Compartmentalization and It's Effects on Fruits

Compartmentalization and its effects on Fruits

Harsh. Chandarana

Abstract: Compartmentalization properties of three different fruits, namely apples, bananas and oranges were observed. Physical properties of the cell structure of apples were observed by bruising one apple and keeping the other as control, it was seen that the browning in apples was mainly due to activity of polyphenol oxidase. Ripening properties of bananas were observed by comparing the bananas kept in different conditions for a period of one week. The browning in bananas was also accredited to the activity of polyphenol oxidase. Oranges were kept in ambient and frozen condition respectively, it was observed that oxidative stress and chlorophyll activity in the oranges were a major cause of changes in the texture and internal loss of the oranges' cell structure.

Key Words: Apples, Oranges, Browning, Ripening, Enzyme

Introduction:

Cells walls and membranes in fruits are major contributors of their textural properties as well as the separation of compounds that may react with each other. The texture of a fruit begins changing when the cellular structure of the fruit is damaged by either harvesting or ripening. Due to the damage in the cellular structure, textural changes (softening) and discoloration which in turn have a bad impact on the quality of the fruit. Ripening-associated softening of fleshy fruit is a direct consequence of enzyme mediated cell wall degradation (Vincente and others, 2007). Browning of fruits is also associated to cell wall damage as well as internal enzymes that start acting as soon as cell wall integrity is lost. It causes deleterious changes in the appearance and organoleptic properties of food (Quevedo and others, 2009). Browning may also take place rapidly following mechanical injury as in the preparation of certain fruits for serving. Phenolic content of fruits usually reaches a maximum during growth and declines during ripening (Weaver, 1974).

The banana peel consists of an epidermis interrupted by stomata, parenchyma cells and fibrovascular bundles parallel to the long axis (Weaver, 1974). "A thin layer of protoplasm in which plastids are embedded lines the inner walls of parenchyma cells. In outer layers of tissue the plastids have pigments, but in deeper layers the plastids serve as centers for accumulation of starch. A vacuole is found in the center of each cell which accumulates sugars as the starch is hydrolyzed to sugars during ripening" (Weaver, 1974). Chilling injury in banana fruit is caused by prolonged exposure of the fruit to temperatures less than 13o C (Harvey, 2005). As Harvey clearly explains, exposure of bananas to low temperatures has a negative impact on the quality of banana as a whole. But, he also mentions, that during exposure to lower temperatures, the browning activity on the peel of the banana is minimum as it lowers the activities of the enzymes.

Unripe apple, is generally firm and hard, has pectic cementing substance, protopectin. As the apple ripens, pectinases hydrolyze the protopectin to pectinic substances dominating in a ripe apple and pectic acids dominating in an over ripe apple (Oregon State, 2012). Discoloration of apple tissue is mainly the result of oxidation of phenolic compounds by polyphenoloxidase (Banks and Samim, 1993). Banks and Samim also observed that in a bruised apple, cortical tissue became darker, browner, and increased in color intensity in the first few hours following impact. This is an important study as the color changes in the control apple and bruised apple can be explained using this phenomena. As soon as the bruised apple is cut, one sees a lot of discoloration near the places of the bruise, the color slowly fades out as there is loss in both fresh and dry weight from the bruise area presumably because of loss of sap from the bruise to surrounding healthy tissues (Banks and Samim, 1993).

Exposure of citrus fruit to frost often results in the development of freeze injury

during their maturation in plants (Ferreyra and all, 2006). Tests conducted by Ferreyra and all (2006) suggest that freezing temperatures provoke a notable metabolic switch in orange fruit resulting in low-quality fruits. They also noticed that there was a considerable damage to the internal quality of the fruit that was frozen, resulting in low carbohydrate metabolism as well as a decrease in the juice content that the fruit initially had.

The main objective in this lab was to observe the changes that occur in fresh fruits when cellular integrity is lost and what happens when the molecules in the fruit come in contact with the other molecules come around.

Materials and Methods:

Physical Damage:

For measuring the effects of physical damage on a fruit, a macintosh apple was continuously bounced on a counter until bruised. The bruised apple was compared to a control apple which was not bounced at the table. The apples were cut and later observed at 0 time, 30 minutes, 60 minutes during the time period of the lab. Later, the apples were refrigerated for a week for a latter observation. Calculations for the browning index were carried out using Adobe Photoshop.

Fruit Ripening:

For this experiment, three unripe bananas were stored in different conditions for a week. One banana was stored in a refrigerator, the second one was stored in a brown paper bag at room temperature and the third one was left uncovered at room temperature. A picture of the bananas was clicked every day to observe the changes over time in each one.

Freeze Damage:

Valencia oranges were taken into observation for measuring freeze damage. Oranges were externally observed and weighed. One of the orange was kept in a home freezer for a week. Pictures were taken before and after one week. The oranges were not subjected to any type of physical damage. After a week, the frozen orange was thawed at room temperature and was cut into half along with the control orange to observe the changes that incurred internally. The oranges were weighed to see if there was any change in the weight as compared to the previous week.

Results and Discussion:

Fruit Ripening:

All the bananas on day one were hard and green in color with no spots on them. There was a gradual increase in the browning of the bananas that were stored in ambient conditions as well