Bitter Melon (Momordica charantia)

The Bitter Melon (Momordica charantia: Family: Curcurbitaceae) a.k.a. Bitter Gourd or Karela (in India) and Shan Ku Gua in Taiwan is a vegetable which is grown widely in Asia, South America, the Caribbean and some parts of Africa. Varieties include India White, India Green, China White and China Green and has a long history within Chinese and Ayurvedic medicine.

The gourd is used in some classic Japanese cuisine to make for example the iconic Okinawan dish, Goya Chanpuru. This is a stir fried dish and is one of the staples of the Okinawan Diet and should be tried simply to make use of some of the remarkable compounds which are found in this particular gourd.

The Plant 

The plant is a herbaceous vine about 5m long when fully grown. It flowers in June to July and the fruit develops into November. It appears as a small cucumber – like a gherkin that turns from green to orange-yellow when ripe although the unripe form is best consumed (Grover and Yadaf, 2004). The fruit is crunchy and watery like a typical squash. In culinary terms, it is used in pickles, deep-fried, boiled and dried to produce a tea.  It becomes more intensely bitter as the fruit ages but is often used in cooking. Heating appears to reduce this bitterness (Wang et al., 2008). Various parts of the fruit are used – the whole fruit itself, seeds and pulp. Its extract is also a valuable medicine with properties in treating diabetes and even some cancers although the unripe form is perhaps the most valuable medically.

Cultivation Of Momordica (Bitter Melon)

It grows as a vine preferring humid tropical or sub-tropical regions, and its cultivation is similar to cucumber. There are many varieties, all differing in size, texture, levels of bitterness and vitamins/minerals content. About 2 melons is enough in a daily diet because it can cause cramps and even diarrhoea which is not surprising given the compounds present in the fruit

Choosing, Storing And Cooking Bitter Melon

Choosing the best bitter melon:

Most bitter melons are available from July to September in the Far East and in particular Japan. In the USA and UK, they are available in farmer’s markets and many Asian grocery stores. I buy mine from Indian groceries. It’s also possible to grow your own.

If you want the best tasting fruits, choose bitter melons at a relatively small size which has plenty of ridges and bumps. The surface should be a fresh and shiny green and needs to be firm to the touch. Overripe melons tend to have a yielding feel.

Storage Of Bitter Melon:

Bitter melons will keep fresh and firm for a considerable length of time but remove any seeds and pith first as they have a tendency to rot quickly once the process of ripening has started. The bitter compounds are generally concentrated in the inner white pith or albedo. Most melon is sliced and stored in a dry, airtight container where they will last for 2 weeks before use.

Recipe: Goya Chanpuru  (ゴーヤチャンプル)

If you like stir fries then this particularly savoury one using bitter melon, tofu, egg and pork belly is fantastic. It is a balanced dish which is often served with side of steamed rice and some piping hot miso soup. The dish makes wonderful use of bonito flakes known as katsuobushi to add a bit of umami flavour.

Ingredients:

Serves 4 people

• two bitter melons (bitter gourd, goya) – large enough for 4 people.
• salt for seasoning and to taste
• 14 oz. (400g) medium firm tofu.
• 6 pieces of sliced bacon or pork belly. Some people use proscuitto for a finer texture but it isn’t necessary.
• 2 large eggs
• vegetable or corn oil
• black pepper freshly ground
• 1 tbsp soy sauce or more to taste

Preparation:

1. Slice the bitter melon length ways. Scoop out the seeds and scrape out the inner pith which is extremely bitter. Use a teaspoon.

2. Slice the gourd into 1/2cm (1/8 inch) pieces. Sprinkle with some salt and allow to stand for about 10 minutes. Wash the slices in a colander or use a salad spinner. Some people retain the salt as this will help later with boiling but be careful not to make the dish too salty later on.

3. Bring a pan to the boil and add the slices. Simmer for about a minute to just blanch the vegetable. It should develop a fine vibrant green colour which indicates it is ready for further work. Drain.

4. Unwrap the tofu onto a paper towel. Squeeze out the water using a heavy board (chopping or bread board really work well here).

5. Place some katsuobushi (bonito or tuna flakes) in a measuring jug and 1/4 cup of boiling water. Allow to steep so those beautiful flavours start permeating out of the flakes into the water. This will be the dashi.

6. Strain off the dashi and discard the flakes. Some people retain those flakes later on for a furikake but I think they have probably exhausted themselves – the flavour is largely gone. Keep the kasuo dashi for later use.

