Physical properties and in-vitro gastrointestinal digestion of oil-in-water emulsions stabilized by single- and dual-modified cassava starches with cross-linking and octenylsuccinylation.

The different modified cassava starches (MCS) obtained by either single or dual modifications with cross-linking (CL) and octenylsuccinylation (OS), including 2%CL, 3%OS, 2%CL-3%OS, and 3%OS-2%CL, were used to stabilize soybean oil-in-water emulsions (oil content 10% (w/w)) at a concentration of 4.5% (w/w) compared to native cassava starch (NCS) and their physical properties and in-vitro gastrointestinal digestion were investigated. The emulsions stabilized with NCS and 2%CL-MCS had larger oil droplet sizes, higher viscosity, and lower negative charge than the emulsions stabilized by single- or dual-MCS with 3%OS. All MCS-stabilized emulsions showed a higher emulsion stability against creaming than the NCS-stabilized emulsion. Under a simulated gastrointestinal tract, all 3%OS-MCS promoted droplet flocculation, while the less ionic NCS and the 2%CL-MCS showed a decrease in droplet size after passing through the mouth and stomach stages. The lipid digestion rate of emulsions stabilized with different MCS and NCS followed the following order: 3%OS >2%CL-3%OS > 3%OS-2%CL > 2%CL > NCS. The NCS- and 2%CL-stabilized emulsions had a lower lipid digestion rate, possibly due to the larger droplet sizes and higher viscosity of the initial emulsions, which delays access of lipase enzymes to lipid droplet surfaces, compared to all 3%OS-MCS-stabilized emulsions.

Valorization of Spent Grains from Beer Production through ß-Glucan Extraction.

Brewers' spent grains (BSG) are the major byproduct of the brewing industry. Recently, it has been found that ß-glucan, which can be used as a food supplement, can be extracted from BSG and offers the greatest added value. This study aimed to investigate the effects of temperature (45-90 °C) and time (30-120 min) on ß-glucan extraction efficiency when using hot water extraction. ß-glucan was precipitated upon 80% ethanol addition. The chemical compositions were examined. The highest ß-glucan concentration and yield were obtained at a temperature and time of 60 °C and 90 min, respectively. The functional properties of the extracted ß-glucan were analyzed and compared with other commercial stabilizers such as sodium carboxymethyl cellulose (CMC), xanthan gum, gum arabic, and oat ß-glucan. All stabilizers exhibited non-Newtonian flow behavior, except for gum arabic, which exhibited Newtonian flow behavior. The water holding capacity of BSG ß-glucan was 6.82 g/g and the creaming index of the emulsions stabilized with BSG ß-glucan was 89.05%. BSG ß-glucan improved the color and stability of orange juice by reducing the precipitation of orange pulp. This study illustrated that BSG ß-glucan can be used as a stabilizer and viscosity enhancer in foods, depending on the concentration, which can be applied to a variety of foods.

Impact of Oil Addition on Physicochemical Properties and In Vitro Digestibility of Extruded Pineapple Stem Starch.

The effects of palm oil (PO) and coconut oil (CO) additions on the physicochemical properties and in vitro starch digestibility of extruded pineapple stem starch (PSS) were studied. The native PSS was adjusted to 15% moisture and blended with PO or CO in amounts of 5 and 10% (w/w of starch), while the control sample without added oil was adjusted to 25% moisture before being extruded with a twin-screw extruder at a maximum barrel temperature of 140 °C. Due to the lubricating effect, the added oils reduced the expansion ratio of the extrudates, which led to an increase in cell wall thickness, bulk density, hardness, and water adsorption index, but to a reduction in the water solubility index, especially with 10% oils. PO had a greater impact on the physicochemical changes in the extrudates than CO. Surprisingly, no amylose-lipid complex was observed in the extrudates with added oil, as shown by XRD, DSC, and FTIR results. The phenolic compounds contained in PSS remained in all extrudates, which could affect the formation of the amylose-lipid complex during extrusion. The addition of 5% oil had no effect on the digestibility of the starch compared to the control extrudates, while the 10% oils, both PO and CO, reduced the rapidly digestible starch content but significantly increased the resistant starch content of the extruded PSS.

