Transcript Legumes
Legumes Legumes are dicotyledonous plants in the family Fabaceae. They have in common a number of structural and functional characteristics: • Their fruits are ‘pods’ – simple, dry fruits with (generally) multiple embryos (seeds) attached to an elongated carpel that dehisces (opens) along seams on two sides. Not all legumes dehisce – alfalfa (Medicago sativa) does not. • They are involved in a mutualistic association with nitrogenfixing bacteria (Rhizobium spp.) present in root nodules that result in legumes having high levels of protein, as well as adding available nitrogen to the soil • Their flowers are not radially symmetric, but bilaterally symmetric. Legumes are frequently divided into two groups: forage species like alfalfa, clover and vetch that are eaten by grazing herbivores ‘grain’ species, cultivated for their seeds, like various beans, peas, peanuts and lentils. This group are also known as “pulse” crops. All have high protein content. All add nitrogen to the soil (90 million metric tons/yr). Let’s first consider beans… There are many types of beans, and taxonomic distinctions between them: • broad bean (Vicia faba) is an Old World species that originated in the Mediterranean area (or possibly Africa). It was cultivated 6000 YBP. Since I’m not a fan, here are some of the health problems they can cause: favism – caused by the presence of vicine and convicine in them. Individuals who are deficient in the titre of the enzyme glucose 6 phosphate dehydrogenase (G6PDH) suffer from a hemolytic anemia these beans have high tyramine, and should be avoided when taking MAO (monoamine oxidase) inhibitors a health benefit – they are rich in L-dopa, which is used to treat Parkinson’s disease Broad beans Broad bean flowers The fruit (the pod) is 15 – 25 cm long in modern food cultivars. Pods contain 3 – 8 seeds, each ~20 x 15 x 7.5 mm. Broad beans are eaten before complete maturity, while young and tender. • Other dry beans (kidney, pinto, black, haricot) and some we consume with the enclosing carpel (green, string) are all varieties (cultivars) of a single species, Phaseolus vulgaris L. These beans are originally from the Americas and were first cultivated in MesoAmerica. They are a staple food. Nutritional content per 100g: carbohydrates 60 g dietary fiber 25 g lipids 1g protein 24 g B5 (pantothenic acid) 0.8 mg (19% RDI) B9 (folic acid) 394 mg (99% RDI) Fe 8 mg (64%) Mg 140 mg (38%) There is one health concern (that normally doesn’t apply): dry beans should be soaked, then boiled for at least 10 minutes. They (particularly red kidney beans) contain a lectin phytohaemagglutinin, which can cause severe gastric upset. What about flatulence? Caused by complex sugars that are removed by soaking. Compared to the dry beans, green and string beans provide less starch and protein, but more vitamins A and C. Some uses: pinto beans – refried beans in Mexican foods white (haricot, navy) beans – Boston baked beans kidney beans – chili, Louisiana creole dishes, southern U.S. red beans and rice black (turtle) beans – burritos, feijoada (a national dish of Brazil) • Lentils (Lens culinaris) Originate in the Near East, and one of the first crops domesticated there. They are second only to soybeans in protein content – 26%. As a result they are very important in vegetarian diets. The optical lens draws its name from the lentil, because the seed has a ‘lens’ shape. The largest producer is India, but Canada is both a significant producer and a large exporter. Of a world total production of 3.2 million metric tons, Canada (mostly Saskatchewan) produces about 520,000 tons, and exports around 400,000 tons. This is a map of lentil growing areas (area of origin in red): In India lentils are boiled to a thick stew-like consistency and mixed with oil and spices to make dal. In Ethiopia they are roasted then boiled to a very thick, stewlike consistency and mixed with berber sauce (long-cooked cayenne pepper, onions and water). In Europe and North America they are added to soups. • A different genus of beans, Vigna, includes black-eyed peas (V. unguiculata), mung beans (V. radiata) and black gram (V. mungo). Growing areas and uses differ: Black-eyed peas are originally native to Africa, but are now grown in southern Asia, Africa, the West Indies, and the southern U.S. Along with peanuts, George Washington Carver promoted cultivation of this bean. In the south the traditional dish is called “hoppin John”, and consists of black-eyed peas and pork (jowls, fatback or hocks). It is also traditionally served with greens (mustard or collard) and cornbread. In the West Indies, the traditional dish is rice and beans. mung beans are native to India, even the name comes from a word in Hindi. In Chinese cuisine they may be eaten whole or as bean sprouts. They are also ground up to produce bean thread (or cellophane) noodles. Black gram (or black turtle bean) is originally from India, where it is still used to make urad dal. It is also ground to make various dishes. Though it is late in the story of beans, it’s worth mentioning that beans are valuable in a diabetic diet. Two more bean genera: first the chick pea or garbanzo bean (Cicer arietinum): chick peas are tropical and need a lot of rain (400 mm). There are two types: Desi-type is a smaller seed with a rougher coat, and closely resembles archaeological evidence of origin. It is now grown in India, Ethiopia and Mexico, but originated in the fertile crescent (southeast Turkey). This type has a notably low glycemic index (particularly good for diabetics). In India it is ground as a coating flour and roasted as a snack. Kabuli-type is grown around the Mediterranean and Afganistan. This is the type used in the mid-East to make falafal and hummus. Chickpeas are a good source of zinc and protein. They are also very high in dietary fiber. They are low in fat, and most of the fat content is monounsaturated. There are other legumes than beans. Peas (Pisum sativum), due to their rapid growth (they, like the beans, are annual plants) and