All you need to know about Yoghurt!!

 YOGHURT

It is a dairy-based fermented product produced by probiotic microbial strains such as Lactobacillus Bulgaricus, and Streptococcus Thermophilus. Probiotic bacterial strains are known for providing good gut health.

What is the difference between curd (known as dahi in India) and Yoghurt??

Both are fermented products. However, the strains used in the dahi and yoghurt are completely different. In addition to that, the total solids in the yoghurt is higher than the dahi. Other similarities between the two products include that during pre-treatment in pasteurization both curd milk and yoghurt milk are held for a long time in a holding cell. This long holding time is helpful for protein denaturation. Hence, results in good texture and mouthfeel of the end products. 

Process Flow:

Milk is initially standardised for the fat content and dry matter content. Ingredients like sugar, thickeners and stabiliser are added. Then Yoghurt milk is deaerated, homogenized and pasteurized at (90-98 deg C) for 5 minutes. After pasteurisation, at cold conditions, the inoculum is added to the yoghurt milk for fermentation. Based on the fermentation and further processing yoghurt has been classified as follows. After fermentation, inclusion is added (optional) before packaging and distributed at cold (less than 8 deg C) or ambient conditions depending on the type of yoghurt.

Types of yoghurt depending on the processing method:

1. Set yoghurt (usually fermented in the package during storage) similar to curd
2. Stirred Yoghurt (fermented in the tanks)
3. Drinking Yoghurt (fermented in tanks then viscosity is reduced by homogenizer during cooling)
4. Concentrated Yoghurt (fermented in tanks and then concentrated by means of centrifugation or filtration)- Ex. Greek yoghurt
5. Ambient Yoghurt based products (stirred yoghurt and drinking yoghurt are subjected to further heat treatment (sterlisation) for ambient distribution)

Shear sensitive:

Yoghurt is a Non-Newtonian fluid with shear thinning characteristics. This means the apparent viscosity of the yoghurt will be decreased during the increased shear rate. Shear rate during pumping and agitation disrupt the structure of yoghurt. It will reduce the viscosity of prepared yoghurt. Stirred yoghurt is the shear sensitive yoghurt.

 

GATE 2023 - XL Life science Food Technology

 Water activity Problem

The average moisture binding energy of a textured protein product (TPP) at 8% moisture content (dry basis) is 3200 cal.mol-l. If the water activity of the T PP at the above moisture content is 0.30 at 30 degC, the water activity of the sample at 45 deg c is ________________ (rounded off to 2 decimal places). The value of Gas constant R = 1.987 cal.mol-1 K-1 

solution: https://youtu.be/PgaDzC3Emm0

High pressure Homogenization

High pressure Homogenizers are basically positive displacement pump. Majorly used in the food industry for break down of fat globules and size reduction of the fibres in the food products.

These process have significant on the physical properties such as,

• Colour
• viscosity
• particle size 
• density

UHT Products Spoilage

Have you ever wondered why UHT products have a shelf life of only three months even though it's completely sterile (free from microbes and its spore) ??

The shelf life of UHT products is not only limited to microbial spoilage. The spoilage of UHT products also happens in physical means. 

These spoilage includes 

• development of rancid/bitter flavour, 
• sediment and separation of ingredients,
• proteolytic and lipolytic activity facilitated by the bacterial enzymes (basically from psychotrops) and native enzymes Ex.plasmin (native proteolytic enzyme in milk)
• colour changes
• gelation caused by enzymes.
• destruction of vitamins over time.

Figure. Sedimentation of UHT milk in the package.

Ocassionly, the survival of thermoduric spores during UHT processing also germinate over time and also spoils the UHT product. Clearly, this issue comes with quality of UHT processing equipment and raw milk quality.

Carbonation of Beverage and CO2 solubility

 At atmospheric pressure, the solubilities of CO2 in a beverage at 15.5 deg C and 0 deg C are 1.0 volume and 1.7 volume respectively. The pressure (in atm) required to carbonate the beverage at 4.5deg C so as to maintain the gas volume 4.0 is  

(GATE XE- Food Technology)

a) 1.04

b) 1.47

c) 1.67

d) 1.76

solution: https://youtu.be/gxBMLM_ySbg

Food Packaging Problems

Resistance to permeability of the packaging film 

1. Apple is stored at 30° celsius in MAP of laminated films made up of 150 micro-metre thick polyethylene and 100 micro metre thick nylon the partial pressure of oxygen outside and inside the package are 0 and 0.21 atm respectively. The permeability values of polyethylene and nylon in m³ solute STP meter-2 s-1 atm -1 per metre thickness or 4.17×10 ^ -12 and 1.52x 10^-14 respectively,then the ratio of resistance to permeation between nylon and polyethylene films will be _______________________

        solution:https://youtu.be/sl3FpPogpXw

Microbial Inactivation Kinetic Problems

Raw milk containing 4*10^5 bacterial cells ml is pasteurised at 77degC for 21 s. The average D-value of the bacteria present in the milk is 7 min at 63degC and their z-value is 7degC. Calculate the number of viable bacteria that will remain after pasteurisation and the processing time required at 63degC to achieve the same degree of lethality.

Find solution : https://youtu.be/ELvu3stiPzM

Introduction to this Blog!!

Looking for a blog that covers all things related to food process engineering? Look no further than our blog! We cover everything from food packaging to heat and mass transfer, dairy engineering, refrigeration and freezing calculations, drying, evaporation psychrometry, fluid mechanics, and all other unit operations related to food processing and food products.

Our blog is also a valuable resource for those preparing for competitive exams such as GATE and ICAR. We provide detailed solutions to the problems typically asked in these exams, allowing you to practice and prepare more effectively.

Whether you're a student, a professional in the food industry, or simply interested in learning more about food process engineering, our blog has something for you. Join us as we explore the concepts and problem-solving strategies that are crucial to success in this fascinating field. 

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