Chemical preparation and structural characterization of a homogeneous series of chitin/chitosan oligomers

The preparation of a homogeneous series of chitin/chitosan oligomers (chito-oligomers) with the same distribution of degrees of polymerization (DP) ranging from 2 to 12, but with various average degrees of N-acetylation (DA) from 0 to 90% is described. This DA-series was obtained according to a two-step chemical process involving (i) the production of a well-defined mixture of glucosamine (GlcN) oligomers obtained by acid hydrolysis of a fully N-deacetylated chitosan and after selective precipitations of the hydrolysis products, and (ii) the partial N-acetylation of the GlcN units of these oligomers from a hydro-alcoholic solution of acetic anhydride in a controlled manner. The characterization of this series of samples with different DAs by proton nuclear magnetic resonance (1H NMR) spectroscopy and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) allowed us to determine their average DA and identify the main oligomer structures constituting each mixture. Furthermore, MALDI-TOF MS was particularly helpful to study the distribution evolution of the diverse oligomers as a function of DA for the main DPs from 3 to 7. The modeling of these distributions by means of a binomial law displayed that the chemical N-acetylation of low DP GlcN oligomers, produced in a homogeneous medium, occurs randomly along the oligosaccharide chains in accordance with a statistical (Bernoullian) arrangement. In this case, the relative proportion of each chito-oligomer present in the mixture can be estimated precisely as a function of DA considering oligomers of same DP.

Response surface methodology for autolysis parameters optimization of shrimp head and amino acids released during autolysis

Protein hydrolysates were prepared from the head waste of Penaens vannamei, a China seawater major shrimp by autolysis method. Autolysis conditions (viz., temperature, pH and substrate concentration) for preparing protein hydrolysates from the head waste proteins were optimized by response surface methodology (RSM) using a central composite design. Model equation was proposed with regard to the effect of temperature, pH and substrate concentration. Substrate concentration at 23% (w/v), pH at 7.85 and temperature at 50°C were found to be the optimal conditions to obtain a higher degree of hydrolysis close to 45%. The autolysis reaction was nearly finished in the initial 3h. The amino acid compositions of the autolysis hydrolysates prepared using the optimized conditions in different time revealed that the hydrolysates can be used as a functional food ingredient or flavor enhancer. Endogenous enzymes in the shrimp heads had a strong autolysis capacity (AC) for releasing threonine, serine, valine, isoleucine, tyrosine, histidine and tryptophan. Endogenous enzymes had a relatively lower AC for releasing cystine and glycine.

High yield production of monomer-free chitosan oligosaccharides by pepsin catalyzed hydrolysis of a high deacetylation degree chitosan

The high molecular weight of chitosan, which results in a poor solubility at neutral pH values and high viscosity aqueous solutions, limits its potential uses in the fields of food, health and agriculture. However, most of these limitations are overcome by chitosan oligosaccharides obtained by enzymatic hydrolysis of the polymer. Several commercial enzymes with different original specificities were assayed for their ability to hydrolyze a 93% deacetylation degree chitosan and compared with a chitosanase. According to the patterns of viscosity decrease and reducing end formation, three enzymes--cellulase, pepsin and lipase A--were found to be particularly suitable for hydrolyzing chitosan at a level comparable to that achieved by chitosanase. Unlike the appreciable levels of both 2-amino-2-deoxy-D-glucose and 2-acetamido-2-deoxy-D-glucose monomers released from chitosan by the other enzymes after a 20h-hydrolysis (4.6-9.1% of the total product weight), no monomer could be detected following pepsin cleavage. As a result, pepsin produced a higher yield of chitosan oligosaccharides than the other enzymes: 52% versus as much as 46%, respectively. Low molecular weight chitosans accounted for the remaining 48% of hydrolysis products. The calculated average polymerization degree of the products released by pepsin was around 16 units after 20h of hydrolysis. This product pattern and yield are proposed to be related to the bond cleavage specificity of pepsin and the high deacetylation degree of chitosan used as substrate. The optimal reaction conditions for hydrolysis of chitosan by pepsin were 40 degrees C and pH 4.5, and an enzyme/substrate ratio of 1:100 (w/w) for reactions longer than 1h.

Effects of chito-oligosaccharide supplementation on performance, nutrient digestibility, and serum composition in broiler chickens

A total of 196 day-old male broiler chicks were randomly allocated to 1 of 4 treatments in a study conducted to determine the effects of dietary supplementation of chito-oligosaccharide (COS) on growth, nutrient digestibility, and serum composition. The experimental diets consisted of an unsupplemented control diet based on corn, soybean meal, and fish meal or similar diets supplemented with either chlortetracycline, 50 mg/kg of COS, or 100 mg/kg of COS. Each treatment was fed to 7 replicate pens of birds, with 7 birds per pen. Broiler performance, nutrient digestibility, cecal microbial concentrations, and serum indices were measured at the end of the starter (d 21) and grower phases (d 42). During the starter period and overall, broilers fed 50 or 100 mg/kg of COS had better (P<0.05) average daily gain, average daily feed intake, and feed conversion than the control birds. The performance of birds fed chlortetracycline was generally intermediate between that of the control and the 2 COS treatments. Compared with the birds in the control or chlortetracycline treatments, the birds receiving 100 mg/kg of COS had better nutrient digestibility of DM, energy, calcium, and phosphorus; higher (P<0.05) concentrations of cecal Lactobacillus; and lower (P<0.05) serum triglyceride and total cholesterol during the starter phase. During the grower phase, the birds fed 100 mg/kg of COS had higher (P<0.05) calcium digestibility and CP retention than those fed the chlortetracycline treatment, and lower concentrations of cecal Escherichia coli than birds in the control treatment. The serum growth hormone level in birds fed 50 mg/kg of COS was higher (P<0.05) than in the other treatments. The birds fed 100 mg/kg of COS had lower (P<0.05) serum triglyceride, higher (P<0.05) serum high-density lipoprotein cholesterol, and higher serum total protein content than birds in the other treatments. In conclusion, dietary supplementation with COS appeared to improve the average daily gain of broilers by increasing the average daily feed intake and nutrient digestibility and modulating the concentrations of cecal microbial flora. Additionally, COS increased serum protein and high-density lipoprotein cholesterol and decreased serum triglyceride.

