Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Modelling the effect of guar gum on physical, optical, barrier and mechanical properties of potato starch based composite film Sujosh Nandi ⁎ , Proshanta Guha Agricultural and Food Engineering Department, Indian Institute of Technology Kharagpur, West Bengal, India ARTICLE INFO Keywords: Potato starch Guar gum Biodegradable polymer Response surface methodology FE-SEM XRD ABSTRACT The composition of potato starch (PS) and guar gum (GG) based biodegradable composite film was optimised based on physical, optical, mechanical and barrier properties. The rotatable central composite design applying desirability function was used to assess the effect of PS (2.5–4.5%), GG (0.2-0.8%) and glycerol (15–35%). The optimisation was performed considering minimization of film solubility, opacity, yellowness index and water vapour permeability; and maximization tensile strength and percentage elongation at break. Viscosity of film forming solution; thickness, moisture content and whiteness index of the films were also evaluated. The optimum value of PS, GG and glycerol was 3.7%, 0.4% and 15% (of total solids), respectively. All the independent variables depicted significant effect on the responses (p < 0.05) except starch which did not exhibit any sta- tistically significant effect on WVP. The structural characterisation of the optimised film was also analysed by FESEM and XRD which point to the semi-crystalline nature of the developed film. 1. Introduction Pollution caused by synthetic plastics is a serious concern in modern civilization. Synthetic plastics derived from petroleum sources are re- sistant to microbial degradation. Therefore, continuous use of these plastics generate enormous solid waste, which are harmful to wild life as well as marine ecosystem. However, synthetic plastics are preferred for food packaging application due to high strength, stretch-ability, good water vapour and gas barrier properties, transparency and low cost (Bae et al., 2008). Moreover, recycling of these food-contaminated packaging materials are often costly (Siracusa et al., 2008). In view of aforementioned drawbacks, the use of eco-friendly biodegradable polymer as a substitute of synthetic plastics has attracted the attention of the research workers over the years. The different polysaccharides, such as starch, cellulose derivatives, chitosan, pectin and others have been extensively studied for bio-de- gradable film preparation (Rhim & Ng, 2007). Among these, starch is widely studied because of its abundance in nature and thermoplastic behaviour. Moreover, the cost of starch obtained from plant sources is comparable with respect to other synthetic polymers, such as low density polyethylene (LDPE), polystyrene (PS) and Polyethylene ter- ephthalate (PET) (Krochta & De Mulder-Johnston, 1997). Starch is a polymer of D-glucose units linked by α-D-glycosidic bonds, which consists of amylose and amylopectin molecules. Depending on the sources, the amylose and amylopectin content of the starch varies and therefore, starch based films exhibit different prop- erties. High amylose starch shows high tensile strength and high young modulus, but low strain at break (Rindlav-Westling et al., 1998) and better stability on aging (Hu et al., 2009. Therefore, potato starch with high amylose content can be used for developing biodegradable film. However, potato starch cannot produce efficient polymer film owing to high water affinity and poor mechanical properties compared to syn- thetic plastics (Wu et al., 2009). It was observed that physicochemical characteristics of starch-based films depend on crystallinity of the polymer matrix. In this context, researchers have noticed that in- corporation of other carbohydrates having similar structural compat- ibility, into starch matrix can modify the physicochemical properties of the films (Jiménez, Fabra, Talens, & Chiralt, 2012). Therefore, in- corporation of guar gum, a polysaccharide, into potato starch in op- timum proportion can introduce a potential film to the realm of bio- degradable polymer. Guar gum is a galacto-mannan having a mannose to galactose ratio of 1:6 obtained from the Indian cluster bean (Cyamopsis tetragonoloba) (Dea & Morrison, 1975). The backbone of guar gum is a linear chain of β-(1–4)-mannopyranose units with α-(1–6) - galactopyranose units as a side chain of every second mannose (Fernandes et al., 1993). In the food and non-food industries, such as pharmaceutical, biomedical and cosmetic industries, guar gum is used as a stiffener. The synergistic https://doi.org/10.1016/j.carbpol.2018.08.028 Received 22 May 2018; Received in revised form 2 August 2018; Accepted 7 August 2018 ⁎ Corresponding author. E-mail address: sujoshniitkgp@gmail.com (S. Nandi). Carbohydrate Polymers 200 (2018) 498–507 Available online 12 August 2018 0144-8617/ © 2018 Elsevier Ltd. All rights reserved. T