Arianne
van Eck
ab,
Erin
Franks
c,
Christopher J.
Vinyard
c,
Verónica
Galindo-Cuspinera
d,
Vincenzo
Fogliano
ab,
Markus
Stieger
ab and
Elke
Scholten
*ae
aTiFN, P.O. Box 557, 6700 AN Wageningen, The Netherlands
bFood Quality and Design, Wageningen University, P.O. Box 17, 6700 AA Wageningen, The Netherlands
cDepartment of Anatomy and Neurobiology, Northeast Ohio Medical University, Rootstown, OH 44272, USA
dUnilever Innovation Centre Wageningen BV, Bronland 14, 6708 WH Wageningen, The Netherlands
ePhysics and Physical Chemistry of Foods, Wageningen University, P.O. Box 17, 6700 AA Wageningen, The Netherlands. E-mail: elke.scholten@wur.nl
First published on 17th June 2020
Condiments are rarely consumed on their own. Although addition of condiments to carrier foods is known to affect oral processing behavior and sensory perception, an understanding of how different condiment properties impact oral processing behavior and sensory perception of solid carrier foods is lacking. This study aimed to understand the role of condiments varying in composition and/or rheological properties in bolus formation facilitation, and how they influence oral processing behavior and sensory perception of solid carrier foods. Two carriers (bread, cooked potato) were combined with mayonnaises differing in fat content and viscosity. Addition of mayonnaises changed bolus properties of solid carrier foods considerably (i.e. decreased bread firmness, increased potato cohesiveness, increased lubrication of both bread and potato bolus) and, consequently, facilitated faster bolus formation. While addition of mayonnaises to bread and potatoes decreased the number of chewing cycles before swallowing, consumers did not change muscle activities or jaw movements per chew. No effect of mayonnaise fat content on oral processing behavior of composite foods was observed. Low viscosity mayonnaise resulted in faster bolus formation and swallowing compared to high viscosity mayonnaise. Low viscosity mayonnaise penetrated faster into bread boli leading to faster softening of bread boli. Also in the case of potato, low viscosity mayonnaise lead to faster bolus formation than for high viscosity mayonnaise. The low viscosity mayonnaise mixed more easily with potato bolus pieces, enhancing adhesion between pieces. Both mayonnaise fat content and viscosity influenced sensory perception of composite foods considerably, especially in terms of fattiness and creaminess. We conclude that oral processing behavior, bolus formation and sensory perception of solid carrier foods can be modified considerably by condiments. While composition and rheological properties of condiments have a large effect on bolus formation and sensory perception of solid carrier foods, these aspects have a limited effect on oral processing behavior of composite foods. Oral processing behavior is dominated by the properties of the solid carrier food. Tailoring condiment-carrier combinations could be an effective strategy to increase healthy eating, alter food intake for populations such as the elderly, and increase food appreciation.
Condiments are frequently added to solid carrier foods such as bread, vegetables, potatoes, fish and meat. (Throughout, we refer to the combination of a solid carrier food with a condiment as a composite food.) Addition of condiments has been suggested to complement or enhance the flavor perception of carrier foods and to increase sensory pleasure.1 Sensory complexity increases when two foods differing in mechanical properties and composition are combined into a composite food.3–6 Such inhomogeneous composite foods are generally well liked by consumers, presumably because of intra-oral sensory variety perceived throughout consumption.7–9 Yet, composite foods receive surprisingly little scientific attention in the field of sensory science and oral processing behavior.
Addition of condiments affects oral processing behavior (i.e. chewing behavior and bolus formation) of solid carrier foods. When condiments were added to bread or crackers, fewer chews, shorter mastication times until swallowing and, consequently, faster eating rates have been observed.10–12 Condiments moistened and softened bread boli, leading to faster formation of safe-to-swallow boli.12 Condiments also facilitated mastication of raw vegetables. Addition of mayonnaise to raw carrots resulted in fewer chews, shorter mastication times and faster eating rates.13 However, faster eating could not be explained by moisture uptake of boli, as carrots are suggested to not absorb moisture like bread and cracker boli. The mechanisms for changes in oral processing behavior caused by addition of condiments to solid carrier foods may therefore differ with composite foods. Little is known about how rheological and physicochemical properties as well as composition of condiments influence oral processing behavior of composite foods.
As condiments are commercially available in a wide range of compositions (e.g. fat content, moisture content) and/or textural properties (e.g. viscosity, friction), we previously studied the effect of type of condiment (solid cheese, cheese spread, mayonnaise) on oral processing behavior of bread and crackers.12 Mayonnaise had the largest impact on oral processing behavior of composite foods (i.e. fewest number of chews, shortest mastication time, fastest eating rate), followed by cheese spread and solid cheese which had only limited impact on oral processing behavior. The different effects of the three types of condiments are likely due to their initial food properties, suggesting that condiment consistency affects bolus formation of resulting composite foods.12 Differences in bolus formation were also found for bread and crackers as food structure breakdown and bolus formation was affected by the textural properties of such carriers. Addition of condiments to solid carrier foods seems to facilitate bolus formation of composite foods in different ways. We hypothesize that adherence of separate solid carrier bolus pieces is enhanced by condiments, which provide lubrication to composite food boli. However, an understanding of how condiment properties and composition contribute to chewing behavior, bolus formation and sensory perception of solid carrier foods is still lacking.
Using a multidisciplinary approach to investigate the link between food structure, chewing behavior and bolus properties is therefore necessary to better understand the transformation of food properties during mastication of composite foods that trigger sensory sensations.14–16 This approach has been used previously for a broad range of single foods including model gels,17–21 meat,22–24 bread25–27 and biscuits.28 As composite foods involve textural changes of two separate foods simultaneously, linking composite food structure to oral processing behavior and sensory perception becomes more challenging.
The aim of this study was to understand the role of condiments, themselves varying in composition or rheological properties, in bolus formation facilitation and how they influence oral processing behavior and sensory perception of solid carrier foods. Condiments (mayonnaises) varying in fat content and viscosity were combined with different carrier foods (bread and cooked potato). These two carrier foods were chosen based on their difference in water absorption capability. We hypothesize that bolus formation of composite foods is affected by condiment viscosity with moisture being absorbed faster by carrier foods when condiment viscosity is low. We hypothesize that high fat of condiments facilitates adherence of composite food boli, and thereby influence bolus properties and sensory perception. By systematically varying the properties of the condiments, this study provides new insights into food oral processing of composite foods, which enables us to gain a better understanding of the structural transitions of foods that contribute to perception. Such knowledge may be useful to increase healthy food intake with high consumer appreciation.
