Food & Function PAPER Cite this: Food Funct., 2018, 9, 5443 Received 23rd July 2018, Accepted 20th September 2018 DOI: 10.1039/c8fo01483c rsc.li/food-function Impact of composition and texture of protein- added yogurts on oral activity Pere Morell, a Amparo Tárrega, a Edward Allen Foegeding b and Susana Fiszman * a Understanding how oral processing is altered in response to changes in the composition and mechanical properties of food provides useful information to design food with improved satiating capacity which is largely influenced by oral exposure. In turn, this information deepens the knowledge about the physiology of texture perception. Six yogurts were formulated with different amounts of protein and protein sources and addition of apple cubes: control (C), extra skimmed milk powder-added (MP), whey protein isolate- added (WPI), and whey protein microgels-added (WPM). In addition, MP was also added with maltodextrin (MPMD) and with fresh apple cubes (MPF). Activities of masseter, anterior temporalis and anterior digastric muscles during oral processing of each sample were recorded (electromyography), and jaw movement amplitudes in three dimensions were determined (jaw tracking system). The jaw muscle activities were highly dependent on the type of yogurt. Addition of apple cubes (MPF) almost doubled the oral processing time, number of chews, and muscle activity of all samples. MP and MPMD required similar but lower values of oral processing than MPF attributed to their reinforced network of milk protein. The lowest values were found for WPI, C and WPM, indicating a weaker, more fluid material. These behavioral results, which clearly differen- tiate the samples, are discussed in connection to the rheological and sensory properties of the yogurts. This study suggests that adding apple cubes significantly alters the oral processing pattern, such that they may be a more effective way of increasing the oral processing time (time exposure) compared to more subtle changes in the protein amount or source. Nevertheless, changes in the protein amount and source also affected, although to a lesser extent, the behavioral, rheological, and sensory properties of yogurt. 1. Introduction Oral food processing collectively accounts for all the physio- logical processes and sensations occurring from the moment a food enters the mouth to when it is swallowed. The signals obtained during oral processing are involved in determining likes and dislikes, the cephalic phase of digestion, and the start of the satiety cascade. 1–3 One aspect of oral processing is the oro-sensory exposure time, simply the time from placement in the mouth to swal- lowing. According to a recent systematic literature review and meta-analysis, prolonged oro-sensory exposure of food can enhance the processes that promote satiation. 4 Food oral exposure is affected by many food characteristics, 5,6 such as viscosity, 5,7 bite size, oral processing rate, or chewing frequency, 8–10 among others. Altering the food matrix 11,12 or increasing the food texture complexity 13 to prolong oral processing is associated with decreased food consumption. 2 While an increased oro-sensory exposure would contribute to controlling further energy intake, 14 the influence of specific jaw movements and muscle activity. It has been shown that modifications in food composition and processing that produced changes in sensory texture change the oral processing parameters of muscle activity and jaw movement. Evaluating the alterations in chewing physi- ology (and thereby signals going to the brain) in response to changes in the food matrix would contribute to an understand- ing of the dynamics of texture perception during oral food processing. 15 Once placed in the mouth, food is subjected to a complex series of manipulations by the tongue, teeth, lips and cheeks, during which it is converted into a form suitable for swallow- ing. 16 Sensory assessments of the food are gathered during each phase of oral food processing. Sensory signals have an early onset during eating and primarily influence satiation. Initial perceptions occurring at low shear rates include attri- butes related to touch (e.g. perceived homogeneity based on the presence, size, and shape of particles) and those requiring a Instituto de Agroquímica y Tecnología de Alimentos (IATA-CSIC), Agustín Escardino 7, 46980 Paterna, Valencia, Spain. E-mail: sfiszman@iata.csic.es b Department of Food, Bioprocessing and Nutrition Sciences. North Carolina State University, 236 Schaub Hall, Raleigh, NC 27695-7624, USA This journal is © The Royal Society of Chemistry 2018 Food Funct. , 2018, 9, 5443–5454 | 5443