Mango

Introduction

Native to Southeast Asia, Mango (Magnifera indicia) is one of the worlds major tropical fruits. Many hundreds of named cultivar exist (list), with total production worldwide being around 25 million metric tonnes a year.

Mango is a seasonal fruit that is consumed in a ripe state. Because of this, large quantities are processed into various other forms, such as puree, juices, nectars, concentrates, pickles and chutneys, canned slices, and dried fruit, products which have worldwide popularity.

Mango consist of between 33-85% edible pulp, with 9-40% inedible kernel and 7-24% inedible peel. Because of this, a huge amount of waste is generated during industrial processing. Such by-products are a serious disposal problem, so a commercial purpose for mango peel and kernels is sought after.
Mango
Mango

T
he utilisation of kernels has been investigated extensively in the past (source of fat, natural antioxidants, starch, flour and feed), however the use of mango peel has only just recently been researched in detail. For this reason, this article will review research on mango peel utilisation alone.


Peel utilisation

Mango peel has been researched as a dietary fibre and natural antioxidant source

Fibre

Dietary fibre (DF) is indigestible plant matter comprising of compounds such as cellulose, hemicellulose, lignin, pectin, β-glucans and gums. In the case of fruits and vegetables, cell walls and parenchymatous tissues are the dietary fibre supply.
Dietary fibre is grouped into two major classes: polymers soluble in water (SDF), such as pectins and gums, and those that are insoluble (IDF) – cellulose, hemicellulose and lignin.

A high dietary fibre intake has been related to several positive physiological and metabolic effects. In the digestive tract, DF increases faecal bulk and stimulates a more frequent intestinal evacuation, reduces excess stomach acid, and provides a favourable environment for the growth of beneficial intestinal flora. IDF has direct effects on faecal bulk and gut transit times, while SDF has indirect effects on blood glucose and cholesterol absorption. It has been shown that these specific properties play an important role in the prevention and treatment of obesity, cardiovascular diseases, colorectal cancer and diabetes.

Because of the well recognised benefits of increased fibre intake, food manufacturers nowadays tend to supplement products with additional fibre. Because of this, a trend has developed to find new sources of fibre. These are usually derived from cereals, however fibres from fruit generally have a better nutritional quality than those found in cereals, due to their more balanced composition -

· higher overall fibre content
· greater SDF to IDF ratio
· water and fat holding capacity
· lower metabolic energy value
· phytic acid content
· bioactive compounds such as flavonoids and carotenoids (to be discussed later)


Peel fibre


Mango peels have recently been shown as a favourable source of high quality DF due to -

  • high starch content
  • high cellulose content
  • high hemicellulose content
  • high lignin content
  • high pectin content (56-66 %: Berardini et al., 2005)
  • low lipid content
  • low cost of the fruit

In addition, in vitro starch studies carried out by Vergara-Valencia et al (2007) predicited low glycaemic responses from mango peel fibre.



Applications in food


Studies by Ajila, Leelavathi and Rao (paper currently in publication) showed mango peel powder incorporated into soft dough biscuits increased SDF content, polyphenols and carotenoids. Sensory evaluation showed these biscuits were more than acceptable. In short, mango peel powder yielded fibre enriched biscuits with improved antioxidant properties


Antioxidants

In food systems and human health, antioxidants function to reduce oxidative reactions by scavenging and eliminating free radicals. Oxidative reactions have deleterious effects on food products, and adverse health effects such as implications in cancer, atherosclerosis and diabetes.
It has been hypothesised that consuming more antioxidant-rich food may help protect against cellular damage and the aid in the prevention of chronic disease development.
Synthetic antioxidant compounds such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) are commonly used in processed foods. However, it has been reported that these compounds have some side effects and are carcinogenic (Branen, 1975; Ito et al., 1983). Natural antioxidants present in foods have therefore attracted considerable interest because of their presumed safety and potential nutritional and therapeutic value. The increased interest in natural antixidants has lad to the antioxidant evaluation in many species of fruits, vegetables, herbs, spices and cereals (plant derived foods).


Peel antioxidants


Ajila et al (2007) analysed antioxidants in ripe and upripe mango peels. They showed:
  • Polyphenols (measured via F-C method) ranged from 90-110 mg/g in unripe peels and 55-100 mg/g in ripe peels
  • Total carotenoids (quantified via absorbance at 470nm) ranged from 74-436 µg/g peel, with more in the ripe peels compared to unripe
  • Anthocyanins(quantified via absorbance at 510nm), ranged from 203-326 mg/100g in unripe peels and 360-565 mg/100g in ripe peels

As well as analysing the quantities of the specific antioxidants mentioned above, these researchers also investigated the overall radical scavenging ability (via DPPH assay), inhibition of lipid peroxidation and inhibition of lipoxygenase activity by mango peel (acetone extract). They reported that -
  • Ripe and unripe mango peel had a higher scavenging potential than BHA
  • Ripe peel extract was more effective than raw peel at inhibiting lipid peroxidation, but both were better than BHA
  • Unripe peel extract inhibited lipoxygenase activity more than ripe peel, but both were more effective than BHA


Biological relevance


The physiological relevance of mango peel antioxidant capacity was shown in a study conducted by Ajila and Rao (2008). Mango peel powder was shown to provide protection against oxidative stress in rat erythrocytes. Hydrogen peroxide-induced oxidative stress was lessened in cells treated with mango peel powder, with membrane protein degradation and morphological changes being less pronounced than the controls.


Processing

Research has also been conducted into extracting specific fractions of fibre and antioxidants from mango peel.
Berardini et al (2005) developed two methods for the combined extraction of pectin and polyphenols from mango peel:

· The first method extracted polyphenols by sulphuric acid from dried mango peels, then adsorbed them using a styrene-divinylbenzene copolymerisate resin. The pectin was then obtained from the effluent by precipitation with ethanol
· In the second method, pectin was precipitated by adding crude mango peel extract to ethanol. After removal of ethanol, the phenolic
compounds were obtained from the aqueous phase of the precipitation bath using the resin described above


It was found that both methods yielded the same amount of polyphenols, showing that the pectin did not interfere in any way with extraction.


Conclusion


To conclude, research on mango peel has shown it may impart health benefits through its fibre and antioxidant content. This suggests that this once-discarded waste product of mango production could now find a valuable use as a food ingredient or nutraceutical product.

References





Written by Tracey Feary
M.Sc. student
Food and Wine Science group, Lincoln University NZ
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