banana

What is a banana

The banana is an edible fruit produced by several kinds of large herbaceous flowering plants in the genus Musa 1). Bananas are vital for food security in many African countries, tropical and subtropical countries and the most popular fruits in industrialized countries 2). As such, bananas constitute a fundamental source of energy, vitamins and minerals for tropical countries 3). India produces 28,455 million tonnes of bananas from an area of 796.5 ha. It is the largest producer of banana not only in Asia but also in the world and contributes 37.2 % to global production followed, by China (6.60 %) and Philippines (6.14 %) 4). In some countries, bananas used for cooking may be called plantains, in contrast to dessert bananas. Worldwide, there is no sharp distinction between “bananas” and “plantains”. Especially in the Americas and Europe, “banana” usually refers to soft, sweet, dessert bananas, particularly those of the Cavendish group, which are the main exports from banana-growing countries. By contrast, Musa cultivars with firmer, starchier fruit are called “plantains”. In other regions, such as Southeast Asia, many more kinds of banana are grown and eaten, so the simple two-fold distinction is not useful and is not made in local languages. The fruit is variable in size, color and firmness, but is usually elongated and curved, with soft flesh rich in starch covered with a rind which may be green, yellow, red, purple, or brown when ripe. The fruits grow in clusters hanging from the top of the plant. Almost all modern edible parthenocarpic (seedless) bananas come from two wild species – Musa acuminata and Musa balbisiana and to a lesser extent, Musa schizocarpa and Australimusa species 5). The scientific names of most cultivated bananas are Musa acuminata, Musa balbisiana, and Musa × paradisiaca for the hybrid Musa acuminata × M. balbisiana, depending on their genomic constitution. The old scientific name Musa sapientum is no longer used 6).

Banana nutrition facts

Raw bananas are 75% water, 23% carbohydrates, 1% protein, and contain negligible fat (Table 1). In a 100 gram amount, bananas supply 89 calories and are a rich source of vitamin B6, providing 31% of the US recommended Daily Value, and contain moderate amounts of vitamin C, manganese and dietary fiber (2.6 g). Although bananas are commonly thought to supply exceptional potassium content, their actual potassium content is relatively low per typical food serving at only 8% of the US recommended Daily Value (table). Vegetables with higher potassium content than raw bananas (358 mg per 100 grams) include raw spinach (558 mg per 100 grams), baked potatoes without skin (391 mg per 100 grams), cooked soybeans (539 mg per 100 grams), grilled portabella mushrooms (437 mg per 100 grams) and processed tomato sauces (413–439 mg per 100 grams). Raw plantains contain 499 mg potassium per 100 grams. Dehydrated dessert bananas or banana powder contain 1491 mg potassium per 100 grams 7).

The 23 g sugars in a medium banana are a mixture of glucose (9.4 g), fructose (9.1 g), and sucrose (4.5 g). The glycemic index of bananas is 51 (low-to-medium rating), similar to grapes, mangos, pineapples, raisins, macaroni, orange juice, and honey 8). The antioxidant value of bananas described in Oxygen Radical Absorbance Capacity (ORAC) units is 1,037 µmol TE, which is similar to kiwi fruit and orange juice 9). Thus bananas appear to be a unique mixture of carbohydrates, nutrients, and antioxidants that may provide good nutrition support.

Table 1. Banana (raw) nutrition facts

[Source: United States Department of Agriculture Agricultural Research Service 10)]

Bananas Ripening

To obtain maximum shelf life, bananas are picked green, and  stored and transported for 3–4 weeks at 13 °C (55 °F). The goal is to prevent the bananas from producing their natural ripening agent, ethylene. Ripening occurs in special rooms upon arrival in the destination country. These rooms are air-tight and filled with ethylene gas to induce ripening. The vivid yellow color consumers normally associate with supermarket bananas is, in fact, caused by the artificial ripening process. Flavor and texture are also affected by ripening temperature. Bananas are refrigerated to between 13.5 and 15 °C (56.3 and 59.0 °F) during transport. At lower temperatures, ripening permanently stalls, and the bananas turn gray as cell walls break down. The skin of ripe bananas quickly blackens in the 4 °C (39 °F) environment of a domestic refrigerator, although the fruit inside remains unaffected.

