Lactobacillus plantarum amylase acting on crude starch granules. Native isoforms and activity changes after limited proteolysis.

The microheterogeneous native amylolytic complex secreted by the isolate A6 of Lactobacillus plantarum revealed a selective enzyme specificity loss when submitted to a limited proteolysis under a suboptimum pH condition. A clear electrophoretic profile change toward just one shorter, more acidic, and equally active polypeptide fragment resulted from the pronase E pretreatment. Although the whole enzyme activity remained apparently unaffected for soluble starch, the native parallel activity on intact and non-gelatinized starch granules either from cereals or tubers was dramatically reduced. This phenomenon was more clearly documented by scanning electron microscopy using the easiest accessible native substrate: wheat starch granules. The anion-exchange-purified native enzymes from L. plantarum displayed a different optimum pH curve when compared with the thermotolerant alpha-amylase from Bacillus licheniformis. The alpha-amylases from the lactic-acid-producing A6 isolate presented an electrophoretic profile easily distinguishable from those from B. liqueniformis and B. subtilis species.

Astaxanthinogenesis in the yeast Phaffia rhodozyma : optimization of low-cost culture media and yeast cell-wall lysis.

Astaxanthin is a diketo-dihydroxy-carotenoid produced by Phaffia rhodozyma, a basidiomicetous yeast. A low-cost fermentation medium consisting of raw sugarcane juice and urea was developed to exploit the active sucrolytic/urelolytic enzyme apparatus inherent to the yeast. As compared to the beneficial effect of 0.1 g% urea, a ready nitrogen source, mild phosphoric pre inversion of juice sucrose to glucose and fructose, promptly fermentable carbon sources, resulted in smaller benefits. Corn steep liquor (CSL) was found to be a valuable supplement for both yeast biomass yield (9.2 g dry cells/L) and astaxanthin production (1.3 mg/g cells). Distillery effluent (vinace), despite only a slightly positive effect on yeast growth, allowed for the highest pigment productivity (1.9 mg/g cells). Trace amounts of Ni2 (1 mg/L, as a cofactor for urease) resulted in controversial effects, namely, biomass decrease and astaxanthin increase, with no effect on the release (and uptake) of ammonium ion from urea. Since the synthesized astaxanthin is associated with the yeast cell and the pigment requires facilitated release for aquaculture uses (farmed fish meat staining), an investigation of the yeast cell wall was undertaken using detergent-treated cells. The composition of the rigid yeast envelope was found to be heterogeneous. Its partial acid or enzymatic depolymerization revealed glucose and xylose as common monomeric units of the cell-wall glycopolymers. Yeast cell-wall partial depolymerization with appropriate hydrolases may improve the pigment bioavailability for captive aquatic species and poultry.