PROPERTIES OF AMINOPEPTIDASE FROM JAPANESE CLASSIFIED BARLEY FLOUR

An aminopeptidase (AP) was purified from classified barley flour obtained from the outer layer of Japanese grain. To characterize the enzyme, the substrate specificity and pH optimum were determined with 9 aminoacyl‐p‐nitroanilide (p‐NA) and 6 aminoacyl‐β‐naphthylamide (β‐NA). Furthermore, the effects of inhibitors and the hydrolysis of natural substrates were investigated. The optimum pH was between 6.5 and 8.0 in all cases in which these artificial substrates were used. Phe‐β‐NA had the highest affinity for the enzyme and the Km value was 0.084 mM. The enzyme also showed a strong preference against leucine‐, arginine‐, and lysine‐p‐NA (Km = 0.18 mM, 0.10 mM, and 0.48 mM, respectively). Chymostatin slightly inhibited the activity, whereas AP was not affected by leupeptin and pepstatin A. The enzyme did not hydrolyze the proteins tested, but it cleaved peptide hormones.     

POLYSACCHARIDE 13140: A NEW THERMO-GELABLE POLYSACCHARIDE

Polysaccharide 13140, a curdlan-type polysaccharide produced from a culture filtrate of Alcaligenes faecalis var. myxogenes strain NTK-u, has the unique property of forming a gel on heating. This polysaccharide is composed of β-1,3 linked glucose residues. When heated, aqueous suspension of the polysaccharide forms an elastic gel which is thermally irreversible, heat stable and acid stable. The texture properties of the polysaccharide gel lie in between agar-agar gel and gelatin gel. Potential applications of the polysaccharide in food processing are quite diverse and promising because it can improve such properties as viscoelasticity, palatability, binding quality, water holding capacity, heat stability and compatibility     

AN ENZYMATIC PROCESS FOR A PROTEIN-CONTAINING BEVERAGE BASED ON SOYBEAN PROTEIN AND LEMON JUICE

SUMMARY —An acidic enzymatic process for a bland soybean protein hydrolysate is described. Cooked suspensions (5.0%) of isolated soybean protein are mixed with small amounts of an acid-protease preparation from Trametes sanguinea, adjusted to pH 3.3–3.5 with concentrated lemon juice and incubated at 50°C for 8–10 hr. After stopping the proteolysis by heat treatment, the clear supernatant is separated from any insoluble residue by centrifugation. A solubilized nitrogen recovery of 88–90% is obtained. All nitrogenous substances in the hydrolysate are 5% trichloroacetic acid-soluble, and the dehydrated hydrolysate easily reconstitutes to a clear solution with cold water. After being diluted about twice and sweetened with sugar, the hydrolysate constitutes a clear, slightly yellowish lemonade-like flavored beverage. The data on chemical analysis, gel-filtration and rheological behavior of the hydrolysate are also described and discussed.     

Curdlan: Properties and Application to Foods

Gel formation of curdlan at 100–130°C and behaviors of curdlan gels under frozen state were investigated by measuring gel strength and syneresis. Even when aqueous suspensions of curdlan were heated to 100°C or higher, they formed a gel, and gel strength increased with temperature. Curdlan gel was also stable against freezing and thawing. The syneresis of a 4% curdlan gel after freezing and thawing was reduced from 20.6% to about 2.1% by addition of 5% waxy corn starch and to 8.9% by addition of 20% sucrose. Suggested by these findings, new applications to foods have been developed, especially those subject to retorting and/or freezing.     

Volatile Flavor Components of Nira (Allium tuberosum Rottl.)

The flavor components of Nira (Allium tuberosum Rottl.) have been studied by a combination of gas chromatography and mass-spectrometry. Twenty-nine compounds were identified in the oil obtained from extraction of the steam distillate of Nira. The identified compounds include 7 sulfides, 2 ketones, 18 alcohols and 2 esters. The main volatile components were dimethyl disulfide and dimethyl trisulfide.