Temperature had a remarkable impact on the quality and flavour of black garlic. © 2015 Society of Chemical Industry.

Garlic, an economically important vegetable, spice, and medicinal crop, produces highly enlarged bulbs and unique organosulfur compounds. Here, we report a chromosome-level genome assembly for garlic, with a total size of approximately 16.24 Gb, as well as the annotation of 57 561 predicted protein-coding genes, making garlic the first Allium species with a sequenced genome. Analysis of this garlic genome assembly reveals a recent burst of transposable elements, explaining the substantial expansion of the garlic genome. We examined the evolution of certain genes associated with the biosynthesis of allicin and inulin neoseries-type fructans, and provided new insights into the biosynthesis of these two compounds. Furthermore, a large-scale transcriptome was produced to characterize the expression patterns of garlic genes in different tissues and at various growth stages of enlarged bulbs. The reference genome and large-scale transcriptome data generated in this study provide valuable new resources for research on garlic biology and breeding.

Black garlic produced from fresh garlic under controlled high temperature and humidity has strong antioxidant properties. To determine these compounds, five fractions (from F1 to F5) were separated and purified by elution with chloroform:methanol at different ratios (8:1, 6:1, 4:1, 2:1, and 0:1; v/v). The antioxidant activity of each fraction was analyzed. The results showed that F3 and F4 had higher phenolic contents and stronger 2,2-diphenyl-2-picrylhydrazyl radical scavenging activity than the others. Seven purified individual components were further separated using semipreparation high-performance liquid chromatography from these two intensely antioxidant fractions (F3 and F4), their structures were elucidated by high-performance liquid chromatography coupled to diode array detection, electrospray ionization, mass spectrometry, H nuclear magnetic resonance, andC nuclear magnetic resonance spectrometry. Three compounds including adenosine, uridine, and 2-acetylpyrrole were first identified in black garlic, except for 5-hydroxymethylfurfural, (1S, 3S)-1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid, and (1R, 3S)-1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid. The cellular antioxidant activities of uridine, adenosine, carboline alkaloids, 5-hydroxymethylfurfural, and ethyl acetate extracts were consistent with the results of in vitro experimental antioxidant properties. The results provide useful information for understanding the health benefits of black garlic products.

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Because freezing treatment can destroy the cell structure of garlic, we investigated the effect of freezing pretreatment on black garlic processing with the traditional processing method as contrast. Results showed that freezing for 30 h had the greatest impact on the reducing sugar content. The control garlic processing 21–24 days had the best quality. Freezing pretreatment can affect the black garlic quality through the browning degree, reducing sugar content, amino‐N content, total phenolic content and 5‐hydroxymethyl‐2‐furaldehyde (5‐HMF) levels. The freezing garlic had a faster color change than control samples. When the processing ended, the reducing sugar content, total phenols content and 5‐HMF content of freezing pretreated garlic were increased by 51.88, 58.54, 25%, respectively, compared with the control samples. The amino‐N content of freezing‐pretreated garlic decreased 50.97% compared with the control one. The results indicated that freezing pretreatment can promote the generation of functional materials. Practical Applications Although garlic has been used worldwide as food or herbal supplement, some people feel discomfort because of its strong pungent odor. Black garlic is one of the garlic‐processed products, eliminating its stimulating odor. However, the quality of black garlic products on the market is varied and the processing time is long. As is known, freezing is widely used to destroy cell structure. In the present study, the use of freezing pretreatment in black garlic processing can promote the generation of functional materials and significantly reduce processing time from 60–90 to 22 days. These provided potential method to the black garlic processing.