Evaluation of Melanoidins Formed from Black Garlic after Different Thermal Processing Steps

Abstract

The objective of this study was to evaluate the characteristics of melanoidins formed from black garlic (BG) after different thermal processing steps. The melanoidins formed from BG during thermal processing were produced in large amounts, and the initial (280 nm), intermediate (360 nm), and final stage product (420 nm) had similar tendencies. Compounds like degraded proteins, peptides, and phenolic acids were present in the melanoidins during thermal processing. All the melanoidin samples showed different absorptions in the UV-visible spectra, although these had similar shapes. Moreover, the carbon, hydrogen, and oxygen content of melanoidins formed from BG during thermal processing decreased initially, and then increased. However, the nitrogen content increased during thermal processing. As thermal processing progressed, the molecular weight of all the melanoidin samples showed increasing intensities, whereas the major peaks of each melanoidin sample had different retention times. Furthermore, the melanoidins formed from BG after different thermal processing steps contained -OH, -CH, amide I, and III groups. The crystallinity of the melanoidins was majorly formed at 31.58° and 43.62° (2θ).

Keywords: black garlic; melanoidins; thermal processing.

Fig. 1

Browning measurements at 280, 360, and 420 nm of melanoidins formed from black garlic after different thermal processing steps. BG1, black garlic cloves at step 1; BG2, black garlic cloves at step 2; BG3, black garlic cloves at step 3; BG4, black garlic cloves at step 4; BG5, black garlic cloves at step 5. Different letters (a–e) within same absorbance are significantly different at P<0.05, as analyzed by Duncan’s multiple range test.

Fig. 2

Wavelength spectra of melanoidins formed from black garlic after different thermal processing steps. BG1, black garlic cloves at step 1; BG2, black garlic cloves at step 2; BG3, black garlic cloves at step 3; BG4, black garlic cloves at step 4; BG5, black garlic cloves at step 5.

Fig. 3

Molecular weights of melanoidins formed from black garlic after different thermal processing steps. BG1, black garlic cloves at step 1; BG2, black garlic cloves at step 2; BG3, black garlic cloves at step 3; BG4, black garlic cloves at step 4; BG5, black garlic cloves at step 5.

Fig. 4

FT-IR spectra of melanoidins formed from black garlic after different thermal processing steps. BG1, black garlic cloves at step 1; BG2, black garlic cloves at step 2; BG3, black garlic cloves at step 3; BG4, black garlic cloves at step 4; BG5, black garlic cloves at step 5.

Fig. 5

X-ray diffraction patterns of melanoidins formed from black garlic after different thermal processing steps. BG1, black garlic cloves at Step 1; BG2, black garlic cloves at Step 2; BG3, black garlic cloves at Step 3; BG4, black garlic cloves at Step 4; BG5, black garlic cloves at step 5.