Inulin at low concentrations significantly improves the gelling properties of oat protein e A molecular mechanism study Talina Vanessa Nieto-Nieto, Yi Xiang Wang, Lech Ozimek, Lingyun Chen * Department of Agricultural, Food Nutritional Science, University of Alberta, Edmonton T6G 2P5, Canada article info Article history: Received 7 January 2015 Received in revised form 10 March 2015 Accepted 19 March 2015 Available online 25 April 2015 Keywords: Oat protein Inulin Thermal gelation Phase separation Proteinepolysaccharide interactions abstract The effect of inulin addition at low concentrations (0.1e0.5%) on the thermal gelation of oat protein gels was investigated using textural profile analysis, rheological measurements and microstructure obser- vation through scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Results indicate that oat protein hexamers were dissociated with heat into monomers, which then became the reactive units involved in the development of a unique percolating network. The major forces responsible for the establishment of the structure were disulphide bonds, as well as hydrogen bonds and hydrophobic forces. A small amount of inulin can greatly increase the compressive stress of the gels prepared at pH 7 from 13.93 to 22.98 kPa. This is related to the phase separation phenomena produced during heating, which increased the apparent protein concentration. Moreover, inulin formed nano- particles in the void spaces of the protein network performing a filling effect and creating junction zones. Localized interactions such as hydrogen and hydrophobic bonds were possible between protein and inulin at the borders of junction zones. This research has provided a new approach to make strong oat protein gels at neutral pH. Future applications may promote the utilization of oat protein as a plant derived gelling ingredient in a wide range of food applications. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Oats are an important crop worldwide, with an annual pro- duction of approximately 21 million tonnes. Canada is a major supplier of oats, making up the majority of world oat trade (Food and Agricultural Organization (FAO), 2012). This grain has recently attracted research and commercial attention mainly due to the growing public awareness of the health benefits of b-glucan, which is known to reduce blood cholesterol and glucose levels. Several techniques have been developed to isolate b-glucan from oat grain as a health ingredient in food products. Protein is the second largest component (12e20%) in oats after starch. Oat pro- tein have a superior amino acid profile due to a higher content of lysine because globulins represent 70e80% of the total protein in oats, whereas alcohol-soluble prolamines are the major storage proteins in other cereals (Robert, Nozzolillo, Cudjoe, & Altosaar, 1983). The 12S globulin is the major oat protein fraction, which resembles the structure of 11S globulin of soy (glycinin). Thus, oat protein possesses gelling potential (Ma, Khanzada, & Harwalkar, 1988; Ma and Wood, 1987; Nieto-Nieto, Wang, Ozimek, & Chen, 2014). Plant proteins are normally considered inferior to animal proteins (e.g. gelatin, egg white and whey protein) in terms of gelling properties. In our recent work, trypsin treated oat protein could form gels with comparable mechanical strength to egg white protein at pH 9 (Nieto-Nieto et al., 2014). This has provided op- portunity for oat protein to be used a new gelling ingredient from plant resources in food formulations such as meat binder and fat replacer, or used in meat analogues for vegetarian foods. However, strong gels could be only obtained at alkali pH when heated to 110e120  C. The gels were weak when formed under acidic and neutral pH at 100  C. This has significantly limited the application of oat protein in food systems that normally have pH values in the range of 2.5e7 and heating temperature at 100  C or lower. Therefore novel approaches to enable formation of stronger oat protein gels within a more appropriate pH and temperature for food processing are necessary to promote the utilization of oat protein as a gelling agent. Inulin is a non-digestible polysaccharide naturally occurring in several edible fruits and vegetables. It is formed by fructose mol- ecules linked by b-(2e1) glycosidic bonds, generally with a terminal * Corresponding author. Tel.: þ1 780 492 0038; fax: þ1 780 492 4265. E-mail address: lingyun.chen@ualberta.ca (L. Chen). Contents lists available at ScienceDirect Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd http://dx.doi.org/10.1016/j.foodhyd.2015.03.031 0268-005X/© 2015 Elsevier Ltd. All rights reserved. Food Hydrocolloids 50 (2015) 116e127