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The extent of adsorption (Γ2 1) of DNA from aqueous solution on different hydrophobic and hydrophilic solid surfaces has been compared as a function of pH, temperature, ionic strength of the medium, and denaturants. Γ2 1 at a given surface (except sephadex) increases with an increase of the nucleotide concentration (X 2) of DNA in mole fraction units, but it attains a monolayer saturation value Γ2 m when X 2 attains a value X 2 m . In most cases Γ2 1 increases further when X 2 ≫ X 2 m . Various neutral electrolytes like LiCl, KCl, CsCl, KBr, CaCl2, and Na2SO4, surfactants like SDS and Triton-X 100, the denaturing action of heat, and the addition of acid and alkali have been observed to play an important role during the study of the adsorption of DNA on charcoal powder. Further, a comparative study has been performed to examine the relative affinity of DNA toward different types of solid surfaces. The significant role of different types of surfaces in controlling the adsorption process has been explained in terms of Gibbs' surface excess quantities. The experimental results have been interpreted in terms of maximum work due to the free energy change of DNA adsorption on various solid surfaces and more quantitatively in terms of the standard free energy change (ΔG°) for the saturation of the surface by DNA as a result of the change in the nucleotide concentration in the bulk from zero to unity in mole fraction units.

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Cow milk curd was prepared using 2% v/v of Streptococcus thermophilus DG1 and a mixed culture (0.5:1.5 v/v) of S. thermophilus DG1 and Lactobacillus plantarum and incubating at 37 °C for 16 h. Soy milk curd was prepared using different ratios of lactic cultures as stated earlier and also a mixed culture containing S. thermophilus DG1, L. plantarum and Leuconostoc mesenteroides sub spp. mesenteroides in the ratio 1:1:1 v/v along with beet pulp (2% w/w) and incubating at 37 °C for 18 h. This improved functional and probiotic properties of curd. Structural changes in curd samples during fermentation were observed by Scanning Electron Microscope (SEM). Soy milk curd showed loosened structure. The degradation of proteins into peptides and amino acids were evaluated by SDS PAGE and amino acid analysis. Maximum production of amino acids i.e. cystine, histidine and asparagine were observed in both the cow and soymilk after fermentation.

The extent of adsorption (Γ2 1) of cetyltrimethylammonium bromide (CTAB), myristyltrimethylammonium bromide (MTAB), and dodecyltrimethylammonium bromide (DTAB) from aqueous solution onto a cellulose−water interface has been measured analytically in a wide range of surfactant concentrations below and above the critical micelle concentration (cmc) at different physicochemical conditions and in the presence of different electrolytes and urea. Γ2 1 is found to increase with increase of bulk surfactant concentration C 2 until it reaches a maximum value Γ2 m when C 2 reaches a critical value, C 2 m. With further increase of C 2 beyond C 2 m, Γ2 1 decreases from Γ2 m and becomes zero with attainment of surface azeotropic state at a surfactant concentration C 2 azeo. For C 2 > C 2 azeo, values of Γ2 1 are negative due to the excess hydration of cellulose fibril and desorption of surfactant micelles from the surface to the bulk phase. The value of Γ2 m depends upon the different physicochemical conditions and presence of different electrolytes and urea. Values of C 2 m lie considerably below the cmc in most cases. Γ2 m decreases with decrease of hydrocarbon chain length of surfactant molecules, and in the case of DTAB all values of Γ2 1 are negative. The results also predict involvement of hydrophobic interaction in the adsorption process. The standard free energy change ΔG° for the transfer of surfactant molecules to 1 kg of cellulose at the state of surface saturation has been calculated using an integrated form of the Gibbs adsorption equation. The values of ΔG° follow the same order as those of Γ2 m. The average slope of the linear plot of ΔG° vs Γ2 m is equal to −34.3 ± 0.1 kJ/mol. This corresponds to the standard free energy change (ΔG B°) for the transfer of 1 mol of surfactant from the bulk solution to the cellulose surface when bulk mole fraction of surfactant is altered from zero to unity. The values of ΔG hi° for different systems at high surfactant concentration (>C 2 azeo) have been also calculated using a linear extrapolation method, and they are found to be positive in all cases due to excess positive hydration of cellulose.

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The extent of adsorption (Gamma2(1)) of bovine serum albumin (BSA), beta-lactoglobulin, lysozyme, gelatin, and DNA from aqueous solution onto the hydrophilic surface of cellulose has been measured as function of biopolymer concentration at different temperatures, pHs, and ionic strengths, and in the presence of a high concentration of inorganic salts and denaturants. In all cases, the value of Gamma2(1) increases with the increase of biopolymer concentration (X2) in bulk and it attains a maximum value at a critical mole fraction concentration X2m. The value of Gamma2m depends upon the nature of protein, temperature, pH, and ionic strength, as well as the nature of neutral salts present in excess. Gamma2m for proteins at a fixed physicochemical condition stands in the following order: Gelatin>betalactoglobulin>lysozyme>BSA. The isotherms for adsorption of DNA nucleotides on cellulose surface at pH 4.0 have been compared at different temperatures and ionic strengths, and in the presence of high concentration of inorganic salts LiCl, NaCl, KCl, and Na2SO4. Values of Gamma2m for different systems have been evaluated and critically compared. At pH 6.0 and 8.0, Gamma2(1) values of DNA nucleotides on cellulose are all negative due to the excess positive hydration of cellulose. At pH 4.0, adsorption of nucleotides of acid, alkali, and heat-denatured DNA widely differ from each other and in the presence of excess concentration of urea becomes negative. The probable mechanisms of biopolymer-cellulose adsorption in terms of polymer hydration, steric interaction, London-van der Waals, hydrophobic, and other types of interactions have been discussed qualitatively. The standard free energy change for the adsorption of protein and DNA nucleotides on the cellulose surface at the state of adsorption saturation has been calculated in kJ per kg of cellulose using an integrated form of the Gibbs adsorption equation. The relation between DeltaG degrees and maximum affinities between biopolymers and the polysaccharide interface have been discussed for various systems.