FF-HV | LF-HV-starch | LF-HV-xanthan | LF-LV | |
---|---|---|---|---|
Fat content | Full fat (FF) | Low fat (LF) | Low fat (LF) | Low fat (LF) |
(% w/w) | 73 | 20 | 20 | 20 |
Viscosity | High viscosity (HV) | High viscosity (HV) | High viscosity (HV) | Low viscosity (LV) |
At 1 s−1 (Pa s) | 60 ± 12 | 92 ± 22 | 149 ± 16 | 2 ± 0.2 |
At 10 s−1 (Pa s) | 9 ± 2 | 13 ± 3 | 16 ± 1 | 0.4 ± 0.04 |
At 100 s−1 (Pa s) | 1.3 ± 0.3 | 1.9 ± 0.4 | 1.6 ± 0.1 | 0.1 ± 0.01 |
Thickening agent | — | Starch | Xanthan | — |
(% w/w) | — | 5 | 3 | — |
Mayonnaises were combined with solid carrier foods to form composite foods. Two commercial carrier foods were used: bread (whole grain casino bread, Albert Heijn, The Netherlands) and purple potatoes (Solanum tuberosum, Albert Heijn, The Netherlands). Bread and potatoes were selected based on their difference in water absorption capability. Bread is speculated to absorb moisture during oral processing, whereas boiled potatoes are assumed to absorb less moisture. Dark bread and purple potatoes were chosen to increase color contrast between condiment and carrier foods in expectorated boli to facilitate qualitative visualization of mixing behavior of condiments with carriers (see section 2.2.5.1). Fresh bread without crust was cut in squares of 35 × 35 × 8 mm of approximately 3.5 g (moisture content: 44 ± 3 wt%). Potatoes were peeled, cut in small beams of ∼70 × 12.5 × 12.5 mm of approximately 6.5 g, vacuum packed into heat-resistant plastic bags, and cooked sous-vide at 90 °C for 15 min (moisture content: 88 ± 1 wt%). After cooking, all bags were cooled in ice water for 15 min and stored in the refrigerator (4 °C) for up to six days.
For carrier–mayonnaise combinations, mayonnaise was spread on top of bread (simplified model for bread with spread), and potatoes were completely covered by mayonnaise (simplified model for potato salad with mayonnaise dressing). Approximately 3.5 g of mayonnaise was added to the carriers leading to a 1:1 weight ratio for bread–mayonnaise combinations and a 2:1 weight ratio for potato–mayonnaise combinations. This was based on the weight ratios of bread with spreads and vegetables with condiments of previous studies and is representative for weight ratios during normal consumption behavior.12,13 Carrier–mayonnaise combinations were prepared just before serving to minimize moisture transfer of the mayonnaises into the carriers before consumption. In addition, carriers were assessed alone as a reference.
For all sessions, samples were presented with three-digit codes in a random order following a completely randomized design. All samples were served on a spoon. Between each sample, subjects cleansed their palate with cold water and tea (Jasmine green tea, Twinings, UK) for at least 1 minute. They used tongue scrapers to aid the removal of oil from their tongue.
Raw EMG data were band-pass filtered at 100–3000 Hz. To provide a single waveform for analyses, raw EMG data were transformed by calculating the root mean square (rms) of each digitized raw EMG signal at 2 ms intervals over a 42 ms time constant using LabView Graphical Programming System (National Instruments Corporation, Austin, TX).29,30 A chewing sequence was produced for each sample from the simultaneous recordings of jaw movements and rms-EMG activity. As with the video recordings, total mastication time (s), number of chews and chewing frequency (chews per s) were determined. More detailed parameters including chewing cycle duration (opening, closing, power stroke), chewing velocities (during opening, closing), chewing movements (vertical, anterior posterior and medial lateral direction) and muscle activities (temporalis, masseter and digastric; per chew and during the sequence) were also collected to comprehensively analyze jaw-muscle activity and jaw-kinematic patterns.
Two familiarization sessions of 3 hours took place to acquaint the panel with the different carrier–mayonnaise combinations, as although they had years of experience with the evaluation of plain mayonnaises, they did not have experience with composite foods. The first session was used to discuss the attributes with definitions (Table 2). Attributes were based upon past lexicons developed for mayonnaise evaluation, and attributes applicable to carrier–mayonnaise combinations were determined during a panel discussion. The second training session was used to set the attribute order, after which the panel practiced with the FF-HV, LF-HV-xanthan and LF-LV mayonnaises without and with carriers. The panelists used a 15-step categorical scale ranging from 0 to 15, where 0 represented not at all and 15 represented extremely high intensity.
Modality | Attribute | Definition |
---|---|---|
a The sensory attribute bread fibers was assessed for bread samples only. The sensory attribute potato particles was assessed for potato samples only. | ||
Odor | Overall odor intensity | The intensity of the odor totality |
Taste | Overall taste intensity | The intensity of the taste totality |
Mouthfeel | Dry | Dry and rough feeling on the tongue or in the mouth |
Firm | Degree of firmness (the force needed to press the sample between the tong and the palate) | |
Sticky | Degree of stickiness | |
Gummy | Degree of small soft gel particles or lumps | |
Creamy | Degree of creaminess like whipped cream | |
Fatty | Degree of fatty feeling | |
Velvet | Degree of creamy feeling such as Calve full fat mayo (soft and velvet) | |
Smooth | Degree of slippery feeling | |
Salivating | Degree of salivation or mouthwatering due to secretion of saliva | |
Absorbing | Degree of mayonnaise absorbance in the bread/the potato | |
Chewing effort | Degree of effort to chew the sample/form a bolus | |
Homogeneous | Degree of mixing of mayonnaise with the bread/the potato (in the mouth) | |
Bread fibersa | Degree of a fiber feeling, due to the presence of bread in the mouth | |
Potato particlesa | Degree of a particles feeling, due to the presence of potato pieces in the mouth | |
Afterfeel | Residue | A substance remains in the mouth (in the molars) |
Fatty film layer | A fatty film, coating remains in the mouth | |
Dry, rough | Dry and rough feeling remains on the tongue or in the mouth | |
Cleaning effort | Degree of effort to clean the mouth after eating the sample |
The panel attended two evaluation sessions of 2.5 hours each (1 hour – 30 min break – 1 hour) over a period of two weeks. The sessions were organized by sample type: bread without/with mayonnaise was evaluated in the first session and potato without/with mayonnaise was evaluated in the second session. At the start of each session, the panel evaluated one warm-up sample (FF-HV) to avoid first-order-effects. All samples were coded with 3-digit random codes, evaluated in duplicate and presented in a random order following a balanced design. Between each sample, subjects cleansed their palate with cold water, tea (jasmine green tea, Twinings, UK) and crackers (Barber cream crackers, Burton's Biscuit Co., UK) for at least 2–3 minutes.