Effect of Pulsed Electric Field Treatment on the Protein, Digestibility, and Physicochemical Properties of Starch Granules in Wheat Flour.

The effect of pulsed electric field (PEF) treatment depends mainly on the electric field strength and treatment time. In this study, wheat flour-water suspensions were treated with PEF at an electric field strength of 3 kV/cm for 0 to 1400 pulses to obtain a specific energy input of 0 to 656 kJ/kg. The effect of PEF on the removal or unfolding of proteins from the starch surface, digestibility, starch granule structure, and physicochemical properties of wheat flour was studied. The removal of proteins from the surface and the damage to the internal structure of wheat starch granules after PEF treatment was detected by confocal laser scanning microscopy (CLSM) and FTIR. The damage of the PEF-treated wheat starch granules was observed by scanning electron microscopy (SEM). From CLSM results, penetration of dextran (Mw 10,000 Da) into starch granules of wheat flour was dependent on the energy input of PEF. The high the energy input showed the intense penetration of the biopolymer. The benefits of the accessibility of biopolymer in starch granules are to increase enzyme digestion, especially rapidly digestible starch (RDS). The RDS of wheat flour treated with PEF at 656 kJ/kg was 41.72%, whereas the RDS of wheat flour control was 27.59%.

A Review on Isolation, Characterization, Modification, and Applications of Proso Millet Starch.

Proso millet starch (PMS) as an unconventional and underutilized millet starch is becoming increasingly popular worldwide due to its health-promoting properties. This review summarizes research progress in the isolation, characterization, modification, and applications of PMS. PMS can be isolated from proso millet grains by acidic, alkaline, or enzymatic extraction. PMS exhibits typical A-type polymorphic diffraction patterns and shows polygonal and spherical granular structures with a granule size of 0.3-17 µm. PMS is modified by chemical, physical, and biological methods. The native and modified PMS are analyzed for swelling power, solubility, pasting properties, thermal properties, retrogradation, freeze-thaw stability, and in vitro digestibility. The improved physicochemical, structural, and functional properties and digestibility of modified PMS are discussed in terms of their suitability for specific applications. The potential applications of native and modified PMS in food and nonfood products are presented. Future prospects for research and commercial use of PMS in the food industry are also highlighted.

Physicochemical, Rheological, In-Vitro Digestibility, and Emulsifying Properties of Starch Extracted from Pineapple Stem Agricultural Waste.

In this study, the physicochemical, rheological, in vitro starch digestibility, and emulsifying properties of starch extracted from pineapple stem agricultural waste were investigated in comparison with commercial cassava, corn, and rice starches. Pineapple stem starch had the highest amylose content (30.82%), which contributed to the highest pasting temperature (90.22 °C) and the lowest paste viscosity. It had the highest gelatinization temperatures, gelatinization enthalpy, and retrogradation. Pineapple stem starch gel had the lowest freeze-thaw stability, as evidenced by the highest syneresis value of 53.39% after five freeze-thaw cycles. Steady flow tests showed that pineapple stem starch gel (6%, w/w) exhibited the lowest consistency coefficient (K) and the highest flow behavior index (n), while dynamic viscoelastic measurements gave the gel strength in the following order: rice > corn > pineapple stem > cassava starch gel. Interestingly, pineapple stem starch provided the highest slowly digestible starch (SDS) (48.84%) and resistant starch (RS) (15.77%) contents compared to other starches. The oil-in-water (O/W) emulsion stabilized with gelatinized pineapple stem starch exhibited higher emulsion stability than that stabilized with gelatinized cassava starch. Pineapple stem starch could therefore be used as a promising source of nutritional SDS and RS, and as an emulsion stabilizer for food applications.