Tree-ripened” Cavendish bananas have a greenish-yellow appearance which changes to a brownish-yellow as they ripen further. Although both flavor and texture of tree-ripened bananas is generally regarded as superior to any type of green-picked fruit this reduces shelf life to only 7–10 days. Ripe bananas can be held for a few days at home. If bananas are too green, they can be put in a brown paper bag with an apple or tomato overnight to speed up the ripening process.

Bananas can be ordered by the retailer “ungassed” (i.e. not treated with ethylene), and may show up at the supermarket fully green. Green bananas that have not been gassed will never fully ripen before becoming rotten.

Banana as a Prebiotic

“A prebiotic is a selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host well-being and health” 11). The classification of a food or a food ingredient as prebiotic requires the scientific demonstration of resistance to gastric acidity, hydrolysis by mammalian enzymes, and gastrointestinal absorption; fermentation by intestinal microflora; and selective stimulation of the growth and/or activity of intestinal bacteria associated with health and well-being 12). Indeed, fermentation of a prebiotic food ingredient must be directed toward bacteria recognized as health promoting, with indigenous lactobacilli and bifidobacteria currently being the preferred targets.

Fructans (fructooligosaccharides) naturally present in almost all plant foods as reserve carbohydrate, are also used as functional ingredients by the food industry to modify the texture and taste due to their properties as gelling agents, fat substitutes, soluble dietary fibers and low calorie sweeteners 13). Banana is a moderate source of fructan 14). In banana, fructan is synthesized by the action of two different enzymes, 1-SST and 1-FFT. 1-SST transfers fructosyl residue from one sucrose molecule to another sucrose molecule leading to 1-kestose. 1-FFT transfers fructosyl residue from sucrose to 1-kestose thereby elongating the chain leading to 1-nystose 15). The basic molecule required for synthesizing fructan molecule is sucrose. Wide differences in fructans content of banana cultivars have been reported and these differences in the fructan content can be attributed to several factors such as soil, cultivar, stage of ripening and storage conditions 16). For example, While Campbell et al. 17) from Ohio reported 1.09 mg/100 g of dry mass, Hograrth et al. 18) also from Ohio documented 430 and 600 mg/100 g fruit weight at different stages of maturity and Homme et al. 19) from France reported 130 mg/100 g in banana puree. In contrast, Muir et al. 20) did not detect fructan in Australian banana. On the other hand anana cultivars from Brazil had high and varied content of kestose, while nystose was detected only in one cultivar – Prata 21). Low temperature ripening (16 °C) of banana resulted in higher fructan distribution indicating accumulation of these carbohydrates in cold conditions 22). Treatment of banana with pectinase enhanced fructan extraction significantly 23). The relatively simple enzymatic method developed could provide a basis to optimize extraction from other food sources. Fructan loss during steaming of banana may be due to thermal degradation 24). In contrast, fructan content increased during puree preparation because of the concentration resulting from loss of moisture 25).

The demand for fructans, in food industry is increasing steadily because of their functional properties.

Fructans are oligo and polysaccharides consisting of short chains of fructan units with the single D-glucosyl unit at the reducing end. In humans, there is no enzyme for digesting fructan. They are thus undoubtedly part of the dietary fiber complex and because of their specific fermentative properties, fructans do have characteristic features different from those of other dietary fibers. As dietary fiber, fructans have positive effects on basic physiological functions of the colon, i.e., stool production and fecal excretion. A recent meta-analysis of the published data 26) reveals that consuming inulin-type fructans significantly increases fecal biomass. This also regularizes bowel habit, a classical physiological effect of dietary fiber 27), 28).  Fructans have many health benefits: stimulate the growth of beneficial microorganisms in the gut that limit the pathogens and reduce the risk of colon cancer 29), significantly increase stool frequency and prevent constipation 30), enhance calcium absorption 31) and bone mineralization in young adolescents 32), control blood sugar level and insulin requirement 33), reduce plasma levels of cholesterol and triacylglycerol 34) and stimulate the gastrointestinal immune system 35).

