Whey protein addition to accelerate yoghurt fermentation and facilitate yoghurt structure

Vietnam Journal of Science and Technology 57 (3B) (2019) 69-74 
doi:10.15625/2525-2518/57/3B/14346 
 WHEY PROTEIN ADDITION TO ACCELERATE YOGHURT 
FERMENTATION AND FACILITATE YOGHURT STRUCTURE 
Vu Thu Trang
1, *
, Nguyen Chinh Nghia
1
, Lai The Hung
2
, Do Van Duong
1, 3
1
School of Biotechnology and Food Technology, Hanoi University of Science and Technology, 
1 Dai Co Viet, Ha Noi 
2
Develing International Vietnam, 28 Phung Khac Khoan, Da Kao, Ho Chi Minh City 
3
Moc Chau Milk Co., 29 Cat Linh, Ha Noi 
*
Email: trang.vuthu@hust.edu.vn 
Received: 22 August 2019; Accepted for publication: 1 November 2019 
Abstract. Whey proteins were present in appropriate proportion in milk, during heat-treatment 
at pasteurization temperatures; whey proteins and casein have the ability to form firm gel of 
uniform porosity through heat-induced protein-protein interactions. In this study, the addition of 
whey proteins in fresh milk were carry out to investigate whether whey protein would accelerate 
yoghurt fermentation time and facilitate the yoghurt structure. The results indicated that the 
addition of whey concentrate 80 increased the water retention capacity of the final product. 
Whey protein concentrate 80 supplement at the content of 0.8 % shortened fermentation time for 
the product 12.5 %. The addition of whey protein also improved the properties of water retention 
until 26 %, viscosity and structure of yoghurt products. 
Keywords: whey protein, yoghurt, fermentation, structural analysis. 
Classification numbers: 1.4.3, 1.4.4. 
1. INTRODUCTION 
Yoghurt is a very popular fermented milk product produced by lactic acid fermentation of 
milk by addition of starter culture containing Streptococcus salivarius sp. thermophilus and 
Lactobacillus delbrueckii subsp. bulgaricus [1]. The yoghurt making process is an ancient craft 
since thousands of years. Nowadays, yoghurt is a popular fermented milk product widely 
accepted and consumed worldwide. The main contributor was the ability of lactic acid bacteria 
to grow in milk and to produce lactic acid to reduce the pH of milk to the iso-electric point of the 
caseins, at which these proteins coagulate. In contrast to caseins, whey proteins possess high 
levels of secondary, tertiary and, quaternary structures. On heating to 90-95 
o
C, the denatured 
whey proteins, especially -lactoglobulin could interact with each other and with casein micelles, 
that increase the yoghurt structure [2]. Various milk components (e.g. non-fat dry milk, milk 
protein concentrate and whey protein concentrate) and/or stabilizers (e.g. pectin, gelatin and 
starch) were applied in yoghurt products to ensure appropriate texture through increasing the 
content of milk total solids [3]. 
Vu Thu Trang, Nguyen Chinh Nghia, Lai The Hung, Do Van Duong 
70 
Although final biomass and activity of yoghurt starter cultures are important, short 
fermentation times are industrially advantageous [4]. Acceleration of the yoghurt fermentation 
process by supplementation of nutrients for yoghurt cultures should result in a greater amount of 
product being produced in the same time span, while requiring no additional infrastructure. 
Bacterial growth in milk could be improved by the addition of substances of undefined 
composition to the growth medium, such as whey protein - a reliable source of peptides and 
amino compounds. 
Because -lactoglobulin is one of the major proteins responsible for the gel-forming 
characteristics of whey protein [5], it is of interest whether the addition of whey protein would 
accelerate the yoghurt fermentation process and the texture of final products. Therefore, the aim 
of this study was to investigate the effect of whey protein addition to the fermentation process 
and yoghurt structure. 
2. MATERIALS AND METHODS 
2.1. Materials 
Pasteurized milk was obtained from Moc Chau milk company. The starter FD-DVS YF-
L812 Yo Flex® (Chr – Hansen, Canada) consisting of Streptococcus thermophillus and 
Lactobacillus delbrueckii subsp. bulgaricus was used for all experiments. Whey protein 
concentrate (WPC 80) was provided from Develing International, Vietnam (Hochiminh City, 
Vietnam). Stabilizer Palsgaard® AcidMilk 305 (USA) was used to enhance yoghurt texture if 
needed. A final starter culture inoculum load of 0.104 g/l milk (10
6 
cfu/ml) was applied 
following provider’s recommendation. All other reagents were of the highest commercial grade 
available. 
