Citric acid is a versatile organic acid found in many fruits, especially citrus fruits like lemons, oranges, limes, and grapefruits. Its chemical formula is C6H8O7, and it's classified as a weak acid. Citric acid has a wide range of applications, from food and beverage production to household cleaning and skincare. In this comprehensive description, I'll delve into its properties, uses, production methods, health effects, and environmental impact.
*1. Properties of Citric Acid:*
Citric acid appears as a white crystalline powder or granules. It's odorless and has a tart, sour taste. It's highly soluble in water, making it easy to incorporate into various products. Citric acid is stable at room temperature but decomposes at higher temperatures, losing its acidic properties. It's a chelating agent, meaning it can bind to metal ions, making it useful in certain industrial processes and household cleaners.
*2. Sources of Citric Acid:*
While citric acid occurs naturally in citrus fruits, it's also produced commercially through microbial fermentation, primarily using strains of the fungus Aspergillus niger. This method allows for large-scale production of citric acid to meet the demand in various industries. Additionally, it can be synthesized chemically, although this method is less common due to higher production costs and environmental concerns.
*3. Uses of Citric Acid:*
*- Food and Beverage Industry:* Citric acid is widely used as a flavoring agent, acidity regulator, and preservative in the food and beverage industry. It enhances the flavor of many products and provides a tart taste in sodas, candies, jams, and preserves. It also acts as a preservative, extending the shelf life of packaged foods and preventing discoloration in fruits and vegetables.
*- Pharmaceutical Industry:* Citric acid is used in pharmaceuticals as a pH regulator, excipient in tablets and capsules, and as a flavoring agent in syrups and liquid medications.
*- Cleaning Products:* Due to its chelating properties, citric acid is used in household cleaning products such as descalers, bathroom cleaners, and dishwashing detergents. It effectively removes mineral deposits and stains without the need for harsh chemicals.
*- Cosmetics and Personal Care:* Citric acid is found in skincare products like exfoliating scrubs, facial peels, and anti-aging creams. It helps to promote skin renewal by gently removing dead skin cells and promoting collagen production.
*- Industrial Applications:* Citric acid is used in various industrial processes, including water softening, metal cleaning, and the production of detergents and surfactants.
*4. Production Methods:*
*- Microbial Fermentation:* This is the most common method for commercial production of citric acid. It involves fermenting glucose or sucrose-containing substrates with strains of Aspergillus niger in large-scale bioreactors. The fungus produces citric acid as a byproduct of its metabolism, which is then extracted and purified.
*- C
2. • In animals, amino acids undergo oxidative
degradation in three different metabolic
circumstances
– During the normal synthesis and degradation of
cellular proteins, some are not needed for new
protein synthesis.
– ingested amino acids exceed the body’s needs; amino
acids cannot be stored
– During starvation or in uncontrolled diabetes mellitus:
carbohydrates unavailable or not properly utilized
3. • Under all these metabolic conditions, amino
acids lose their amino groups to form α-keto
acids
– provide three- and four-carbon units that can be
converted by gluconeogenesis into glucose, the
fuel for brain, skeletal muscle, and other tissues
– The α -keto acids undergo oxidation to CO2 and
H2O
4.
5. Metabolic Fates of Amino Groups
• Amino acids derived from dietary protein are the
source of most amino groups
• Most amino acids are metabolized in the liver
• Some of the ammonia generated in this process is
recycled and used in a variety of biosynthetic
pathways
• the excess is either excreted directly or converted
to urea or uric acid for excretion
• Excess ammonia generated in other tissues
travels to the liver (amino groups) for conversion
to the excretory form.
6. • Glutamate and glutamine act as a kind of general
collection point for amino groups
• In the cytosol of hepatocytes, amino groups from
most amino acids are transferred to α-
ketoglutarate to form glutamate, which enters
mitochondria to form NH4
+
• ammonia generated in most other tissues is
converted to the amide nitrogen of glutamine,
which passes to the liver, then into liver
mitochondria
7. • In skeletal muscle, excess amino groups are
generally transferred to pyruvate to form
alanine, which transport amino groups to the
liver.
8.
9. Pyridoxal Phosphate Participates in the Transfer
of α-Amino Groups to α -Ketoglutarate
• in liver, removal of the α -amino
groups, promoted by enzymes called
aminotransferases or transaminases.
• This is to collect the amino groups
from many different amino acids in
the form of L-glutamate
• The prosthetic group is pyridoxal
phosphate (PLP), the coenzyme form
of pyridoxine, or vitamin B6
• Pyridoxal phosphate functions as an
intermediate carrier of amino groups
at the active site of minotransferases
10.
11.
12.
13. Glutamate Releases Its Amino Group As Ammonia in
the Liver
• In hepatocytes, glutamate is transported from
the cytosol into mitochondria for oxidative
deamination by L-glutamate dehydrogenase
• It is the only enzyme that can use either NAD+
or NADP+
• The α-ketoglutarate formed from glutamate
deamination can be used in the citric acid
cycle and for glucose synthesis
