed. Fruit is considered ripe when the skin has changed in color from green to yellow and has begun to split to reveal the flesh inside (Lizana, 1980). Fruit is dry and mealy with consistency similar to that of a hard-boiled egg yolk. In Chile, the harvesting season for lucuma is from June through November. After harvesting, lucuma fruit can be stored at 7 °C without being affected (Sandoval, 1997). However, the fruit does not ship well, so it is often frozen or processed into a flour to be used as a dessert flavoring and shipped abroad.

Nutritional Value

Lucuma fruit is a good source of iron, zinc, calcium, fiber, minerals, β-carotene, and niacin (Yahia 2011). Fruits have significant high protein content and high insoluble dietary fiber, but relatively low vitamin C content. It has highest concentration of of anti-inflammatory polyphenols of any of the Peruvian fruits (Silva et al., 2009). The fruits high insoluble dietary fiber content is linked to prevention of gut diseases such as Colorectal polyp and to regulation of the digestive tract. The polyphenols in lucuma can act as antioxidants that can help prevent cancer and cardiovascular diseases, as well as diabetes (Silva et al., 2009). Lucuma fruit extraction contains a compound that behave as α-glucosidase inhibitors, which have a hypoglycemic effect and attenuate blood glucose level. Due to lucuma's high bioactive compound content and antioxidant and antihyperglycemic properties, lucuma will be able to become a functional food (Fuentealba et al., 2016). Lucuma nut oil promotes skin regeneration and accelerates wound healing. As a result, it may be used in medicine and skin care (Rojo et al., 2010).

Human Experience

Lucuma fruit is a natural sweetener. Before Europeans cultivated sugarcane, sugar was a luxurious good, so people chose natural sweetener as substitutions of sugar (Mintz, 1985). Lucuma fruit has a distinctive flavor that resembling caramel, butterscotch, or maple and can be used to flavor ice cream, yogurt, and other desserts (Ma et al., 2004). In Southern America, lucuma fruit have been used as traditional for many years. In the future, humans are more likely to use lucuma as a natural alternative sweetener to sucrose and artificial sweeteners because of the low glycemic index of lucuma (Mérillon & Ramawat, 2018). Lucuma is dehydrated and milled into a flour but do not undergo refining processes, so high content of beneficial nutrients and bioactives are kept (Belščak-Cvitanović et al., 2015). Lucuma powder is popularly sold in the world because it is easy to be stored.

Reference

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