Ulrike Einhorn-Stoll

Formation of Phenolic Compounds from d-Galacturonic Acid

Aqueous d-galacturonic acid (d-GalA) model systems treated at 130 °C at different pH values show an intense color formation, whereas other reducing sugars, such as d-galactose (d-Gal), scarcely react. GC-MS measurements revealed the presence of several phenolic compounds: e.g., 3,8-dihydroxy-2-methyl-4 H-chromen-4-one (chromone) and 2,3-dihydroxybenzaldehyde (2,3-DHBA). These phenolic compounds, especially 2,3-DHBA, possess an intense browning potential and cannot be found within heated model solutions of reducing sugars. Investigations regarding the formation of these substances show that α-ketoglutaraldehyde plays an important role as an intermediate product. In addition, MS analysis of model systems of norfuraneol in combination with 2,3-DHBA showed the formation of oligomers that could also be detected in d-GalA model systems, leading to the assumption that, in addition to reductic acid, these compounds are jointly responsible for the strong color formation during the heat treatment of d-GalA.

Quark: A Traditional German Fresh Cheese

Quark is a traditional German unripened cheese, produced by acid coagulation or a combined acid/rennet coagulation. It developed from naturally occurring acidification during storage of milk in the nineteenth century. Commercial production started in the twentieth century as a batch process using linen sacks for whey drainage after protein aggregation. Nowadays, in continuous processing using quark separators and membrane filtration more than 840.000 t of fresh cheese and quark are produced in Germany. The chapter provides an overview on this development of the process technology for quark production.