High hydrostatic pressure (HHP) processing is an attractive non-thermal technique because of its potential to achieve interesting functional effects. In spite of the rapid expansion of HHP application to food systems, limited information is available on effects of HHP on modification of starch and their structural and physicochemical properties. Therefore, functional roles of HHP in starch modification such as acid-hydrolysis, hydroxypropylation, acetylation, cross-linking and cationization of starch, as well as physicochemical properties of HHP-assisted modified starches were reviewed. HHP-assisted modified starches revealed similar or different physicochemical properties compared to conventionally modified starches, suggesting the consideration of HHP as a processing parameter for hydrolysis and modification of starch. Moreover, HHP-assisted starch modification would be an attractive technology and can be effectively used in starch industry with relatively low cost and short reaction time.
Acetylation is one of the main obstacles to the effective enzymatic conversion of hemicelluloses to fermentable sugars. In nature, the microbial degradation of hemicellulose involves the action of deacetylating esterases that act synergistically with glycoside hydrolases. In the industrial processing of lignocelluloses biomass, alkaline pretreatments remove acetyl groups by saponification, but other non-alkaline pretreatment methods generate acetylated hemicelluloses. Complete saccharification of plant hemicelluloses can’t be achieved without the deacetylating enzymes. Recent years have witnessed considerale progress in our understanding of the mode of acetylation of hemicellulose and mode of action of microbial polysaccharide deacetylases. In this article we focus on the diversity and role of acetylxylan esterases in the breakdown of acetylxylan, the most abundant hemicellulose in nature.
We have prepared a new type of maltodextrin which yielded by simultaneous combination of enzymes. The enzymes are transglucosidase and maltose-forming amylase at the enzyme unit ratio of 1: 20. This maltodextrin was found to be equivalent to standard one in terms of physicochemical properties including dextrose equivalent (DE), viscosity, osmotic pressure and stability against aging. Methylation analysis revealed that this maltodextrin had around 9% of “→6)-Glcp-(1→” linkage mode, it was not present in standard maltodextrin. Enzymatic analysis showed that molecular weight of this “→6)-Glcp-(1→” maltodextrin has Mn 1,000 to 3,000. Furthermore, we compared digestibility differences between “→6)-Glcp-(1→” maltodextrin with standard maltodextrin, and “→4,6)-Glcp-(1→” maltodextrin (this was prepared by isolating and collecting a component with starch intrinsic branched structure) with standard maltodextrin. In vitro studies revealed that both “→6)-Glcp-(1→” and “→4,6)-Glcp-(1→” maltodextrin were digested slower than standard maltodextrin. Whereas in humans, “→6)-Glcp-(1→” maltodextrin was digested slower than standard one. The blood glucose level elevation after 60 min ingestion was significantly lower, suggesting that this “→6)-Glcp-(1→” maltodextrin was slowly digested and absorbed. Additionally, results from the expired gas analysis in humans suggest that the energy coefficient of “→6)-Glcp-(1→” maltodextrin is 4 kcal/g, similar to that of standard one. Considering these findings, “→6)-Glcp-(1→” maltodextrin is likely a promising source of carbohydrates for diabetic patients and elderly people with poor glucose tolerance.
Acidophilic β-galactosidase is a useful enzyme as digestive supplement used to alleviate symptoms of lactose intolerance. Aspergilli are the source of several acidophilic β-galactosidases that retain enzymatic activity under gastric conditions. In this study, we investigated the extracellular acidophilic β-galactosidase activity of six Aspergillus niger strains, AHU7104, AHU7120, AHU7217, AHU7294, AHU7295 and AHU7296; A. niger AHU7120 was selected as an enzyme source. β-Galactosidase from A. niger AHU7120 (AnBGal) was purified from culture supernatant. Its N-terminal sequence was identical to that of An01g12150, which belongs to the glycoside hydrolase family 35, from A. niger CBS 513.88. The DNA sequence of AnBGal was identical to An01g12150. Recombinant AnBGal (rAnBGal) harboring yeast α-factor signal sequence was expressed in Pichia pastoris, and 21.9 mg of purified rAnBGal with 129 U/mg of enzyme activity was isolated from 200 mL of culture supernatant. Native and recombinant AnBGal enzymes showed similar pH optima, pH stability, and kinetics for p-nitrophenyl β-D-galactopyranoside and lactose; rAnBGal showed slightly lower thermal stability than the native enzyme. Lactose in milk was rapidly degraded by rAnBGal at higher pH values (range, 2.0‒3.5), consistent with the pH optimum of AnBGal. We estimated that 3.5 μM AnBGal may degrade ≥ 66% of lactose before gastric half-emptying of ingested milk. These data indicate that AnBGal may help alleviate symptoms of lactose intolerance.
We characterized two α-1,3-glucoside phosphorylases that belonged to glycoside hydrolase family 65 from Clostridium phytofermentans: Cphy_3313 and Cphy_3314. Cphy_3313 was a typical nigerose phosphorylase that phosphorolyzed nigerose into D-glucose and β-D-glucose 1-phosphate (βGlc1P). Cphy_3314 catalyzed the synthesis of a series of α-1,3-oligoglucans using nigerose as the acceptor and βGlc1P as the donor. Kinetic analyses of their phosphorolytic reactions with α-1,3-oligoglucans (DP = 3 and 4) revealed that Cphy_3314 utilized a typical sequential Bi Bi mechanism, while this enzyme did not exhibit any significant phosphorolytic activity for nigerose. These results suggest that Cphy_3314 is a novel inverting phosphorylase that catalyzes reversible phosphorolysis of α-1,3-oligoglucans with DP of 3 or higher. In this study, we propose 3-O-α-D-oligoglucan: phosphate β-D-glucosyltransferase as the systematic name and α-1,3-oligoglucan phosphorylase as the short name for Cphy_3314.