Sugarcane

Sugarcane (Saccharum officinarum) is a perennial grass forming clumps of upright, unbranched stalks 2–7 m tall (usually 3–4 m) and about 5 cm in diameter. The stalk is jointed like bamboo, its internodes filled with a white fibrous pith soaked in sugary sap; a bud sits at the base of each leaf. The leaves are two-ranked, the blade narrow and 30–60 cm long with a thick midrib and small hard serrated margins; the sheath clasps the stem. The inflorescence is a panicle up to 60 cm long bearing many small spikelets with silky white hairs; the fruit is dry with one seed, but viable seed is rarely set. Sugarcane uses C4 photosynthesis, giving very high biomass, and reproduces mainly vegetatively from setts (stem sections bearing at least one bud). The chromosome number is 2n = 80; modern commercial cultivars are complex hybrids among several species of the genus.

According to Kew POWO the native range of Saccharum officinarum is New Guinea (LSID urn:lsid:ipni.org:names:419977-1); it is a rhizomatous perennial grass of seasonally dry tropical habitat. Sugarcane was domesticated by Papuans in New Guinea and the islands east of the Wallace Line, selected from the wild ancestor Saccharum robustum about 6,000 years ago; New Guinea remains the centre of diversity. From there it spread to maritime Southeast Asia, then with Austronesian voyagers to Polynesia and Micronesia about 3,500 years ago and westward to China and India about 3,000 years ago. Arab traders brought cane to the Mediterranean from the 8th century, and in 1493 Columbus took it to the Caribbean. Today it is grown throughout the tropics and subtropics, mostly between 22°N and 22°S, in places up to 33° and to about 1,600 m near the equator. Brazil is the largest producer (about 40% of world output), followed by India, China and Thailand.

The ripe stalk contains about 63–73% water, 12–16% soluble sugars, 11–16% fibre and 2–3% non-sugar carbohydrates. Pressed cane juice is about 70–75% water, 13–15% sucrose and 10–15% fibre; sucrose (saccharose) is the chief active, giving the sweetness and serving as the sugar industry feedstock, with small amounts of glucose and fructose. Besides sugar, the juice is rich in polyphenols: phenolic acids such as caffeic, chlorogenic, sinapic and hydroxycinnamic acid, together with the flavones apigenin, luteolin and tricin — tricin derivatives being the most abundant — and many flavone C-/O-glycosides (orientin, vitexin, schaftoside, swertisin). The cane wax coating stems and leaves (about 0.1–0.3% by weight) is a source of policosanols — long-chain aliphatic alcohols with octacosanol making up 50–80% — and of the fatty-acid mixture D-003, along with phytosterols and terpenoids. Bagasse is mainly cellulose, hemicellulose and lignin.

Sugarcane is a multi-purpose industrial crop. Cane juice is pressed to make refined sucrose (white sugar); unrefined products include raw sugar, brown sugar, jaggery and molasses; molasses is fermented into bioethanol — Brazil being the largest producer of sugarcane ethanol — as well as rum and vinegar. Bagasse is burned for biomass power (cogeneration) and made into paper, board and animal feed; cane tops and leaves serve as fodder; cane wax is a source of policosanols and is regarded as a carnauba-wax substitute in cosmetics and pharmacy. In research, the policosanol mixture from cane wax lowered total and LDL cholesterol in rabbits (Arruzazabala et al., 1994; 2000); D-003 has antiplatelet and antithrombotic effects (Molina et al., 2000; 2002); a fatty-acid mixture from cane wax has anti-inflammatory and analgesic effects (Ledón et al., 2003); and saccharin A–F glycans from the stalk lower blood glucose in mice (Takahashi et al., 1985). Cane-juice polyphenol extract shows strong antioxidant and DNA-protective activity (Duarte-Almeida et al., 2006), and an acylated tricin glycoside has antiproliferative activity against cancer cells (Duarte-Almeida et al., 2007). Reviews by Singh et al. (2015) and Ali et al. (2021) systematise the pharmacology of sugarcane and its by-products, and sugarcane polyphenol extract continues in clinical trials on metabolism and immunity (Penglase et al., 2022).

On safety, heavy consumption of cane sugar raises the risk of dental caries, excess weight and type 2 diabetes; the World Health Organization recommends keeping free sugars below 10% (ideally below 5%) of dietary energy. Because of the practice of burning cane fields before harvest, cane juice may carry polycyclic aromatic hydrocarbons (PAHs) such as benzo[a]anthracene and benzo[a]pyrene (Silvia et al., 2009); field-burning smoke pollutes the air, and bagasse dust is linked to respiratory disease in workers. Fresh unpasteurised cane juice may carry bacteria and needs hygienic handling. On conservation, the International Union for Conservation of Nature (IUCN) has not assessed Saccharum officinarum (NE) because it is a global crop. The species is a domesticated cultigen; cultivated genetic diversity is held in the many varieties and in genebanks worldwide (such as USDA-ARS, CIRAD and the ICAR Sugarcane Breeding Institute, Coimbatore, India). The main threats are landraces being replaced by a few high-yielding hybrids, monoculture prone to disease outbreaks (smut, mosaic, ratoon stunting disease), pests, drought and climate change; conservation of wild relatives (S. spontaneum, S. robustum) as breeding resources is therefore important.