To investigate the effect of mayonnaise properties on chewing behavior, bolus formation and sensory perception of carrier–mayonnaise combinations, linear mixed models were performed using Lmer package in R.32Mayonnaise, carrier and mayonnaise:carrier interaction were set as fixed effects and subject, serving order, session (if applicable) and replicate (if applicable) were set as random effects. Data on single carriers (i.e. without mayonnaise) were used illustratively, and were not included in the linear mixed models. Multiple factor analysis (MFA) was performed to compare the different data sets (video recordings, EMG and jaw tracking, bolus properties at moment of swallowing and static sensory characteristics) simultaneously, using FactoMineR package.33 For this analysis, only those parameters with a significant mayonnaise effect during mixed models were considered. Furthermore, Pearson's product-moment correlations (r) were used to determine relationships between averaged coefficient of friction of boli and sensory perception (smoothness, dry and rough afterfeel). R language (RStudio, version 1.0.143) was used to perform all statistical tests. Significance level of p < 0.05 was chosen.
Mayonnaise | Carrier | M × C | Bread | Bread FF-HV | Bread LF-HV-starch | Bread LF-HV-xanthan | Bread LF-LV | Potato | Potato FF-HV | Potato LF-HV-starch | Potato LF-HV-xanthan | Potato LF-LV | ||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
F | p | F | p | F | p | Mean ± SEM | Mean ± SEM | Mean ± SEM | Mean ± SEM | Mean ± SEM | Mean ± SEM | Mean ± SEM | Mean ± SEM | Mean ± SEM | Mean ± SEM | |
a The sensory attribute bread fibers was assessed for bread samples only. The sensory attribute potato particles was assessed for potato samples only. | ||||||||||||||||
(A) EMG/Jaw tracking | ||||||||||||||||
Eating behavior | ||||||||||||||||
Number of chews | 18.6 | <0.001 | 8.2 | 0.005 | 0.2 | 0.922 | 23 ± 2 | 16 ± 1b | 16 ± 1b | 18 ± 1a | 15 ± 1b | 20 ± 1 | 17 ± 1b | 18 ± 1b | 19 ± 1a | 16 ± 1b |
Chewing time (s) | 16.0 | <0.001 | 2.9 | 0.090 | 0.5 | 0.694 | 14.7 ± 0.9 | 10.4 ± 0.7bc | 10.4 ± 0.8b | 11.1 ± 0.7a | 9.2 ± 0.8c | 12.5 ± 0.7 | 10.1 ± 0.7bc | 11.1 ± 0.8b | 11.9 ± 0.5a | 9.7 ± 0.7c |
Chewing cycle duration (s) | 3.6 | 0.015 | 22.5 | <0.001 | 0.2 | 0.867 | 0.67 ± 0.02 | 0.66 ± 0.02ab | 0.66 ± 0.02ab | 0.66 ± 0.02a | 0.64 ± 0.02b | 0.61 ± 0.01 | 0.62 ± 0.01ab | 0.64 ± 0.02ab | 0.64 ± 0.02a | 0.61 ± 0.01b |
Opening duration (s) | 6.5 | <0.001 | 23.5 | <0.001 | 2.6 | 0.052 | 0.23 ± 0.01 | 0.23 ± 0.01ab | 0.24 ± 0.01a | 0.23 ± 0.01a | 0.22 ± 0.01b | 0.21 ± 0.01 | 0.22 ± 0.01ab | 0.23 ± 0.01a | 0.23 ± 0.01a | 0.21 ± 0.01b |
Closing duration (s) | 0.4 | 0.764 | 12.3 | <0.001 | 0.2 | 0.918 | 0.27 ± 0.01 | 0.26 ± 0.01 | 0.26 ± 0.01 | 0.26 ± 0.01 | 0.26 ± 0.01 | 0.26 ± 0.01 | 0.27 ± 0.01 | 0.27 ± 0.01 | 0.27 ± 0.01 | 0.27 ± 0.01 |
Power stroke duration (s) | 1.1 | 0.345 | 67.0 | <0.001 | 0.6 | 0.599 | 0.16 ± 0.01 | 0.15 ± 0.01 | 0.15 ± 0.00 | 0.16 ± 0.01 | 0.15 ± 0.01 | 0.14 ± 0.01 | 0.14 ± 0.01 | 0.14 ± 0.01 | 0.14 ± 0.01 | 0.14 ± 0.01 |
Chewing frequency (chew per s) | 3.1 | 0.026 | 20.1 | <0.001 | 0.3 | 0.824 | 1.5 ± 0.0 | 1.5 ± 0.0ab | 1.5 ± 0.0ab | 1.5 ± 0.0b | 1.6 ± 0.0a | 1.6 ± 0.0 | 1.6 ± 0.0ab | 1.6 ± 0.0ab | 1.6 ± 0.0b | 1.6 ± 0.0a |
Eating rate (g min−1) | 18.0 | <0.001 | 102.7 | <0.001 | 0.9 | 0.420 | 16 ± 1 | 46 ± 3b | 46 ± 3b | 41 ± 3c | 55 ± 4a | 35 ± 2 | 64 ± 3b | 61 ± 3b | 51 ± 3c | 70 ± 4a |
Jaw movements | ||||||||||||||||
Opening veloctiy (mm s−1) | 1.0 | 0.388 | 0.7 | 0.412 | 0.9 | 0.443 | 40 ± 7 | 38 ± 7 | 38 ± 7 | 40 ± 7 | 36 ± 7 | 40 ± 7 | 39 ± 7 | 37 ± 7 | 37 ± 7 | 36 ± 7 |
