Amino acids all have the general structure see Figure 2. The R in the diagram represents a functional group that varies depending on the specific amino acid in question. For example, R can be simply an H atom , as in the amino acid glycine, or a more complex organic group. When two amino acids bond together, the two ends of nearby amino acids shown in red are released and the carbon called a carboxyl end of one amino acid bonds to the nitrogen end of the adjacent one forming a peptide bond, as illustrated in Figure 3.
When many amino acids bond together to create long chains, the structure is called a protein it is also called a polypeptide because it contains many peptide bonds.
Proteins serve two broad purposes in the human body:. Structural proteins form most of the solid material in the human body. For example, the structural proteins keratin and collagen are the main component of your hair, muscles, tendons and skin.
Functional proteins help carry out activities and functions in the human body. For example, hemoglobin is a functional protein that occurs in the red blood cells and helps to transport oxygen in the body. Myosin is a protein that occurs in muscle tissue and is responsible for the ability of muscles to contract. Insulin is a functional protein that helps regulate the storage of the sugar glucose in the human body.
A subclass of the functional proteins is the group of polypeptides referred to as enzymes. Enzymes help to carry out specific chemical reactions in the body. For example, amylase is an enzyme that occurs both in human saliva and in the intestines that helps to break apart the glucose-glucose bonds in the carbohydrate starch, thus allowing your body to absorb the glucose and use it for energy. There are an estimated , different proteins in the human body alone, and each of them is made up of a combination of different combinations of only 20 amino acids.
Each protein has a different structure and performs a different function in the body. When we eat protein-containing foods such as meat, fish, beans, eggs, cheese, etc. These amino acids are then recombined into proteins specific to each individual person in a process called protein synthesis.
There are hundreds of thousands of proteins that exist in nature. This is possible. In order to carry out these very precise jobs in the body, each individual protein has to be unique and specific to the job in question. The in vitro starch digestibility results illustrate that the incorporation of SFP into wheat bread decreased the potential glycemic response of bread and increased the antioxidant capacity of bread.
In conclusion, this nutrient-rich SFP bread has the potential to be a technological alternative for the food industry. These nutrients have been shown to have a positive effect on human health, such as prevention of cardiovascular disease, hypertension, cancer, and diabetes, as well as containing micronutrients such as vitamins A, D, B6, and B12 and minerals iron, zinc, iodine, selenium, potassium, and sodium [ 1 ].
The human body is unable to synthesize EPA and DHA, and therefore these nutrients need to be acquired through dietary interventions. One such dietary intervention could be the fortification of common food products with fish powder. The high protein content of fish powder may also have an effect in reducing the glycemic index of foods and this in turn may have a potential beneficial health effect with regard to weight control and obesity [ 2 ].
Fish proteins also exhibit antioxidant activities, which may be used to control health diseases via the reduction of oxidative stress [ 4 ]. Throughout the world, bread is an important staple food and widely consumed, and are made from grain-based carbohydrates [ 5 ]. These cereal products are often low in protein, vitamins, and minerals, and are usually deficient in essential amino acids and fatty acids and, therefore, are not a balanced food [ 6 ].
Due to their relatively low cost, availability, acceptability, and widespread consumption, cereal food products are considered to be one the best vehicles for food fortification [ 7 ]. Proteins and amino acid derived from fish are considered nutritionally superior to that of plant origin ingredients.
As consumer attention has become focused on the prevention of diseases, such as cardiovascular disease, type-2 diabetes, colon cancer, and obesity through diet [ 9 ], there has been an increased demand for enrichment of food with improved physical volume, color, and texture , nutritional amino acid and fatty acid content, protein digestibility, and starch digestibility , and antioxidant properties [ 10 ].
Low glycemic index foods can be achieved through the utilization of protein and lipid rich ingredients combined with cereal gains in products such as bread. Phenolic compounds exhibit biological properties, such as antioxidant activity.
Food rich in polyphenols have the potential to protect against various diseases associated with oxidative damage, such as cancer, and cardiovascular and neurological disease [ 11 ].
In recent years, to achieve this, many nutritional ingredients such as carob [ 12 ], flaxseed and lupin [ 5 ], mushroom powder [ 6 ], cobia [ 13 ], and Chlorella vulgaris [ 8 ] have been incorporated into bread to improve its nutritional composition and product quality. Other products, such as pasta [ 14 ] and pizza [ 15 ], have been developed with the inclusion of fish powder in their formulation.