Table 2. Nutritional effects and potential health benefits of inulin-type fructans 

Enhanced functions
    Composition and activities of the gut microflora
    Stool production
    Absorption of Ca and other minerals
    Production of gastrointestinal endocrine peptides
    Immunity and resistance to infections
    Lipid homeostasis
Reduction of disease risks
    Intestinal infections
    Irritable bowel diseases
    Colon cancer
    Osteoporosis
    Obesity
[Source 36)]

Table 3. Experimental and human data that substantiate claims on inulin-type fructans: summary presentation

Property or target functionSupportive evidenceClaims: Inulin-type fructans…
Dietary fiberOligo/polysaccharideAre dietary fiber
Resistant to digestion
Fermentation
Bowel functionsBulking effectRegularize bowel functions
Stool productionRegulation of stool production
Improved stool consistency
Colonic microfloraSubstrates for anaerobic saccharolytic fermentationAre prebiotic
Selective stimulation of growth of health-promoting bacteria (e.g., bifidobacteria)
Bioavailability of Ca and MgIncreased absorption of Ca/MgIncrease Ca/Mg absorption
Increased bone mineral content/densityIncrease bone mineral content/density in adolescents
Lipid homeostasisReduction of triglyceridemiaReduce triglyceridemia in slightly hypertriglyceridemic individuals
Mechanistic data
[Source 37)]

Table 4. Data on inulin-type fructans that support hypotheses to be tested in human nutrition and clinical intervention studies: summary presentation

Target functions or disease riskSupportive evidence
Lipid homeostasisReduced cholesterolemia
ImmunostimulationImproved resistance to common infections in children
Improved response to vaccination
Gastrointestinal endocrinologyStimulation of production of intestinal hormonal peptides (GIP, GLP-1, PYY, ghrelin…)
Regulation of appetite
Inflammatory bowel diseases (IBDs)Improved management of the diseases
Improved clinical symptoms
Improved biomarkers
Colon cancerAnimal data in different experimental models
[Source 38)]

The gastrointestinal functions are primary endpoints that benefit most from fructans. One of the most promising effects is modulation of activities of the colon, an organ of the gastrointestinal tract that is recognized more and more as playing a variety of key roles in maintaining health and well-being as well as reducing the risk of diseases 39), 40), 41), 42), 43).

The concept of “colonic health” has thus emerged as a major target for functional food development in the area of enhanced function claims 44).

In addition to its important physiological and immunological functions, the colon is also involved in miscellaneous diseases from acute infections and diarrhea or constipation to chronic diseases such as inflammatory bowel diseases, irritable bowel syndrome, or cancer 45). Through modulation of the colonic functions, inulin-type fructans thus also have the potential to reduce the risk of some diseases.

Concept of balanced colonic microflora

The composition of the symbiotic colonic microflora is a key player in maintaining the colon (and thus the whole body) health. That composition is largely determined by the flora that establishes at and immediately after birth, is mostly “individual,” can be modulated by specific compounds in the diet, and may change during the lifetime, becoming more and more complex as we age 46).

