Expolysaccharides from lactic acid bacteria: Technological bottlenecks and practical solutions

Biobased technologies for the efficient extraction of biopolymers from waste biomass

Regardless of considerable progress in synthetic plastic or polymer-based industry, its low biodegradability is a critical issue. Nevertheless, natural "biopolymers" are gradually replacing them for being inherently biodegradable, eco-friendly with other unique properties. This article aims to present a review regarding different extraction techniques of biopolymers [natural (cellulose, chitin, lignin, pectin, starch, xylan), synthetic (polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyvinyl alcohol (PVA), polymethayl methacrylate (PMMA)] from waste using bio-based methods. The role of bio-based techniques in terms of conventional/ecologically stable strategies for biomass pre-treatment was investigated for proper utilization of waste. The review summarizes strong interplay between technological and future challenges of biopolymer extraction from waste and paints a discussion of how conventional resources could be replaced with more environmentally friendly materials. Therefore, we advocate the implementation of biomass waste from food, organic, and other bio-based industries that revolutionizes the stance of biopolymer in various emerging fields.

Studies on the Preliminary Characterization of a Novel Exopolysaccharide Produced by Streptococcus thermophilus Strain from Tibetan Kefir Grain

The novel exopolysaccharide (EPS) was produced by a streptococcus thermophilus strain isolated from Tibetan kefir grain, and it was purified using DEAE cellulose 52 and DEAE Sepharose CL-6B column chromatography. Then it was eluted as a single symmetrical narrow peak on high-performance gel-permeation chromatography (HPGPC) and the average molecular mass was estimated to be 30,092Da. Infrared spectrum analysis indicated it had characteristic glycosidic structures. Gas chromatography showed that the EPS is composed of mannose and glucose in a molar ratio of 2.6:1 with trace galactose. The structural features of EPS were investigated by partial hydrolysis with acid, methylation analysis and NMR spectroscopy analysis. The results revealed that the main backbone chain of EPS was (23)-β-D-Manp, (34)-β-D-Manp, (23,6)-α-D-Glcp and trace amounts of galactose.

Disruption of ste23 gene affects composition profile and bioactivity of exopolysaccharide produced by Streptomyces sp. 139

AIMS

To study the function of the gene ste23 involved in the biosynthesis of Ebosin.

METHODS AND RESULTS

In search of databases, the deduced product of the gene ste23 showed high homology to dTDP-4-dehydrorhamnose 3,5-epimerases. ste23 was replaced by a kanamycin resistance gene through double crossover. Compared with Ebosin, an exopolysaccharide (EPS) produced by wild-type Streptomyces sp. 139, the EPS produced by the ste23 mutant (designated EPS1) had a remarkably different monosaccharide composition and significantly diminished rhamnose content, though the molecular mass of EPS1 was similar to that of Ebosin. In addition, EPS1 lost the interleukin 1 (IL-1) antagonist activity in vitro.

CONCLUSIONS

ste23 may be involved in the Ebosin biosynthesis in S. sp. 139. and its bioactivity.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first genetic work investigating functions of genes involved in EPS production in streptomyces by gene replacement of the pathway genes.

Comparison of the Functionality of Exopolysaccharides Produced In Situ or Added as Bioingredients on Yogurt Properties

The effect on yogurt properties of in situ production of exopolysaccharides (EPS) and addition of 2 EPS powders (crude and purified EPS from Lactobacillus rhamnosus RW-9595M fermentation in whey-based medium) at different concentrations was studied. No effect of purified powder addition for EPS concentrations up to 500 mg/L was observed on acidification rate to the difference of milks supplemented with crude EPS, which exhibited longer acidification times. The addition of EPS from 125 to 500 mg/L or the use of EPS-producing cultures resulted in yogurts with lower yield stress and viscoelastic moduli compared with control yogurts without EPS, with no apparent effect of EPS concentration. However, the consistency index was higher for yogurts produced with the commercial EPS-producing culture, and to a lesser extent with the mixed culture containing Lb. rhamnosus RW-9595M, compared with yogurts supplemented with EPS powders, which were not different from that for control yogurts. Our study showed that the mode of EPS incorporation in yogurts has a major effect on the rheological properties of the final product.

Exopolysaccharide production during batch cultures with free and immobilized Lactobacillus rhamnosus RW-9595M

AIMS

Exopolysaccharides (EPS) were produced by Lactobacillus rhamnosus RW-9595M during pH-controlled batch cultures with free cells and repeated-batch cultures with cells immobilized on solid porous supports (ImmobaSil).

METHODS AND RESULTS

Cultures were conducted in supplemented whey permeate (SWP) medium containing 5 or 8% (w/w) whey permeate. For free-cell batch cultures in 8% SWP medium, very high maximum cell counts (1.3 x 10(10) CFU ml(-1)) and EPS production (2350 mg l(-1)) were measured. A high EPS production (1750 mg l(-1)) was measured after four cycles for a short incubation period of only 7 h. Several methods for immobilized biomass determination based on analysis of biomass components (proteins, ATP and DNA) were tested. The DNA analysis method proved to be the most appropriate under these circumstances. This method revealed a high maximum immobilized biomass of 8.5 x 10(11) CFU ml(-1) support during repeated immobilized cell cultures in 5% SWP. The high immobilized biomass increased maximum EPS volumetric productivity (250 mg l(-1) h(-1) after 7 h culture) compared with free-cell batch cultures (110 mg l(-1) h(-1) after 18 h culture).

CONCLUSIONS

High EPS productions were achieved during batch cultures of Lact. rhamnosus RW-9595M in SWP medium, exceeding 1.7 g EPS per litre. Repeated-batch cultures with immobilized cells resulted in increased EPS productivity compared with traditional free-cell cultures.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study clearly shows the high potential of the strain Lact. rhamnosus RW-9595M and immobilized cell technology for production of EPS as a functional food ingredient.

Exopolysaccharides from lactic acid bacteria: perspectives and challenges

Some lactic acid bacteria (LAB) secrete a polysaccharide polymer. This extracellular polysaccharide, or "exopolysaccharide" (EPS), is economically important because it can impart functional effects to foods and confer beneficial health effects. LAB have a "Generally Recognized As Safe" (GRAS) classification and are likely candidates for the production of functional EPSs. Current challenges are to improve the productivity of EPSs from LAB and to produce EPSs of a structure and size that impart the desired functionality. The engineering of improvements in these properties will depend on a deep understanding of the EPS biosynthetic metabolism and of how the structure of EPSs relates to a functional effect when incorporated into a food matrix.