S. Basu, S. Malik, G. Joshi et al.
Carbohydrate Polymer Technologies and Applications 2 (2021) 100050
to 9.4 MMT availability of cotton seed protein ( Balandrán-Quintana, Mendoza-Wilson, Montfort, & Huerta-Ocampo, 2019 ). Globulins are the predominant cottonseed proteins followed by albumins and gliadins. Utilization of cotton seed protein as a wet and dry strength additive in paper was studied by Cheng et al., 2017 . The authors reported that on addition of 11% cottonseed solution to paper, the dry and wet strength increased by 33 and 16% respectively. Moreover, the combined use of cottonseed protein and an acid (acetic, adipic, aspartic, and citric acids) to promote adhesion resulted in even greater dry paper strength as com- pared to wet strength of paper. Since very limited work has been done on the use of cotton seed protein as strength additive during paper man- ufacturing, there is a scope for research and development.
glutens can be classified as gliadins (alcohol soluble) and glutenins (al- cohol insoluble). Commercially available glutens (purity 80–90%) can be used in coating formulations for improved oxygen as well as chemical contaminant (grease) barriers in paperboards and packaging materials ( Guazzotti et al., 2014 ). Wheat gluten, corn gluten and calcium caseinate have been combined to generate coating formulations and their rela- tive adsorption rates were determined with chemical analytics. Wheat gluten has superior adsorption potential followed by corn gluten and caseinate; however, the relative amount varies with raw material of the paperboards ( Andersson, 2008 ; Gastaldi, Chalier, Guillemin & Gontard, 2007 ; Guazzotti et al., 2014 ).
6. Gums
5.3. Casein based
6.1. Alginates
Caseins are special classes of phosphorylated proteins ( 𝛼 S1 -, 𝛼 S2 -, 𝛽 - and 𝜅 -caseins) with high surface activity present in milk in an ag- gregated form. 𝛼 - and 𝛽 -Caseins although has the tendency to precipi- tate in low ionic solutions, 𝜅 -casein oppose the precipitation, forming stable colloidal suspensions. Caseinates (sodium, calcium) are gener- ated by precipitating casein micelles through lowering the pH of milk to 4.6. The property of caseinates to generate stable colloids and self- assembly makes it a promising agent imparting superior bonding capa- bilities as well as electrostatic attractions. Caseinates have been found to form stable films in aqueous medium due to inter-chain cohesion. They have also been shown to improve mechanical properties when used as coating additives in cellulose-based packaging materials (Khaoula Khwaldia, Basta, Aloui & El-Saied, 2014 ). Strength, moisture barrier, oil barrier and ductile properties of paperboards have improved by coat- ing with sodium caseinate. Combinations of sodium caseinate (10–13%) with carnauba wax (0.8%), mica (1.2%) and glycerol (0.6%) have gener- ated superior coating formulations conferring water vapour barrier and mechanical strength to coated papers. Conjugate of caseinate with chi- tosan imparts thermal stability as an additive when applied to paper and paper products ( Horne, 2002 , 2008 ; Huppertz, 2013 ; Khwaldia, 2010 ; Khwaldia et al., 2014 , 2006 ).