2.2. Methods 
2.2.1. Yoghurt manufacture 
Yoghurt was prepared as described by Tetra Pak, 2004, similar to the Moc Chau milk Co 
processing. Yoghurt base mix was made by fresh pasteurized milk containing 12 % of milk 
solids content and 4 % of sucrose. WPC80 was added to the mixture with different 
concentrations (0.6 %, 0.8 % and 1 %). No WPC was added to control sample. After heating at 
95 
o
C for 5 min, the mixes were cooled in a water bath to the inoculation temperature of 45 °C. 
The starter FD-DVS YF-L812 Yo Flex® was added at a concentration recommended by the 
manufacturer. The inoculated milks were poured into 200-g plastic cups with lids and incubated 
at 45 °C. The incubation was finished when samples reached the pH of 4.6. During the 
fermentation, acidity and pH of samples were identified. After incubation, yoghurts were 
immediately cooled in an ice water bath and stored at 5 °C. The percentage increase or decrease 
in fermentation times by the addition of whey protein reported in this study refers to the 
difference in times to reach pH 4.6 in comparison with the control. All fermentation batches 
were carried out in three replicates. 
2.2.2. Yoghurt product analysis 
Determination of Titratable Acidity using Thorner (ºT) as described in TCVN 6509:1999 
Whey protein addition to accelerate yoghurt fermentation and facilitate the yoghurt structure 
71 
Yoghurt viscosity was measured using Brookfield DV2T Viscometer [6]. The spindle 
speed was adjusted according to the thickness of yoghurt sample. In this case, the specification 
combination used was at 20 rpm using the spindle Spindle LV- 64. The readings were taken at 
10 ºC, the temperature at which the yoghurt is consumed. Three readings from every sample 
were taken and an average was reported. 
The water-holding capacity of yoghurt was determined according to Wacher-Rodarte et al., 
[7]. A sample of about 20 g of yoghurt (Y) was centrifuged at 1250 × g for 10 min at 4 °C. The 
whey expelled (W) was removed and weighed. The water holding capacity (WHC, g.kg
−1
) was 
calculated as: 
(WHC) = 
×100 (%). 
A textural parameter – yoghurt hardness- was determined using Texture Profile Analysis 
(TPA) Instron TA.TX2 with mechanical compression of a food. The peak force during the first 
compression cycle is defined as hardness or firmness. Samples of yoghurt with a height of 50 
mm contained in a 70-mm diameter plastic jar were prepared for the measurement. The circular 
probe (diameter of 20 mm) was used with penetration speed of 1 mm/s; penetration distance of 
20 mm into surface. The puncture gap between the probe and sample was fixed to 20 mm [6]. 
2.2.3. Sensory Evaluation 
Twenty semi-trained panelists regularly yoghurt consumers (60% female; 20-22 years old) 
were selected on the basis of their willingness to participate and previous experience and 
knowledge on sensory evaluation of dairy and dairy-associated products. They were instructed 
on the sensory evaluation procedure by students of School of Biotechnology and Food 
Technology, Hanoi University of Science and Technology, Vietnam. Yoghurt samples were 
served in 40-mL plastic cups and fitted with lids at room temperature (20 ± 1 °C). All samples 
were marked with 3-digit codes, and the order of presentation of samples was randomized for 
each panelist. Descriptive sensory analysis was conducted on yoghurts using the Spectrum 
procedure described by Meilgaard et al. [8]. The panelists rated the total evaluation, whiteness, 
water holding capacity (WHC), yoghurt flavor, smoothly, texture, sweetness, sourness, firmness, 
sour aftertaste using a point hedonic scale (1 point for “dislike extremely” and 7 points for “like 
extremely”) [9]. The results of evaluation were written down by all panelists for every sample. 
Consumers were also asked to rank samples according to their acceptance. 
3. RESULTS AND DISCUSSION 
3.1. The effect of WPC80 addition on the yoghurt fermentation process 
Normally, yoghurt fermentation proceeds until 20 - 30 % of the lactose in the milk 
converted to lactic acid and a pH value below 4.6 is reached, which indicates appropriate levels 
of acidity not less than 0.9 % and the milk is coagulated. In purpose to reduce the fermentation 
time by the addition of WPC, the concentration of WPC from 0.6 – 1 % was added into the milk 
base and the acidification process during yoghurt fermentation can be monitored by pH 
measurement and coagulation time. According to the milk protein properties, the fermentation 
process finishes at pH value of 4.6 or 64 - 65 
o
T in acidity level and the milk is coagulated [10]. 
The effects of different WPC concentrations on yoghurt fermentation were showed in Figure 1. 
