Debittered

The most widely available yeast biomass is a by-product of the brewing industry, where the multiplication of yeast during brewing results in a surplus of ceUs. Eor every barrel (117 L) of beer brewed, 0.2—0.3 kg of yeast soHds may be recovered. In the U.S., a substantial fraction is recovered and made available about 40 x 10 kg of brewers yeast aimually. The yeast is recovered from beer by centrifuging and dried on roUer dmms or spray dryers and sold as animal feed or a pet-food supplement. It can be debittered by alkaline extraction to remove the bitter hop residues, and is then sold mainly by the health-food industry. It is available as tablets, powder, or flakes and is often fortified with additional vitamins. Distillers yeast caimot be readily separated from the fermented mash and the mixture is sold as an animal feed supplement. 

Both enantiomers of rhamnose, 6-deoxy-mannose, occur naturally. L-Rhamno-se is a constituent of glycosides such as naringin (89) as well as hesperidin, and a constituent in plant tissues as well as of bacterial cell walls. a-L-Rhamnosida-ses have been employed to debitter fruit juices [145]. 

The gross proteolysis of casein is probably due solely to rennet and plasmin activity (O Keeffe et al. 1978). Bacterial proteases and peptides are responsible for subsequent breakdown of the large peptides produced by rennet and plasmin into successively smaller peptides and finally amino acids (O Keeffe et al. 1978). If the relative rate of proteinase activity by rennet, plasmin, and bacterial proteases exceeds that of the bacterial peptidase system, bitterness in the cheese could result. Bitter peptides can be produced from a,-,- or /3-casein by the action of rennet or the activity of bacterial proteinase on /3-casein (Visser et al. 1983). The proteolytic breakdown of /3-casein and the subsequent development of bitterness are strongly retarded by the presence of salt (Fox and Walley 1971 Stadhouders et al. 1983). The principal source of bitter peptides in Gouda cheese is 3-casein, and more particularly the C-terminal region, i.e., 3(193-209) and 3(193-207) (Visser et al. 1983). In model systems, bitter peptides are completely debittered by a peptidases system of S. cremoris (Visser et al. 1983). 

Enzyme Debittering. One of the more promising ways to reduce naringin bitterness is to use enzymes to convert the bitter fla-vone neohesperidoside into a less bitter glucoside or non-bitter... 

Investigations on possible commercial use of enzymes to remove naringin bitterness were carried out for juice (70, 71), concentrate (71), and fruit sections (72). Those investigations showed that it was technically possTFle to use enzymes to reduce naringin bitterness on a commercial scale. However, due to enzyme expense, most of the industry has found it more cost effective to use more mature (less bitter) fruit rather than employ debittering enzymes. 

Hasegawa, S. Brewster, L. C. Limonoate dehydrogenase and debittering of citrus juice therewith. U. S. Patent 3,911,103. 

Umetsu, H., Matsuoka, H., and Ichishima, E. (1983). Debittering mechanism of bitter peptides from milk casein by wheat arboxypeptidase. J. Agric. Food Chem., 31, 50-53. 

Removal of polyphenolic compounds Recovery of starch from wheat flour Debittering citrus pectin juice by hydrolysis of the glucoside, naringin... 

The traditional way to debitter the grains is leaching with water for several days. Nowadays this process is still used and it takes place in three steps wetting, boiling and rinsing with water. 

Santana, F. C., Beirao da Costa, M. L., Empis, J. M. A. Evaluational enzimatic preparations in the debittering of lupin seeds flowers. Proc. of the 6th International Lupin Conference, Chile (1990). 

Most of the bitter glucosides are in the albedo and segment membranes so that commercial production of grapefruit juice without removal of naringin is possible. Production of juice from natsudaidai oranges 180) and restoration of the pink color to pink grapefruit juice by addition of pulp 181) require debittering. 

Enzymatic debittering of citrus juice by rhamnosidase action is a practical process although not now economically important in the United States. It could be a particularly attractive use for an immobilized enzyme. 

---