Closing velocity (mm s−1) | 2.0 | 0.108 | 13.8 | <0.001 | 0.6 | 0.628 | 36 ± 6 | 36 ± 6 | 37 ± 7 | 37 ± 7 | 34 ± 6 | 36 ± 6 | 34 ± 6 | 32 ± 6 | 34 ± 6 | 30 ± 6 |
Vertical movement (mm) | 5.1 | 0.002 | 20.8 | <0.001 | 0.6 | 0.642 | 17.1 ± 0.5 | 17.5 ± 0.5a | 17.9 ± 0.5a | 17.2 ± 0.5ab | 16.3 ± 0.6b | 15.8 ± 0.3 | 16.4 ± 0.4a | 16.5 ± 0.4a | 16.3 ± 0.4ab | 15.6 ± 0.4b |
Anterior posterior movement (mm) | 1.2 | 0.323 | 6.7 | 0.010 | 0.1 | 0.969 | 7.1 ± 0.8 | 7.4 ± 0.7 | 7.6 ± 0.9 | 7.2 ± 0.7 | 6.9 ± 0.7 | 6.5 ± 0.8 | 6.5 ± 0.6 | 7.0 ± 0.8 | 6.9 ± 0.7 | 5.9 ± 0.5 |
Medial lateral movement (mm) | 1.5 | 0.222 | 1.5 | 0.230 | 1.0 | 0.392 | 7.9 ± 0.5 | 7.7 ± 0.4 | 8.2 ± 0.4 | 7.3 ± 0.4 | 7.4 ± 0.4 | 7.1 ± 0.3 | 7.3 ± 0.4 | 7.5 ± 0.4 | 7.5 ± 0.4 | 7.2 ± 0.4 |
Muscle activities | ||||||||||||||||
Total activity per sequence | 14.2 | <0.001 | 17.4 | <0.001 | 1.0 | 0.392 | 67 ± 5 | 47 ± 3b | 46 ± 3b | 51 ± 4a | 39 ± 3b | 48 ± 3 | 39 ± 2b | 41 ± 3b | 48 ± 3a | 38 ± 3b |
Total activity per chew | 1.0 | 0.374 | 157.8 | <0.001 | 1.6 | 0.193 | 3.0 ± 0.1 | 3.0 ± 0.1 | 3.0 ± 0.1 | 2.9 ± 0.1 | 2.8 ± 0.1 | 2.4 ± 0.1 | 2.5 ± 0.1 | 2.4 ± 0.1 | 2.4 ± 0.1 | 2.5 ± 0.1 |
Temporalis activity per sequence | 10.5 | <0.001 | 27.3 | <0.001 | 1.1 | 0.343 | 23 ± 2 | 16 ± 1b | 16 ± 1b | 18 ± 1a | 14 ± 1b | 16 ± 1 | 13 ± 1b | 13 ± 1b | 16 ± 1a | 13 ± 1b |
Temporalis activity per chew | 0.2 | 0.924 | 146.4 | <0.001 | 1.2 | 0.318 | 1.04 ± 0.04 | 1.03 ± 0.04 | 1.05 ± 0.03 | 1.03 ± 0.04 | 1.01 ± 0.04 | 0.80 ± 0.04 | 0.80 ± 0.05 | 0.76 ± 0.04 | 0.80 ± 0.04 | 0.84 ± 0.05 |
Temporalis activity per chew (working-side) | 0.2 | 0.918 | 124.4 | <0.001 | 1.4 | 0.234 | 0.52 ± 0.02 | 0.52 ± 0.02 | 0.53 ± 0.02 | 0.52 ± 0.02 | 0.51 ± 0.02 | 0.41 ± 0.02 | 0.41 ± 0.03 | 0.38 ± 0.02 | 0.40 ± 0.02 | 0.43 ± 0.02 |
Temporalis activity per chew (balancing-side) | 0.2 | 0.912 | 135.4 | <0.001 | 0.8 | 0.505 | 0.52 ± 0.02 | 0.51 ± 0.02 | 0.52 ± 0.02 | 0.51 ± 0.02 | 0.50 ± 0.02 | 0.39 ± 0.02 | 0.39 ± 0.03 | 0.38 ± 0.02 | 0.40 ± 0.02 | 0.41 ± 0.02 |
Masseter activity per sequence | 13.8 | <0.001 | 31.4 | <0.001 | 1.0 | 0.376 | 21 ± 1 | 16 ± 1b | 16 ± 1b | 18 ± 1a | 13 ± 1b | 15 ± 1 | 12 ± 1b | 13 ± 1b | 16 ± 1a | 12 ± 1b |
Masseter activity per chew | 1.4 | 0.252 | 165.6 | <0.001 | 2.0 | 0.116 | 1.00 ± 0.04 | 1.00 ± 0.04 | 1.02 ± 0.03 | 1.00 ± 0.04 | 0.94 ± 0.04 | 0.77 ± 0.03 | 0.78 ± 0.04 | 0.76 ± 0.04 | 0.78 ± 0.03 | 0.79 ± 0.04 |
Masseter activity per chew (working-side) | 1.0 | 0.379 | 132.3 | <0.001 | 1.6 | 0.202 | 0.49 ± 0.02 | 0.50 ± 0.02 | 0.50 ± 0.02 | 0.50 ± 0.02 | 0.46 ± 0.02 | 0.38 ± 0.02 | 0.39 ± 0.02 | 0.38 ± 0.02 | 0.38 ± 0.02 | 0.39 ± 0.02 |
Masseter activity per chew (balancing side) | 1.2 | 0.301 | 121.7 | <0.001 | 1.6 | 0.197 | 0.50 ± 0.02 | 0.50 ± 0.02 | 0.52 ± 0.02 | 0.50 ± 0.02 | 0.47 ± 0.02 | 0.39 ± 0.02 | 0.39 ± 0.02 | 0.38 ± 0.02 | 0.40 ± 0.02 | 0.40 ± 0.02 |
Digastric activity per sequence | 13.0 | <0.001 | 0.7 | 0.420 | 0.2 | 0.911 | 21 ± 1 | 14 ± 1bc | 15 ± 1b | 16 ± 1a | 13 ± 1c | 17 ± 1 | 14 ± 1bc | 15 ± 1b | 16 ± 1a | 13 ± 1c |
Digastric activity per chew | 3.4 | 0.019 | 37.0 | <0.001 | 0.5 | 0.685 | 0.96 ± 0.04 | 0.94 ± 0.04ab | 0.97 ± 0.04a | 0.92 ± 0.04ab | 0.90 ± 0.03b | 0.85 ± 0.03 | 0.87 ± 0.03ab | 0.84 ± 0.04a | 0.84 ± 0.03ab | 0.85 ± 0.03b |
Digastric activity per chew (working-side) | 3.2 | 0.025 | 31.2 | <0.001 | 0.8 | 0.489 | 0.49 ± 0.02 | 0.47 ± 0.02ab | 0.49 ± 0.02a | 0.45 ± 0.02ab | 0.45 ± 0.02b | 0.43 ± 0.02 | 0.43 ± 0.02ab | 0.42 ± 0.02a | 0.42 ± 0.02ab | 0.42 ± 0.02b |
Digastric activity per chew (balancing-side) | 2.6 | 0.056 | 22.7 | <0.001 | 0.4 | 0.752 | 0.47 ± 0.02 | 0.47 ± 0.02 | 0.48 ± 0.02 | 0.45 ± 0.02 | 0.45 ± 0.02 | 0.42 ± 0.02 | 0.44 ± 0.02 | 0.42 ± 0.02 | 0.42 ± 0.02 | 0.43 ± 0.02 |