ability to control parentage, were the plants used by Gregor Mendel to develop the basic laws of genetics. There are many types: green peas, split peas, and snow peas (with edible pods) among them. Unlike many beans, that are tolerant of heat and drought, peas are ‘cool season’ plants. The cultivars you see grown around here are among the many that grow best at a temperature of about 13°C. Comparing dry split peas and fresh peas, there are clear differences in nutritional value (per 100 g): Green peas split peas Carbohydrates 14.5 g 60 g Fiber 5.1 g 26.1 g Protein 5.4 g 25 g Vitamin C 40 mg (67%) ----Vitamin B1 ----0.7 mg (54%) Pantothenic acid (B5) ----1.7 mg (34%) Folic acid (B9) ----274 g (69%) In Asia, dry peas are roasted, salted and eaten as a snack. In England, dry peas are rehydrated and mashed as “mushy peas” Soybeans (Glycine max) are native to and were first cultivated in China about 5,000 years ago. They were brought to Europe in the 17th century. They were then brought to North America only about a century later, but not widely grown until the 1920s. Soybeans are very nutritious. In dry soybeans, protein is about 40% of seed weight and highly unsaturated (‘good’) oil about 20%. The protein contains all essential amino acids. Soybean oil (along with canola oil) are the only vegetable sources for omega-3 fatty acids. Soybeans contain isoflavones (phytoestrogens) that may either aid in cancer prevention or cause cancers (an active debate). These same isoflavones have been suggested to reduce cholesterol. The FDA and American Heart Association think this is only meaningful for individuals with very high cholesterol. Unlike many kinds of protein, that in soybeans is heat stable, so that soy products can be cooked at high temperatures without destroying protein value. Soybeans also contain useful amounts of many vitamins and minerals. Soybeans are used in many different ways and products. Among them: • fermented to make soy sauce • extracted to make soy milk (for the lactose intolerant) • made into a ‘cheese’ we call tofu which is then used in many products, e.g. tofutti • boiled green as edamame (Japanese additive to dishes) • made into a paste with rice and fermented (miso) used in Japanese soups • sprouted for use as an alternative to mung beans • made into textured vegetable protein (TVP) added as a high protein extender to many meat products • extracted for soy oil used in many products (and the ‘waste’ dry protein is then used in animal feed) • lecithin is an additive in chocolate and many baked goods. It’s a lipid extracted from soybeans. It should be obvious that soybeans are widely used, and I haven’t even mentioned industrial uses for soy oil. One possible concern: most (89%) of the soybeans now grown in the U.S. are GMO. In 1995 Monsanto introduced a “Roundup Ready” soybean that, unlike previous genotypes, was not killed by glyophosphate, the active ingredient in the herbicide. The gene that made the soybean resistant came from a bacterium, Agrobacterium sp. The gene, EPSP (5enolpyruvyl shikimic acid-3-phosphate synthase) is also in soybeans, but in an alternative allele that leaves ‘natural’ soybeans sensitive and vulnerable. Like it or not, we’re all consuming GMO foods through this transgenic plant. Lastly, peanuts (Arachis hypogaea) are native to South America (probably Argentina or Bolivia). It gets its species name from the strange way its fruit matures. After pollination, the fruit develops into a legume pod 3 to 7 cm (1 to 2 inches) long containing 1 to 3 (rarely 4) seeds, which forces its way underground to mature. You know, because you have to crack the pod open, that this fruit, unlike most other legumes, is indehiscent (doesn’t open). Raw peanuts are very nutritious. Contents (per 100 g) are: Carbohydrate 20.91 g dietary fiber 8.7 g protein 25.09 g fat (oil) 47.58 g 20% or more of RDIs of thiamin, riboflavin, niacin, pantothenic acid, folic acid, B6, Mg, P, Zinc, and less of many others How many ways do we use them? Give George Washington Carver credit for a large number of the literally 100s (~300) of ways. A short list would include peanut butter, roasted snacks, as ‘beer nuts’, in candies, boiled… Peanut oil is widely used in cooking because it has the highest smoke and flash point of all vegetable oils. Peanut oil is used in the manufacture of paint, varnish, lubricating oil, leather dressings, furniture polish, insecticides, and nitroglycerin. Soap is made from saponified peanut oil, and many cosmetics contain peanut oil and its derivatives. Peanut shells are put to use in the manufacture of plastic, wallboard, abrasives, and fuel. They are also used to make cellulose (used in rayon and paper) and mucilage (glue). Problems with peanuts: • peanuts are considered an incomplete protein, with relatively low amounts of the essential amino acids lysine, cystine and methionine • peanuts are also an unbalanced source of fat because they are devoid of required omega-3 fatty acids • peanuts may be contaminated with the mold Aspergillus flavus which produces aflatoxin, a carcinogen • some people have severe allergic reactions to peanuts. Exposure can cause fatal anaphylactic shock. It is now believed that the underlying mechanism is a result of the tendency in North America to roast peanuts. Roasting makes the allergin, Ara h2, inhibit the digestive enzyme trypsin more strongly, so that it doesn’t get digested. That also protects one of the other strong allergins, Ara h1, from digestion. as well. In Asia, where peanuts are not roasted, the occurrence of peanut allergies is very rare. Major producers are the India, China (both almost entirely for the oil), U.S., Argentina, Sudan, Senegal, and Brazil. We are major importers. Apparent Group topics: Cacao/chocolate Teas (green/black/white/herbal) Fruit crops (dates/pomegranates/figs/durian) Coffee (arabica/robusta/fair trade) Ginger/ginger root Plants as drugs (marijuana/cocaine/painkillers/cancer cures) Peanuts and peanut allergies GMO Cinnamon Plants as herbal medicines (ginseng/aloe vera)