Alginates are natural polysaccharides found extensively in brown seaweeds (Family Phaeophyceae) typically from the genera Lami- naria and Macrocystis as well as bacterial genera Pseudomonas and Azotobacter . Having a chemical backbone of 𝛽 - d -mannuronate and its epimer 𝛼 - l -guluronate linked by 1–4 glycosidic bonds ( Fig. 4 a) ( Szekalska, Puci ł owska, Szyma ń ska, Ciosek & Winnicka, 2016 ), alginate may constitute around 40% dry weight of the organism, representing a striking analogy with cellulose in terrestrial plants ( Draget, Smidsrød & Skjåk-Bræk, 2005 ). Bacterial alginate is synthesized by a 12-gene ( alg genes) operon family under tight regulation but their polymeriza- tion as well as translocation is poorly understood ( Draget et al., 2005 ; Remminghorst & Rehm, 2006a , 2006b ; Remminghorst, Hay & Rehm, 2009 ). Alginates are used as thickening, stabilizing, adhesive and film- forming agents ( Shen et al., 2014 ). Alginates are produced on a com- mercial scale in the form of fine fibres as sodium and/or calcium ionic forms. Sodium alginate (SA) by virtue of its film-forming abil- ity has been proven to have enhanced bonding homogeneity with pa- per fibres and can be successfully utilized in combination with other additives/complexes resulting improved dry as well as wet strength ( Rhim, Lee & Hong, 2006 ). SA has been used in eco-friendly paper ad- ditive formulations by Song, Yao and Jin (2012) . From the study it was observed that, SA enhanced the adsorption of poly-electrolytes on paper- sheets (from bleached pine kraft pulp) and subsequently enhanced the tensile index by a maximum of ∼ 40–45%. Algin has also been combined with natural gums (guar, tamarind kernel polysaccharide) and used in pigment coating as well as surface sizing agents Yin & Lewis (1981) . However, hydrophilic properties of alginate limits its application since it decreases water resistivity of paperboard ( Hay, Rehman, Moradali, Wang & Rehm, 2013 ; Rhim et al., 2006 ; Rinaudo, 2014 ; Song et al., 2012 ; Yin & Lewis, 1981 ).
5.4. Whey proteins
Whey proteins comprise of 18–20% of total milk proteins primarily constituted by 𝛼 -lactalbumin and 𝛽 -lactoglobulin. Other smaller frac- tions like serum albumin, immunoglobulins, lactoferrin, lactolin etc. are also present in whey protein. The diversity of amino acid composition gives whey protein high levels of structural complexities. Whey protein is heat labile and its thermal denaturation is dependant upon the pH of the medium (denaturation is inversely proportional to pH). Heat de- pendant co-aggregation is another astounding property of whey protein. Heat denaturation exposes the sulphahydril groups in lactoglobulins and makes it susceptible to form disulphide bonds with other proteins in the vicinity. Whey protein isolate/cellulose-based films, produced by the ac- tion of glycerol in aqueous medium with glutaraldehyde and cellulose xanthate was combined with bee wax to form a bilayer coating sys- tem onto paperboards by heating compression ( Han, Salmieri, Le Tien & Lacroix, 2010 ). The coating improves water barrier capacities by di- minishing WVTR by 77–78%. Whey protein concentrates (80% w/w, plasticized with glycerol, sorbitol or polyethylene glycol) have also been proved to impart superior grease resistance capability hence facilitating long term storage of paperboards ( Andersson, 2008 ; Han et al., 2010 ; Jovanovi, Bara & Ma, 2005 ; Lin & Krochta, 2003 ).
6.2. Guar gum
Guar gum is a versatile and popular plant-based gum (exudate) obtained from Guar plant (Cluster bean or Cyamopsis tetragonolobus; Family: Leguminosae ). The natural gum contains around 87% polysac- charide composed primarily of poly- d -galactose and d -mannose unit- susually in the ratio of 1:2 (polygalactomannans). The linear 𝛽 - d - mannopyranosyl chain has side branches of 𝛼 - d -galactopyranosyl units ( Fig. 4 b) ( Mudgil, Barak & Khatkar, 2014 ). Guar gum has the astounding property of maintaining a solution of constant viscosity for a prolonged period either in unmodified form or modified forms (oxidized, car- boxymethylated, hydroxyalkylated etc.). Guar gum although like other galactomannan gums serve as thickeners in textile and paper industries; it has applications in various other industries on a commercial scale. Dasgupta (1999) emphatically established the strength enhancing ef- fects of cationic and anionic guar gum by using wide range of commer- cially available gum forms. The study demonstrates that anionic guar gum (by reacting guar gum with caustic soda followed by monochloroac- etate, propylene oxide etc. generating carboxymethyl, hydroxypropyl
5.5. Glutens
Glutens are abundant storage proteins typically found in wheat and corn. The diverse protein constituents of gluten make it highly viscous and elastic. Additionally, the low hydrophilicity of gluten is attributed by its higher non-polar amino acid composition. In a broader sense,
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