Abstract
Esterases are enzymes that present good potential for industrial applications since they catalyze the formation or cleavage of ester bonds in water-soluble substrates, and sorghum seeds can represent an alternative source of this enzyme. The extraction of esterase from sorghum seeds is an economical alternative to obtain an enzyme of great interest. Esterases may improve the quality or accelerate the maturation of cheeses, cured bacon and fermented sausages and may also resolve racemic mixtures. Recently, seed esterases have been the focus of much attention as biocatalysts. In some cases, these enzymes present advantages over animal and microbial lipases due to some quite interesting features such as specificity and low cost, being a great alternative for their commercial exploitation as industrial enzymes The esterase studied here was extracted from sorghum seeds and some of its biochemical properties determined using synthetic substrates (p-nitrophenyl butyrate, caprylate, laurate and palmitate). The enzyme presented optimum activity at pH 8.0 and was stable in all the pH ranges studied. The optimum temperature for its activity was 40ºC but it showed low stability at this temperature (40% relative activity). The values derived for Km and Vmax were 0.67mM and 125 U.mg-1, respectively, obtained using p-nitrophenyl butyrate as the substrate. The enzyme showed an increase in activity when K2HPO4 was added to the reaction medium, but the ions Mn2+, CO+, Hg+ and Fe2+ strongly inhibited the enzyme activity. This enzyme showed a preference for the hydrolysis of short chain fatty acids. The characteristics of sorghum esterase are very similar to those of the microbial esterases used in detergent processing.
Highlights
Esterases or carboxylesterases belong to the international enzymatic class of hydrolases and comprise a group of “lipolytic enzymes” able to hydrolyze hydrophobic short and long chain carboxylic acid esters (Singh, Gupta, Goswami, & Gupta, 2006; Barros, Celligoi, & Macedo, 2016)
The sorghum seeds studied were donated by VITAO Polinutri Industry LTDA, Brazil, and the commercial lipase used was Lipozyme TLIM obtained from Thermomyces lanuginosus (Novozymes®) and used at a concentration of 2 mg.mL-1
The sorghum esterase was assayed in the reaction buffer with different concentrations of pNPB (p-nitrophenyl butyrate) as the substrate (0.5 – 2mM)
Summary
Esterases or carboxylesterases (carboxylic–ester hydrolases; EC 3.1.1.1) belong to the international enzymatic class of hydrolases and comprise a group of “lipolytic enzymes” able to hydrolyze hydrophobic short and long chain carboxylic acid esters (Singh, Gupta, Goswami, & Gupta, 2006; Barros, Celligoi, & Macedo, 2016). The growing interest in esterases is due to the fact that these enzymes can be applied in many sectors (dairy products, wine production, fruit juices, beer, alcohol, the synthesis of low molecular weight esters, cosmetics, detergents, the transformation of low molecular weight fats into oils with greater commercial value and the resolution of racemic compounds, amongst others) in addition to presenting some advantages in comparison to esterases from microorganisms in some cases, they can be applied without being purified (Barros & Macedo, 2011). Nwanguma, Eze, and Ezenowa, (1996) detected lipase-like lipolytic activity in non-germinated seeds during grain malting and mashing in three sorghum species studied These authors observed a slight decrease in enzyme activity during steeping for 24 hours, but it increased several-fold during the course of germination. The present study aimed to observe and quantify the presence of esterase activity in nongerminated sorghum seeds, assess the specificity and study the biochemical characteristics of the esterase
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