Application as a Cryoprotectant/Support Carrier

The antifreeze property of poly (glutamic acids) (PGAs) was investigated and a higher

antifreeze activity was recorded when the molecular weight of PGAs was in the range of

20,000 than glucose which is known to have high antifreeze property (Misuiki et al., 1998).

Almost all substances that have high antifreeze property also possess cryoprotective effect

(Mitsuiki et al., 1998). Bhat et al., (2013) investigated the cryoprotective effect of γ-PGA since its antifreeze property is well known. The study was aimed at testing the effect of γ- PGA produced by B. subtilis natto ATCC 15245 on the viability of probiotic bacteria (L.

paracasei, B. breve and B. longum) during freeze drying. The study demonstrated that 10% γ-

PGA protected L. paracasei better than sucrose; a well-known cryoprotectant. It also

demonstrated comparable cryoprotectant activity to sucrose with B. breve and B. longum.

Bhat et al. (2015) also studied the survival of probiotic bacteria (B. breve and B. longum) when combined with a γ-PGA matrix during storage in fruit juices and during ingestion. Results demonstrated that the combination of probiotic bacteria with a γ-PGA matrix improved survival of B. breve and B. longum during storage in fresh orange juice over a

period of 39 days. It was also reported that survival of B. breve and B. longum was improved with the γ-PGA matrix during exposure to simulated gastric juice (pH 2) for 4 hours compared with free cells, a total loss in viability was recorded after 1 hour in free cells while in γ-PGA-protected cells, an average of 8 Log CFU/ml was recorded after 4 hours of exposure to simulated gastric juice.

Gomaa (2016) reported that γ-PGA is able to improve the survival of probiotic bacteria (L.

rhamnosus, L. paracasei and L. plantarum) during freeze drying and during storage in orange

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the orange juice did not change which suggested γ-PGA can be used as a non-dairy delivery

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Table 2.3: Application of γ-PGA and its Derivatives

Field Application Chemical /Biochemical Functions

Medicine Drug delivery Paclitaxel poliglumex (PPX) a macromolecular conjugate of paclitaxel and poly-l-glutamic acid demonstrated better effect than the standard paclitaxel. Results also revealed accumulation of PPX in tumour tissue where the active ingredient paclitaxel was slowly and progressively released (Singer, 2005).

Tissue engineering A polyelectrolyte complex (PEC) made up of chitosan and γ-PGA was designed for wound dressing. PEC provided suitable moisture content and demonstrated excellent mechanical properties that allowed the dressings to be easily removed from the wound surface without destroying newly formed tissue (Tsao et al., 2011).

The surface hydrophilicity, rate of water absorption, swelling ratio of composite biomaterial and mechanical strength of chitosan matrices has been improved by modification with γ-PGA (Bajaj and Singhal, 2011).

Biological adhesives A hydrogel glue produced when gelatine and poly (L-glutamic acid) were mixed with a water soluble carbodiimide demonstrated a superior sealing effect of the lung air leak than the conventional fibrin glue (Otani et al., 1999).

Metal chelator Super paramagnetic iron oxide nanoparticles coated with γ-PGA exhibited high heavy metal removal capabilities from simulated gastrointestinal fluid and a meal solution (Inbaraj and Chen, 2012).

Food Cryoprotectant γ-PGA sodium salt produced by B. licheniformis has antifreeze activity and is an effective cryoprotectants for frozen foods due to its weaker taste and it can be added to food in large quantity without altering the taste of the food (Najar and Das, 2015).

Bitterness relieving agent γ-PGA can be used to relief the bitter taste of amino acids, peptides, caffeine, quinines, etc. in food (Shih and Van, 2001). Texture enhancer γ-PGA can be used to improve the texture of starch-based baked products, noodles and as ice-cream stabilizer (Najar and

Das, 2015).