However, the technological and nutritional properties of bread fortified with partial replacement of wheat flour by salmon fish O. Therefore, this study evaluated the effects of fortification of different levels SFP on the bread nutritional quality including protein, amino acid, fatty acid composition, and in vitro starch and protein digestibility, i.
The salmon fish material O. Salmon meat was prepared from the meat components of the fish after deheading and deboning. The formulation for the bread products is shown in Table 1 A and is derived from a previous study [ 17 ].
It was then kneaded by hand for 5 min and rested at room temperature for 5 min. The bread samples were allowed to cool for 2 h after baking. Bread formulations, proximate compositions, and physical properties of bread.
A: Ingredients used in salmon powder SP enriched bread. B: Proximate composition of bread elaborated with SP. C: Physical properties of bread made with SP. Control bread. The AACC method The Soxhlet extraction method determined the fat content of the samples, and ash content of the materials was determined according to our previously published methods [ 18 ].
The energy valve was calculated using the formula described in Reference [ 18 ]:. The moisture content of the bread was determined using the oven-drying method, and the general operation procedures for this method described in Reference [ 19 ]:. Bread height, specific volume, texture, and color attributes were all measured.
The bread volume was determined by the rapeseed displacement method, following the AACC, The specific volume of bread was obtained through dividing the bread volume mL by the bread weight g. Texture analysis of the bread was determined on slices of 25 mm thickness, using a texture analyzer TA. The test settings were as follows: pretest speed—1. The bread was compressed twice to provide insight into how samples behave when chewed.
An in vitro starch digestion process was used to determine the rate and extent of starch digestion of the bread as described in Reference [ 10 ]. The process mimicked stomach digestion via the use of 0.
Aliquots 1 mL were taken time 0 and added to 4 mL absolute alcohol. Small intestine digestion was mimicked via the addition of enzyme solution 5 mL of 2. The samples were analyzed for reducing sugar content using 3.
Column flow rate was 0. O-phthaldialdehyde was used as a fluorescence derivative reagent for primary amino acids, and 9-fluorenylmethyl chloroformate for secondary amino acids. Detection utilized a fluorescence detector with an excitation of nm and emission of nm for primary amino acids. At 22 min, the detector was switched to excitation nm, emission nm to detect secondary amino acids such as proline.
The amino acid results are expressed in mg of amino acids per g protein. The multi-enzyme technique described in Reference [ 22 ] was used for the determination of in vitro protein digestibility of the bread sample.
Protein digestibility of foods is frequently assessed using in vivo rat experimental models as originally proposed in Reference [ 23 ]. Aside from in vivo methods, Reference [ 21 ] also recommends the use of in vitro methods using enzymes.
A 50 mL of protein suspension was prepared in distilled water 6. The multi-enzyme solution 1. EAAI was calculated according to the procedure of Oser It considers the ratio between the EAA of the test protein and the EAA of the reference protein, according to the equation:. The biological value BV indicates the utilizable fraction of the test protein. The nutritional index NI normalizes the qualitative and quantitative variations of the test protein compared to its nutritional status.
An aliquot of the extracted samples 1. The fatty acid content was expressed as a percentage of the total fatty acids detected. The methyl ester was quantified through the integration of the peak area using the software Star 6. Helium gas was utilized as the carrier gas with a flow rate of Total phenolic content of supernatant obtained from in vitro gastro-intestinal digestion was measured using the Folin-Ciocalteu method as described in Reference [ 25 ].
The DPPH 2,2-diphenylpicrylhydrazyl assay was used to determine the antioxidant activity of the material using the method as previously described [ 26 ]. All experiments were performed in triplicate unless otherwise stated. Statistical software version 16 Minitab, Melbourne, Australia was used to perform the statistical analysis of the data.
Table 1 B illustrates the physico-chemical properties of breads that were enriched with different levels of SFP. Inclusion of SFP increased the protein content of the breads from The lipid content of SFP-enriched breads varied from 6. The ash contents of SFP breads ranged from 2. Samples with added SFP exhibited lower moisture contents as compared to the control breads.
