Energy is required at various stages of food processing and production. Between 50 to 100 MJ of energy is needed to produce and package each kilogram of a retail food product. This energy is used for power, heating and cooling. Food molecules like sugars and fats are broken down into smaller molecules through digestion and various cellular processes to produce energy molecules like ATP. This breakdown occurs in three stages - digestion, glycolysis/citric acid cycle, and oxidative phosphorylation in the mitochondria. The chemical energy from food is ultimately captured and stored in ATP molecules, which are then used to power various cellular functions.

1. Energy for food process
May 7, 2023admin
Energy for food process: According to estimates, a retail food product requires
between 50 and 100 MJ (megajoules) of energy to produce and package each
kilograms. Energy is needed in the food processing sector for power, heating,
and cooling.
How Cells Obtain Energy from Food
As we just saw, for cells to create and sustain the biological order that keeps
them alive, they need a steady flow of energy. Food molecules’ chemical
bonds, which act as the fuel for cells, are the source of this energy.
Particularly significant fuel molecules include sugars, which are gradually
converted to carbon dioxide (CO2) and water (Figure 2-69). In this part, we
outline the key processes involved in the catabolism, or breakdown, of sugars
and demonstrate how ATP, NADH, and other activated carrier molecules are
created in animal cells as a result. Since it accounts for the majority of energy
generation in most animal cells, we concentrate on glucose breakdown.
Additionally, fungi, many bacteria, and plants all use a very similar
mechanism. Various more compounds, such Proteins and fatty acids can also
be used as energy sources if the proper enzymatic pathways are followed.
Food Molecules Are Broken Down in Three Stages to
Produce ATP:
Before our cells can utilize the proteins, lipids, and polysaccharides that make
up the majority of the food we consume—either as a source of energy or as
building blocks for other molecules—they must be divided into smaller

2. molecules. Food consumed from the outside must be broken down, but not
the macromolecules found inside our own cells. Therefore, digestion is the
first stage of the enzymatic breakdown of food molecules and takes place
either outside of cells, in the gut, or inside of cells, in the lysosome, a
specialized organelle. (A membrane around the lysosome prevents the
digesting enzymes from mixing with the cytoplasm, In any case, during
digestion, enzymes break down the huge polymeric molecules in food into
their monomer subunits—proteins into amino acids, polysaccharides into
sugars, and fats into fatty acids and glycerol. Small organic molecules from
meals reach the cell’s cytosol after being digested to start the process of
progressive oxidation. Figure shows two further phases of cellular catabolism
in which oxidation takes place: stage 2 begins in the cytosol and concludes in
the mitochondrion, the main organelle responsible for turning food into energy;
stage 3 is exclusively restricted to the mitochondrion.
Each molecule of glucose is split into two smaller molecules of pyruvate
during stage 2, a process known as glycolysis. When sugars other than
glucose are transformed to one of the sugar intermediates in this glycolytic
pathway, they are then similarly reduced to pyruvate. ATP and NADH are two
different classes of active carrier molecules that are created during pyruvate
synthesis. After that, the pyruvate moves from the cytosol into the
mitochondria. Each pyruvate molecule there undergoes a transformation into
CO2 and a two-carbon acetyl group, which is then joined to coenzyme A
(CoA) to create acetyl CoA, another active carrier molecule . The sequential
oxidation and breakdown of fatty acids formed from lipids, which are
transported in the circulation and brought into cells as fatty acids, also
produces significant quantities of acetyl CoA.
All of stage 3 of the oxidative disintegration of food molecules occurs in
mitochondria. Since coenzyme A and acetyl CoA are connected by a high-
energy bond, the acetyl group in acetyl CoA is readily transferred to other
molecules. The acetyl group enters the citric acid cycle after being transferred
to the four-carbon oxaloacetate molecule. In these processes, the acetyl
group is oxidized to CO2, as we will explore momentarily, and significant
quantities of the electron carrier NADH are produced.In the mitochondrial
inner membrane, the high-energy electrons from NADH are then sent through
an electron-transport chain, where the energy produced during their
transmission is used to power a process that generates ATP and uses
molecule oxygen (O2). The majority of the energy generated by oxidation is
used in these last processes to make the majority of the cell’s ATP.

