Key enzymes, physicochemical properties and volatile compounds in garlic (Allium sativum L.) cloves at different storage temperatures

Abstract

The dynamic changes in key enzyme activities, physicochemical properties and volatile compounds of garlic cloves were evaluated after storage at −20, 4, 25 and 60 °C for 64 d and 28 d, respectively. Samples stored at −20 °C exhibited no significant changes in physicochemical properties. A rapid increase in gamma-glutamyl transferase (γ-GT) activity was observed in samples stored at 4 °C. Furthermore, samples stored at 25 °C or 60 °C facilitated the development of reducing sugar, total acids, total polyphenols and superoxide dismutase with prolonged storage time. Gas chromatography-mass spectrometry (GC-MS) identified 69 volatile compounds in garlic cloves treated at 4 °C and 25 °C, with sulfur-containing compounds (46 types) being the primary components of the garlic clove aroma profile. Interestingly, garlic with a strong spicy flavor developed a rich fruity aroma during storage at 25 °C. This may be related to the increase in the content of ester compounds such as (E)-2-butenoic acid ethyl ester, ethyl tiglate and β-phenylethyl butyrate. Correlation analysis suggested that peroxidase activity was positively correlated with the content of free amino acids (r = 0.972, p < 0.01) and reducing sugar (r = 0.724) in garlic cloves stored at 4 °C, while the activity of γ-GT (−0.969<r < −0.507) and alliinase (−0.665<r < −0.230) was negatively correlated with the content of most characteristic sulfur-containing compounds at 25 °C. These results provide deeper insights into the changes in garlic cloves during storage, which is essential for the quality assessment and development of garlic products.