To support health and well-being and to reduce the risk of various diseases, it was hypothesized that the gut (and especially the colon) microflora must remain a “balanced microflora,” i.e., a microflora composed predominantly (in numbers) of bacteria recognized as potentially health-promoting (such as lactobacilli, bifidobacteria, fusobacteria, plus others yet to be determined and discovered) to prevent, impair, or control the proliferation of potentially pathogenic/harmful microorganisms (including some species of E. coli, clostridia, veillonellae, or Candida) 47). Evidently, that hypothesis does not imply that the so-called potentially pathogenic/harmful microorganisms are useless and must be eliminated. Indeed, the colonic microflora is a complex “ecosystem” with a wide variety of potential interactions among the different populations of microorganisms, and it cannot be excluded that some interactions between potentially health-promoting and (a low number of) potentially harmful bacteria and/or microorganisms do in fact play a role in maintaining health and well-being and in reducing the risk of some diseases. It is thus possible that some populations of potentially harmful or even pathogenic bacteria are necessary, provided they remain small compared with the health-promoting species. This is particularly true for the species that are recognized as being both potentially health promoting and potentially harmful. Thanks to the new molecular methodologies now available to analyze its composition in terms of phyla, genera, species, or even strains, researchers are now in a new phase of exploration of the gut microflora, the activities of these microorganisms and even more so the interactions, exchanges, and complementarities that exist in that extremely complex microbiota.

The prebiotic properties of fructans

Inulin and oligofructose are the most studied and well-established prebiotics. As previously mentioned, they escape digestion in the upper gastrointestinal tract and reach the large intestine virtually intact, where they are quantitatively fermented and act as prebiotics. Indeed, in the studies 48), 49) that investigated the effects of inulin and oligofructose on the human gut microbiota, a selective stimulation of growth of the beneficial flora, namely bifidobacteria, to a lesser extent lactobacilli, and possibly other species such as the Clostridium coccoides-Eubacterium rectale cluster known to be butyrate producers has been reported 50). According to these data, and even though all inulin derivatives induce a significant stimulation of growth of bifidobacteria, they do not have, qualitatively, the same effects in the different segments of the large bowel, which might be differently influenced.

The bacterial flora colonizing surfaces in the large intestine, especially the mucosa, the mucus layer, or eventually the particulate materials in the colonic lumen 51), is a topic of growing interest. Indeed, studies using either biopsies or resected samples have demonstrated the presence, in the mucus layer, of a microflora with a specific composition, different from the luminal colonic microflora 52), and it has been speculated that this mucosal microflora could play specific roles in the protection of the mucosal epithelium and that changes in the composition of that intestinal environment could influence the miscellaneous functions of the epithelium. In an ex vivo protocol in which 15 healthy volunteers selected from the colonoscopy waiting list had been asked to supplement their usual diet with Synergy (15 g/d) for 2 wk, preliminary data have shown increases in both bifidobacteria and lactobacilli counts in the mucosa 53). Using the model of rats harboring a human fecal flora, Kleessen et al. 54) have similarly reported that feeding an inulin-supplemented diet significantly increased (16-fold) mucosal bifidobacteria (cells/mm2 mucosal surface) even though the stimulation was not significant in the intestinal lumen. Thus, the prebiotic effect of inulin-type fructans concerns both the luminal and the mucosa-associated microflora.

The daily dose of a prebiotic does not correlate with the absolute numbers of “new” bacterial cells that have appeared as a consequence of the prebiotic treatment. The daily dose of an inulin-type fructan is thus not a determinant of its prebiotic effect, even if, in 1 group of volunteers with relatively similar initial counts of fecal bifidobacteria, a limited dose-effect relation has been established 55). The reason is that an important parameter, i.e., the initial number of bifidobacteria, is usually not taken into account. In the first report of a prebiotic effect, Hidaka et al. 56) have already argued that the initial numbers of bifidobacteria influence the prebiotic effect after observing an inverse correlation between these numbers and their “crude” increases after oligofructose feeding. Rao 57), Roberfroid et al. 58), and Rycroft et al. 59) have reached essentially the same conclusion. At the population level, it is the fecal flora composition (especially the number of bifidobacteria before the prebiotic treatment) characteristic of each individual that determines the efficacy of a prebiotic but not necessarily the dose itself. The ingested prebiotic stimulates the whole indigenous population of bifidobacteria to growth, and the larger that population is, the larger is the number of new bacterial cells appearing in feces. The “dose argument” (often used as a marketing argument) is thus not straightforward, and it cannot be generalized because, as supported by the scientific data, the factors controlling the prebiotic effect are multiple. The “dose argument” can thus be misleading for consumers and should not be allowed.