Effect of heat-moisture treatment on the physicochemical properties and digestibility of proso millet flour and starch.

Proso millet flour (PMF) and starch (PMS) were subjected to heat-moisture treatment (HMT) at 25 % moisture content and 110 °C for 4 h. The effects of HMT on physicochemical and structural properties and in vitro digestibility of PMF and PMS were analyzed. After HMT, SEM showed aggregation and damage to the surface of starch granules, while CLSM showed proteins wrapped around the granules. The amylopectin chain length distribution (CLD) remained unchanged in PMF and PMS after HMT, indicating intact covalent bonds between glucose units. HMT decreased the swelling power, solubility, viscosity of the paste, and gelatinization enthalpy and increased the pasting temperature and gelatinization temperature of PMF and PMS. HMT changed the XRD pattern of PMF from A to A + V type starches, whereas that of PMS remained unchanged. FTIR study showed an increase in the degree of short-range molecular order of PMF and PMS after HMT. In vitro digestibility evaluation showed that the rapidly (RDS) and slowly digestible starch (SDS) contents of PMF and PMS increased, whereas the resistant starch (RS) content decreased after HMT. HMT flour and starch have suitable properties for use in a wide range of food products, from canned to frozen, as well as non-food products.

Astaxanthin-Loaded Pickering Emulsions Stabilized by Nanofibrillated Cellulose: Impact on Emulsion Characteristics, Digestion Behavior, and Bioaccessibility.

Astaxanthin (AX) is one of the major bioactives that has been found to have strong antioxidant properties. However, AX tends to degrade due to its highly unsaturated structure. To overcome this problem, a Pickering O/W emulsion using nanofibrillated cellulose (NFC) as an emulsifier was investigated. NFC was used because it is renewable, biodegradable, and nontoxic. The 10 wt% O/W emulsions with 0.05 wt% AX were prepared with different concentrations of NFC (0.3-0.7 wt%). After 30 days of storage, droplet size, ζ-potential values, viscosity, encapsulation efficiency (EE), and color were determined. The results show that more stable emulsions are formed with increasing NFC concentrations, which can be attributed to the formulation of the NFC network in the aqueous phase. Notably, the stability of the 0.7 wt% NFC-stabilized emulsion was high, indicating that NFC can improve the emulsion's stability. Moreover, it was found that fat digestibility and AX bioaccessibility decreased with increasing NFC concentrations, which was due to the limitation of lipase accessibility. In contrast, the stability of AX increased with increasing NFC concentrations, which was due to the formation of an NFC layer that acted as a barrier and prevented the degradation of AX during in vitro digestion. Therefore, high concentrations of NFC are useful for functional foods delivering satiety instead of oil-soluble bioactives.

Effect of single and dual modifications with cross-linking and octenylsuccinylation on physicochemical, in-vitro digestibility, and emulsifying properties of cassava starch.

Native cassava starch (NCS) was chemically modified by cross-linking (CL), octenylsuccinylation (OS), CL followed by OS, and OS followed by CL. The modified cassava starches (MCS) were determined for physicochemical, in-vitro digestibility, and emulsifying properties. For the dual modifications, the functional groups introduced in the first modification were partially replaced by the ones that introduced in the second modification. The X-ray diffraction pattern and relative crystallinity of cassava starch did not change by both modifications, indicating that both reactions occurred predominantly in amorphous regions as well as on the surface of starch granules and did not alter the crystalline pattern in the granules. The physicochemical and emulsifying properties of the dual MCS were predominantly affected by the functional groups introduced in the second modification. For the in-vitro digestibility, the dual MCS exhibited the highest resistant starch content of 19.48-22.00% in comparison with the NCS (6.05%) and the single MCS (10.76-14.49%), possibly due to a synergistic effect of the functional groups introduced in the first and second modifications.

Influence of Degree of Polymerization of Low-Molecular-Weight Chitosan Oligosaccharides on the α-Glucosidase Inhibition.