(B) Bolus properties | ||||||||||||||||
Compositional bolus properties | ||||||||||||||||
Moisture content at swallowing (%wt) | 613.1 | <0.001 | 1819.7 | <0.001 | 10.6 | <0.001 | 59.8 ± 2.0 | 48.4 ± 1.1b | 67.1 ± 0.8a | 66.5 ± 0.6a | 67.3 ± 0.5a | 83.0 ± 0.6 | 65.7 ± 0.4b | 79.8 ± 0.4a | 80.1 ± 0.5a | 80.2 ± 0.4a |
Saliva content at swallowing (g per g dry product) | 7.6 | <0.001 | 80.0 | <0.001 | 3.3 | 0.024 | 0.86 ± 0.10 | 0.57 ± 0.04a | 0.72 ± 0.08a | 0.51 ± 0.05a | 0.58 ± 0.05a | 1.51 ± 0.18 | 0.73 ± 0.04b | 1.17 ± 0.11a | 1.02 ± 0.12ab | 1.03 ± 0.10a |
Fat content at swallowing (g per g dry product) | 1268.9 | <0.001 | 48.5 | <0.001 | 4.1 | 0.009 | — | 54 ± 1a | 25 ± 1b | 19 ± 1c | 28 ± 1b | 60 ± 1a | 27 ± 1b | 23 ± 1c | 29 ± 1b | |
Mechanical bolus properties | ||||||||||||||||
Peak force at swallowing (N) | 10.0 | <0.001 | 14.7 | <0.001 | 2.3 | 0.079 | 0.27 ± 0.02 | 0.10 ± 0.01b | 0.08 ± 0.01b | 0.15 ± 0.01a | 0.09 ± 0.01ab | 0.13 ± 0.01 | 0.06 ± 0.01b | 0.06 ± 0.01b | 0.10 ± 0.01a | 0.09 ± 0.02ab |
Adhesiveness at swallowing (N s) | 65.2 | <0.001 | 117.7 | <0.001 | 1.2 | 0.312 | 0.029 ± 0.002 | 0.016 ± 0.001b | 0.013 ± 0.001c | 0.024 ± 0.002a | 0.013 ± 0.001bc | 0.009 ± 0.001 | 0.008 ± 0.001b | 0.003 ± 0.000c | 0.017 ± 0.001a | 0.006 ± 0.001bc |
Cohesiveness at swallowing | 19.8 | <0.001 | 148.0 | <0.001 | 11.9 | <0.001 | 0.52 ± 0.01 | 0.55 ± 0.01a | 0.54 ± 0.01a | 0.56 ± 0.02a | 0.51 ± 0.01a | 0.29 ± 0.01 | 0.41 ± 0.02b | 0.28 ± 0.02c | 0.52 ± 0.02a | 0.38 ± 0.02b |
Tribological bolus properties | ||||||||||||||||
Friction coefficient at swalllowing (8 mm s−1) | 10.9 | <0.001 | 469.3 | <0.001 | 12.2 | <0.001 | 1.21 ± 0.06 | 1.04 ± 0.05a | 0.92 ± 0.05b | 0.90 ± 0.02b | 0.86 ± 0.04b | 0.70 ± 0.03 | 0.52 ± 0.02b | 0.45 ± 0.01b | 0.67 ± 0.02a | 0.48 ± 0.01b |
(C) Sensory characteristics | ||||||||||||||||
Odour attribute | ||||||||||||||||
Overall intensity | 0.3 | 0.842 | 2.5 | 0.116 | 0.6 | 0.634 | 8.6 ± 0.4 | 8.2 ± 0.4 | 8.6 ± 0.3 | 8.2 ± 0.4 | 8.4 ± 0.4 | 10.1 ± 0.3 | 8.5 ± 0.2 | 8.5 ± 0.3 | 8.8 ± 0.3 | 8.5 ± 0.3 |
Taste attribute | ||||||||||||||||
Overall intensity | 11.1 | <0.001 | 0.7 | 1.000 | 2.6 | 0.051 | 6.8 ± 0.4 | 10.6 ± 0.4a | 10.1 ± 0.4a | 8.5 ± 0.4b | 9.7 ± 0.4a | 6.9 ± 0.4 | 8.3 ± 0.3a | 8.5 ± 0.3a | 7.6 ± 0.3b | 8.1 ± 0.4a |
Mouthfeel attributes | ||||||||||||||||
Dry | 2.6 | 0.051 | 2.4 | 1.000 | 0.1 | 0.931 | 6.8 ± 0.6 | 3.5 ± 0.2 | 3.7 ± 0.3 | 3.9 ± 0.3 | 3.0 ± 0.2 | 7.7 ± 0.3 | 5.1 ± 0.4 | 5.0 ± 0.4 | 5.4 ± 0.3 | 4.7 ± 0.4 |
Firm | 4.1 | 0.008 | 0.7 | 0.398 | 2.7 | 0.051 | 5.6 ± 0.5 | 4.6 ± 0.3ab | 4.8 ± 0.2a | 4.5 ± 0.3a | 3.5 ± 0.3b | 6.9 ± 0.4 | 5.9 ± 0.4ab | 6.4 ± 0.4a | 6.5 ± 0.3a | 6.1 ± 0.4b |
Sticky | 28.4 | <0.001 | 0.5 | 0.461 | 0.7 | 0.525 | 1.6 ± 0.4 | 3.7 ± 0.3b | 4.3 ± 0.3b | 5.0 ± 0.3a | 2.4 ± 0.3c | 1.9 ± 0.4 | 3.5 ± 0.4b | 3.6 ± 0.4b | 5.0 ± 0.3a | 2.4 ± 0.2c |
Gummy | 35.8 | <0.001 | 2.0 | 0.155 | 1.0 | 0.414 | 0.0 ± 0.0 | 0.6 ± 0.3b | 0.4 ± 0.3b | 4.2 ± 0.6a | 0.0 ± 0.0b | 1.4 ± 0.7 | 1.8 ± 0.6b | 1.9 ± 0.6b | 5.0 ± 0.5a | 2.1 ± 0.7b |
Creamy | 20.9 | <0.001 | 1.4 | 0.245 | 0.0 | 0.986 | — | 4.5 ± 0.4a | 3.9 ± 0.4ab | 3.5 ± 0.4b | 2.3 ± 0.2c | 3.9 ± 0.5a | 3.3 ± 0.4ab | 2.7 ± 0.4b | 1.6 ± 0.3c | |
Fatty | 46.0 | <0.001 | 0.6 | 1.000 | 0.2 | 0.923 | — | 5.6 ± 0.3a | 4.9 ± 0.3b | 4.3 ± 0.3c | 3.3 ± 0.3d | 5.7 ± 0.3a | 5.1 ± 0.4b | 4.7 ± 0.4c | 3.5 ± 0.4d | |
Velvet | 6.0 | <0.001 | 2.2 | 1.000 | 0.7 | 0.537 | — | 4.3 ± 0.5a | 4.0 ± 0.4a | 4.1 ± 0.4ab | 3.2 ± 0.3b | 4.3 ± 0.5a | 3.5 ± 0.4a | 3.2 ± 0.4ab | 2.8 ± 0.3b | |
