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Re-utilization of Sucrose Solution Used in Apple Preservation

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ABSTRACT. Osmotic dehydration, by immersion in sucrose solutions of different concentrations, is commonly used by industries in the production of candied dehydrated fruits. A refractometer is needed in order to read the concentration of the solution after each use. By doing this, the effectivity of the sugar solutions will be maximized. However, several small-scale companies cannot afford an expensive equipment such as the refractometer.

The researchers then decided to work on apple preservation in order to come up with a table of data. This is to check the changes in the concentration of the 2.5 M solution after each use and to determine if the said solution can effectively preserve the apples. Every 12 hours, the immersed apples were replaced by a new batch of sliced fruit. But befor doing so, the concentration of a sucrose solution was read using the refractometer. The results were tabulated and after six readings, the change in the concentration with respect to the number of readings were translated into a graph. This graph serves as a basis for determining the effectivity of the sucrose solution.


Candied dehydrated fruits make good export items because of their desirable flavor. Due to the wider acceptance from consumers today, many small companies have started to produce them.  Industries use osmotic dehydration by immersion on sucrose solution to preserve fruits. The refractometer, an expensive equipment, is used to deter¬mine the concentration of sugar in the solution after its use. With the absence of the refractometer, many of these enterprises do not make use of sucrose solutions again because they are not sure whether the solution is still effective or not.

This research project was therefore designed to help small-scale industries save time, energy, and expenses by accurately graphing and measuring the concentration of the sugar solutions used in dehydration and preservation of six batches of apples without necessarily obtaining an expensive refractometer.


I. Fruit Preservation

Mailard Reaction. Sugar may interact with or-ganic constituents and it is known as mailard reaction. Preserves that are stored for unduly long periods darken and lose their fresh flavor as a result of chem¬ical spoilage.

Freezing and Thawing. The purpose of freezing storage is to retain to, as great degree as possible, the properties of the fresh fruits, vegetable, or other food products. However, during freezing and thawing, certain irreversible changes occur that render the frozen and thawed products quite different from the fresh ones in texture and general appearance.

Sugar Preservation. Studies on the manufacture of candied mangoes have been conducted by re¬search agencies so as to standardize the procedure.

Local sugar preservation of fruits only require higher amount of sugar and choice fruits.  The procedure basically involves a two-step drying process: 1) osmotic dehydration by sugar or syrup solution; and 2) conventional dehydration such as the air and sun drying (Ponting, 1973). Osmosis. Osmosis is the diffusion or the move¬ment of a substance in a form of small particles (molecules or ions), under their own kinetic energy, through a differentially permeable membrane. The expression, differentially permeable, is more accu¬rate than the commonly used semipermeable, since no membrane is strictly semipermeable. A differentially permeable membrane contains pores which are large enough to allow the passage of distilled water molecules, but too small to allow the particles of a solute in water to pass through in appreciable quantity. Consequently, if two solutions of different concentrations are separated by such a membrane, unequal pressure—usually called osmotic pressure—is exerted upon its two sides (Courchaine, 1950).

Fruits contain from 70-90% water. When they are cooked in syrup, the osmotic pressure of sugar draws out this water as well as that from the microbial cells to attain a concentration of 40-65% or to saturated sucrose sugar level. A fruit may be whole, cut, or pureed. Acid and Pectin. In local sugar preservation, acid does not seem to feature as an important ingredient in the process, but if present in judicious amount, it aids in the preservation. Bacteria are generally deterred from growing in an acid medium. Desired ratios are attained by the addition of corn syrup to the sucrose solution or by facilitating sucrose inversion by theaddition of an organic acid such as nitric acid (Bernad, 1986).

