Cloning and characterization of an oxiranedicarboxylate hydrolase from Labrys sp. WH-1.

OBJECTIVE: This study aimed to clone and characterize the oxiranedicarboxylate hydrolase (ORCH) from Labrys sp. WH-1. METHODS: Purification by column chromatography, characterization of enzymatic properties, gene cloning by protein terminal sequencing and polymerase chain reaction (PCR), and sequence analysis by secondary structure prediction and multiple sequence alignment were performed. RESULTS: The ORCH from Labrys sp. WH-1 was purified 26-fold with a yield of 12.7%. It is a monomer with an isoelectric point (pI) of 8.57 and molecular mass of 30.2 kDa. It was stable up to 55 °C with temperature at which the activity of the enzyme decreased by 50% in 15 min (T5015) of 61 °C and the half-life at 50 °C (t1/2, 50 °C) of 51 min and was also stable from pH 4 to 10, with maximum activity at 55 °C and pH 8.5. It is a metal-independent enzyme and strongly inhibited by Cu2+, Ag+, and anionic surfactants. Its kinetic parameters (Km, kcat, and kcat/Km) were 18.7 mmol/L, 222.3 s-1, and 11.9 mmol/(L·s), respectively. The ORCH gene, which contained an open reading frame (ORF) of 825 bp encoding 274 amino acid residues, was overexpressed in Escherichia coli and the enzyme activity was 33 times higher than that of the wild strain. CONCLUSIONS: The catalytic efficiency and thermal stability of the ORCH from Labrys sp. WH-1 were the best among the reported ORCHs, and it provides an alternative catalyst for preparation of L(+)-2,3-dihydrobutanedioic acid.

The aroma volatile repertoire in strawberry fruit: a review.

Aroma significantly contributes to flavor, which directly affects the commercial quality of strawberries. The strawberry aroma is complex as many kinds of volatile compounds are found in strawberries. In this review, we describe the current knowledge of the constituents and of the biosynthesis of strawberry volatile compounds, and the effect of postharvest treatments on aroma profiles. The characteristic strawberry volatile compounds consist of furanones, such as 2,5-dimethyl-4-hydroxy-3(2H)-furanone and 4-methoxy-2,5-dimethyl-3(2H)-furanone; esters, including ethyl butanoate, ethyl hexanoate, methyl butanoate, and methyl hexanoate; sulfur compounds such as methanethiol, and terpenoids including linalool and nerolidol. As for postharvest treatment, the present review discusses the overview of aroma volatiles in response to temperature, atmosphere, and exogenous hormones, as well as other treatments including ozone, edible coating, and ultraviolet radiation. The future prospects for strawberry volatile biosynthesis and metabolism are also presented. © 2018 Society of Chemical Industry.

[Changes in cell wall component metabolism and ultrastructure of postharvest persimmon fruit during softening].

The changes in cellular wall hydrolases, cellular wall components and cellular wall ultrastructure of postharvest persimmon (Diospyros kaki L. cv. Bianhua) fruit during softening were studied. Pectinesterase activity increased sharply at first and reached a peak (Fig.3A). Significant correlation was observed between the pectinesterase activity and the loss of flesh firmness (r= -0.74). Polygalacturonase activity increased slowly (Fig.3B), but there was no significant correlation between the polygalacturonase activity and the loss of flesh firmness. Beta-galactosidase activity increased sharply (Fig.3C), with a negative correlation between the b-galactosidase activity and the loss of flesh fruit firmness (r= -0.77). Cellulase activity increased markedly during ripening (Fig.3D). Significant correlation was observed between cellulase activity and the loss of flesh firmness (r= -0.90). Consistent with the increases in activity of cell wall hydrolases of cell wall constituents, fruit softening was accompanied by a progressive increase in WSP (water soluble pectin) content and a progressive decrease in protopectin and cellulose content (Fig.4). The cell wall structure was integrated when persimmon was harvested (Fig.5A). After 3 d of ripening, the middle lamella became liquefied (Fig.5B), or even the primary cell wall was dissolved in some regions (Fig.5C).