Chitosan oligosaccharide (COS) is a bioactive compound derived from marine by-products. COS consumption has been demonstrated to lower the risk of diabetes. However, there are limited data on the inhibitory effect of low-molecular-weight COSs with different degrees of polymerization (DP) on α-glucosidase. This study investigates the α-glucosidase inhibitory activity of two low-molecular-weight COSs, i.e., S-TU-COS with DP2−4 and L-TU-COS with DP2−5, both of which have different molecular weight distributions. The inhibition constants of the inhibitors binding to free enzymes (Ki) and an enzyme−substrate complex (Kii) were investigated to elucidate the inhibitory mechanism of COSs with different chain lengths. The kinetic inhibition model of S-TU-COS showed non-completive inhibition results which are close to the uncompetitive inhibition results with Ki and Kii values of 3.34 mM and 2.94 mM, respectively. In contrast, L-TU-COS showed uncompetitive inhibition with a Kii value of 5.84 mM. With this behavior, the IC50 values of S-TU-COS and L-TU-COS decreased from 12.54 to 11.84 mM and 20.42 to 17.75 mM, respectively, with an increasing substrate concentration from 0.075 to 0.3 mM. This suggests that S-TU-COS is a more potent inhibitor, and the different DP of COS may cause significantly different inhibition (p < 0.05) on the α-glucosidase activity. This research may provide new insights into the production of a COS with a suitable profile for antidiabetic activity.

Effect of hydrocolloids on physicochemical properties, stability, and digestibility of Pickering emulsions stabilized by nanofibrillated cellulose.

In this study, the effect of hydrocolloids with different electrostatic characteristics, namely negatively charged xanthan gum (XG), positively charged chitosan (CH), and non-ionic guar gum (GG), on the physicochemical properties, stability, and lipid digestibility of 10% (w/w) soybean oil-in-water Pickering emulsions stabilized by nanofibrillated cellulose (NFC) was investigated. Addition of XG and CH to the NFC-stabilized emulsions significantly increased the oil droplet sizes and apparent viscosity at high shear rates as compared with the addition of GG. The XG added emulsion showed the lowest rate and extent of creaming, whereas the CH added emulsion gave the highest extent of creaming. The addition of XG and CH led to a more pronounced effect on in vitro lipid digestion, i.e. changes in droplet sizes, surface charges, microstructure, and free fatty acid (FFA) release, than the addition of GG. The XG added emulsion showed the lowest rate and extent of lipid digestion possibly due to the high viscosity of the aqueous phase, large oil droplet sizes, and interaction of XG and calcium, resulting in the reduction of lipase activity. The CH added emulsion exhibited the highest extent of lipid digestion possibly due to binding between CH and FFAs and move away from the droplet surfaces, thereby facilitating the lipase activity. In summary, it can be concluded that ionic hydrocolloids exerted more influence on NFC-stabilized Pickering emulsions than non-ionic ones. These results may facilitate the design of highly stable emulsion-based functional food products with added hydrocolloids to promote health and wellness.

A fixed-film bioscrubber of Microbacterium esteraromaticum SBS1-7 for toluene/styrene biodegradation.

In the present study, a fixed-film bioscrubber (FFBS) of BTEX-degrading bacterium Microbacterium esteraromaticum SBS1-7 with 'AQUAPOROUSGEL® or APG' supporting material was continuously fed with toluene- or styrene-contaminated gas stream for 172 days. Response Surface Methodology (RSM) was used to optimize the biofilm formation on APG as well as the toluene biodegradation in mineral salt medium (MM). The results suggested that 1000 ppm of yeast extract (YE) was necessary for biofilm formation of SBS1-7. The optimized combination of YE and toluene concentration exhibiting the highest biofilm formation and toluene removal was further employed in an up-scale FFBS operation. The maximum Elimination Capacity (ECmax) of 203 g·m-3·h-1 was obtained at the toluene Inlet Loading Rate (ILR) of 295 g·m-3·h-1. FFBS of SBS1-7 was able to withstand a 5-day shutdown and required only 24 h to recover. Moreover, when the inlet Volatile Organic Compound was shifted to styrene, FFBS required only 24 h for adaptation and the system was able to efficiently remove ~95% of styrene after that. Finally, the performance of the bioscrubber when operated in 2 different modes of operation (FFBS vs Biotricking Filter or BTF) were compared. This study evidently demonstrated the robustness and stability of FFBS with M. esteraromaticum SBS1-7.

