|M.Sc Student||Sharabi Sion|
|Subject||Effect of Ultra-High Pressure Homogenization on Vitamins|
Stability and Anti-Oxidative Properties of Milk
|Department||Department of Biotechnology and Food Engineering||Supervisor||Dr. Avi Shpigelman|
|Full Thesis text|
Milk is a highly consumed product worldwide due to its high nutrient content. It is well known that the content of some vitamins and anti-oxidant capacity (AOC) is negatively affected even by short thermal treatment during pasteurization. Ultra-high pressure homogenization (UHPH) is a novel processing technology capable of ensuring microbial safety of milk with a lower thermal detrimental effect. Due to the fact that riboflavin and vitamin C (VC) have an anti-oxidative ability, a measurement of the changes in the AOC of whole milk during processing and shelf life as a result of changes in the stability of these vitamins after UHPH process was conducted. The hypothesis was that the AOC of processed (to ensure microbial safety) milk during the shelf life can be improved by utilization of UHPH in a one-step preservation-homogenization process. Therefore, initially evaluation of the effect of UHPH on microbial destruction was made. At the next step, the effect of UHPH on stability of riboflavin and VC after processing and during shelf life of milk (under white fluorescent light exposure, 4°C) was conducted. The effect of the different homogenization pressures, resulting in different particle size, on riboflavin photo-oxidation kinetics was explored. The effect of thermal pasteurization compared to UHPH effect on VC content and degradation during shelf life was also studied. In order to better understand the mechanism of the effect of homogenization pressure and the consecutive shelf life on the riboflavin degradation, two model systems (synthetic and milk protein) were used. In order to test the reliability of the storage conditions simulating storage/display of milk in supermarkets, on the homogenized whole milk samples, the effect of light on VC, riboflavin and antioxidant capacity in commercial milk products during shelf life was evaluated.
The results showed that with increasing homogenization pressures/cycle number, a decrease in the total bacteria count is observed. Additionally, a decrease in pH for higher homogenization pressure during shelf life was observed. The reduced thermal effect during UHPH compared to thermal pasteurization resulted in lower degradation of VC after processing and in higher AOC during shelf life compared to heat pasteurized milk (although no difference were observed between the different UHPH pressures). Additionally, the smaller milk particle size, yet with a larger number of particles, likely increased light scattering, leading to a lower photo-degradation of riboflavin during storage. As for the β-lactoglobulin model, an optimum size for riboflavin stability was observed. Whereas for the Tween80/Span 80 model, smaller particle size increased the photo-degradation of riboflavin, possibly due to such small particle sizes that decreased the light scattering.
As milk is a primary product consumed practically during all life stages it is possible that even small improvements in its health promoting properties, like anti-oxidative capacity, can result in a large and continues beneficial contribution and to prevention of many chronic illnesses.