An in vitro cellular analysis of the radical scavenging efficacy of chitooligosaccharides

Despite extensive study on biological activities of chitosan and chitooligosaccharides (COS), there is no experimental evidence available as to COS mediated inhibition of free radical damage in cellular oxidizing systems. In this study, radical scavenging efficacies of different molecular weight bearing COS were assessed and their intracellular radical scavenging effects were tested employing B16F1, murine melanoma cell line. The results exhibited appreciable suppression in occurrence of intracellular radical species in the presence of low molecular weight bearing COS (<1 kDa) confirming low molecular weight is important for observed activities in biological systems. However, DNA oxidation carried out in the presence of COS clearly exhibited that COS exert protective effect on oxidative damage of purified genomic DNA regardless of molecular weight. Low molecular weight bearing COS was observed to be successively participated in suppression of NF-kappaB gene promoter activity suggesting its capability to prevent oxidative stress related disease complications. Moreover, induction of intracellular glutathione (GSH) level in the presence of COS promoted the effectiveness of COS to act against cellular oxidative stress.

Inhibitory effect of chitooligosaccharides on matrix metalloproteinase-9 in human fibrosarcoma cells (HT1080)

Matrix metalloproteinase-9 (MMP-9) has gelatinase activity and plays an important role in cancer invasion and metastasis. Therefore, inhibition of specific types of MMPs including MMP-9 has become an attractive target for therapeutic intervention. The aim of this study was to investigate the effect of chitooligosaccharides (COS) on activity and expression of MMP-9 in HT1080 cells. The inhibitory effect of COS with different molecular masses was examined by gelatin zymography, reverse transcriptase-polymerase chain reaction (RT-PCR), gene reporter assay, and Western blot analysis. MMP-9 inhibition in the presence of COS was clearly observed in gelatin zymography. Specifically, 1- to 3-kDa COS (COS-I) exhibited the highest inhibitory effect on MMP-9 activity in HT1080 cells among tested molecular mass fractions. It was also found that COS-I was capable of inhibiting both gene and protein expression of MMP-9 (P<0.01). These results suggest that low molecular mass COS can be considered as a potent inhibitor of MMP-9.

Improvement of ACE inhibitory activity of chitooligosaccharides (COS) by carboxyl modification

In the present research, chitooligosaccharides (COS) were carboxylated with -COCH(2)CH(2)COO(-) groups to obtain specific structural features similar to Captopril. Angiotensin I converting enzyme (ACE) inhibitory activity of carboxylated COS was studied and observed to enhance its activity with increased substitution degree. Further, Lineweaver-Burk plot analysis revealed that inhibition was competitive via obligatory binding site of the enzyme. This was accompanied with substitution of positively charged quarternized amino groups to COS with different substitution degrees, in which negative impact on ACE inhibition was observed.

Biodegradable plastics from renewable sources

Plastic waste disposal is a huge ecotechnological problem and one of the approaches to solving this problem is the development of biodegradable plastics. This review summarizes data on their use, biodegradability, commercial reliability and production from renewable resources. Some commercially successful biodegradable plastics are based on chemical synthesis (i.e. polyglycolic acid, polylactic acid, polycaprolactone, and polyvinyl alcohol). Others are products of microbial fermentations (i.e. polyesters and neutral polysaccharides) or are prepared from chemically modified natural products (e.g., starch, cellulose, chitin or soy protein).

Themes for mushroom exploitation in the 21st century: Sustainability, waste management, and conservation

Because many natural resources are limited, sustainability becomes an important concept in maintaining the human population, health, and environment. Mushrooms are a group of saprotrophic fungi. Mushroom cultivation is a direct utilization of their ecological role in the bioconversion of solid wastes generated from industry and agriculture into edible biomass, which could also be regarded as a functional food or as a source of drugs and pharmaceuticals. To make the mushroom cultivation an environmentally friendly industry, the basic biology of mushrooms and the cultivation technology must be researched and developed. This is very true for Lentinula edodes, Volvariella volvacea, and Ganoderma lucidum, which are commonly consumed in Asian communities but are now gaining popularity worldwide. Besides the conventional method, strain improvement can also be exploited by protoplast fusion and transformation. Biodiversity is the key contribution to the genetic resource for breeding programs to fulfill different consumer demands. The conservation of these mushrooms becomes essential and is in immediate need not only because of the massive habitat loss as a result of human inhabitation and deforestation, but also because of the introduced competition by a cultivar with the wild germ plasm. Spent mushroom compost, a bulky solid waste generated from the mushroom industry, however, can be exploited as a soil fertilizer and as a prospective bioremediating agent.