Starch digestion in tropical fishes: isolation, structural studies and inhibition kinetics of alpha-amylases from two tilapias Oreochromis niloticus and Sarotherodon melanotheron

Cyclodextrin in starchy foods

Cyclodextrins are widely used in various fields including food industry. In this review, their role in high carbohydrate-containing, starchy foods are reviewed and discussed. Both the effects as functional ingredients affecting the structural properties of starch and as active ingredients slowing down starch digestion and, as a consequence, decreasing the glycaemic index of starchy foods are overviewed without considering the traditional applications as carriers and stabilisers of aroma and flavour, essential oils, polyunsaturated fatty acids, and other bioactive components to enrich foods, even if they are carbohydrate foods. The effect on starch metabolism is explained by the structural transformations caused by cyclodextrins on starch amylose and amylopectin. Several examples are shown how the technological and sensorial properties of bread, rice products, pasta, and other starchy foods are modified by cyclodextrin supplementation, and how the digestibility is changed resulting in reduced glycaemic and insulinaemic effects.

Diverse activities and biochemical properties of amylase and proteases from six freshwater fish species

This study investigated the biochemical properties, enzyme activities, isoenzyme pattern, and molecular weight of three types of digestive enzyme from six freshwater fish species: Puntius gonionotus (common silver barb), Puntioplites proctozysron (Smith’s barb), Oreochromis niloticus (Nile tilapia), Hemibagrus spilopterus (yellow mystus), Ompok bimaculatus (butter catfish), and Kryptopterus geminus (sheatfish). The optimum pHs for amylase and alkaline protease activities were 7.0–8.0 and 8.0–10.0, and the optimum temperatures were 45–60 °C and 50–55 °C, respectively. A pepsin-like enzyme was detected in all three carnivorous fishes (Ompok bimaculatus, Kryptopterus geminus, and Hemibagrus spilopterus) with optimum reaction pH of 2.0 for each and optimum reaction temperatures 50–55 °C. In optimum reaction conditions, the amylase and alkaline protease from Puntioplites proctozyron showed the highest activities. Lower activities of all enzymes were observed at temperature (29 °C) of Lam Nam Choen swamp than at the optimum reaction temperatures. The fish species contained one to three and five to eight isoforms of amylase and alkaline protease, respectively, with molecular weights from 19.5 to 175 kDa. Both the alkaline proteases and amylases were stable in wide pH and temperature ranges.

Growth Performance, Nutrient Digestibility, Hematological Parameters, and Hepatic Oxidative Stress Response in Juvenile Nile Tilapia, Oreochromis niloticus, Fed Carbohydrates of Different Complexities

A 45-day feeding trial was conducted to assess the capacity of juvenile Nile tilapia (2.12 ± 0.02 g) to utilize different sources of carbohydrate in their diets. Growth performance, nutrient digestibility, hematological parameters, and hepatic oxidative stress were evaluated. Four experimental diets were formulated to be isonitrogenous (25% crude protein) and isolipidic (10% crude lipid), each containing 20% glucose (GLU-diet), maltose (MAL-diet), dextrin (DEX-diet), and corn starch (CST-diet), respectively. At the end of feeding trial, survival in all groups was above 90% and was not significantly different among groups. The results indicated that fish fed the DEX-diet and CSTA-diet showed significantly (p < 0.05) better specific growth rate (SGR), feed conversion ratio (FCR), and protein efficiency ratio (PER) compared with those fed the other diets. The dry matter and carbohydrate digestibility were significantly higher (p < 0.05) in groups fed on dextrin and corn starch diets. However, the digestibility of crude protein and energy in diets did not differ significantly (p > 0.05) among groups fed on experimental diets. The activities of analyzed antioxidant enzymes in the liver were significantly (p < 0.01) higher in groups fed on glucose and maltose diets when compared to other groups. Hematological parameters were affected by the dietary carbohydrate sources; there was a significant increase in hematocrit (Ht), hemoglobin (Hb), and mean corpuscular volume (CMV) in the blood of fish fed on dextrin and cornstarch diets compared to other experimental diets. These results indicated that low complexity carbohydrate sources induced oxidative stress and depressed growth performance. Overall, these results indicate that dietary dextrin and starch were more efficiently utilized than glucose as an energy source by juvenile Nile tilapia. This information is of increasing interest in fish nutrition to provide healthy and economically feed formulations.

