*5.1.2 Fourier transform infrared spectroscopic profile identification (FT-IR)*

Infrared absorption spectroscopy is used in the literature to identify possible characteristic functional groups in organic compounds, providing important information on the chemical structure of the sample [38].


*Results are expressed as mean triplicate ± standard deviation.*

*a GAE = gallic acid equivalent.*

*b EQE = quercetin equivalent.*

*c ECA = catechin equivalent.*

*d ERT = rutin equivalent.*

#### **Table 3.**

*Total polyphenol (TP) and total flavonoid (TF) content of crude extracts of CA, CP, PX, and TM by-products.*

The identification of the functional bands using the Fourier transform infrared absorption spectroscopy (**Figure 4**) was performed in the CA by-product extract, where it was possible to observe bands at 1600, 2920, and 3331 cm<sup>−</sup><sup>1</sup> , which correspond to C-C stretching of aromatic ring by phenol group, C-H stretching of aromatic ring by phenol group, and O-H stretching of phenol group, respectively [27, 41]. In the CP by-product extract, the bands 1037 cm<sup>−</sup><sup>1</sup> corresponding to acid vibrations, 1120 cm<sup>−</sup><sup>1</sup> alcohol vibrations, 1668 cm<sup>−</sup><sup>1</sup> esters and sulfonic vibrations, and 2931 cm<sup>−</sup><sup>1</sup> O-H axial deformation of alcohol groups were displayed [33]. In PX, bands were shown at 1037, 1384, 1635, and 3448 cm<sup>−</sup><sup>1</sup> for C-O axial deformation of alcohol and phenols, C-H axial deformation vibration of methyl, C〓C axial deformation of carbonyl ring, and −OH deformation vibration of carbohydrates and carboxylic acids, respectively [38]. And the TM by-product extract exhibited bands at 1403 cm<sup>−</sup><sup>1</sup> aromatic ring stretching vibration, 1609 cm<sup>−</sup><sup>1</sup> ketone C〓O stretching vibration, and 3381 cm<sup>−</sup><sup>1</sup> free −OH stretching vibration [42]. All bands observed in CA, CP, PX, and TM were correlated to chemical structures present in polyphenols [27, 33, 38, 42].

#### *5.1.3 Thermal analysis*

Thermogravimetric analysis (TGA) is a technique that assesses the loss in mass of a substance as a function of temperature, it allows a variability of results to be observed, such as the temperature range at which the sample is degraded, until the temperature of the sample remains stable, at which temperature a change in physical state such as melting, among others, occurs. In addition, it is possible to plot a derivative on top of the TGA curve; this analysis can show which temperature range the greatest loss of

#### **Figure 4.**

*Identification of the functional bands using FT-IR absorption spectroscopy. The extracts of the by-products were compressed into Kbr and scanned in the 4000-400 cm<sup>−</sup><sup>1</sup> wavelength absorption range, with a resolution of 2.0 cm<sup>−</sup><sup>1</sup> and a scan number of 20 scans. a) CA [27], b) CP [33], c) PX [14], and d) TM [15].*

#### *Agro-industrial By-Products from Amazonian Fruits: Use for Obtaining Bioproducts DOI: http://dx.doi.org/10.5772/intechopen.91174*

mass occurs in [27]. This technique has been used for the evaluation of by-products and their extracts, such as CA [27], CP [10], PX [14], and TM [15].

The analysis of behavior and thermal stability can be employed in the quality control of raw materials and evaluation in the development of herbal medicines [43]. The thermogravimetric analysis (**Figure 5**) of the CA, CP, PX, and TM extracts presented on average three events of mass loss. The first corresponds to the evaporation of solvents, such as water. The second event represents successive reactions and may be related to loss of sugars. And the latter confers with the degradation and carbonization of organic matter from biocompounds [14, 15, 27, 28].

Such analysis is important to evaluate the thermal stability of the extracts, bearing in mind that prior knowledge has the purpose of guaranteeing the physical–chemical stability of the thermal constituents present in the extracts [38, 44]. The thermogravimetric study makes it possible to obtain information on the relationship between humidity and the maximum temperature of stability of the extract [44].

### **5.2 Quantitative analysis**

#### *5.2.1 High-performance liquid chromatography (HPLC)*

High-performance liquid chromatography is a separation technique that is among the main techniques used to determine polyphenol and flavonoid levels. Natsume et al. [45] point out that it is possible to carry out the identification and quantification of those elements in plant extracts and their derivatives; the analysis applied may be: reverse-phase HPLC (RP-LC) and reverse-phase HPLC-mass spectrometry (RP-LC/MS), and in particular, when it comes to the genus *Theobroma*, the majority of flavonoids observed in the species were catechin and epicatechin (**Figure 6**).

The literature points to the activity of certain flavonoids (**Table 4**), such as those identified and quantified in CA and CP a possible correlation with interesting

#### **Figure 5.**

*TGA and DTG curves of the by-product extracts obtained at 25 to 600° C at 10° C/ min under N2 atmosphere and flow of 50 mL/min: a) CA [28], b) CP [10], c) PX [14], and d) TM [15].*

#### **Figure 6.**

*Chromatograms about the phenolic compounds (280 nm) identified in the extracts of the by-products of a) CA [28], where 1—gallic acid, 2—protocatechuic acid, 3—catechin, 4—epigallocatechin-3-gallate, and 5—epicatechin; b) CP [33], where 1—gallic acid, 2—protocatechuic acid, 3—epigallocatechin-3-gallate, 4 epicatechin, 5—-*p*-coumaric acid, and 6—glycosylated quercetin; c) PX [14], where 1—catechin; d) TM [15], where 1—gallic acid.*


*b Concentration (mg/g).*

*c Viewed at 369 nm.*

#### **Table 4.**

*Polyphenolic compounds detected at 280 nm by HPLC in the extract of CA, CP, and PX by-products and UHPLC in the extract of TM by-product [10, 13–15].*

pharmacological activities, such as cardiac protector [46] reducing oxidative stress [47]. The phenolic acids, such as gallic acid, found in CA, CP, and TM, confers antioxidant properties both to food and to the body, so they are indicated for the treatment and prevention of cancer, cardiovascular diseases, and other illnesses [48]. According to Natsume et al. [45], some flavonoids may be related to the reduction of the probability of developing atherosclerosis, since the ingestion of these biocomposites contribute to the inhibition of oxidation of low-density lipoprotein (LDL).