One other component which is not given much importance in local sugar preservation of fruits is pectin. This substance ties up water when a jel forms in the presence of suitable concentrations of sugar and acid. The water is, thus, unavailable to the organisms (Guzman, 1977), Invert Sugar. The sugar used for the sugar preservation affects the quality of candied product (Cruess, 1958). Unless glucose or invert sugar is used, the product will dry too ‘completely and become hard and granular. Crystallization of the fruit surface may be prevented. Although there have been many proposed methods of fruits preservation, addition of sugar has been considered as one of the most acceptable means. It is observed that the addition of sucrose to fruit products enhances their natural fruit flavors beside acting as a preservative (Gatchalian et al., 1978). H. Re fractometer

The functional design of most refractometers are divided largely as to its use of scale, light, and measurement. Pointers on How to Effectively
Use the Refractometer
1. Check the scale. Prior to the practical measure-ment, the scale should be checked if it is correct or not. If not, the scale should be adjusted by using the accessoried driver to turn the scale adjustment screw. For this check, some different standard specimens for each type of hand refractometer are used. These are distilled water, saturated salt solution, and test piece. 2. Light guide. Usually, daylight is good enough for all types of refractometers. But the direction of the light guide is different in accordance with the type of refractometer. In disregard of this direction, sufficient measuring is quite difficult. 3. Practical measurement. Wipe off the distilled wa-ter, saturated salt solution or others that were used to check the scale. Then put a few drops of the specimen on the prism. Close the cover plate. You can see the percentage, which is the position of the cross of the horizontal demarcation and the vertical scale in the field of view.

High quality apples were brought from a fruit vendor in Balintawak market. A kilo of white sugar was bought from the same vendor. Four-hundred twelve and a half grams of white sugar were placed in a 0.5-L flask and distilled water was added halfway to make the sugar dissolved easily then distilled water was poured until the 0.5-L mark was reached. The apples were washed with running water. They were peeled then sliced into small pieces. The chopped apples were placed in a clean jar, then weighed, using a triple-beam balance. The combined mass of the container and apples was 300g. The 2.5 M sucrose solution was poured into the container with the apples. Then stored in the refrigerator for 12 hours. After 12 hours, the apples were removed from the solution and the volume of the solution was measured using the 500-mL graduated cylinder. A refractometer was used to measure the concentration of the sucrose solution. A saturated NaC1 solution was used to calibrate the refractometer. A solution was checked following the removal of the apples. The whole process was repeated ten times. The data were recorded.


The concentration of the sucrose solution de-creased after each batch of apples was preserved. The lower concentration of water outside the apple al¬lowed osmosis to occur, leaving the apple pieces dehydrated. The juice drawn out from the apples through osmosis made the concentration of the sucrose solution lower.

We can see from table 1 that the change in the concentration after the first batch was preserved is 12.06%, but the succeeding changes in concentration ranged from 3.1-5.7%. It is apparent that there is a decrease in the concentration of sugar in the solution. This is because the apples preserved in the solution is hypotonic to the solution so it draws in the sugar and gives out the water inside. There is also noticeable decrease in the rate of decreased sugar concentration. One reason for the decrease is the change in concentration may be because of the presence of microorganisms that may have fermented the solution. The length of time between the removal of apples and the reading of the concentration of the solution can also be considered a source of error, because it might have an effect on the results. Other causes may be the improper handling of the refractometer and inaccurate measurements.


The group was able to produce the table after six readings of the 2.5 m sucrose solution used. The change in the concentration of the sugar was measured with the aid of the refractometer. The table is advantageous to people who want to preserve apples but not own a refractometer which can help to determine whether a 2.5 in solution can be reutilized or not.


Acu, V.S. 1984. Syrup Cellular Penetration and Histological StuoY – of Candied Dehydrated Mango (Mangifera indica Unn.), Unpublished BSFT Thesis.
Bemad, M.C. 1986. ProductOevelopmentand Accelerated Storage Studies of Dehydrated Pineapple (Ananas comosus Unn. mem). Unpublished BSFT Thesis.
Ponting, J.D. 1973. Osmotic Dehydration of Fruits: Recent Modifications and Applications. Unpublished BSFT Thesis.

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