7. Cut the bacon or pork belly into small chunks which are 1 to 1 1/2 inch pieces.

8. Beat the eggs and cut up the tofu into small chunks. Some chefs love to use  their hands for this task because it gives a rustic feel to the dish.

9. Add a 1 Tbsp oil to a large frying pan and begin frying the tofu.

10. Leave the tofu to brown. Avoid too much movement as the tofu will break up as soon as you look at it. Let the tofu dry a little. Add to a side plate.

11. In the same frying pan, add 1 Tbsp oil to fry the bitter melon and allow to cook. If salt hasn’t been added earlier then some may be needed at this point because salt helps reduce some of that bitterness. The other point is that salt in the pork belly which is added next could help reduce that bitterness too.

12. Add the bacon or pork belly pieces. Season with freshly ground black pepper. Stir fry until the bacon/pork belly is nicely browned off

13. Combine the dashi with soy sauce and add to the whole frying mix.

14. Taste the whole mix to check level of seasoning, saltiness in particular and any bitterness. Soy sauce helps here to develop the flavour further.

15. Add the eggs mix which scrambles in the frying pan. Keep frying until the whole egg has scrambled.

16. Serve with the bonito flakes (katsuobushi).

Compounds In Mordica

The componentry in bitter gourd is rich and varied:-  momorcharins, momordenol, momordicilin, momordicins, momordicinin, momordin, momordolol, charantin, charine, cryptoxanthin, cucurbitins, cucurbitacins, cucurbitanes, cycloartenols, diosgenin, elaeostearic acids, erythrodiol, galacturonic acids, gentisic acid, goyaglycosides and goyasaponins (Grover and Yadav, 2004). Caffeic acid and ferulic acid (Raj et al., 2005),  fisetin and isorhamnetin (Lako et al., 2007) have also been identified and characterised.

Effects On Diabetes

The fruit possesses three active substances against diabetes mellitus and has been extensively reviewed (Efird et al., 2014). Charantin has a blood-glucose lowering effect, whilst vicine and polypeptide p, act like  insulin compounds. There is also a lectin which has a hypoglycaemic effect by reducing blood glucose levels by acting on various tissue and suppressing appetite. The hypoglycaemic effect was being assessed in rat models the early 90s (Ali et al., 1993; Srivastava et al., 1993; Jayasooriya et al., 2000). Subsequently, powdered extracts from both fresh and dried fruits were assessed in diabetic rats for their ability to lower blood glucose levels (Virdi et al., 2003). The aqueous extract of a powder from fresh unripe whole fruits which was given at a dose of 20 mg/kg body weight reduced fasting blood glucose by 48%. The effect was claimed to be comparable to the diabetes drug, glibenclamide.

Other Conditions Treated With Bitter Melon (Momordica)

Bitter melon extract also appears to have some efficacy against cancer in certain cell lines (Ganguly et al., 2000) dyslipidemia and even hypocholesterolemic activity (Ahmed et al., 2001). Recent developments on cancer cell lines also appear promising  (Brennan et al., 2012). It is also claimed to be beneficial in the treatment of piles, reducing blood pressure, blood and respiratory disorders and even against cholera (Khattak et al., 2005).

The seeds too have a number of associated medical benefits. The seeds are rich in conjugated linolenic acids especially the relatively unique one, alpha-eleostearic  which was shown to inhibit colon carcinogenesis by raising colonic PPAR gamma expression and beneficially altering  lipid compositions (Kohno et al., 2004; Cao et al., 2014). The oil extract has also been investigated.

The saponin momordin has been the subject of intense speculation over its medical properties.  At the gene level, momordin raises activation and production of PPAR delta, in part by upregulation of the promoter (Sasa et al., 2009). There are a number of other gene modifying effects to be considered (Shih et al., 2014).

Processing Momordica (Bitter Melon)

In processing terms, storage of the fruit requires blast freezing and storage at temperatures below minus 21°C if any of the radical-scavenging activities, the phenolics and vitamin C are to be retained. Blanching is not successful.

Toxicity Of Momordica (Bitter Melon)

One last point, toxicity of extracts is always needs critical examination. The study in rats by Virdi et al., (2003) indicated there were no nephrotoxic or hepatotoxic problems (Virdi et al., 2003).

I continually add items on this vegetable because the story is never ending. At the moment, the various compounds are being assessed at the genetic level and this appears to be where the most excitement is being generated.