Smooth | 0.4 | 0.776 | 1.2 | 0.281 | 0.3 | 0.833 | 0.7 ± 0.3 | 2.2 ± 0.5 | 2.4 ± 0.5 | 2.1 ± 0.5 | 2.1 ± 0.4 | 0.1 ± 0.1 | 1.3 ± 0.5 | 1.0 ± 0.4 | 0.8 ± 0.3 | 1.1 ± 0.3 |
Salivating | 5.4 | 0.001 | 2.1 | 1.000 | 0.5 | 0.651 | 1.5 ± 0.3 | 5.5 ± 0.3a | 5.6 ± 0.3a | 4.7 ± 0.3b | 5.4 ± 0.2a | 3.1 ± 0.4 | 4.6 ± 0.3a | 4.4 ± 0.3a | 4.0 ± 0.3b | 4.5 ± 0.4a |
Absorbing | 26.3 | <0.001 | 3.2 | 1.000 | 8.9 | <0.001 | — | 6.1 ± 0.4ab | 5.0 ± 0.4b | 2.9 ± 0.4c | 7.3 ± 0.5a | 4.5 ± 0.5a | 4.1 ± 0.4ab | 2.8 ± 0.5b | 3.9 ± 0.5ab | |
Chewing effort | 0.7 | 0.540 | 0.4 | 0.514 | 2.8 | 0.044 | 4.0 ± 0.4 | 4.0 ± 0.3a | 4.0 ± 0.2a | 4.3 ± 0.4a | 3.4 ± 0.3a | 5.6 ± 0.4 | 5.1 ± 0.4a | 5.4 ± 0.4a | 5.1 ± 0.4a | 5.4 ± 0.4a |
Homogeneous | 7.6 | <0.001 | 0.0 | 0.886 | 3.8 | 0.012 | 1.6 ± 0.6 | 5.5 ± 0.5a | 4.0 ± 0.5ab | 2.9 ± 0.5b | 5.3 ± 0.4a | 0.9 ± 0.3 | 4.8 ± 0.5a | 4.4 ± 0.4a | 4.0 ± 0.6a | 4.1 ± 0.4a |
Bread fibersa | 1.8 | 0.151 | — | — | — | — | 10.6 ± 0.7 | 8.9 ± 0.4 | 8.2 ± 0.4 | 8.5 ± 0.3 | 8.2 ± 0.4 | — | — | — | — | — |
Potato particlesa | 1.7 | 0.169 | — | — | — | — | — | — | — | — | — | 11.4 ± 0.4 | 9.2 ± 0.4 | 8.8 ± 0.4 | 8.8 ± 0.4 | 9.3 ± 0.4 |
Afterfeel attributes | ||||||||||||||||
Residue | 3.6 | 0.015 | 0.3 | 1.000 | 0.7 | 0.564 | 5.7 ± 0.5 | 5.3 ± 0.4a | 5.0 ± 0.5ab | 5.5 ± 0.5a | 4.7 ± 0.5b | 6.4 ± 0.6 | 5.8 ± 0.5a | 5.4 ± 0.5ab | 5.4 ± 0.5a | 4.8 ± 0.4b |
Fatty film layer | 24.6 | <0.001 | 0.1 | 1.000 | 0.7 | 0.556 | 0.4 ± 0.2 | 5.5 ± 0.3a | 4.6 ± 0.3b | 6.2 ± 0.4a | 4.1 ± 0.3b | 0.4 ± 0.2 | 5.4 ± 0.3a | 4.6 ± 0.4b | 5.6 ± 0.3a | 3.8 ± 0.4b |
Dry rough | 0.3 | 0.797 | 0.3 | 1.000 | 0.4 | 0.741 | 6.2 ± 0.5 | 5.5 ± 0.3 | 5.5 ± 0.3 | 5.5 ± 0.4 | 5.5 ± 0.4 | 6.5 ± 0.3 | 5.5 ± 0.4 | 5.8 ± 0.5 | 6.0 ± 0.3 | 5.5 ± 0.4 |
Cleaning | 5.1 | 0.002 | 0.0 | 1.000 | 0.5 | 0.668 | 4.9 ± 0.4 | 4.6 ± 0.4b | 5.0 ± 0.4ab | 5.5 ± 0.5a | 4.5 ± 0.4b | 5.4 ± 0.5 | 4.9 ± 0.4b | 5.0 ± 0.4ab | 5.5 ± 0.4a | 5.0 ± 0.4b |
To gain further insights into bolus formation during oral processing and the accompanying sensory perception, a full fat mayonnaise with high viscosity (FF-HV), a low-fat mayonnaise with low viscosity (LF-LV), and two low-fat/high viscosity mayonnaises (LF-HV) were assessed. For the LF-HV mayonnaises, a thickening agent was added to compensate for the decrease in viscosity with reduction in fat content. Two different thickeners were investigated, starch (which is frequently used in the preparation of low-fat mayonnaises; LF-HV-starch) and xanthan (LF-HV-xanthan). These thickeners were chosen based on their sensitivity of amylase present in saliva. Starch is broken down by α-amylase, which was expected to decrease the viscosity throughout mastication. As a comparison, we also used xanthan, which is not broken down by α-amylase, and therefore the viscosity was expected to remain the same through consumption. Although the rheological properties of the two mayonnaises were similar (Table 1), perception of the two mayonnaises was quite different according to the trained sensory panel. The structure of LF-HV-xanthan mayonnaise was perceived as gummy (gummy mouthfeel was 7.5 ± 0.7 for LF-HV-xanthan compared to 0.2 ± 0.1, 0.5 ± 0.3 and 0.0 ± 0.0 for FF-HV, LF-HV-starch and LF-LV, respectively). Gummy perception dominated the eating experience and this was strongly disliked by the subjects, as free comments of both the consumer and trained panel indicated. In contrast to xanthan, starch is used commonly as a thickening agent in commercially available low-fat mayonnaises. As a consequence, the following section focuses on comparisons between HF-HV, LF-LV and LF-HV-starch rather than with LF-HV-xanthan.
