Tuesday, 21 August 2012

Preservation of mangoes by cooling



Abstract

This research aims to determine the ideal amount of time for preserving mangoes by cooling. The mangoes were placed in the freezer for different periods of time at a constant temperature, and were tested for their physical appearance, taste, texture, sugar contents, and pH (H+ ) concentration.) After preliminary tests in finding out the best insulator for the mangoes’ stay in the freezer, twenty were placed in the freezer with a constant range temperature of negative five to zero degrees ‘Celsius. Every two weeks, a batch of four mangoes were released from the freezer, tested and observed.

After three months of testing, a conclusion was made that the longest time for freezing a mango without damaging it is about four weeks.

Introduction

The idea Of preservation of mangoes using a cooling process came about through a research done by a scientist name Dr. Alfredo Alvarez from the University Nacional Autonoma de Mexico. Since the local Philippine mango, Manggang kalabaw has similar properties to a grape, both being fruits with a short shelf-life, we decided to experiment with the mango. The variable which will stay constant in this experiment are the temperature and preparation of mangoes. After the mangoes are released from the freezer they will be tested for their appearance, taste, texture, pH, and sugar percentage. The research is divided into two parts. The first part of the research is determining the best insulator or kind of protection the mangoes will have in its long stay in the freezer. The second part of the research is the experiment proper where the length of time the mangoes will stay in the freezer will be manipulated. Knowledge on prolonging shelf-life while maintaining the quality of the mango do different part of the world. A problem with exporting fruits is a short-shelf life

Review of Related Literature

The mango fruit Magnifera inidica, is of great importance, especially in developing countries, like the Philippines, where the annual yield is greater than 10000 tons. Due to its increasing demand for exports storage like and quality is a major concern. (Salokhe, 1989)

Mango cultivated in Thailand is usually harvested from May to June. The problem associated with attempts to increase storage life is chilling injuries and abnormal ripening during prolonged storage. This subtle aromatic is invariably affected when the harvested fruit is subjected to adverse environmental conditions during handling (Lizada, 1991). Results showed that as the fruit matured, the green color disappeared to bring out a yellow color, and Penetrometer values, pH, soluble solids, and Breix-acid ration increased as the mango matured. These problems spur interest for a search for better storage methods to prolong the shelf-life of mangoes.

Studies revealed that ethylene is produced by the fruit even before harvest maturity is attained: low oxygen gas alters carbohydrate metabolism: and the susceptibility of the fruit to chilling or hyperthermal injury is affected by maturity and pre-treatment (Lizada, 1991). The approach of delaying the ripening process in the fruit is to inhibit production of ethylene, or inhibit changes triggerd by this ripening hormone (Philippine Technology Journal, 1991). The use of plastic film came during the 1960s. Plastic slowed down the metabolism of fruits and vegetables which enables exporters to transport in bulk using ships instead of planes making it much cheaper. Another improvement in exporting was the pre cooling process.

Methodology

Testing for Mango’s Appearance, pH, and sugar content:

These tests were made for comparison on the effect of storage in the freezer of the mangoes for different periods of time. Factors considered were color, taste, and texture. No machines were used for this test.

To test for pH, we used a digital pH meter with 0.5 intervals, ranging from 0.5 to 14. Preparing the mango for pH testing, the first step was turning the mango meat to pulp. This was done by placing half a mango without its skin inside a food processor and liquidifying the meat. To test for sugar content, the juice had to be extracted from the mango.


The first pall of the experiment was to determine the best insulator for freezing the mangoes for long periods of time. The five insulators for testing were Reynolds Aluminum foil, Glad Sandwich bags, broadsheet newspaper, Reynolds Wax paper and no insulator. The first ten mangoes from the same tree were used. Mangoes were gently washed with water removing the sap and dust on the skin of the mango before they were wrapped. Then we randomly picked one mango and tested it for its sugar contents, pH, taste and appearance. The other nine mangoes were wrapped with the insulator, two for each insulator except for control. The mangoes were then placed in the freezer for a period of eight weeks.

Test Proper Twenty mangoes that have the same characteristics were picked from the same tree. They were all placed in the freezer fully wrapped with Glad sandwich bags. The mangoes were immediately placed inside a freezer with a constant temperature range of-5 to- IOC. When a batch of mangoes was released, they were immediately placed in a water bath until the skin became soft and were then tested for appearance, pH, and sugar content.

Result Discussion


The first part of our research was determining the best insulator for the mangoes in their stay inside the freezer. Out of the observations of the mangoes we were able to conclude that the plastic bag is the best kind of insulator.

Even if there was a slight freezer taste in the mango wrapped with plastic, it was considerably less compared to that of the taste of the mangoes wrapped in newspaper, wax paper and no insulator at all.


In terms of taste, appearance, texture, pH, and sugar content, the two week batch was very similar to the control. The only difference was the sugar content which almost halved and a slight difference in texture. The four week hatch also had similar characteristics to the control. It kept it tastes, texture and appearance. The mangoes in the six week batch started developing dry areas. It had also developed a freezer taste. The eight week batch was the worst out of all batches. This batch had a definite freezer taste and a large area had dry skin which was not present before the mangoes were placed in the freezer.

Out of the result and observations, the longest time to keep the mangoes in the freezer without damaging the fruit is four weeks.

Recommendation

More tests should be done on the mangoes including the vitamin content test, and using an instron puncture test machine to test the texture, instead of using the hand and fingers to touch and feel the fruits as was done in this research. A more controlled environment freezer for cooling should be used. There is a process in cryogenics where nitrogen is used to freeze the mangoes instantaneously.


Researchers:

 Michelle L. Agripa, Romeo L. Gilbuena,  Janice K. Henson,  Franco C. Lim Jose,  Alejandro Lopez









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