Break-Up of Plant Cell Structures in High Pressure Homogenizers – Prospects and Challenges for Processing of Plant-Based Beverages

For more than a century, the dairy industry has used high-pressure homogenization for size reduction of fat globules. The prevailing break-up mechanism, turbulence, has been thoroughly investigated and the equipment continuously optimized thereafter. However, the high-pressure homogenizer is also used in size reduction of plant cell structures, for example in production lines of plant-based beverages, fruit and vegetable juices and ketchup. This review will provide a scientific basis for homogenization of plant-based materials with focus on break-up mechanisms. A cross-study comparison shows that different raw materials break in different ways, e.g. individual cells breaking into cell wall fragments and cell clusters breaking into smaller cell clusters. In general, raw materials which after intense premixing exist as cell clusters are more difficult to break than raw materials existing as individual cells. The resistance to break-up also appears to follow ‘raw material hardness’, where harder raw materials, e.g., parsnip and almond, are more difficult to break than softer raw materials, e.g., strawberry and orange. It can also be concluded that the initial particle size is of large importance for the size after high pressure homogenization. It is concluded that little is known about the break-up mechanism(s). Much does, however, point towards the mechanism being different from that of emulsion drop break-up. Suggestions for future studies, both regarding fundamental understanding (e.g., cell strength and breakup, HPH mechanistic studies and break up visualisations) and industrial applications (e.g., energy optimal operation, device design and wear) are provided.