Moisture Content and Drying
The relationship between moisture content and drying time is inversely proportional with each other. As the drying time increases the moisture content decreases. . Moisture content decreases as drying time is prolonged because more moisture is removed as drying time is extended. Weight losses resulted from quantitative and rapid volatilization of water. Rapid moisture loss occurred during the first hour of drying because it is the time where the food sample contains most of the free water and when immediately subjected to high temperatures, moisture loss would be at its greatest.
Vegetables as samples
The texture of food products has become an important feature influencing consumers’ acceptance of a food. The properties and distribution of water in food products affects their structure and texture.
Freezing of water decreases the involvement of water in enzymatic and biochemical reactions which are deteriorative in foods the reason why the lettuce stored at the freezer did not demonstrate enzymatic browning compared to the sample stored at room temperature which enzymatic browning was evident.
Most vegetables are over 90 percent water of total weight. The water and dissolved solutes inside the rigid plant cell walls give support to the plant structure, and texture to the vegetable tissue. Moisture migration is the principle physical change occurring in frozen foods affecting the physical, chemical, and biochemical properties, including texture and palatability of the food. It follows that a “wetter” material will have a higher water or water vapor content. The water vapor pressure will be higher and this will drive the water vapor towards areas where the water vapor pressure is lower (or less water is present). In other words, water vapor will diffuse from a damp area into a dry area. This will continue until such time as equilibrium is achieved or until no further migration can take place. Water molecules will migrate from areas of high water vapor pressure (or high relative humidity) towards areas of lower water vapor pressure (lower humidity).
Formation of ice results in expansion. Ice crystals, upon further cooling, contract. Also several other components in the system can also contract due to lowering of the temperature (other solutes). Hence the volume contract as the temperature of the frozen product is lowered, which causes the density to increase. Since the water in the refrigerated pechay was frozen, it had resulted then to lower percent moisture content than the pechay left in the room temperature. Therefore, the increase in weight of the frozen pechay is due to the migration of moisture from the atmosphere of the refrigerator to the pechay. This is so because the relative humidity of the refrigerator is higher than the relative humidity of the vegetable. The decrease in weight of the pechay stored in room temperature is due to the transfer of moisture from the pechay to the atmosphere outside the container.
As food is frozen, the unfrozen material becomes more concentrated and forms a “glass” which encompasses the ice crystals. The temperature range at which this occurs depends on the solute composition and the initial water content of the food. The formation of glass protects the texture of the food and gives good storage stability. In this experiment, the pechay have undergone fast freezing, wherein smaller ice crystals were formed within both cells and intercellular spaces. There is little physical damage to cells, and water vapor pressure gradients are not formed; hence there is minimal dehydration of the cells. The texture of the vegetable is retained to a greater extent. If vegetables were allowed to stand at room temperature, it would have become wilted and tough through loss of moisture.
Freezing of Water
Appearance, texture and mouthfeel evaluation of the solutions, and including frozen ice cream was performed. These differentiates the attributes of each depending to its solute concentration. Our 0% milk and sucrose solutions was colorless, hard, dry, smooth surface and it increased its volume. As stated by Fellows (1990), the volume of ice is 9% greater than that of pure water, and an expansion after freezing would therefore be expected. Eventually, it will expand because it was made of pure water without the presence of any solutes. While, 40% milk and sucrose solutions was light colored, flat and smooth surface, hard, thin texture, creamy and slightly icy mouthfeeling . However, 60% milk solution was dark yellow in color, thick and soft texture, and was smooth- creamy mouthfeel. Another, 60% solution was sucrose. It turns to white solid with gelatinous-viscous sides, thick-gooey texture, and was smooth and sticky. It differs in texture, the higher the solute concentration, and the lesser its hardness. It is also observed that there was an increase of volume on 0%, and slightly on 40% solution. As stated earlier, it should be expected to change because of water and solute quantity.
Finally, the evaluation of frozen ice cream and refrozen after thawing. The major difference was the mouthfeel. Frozen ice cream was thick and soft in texture, and smooth and creamy mouthfeel. However, thawed and refrozen one was thick and rough in texture, and icy, grainy in mouthfeel. It turns icy because, ice crystals have a lower vapor pressure than regions within the cells, and water therefore moves from the cells to the growing crystals. (Fellow, 1990)
Moisture Content and Water Activity
(On the biscuit experiment)
The weight of the biscuit in 100, 80, and 60 % RH bottles increased as the day progressed. While the weight of the biscuit in 40 and 20 % RH bottles decreased as the day progressed. The increase of weight in 100, 80, and 60 % RH bottles were caused by adsorption of water in the environment to produce equilibrium between the sample and the environment. The decrease of weight in 40 and 20% RH bottles were caused by desorption of water from the sample to produce an equilibrium between the sample and the environment.
Water and Enzymatic Activity
(on mung bean experiment)
After comparing both the samples, the group was able to distinguish major differences between the 2 samples. The aroma of sample A was plain. It had a dry smell. Its flavour was also that of plain and dry seeds. This is due to the fact that enzymatic reactions hardly took place due to the lack of moisture. Sample B differed in its aroma as being described as having a grass/leafy smell and its flavour was agreed to be of wet leaves or wet grass, one which had a distinct flavour of mung which was very enhanced by adding few drops of water. These effects are due to the germination of the mung beans due to presence of water. ater participates in the growth and development of these seeds by providing energy to enzymes in order to react with the proteins found in beans.