Fig. 1 Number of chews required until swallowing and eating rate (g min−1) for bread (A, C) and cooked potato (B, D) without and with different mayonnaises, determined using electromyography. Dashed lines represent the averaged value of single carriers. Error bars represent standard error of the mean. Different lower case letters indicate significant differences between means (p < 0.05). The abbreviations are explained in Table 1. |
Fig. 2 Bolus mechanical properties (peak force, cohesiveness) throughout mastication for bread (A, C) and cooked potato (B, D) without and with different mayonnaises. Peak force refers to bolus firmness, cohesiveness refers to the degree to which food sticks together. Error bars represent standard error of the mean. The abbreviations are explained in Table 1. Lines are added to guide the eye. |
The effect of condiment addition on oral processing behavior depended on the type of carrier food. On average, the addition of mayonnaises decreased the number of chews from 23 ± 2 to 16 ± 2 for bread (−30%) and from 20 ± 1 to 17 ± 1 for potato (−15%), showing that condiments facilitated mastication of bread to a larger extent than that of cooked potato (both absolutely and by percentage). Hence, condiments may aid bolus formation of dry carrier foods more than carriers with a high moisture content (moisture content: 44 ± 3 wt% for bread and 88 ± 1 wt% for potato). In the case of low water content carriers, water might be absorbed faster and thus mixed more easily with the carrier, whereas in high moisture content carriers water might be absorbed slower and mixing might occur mostly due to mechanical forces. In view of these findings, it should be noted that mayonnaise was mixed with bread in a 1:1 weight ratio, whereas potato was mixed with mayonnaise in a 2:1 weight ratio. Thus, a relatively higher amount of mayonnaise was present in bread–mayonnaise combinations than in the potato–mayonnaise combinations. This may also contribute to the larger effect for bread. We can therefore not draw firm conclusions on the effect of absorption or speed of mixing on oral processing behavior. The reason why different ratios were chosen was that these weight ratios are naturally applied by consumers when preparing these composite foods and hence provide a more realistic context for consumer consumption.12,13 The larger amount of condiment may therefore also be responsible for the faster moistening. Thus, when considering naturally applied condiment:carrier weight ratios, condiments may assist bolus formation of relatively dry foods such as bread more than carrier foods with a high moisture content such as cooked potatoes due to two reasons: (1) faster moisture absorption and/or (2) the presence of more moisture due to more condiment.
When comparing mayonnaises differing in viscosity (LF-HV-starch versus LF-LV), composite foods with low viscosity mayonnaise were swallowed after slightly shorter chewing time than those with high viscosity mayonnaise (10 ± 1 s compared to 9 ± 1 s for bread and 11 ± 1 s compared to 10 ± 1 s for potato, p = 0.033). This is likely due to the faster migration of low viscosity mayonnaise into and throughout the bread bolus compared to the migration of the high viscosity mayonnaise, leading to faster moistening of the bolus. In the case of potato, the shorter chewing time is not explained by faster moisture migration, as moisture content of potato is already high. The difference in chewing time is likely more related to the fact that mayonnaise is used to adhere the different potato pieces together in a bolus. This mixing step is easier for low viscosity mayonnaise then for a high viscosity one. Although these differences in chewing time seem relatively small (approximately 1 second per bite), we have to consider that carrier–condiment combinations are not eaten as a single bite but as part of a meal. Consequently, over the consumption of multiple bites, adding condiments with a lower viscosity results in a higher eating rate (from 46 ± 3 to 55 ± 4 g min−1 for bread and from 61 ± 3 to 70 ± 4 g min−1 for potato; Fig. 1) compared to that of condiments with high viscosity. Addition of low viscosity condiments might therefore lead to higher food intake.
Fig. 3 Bolus friction coefficient at the moment of swallowing as a function of speed for bread (A) and cooked potato (B) without and with different mayonnaises. Error bars represent standard error of the mean. The abbreviations are explained in Table 1. Lines are added to guide the eye. |
Fig. 4 Bolus saliva content at the moment of swallowing for bread (A) and cooked potato (B) without and with different mayonnaises. Error bars represent standard error of the mean. The abbreviations are explained in Table 1. Lines are added to guide the eye. |
The previous results on chewing behavior (Fig. 1, section 3.1.3) indicate that mayonnaise viscosity seems to be more important in bolus formation than fat content. When comparing mayonnaises differing in viscosity (i.e. LF-HV-starch versus LF-LV), some changes in bolus properties throughout mastication were found. For bread, bolus peak force was lower for low viscosity mayonnaise than high viscosity mayonnaise (Fig. 2A) at 33% of total mastication time. Low viscosity mayonnaise is able to penetrate into the bread bolus faster than high viscosity mayonnaise, as low viscosity liquids have a higher migration rate and are more prone to capillary action by the small pores in the bread structure.36 This leads to faster penetration, reducing the coefficient of friction (Fig. 3A) and time to form a safe-to-swallow bolus. This was evidently perceivable by the trained sensory panel, as bread carriers with low viscosity mayonnaises were rated significantly less firm (3.5 ± 0.3 compared to 4.8 ± 0.2) and more absorbing (7.3 ± 0.5 compared to 5.0 ± 0.4) than those with high viscosity mayonnaise. For potatoes, bolus cohesiveness increased to a larger extent at an earlier stage of consumption for the low viscosity mayonnaise compared to high viscosity mayonnaise (Fig. 2D). This indicates again that low viscosity mayonnaise mixed more easily with the potato pieces to form a cohesive and safe-to-swallow bolus after less time. Thus, viscosity is likely the driving force of fast adherence of particles and bolus formation. As no differences between firmness were observed (Fig. 2B), swallowing of potato–condiment combinations may be more related to cohesiveness than bolus firmness. This is in line with our assumption that mayonnaise helps bolus particles to adhere together.