Dietary electrolyte balance affects growth performance, amylase activity and metabolic response in the meagre (Argyrosomus regius)

Dietary ion content is known to alter the acid-base balance in freshwater fish. The current study investigated the metabolic impact of acid-base disturbances produced by differences in dietary electrolyte balance (DEB) in the meagre (Argyrosomus regius), an euryhaline species. Changes in fish performance, gastric chyme characteristics, pH and ion concentrations in the bloodstream, digestive enzyme activities and metabolic rates were analyzed in meagre fed ad libitum two experimental diets (DEB 200 or DEB 700mEq/kg) differing in the Na₂CO₃ content for 69days. Fish fed the DEB 200 diet had 60-66% better growth performance than the DEB 700 group. Meagre consuming the DEB 200 diet were 90-96% more efficient than fish fed the DEB 700 diet at allocating energy from feed into somatic growth. The pH values in blood were significantly lower in the DEB 700 group 2h after feeding when compared to DEB 200, indicating that acid-base balance in meagre was affected by electrolyte balance in diet. Osmolality, and Na⁺ and K⁺ concentrations in plasma did not vary with the dietary treatment. Gastric chyme in the DEB 700 group had higher pH values, dry matter, protein and energy contents, but lower lipid content than in the DEB 200 group. Twenty-four hours after feeding, amylase activity was higher in the gastrointestinal tract of DEB 700 group when compared to the DEB 200 group. DEB 700 group had lower routine metabolic (RMR) and standard metabolic (SMR) rates, indicating a decrease in maintenance energy expenditure 48h after feeding the alkaline diet. The current study demonstrates that feeding meagre with an alkaline diet not only causes acid-base imbalance, but also negatively affects digestion and possibly nutrient assimilation, resulting in decreased growth performance.

Cyclodextrins in Food Technology and Human Nutrition: Benefits and Limitations

Cyclodextrins are tasteless, odorless, nondigestible, noncaloric, noncariogenic saccharides, which reduce the digestion of carbohydrates and lipids. They have low glycemic index and decrease the glycemic index of the food. They are either non- or only partly digestible by the enzymes of the human gastrointestinal (GI) tract and fermented by the gut microflora. Based on these properties, cyclodextrins are dietary fibers useful for controlling the body weight and blood lipid profile. They are prebiotics, improve the intestinal microflora by selective proliferation of bifidobacteria. These antiobesity and anti-diabetic effects make them bioactive food supplements and nutraceuticals. In this review, these features are evaluated for α-, β- and γ-cyclodextrins, which are the cyclodextrin variants approved by authorities for food applications. The mechanisms behind these effects are reviewed together with the applications as solubilizers, stabilizers of dietary lipids, such as unsaturated fatty acids, phytosterols, vitamins, flavonoids, carotenoids and other nutraceuticals. The recent applications of cyclodextrins for reducing unwanted components, such as trans-fats, allergens, mycotoxins, acrylamides, bitter compounds, as well as in smart active packaging of foods are also overviewed.

Aluminium sulfate exposure: A set of effects on hydrolases from brain, muscle and digestive tract of juvenile Nile tilapia (Oreochromis niloticus)

Aluminium is a major pollutant due to its constant disposal in aquatic environments through anthropogenic activities. The physiological effects of this metal in fish are still scarce in the literature. This study investigated the in vivo and in vitro effects of aluminium sulfate on the activity of enzymes from Nile tilapia (Oreochromis niloticus): brain acetylcholinesterase (AChE), muscle cholinesterases (AChE-like and BChE-like activities), pepsin, trypsin, chymotrypsin and amylase. Fish were in vivo exposed during 14days when the following experimental groups were assayed: control group (CG), exposure to Al₂(SO₄)₃ at 1μg·mL^-1 (G1) and 3μg·mL^-1 (G3) (concentrations compatible with the use of aluminium sulfate as coagulant in water treatment). In vitro exposure was performed using animals of CG treatment. Both in vivo and in vitro exposure increased cholinesterase activity in relation to controls. The highest cholinesterase activity was observed for muscle BChE-like enzyme in G3. In contrast, the digestive enzymes showed decreased activity in both in vivo and in vitro exposures. The highest inhibitory effect was observed for pepsin activity. The inhibition of serine proteases was also quantitatively analyzed in zymograms using pixel optical densitometry as area under the peaks (AUP) and integrated density (ID). These results suggest that the inhibition of digestive enzymes in combination with activation of cholinesterases in O. niloticus is a set of biochemical effects that evidence the presence of aluminium in the aquatic environment. Moreover, these enzymatic alterations may support further studies on physiological changes in this species with implications for its neurological and digestive metabolisms.