Previous research has shown similar results when cobia powder, flaxseed, and lupin have been added to breads [ 5 , 13 ]. A similar result has been obtained previously by researchers fortifying bread with cumin and caraway flour [ 27 ].
The specific volume of the breads decreased from 2. It is well known that the gluten components in wheat are responsible for the visco-elastic nature of dough and that this contributes to the shape of the bread by trapping gases during the fermentation stages of bread making. The replacement of wheat flour with SFP would have diluted the gluten content in the doughs and hence contributed to a weaker dough and reduced bread volume. Our findings agree with previous researchers [ 13 ] who prepared bread enriched with cobia Rachycentron canadum flour and found that increasing the cobia flour levels in wheat bread decreased the bread volume.
In addition, the different nutrient composition had different effects on the gas production during the fermentation process of bread, thus influencing bread volume [ 6 ]. Table 2 A illustrates the textural properties of bread.
The hardness of bread is related to the peak force required to compress the sample, while chewiness represents a quantitative estimation of energy needed to disintegrate bread structure [ 10 ].
Hence, it can be postulated that the addition of SFP, and the dilution of the gluten network in the doughs, attributed to the thickening of gas cell walls within the bread crumb and hence the increased level of hardness in the breads.
Additionally, the increased levels of protein and lipid that were observed in the SFP-enriched bread samples may be partly responsible for a decrease in gas retention causing unstable gas cells resulting in a more compact structure. Previously, researchers have noted similar observations when combining fish or mussels into bread samples [ 13 , 28 ].
Springiness represents the capacity of samples to spring back after a deformation due to the compression. Researchers evaluating the addition of mushroom powders into bread also showed that a reduction in springiness and cohesiveness was related to mushroom powder inclusion and the weakening of the gluten network in the doughs and breads [ 6 ].
Technological characteristic of bread enriched with different levels of salmon powder SB. A: Texture profile analysis. B: Color characteristics of crust and crumb. Bread color is the result of complex reactions that depend on the physico-chemical characteristics of dough water, starch, and lysine content and the temperature used during baking process. The darkening of SFP breads may also be attributed to an increased Maillard reaction taking place during baking due to the higher lysine content.
In the Maillard reaction, reducing carbohydrates react with free amino acid side chains of proteins mainly lysine , and lead to amino acid-sugar reaction products [ 12 ].
In addition, it has been shown that the incorporation of lentil flour into bread doughs significantly affected yellowness and lightness characteristics [ 12 ]. Reshmi et al. Protein quality is considered one of the important characteristics for measuring the nutritional characteristic of a food matrix. The contents of phenylalanine and cysteine decreased in SFP bread compared to the control. Three fatty acids individually form ester bonds with a glycerol molecule to form a triglyceride molecule, which is the main constituent of most of the fat on both animals and plants.
Due to the presence of a long hydrocarbon chain, fatty acids are considered as non-polar molecules. Most fatty acids can be produced by the body. But, the two fatty acids linoleic acid and alpha-linoleic acid cannot be produced by the body; hence, they are considered as essential fatty acids. Figure 2: Saturated and Unsaturated fatty Acids.
Fatty acids can be classified into two based on the saturation of the hydrocarbon chain. In saturated fatty acids , each carbon of the hydrocarbon chain is joined to the adjacent carbon by a single bond. In unsaturated fatty acids , the hydrocarbon chain consists of one or several double bonds. Based on the distribution of atoms around the double bond, unsaturated fatty acids are classified into two: cis and trans fatty acids. Cis -fatty acids are the liquid fats while the trans- fatty acids are the solid fats.
An amino acid refers to a simple organic compound containing both a carboxyl —COOH and an amino —NH2 group while a fatty acid refers to a carboxylic acid consisting of a hydrocarbon chain and a terminal carboxyl group, especially any of those occurring as esters in fats and oils. This explains the basic difference between amino acids and fatty acids. The structural difference between amino acids and fatty acids is that while an amino acid is made up of a hydrogen atom, a carboxylic acid group, an amine group, and an R group arranged around a central carbon atom, a fatty acid is made up of a hydrocarbon chain attached to a terminal carboxylic group.
Furthermore, most R groups of amino acids are complex and contain atoms like sulfur and nitrogen apart from carbon and hydrogen while the R groups of fatty acids are mainly long chain hydrocarbons. This is another difference between amino acids and fatty acids.
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