References

Ahmed, I., Lakhani, M.S., Gillett, M., John, A., Raza, H. (2001) Hypotriglyceridemic and hypocholesterolemic effects of anti-diabetic Momordica charantia (karela) fruit extract in streptozotocin-induced diabetic rats. Diabetes Res Clin Pract 51(3) pp. 155–61.

Ali, L., Khan, A.K.A., Mamun, M.I.R., Mosihuzzaman, M., Nahar, N., Alam, M.N., Rokeya, B. (1993) Studies on hypoglycemic effects of fruit pulp, seed and shole plant of Momordica charantia on normal and diabetic model rats. Planta-Medica 59(5) pp. 408–12.

Brennan, V.C., Wang, C.M., Yang, W.H. (2012) Bitter melon (Momordica charantia) extract suppresses adrenocortical cancer cell proliferation through modulation of the apoptotic pathway, steroidogenesis, and insulin-like growth factor type 1 receptor/RAC-alpha serine/threonine-protein kinase signaling. J Med Food 15 pp.  325–334. doi: 10.1089/jmf.2011.0158

Efird, J.T., Choi, Y.M., Davies, S.W., Mehra, S., Anderson, E.J., et al. (2014) Potential for improved glycemic control with dietary Momordica charantia in patients with insulin resistance and pre-diabetes. Int J Environ Res Public Health 11: pp. 2328–2345. (Article) doi: 10.3390/ijerph110202328

Ganguly, C., De, S., Das, S. (2000) Prevention of carcinogen induced mouse skin papilloma by whole fruit aqueous extract of Momordica charantia. Eur J.  Cancer Prev. 9 pp. 283–8.

Grover, J.K. and Yadaf, S.P. (2004) Pharmacological actions and potential uses of Momordica charantia: a review. J. Ethnopharmacology 93 pp. 123-132.

Jayasooriya, A.P., Sakono, M., Yukizaki, C., Kawano, M., Yamamoto, K., Fukuda, N. (2000) Effects of Momordica charantia powder on serum glucose levels and various lipid parameters in rats fed with cholesterol-free and cholesterol-enriched diets. J Ethnopharmacol. 72 pp. 331–6.

Khattak, M.K., Bibi, N., Khattak, A.B., Chaudry, M.A.(2005) Effect of irradiation on microbial safety and nutritional quality of minimally processed bitter gourd (Momordica charantia). J Food Sci . 70 M255–9.

Kohno, H., Yasuim Y., Suzuki, R., Hosokawa, M., Miyashita, K., et al. (2004) Dietary seed oil rich in conjugated linolenic acid from bitter melon inhibits azoxymethane-induced rat colon carcinogenesis through elevation of colonic PPARgamma expression and alteration of lipid composition. Int. J Cancer 110 pp. 896–901. doi: 10.1002/ijc.2017

Myojin, C., Enami, N., Nagata, A., Yamaguchi, T., Takamura, H., Matoba, T. (2008) Changes in the radical-scavenging activity of bitter gourd (Momordica charantia L.) during freezing and frozen storage with or without blanching. J. Food Sci. 73(7): C546-C550.

Raj, S. K., Khan, M. S., Singh, R., Kumari, B., & Prakash, D. (2005). Occurrence of yellow mosaic geminiviral disease on bitter gourd Momordica charantia and its impact on phytochemical contents. Int. J.Food Science Nutr. 56 pp. 185–192.

Sasa, M., Inoue, I., Shinoda, Y., Takahashi, S., Seo, M., Komoda, T., Awata, T., Katayama, S. (2009) Activating effect of momordin extract of bitter melon (Momordica charantia L.), on the promoter of human PPAR Delta. J. Atheroscler. Thromb. 16, pp. 888–892.

Shih, C.C., Shlau, M.T., Lin, C.H., Wu, J.B. (2014) Momordica charantia ameliorates insulin resistance and dyslipidemia with altered hepatic glucose production and fatty acid synthesis and AMPK phosphorylation in high-fat-fed mice. Phytother Res 28 pp. 363–371. doi: 10.1002/ptr.5003

Srivastava, Y., Venkatakrishna-Bhatt, H., Verma, Y., Venkaiah, K., Raval, B.H. (1993) Antidiabetic and adaptogenic properties of Momordica charantia extract: an experimental and clinical evaluation. Phytother. Res. 7 pp. 285–9.