The results indicated that the addition WPC decreased the fermentation time in comparison with 
Vu Thu Trang, Nguyen Chinh Nghia, Lai The Hung, Do Van Duong 
72 
the control sample. Among them, the sample containing 0.8 % of WPC was the fastest sample 
reached the coagulation stage, that reduced 40 min of fermentation time (15 %). Previously, 
WPC was known to mainly contain of dissolved and easy to digest protein. Thus, the 
acceleration of yoghurt fermentation process by supplementation of WPC for lactic acid bacteria 
might be the reason for the reduction of fermentation time to reach a pH of 4.6. 
Figure 1. The effect of WPC80 addition on the yoghurt fermentation process. 
(◆: Control sample; ■: Addition of 1 % WPC80; ●: Addition of 0.8 % WPC80; 
▲: Addition of 0.6 % WPC80) 
However, higher concentration of added WPC prolonged the fermentation time. This result 
might be due to the interaction linking of whey protein with casein after heating, that obstructed 
the bacterial dispreads in the milk sample. Hence, the higher concentration of WPC80, the lower 
dispersion capacity of bacteria in milk sample. On the basic of the study, the addition of WPC 
0.8 % could be the most suitable concentration to reduce the fermentation time of yoghurt 
processing. 
3.2. Effect of WPC80 addition to yoghurt viscosity, water-holding capacity and yoghurt texture 
Figure 2. The effect of WPC80 addition on the yoghurt quality. 
KC: Control sample; BS WPC 80 (0.6 %): Addition of 0.6 % WPC80; BS WPC 80 (0.8 %): Addition of 
0.8 % WPC80; BS WPC 80 (1.0 %): Addition of 1.0 % WPC80. 
Whey protein addition to accelerate yoghurt fermentation and facilitate the yoghurt structure 
73 
One of the most important attributes for yoghurt quality is texture. The main processing 
parameters influencing the yoghurt texture are type of stabilizers and their usage levels, 
homogenization conditions, milk heat treatment conditions, starter culture, incubation 
temperature (influences growth of starter cultures, gel aggregation, bond strength) [11]. Using 
the procedure parameters from Moc Chau yoghurt processing in this study, the results indicated 
that WPC 80 addition enhanced the yoghurt texture by the increase of yoghurt viscosity, the 
reducing of water-holding capacity and increasing of yoghurt hardness (Fig. 2). The gel strength 
of yoghurt is enhanced by the addition of WPC due to the denaturation β-lactoglobulin in WPC. 
The binding of denatured β-lactoglobulin with the κ-casein on the casein micelle surface by 
disulfide bridging is responsible for the increase of gel strength and viscosity of yoghurt [12-13]. 
There was no different in texture of WPC addition at the concentration of 0.6 to 0.8 %. However, 
the addition of WPC 0.8 % was chosen to decrease the fermentation time and increase the 
structure of the final products. 
Compared to other stabilizers, WPC is a dairy product containing many soluble proteins 
that are good for human health [14]. Besides, when these proteins are denatured, they could 
combine with casein to increase the water-holding capacity of yoghurt. The use of milk-original 
products to replace stabilizers with E index could be a suggestion for production only from 
natural raw material in dairy plant. 
3.3. Effect of WPC 80 addition to yoghurt sensory quality 
The texture of yoghurt related to sensory perception of the product. Physical and sensory 
attributes are important factors that influence food acceptance and choices. The most common 
sensory attributes related to yoghurt texture are thickness viscosity, smoothness, water holding 
capacity, yoghurt flavor, texture, sweetness, sourness, fatty, sour aftertaste. The results showed 
that the addition of WPC enhanced the quality of the final yoghurt products in physical 
properties compared to control sample (Fig. 3). The addition of WPC could not change the other 
sensory properties such as: yoghurt flavor, taste and color. The results in this study strongly 
indicate that it was possible to make yoghurt of acceptable structure, good final quality and 
quick fermentation process by the addition of WPC at the rate of 0.8 %. 
Figure 3. Comparison between yoghurt products with WPC addition and control sample. 
4. CONCLUSIONS 
The addition of WPC at the rate of 0.8 % could reduce the fermentation time of yoghurt to 
12.5 % with the increase of yoghurt physical and sensory properties. The yoghurt viscosity 
reached 20.2 Pa.s and the product hardness reached 414 kG compared to 374 kG in control. The 
water separation also decreased significantly from 28.62 % to 16.35 %. It can be concluded that 
0
5
10
Whitenn
Water
Yoghurt
Smoothies
Texture
Sweeten
Sourness
Fatty
Sour
Total
Control
0.8 % WPC
Maximum value
Vu Thu Trang, Nguyen Chinh Nghia, Lai The Hung, Do Van Duong 
74 
whey protein could induce good effect to the structure of product. Thus, the addition of WPC 
might reduce the amount of additional stabilizer to the final products. 
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