3. The phosphorylation of ADP to produce ATP that is fueled by electron
transport in the mitochondrion is known as oxidative phosphorylation because
the energy to drive ATP production in mitochondria ultimately originates from
the oxidative breakdown of food molecules. Chapter 14 primarily focuses on
the intriguing processes that take place within the mitochondrial inner
membrane during oxidative phosphorylation. The energy released during the
breakdown of carbohydrates and fats is redistributed as packets of chemical
energy in a form that is useful for usage in other parts of the cell through the
generation of ATP. A normal cell has around 109 ATP molecules in solution at
any given time, and in many cells, all of this ATP is changed over (that is,
used up and replenished) every one to two minutes.
The energetically unfavourable process Pi + ADP ATP is driven by
approximately half of the energy that might, in theory, come from the oxidation
of glucose or fatty acids to H2O and CO2. (In comparison, a normal
combustion engine, like one in a car, can only convert up to 20% of the fuel’s
potential energy into usable work.) Our bodies get heated as a result of the
cell discharging the remaining energy as heat.
Glycolysis Is a Central ATP-producing Pathway:
The decomposition of glucose through the series of processes known as
glycolysis—from the Greek glukus, “sweet,” and lusis, “rupture”—is the most
significant step in stage 2 of the breakdown of food molecules. ATP is created
during glycolysis without the help of molecule oxygen (O2 gas). Most cells,
including many anaerobic bacteria (those that can survive without using
molecular oxygen), include it in their cytoplasm. Prior to the introduction of
oxygen into the atmosphere by photosynthetic organisms, glycolysis likely
originated early in the history of life. A glucose molecule with six carbon atoms
is split into two pyruvate molecules, each with three, during the glycolytic
process.

4. Two molecules of ATP are hydrolyzed for every molecule of glucose to give
energy for the early processes, whereas four molecules of ATP are created in
the latter phases. As a result, towards the end of glycolysis, there is a net gain
of two ATP molecules for each glucose molecule that was broken down.
Figure presents the glycolytic route in broad strokes. A series of 10 distinct
processes, each of which produces a different sugar intermediate and is
catalyzed by a different enzyme, make up glycolysis. These enzymes, like the
majority of enzymes, all have names that end in ace, such as dehydrogenase
and isomerase, which describe the sort of process they catalyze.
Although there is no molecular oxygen involved in glycolysis, oxidation does
take place because some of the carbons released from the glucose molecule
are subjected to electron removal by NAD+ (forming NADH). Since the
process is stepwise, the energy of oxidation can be released in modest
amounts, allowing for the storage of some of it in activated carrier molecules
rather than its whole release as heat . As a result, part of the energy
generated during oxidation is used to directly synthesize ATP molecules from
ADP and Pi, while some of it is stored as electrons in the highly energetic
electron transporter NADH.
In the process of glycolysis, two molecules of NADH are created for every
molecule of glucose. These NADH molecules transfer their electrons to the
electron-transport chain outlined in aerobic organisms, and the NAD+
produced from the NADH is then utilized once more for glycolysis.

5. Fermentations Allow ATP to Be Produced in the
Absence of Oxygen:
Glycolysis is often just the first step in the third and final stage of the
breakdown of food molecules in most animal and plant cells. The pyruvate
produced in these cells at the last stage of stage 2 is swiftly carried into the
mitochondria where it is transformed into CO2 plus acetyl CoA and fully
oxidized to CO2 and H2O.
In contrast, glycolysis serves as the main source of ATP in the cells of many
anaerobic species, which do not use molecular oxygen and can grow and
divide without it. This is also true for some animal tissues, such skeletal
muscle, which may continue to work even when there is a shortage of
molecular oxygen. The NADH electrons and pyruvate remain in the cytosol
under these anaerobic circumstances. Pyruvate is transformed into
compounds that are expelled from the cell, such as lactate in muscle or
ethanol and CO2 in yeasts used in brewing and breadmaking. The NADH
surrenders its electrons during this phase, turning back into NAD+. To keep
the glycolysis processes going, NAD+ must be replenished.
These types of anaerobic energy-producing pathways are known as
fermentations. Early biochemistry was greatly influenced by studies of the
commercially significant fermentations carried out by yeasts. The discovery
that these processes could be investigated in cell extracts rather than living
beings was a remarkable development in 1896 as a result of work done in the
nineteenth century. Eventually, this ground-breaking finding allowed for the
dissection and examination of each individual fermentation reaction. The
discovery of the whole glycolytic pathway in the 1930s was a significant

