Yeast autolysates

Each strain was received on a Czapek yeast autolysate agar plate from the culture collection. Spores were transferred to a potato dextrose agar (PDA) (Difco, Detroit, MI) plate and the PDA plates were kept at the optimal temperature for growth (Table 1). After 2 wk the strains on the PDA... 

Mr< 10,000 Da Yeast autolysed in a model Relative molecular masses HPLC profiles Martinez-Rodriguez and... 

Glucanase Lysozyme Mixed Glucolytic and Proteolytic Activities Arthrobacter ssp. Yeast Cell Wall Lysis-supporting Autolysis for Production of Yeast Autolysates... 

Yeast autolysates may be obtained from waste yeasts from breweries and dairies. If specific flavour types are required also cultured yeasts and yeast lines with special properties are used (species Saccharomyces, Torula). 

The taste-delivering principle of a yeast autolysate is mostly derived from the natural contents of the yeasts of special amino acids, especially glutamic acid. Also nucleotides from the naturally occurring ribonucleic acid are important as well as the... 

Table 3.29 Typical composition of a spray-dried yeast autolysate...

A patent application from 1918 deals with the formulation of malt flavours ]105] claiming the reaction of raw materials which are rich in amino acids (e.g. yeast autolysate) with sugars to produce a malt flavour. However, no reference is made to specific amino acids. 

All industrial biotechnological production processes use complex cultivation media which consist of agricultural by-products (beet or cane molasses, corn-steep liquor, cottonseed meal, whey permeate, peanut floiu-, soybean meal, distillation residues, etc.). In addition polysaccharides (starch, dextrose, malt extract, maltodextrins, etc.) and proteins (e.g. caseinate, yeast autolysates, etc.) are used as energy sources for the microorganisms and cells. These systems... 

A high proportion of yeast dry weight is made up of nucleic acids (principally ribonucleic acid). This renders yeast unsuitable for use as a primary foodstuff because of the undesirable physiological effects produced by the end-products of nucleic acid metabolism. Much research has been directed towards lowering the levels of nucleic acids (in for example yeast autolysates) with only limited success. 

The first step in the preparation of a yeast extract (YE) involves autolysis of a yeast slurry or cream at 50°C. A yeast autolysate (YA) results and removal of the unhydrolyzed cell walls from the soluble autolysate yields a clear extract (7). Caramel, vegetable concentrates, spice infusions, monosodium glutamate and 5 -ribonucleotides, all of which are flavor modifiers, may be added to the YE (7,2). Products are marketed as liquids, pastes or powders and find uses as flavoring agents for a range of foods, especially when a meaty flavor is demanded (5). 

Table I. Volatile sulfur components of yeast autolysates and yeast extracts...

Yeast (autolysed, cell wall, membranes of autolysed yeast) hydrochloride Thiamin... 

Ribose, ribose-5-phosphate, hydrolyzed polysaccharides, yeast, and yeast autolysates also appear in the patent literature as carbohydrate sources for these flavorings. There are no economical sources of ribose or ribose-5-phosphate. Yeast and yeast autolysates both will contribute some free carbohydrate. 

Meat extract, hydrolysates of vegetable proteins, and yeast autolysate are used to a large extent in the production of dry soups amd dry sauces. For this reason, these substances will be described here. The industrial production of these products for use in home and canteen kitchens has become increasingly important in the past 20 years. In particular, a special pretreatment of the raw materials made possible the development of products which, after quick rehydration, give ready-to-consume complete meals (dry stews), snacks between meals (dry soups, instant soups), or sauces. 

Not only meat extracts, protein hydrolysates, and yeast autolysates, but also glutamate, ribonucleotides (inosinate/guanylate), and reaction... 

Biotin is found in a range of foods, but the concentration in most of them is usually low (Table 5.8). It is partly present as a free compound (milk, fruits and vegetables) and partly bound to proteins (animal tissues, plant seeds and yeast). Yeast autolysates, for example, contain free biotin and its precursors and analogues. These biotin vitamers, mainly dethiobiotin (5-85), biotin sulfone (5-90) and biocytin (5-87), are degradation products of enzymes containing biotin. 

Several carboxylic acids are also derived from various S- and AT-heterocycKc compounds. Many of them are natural biologically active compounds and other acids are formed during food processing. Examples are some vitamins, such as biotin, lipoic acid, nicotinic acid, 4-pytidoxic acid or orotic acid. Yeast autolysates, for example, contain a number of carboxylic acids derived from thiophene. 

Many authors have used this idea of reactivation. Although many different procedures have been proposed, that of Lafon-Lafourcade et al. (1983) is the most used. Non-sulfited grape juice is diluted to half its original concentration (80 g/1 of sugar per liter) a commercial yeast autolysate is added (5 g/1) and the pH is adjusted to 4.5 with CaCOs. After several hours, commercial biomasses inoculated at 10 cells/ml at 25°C produce fermentation starters rich in malolactic enzymes. These starters are also more resistant in wine than non-reactivated starters. Populations increase to 10, 10 and 10 cells/ml after 2 hours, 24 hours and 6 days of reactions, respectively. 

The enzyme catalyzing reaction (3a) has been purified from yeast autolysates and acetone powders of human eiythrocytes. Enzymes promoting reaction (3b) have been purified from rat liver, yeast, and human erythrocytes. The enzyme catalyzing the formation of DPN from nicotinic acid- DPN (Eq. 3c) has been purified from yeast autolysates it has also been studied in liver as well as in human erythrocytes. 

J Velisek, J Davidek, V Kubelka, T Tran Thi Bich, J Hajslova. Succinic acid in yeast autolysates and its sensory properties. Nahrung 22 735-743, 1978. 

Rakin, M., Vukasinovic, M., Siler-Marinkovic, S. and Maksimovic, M. (2007) Contribution of lactic acid fermentation to improved nutritive quality vegetable juices enriched with brewer s yeast autolysate. Food Chem 100,599-602. 

---