Dynamics of soil carbon storage under different land use years in arid agriculture

Abstract：Garlic is considered as a kind of popular food and condiment in our daily life. It has numerous health benefits in the prevention of cancer and cardiovascular disease because of its antioxidant and antimicrobial ability. However, the acceptance of garlic product is limited largely due to its unique odor. Hence, it is critical to develop a processing method to minimize the garlic odor but keep its antioxidant and antimicrobial ability at the same time. Here we reported the effect of high pressure processing (HPP) on the flavor, antioxidant compounds, and antimicrobial property of garlic at 200, 300, 400, and 500 MPa for 10 min. The volatile compounds contributing to the unique garlic odor are analyzed by GC-MS (gas chromatography - mass spectrometer), and the most abundant component is diallyl disulfide (DADS). Compared to the traditional thermal treatment (steam bleaching for 60 s), HPP method (500 MPa, 10 min) decreases DADS contents in garlic by 21.28%, which leads to significant reduction in garlic odor. The 300, 400, and 500 MPa HPP treatments decrease the enzyme activity of allinase to 75.44%, 68.53%, and 68.17%, respectively, compared to the untreated garlic. Since allinase is the key enzyme in the degradation of allicin, the allicin contents in garlic have increased under HPP treatment significantly (P<0.05). The better antioxidant activity in HPP treated garlic is approved through analyzing its ferric reducing antioxidant power (FRAP) and DPPH (1,1-diphenyl-2-picrylhydrazyl) scavenging ability, Which are both higher than that in the thermal treated samples. Thermal treatment has significantly decreased the total phenolic contents in garlic by 32.72 mg/100g, while HPP treatments have no significant effect on total phenolic contents, which indicates that HPP method can retain more antioxidant compounds in garlic. The antimicrobial activities of the garlic samples under different treatments are investigated against 4 types of bacteria, Escherichia coli, Staphylococcus aureus, Penicillium spp., and Aspergillus niger. The untreated garlic samples produce inhibition zone with a diameter of 28.82±0.58, 39.25±1.24, 33.5±1.06, and 11.13±0.23 mm for E. coli, S. aureus, Penicillium, and A.niger, respectively. The thermal treated garlic samples produce no inhabitation zone against the 4 aforementioned bacteria, which indicates that they have lost their antimicrobial properties entirely. On the contrary, HPP treated garlic samples have shown inhabitation zone against all 4 bacteria tested, although the diameters of such zones are smaller than those of the untreated samples, except the ones against A. niger. This indicates that unlike thermal treatment, the HPP treated garlic samples still retain their antimicrobial ability. In addition, the correlations between the total thioethers content, DADS content, total phenolic content, and antimicrobial property, antioxidant property of the HPP treated garlic samples are investigated. There is a significant positive correlation between the total thioethers content and the antimicrobial property, and it may result from the sulfur compound. The results presented in this paper suggest that, compared to thermal processing, HPP method can effectively reduce the unpleasant odor in garlic, especially the DADS, while retain the antioxidant and antimicrobial property of garlic. Therefore, HPP is an appropriate non-thermal processing method for garlic products.