Comparison between various commercial sources of almond β-glucosidase for the production of alkyl glucosides

Unconventional β-Glucosidases: A Promising Biocatalyst for Industrial Biotechnology

β-Glucosidases primarily catalyze removal of terminal glucosyl residues from a variety of glucoconjugates and also perform transglycosylation and reverse hydrolysis. These catalytic properties can be readily exploited for degradation of lignocellulosic biomass as well as for pharmaceutical, food and flavor industries. β-Glucosidases have been either isolated in the native form from the producer organism or recombinantly expressed and gaged for their biochemical properties and substrate specificities. Although almond and Aspergillus niger have been instantly recognizable sources of β-glucosidases utilized for various applications, an intricate pool of novel β-glucosidases from different sources can provide their potent replacements. Moreover, one can envisage the better efficacy of these novel candidates in biofuel and biorefinery industries facilitating efficient degradation of biomass. This article reviews properties of the novel β-glucosidases such as glucose tolerance and activation, substrate specificity, and thermostability which can be useful for their applications in lignocellulose degradation, food industry, and pharmaceutical industry in comparison with the β-glucosidases from the conventional sources. Such β-glucosidases have potential for encouraging white biotechnology.

Glycosyl hydrolase catalyzed glycosylation in unconventional media

The reversible hydrolytic property of glycosyl hydrolases (GHs) as well as their acceptance of aglycones other than water has provided the abilities of GHs in synthesizing glycosides. Together with desirable physiochemical properties of glycosides and their high commercial values, research interests have been aroused to investigate the synthetic other than the hydrolytic properties of GHs. On the other hand, just like the esterification processes catalyzed by lipases, GH synthetic effectiveness is strongly obstructed by water both thermodynamically and kinetically. Medium engineering by involving organic solvents can be a viable approach to alleviate the obstacles caused by water. However, as native hydrolyases function in water-enriched environments, most GHs display poor catalytic performance in the presence of organic solvents. Some GHs from thermophiles are more tolerant to organic solvents due to their robust folded structures with strong residue interactions. Other than native sources, immobilization, protein engineering, employment of surfactant, and lyophilization have been proved to enhance the GH stability from the native state, which opens up the possibilities for GHs to be employed in unconventional media as synthases. KEY POINTS: • Unconventional media enhance the synthetic ability but destabilize GHs. • Viable approaches are discussed to improve GH stability from the native state. • GHs robust in unconventional media can be valuable industrial synthases.

Plant Defensive β-Glucosidases Resist Digestion and Sustain Activity in the Gut of a Lepidopteran Herbivore

Two-component activated chemical defenses are a major part of many plants' strategies to disrupt herbivory. The activation step is often the β-glucosidase-catalyzed removal of a glucose moiety from a pro-toxin, leading to an unstable and toxic aglycone. While some β-glucosidases have been well studied, several aspects of their roles in vivo, such as their precise sites of enzymatic activity during and after ingestion, and the importance of particular isoforms in plant defense are still not fully understood. Here, plant defensive β-glucosidases from maize, white mustard and almonds were shown to resist digestion by larvae of the generalist lepidopteran Spodoptera littoralis, and the majority of the ingested activities toward both general and plant pro-toxic substrates was recovered in the frass. Among other proteins potentially involved in defense, we identified specific plant β-glucosidases and a maize β-glucosidase aggregating factor in frass from plant-fed insects using proteomic methods. We therefore found that, while S. littoralis larvae efficiently degraded bulk food protein during digestion, β-glucosidases were among a small number of plant defensive proteins that resist insect digestive proteolysis. These enzymes remain intact in the gut lumen and frass and can therefore further catalyze the activation of plant defenses after ingestion, especially in pH-neutral regions of the digestive system. As most of the ingested enzymatic activity persists in the frass, and only particular β-glucosidases were detected via proteomic analyses, our data support the involvement of specific isoforms (maize ZmGlu1 and S. alba MA1 myrosinase) in defense in vivo.

Effects of food formulation and thermal processing on flavones in celery and chamomile

Flavones isolated from celery varied in their stability and susceptibility to deglycosylation during thermal processing at pH 3, 5, or 7. Apigenin 7-O-apiosylglucoside was converted to apigenin 7-O-glucoside when heated at pH 3 and 100°C. Apigenin 7-O-glucoside showed little conversion or degradation at any pH after 5h at 100°C. Apigenin, luteolin, and chrysoeriol were most stable at pH 3 but progressively degraded at pH 5 or 7. Chamomile and celery were used to test the effects of glycosidase-rich foods and thermal processing on the stability of flavone glycosides. Apigenin 7-O-glucoside in chamomile extract was readily converted to apigenin aglycone after combination with almond, flax seed, or chickpea flour. Apigenin 7-O-apiosylglucoside in celery leaves was resistant to conversion by β-glucosidase-rich ingredients, but was converted to apigenin 7-O-glucoside at pH 2.7 when processed at 100°C for 90min and could then be further deglycosylated when mixed with almond or flax seed. Thus, combinations of acid hydrolysis and glycosidase enzymes in almond and flax seed were most effective for developing a flavone-rich, high aglycone food ingredient from celery.

A new thermostable β-glucosidase mined from Dictyoglomus thermophilum: properties and performance in octyl glucoside synthesis at high temperatures

A new β-glucosidase (DtGH) representing 40% identity with an apple seed glycosidase (ASG) was cloned from Dictyoglomus thermophilum. DtGH showed extremely high thermostability in aqueous solution, with half-lives of 533, 44, and 5 h measured at 70, 80 and 90 °C, respectively. Therefore it was used for direct glycosylation of n-octanol at 70 °C instead of 50 °C as usually. As a result, the glucose based conversion was increased by 27%, but the time spent to reach equilibrium was decreased from 7 d to 3 d. This enzyme also exhibited excellent stability under the reaction environment, retaining 70-80% of its initial activity after 7 d of incubation at 70 °C in either 1.7 M glucose solution or octanol-aqueous (85:15, v/v) system. It could retain part of synthetic activity even in boiling water. Owing to the strong glucose-tolerance and extremely high thermostability, DtGH should be promising for various glucosides synthesis.