Molecular, Biochemical, and Dietary Regulation Features of α-Amylase in a Carnivorous Crustacean, the Spiny Lobster Panulirus argus

Alpha-amylases are ubiquitously distributed throughout microbials, plants and animals. It is widely accepted that omnivorous crustaceans have higher α-amylase activity and number of isoforms than carnivorous, but contradictory results have been obtained in some species, and carnivorous crustaceans have been less studied. In addition, the physiological meaning of α-amylase polymorphism in crustaceans is not well understood. In this work we studied α-amylase in a carnivorous lobster at the gene, transcript, and protein levels. It was showed that α-amylase isoenzyme composition (i.e., phenotype) in lobster determines carbohydrate digestion efficiency. Most frequent α-amylase phenotype has the lowest digestion efficiency, suggesting this is a favoured trait. We revealed that gene and intron loss have occurred in lobster α-amylase, thus lobsters express a single 1830 bp cDNA encoding a highly conserved protein with 513 amino acids. This protein gives rise to two isoenzymes in some individuals by glycosylation but not by limited proteolysis. Only the glycosylated isoenzyme could be purified by chromatography, with biochemical features similar to other animal amylases. High carbohydrate content in diet down-regulates α-amylase gene expression in lobster. However, high α-amylase activity occurs in lobster gastric juice irrespective of diet and was proposed to function as an early sensor of the carbohydrate content of diet to regulate further gene expression. We concluded that gene/isoenzyme simplicity, post-translational modifications and low Km, coupled with a tight regulation of gene expression, have arose during evolution of α-amylase in the carnivorous lobster to control excessive carbohydrate digestion in the presence of an active α-amylase.

Cloning and characterization of α-amylase from Atlantic salmon (Salmo salar L.)

Amylase has a lower activity in carnivorous fish species, particularly in Atlantic salmon. We report the first cloning of a salmonid alpha-amylase cDNA from Atlantic salmon, a major species in aquaculture. By amino acid alignment of several species, we identified a seven amino acid deletion in one of the large loops of the enzyme in relatively close proximity to the active site, that could impair substrate binding. We also found the signal peptide to be less hydrophobic compared to other species. This may affect import into ER during protein synthesis. Active site residues were shown to be conserved. Amylase mRNA expression was shown in pancreatic tissue, liver, and in the heart. Using blocked p-nitrophenyl-maltoheptaoside as a substrate, we measured a low amylase activity in Atlantic salmon intestinal content, which was about half of the activity measured in Atlantic cod, whereas activity measured in rainbow trout was fourteen times higher. Amylase activities in all three species showed similar degree of reduction in hydrolytic activity in a dose-response trial with a wheat amylase inhibitor preparation. This indicates similar specific activity per amylase molecule.

On the mechanism of α-amylase

Two inhibitors, acarbose and cyclodextrins (CD), were used to investigate the active site structure and function of barley alpha-amylase isozymes, AMY1 and AMY2. The hydrolysis of DP 4900-amylose, reduced (r) DP18-maltodextrin and maltoheptaose (catalysed by AMY1 and AMY2) was followed in the absence and in the presence of inhibitor. Without inhibitor, the highest activity was obtained with amylose, kcat/Km decreased 103-fold using rDP18-maltodextrin and 10(5) to 10(6)-fold using maltoheptaose as substrate. Acarbose is an uncompetitive inhibitor with inhibition constant (L1i) for amylose and maltodextrin in the micromolar range. Acarbose did not bind to the active site of the enzyme, but to a secondary site to give an abortive ESI complex. Only AMY2 has a second secondary binding site corresponding to an ESI2 complex. In contrast, acarbose is a mixed noncompetitive inhibitor of maltoheptaose hydrolysis. Consequently, in the presence of this oligosaccharide substrate, acarbose bound both to the active site and to a secondary binding site. alpha-CD inhibited the AMY1 and AMY2 catalysed hydrolysis of amylose, but was a very weak inhibitor compared to acarbose.beta- and gamma-CD are not inhibitors. These results are different from those obtained previously with PPA. However in AMY1, as already shown for amylases of animal and bacterial origin, in addition to the active site, one secondary carbohydrate binding site (s1) was necessary for activity whereas two secondary sites (s1 and s2) were required for the AMY2 activity. The first secondary site in both AMY1 and AMY2 was only functional when substrate was bound in the active site. This appears to be a general feature of the alpha-amylase family.