6. biochemical achievement, and it was soon followed by the identification of
ATP’s crucial function in cellular functions. As a result, the majority of the
fundamental ideas covered in this chapter have been known for more than 50
years.
Glycolysis Illustrates How Enzymes Couple Oxidation
to Energy Storage:
We have previously used a “paddle wheel” analogy to illustrate how cells
employ enzymes to connect an energetically unfavorable process to an
energetically favorable one in order to obtain usable energy from the oxidation
of organic molecules. We now return to a stage in glycolysis that we have
previously covered to further show how coupled reactions take place.
Enzymes serve as the paddle wheel in our example. The three-carbon sugar
intermediate glyceraldehyde 3-phosphate (an aldehyde) is transformed into 3-
phosphoglycerate (a carboxylic acid) through two key events in glycolysis
(steps 6 and 7). This involves the two-step oxidation of an aldehyde group to a
carboxylic acid group. While still releasing enough heat to the environment to
make the overall reaction energetically favorable (G° for the overall reaction is
-3.0 kcal/mole), the overall reaction releases enough free energy to convert a
molecule of ADP to ATP and to transfer two electrons from the aldehyde to
NAD+ to form NADH.
Figure 2-73 depicts the process through which this amazing achievement is
performed. Two enzymes, to which the sugar intermediates are firmly linked,
direct the chemical processes. Through a reactive -SH group on the enzyme,
the first enzyme (glyceraldehyde 3-phosphate dehydrogenase) establishes a
transient covalent link with the aldehyde and then catalysis its oxidation while
still attached. An inorganic phosphate ion subsequently displaces the high-
energy enzyme-substrate bond formed by the oxidation to generate a high-
energy sugar-phosphate intermediate, which is then released from the
enzyme. This intermediate then joins with the phosphoglycerate kinase, the
second enzyme. In order to produce ATP and complete the reaction, this
enzyme catalysis the energetically advantageous transfer of the recently
formed high-energy phosphate to ADP.
Sugars and Fats Are Both Degraded to Acetyl CoA in
Mitochondria:
We now discuss catabolism’s third step, which calls for a lot of molecule
oxygen (O2 gas). Since abundant life-forms have been known to exist on
Earth for 3.5 billion years and the Earth’s atmosphere is thought to have

7. developed between one and two billion years ago, the use of O2 in the
reactions we will discuss next is thought to be of relatively recent origin.
Depicts a process for making ATP that does not require oxygen, suggesting
that cousins of this beautiful pair of linked events may have first appeared
relatively early in the evolution of life on Earth.
In aerobic metabolism, a massive trio of enzymes known as the pyruvate
dehydrogenase complex quickly decarboxylates the pyruvate generated by
glycolysis. A molecule of CO2 (waste product), a molecule of NADH, and
acetyl CoA are the byproducts of pyruvate decarboxylation. The structure and
method of action of the three-enzyme complex, which is found in the
mitochondria of eukaryotic cells, are described.
Summary
By using regulated stepwise oxidation to break down glucose and other
dietary components, chemical energy in the form of ATP and NADH is
produced. The citric acid cycle, which takes place in the mitochondrial matrix,
glycolysis, which takes place in the cytosol, and oxidative phosphorylation,
which occurs on the inner mitochondrial membrane, are the three primary sets
of processes that function in sequence, with the byproducts of one serving as
the raw material for the next. In addition to serving as sources of metabolic
energy, the intermediate products of glycolysis and the citric acid cycle are
also employed to create a large number of the tiny molecules that serve as
the building blocks for biosynthesis. Animal and plant cells store sugar
molecules as glycogen and starch, respectively; both plants and animals also
extensively employ lipids as a food storage. Together with the proteins that
make up the majority of the dry mass of the cells we consume, these storage
resources in turn serve as a significant source of food for us.
Reference
 https://www.theconsciouschallenge.org/ecologicalfootprintbibleoverview/food-
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energy#:~:text=Food%20and%20beverage%20processing,for%20heating%2C%
20cooling%20and%20electricity.
 https://gcwgandhinagar.com/econtent/document/1587461405Unit%20III%20Ener
gy%20in%20food%20processing.pdf