Study of tomato fiber fragmentation in the high-pressure homogenizer

Abstract

Homogenization is commonly used in many food processes in which products pass through a narrow gap causing break down of large particles into smaller one thereby reducing creaming and sedimentation of the products.
This study aims to investigate fragmentation of tomato fibers and test which breaking mechanisms are dominating in a high-pressure homogenizer. The study also includes the influence of several passages’ homogenization.
Numerous mechanisms of particles disruption have been proposed, including viscous shear, turbulence, cavitation, squeezing and impingement with a solid surface. However recent researches suggested fragmentation by turbulence, and cavitation as the primary mechanisms for emulsions drop break up in the homogenization valve. The study discusses fragmentation by laminar shear, turbulent inertial, turbulent viscous as well as squeezing.
Several hypotheses have been suggested to explain which breaking mechanisms are controlling fiber fragmentation in the high-pressure homogenizer. Each of the mechanism results in quantifiable predictions about operating conditions: The laminar viscous mechanism implies that increasing of homogenization pressure and continuous phase viscosity would lead to smaller particles size for the tomato suspension. Turbulent inertial implies no impact of serum viscosity on the particles break up, while turbulent viscous predict that higher continues phase viscosity results in smaller particles size. Both of turbulent theories agreed on smaller suspension particles obtained by higher homogenization pressure with a relation described as d

Popular Abstract

Over the years, the industry has succeeded to provide the market needs with different types of beverages and juices that satisfy the consumers' demands. To be able to do that the industry has to process the beverages using several steps before it reaches to the consumer on the form that exists in the markets. One of these steps is homogenization. Homogenization is a mechanical process in which products are pressurized and forced to pass through a narrow gap where fluid particles confront several forces leading to fluids particles break up into smaller ones.
The most common food application of the homogenizer is probably the homogenization of milk, which serves to make the size of fat droplet smaller. Other applications include homogenization of ketchup and juices.
The researchers have established several theories and mathematical models explaining how the fat and particles break up inside the high-pressure homogenizer. The most convenient ones for milk products are called laminar shear, turbulent inertial, turbulent viscous as well as cavitation. In this project, these theories were tested on the product with fibers which is in our case tomato juice. Tomato juice is a popular beverage that provides a wide variety of vitamins and minerals. Tomato juice is a rich source of antioxidants that may improve the health of humans. In this project, the juice was produced by diluting concentrated tomato paste with tap water to the desire tomato juice concentration.
In the laminar flow, the drop starts to rotate and elongates until it breaks up into two. In turbulent, the fluid going through the homogenizer valve generates intense turbulent eddies of different size. Particles are thus torn apart by these eddies. It is also possible for tomato cells to be squeeze by the gap and break up while cells were passing through it.
The method used to test breaking theories was by comparing the particles size of the homogenized juice in different operations conditions with the expected size form theory.
So why we homogenized juice?
The main reason for homogenization is to avoid phase separation by reducing creaming or sedimentation of the particles by reducing the large particles into small, and the small particles even smaller leads to the longer shelf life of the products that will be most attractive to consumers who favor without sedimented or creamy layer. Homogenization also improves the quality of beverage by increasing the viscosity and consistency of products through releasing some natural stabilizer such as pectin. Other benefits, including improvements in products colors and flavor as well as better digestible products.
The results showed no agreement between the obtained particles size form the experimental works, and the expected size form the theory. Thus, we are not able to say which breaking theory is causing fibers breakup in high pressure. Furthermore, the results showed that the homogenization leads to improvement of the viscosity of tomato juice.

• author: Al-Ameri, Maytham
• supervisor: Andreas Håkansson; Fredrik Innings
• organization: Food Technology and Nutrition (M.Sc.)
• course: KLTM01 20181
• year: 2019
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: food engineering, livsmedelsteknik
• language: English
• id: 8988967
• date added to LUP: 2019-10-29 13:24:55
• date last changed: 2019-10-29 13:24:55