The fruit market in Vietnam is now diversity of both domestic and imported fruits. Banana is one of the most popular and widely used fruit all over the world. Bananas are cultivated over 130 countries. Vietnam is in the top 15 banana production countries in the world. In Vietnam, banana also account for a high percentage of total fruit consumption per capita annually. Due to climacteric respiration, although harvested at immature stage banana is ripening quickly, especially in high ambient temperature. On the other hand, the nutritional and sensory quality of the fruit deteriorates rapidly after ripening. The short shelf-life of banana is the main cause of postharvest losses and low access both domestic and international market.
Tieuhong banana variety is a fruit tree with high economic value, outstanding quality because of its beautiful yellow color, delicious taste, firm and not sour as other banana varieties. In particularly, Tieuhong bananas propagated by tissue culture method have uniform size, less disease, harvest in short time and 10 – 20 % higher yield than by bud method.
To prevent postharvest losses of ripe banana, there are many methods of processing banana when green such as green banana starch, green banana powder and microbial products from green banana… Powder and starch product from cassava, sweet potato, corn are quite familiar however, powder and starch isolation from green banana in Vietnam is not yet popular.
The main ingredient of green banana is starch, 70 – 80% starch by dry weight. During ripening, starch converted into sucrose, fructose and glucose, which account for 16% of fresh weight. Green bananas have a low glycemic index (GI) compare to ripe bananas, less than 40% due to their high starch and fiber content, which helps to minimize blood sugar. Green bananas are rich in potassium, which helps the nervous system function well. Green banana also contain many healthy vitamin such as vitamin C and vitamin B. vitamin B helps in production of hemoglobin and regulates blood sugar level effectively. One of the top health benefits of green banana is that green banana contain high fiber content that helps keep the intestinal system healthy, support and prevent diarrhea, good for diabetes people and also helps obese people have an effective weight loss diet. The highest starch content is found in green and unripe fruits such as banana and mango reaching 70% of the dry matter content. Therefore, green banana can be used as an alternative source starch for corn, wheat and rice.
In particular, the starch in green banana has a very high percentage of resistant starch, the highest among fruit (48,99g/100g). Thus, the research on production of green banana powder and starch applied in food products for dieters is very effective.
Resistant starch is starch and its degradation products that escape from digestion in the small intestine. Resistant starch occurs naturally in foods or is added to foods by synthetic resistant starches.
Some types of resistant starches (RS1, RS2 and RS3) are fermented by the large intestinal microbiota, conferring benefit to human health through the production of short-chain fatty acids, increased bacterial mass. In some ways, resistant starch has some of the same physiologic effects as dietary fiber, acting as a mild laxative.
The definition of resistant starch comes from researches in the 1970s, whereby researchers divided into 3 types of starch: fast digesting starch, slow digesting starch and resistant starch. The Commission of the European Communities supports researches and identification of resistant starch into 4 types:
(1) RS1 - Physically inaccessible or indigestible resistant starch, such as that found in seeds or legumes and unprocessed whole grains
(2) RS2 - Resistant starch is inaccessible to enzymes due to starch conformation, as in green bananas and high amylose corn starch
(3) RS3 - Resistant starch is formed when starchy food are cooked causing the soluble starch to become less soluble like pasta
(4) RS4 - Starches that have been chemically modified to resist digestion
It should be noted that food processing can affect the resistant starch content of foods. In general, processing often reduce the content of resistant starch, for example whole wheat grain contains 14% resistant starch while ground powder is only 2 %, resistant starch content in cooked-rice is usually lower than in rice. However, there are also ways of processing increases resistant starch content, for example the starch is gelatinized and becomes more digestible, but these starch gels are then cooled can form starch crystal resistant to digestive enzyme (type RS3 or retrograded resistant starch), potatoes salad or boiled potatoes have a higher content of resistant starch than regular potatoes. Resistant starch does not release glucose within the small intestine, but rather reaches the large intestine where consumed of fermented by colonic bacteria. The fermentation of resistant starch produces short-chain fatty acids, including acetate, propionate and butyrate and increased bacterial cell mass. Butyrate is the main source of energy for colon cells, it also increase metabolism, reduces inflammation and against stress.
The short-chain fatty acids are produced in the large intestine where they are rapidly absorbed and metabolized in colonic epithelial cells, liver or other tissues hence foods contain resistant starch have low GI, not increase blood sugar suddenly. Therefore, in 2016, the FDA approved that resistant starch can reduce the risk of type 2- diabetes.
Resistant starch also reduces the risk of colorectal cancer through various mechanisms such as protection from damage caused by DNA alterations. Altered gene expression and increased apoptosis of cancer cells.
Green bananas are a valuable source of resistant starch. Starch in green banana has a high rate of resistant starch which is the highest among fruits.
Thus, the use of green Tieuhong banana variety as raw material for processing green banana powder and starch not only prevent postharvest losses of ripe banana but also bring high benefits to human health such as improve digestive tract diseases, promote colon to work effectively, support weight loss, reduce sensitivity to insulin…
The suitable harvesting stage of Tieuhong banana variety for production of green banana flour and starch is 90 days after flowering. For green banana powder, it is possible to use sulfite salts at the allowable concentration to process the material in a suitable time to improve the color of green banana powder. For green banana starch, the concentration of citric acid is 1.5% in 20 minutes, starch settling and washing mode is 4 times, drying mode is 60℃ in 7 hours is suitable to obtain good quality green banana starch. Green banana powder and green banana starch are suitable for partial replacement of starch sources in the production of starch-based products such as bread, cake, noodles…
References
Perez, B., L. A., Agama-Acevedo, E., Sa´nchez-Herna´ndez, L., & Paredes-Lo´pez, O. (1999). Isolation and Partial Characterization of Banana Starches. Journal of Agricultural and Food Chemistry 47. Hal : 854–857.
Widjaya, E.R., 2009. Flour Processing Equipment and Machinery. http://elita75.wordpress .com/2009 /02/09/ unit-pengolahan-tepungpisang/ [ 21 Oktober 2009]
Alvi Yani, Ratna Wylis Arief, Nina Mulyanti (2013), Processing of Banana Flour Using a Local Banana as Raw Materials in Lampung. International Journal onAdvanced Science Engineering Information Technology.
Debabandya Mohapatra (2010), Banana and its by product utillisation: an overview, Journal of scientific & Industrial Reasearch.
Nguyen Thi Thu Nga – Postharvest Technology Department - nttnga@vnua.edu.vn