Osteoporosis preventing agent γ-PGA is able to dissolve calcium and magnesium compounds and in turn form stable coordinated stable ionic complexes. This will increase the bioavailability of calcium and magnesium hence reducing old-age osteoporosis conditions and as well as improve the formation of healthy bones. (Ho et al., 2006).

Mends taste and drinkability of certain drinks

Low concentrations of γ-PGA have been reported to mend the taste and drinkability of juices and other drinks (Najar and Das, 2015).

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Table 2.3 Continued

Field Application Chemical /Biochemical Functions

Cosmetics Moisturiser The use of moisturisers containing γ-PGA (Na+ _{form) and γ-polyglutamate hydrogels (Na}+ _{form) was examined and} results showed that moisturisers containing γ-PGA were better for the improvement of skin elasticity (Ho et al., 2006). Increases hair strength γ-PGA has been reported to be able to increase hair strength and to allow hair to withstand bleaching process by

increasing its ability to retain moisture and by forming a barrier that is able to dilute the chemical interactions of the colourings applied with the protein contents of the hair (Bajaj and Singhal 2011).

Treatment of waste water

Removal of heavy metals γ-PGA functionalized cellulosic membranes were tested on water waste that contained lead and a minimum of 380-fold volume reduction can be attained through membrane encapsulation (Shih and Van, 2001).

Removal of dye γ-PGA can be used for the effective removal of basic dyes from aqueous solution. It was reported that at pH 1.0; 98% of the dye absorbed in γ-PGA can be recovered; this enhances reuse of spent γ-PGA (Inbaraj et al., 2006b).

Biopolymer flocculant The flocculation properties of γ-PGA from B. subtilis was investigated and it was reported that γ-PGA possesses flocculating activity in various organic and inorganic suspensions (Yokoi et al., 1996).

Agriculture Animal feed additives Absorption of minerals is promoted by γ-PGA (Najar and Das, 2015) and it also increases the strength of egg-shells (Luo

et al., 2016).

Biocontrol agent and fertilizer synergist

γ-PGA obtained from the fermentation of B. subtilis strain B6-1 and soybean and sweet potato residues effectively supressed cucumber wilts and also increased the dry weights of roots and shoots of cucumber seedlings (Wang et al., 2008).

Others Biodegradable plastics γ-PGA can be used as a substitute for chemically synthesised non-biodegradable plastics (Shih and Van, 2009).

A complex made up of L-PGA and hexadecylpyridinium cation (HDP+_{) has been reported to be able to form} thermoplastics. HDP+ _{acts to suppress the hydrophilicity of γ-PGA and the complex formed can be moulded into various} shapes and sizes by pressurization (Najar and Das, 2015).

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Table 2.3 Continued

Field Application Chemical /Biochemical Functions

Antibacterial activity It has been reported that magnetite nanoparticles (MNPs) that are modified with the sodium (NaPGA) and calcium (CaPGA) salts of γ-PGA are cytocompatible and possess antibacterial activity in vitro against Salmonella enteritidis (SE01) than the commercial antibiotics linezolid and cefaclor. CaPGA was effective against E. coli 0157:H7 TWC01 while Na PGA was effective against E. coli ATCC 8739 and S. aureus ATCC 10832 (Inbaraj et al., 2011).

Treatment of xerostomia (dry mouth)

A sialagogue made up of γ-PGA or its salt if blended into an oral suspension and food product is able to make the oral mucosal pleasant even in severe cases of xerostomia (Uotani et al., 2011).

Gene delivery A γ-PGA complex (pDNA/PEI/γ-PGA) was developed and it was reported to be a useful gene delivery system with low toxicity and high transfection efficiency (Kurosaki et al., 2009).

Glucose sensor Fine needle-type glucose sensors were made using γ-PGA as a glucose oxidase and a permselective inner membrane. The presence of electroactive compounds such as ascorbic acids and uric acids had no effect on the obtained glucose sensor. The glucose sensor also provided long term stability of about one month. γ-PGA was reported to function as a sufficient perselective film material (Yasuzawa et al.,2011).

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