BTEX biodegradation by Bacillus amyloliquefaciens subsp. plantarum W1 and its proposed BTEX biodegradation pathways.

Benzene, toluene, ethylbenzene and (p-, m- and o-) xylene (BTEX) are classified as main pollutants by several environmental protection agencies. In this study, a non-pathogenic, Gram-positive rod-shape bacterium with an ability to degrade all six BTEX compounds, employed as an individual substrate or as a mixture, was isolated. The bacterial isolate was identified as Bacillus amyloliquefaciens subsp. plantarum strain W1. An overall BTEX biodegradation (as individual substrates) by strain W1 could be ranked as: toluene > benzene, ethylbenzene, p-xylene > m-xylene > o-xylene. When presented in a BTEX mixture, m-xylene and o-xylene biodegradation was slightly improved suggesting an induction effect by other BTEX components. BTEX biodegradation pathways of strain W1 were proposed based on analyses of its metabolic intermediates identified by LC-MS/MS. Detected activity of several putative monooxygenases and dioxygenases suggested the versatility of strain W1. Thus far, this is the first report of biodegradation pathways for all of the six BTEX compounds by a unique bacterium of the genus Bacillus. Moreover, B. amyloliquefaciens subsp. plantarum W1 could be a good candidate for an in situ bioremediation considering its Generally Recognized as Safe (GRAS) status and a possibility to serve as a plant growth-promoting rhizobacterium (PGPR).

Effect of spent brewer's yeast ß-D-glucan on properties of wheat flour dough and bread during chilled storage.

Effect of spent brewer's yeast ß-D-glucan incorporation (0.25-2.00%, w/w wheat flour) on the characteristics of wheat flour dough and bread during chilled storage at 4 °C for 8 days was investigated. The dough containing 0.75% yeast ß-D-glucan had the highest strength, work of adhesion, and stickiness. The addition of yeast ß-D-glucan up to 0.75% yielded the breads with an appearance comparable to the control bread (without yeast ß-D-glucan). The staling of bread was retarded by the addition of yeast ß-D-glucan up to 0.75% as evidenced by the higher retained moisture content and cohesiveness and the lower L* value and hardness of the bread crumb during chilled storage compared to the control and the 1.00-2.00% yeast ß-D-glucan breads. The 0.75% yeast ß-D-glucan bread exhibited the lowest melting enthalpy of retrograded starch (ΔHret), the lowest B-type- and total crystallinities, the least microstructure change of the crumb matrix, and the highest consumer acceptance after 4 days chilled storage. These results suggested that the incorporation of an appropriate amount of yeast ß-D-glucan could improve the quality and shelf life of bread or other starch-based food products during chilled storage.

Digestion behavior and gastrointestinal fate of oil-in-water emulsions stabilized by different modified rice starches.

