Page 51 - FoodFocusThailand No.163 October 2019

STAND OUT TECH
STAND OUT TECHNOLOGYNOLOGY
Kartik S. Pondicherry, Ph.D.
Principal Scientist for Tribology
Anton Paar GmbH
kartik.pondicherry@anton-paar.com
Translated By: ภาสกร วุนวิริยะกิจ Mouthfeel
Passakorn Woonwiriyakit
Anton Paar (Thailand) Ltd.
Through Tribology
passakorn.woonwiriyakit@anton-paar.com

Human perception of food and beverages is quite complex and comprises of multiple sensory
stimuli, including visual, olfactory, and the taste buds. As food and beverages pass through
our oral cavity, we experience different physical sensations such as creaminess, thickness,
softness, etc.

These attributes contribute towards the mouthfeel of food or beverages and they are determined by experienced
human sensory panels, which are both time and cost intensive. While some of these attributes can be correlated with
the mechanical and rheological properties of the food samples, others are a bit more complicated to describe. In this
context, tribology – the study of friction, lubrication, and wear – has been applied to understand what happens at the
interface between the tongue and the palate, with the food bolus in between.

รูปที่ 1 การทดสอบโดยการตั้งลูกบอล 1 ลูก บนพิน 3 จุด และเติมอาหารหรือเครื่องดื่มปริมาณ
1.5-2 มิลลิลิตร ในตัวอย่างระหว่างการทดสอบ
Fig. 1 Ball-on-three-pins test setup. During the test, around 1.5 to 2 ml of the food/beverage
sample is filled into the sample holder.
Tribological Testing
In order to mimic the oral cavity, a glass ball and a polydimethylsilosane
(PDMS) surface were considered as surrogates for the palate and the tongue
respectively. Milk with different fat content, and coffee in form of espresso
and filter coffee were used as test samples. During the test, these beverages
act as a lubricant as the glass ball slides against the PDMS surface. The
tests were carried out on an MCR Tribometer with a ball-on-three-pins test configuration.
A schematic of the test configuration is presented in Fig. 1. During the test, a set normal force of 1 N was applied
at the contact. The ball was then slowly accelerated from sliding velocities as low as a nanometer per second to around
200 mm/s or 1 m/s. The frictional resistance of the glass/food/PDMS system is plotted as a function of sliding velocity
and these curves are known as extended Stribeck curves. The aim here is to create a model by correlating frictional
data with the data from the sensory panel. Such models could be used for predicting sensory attributes of food and
beverage samples based on their tribological behavior.
In the case of tests with milk samples, shown in Fig. 2, increasing fat content leads to a decrease in the frictional
resistance of the system, especially in the low to medium-speed regime. While fat acts as a lubricant in the case of milk
samples, the higher content of oil droplets in an espresso, as compared to a filter coffee, contributes towards reduction
in friction, as seen in Fig. 3.

รูปที่ 2 กราฟแสดงภาพรวมการเปลี่ยนแปลงของแรงเสียดทานในตลอดช่วง รูปที่ 3 กราฟแสดงภาพรวมการเปลี่ยนแปลงของแรงเสียดทานใน
ของการหล่อลื่น ผลจากตัวอย่างนมที่มีปริมาณไขมันแตกต่างกัน ตลอดช่วงของการหล่อลื่น ผลจากกาแฟเอสเปรสโซและกาแฟดริป
Fig. 2 Extended Stribeck curves of three milk samples with Fig. 3 Extended Stribeck curves of filter coffee and espresso.
different fat content.
While these are some simple examples, studies have also been carried out on complex samples, such as cheese
spread, aerated soft drinks, etc., wherein advanced statistical tools are being used to build a model to predict mouthfeel
behavior from the tribological data.
The author would like to clarify that is not an attempt at replacing human sensory panel, but just a tool to prescreen
samples that are taken to the sensory panel, making the process more time and cost effective.

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