Regarding sensory perception, as assessed by a trained sensory panel, it is important to mention that sensory evaluations were largely impacted by mayonnaise viscosity (Table 3C). Sensory perception therefore seems to be dominated by viscosity more than fat content. For bread, 7 out of 20 attributes were significantly different for LF-HV-starch and LF-LV mayonnaise while 5 out of 20 attributes were significantly different for potatoes. In particular, carrier–mayonnaise combinations were perceived as significantly less creamy, fatty and velvety when low viscosity mayonnaise was added. These are desired mouthfeel attributes that contribute to food appreciation.37,38 Thus, in case of mayonnaise, decreasing viscosity probably leads to a lower food liking.
To better understand how condiments affect oral processing behavior and smoothness perception of composite foods, we also sought to gain information on the lubrication ability of the ingredients present in the food boli (i.e. the role of fat content and viscosity). Although condiment properties tend to impact lubrication behavior of bread–mayonnaise combinations (Fig. 3A), this effect is not clearly observed in potato–mayonnaise combinations (Fig. 3B). It is not yet clear how fat and moisture are distributed throughout the bolus and how that may influence lubrication. In addition, for similar moisture content, particle sizes of boli fragments has been shown to influence lubrication.31 We hypothesize that dry foods, such as bread, soften via moisture uptake by which lubrication is more effectively facilitated than by adding fat. In the case of potato, either water or fat is used to keep the particles together without a softening effect. Therefore, we observed a reduced effect of condiment properties on lubrication for potato.
To visualize the relation of the different aspects on oral processing behavior, we have summarized the results in MFA individuals map (Fig. 5). The fat content of condiments did not have a large impact on oral processing behavior, bolus properties or sensory characteristics of carrier–condiment combinations as the FF-HV and LF-HV-starch are positioned close to each other. Changing the viscosity of condiments, on the other hand, had a larger effect on both the oral processing behavior and sensory perception of the carrier–condiment combinations as LF-HV-starch and LF-LV mayonnaises are positioned further apart. Carriers with low viscosity mayonnaise were processed using fewer chews for a shorter time, resulting in faster bread softening and faster potato adherence. Additionally, when assessed by a trained sensory panel, they were perceived as less creamy, fatty and velvety than the high viscosity mayonnaise combinations.
Fig. 5 Multiple Factor Analysis (MFA) on the four different datasets (video recordings, EMG and jaw tracking, bolus properties at the moment of swallowing, and sensory characteristics) for bread with different mayonnaises (A) and cooked potato with different mayonnaises (B). Only those parameters with a significant mayonnaise effect during mixed models were considered (37 parameters; see Table 3). The individuals map (samples) is shown on the left, and the variables map (parameters) is shown on the right. Different colors indicate different datasets, and only the 20 variables with the highest contribution are displayed in words. The abbreviations are explained in Table 1. |
Modest nuances in energy intake of composite foods could be achieved by changing specific condiment properties. Fat content is inherently related a high energy density of foods, and full fat condiments increase both fat and calorie intake, which is usually undesirable. The present study highlights that changing the fat content of condiments did not affect chewing behavior and only modestly affected sensory perception of composite foods. This implies that replacing full-fat condiments with low-fat options with a comparable viscosity could be a promising strategy to reduce fat and, ultimately, energy intake among the general population in a relatively unconscious way. In addition to changing the fat content, also the viscosity can be used to change food intake. Changing the viscosity of condiments influences eating rate and is also likely to affect food appreciation. Low viscosity condiments can increase eating rate, while high viscosity condiments reduce eating rate. Modification of eating rate is emerging as a key parameter to impact energy intake in unrestrained consumers.47 Therefore, such changes may be used to target energy intake behavior of different consumer groups. For example, increasing viscosity with less fat could be used to decrease total food and energy intake by increasing eating rate. Similarly, adding low viscosity condiments to foods may increase food intake, which can be used to increase uptake of vegetables by children or increase total food intake by the elderly.
We must note that these results have been obtained for bread and potato only, and should be confirmed for other categories of carrier foods. However, as we see the same effects in two different food categories (dry foods and foods with higher moisture content), we speculate that these effects can be generalized to a large variety of foods. It would be interesting to see how condiments influence oral processing behavior, bolus formation and sensory properties of foods that are more sticky or more brittle. In addition, the effects should also be further confirmed by a consumer panel to confirm generalizability towards the general consumer population.
We conclude that oral processing behavior of carrier–condiment combinations is mainly affected by the presence of condiments and, to a smaller extent, the specific properties of the condiment. When comparing the influence of different condiment properties (fat content, viscosity), only small effects on chewing behavior were observed. For bolus formation, larger effects of condiment properties were seen. Viscosity played an important role in bolus formation for two different reasons: (1) water absorption of dry foods softens the bolus, and (2) moisture assists in adhering separate particles into a bolus. Both mayonnaise fat content and viscosity influenced sensory perception of composite foods considerably.
This is the first study that shows the potential of systematically modifying single food properties to influence oral processing behavior and sensory perception of composite foods. These results suggest that tailoring carrier–condiment combinations might largely alter food intake, which could be an effective strategy for modulating food intake in different consumer groups. Further studies with consumers are required to investigate whether such single food modifications affect food intake sustainably throughout an entire meal and after multiple exposures.
The project is funded by TiFN, a public–private partnership on precompetitive research in food and nutrition. The public partners are responsible for the study design, data collection and analysis, decision to publish, and preparation of the manuscript. The private partners have contributed to the project through regular discussion. The private partners are Royal Friesland Campina, Fromageries Bel and Unilever. This research was performed with additional funding from the Top Consortia for Knowledge and Innovation of the Dutch Ministry of Economic Affairs.
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