Native rice starch was modified using different methods which included debranching (DB), octenyl succinylation (OSA), debranching followed by octenyl succinylation (DBOS) and octenyl succinylation followed by debranching (OSDB). The effect of different modifications and the impact of modified starch properties (resistant starch content (RS) and degree of substitution (DS)) on the gastrointestinal fate of emulsified lipids are elucidated using an in vitro digestion model that included the mouth, stomach, and small intestine phases in order to understand their functionality for further applications. The effect of the different modified rice starches on the particle size distribution of the lipid droplets, surface charge (ζ-potential), microstructure, lipid digestion (free fatty acid (FFA) release), and starch hydrolysis was also assessed. The OSA-modified starch and DBOS starch-based emulsions were found stable during the mouth phase and were also found to demonstrate lesser flocculation and coalescence in comparison with the other emulsions due to the presence of more OSA groups that provide greater steric hindrance and better protection from the gastrointestinal conditions. Furthermore, the DBOS starch was found to form emulsions that were more resistant to digestion with a degree of FFA release like dietary fibers and a lower extent of starch digestion that can be attributed to their higher resistant starch content (RS). Thus, the DBOS starch-based emulsions were found to be suitable for further applications such as developing functional foods to control satiety or for designing delivery systems for the sustained release of bioactive compounds.

Encapsulation of Vitamin D3 in Pickering Emulsion Stabilized by Nanofibrillated Mangosteen Cellulose: Effect of Environmental Stresses.

Vitamin D3 was encapsulated in 10% wt soybean oil-in-water (O/W) Pickering emulsions stabilized by either nanofibrillated cellulose (NFC) or whey protein isolate (WPI) at 0.3%, 0.5%, and 0.7% w/w. The vitamin D3 -enriched emulsions were tested for their stability against temperature (30 °C to 90 °C), pH (2 to 8), and ionic strength (0 to 500 mM NaCl). The mean particle diameter (d32 ), ζ-potential, and creaming stability of the oil droplets in the emulsions were measured, as well as their vitamin D3 encapsulation efficiency (EE). After preparation, the oil droplet size (d32 ) of the emulsions stabilized by NFC increased with increasing emulsifier concentration, whereas the droplet size of emulsions stabilized by WPI decreased. NFC provided good stability to the emulsions through a combination of steric and electrostatic repulsion. The EE of vitamin D3 increased with increasing emulsifier concentration. Heating or ionic strength did not significantly (P < 0.05) affect the emulsions properties and EE. On the other hand, the NFC-stabilized emulsions were sensitive to highly acidic conditions (pH 2), with an increase in particle size and decrease in EE. The WPI-stabilized emulsions aggregated around the isoelectric point of the adsorbed proteins (pI ≈ 4.8). Increasing NFC or WPI concentration improved the stability and EE of the emulsions against environmental stresses. NFC-stabilized emulsions had good long-term stability. The results show that NFC can be used as an effective emulsifier for creating vitamin-enriched emulsions with good stability. PRACTICAL APPLICATION: This study can be used to develop more effective encapsulation technologies for fat-soluble vitamins in emulsion-based food products. Encapsulation using nanofibrillated cellulose effectively protected the encapsulated vitamins against environmental stresses which occur in industrial food production (such as pH changes, salt addition, and thermal processing). Moreover, nanofibrillated cellulose extracted from mangosteen rind is a nature-derived emulsifier that is environmental friendly.

Physicochemical and rheological properties of flour and starch from Thai pigmented rice cultivars.

Flour and starch from four Thai pigmented rice cultivars, i.e., Riceberry (RB), Hom Nil (HN), Niaw Dang (ND), and Kum Pleuak Khao (KP) were compared for their physicochemical and rheological properties. Amylose content of all rice starches decreased in the following order: RB (12.09%) > HN (8.14%) > KP (2.87%) ~ ND (2.77%). The HN starch had the lowest proportion of amylopectin short A chains, while the KP starch showed the highest. Pasting temperature, setback, and final viscosity increased, while breakdown and swelling power decreased with increasing amylose content for both flour and starch samples. The flours and starches from the RB and HN showed greater onset and peak temperatures and enthalpy change (ΔH) of gelatinization than those from the ND and KP. Moreover, the gelatinization temperatures of all starches were significantly lower, but ΔH was higher than their flour counterparts. Dynamic viscoelastic tests revealed weak-gel like behavior of all flour and starch gels as evidenced by their G' > G″ and tan δ values were smaller than unity.

