Determination of alginate in dairy products.
Abstract Comprehensive study was made of the precipitability of several hydrocolloids and other related compounds by divalent cations and, specifically, of the optimum conditions for recovering alginate from milk and dairy products by precipitation as calcium, strontium, and manganese salts. In aqueous dispersion, these cations selectively precipitated alginate, pectinic acids, and pectic acid. Alginate was recovered from milk, chocolate milk, ice cream, cheese spreads, cream cheese spreads, and other products by predigesting the mixture with papain, clarifying the digest with Celite 535 and charcoal, filtering and converting any pectin, pectinic acid, and pectic acid to galacturonic acid by pectinmethylesterase (pectinesterase) and polygalacturonase. Then, calcium chloride was added to the filtrate. The calcium alginate precipitate was washed free of sugars, dispersed by sodium hexametaphosphate, and the amount of alginate in the dispersion determined by the phenol-sulfuric acid test. Recoveries obtained were 96-101% for water dispersions, 92-96% for milk, 90-95% for ice cream, and 85-95% for cheese products.
The complete enzymic hydrolysis of proteins.
The strong acids that are required for complete hydrolysis of proteins destroy some amino acids, such as tryptophan, asparagine, and glutamine. Other amino acids are destroyed to a lesser extent or in certain cases are released incompletely from peptide linkage. It is evident that these difficulties, as well as others, could be overcome by employing proteolytic enzymes as the sole agents for hydrolysis. The complete enzymic degradation of proteins was studied by several investigators in the late nineteenth and early twentieth century. Meissner (2), Kiihne and Chittenden (3, 4), Chittenden and Goodwin (5), and Neumeister (6, 7) demonstrated that pepsin and trypsin hydrolyzed proteins to produce a complex mixture of peptides called proteoses and peptones. These were considered to be the ultimate end products of proteolysis until 1901, when Cohnheim (8) showed that intestinal extracts (erepsin) hydrolyzed peptones to amino acids. Subsequent studies, in particular those of Frankel (9), showed that the combined action of pepsin, trypsin, and erepsin resulted in cleavage of over 90% of the peptide bonds in several purified proteins.1 Although it was evident from these early investigations that proteins could be degraded by enzymes to amino acids, later investigators did not develop a system for complete enzymic hydrolysis. This can be attributed to a variety of causes, but two major problems which only recently have been satisfactorily solved presented the most difficulty. Micromethods for the precise analysis and characterization of amino acids and peptides were not available, and secondly, purified proteolytic enzymes were not characterized sufficiently to be used as hydrolytic agents. With these considerations, we have developed methods that employ proteolytic enzymes for hydrolysis of proteins. Our studies demonstrate that digestion of a protein by papain (12), followed by treatment with the purified kidney peptidases, leucine aminopeptidase (13), and prolidase (14) results in essentially complete hydrolysis of all peptide bonds and gives high yields of tryptophan, glutamine, and asparagine.
Inhibition of Root Growth and Polyamine Metabolism in Sunflower (Helianthus annuus) Seedlings Under Cadmium and Copper Stress
Although sunflower is usually regarded as a highly tolerant crop, impairment of root growth at initial stages of plant development may result in poor crop establishment and higher susceptibility to pathogen attack. In order to evaluate if Cd2+ and Cu2+ may impact on sunflower germination and initial root development, a pot experiment under controlled conditions was carried out. Possible involvement of polyamine metabolism in sunflower response to these stressors was also investigated. Although Cd2+ and Cu2+ treatments affect neither seed germination nor radicle emergence, sunflower seedlings grown in the presence of these heavy metals showed significant inhibition of root growth, being this inhibition greater for Cd2+. Both metals caused significant increases in proline contents at the highest concentrations tested (0.5 and 1 mM), and these increments were more pronounced for Cd2+ treatments, especially between days 3 and 10. Metals also increased putrescine (Put) contents at all concentrations assayed from the seventh day onward, causing no variations on this polyamine time-course pattern. Spermine and spermidine contents, however, were increased only by 1 mM Cd2+. Arginine decarboxylase seems to have been the enzyme responsible for Put increases under both metal treatments. This work demonstrates that initial root growth of sunflower seedlings may be significantly impaired in Cd2+ or Cu2+ contaminated soils. It also shows that polyamines are key biological compounds, which are probably involved in signaling pathways triggered under stress environmental conditions.