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Raman spectroscopy as a useful tool in nutritional determination and distinction of Allium species
* 1 , 1 , 2 , 1 , 1 , 1 , * 1
1  Faculty of Agriculture, University of Belgrade, Serbia
2  Institute of Field and Vegetable Crops, Novi Sad, Serbia
Academic Editor: Alessandra Durazzo


Allium species, especially Allium sativum or garlic, have been known for centuries, due their health benefits on human health. Phytochemicals present in these species exhibit numerous health effects that are well described in the scientific literature.

Raman spectroscopy combines with a microscope could give detailed information on the spatial distribution of different bioactive components of fresh food samples, and could give important insight in characterization and evaluation of the crops, widely known as plants for different agricultural applications. The application of modern spectroscopy methods gives us the opportunity to enrich the diet by examining new, poorly tested, Allium species that are a potential source of bioactive components.

Our study aimed to nutritional characterization and discrimination of Allium fistulosum (F), A. nutans (N), A. odorum (O), A. schoenoprasum (S), A. ampeloprasum var. ampeloprasum (AA), A. sativum var. sagittatum (SS) samples grown in Serbia. Selected Allium species were grown in open field conditions, from October 2018 to July 2019.

Samples were recorded using XploRA MicroRaman spectrometer at a 532 nm wavelength, spectra were preprocessed using Spectragryph software, and PCA was performed using PAST software.

According to raw vibrational spectra, onion samples are rich in carbohydrates, mostly pectin and cellulose as well as pectic acids, carotenoids, while the lower intensity bands indicated the attendance of proteinous structure.

Multivariate analysis, based on PCA, was applied in order to differentiate between the chemical compositions of six onion samples. The score plot of PC1 versus PC2 shows a reasonably good separation between the samples. The score plot suggests the existence of two groups of objects along PC1 axis (SK, NK, FK, OK and SSK, AAK). The loading plot shows that the variables with the positive contribution along PC1 axis corresponded to the signals at 754, 955, 1148, 1309, 1428 cm-1, indicated on polysaccharide, pectin, stretching vibration of glycosidic linkages while in the higher extend on the differences indicated band positioned at 1564 cm-1, probably directed to proteins. On the other side the signal at 1057 cm-1 is mostly responsible for the differentiation of SSK and AAK mainly depending on polysaccharide. According to PC2, FK, NK showed differences comparing to SSK and SK. The most influential parameters along PC2 axis corresponded to the signals at 1470 and 1516 cm-1, indicated on methyl ester groups in pectin and carotenoids.

Raman spectroscopy in a fast and noninvasive way could give preliminary discrimination in nutritional characteristics of six onion species grown in Serbia.

Keywords: Allium species, PCA, fingerprint region of carbohydrates, carotenes, proteins.