Casein and whey protein concentrate (WPC) films, plasticized with glycerol and sorbitol independently, were prepared by casting. The film thickness, water vapour and oxygen permeation and tensile and moisture sorption properties of the films were determined. The tensile strength (TS), tensile strain (TE) and elastic modulus (EM) of the films ranged from 0.71 to 4.58 MPa, 19.22 to 66.63 % and 2.05 to 6.93 MPa, respectively. The film properties were influenced by the type of biopolymer (casein and whey protein concentrate), plasticizer and its concentration. Increasing the plasticizer concentration, increased the film thickness, TE and water vapour permeability (WVP), but decreased the TS and EM. As the concentration of plasticizer increased to the highest level, the film thickness increased from 0.168 to 0.305 mm for glycerol-plasticized films and from 0.251 to 0.326 mm for sorbitol-plasticized films. The film thickness increased because the amount of plasticizer in the film network increased and the amount of biopolymer remained same. Casein films showed superior tensile properties as compared to WPC films. The WVP of both casein and WPC films lied between 3.87 and 13.97 g.mm./(m 2 .h.kPa). The moisture sorption isotherms of both films were typical of high-protein material, and were adequately described by the GAB model. The oxygen permeability of casein films was relatively lower than that of WPC films, regardless of the plasticizer used. The sensory data revealed that the organoleptic quality of Cheddar cheese was unaffected by milk-protein film packaging.

A mathematical model to predict the shelf life of gulabjamun mix based on moisture‐induced spoilage by stickiness (caking) and nonenzymatic browning (NEB) was developed. The moisture adsorption isotherms of gulabjamun were determined at 10, 25 and 40C. The water vapor permeabilities of the packaging materials were also calculated. The critical moisture contents for stickiness and NEB to occur were determined and the moisture‐limiting shelf life was predicted. Validation of the prediction model was done by accelerated shelf life testing at 38C and 90% RH. At 4.8% moisture content, the experimental shelf life of gulabjamun mix based on stickiness and NEB was observed respectively as 41 and 54 days in low‐density polyethylene (LDPE) and 280 and >360 days in polyethylene terephthalate (PET)/Al foil/PET/LDPE pouches. The corresponding predicted values were 34 and 46 days in LDPE and 247 and 342 days in PET/Al foil/PET/LDPE, respectively. The simulation model was fairly accurate and reliable in predicting the shelf life of this product. Practical Applications Stickiness and nonenzymatic browning reactions, induced by moisture gain, affect the shelf life of gulabjamun mix. For dry powders like gulabjamun mix, having a regular shelf life of 6–12 months, accelerated shelf life testing (ASLT) is cumbersome and sometimes unfeasible. Simulation and mathematical modeling of shelf life is an alternative to long‐term ASLT. In this study, a model for predicting the shelf life of gulabjamun mix was developed, incorporating the water vapor permeability of the packaging material, the adsorption of moisture from headspace of the package and the weight of moisture in the product. The shelf life prediction will be useful to monitor the product quality and stability against deteriorative reactions. The model could also be used for shelf life estimation of new products in flexible packaging materials.

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The performance and bio‐kinetic coefficients of the activated sludge process (ASP) treating synthesised dairy wastewater were evaluated in a lab‐scale setup. The step‐loading experiment showed that the chemical oxygen demand (COD) removal efficiency, in general, increased with increasing influent wastewater COD concentration from 180 to 1200 mg/L (correlation coefficient was 0.80). The COD removal efficiency ranged from almost 80–88.4% depending on the COD concentration of the influent wastewater. Also, it could be stated that the ASP was probably underfed with organics at COD concentrations <725 mg/L. Monod, Moser, Contois and Chen & Hashimoto substrate utilisation models, relating the growth of micro‐organisms to substrate utilisation, were employed to describe the bio‐kinetics of the ASP at an organic loading rate of 1200 mg/L. Amongst them, the Contois and Monod models predicted the bio‐kinetic reactions of the ASP very well with coefficient of determination (R2) values of 0.95 and 0.93, respectively. The estimated bio‐kinetic coefficients of the Contois model (on COD basis) were as follows: half‐velocity constant (0.20 mg/L), maximum substrate utilisation rate (3.13 per day), biomass yield coefficient (0.68), endogenous decay coefficient (0.07 per day) and maximum specific growth rate (2.13 per day).

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