One important question remaining unanswered is the effect of prebiotic, especially inulin-type fructans, not on the numbers of bacteria, especially bifidobacteria, but rather on activities associated with these bacteria. Indeed, the health benefits for the host are part of the definition (“confers benefits upon host well-being and health”) 60), and these benefits are directly dependent on what these bacteria do, how they interact with the others, and how they modulate intestinal functions. Miscellaneous bacterial enzyme activities such as glucuronidase, glycosidases, nitroreductase; metabolites such as SCFAs (short chain fatty acids); or end products of the fermentation of amino acids, mucins, or sterols (especially primary and secondary bile acids) have been measured and shown to vary (increase or decrease) after feeding of prebiotics. But the relevance of these parameters still remains to be established, especially in terms of their value as biomarkers of colonic and eventually host health and well-being or disease risk reduction. In that context, the effects of inulin-type fructans on these parameters reported so far are contradictory and difficult to interpret.

Bananas as an Energy Source during Exercise

In a study on banana as a source of energy in sport and exercise 61), this study compared the acute effect of ingesting bananas versus a 6% carbohydrate drink on 75-km cycling performance. 14 male cyclists (ages 18–45) who regularly competed in road races, completed two 75-km cycling time trials (randomized, crossover) while ingesting bananas or 6% carbohydrate drink (0.2 g/kg carbohydrate every 15 min). Pre-, post-, and 1-h-post-exercise blood samples were analyzed for glucose, granulocyte and monocyte phagocytosis and oxidative burst activity, nine cytokines, F2-isoprostanes, ferric reducing ability of plasma and metabolic profiles (inflammatory markers). Data from this study with 14 trained cyclists indicate that acute ingestion of bananas or 6% carbohydrate drink supported 75-km cycling performance and underlying metabolic processes to a similar degree when the rate of carbohydrate delivery was equated. Exercise-induced inflammation, oxidative stress, and changes in innate immune function were also comparable between bananas and 6% carbohydrate drink trials, with the exception of a few biomarkers including IL-10 and IL-8. Bananas compared to 6% carbohydrate drink resulted in higher antioxidant capacity and serum dopamine levels. The 75-km cycling time trials caused wide ranging increases in serum metabolites, and the data support a similar pattern of intensified production of glutathione and utilization of fuel substrates in several pathways during both bananas and 6% carbohydrate drink. In summary, ingestion of bananas before and during prolonged and intensive exercise is an effective strategy, both in terms of fuel substrate utilization and cost, for supporting performance 62).

Banana and type 2 diabetes and high cholesterol

In this small pilot study 63), the researchers were exploring the effects of consumption of banana in thirty hyper-cholesterolemic and fifteen type 2 diabetic subjects. They were given a daily dose of 250 or 500 grams of banana for breakfast for 12 weeks. Fasting serum lipid, glucose and insulin levels were measured initially as well as every 4 weeks. Daily consumption of banana significantly lowered fasting blood glucose after consuming banana 250 or 500 g/day for 4 wk and LDL-cholesterol/HDL-cholesterol ratio in hypercholesterolemic volunteers 64). Analysis of blood glycemic response after eating banana showed significantly lower 2 h-postprandial glucose level compared to baseline in hypercholesterolemic volunteers given a dose of 250 g/day. The changes of blood glucose and lipid profile in diabetic patients were not statistically significant, but for plasma levels of adiponectin, there were significantly increased compared to baseline. Although it remains to be confirmed with larger group of volunteers, this pilot study has demonstrated that daily consumption of banana (@ 250 g/day) is harmless both in diabetic and hypercholesterolemic volunteers and marginally beneficial to the later 65).

 

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