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The effect of glucose concentration and insulin on protein synthesis was investigated using the isolated rat diaphragm and C14-labeled amino acids. When the donor rat has been well fed, the incorporation of histidine-2-C14, lysine-2-C14, phenylalanine-3-C14, and alanine-1-C14 into muscle protein is uninfluenced by glucose concentration in the medium over the range 0–600 mg %. Insulin leads to an increase in C14-amino acid incorporation into muscle protein in the absence of glucose in the medium. This positive effect of insulin in the absence of added glucose is still observed when the diaphragms are pre-incubated for 2 hours prior to adding insulin. These findings suggest an effect of insulin on protein metabolism independent of its action in promoting glucose entry.

A detailed study on the degradation of iso-α-acids was conducted. Because of the complexity of the wort matrix and interfering interactions during real wort boiling, the investigation of degradation kinetics was performed in an aqueous solution. Degradation was investigated as a function of time (0-90 min), temperature (80-110°C), pH value (4-7), original gravity (10-18°P) and ion content of the water (0-500 ppm Ca 2+ and Mg 2+ ). After 90 min of boiling, over 20% of the dosed iso-α-acids could no longer be detected. A strong dependence of degradation could be shown due to high temperature, low pH, high original gravity and a high Mg 2+ content. The cis:trans ratio and co-iso-α-acid content did not change significantly. Losses of isohumulones could be lowered by reducing the temperature and original gravity, as well as by heightening the pH value. High amounts of Ca 2+ and Mg 2+ salts also led to an increase in degradation products. Solutions to decrease degradation and thereby possible improvements in sensory bitter quality are discussed.