Hydroxypropyl methylcellulose enhances the stability of o/w Pickering emulsions stabilized with chitosan and the whole cells of Lactococcus lactis IO-1.

Hydroxypropyl methylcellulose (HPMC) was used as a co-emulsifier with chitosan and the whole cells of bacteriocin-producing Lactococcus lactis IO-1 (L. lactis IO-1) for the preparation of bacteria interface Pickering emulsion. The obtained emulsion exhibited a high stability against centrifugation force, ionic strength and low temperature, with the whole cells of L. lactis IO-1 located at the oil/water interface. Because L.lactis IO-1 was found to produce peptide lantibiotic against several strains of Gram-positive food pathogen, the highly stable emulsion demonstrated in this study exhibited high potential as an antimicrobial emulsion with several health benefits of chitosan and HPLC useful for food industry.

BTEX- and naphthalene-degrading bacterium Microbacterium esteraromaticum strain SBS1-7 isolated from estuarine sediment.

In this study, a non-pathogenic, BTEX-degrading Microbacterium esteraromaticum SBS1-7 was isolated from estuarine sediment in Thailand via an enrichment technique. M. esteraromaticum SBS1-7 was able to degrade all six BTEX components, in both liquid medium and soil slurry system, when BTEX was supplied as an individual component or a mixture. It exhibited a high level of tolerance towards a wide range of hydrocarbons and also utilized alkanes and naphthalene. Detection of metabolites produced during BTEX and naphthalene degradation revealed highly extensive biodegradation pathways used by M. esteraromaticum SBS1-7. Toluene was metabolized via activities of both monooxygenase (toluene 4-monooxygenase or T4MO) and dioxygenases (toluene dioxygenase or TDO and naphthalene 1,2-dioxygenase or NDO). Benzene was metabolized via phenol, possibly by an activity of T4MO. Ethylbenzene was converted into styrene and 1-phenethyl alcohol by a well-documented activity of NDO. Dioxidation of ethylbenzene, possibly by ethylbenzene dioxygenase or EBDO, was also found. All xylene isomers were converted into their corresponding alcohols via an activity of NDO while naphthalene was metabolized via dioxidation reaction by the same enzyme. This study is, by far, the first direct evidence of BTEX biodegradation by a non-pathogenic, rhizosphere bacterium M. esteraromaticum.

Emulsification efficiency of adsorbed chitosan for bacterial cells accumulation at the oil-water interface.

The use of bacterial cell or biocatalyst for industrial synthetic chemistry is on the way of significant growth since the biocatalyst requires low energy input compared to the chemical synthesis and can be considered as a green technology. However, majority of natural bacterial cell surface is hydrophilic which allows poor access to the hydrophobic substrate or product. In this study, Escherichia coli (E. coli) as a representative of hydrophilic bacterial cells were accumulated at the oil-water interface after association with chitosan at a concentration range of 0.75-750 mg/L. After association with negatively charged E coli having a ζ potential of -19.9 mV, a neutralization of positively charged chitosan occurred as evidenced by an increase in the ζ potential value of the mixtures with increasing chitosan concentration up to +3.5 mV at 750 mg/L chitosan. Both emulsification index and droplet size analysis revealed that chitosan-E. coli system is an excellent emulsion stabilizer to date because the threshold concentration was as low as 7.5 mg/L or 0.00075% w/v. A dramatic increase in the surface hydrophobicity of the E. coli as evidenced by an increase in contact angle from 19 to 88° with increasing chitosan concentration from 0 to 750 mg/L, respectively, resulted in an increase in the stability of oil-in-water emulsions stabilized by chitosan-E. coli system. The emulsion was highly stable even the emulsification was performed under 20% salt condition, or temperature ranged between 20 and 50 °C. Emulsification was failed when the oil volume fraction was higher than 0.5, indicating that no phase inversion occurred. The basic investigation presented in this study is a crucial platform for its application in biocatalyst industry and bioremediation of oil spill.