The cells of fruits and vegetables are typical of plant cells with principal components as cell wall, chloroplast, golgi complexes, mitochondria, endoplqsmic recticulum etc.
Chemical Composition Of Fruits and Vegetables
- Water: most fruits and vegetables contain more than 80% water with some tissues such as lettuce, melons, cucumbers containing about 95% water. There is fluctuation in water content during the day as the temperature changes so it is better to harvest when the maximum amount of water content is possible. Time of harvest is important in leafy vegetables because of rapid loss of water content.
- Carbohydrates: are the next most abundant group, they can be available as low molecular weight sugars or high molecular weight polymers. They account for 2-40% of tissue. In fruits, carbohydrates exists as sugars but you would find starch in vegetables and unripe fruits.
- Protein: fresh fruits and vegetables are not important sources of protein to the human diet. It provides about 1-2%.
- Lipids: comprises of less than 1% of most fruits and vegetables and they are associated with the protective cuticle layers of the produce. Exception to this would be avocado which have 20% lipids and olives which have 15% lipids.
- Organic Acids: most fruits and vegetables obtain organic acids at levels in excess of what is needed for metabolic pathways. The excess organic acid is generally stored in the vacuoles. Besides their bio-chemical importance, organic acids contribute greatly to the taste of fruits e.g, citric acid in oranges and lemons, magic acids in apples, tartaric acid in grapes. These acids provide tartness and slow down bacteria spoilage. With respect to bacteria spoilage, the most important contribution of organic acids is in lowering, reducing the food pH under anaerobic conditions and slightly above pH of over 4.6.
- Nitrogen: nitrogen containing substances; these substances are found in plants as different combinations. Proteins, amino acids, amides, nitrates etc. Vegetables contain between 1.0-5.5% while fruits contain less than 1%.
- Vitamins: are defined as organic materials which must be supplied to the human body in small amounts apart from the essential amino or fatty acids. Vitamins function as enzyme systems which facilitates the metabolism of proteins, carbohydrates and fats but there is growing evidence that their roles in maintaining health may extend further. Vitamin A or retinol is required to maintain the structure of the eye. Vitamin C, in fruits and vegetables is of major importance in human nutrition for the prevention of the disease Virtually all human dietary vit C is obtained from fruits and vegetables. Daily requirement of vit C is about 500mg. Lack of vitamin C causes fragile capillary wall, easy bleeding of the gum, loosening of the teeth and bone joint diseases.
- Enzymes: are biological catalysts that promote most of the biochemical reaction which occur in vegetables cells. Enzymes have an optimal temperature around 50 degrees Celsius where their activity is at maximum, heating beyond this optimal temperature deactivates the enzyme. E.g, lipases and peroxidases.